Tesi sul tema "Carbon dissolution"

Carbon dioxide dissolution into water is a ubiquitous chemical process on earth, and having a full understanding of this process is becoming ever more important as we seek to understand the consequences of 250 years of exponentially-increasing anthropogenic C02 emissions to the atmosphere since the start of the Industrial Revolution. We examine the dissolution of C02 into water in a number of contexts. First, we analyse what happens to a range of chemical species dissolved in water following an injection of additional C02. We consider the well-mixed problem, and use the method of matched asymptotic expansions to obtain new expressions for the changes in the species' concentrations with time, the new final chemical equilibrium, and the time scales over which this equilibrium is reached, as functions of time, the parameters and the initial condition. These results can be used to help predict the changes in the pH and concentrations of dissolved carbonic species that will occur in the oceans as a result of anthropogenic C02 emissions, and in saline aquifer formations after pumping C02 deep underground. Second, we consider what happens deep underground in a saline aquifer when C02 has been pumped in, spreads through the pore space, and dissolves into the resident water, when advection, diffusion, and chemical reaction have varying levels of relative importance. We examine the length scales over which the dissolved C02 will spread out through an individual pore, ahead of a spreading drop of C02, and the concentrations of the different chemical species within the pore, in the steady-state case. Finally, some experiments have been carried out to investigate the effect of an injection of gaseous C02 on the chemical composition and pH of a saturated limestone aquifer formation. As the C02 enters the soil, it dissolves into the water, and we model the changes in the chemical composition of the water/limestone mixture with time.

The overall goal of this Ph.D. study was to investigate the mobilization of arsenic (As) from sedimentary formations under conditions representative of geologic carbon dioxide storage (GCS) i.e., high pressure, temperature, and salinity. GCS is a promising technology for the mitigation of increasing CO2 emissions in the atmosphere. It primarily involves the capture of CO2 from point sources, followed by transport and injection into deep subsurface formations for long-term storage. Of the potential subsurface formations under consideration in the United States, saline formations, characterized by the presence of high salinity brines, are estimated to have the largest storage capacity. Potential for leakage of injected CO2, native brines, and CO2- saturated brines from these reservoirs exists and may lead to an increase in mineral dissolution from reservoir formations, and leakage pathways. Of particular interest in the risk assessment of GCS is the dissolution and mobilization of toxic metals such as arsenic (As) and lead. The primary mineral source of As in high and low permeability sedimentary formations is arsenopyrite (FeAsS (s)). While the oxidative dissolution of FeAsS (s) has been reported in the literature, the dissolution of FeAsS (s) under anoxic, high salinity conditions of GCS remains unexplored. To conduct dissolution experiments at high pressure, temperature, and salinity, a small-scale plug-flow system capable of measuring dissolution rates without mass transfer limitations was designed and constructed. The capacity of the system in measuring dissolution rates under GCS conditions was validated. The plug-flow system is capable of accurate and rapid measurement of dissolution rates for minerals with slow and moderate dissolution rates, with a maximum rate limitation of 5 x10-5 mol/m2s at a flow rate of 10 ml/min. To enable accurate determination of reaction rates, a method for preparation of uniformly sized arsenopyrite particles free of surface oxides was developed. The method involves sonication of crushed minerals with ethanol, washing with 12N HCl, and 50% ethanol, followed by drying in N2. Analysis of the arsenopyrite surface with X-ray photoelectron spectroscopy revelealed that the method was successful in removing all the oxides of As and S on the surface, while only 12% of Fe was left oxidized. Subsequently, the dissolution of arsenopyrite, galena, and pyrite in low-concentration alkali and alkaline metal chloride solutions under anoxic conditions was investigated. Further, the effect of Na-Ca-Cl brines on the release of arsenic was determined under ambient as well as GCS conditions. The result of these experiments revealed that electrolytes traditionally considered inert, such as NaCl, CaCl2, and MgCl2 are capable of effecting sulfide mineral dissolution. In particular, the dissolution of As increased with increasing cation activity, and the dissolution of sulfur decreased with an increase in chloride ion activity in solution. Dissolution experiments with 1.5M Na-Ca-Cl brines resulted in arsenic dissolution rates in the range of 10-10 to 10-11 mol/m2 s under anoxic conditions. The rate of As release was found to be dependent on the CaCl2 content of these Na-Ca-Cl brines. Upon the introduction of CO2 into the system, the dissolution rate of As decreased and was determined to be in the range of 10-11 to 10-12 mol/m2s. For comparison, the rate of As release from arsenopyrite under oxic conditions is in the range of X to Y mol/m2 s. Finally, dissolution experiments aimed at understanding the release of As from naturally occurring seal rocks of a GCS formation were conducted. A primary seal rock and two secondary seal rocks were obtained from the Cranfield oil field CO2- EOR site in Mississippi. The rock samples were characterized by micro Xray adsorption near edge structure analysis, which revealed that multiple sources of As exist in the reservoir seal rocks studied. Dissolution experiments with seal rocks and anoxic brines of 105g/L NaCl resulted in the dissolution of arsenic in concentrations of 70 to 80 ppb at steady state. Dissolution of CO2 in the brine had no discernible effect on the steady state release concentration of As.

In an effort to reduce atmospheric carbon dioxide (CO2) emissions and mitigate climate change, it has been proposed to sequester supercritical CO2 in underground saline aquifers. Geological storage of CO2 involves different trapping mechanisms which are not yet fully understood. In order to improve the understanding of the effect of chemical reaction on the flow and transport of CO2, these storage mechanisms are modelled experimentally and numerically in this work. In particular, the destabilising interaction between the fluid hydrodynamics and a density-increasing second-order chemical reaction is considered. It is shown that after nondimensional scaling, the flow in a given physicochemical system is governed by two dimensionless groups, Da/Ra2, which measures the timescale for convection compared to those for reaction and diffusion, and CBo', which reflects the excess of the environmental reactant species relative to the diffusing solute. The destabilising reactive scenario is modelled experimentally under standard laboratory conditions using an immiscible two-layer system with acetic acid acting as the solute. A novel colorimetric technique is developed to infer the concentrations of chemical species from the pH of the solution making it possible to measure the flux of solute into the aqueous domain. The validity of this experimental system as a suitable analogue for the dissolution of CO2 is tested against previous work and the destabilising effect of reaction is investigated by adding ammonia to the lower aqueous layer. The system is also modelled numerically and it is shown that the aqueous phase reaction between acetic acid and ammonia can be considered to be instantaneous, meaning that Da/Ra2 tends to infinity and the flow is therefore governed only by the initial dimensionless concentration of reactant in the aqueous phase. The results from the experiments and numerical simulations are in good agreement, showing that an increase in the initial concentration of reactant increases the destabilising effect of reaction, accelerates the onset of convection and enhances the rate of dissolution of solute. The numerical model is then applied to a real world aquifer in the Sleipner gas field and it is demonstrated how the storage capacity of a potential CO2 reservoir could be enhanced by chemical reaction.

There have been extensive studies of the kinetics of pristine carbonate minerals in acidified media including (CO2 + H2O) systems at elevated temperature and pressure conditions pertinent to carbon storage. However, most of those studies have not considered the several complexities that occur in real reservoirs. The goal of this study was to investigate some of these complexities and their impacts on reaction rates under reservoir conditions. The variables investigated in this study include: aqueous chemistry and ionic strength, saturation state, surface contaminants and chemical heterogeneity in reservoir minerals. The majority of the reaction rates reported in this study are from batch reactor experiments implementing a form of the rotating disk technique, which is chosen to eliminate mass transport effects. Calcite (CaCO3) dissolution kinetics were investigated in (CO2 + H2O + NaCl), (CO2 + H2O + NaHCO3), (CO2 + H2O + Na2SO4) and (CO2 + H2O + Mixed Salts) systems. These studies were carried out at temperatures ranging from (323 to 373) K and pressures ranging from (6 to 10) MPa. A minor increase in the dissolution rates as a function of ionic strength was observed in every system except for (CO2 + H2O + NaHCO3), where a marked reduction in dissolution rates was measured. These observations are consistent with the predicted changes in the pH of the aqueous system. The influence of saturation states in the dissolution kinetics of calcite was investigated in the (CO2 + H2O) system at a temperature T of 373 K and a pressure p of 6 MPa. Consistent with previous studies, the measured dissolution rates deviate from the classical transition state theory (TST) model which was developed for elementary reactions in homogeneous media. A modified TST expression was subsequently proposed. Next, the dissolution kinetics of three chemically heterogeneous carbonate reservoir rocks were investigated in (CO2 + H2O) system at T = 323 K and p = 10 MPa. For a single carbonate mineral in the heterogeneous matrix, the measured dissolution rates were found to be comparable to those of a chemically homogeneous system under similar experimental conditions. Finally, the impact of surface alterations (including adsorbed biofilms and crude-oil films) on calcite dissolution kinetics was investigated in (CO2 + H2O) systems at temperatures ranging from (325 to 333) K and pressures up to 10 MPa. Some of these films made a minor difference in reaction rates and the effects were found to be dependent on temperature, pressure, exposure time and reactor configurations. In this study, extensive characterizations were performed on both fluid and solid phases, and geochemical simulations were implemented in the PHREEQC software. Further, preliminary insights from Lattice Boltzmann modelling and reactive core flooding studies are presented.

Crystalline carbon nitride has been a hot topic for the last ten years because of reports claiming it could work as a photocatalyst for cheap water splitting, a catalyst for difficult reactions inorganic chemistry and the use as a potential two-dimensional semiconductor.The carbon nitride of interest in this project is poly(triazineimide) (PTI), which has a layered structure similar to graphite. Oneof the goals was to examine the synthesis parameters to try tounderstand what makes these crystallites grow. The material was primarily analyzed using scanning electron microscopy and powder x-ray diffraction. The other goal of this project was to examine the physical properties of dissolved PTI. It is currently not understood how PTI behaves in various solvents. The effect on how the freezing point depression varies in different solvents was, therefore, tested.No strong correlations of how the morphology of the produced PTIdiffered with different synthesis parameters. Freezing point measurements suggest that a solution of PTI follows Raoult's law and can be described as a true solution.

A significant body of work exists around coke dissolution into liquid iron, however there are key aspects of this important reaction that are not well described. This study was focused on gaining the answers to the questions “How does the coke mineral matter behave during coke dissolution?” and “Can the effects of sulphur and oxide layer formation on the dissolution rate be separated and quantified?”. Issues that must be addressed if the understanding of the kinetics of this reaction is to be advanced and coke's use in the blast furnace further optimised.To this end, a detailed investigation was conducted examining the influence of coke mineral matter on coke (carbon) dissolution into liquid iron. This project was focused on the mineral matter layer that forms at the coke/iron interface and how the presence of this layer affects the kinetics of carbon dissolution from the coke into the liquid iron. A range of experimental techniques were used to identify and characterise the mineral layer as it formed at the coke/iron interface and to assess the layers influence on the carbon dissolution kinetics.Carbon dissolution experiments, utilising a carburiser cover technique, were carried out where carbon and sulphur transfer to an iron-carbon melt was measured over time at temperatures of 1450°C, 1500°C and 1550°C. This technique allowed fundamental data on the dissolution rate constant to be calculated, and the effects of temperature, melt sulphur and different carbonaceous materials to be explored.Development of the mineral layer at the coke/iron interface as a function of both time and temperature was studied utilising a quenched carbon dissolution technique that was developed during the project. This technique had the additional benefit of allowing the composition of the melt to be determined for a larger range of elements than the dissolution experiments. The quenched carbon dissolution experiments complemented the carbon dissolution experiments and allowed direct comparisons between the dissolution behaviour measured in the dissolution experiments and the composition and morphology of the mineral layer observed in the quenched samples.The dissolution studies were further complemented by sessile drop measurements of the wetting behaviour of iron on the mineral phases that were identified in the mineral layer present at the coke/iron interface, thermodynamic modelling utilising the MTDATA software package and a conceptual model of the interfacial mineral layer.A mineral layer was observed to have formed at the coke/iron interface during coke dissolution into liquid iron at experimental temperatures ranging from 1450°C to 1550°C. The mineral layer was solid at these temperatures and persistent at the interface. The amount of mineral matter present in the mineral layer was observed to be increasing with increased reaction time. The composition and structure of the mineral layer changed with both experimental time and temperature. The composition of the mineral layer was principally composed of oxides of aluminium and calcium, present as various calcium aluminates and calcium sulphides. Initially the mineral layer was a loose agglomeration of particles of which a majority were alumina particles. As the dissolution reaction proceeded, the loose agglomeration of particles was replaced by an open acicular layer that was predominantly the calcium aluminate CaO.6Al2O3 (CA6). As the dissolution reaction continued further, the calcium aluminates became increasingly richer in calcium oxide, with the predominate phase present in the mineral layer progressing through the calcium aluminates phases CA6 to CaO.2Al2O3 (CA2) and onto CaO.Al2O3 (CA). The apparent calcium enrichment of the mineral layer was observed to occur more rapidly as the experimental temperature increased. Accompanying the compositional changes in the mineral layer, the morphology of the mineral layer was also observed to change. The mineral layer was formed as an initial loose agglomeration of alumina particles, changing to an open acicular structure consisting of CA6/CA2 before being converted to a dense layer as the dissolution reaction proceeded and the composition of the mineral layer changed to CA and calcium sulphide (CaS) appeared at the interface.It was found that the formation of the calcium sulphide layer was preceded by the formation of the calcium aluminate layer. Only after the calcium aluminate layer had experienced progressive calcium enrichment and the CA and CA2 phases had formed did the CaS phase appear at the iron interface. Thermodynamic analysis of the experimental results confirmed that the formation of the calcium enriched calcium aluminates, CA2 and CA, were a necessary requirement to stabilise the calcium sulphide layer for the coke composition studied.The kinetics of carbon dissolution from the coke to the liquid iron were observed to be dependent on the structure of the interfacial mineral layer. This dependence was manifest as two stage behaviour in the first order mass transfer plots. The initial stage, characterised by rapid carbon dissolution, was observed while the mineral layer was developing or had the open acicular structure of the CA6/CA2 layer. The second stage was characterised by a significant reduction in the rate of carbon dissolution. The onset of the second stage was coincident with the change in the composition of the mineral layer from CA6/CA2 to CA2/CA and the associated densification of the mineral layer. In stating that the nature of the mineral layer affects the dissolution kinetics, a change in the reaction control mechanism is implied. This represents a change in the coke dissolution kinetics from simple mass transfer control to a mixed control regime where both mass transfer and the mineral (product) layer are active.In an attempt to overcome the problems associated with the heterogeneity of coke a coke analogue was developed. In the coke analogue the composition and dispersion of the carbonaceous and mineral matter (oxides) are controlled and the porosity is fixed. When single phase calcium aluminates were introduced into the coke analogues, calcium enrichment of the resulting calcium aluminate mineral layer was observed. The observed carbon dissolution kinetics were dependant on the structure of the interfacial calcium aluminate layer. Consistent with the coke dissolution studies, the calcium aluminate layer formed at the coke analogue iron interface during carbon dissolution was at least in part rate controlling the carbon dissolution reaction for the coke analogues studied.Utilising the sessile drop experimental technique the wettability with liquid ironcarbon-sulphur alloys of the predominate phases that were observed in the mineral layer were measured. It was observed that the contact angle decreased as the proportion of lime (CaO) in the calcium aluminate increased. Further it was observed that while the presence of sulphur in the melt increased the contact angle for the alumina and CA6 substrates, on the CA2 and CA substrates the contact angle was decreased. The improvement in the wetting of the CA2 and CA substrates with sulphur was attributed to the formation of CaS at the substrate/droplet interface.This study has produced new fundamental data on the growth and development of the mineral layer and the wettability of the predominate calcium aluminates observed in the mineral layer. These detailed studies have illuminated the changing nature of the layer in terms of both composition and morphology and found that the kinetics of carbon dissolution from the coke to the liquid iron were dependant on the structure of the interfacial mineral layer.

Previous coreflood experiments show that CO2 sequestration in carbonate rocks is a win-win technology. Injecting CO2 into a depleted gas reservoir for storage also produces hitherto unrecoverable gas. This in turn helps to defray the cost of CO2 sequestration. This thesis reports the results from experiments conducted on a Berea sandstone core. The experiments include displacement experiments and unconfined compressive strength tests. The displacement experiments were conducted at cell pressures of 1500 psig and temperature of 60oC using a 1 foot long and 1 inch diameter Berea sandstone core. Pure CO2 and treated flue gas (99.433 % mole CO2) were injected into the Berea sandstone core initially saturated with methane at a pressure of 1500 psig and 800 psig respectively. Results from these experiments show that the dispersion coefficient for both pure CO2 and treated flue gas are relatively small ranging from 0.18-0.225 cm2/min and 0.28-0.30 cm2/min respectively. The recovery factor of methane at break-through is relatively high ranging from 71%-80% of original gas in place for pure CO2 and 90% to 92% OGIP for treated flue gas, the difference resulting from different cell pressures used. Therefore it would appear that, in practice injection of treated flue gas is a cheaper option compared to pure CO2 injection. For the unconfined compressive strength tests, corefloods were first conducted at high flowrates ranging from 5 ml/min to 20 ml/ min, pressures of 1700-1900 Psig and a temperature of 65oC. These conditions simulate injecting CO2 originating from an electric power generation plant into a depleted gas reservoir and model the near well bore situation. Results from these experiments show a 1% increase in porosity and changes in injectivity due to permeability impairment. The cores are then subjected to an unconfined compressive strength test. Results from these tests do not show any form of weakening of the rock due to CO2 injection.

An often overlooked connection between karst groundwater systems and surface water is spring flow reversal, the flow of river water into karst springs caused by changes in hydraulic gradient. Karst aquifers are subject to the intrusion of river water when the hydraulic head of a base level river is higher than the hydraulic head of a base level spring. When this occurs, the flow out of the spring reverses, allowing river water to enter base level conduits. River water thus becomes a source of recharge into karst basins, transporting both valuable nutrients and harmful contaminants into karst aquifers. The rapid recharge of meteoric water, brief groundwater residence times, and the interconnection of surface and subsurface waters through a variety of karst features necessitates studying groundwater and surface water in karst landscapes as a unified system. This study examines the influence of spring flow reversal on cave dissolution in a telogenetic karst aquifer in Mammoth Cave, Kentucky. Spring flow reversals in Mammoth Cave National Park (MCNP) were first recorded nearly one-hundred years ago, but a high-resolution study measuring the effects of spring flow reversals on dissolution in MCNP, or any other telogenetic karst system, had not been conducted until recently. In this study, high-resolution data were collected for pH, SpC, temperature, and stage, as well as weekly samples for major ion concentrations, alkalinity, and carbon isotopes, from June 2018 to December 2018. Surface water and groundwater data were used to quantify the complex hydrologic processes associated with the spring flow reversals, including seasonal changes in karst geochemistry and dissolution taking place between the Green River, River Styx Spring, and Echo River Spring. Data show distinct changes in geochemical parameters as flow reversals occur, with temperature being the principal indicator of flow direction change. During this study, all ten stable reverse flows coincided with increased discharge from the Green River Dam. The predominant drivers of dissolution in the River Styx and Echo River karst basins are storm events and seasonal changes in the hydrologic regime, rather than seasonal CO2 production, normal baseflow conditions, or stable reverse flow events. Estimated dissolution rates generally show that stable reverse flows contribute no more to dissolution than normal baseflow conditions – the highest amount of dissolution during a single stable reverse flow was only 0.003 mm. This is contrary to flow reversal studies in an eogenetic karst system in Florida, which estimated 3.4 mm of wall retreat during a single spring flow reversal. These contrasting results are likely due to significant differences in pH of river water, matrix porosity of the bedrock, basin morphology, and flow conditions.

Cette thèse porte sur l’étude de l’enthalpie de dissolution du dioxyde de carbone dans des solutions aqueuses d’électrolyte. Pour développer des modèles théoriques décrivant les systèmes {CO2-eau-sel} pour les conditions appliquées aux conditions de stockage géologique du dioxyde de carbone, il est nécessaire d’avoir des données expérimentales reliant la solubilité et l’enthalpie. Dans cette étude, une unité de mélange à écoulement construite au laboratoire a été adapté à un calorimètre SETARAM C-80 pour mesurer l’enthalpie de solution du CO2 dans des solutions aqueuses d’électrolyte (NaCl, CaCl2 et Na2SO4) aux forces ioniques comprises entre 2 et 6 et a des températures comprises entre 323.1 K et 372.9 K et des pressions allant de 2 à 16 MPa. Les données de la littérature ont été utilisées pour ajuster le modèle thermodynamique d’équilibre de phase dans l’approche Υ-φ. Le modèle thermodynamique reproduit les enthalpies expérimentales à plus ou moins 10%. Le calcul de l’enthalpie dans le modèle rigoureux est fortement dépendant des données de la littérature. Un dispositif expérimental a été mis en place pour la détermination du volume molaire du CO2 à dilution infinie, propriété nécessaire à modélisation thermodynamique. Le dioxyde de carbone à stocker peut contenir des impuretés telles que les gaz annexes (O2, N2, SOx, H2S, NyOx, H2, CO et Ar). Dans l’objective d’étudier la dissolution du CO2 dans des solutions aqueuses d’électrolyte en présence de ces impuretés, un dispositif expérimental a été mis en place pour la mesure des enthalpies de solution du SO2 dans l’eau et solutions aqueuses de NaCl et les premières résultats sont prometteurs
This thesis studies the enthalpy of solution of carbon dioxide in electrolyte aqueous solutions. To develop theoretical models describing the systems {CO2-water-salt} under the geological storage conditions of carbon dioxide, it is necessary to have experimental data, namely solubility and enthalpy. In this study, a customized flow mixing unit was adapted to a SETARAM C-80 calorimeter to measure the enthalpy of CO2 solution in aqueous electrolyte solutions (NaCl, CaCl2 and Na2SO4) at the ionic strengths between 2 and 6 and at temperatures between 323.1 K and 372.9 K and pressures ranging from 2 to 16 MPa. Data from the literature were used to adjust the thermodynamic phase equilibrium model in the Υ-φ approach. The thermodynamic model reproduces the experimental enthalpies to plus or minus 10%. The calculation of the enthalpy in the rigorous model is strongly dependent on the data of the literature. An experimental device has been set up for the determination of the molar volume of CO2 at infinite dilution, which is necessary for thermodynamic modeling. The carbon dioxide to be stored may contain impurities such as annexes (O2, N2, SOx, H2S, NyOx, H2, CO and Ar). Under the objective of studying the influence of these impurities, an experimental apparatus has been set up for the measurement of enthalpies of solution of SO2 in water and aqueous solutions of NaCl and the first results are promising

As carbon dissolution rates have been determined for a few chars only, a systematic and comprehensive study was undertaken in this project on the dissolution behaviour of carbon from non-graphitic materials into liquid iron. In addition to measuring the kinetics of carbon dissolution from a number of coal chars into liquid iron as a function of parent coal and coal ash composition, the influence of chemical reactions between solute/solid carbon and ash oxides was also investigated. These studies were supplemented with investigations on one metallurgical coke for the sake of comparison. The wettability of coal chars and coke with liquid iron at 1550 degrees C was measured as a function of time. Being essentially non-wetting, only a marginal improvement in contact angles was observed with time. The accumulation of alumina at the interface was detected for all materials and was seen to increase with time in all cases. Calcium and sulphur also appeared to preferentially accumulate at the interface, concentrating at levels in excess of those expected from the ash composition alone. Despite the high levels of silica in the ash initially, very little silica was detected in the interfacial region, implying ongoing silica reduction reactions. A small amount of silicon was however detected in the iron droplets, indicating silica reduction with solute carbon. It was identified that the reduction reactions can also consume solute carbon in the liquid iron. As this is occurring simultaneously with carbon dissolution into liquid iron, the interdependency of silica reduction and carbon dissolution could potentially limit the observed carbon dissolution rate. A theoretical model was developed for estimating the interfacial contact area between chars and liquid iron. Wettability was found to have a very significant effect on the area of contact. A two-step behaviour was observed in the carbon dissolution of two chars and coke. Slow rates of carbon dissolution in stage II were attributed to very high levels of interfacial blockage by reaction products leading to much reduced areas of contact between carbonaceous material and liquid iron. The first order dissolution rate constants for four chars/coke and the observed trend in first order dissolution rate constants were calculated. These dissolution results compare well with the previously measured dissolution rate constants. The trends in dissolution can be adequately explained on the basis of carbon structure, silica reduction, sulphur concentration in the metal and ash impurities.

Organic matter which is insoluble in common solvents and non-oxidising acids often comprises the quantitatively most important fraction of organic matter in sediments. This operationally defined material is usually simply termed 'insoluble organic matter' (IOM) or 'kerogen' when it is isolated from ancient sediments. Indeed, kerogen is regarded as the most abundant form of carbon on the planet. The molecular character of this generic material has not been fully elucidated, principally because of its insolubility which limits instrumental methods of analysis to those applicable to solid substrates. This thesis describes the quantitative isolation of IOM from lacustrine and marine sediments and two species of methanogenic bacteria using a sequential isolation procedure. A range of synthetic IOMs (melanoidins) was also prepared. The dissolution of IOM and melanoidins obtained in this manner was then attempted using the acidic ionic liquid l-ethyl-3- methylimidazolium chloride-aluminium (III) chloride. Two synthetic dendrimers containing similar functional groups to those observed in sedimentary IOM were used to try and assess the mode of action of the ionic liquid. Ionic liquid treatment of the DCM soluble dendrimers resulted in the formation of 7 - 62 % of material that was no longer soluble in DCM, whilst the soluble components had been substantially altered. The ionic liquid was found to non-quantitatively promote ether cleavage, protonation and rearrangement reactions. IOM was isolated from lacustrine Rostherne Mere, UK, sediments (7 - 3 0 % dry weight), Kimmeridge Clay, Dorset (11 - 12 %) and methanogenic bacteria (Methanococcus jannaschii, 3 %; Methanobacterium thermoaiitotrophicum, 0.1 %) using a time-consuming isolation procedure involving over forty separate chemical manipulations. Monitoring of the sequential isolation of IOM and characterisation of the final isolates was carried out using solid-state NMR, IR, elemental analysis, pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), scanning electron microscopy, and the newer surface sensitive technique of time of flight-secondary ion mass spectrometry (ToF-SIMS). Less than 1 % of sedimentary IOM and 5 % of Kimmeridge Clay IOM was soluble in DCM following ionic liquid treatment, whilst alkyl chains were lost from the insoluble portion which also increased in aromaticity. The poor yield recovered following ionic liquid treatment of M. jannaschii IOM (5 %) was attributed to loss of volatile material during hydrolysis. Following ionic liquid treatment 93 - 96 % of the melanoidins remained insoluble in DCM although their character had been altered, becoming more condensed. This ionic liquid dissolution procedure has not provided the substantial progress in elucidating the molecular character of IOM promised by earlier reports.

Knowledge about whether/how natural water chemistry influences the fate, dissolution, and toxicity of silver nanoparticles (AgNPs) should contribute to ecological risk assessment and informed decision making. The effects of three critical water chemistry parameters – dissolved organic carbon (DOC), pH, and hardness – were investigated on the colloidal stability, dissolution dynamics, and antimicrobial activity of citrate-functionalized AgNPs (citrate–AgNPs) against Escherichia coli. Toxicities of citrate–AgNPs and AgNO3 were also determined in the river water samples collected across three seasons (for seven months). Detectable changes in hydrodynamic diameter, surface charge, and plasmonic resonance revealed the modulating effects of the water chemistry parameters on the colloidal stability of citrate–AgNPs. Although, overall Ag release from citrate–AgNPs was low (0.33–3.62%), it increased with increasing DOC concentrations (0–20 mg L−1) but decreased with increasing pH (5–7.5) or hardness (150–280 mg L−1). Citrate–AgNP toxicity was 3–44 fold lower than of AgNO3 (Ag mass basis). Notably, higher DOC or pH conferred protection to E. coli against citrate–AgNPs or AgNO3; increasing solution hardness tended to enhance toxicity, however. Citrate–AgNPs or AgNO3 toxicity in the river water matrix revealed no seasonality. Generalized linear models developed, by parameterizing particle properties, could fairly predict empirically-derived nanotoxicity. Our results show that particle size, surface properties, ion release kinetics, and toxicity of citrate–AgNPs can be modified upon release into aquatic environments, suggesting potential implications to ecosystem health and functions.

Today, ethanol, as well as other biofuels, has been increasingly gaining popularity as a major alternative liquid fuel to replace conventional gasoline for road transportation. One of the key challenges for the future use of bioethanol is to increase its availability in the market via an efficient and economic way. However, one major concern in using the existing gas-pipelines to transport fuel-grade ethanol or blended fuel is the potential corrosion and stress corrosion cracking (SCC) susceptibility of carbon steel pipelines in these environments. Both phenomenological and mechanistic investigations have been carried out in order to address the possible degradation phenomena of X-65 pipeline carbon steel in simulated fuel-grade ethanol (SFGE). Firstly, the susceptibilities of stress corrosion cracking of this steel in SFGE were studied. Ethanol chemistry of SFGE was shown to have great impact on the stress corrosion crack initiation/propagation and the corrosion mode transition. Inclusions in the steel can increase local plastic strain and act as crack initiation sites. Secondly, the anodic behavior of carbon steel electrode was investigated in detail under different ethanol chemistry conditions. General corrosion and pitting susceptibility under unstressed condition were found to be sensitive to the ethanol chemistry. Low tendency to passivate and the sensitivity to ethanol chemistry are the major reasons which drive corrosion process in this system. Oxygen plays a critical role in controlling the passivity of carbon steel in ethanol. Thirdly, the detailed study was carried out to understand the SCC mechanism of carbon steel in SFGE. A film related anodic dissolution process was identified to be a major driving force during the crack propagation. Fourthly, more detailed electrochemical impedance spectroscopy (EIS) studies using phase angle analysis and transmission line simulation reveal a clearer physical picture of the stress corrosion cracking process in this environment. Fifthly, the cathodic reactions of carbon steel in SFGE were also investigated to understand the oxygen and hydrogen reactions. Hydrogen uptake into the pipeline steel and the conditions of the fractures related to hydrogen embrittlement were identified and studied.

In present thesis, the fundamental studies on the reaction between MgO based refractories and slag were undertaken for the development of a carbon-free bonding MgO lining material. Alumina was selected as a potential binder material. Due to MgO-Al2O3 chemical reaction, the developed refractory was bonded by MgO·Al2O3 spinel phase. To begin with, an investigation of the dissolution process of dense MgO and MgO·Al2O3 spinel in liquid slag was carried out. To obtain reliable information for dissolution study, a new experimental method was therefore developed. In this method, a cylinder was rotating centrally in a special designed container with a quatrefoil profile. This method also showed a good reliability in revealing the dissolution mechanism by quenching the whole reaction system. The experimental results showed that the dissolution process of MgO and spinel was controlled by both mass transfer and chemical reaction. It was found that the rapid dissolution of spinel was mainly because of its larger driving force. To improve the resistance against slag penetration, two aspects were studied to develop carbon-free MgO refractory. First, colloidal alumina was used and the effect of its addition into MgO matrix was investigated. The use of colloidal alumina was to form bonding products in the grain boundary of MgO. The results showed that the alumina addition greatly improved the resistance of MgO based refractory against slag penetration in comparison with the decarburized MgO-carbon refractory. It was found that the improvement of resistance was mainly related to the spinel-slag reaction products of CaO·Al2O3 and CaO·MgO·Al2O3 solid phases at the grain boundaries. Second, the effect of particle size distribution on the penetration resistance of MgO was investigated. The most profound improvement against the slag penetration was obtained by using a proper particle size distribution. The results highlighted the importance of considering the refractory structure. Experiments were undertaken to investigate the dissolution mechanism of different types of MgO based refractories in liquid slag. It was observed that the dissolution of spinel bonded MgO refractory was much slower than the decarburized MgO-carbon refractory. The primary dissolution in spinel bonded MgO refractory occurred at the slag-penetrated layer, and the removal of this layer by peeling off enhanced the dissolution rate rapidly.

QC 20170918

European RFCS LEANSTORY project

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Geologic sequestration of carbon dioxide (CO 2) in a deep, saline aquifer is being proposed for a power-generating facility in Florida as a method to mitigate contribution to global climate change from greenhouse gas (GHG) emissions. The proposed repository is a brine-saturated, dolomitic-limestone aquifer with anhydrite inclusions contained within the Cedar Keys/Lawson formations of Central Florida. Thermodynamic modeling is used to investigate the geochemical equilibrium reactions for the minerals calcite, dolomite, and gypsum with 28 aqueous species for the purpose of determining the sensitivity of mineral precipitation and dissolution to the temperature and pressure of the aquifer and the salinity and initial pH of the brine. The use of different theories for estimating CO2 fugacity, solubility in brine, and chemical activity is demonstrated to have insignificant effects on the predicted results. Nine different combinations of thermodynamic models predict that the geochemical response to CO2 injection is calcite and dolomite dissolution and gypsum precipitation, with good agreement among the quantities estimated. In all cases, CO2 storage through solubility trapping is demonstrated to be a likely process, while storage through mineral trapping is predicted to not occur. Over the range of values examined, it is found that net mineral dissolution and precipitation is relatively sensitive to temperature and salinity, insensitive to CO2 injection pressure and initial pH, and significant changes to porosity will not occur.

The electrochemical passivation of pure Fe in ammoniacal solution was investigated to determine the stability of both Fe-oxides and Fe-ammines during anodic polarization. The potentiodynamic experiments were done in 6M total NH₃[3M NH₄OH and 1.5M (NH₄4)₂CO₃] solution. Different experimental parameters such as temperature (15°, 25°, 35°, 45° and 55°C) and pH (6, 8, 10 and 12) were used. Pure oxygen and argon gas was sparged during the experiment to oxygenate or de-oxygenate the solution with no stirring in either case. Polarization plots show that both active anodic dissolution and passive regions are present for pure iron in ammoniacal solution. It also shows that as the temperature increased the dissolution rate increased in both anodic and passive regimes. At the same time, the active region for iron dissolution is present across a wider potential range. For pH 10 the highest dissolution rate is around 0.025A/cm² or 260 g/m²hr¹ at 55°C and passivation of iron generally occurs at ca. -0.36 V (SHE) irrespective of the temperature. The peak anodic dissolution rate (0.2 A.cm₋² or 2080 g/m²hr¹) surprisingly occurs at pH 6. Potentiostatic experiments were done at different fixed potentials at pH 9 and 25°C. The highest current density was registered at -0.6 V. The peak dissolution current observed for the potentiostatic tests is roughly two orders of magnitude lower than that observed in the potentiodynamic test for pH 9 and at 25°C. Solution and morphological analyses were done by ICP and SEM, respectively for pH 6 and 9 solutions. The current efficiency for pH 6 is far lower than at pH 9 which implies that the current registered at pH 6 is used for the formation of a product film. Speciation calculations indicate that this film may be siderite (FeCO₃) at low potential. From XPS analyses, it is believed that the passive layer formed at higher potentials (more than 0.40V) is Fe₂O₃. Speciation diagrams point to the stability of iron tetra-ammines at pH 10. It was shown that metastable Eh-pH diagrams for Fe/NH₃/CO₃/H₂O system can be generated through potentiodynamic measurements aimed at active and passive behavior of iron.

Cette thèse porte sur l'étude de l'enthalpie de dissolution du dioxyde de carbone dans des solutions aqueuses d'amine. Pour développer des modèles théoriques décrivant les systèmes (CO2-amine-eau) pour les conditions appliquées aux procédés industriels, il est nécessaire d'avoir des données expérimentales reliant la solubilité et l'enthalpie. Dans cette étude, nous avons utilisé une unité de mélange construite au laboratoire que nous avons adapté à un calorimètre SETARAM C-80 pour mesurer l'enthalpie de solution du CO2 dans cinq solutions aqueuses d'amine, (la 2-Amino-2-méthyl-1-propanol (AMP), la monoéthanolamine (MEA), la diéthanolamine (DEA), la triéthanolamine (TEA) et la méthyldiéthanolamine (MDEA) (15 et 30 mass%) à des températures comprises entre 322.5 K et 372.9 K et des pressions allant de 0.5 à 5 MPa. Les données de la littérature ont été utilisées pour ajuster deux modèles thermodynamiques d'équilibre de phases (un simple et un rigoureux). Le premier modèle résume l'absorption du CO2 par une seule réaction, tandis que le second prend en compte toutes les réactions à l'équilibre. Le modèle simple reproduit nos enthalpies expérimentales à plus ou moins 10%, tandis que le modèle rigoureux reproduit nos données avec un écart compris entre 5 et 20% selon l'amine considérée. Le calcul de l'enthalpie dans le modèle rigoureux est fortement dépendant des données de la littérature utilisées pour la réaction de protonation de l'amine. Ceci souligne la nécessité d'acquérir de nouvelles données expérimentales sur ces constantes d'équilibre pour améliorer le modèle.

L’augmentation de la teneur en carbone dans l’atmosphère provoquée par les activités anthropiques est freinée par l’effet « puit de carbone » de certaines régions de l’océan, en particulier grâce à la pompe biologique de carbone. La forte participation des diatomées à la production primaire océanique ainsi que leur capacité à former des agrégats nous ont conduit à étudier le rôle des diatomées, et en particulier l’impact de l’agrégation sur la pompe biologique de carbone. Des expériences en laboratoire ont permis de déterminer que la vitesse de dissolution des frustules de diatomées est plus faible pour les cellules agrégées que pour les cellules libres. Le modèle d’agrégat utilisé pour mieux comprendre les paramètres conduisant à ces mesures expérimentales, confirme que la dissolution de la BSiO2 est ralentie et démontre que la diffusion de la DSi dans l’agrégat est plus faible que dans l’eau de mer. Le ralentissement de la dissolution est attribué aux fortes teneurs en DSi mesurées dans l’agrégat et à une viabilité plus longue des diatomées agrégées. Les résultats expérimentaux sont ensuite combinés avec des mesures in situ de flux de BSiO2 dans neuf provinces de l’océan, dans un modèle simplifié reconstruisant les flux de BSiO2 de la colonne d’eau. Ce modèle détermine la répartition de la BSiO2 du flux entre cellules libres et grosses particules et donne des informations sur la dynamique des particules. Les flux de BSiO2 reconstruits, associés à une relation empirique donnant l’évolution des rapports Si:C avec la profondeur, permettent d’évaluer le véritable rôle des diatomées dans la pompe biologique de carbone en calculant les flux de carbone au bas de la couche hivernale de mélange. L’utilisation des flux de Si comme traceur des flux de C permet de s’affranchir des difficultés liées à la chimie complexe à laquelle est soumis le C. Le rôle des diatomées dans l’export ou le transfert de carbone dépend de la façon d’estimer l’export hors de la couche de surface
The dramatic increase of carbon concentration in the atmosphere is limited by the action of some oceanic areas that act like a “sink of carbon” mainly thanks to the biological pump. Because of the strong participation of diatoms to the primary production and their ability to aggregate, we study the role of diatoms and the impact of aggregation on the biological pump. Laboratory experiments determined that the BSiO2 dissolution rate of aggregated cells is lower than the one of freely suspended cells. The model of aggregate used to better understand aggregate internal parameters that provoke the decrease of the dissolution rate, confirmed that the dissolution is lower in aggregates and added that the DSi diffusion in aggregate is lower than in seawater. The decrease of the BSiO2 dissolution rate is attributed to the strong DSi concentrations measured into aggregates and to the higher viability of aggregated cells. Experimental results were then combined with in situ measurements of BSiO2 fluxes in nine areas cf the ocean, intc a simple model that reconstruct BSiO2 fluxes in the water column. This model allows to calculate the repartition of the BSiO2 between large particles and freely suspended cells and to better understand particles dynamic. The BSiO2 fluxes reconstructed using the model, were then associated with a relation between Si/C ratios and water column depth to determine the real importance of diatoms in the biological pump cf carbon. We then calculated the carbon fluxes at the maximum depth of the mixing layer. The use of the Si fluxes as a proxy of the carbon fluxes allow to ignore difficulties due to the cornplexity of the carbon chemistry. The role of diatoms in the export and transfer of carbon strongly depend on the way used to calculate the export out of the surface layer

La compréhension des mécanismes de compaction des roches et des sédiments est importante dans différents domaine des géosciences en particulier pour caractériser la compaction dans les bassins sédimentaires ou le colmatage dans les failles actives. Les objectifs de cette thèse sont d'une part de séparer et de quantifier le rôle respectif de la compaction mécanique et chimique dans les sédiments carbonatés. D'autre part d'obtenir une meilleure compréhension des procédés aboutissant au fluage des roches sédimentaires carbonatées. La perte de porosité par compaction mécanique a été étudiée en réalisant des essais triaxiaux K0 sur des échantillons provenant de plateformes carbonatées. Onze échantillons cimentés par de la calcite faiblement magnésienne et cinq échantillons dolomitisés provenant du Marion Plateau au large de la côte nord-est Australienne (ODP (ocean drilling program) Leg194) ont été compactés de manière uniaxiale à des contraintes effectives allant jusqu'à 70 MPa. La cimentation à faible profondeur à laquelle ces échantillons ont été soumis a créé une structure cimentée stable ayant un fort degré de sur–consolidation et une faible compressibilité. La plupart des échantillons testés étaient tellement cimentés à 30–400 mètres que la perte de porosité à des profondeurs atteignant 4–5 km doit être principalement liée à des procédés chimiques et non à des procédés mécaniques. Pour étudier ces processus chimiques deux autres types d'expériences ont été réalisées. La dissolution sous contrainte est le principal mécanisme responsable du fluage des roches sédimentaires pendant leur enfouissement. Par conséquent la vitesse de déformation de la calcite par dissolution sous contrainte à l'échelle d'un contact a été étudiée. Les résultats obtenus permettent l'identification de l'importance respective de la dissolution sous contrainte résultant de l'application de la contrainte normale et celle de la dissolution au niveau des surfaces 'libres' résultant de l'accumulation de l'énergie élastique ou plastique. Deux mécanismes différents se produisent lors de la dissolution sous contrainte de cristaux de calcite à l'échelle du grain. Dans un premier cas, la diffusion du solide en solution se produit dans le fluide présent à l'interface rugueuse entre la calcite et le poinçon. Dans un deuxième cas, la diffusion se produit le long de fractures qui se propagent du contact vers la partie du cristal soumise à des contraintes plus faibles. Les vitesses de déformation sont plus élevées dans les expériences pour lesquelles la propagation de fractures se produit. De manière générale la vitesse de déformation n'apparait pas comme étant dépendante de la contrainte, mais plutôt de la propagation ou non de fractures. Finalement, les procédés mécaniques et chimiques actifs pendant la compaction ont été étudiés sur des agrégats de cristaux de calcite ou de sables bioclastique. Les expériences montrent que la compaction des sables carbonatés doit être modélisée en prenant en compte à la fois la compaction mécanique et chimique. Dans toutes les expériences la nature du fluide saturant, l'organisation initiale des grains et la taille des grains sont des paramètres important contrôlant la déformation finale ainsi que la vitesse de déformation à une contrainte donnée. La déformation des échantillons saturés avec des fluides non réactifs, e. G. Air ou décane, est moins importante qu'avec des fluides réactifs, puisque dans ce cas la compaction est seulement mécanique. Pendant la phase de chargement, la compaction chimique se produit par dissolution sous contrainte, dont la vitesse est augmentée par la présence de petites fractures au niveau des contacts intergranulaires. Cette interprétation est confirmée par l'observation des échantillons en lame-minces. Les vitesses ultrasoniques se propageant dans les agrégats saturés avec des fluides réactifs ont été mesurées et il a pu être montré que la dissolution et le transport de matière affectant la géométrie des contacts au niveau des grains, ainsi que la fracturation des grains sont probablement les raison de cette diminution de vitesse. En conclusion, la perte de porosité dans les sédiments carbonatés est principalement due à la compaction chimique et très peu à la compaction mécanique. Les procédés chimique de la compaction sont d'une part la dissolution sous contrainte, et d'autre part la dissolution sous contrainte assistée par la propagation sous–critique de fissures. La prédominance de l'un ou l'autre de ces procédés est liée à la nature du fluide présent dans l'espace poreux ainsi qu'à la nature des grains
Understanding compaction processes in sediments or rocks is important for instance for the characterisation of compaction in sedimentary basins or for sealing of active fault. The aims of the present study are firstly to separate and quantify the relative role of mechanical and chemical compaction in carbonate sediments. Secondly to better understand chemical compaction processes acting on sediments. The potential for porosity loss by mechanical compaction of platforms carbonate strata was investigated by carrying out K0 triaxial tests. Eleven samples cemented with low, Mg calcite and five dolomitized samples from the Marion plateau, offshore northeast Australia (ODP (ocean drilling program) Leg194) were uniaxially compacted at effective stresses up to 70 MPa. Early cementation of bioclastic carbonate samples created a stable cemented framework with a high degree of over, consolidation and low compressibility. Water saturation of the samples produces weakening of the mechanical strength and greater scatter in the correlation of P, wave velocity versus porosity. Most of the tested samples were already so strongly cemented at 30, 400 meters that further porosity loss during burial up to 4, 5 km depth must occur mainly by chemical rather than mechanical processes. To study chemical processes two other types of experiments were carried out. Pressure solution is the main chemical compaction mechanism affecting sediments during burial, therefore the rate of calcite deformation by pressure solution creep at a single contact was studied. The results enable the identification of the relative importance of pressure solution driven by normal load, and free surface dissolution driven by strain energy. Two different processes occur during pressure solution of calcite crystals at the grain scale. In one case, diffusion of the dissolved solid takes place in the pore fluid present along a rough interface between calcite and the indenter. In the second case, diffusion occurs through cracks that propagate from the contact toward the less stressed part of the crystal. Strain rates are higher for experiments in which crack propagation occurred. Overall it seems strain rates are not really stress dependent but rather dependent on whether crack propagation occurs or not. Eventually, both mechanical and chemical compaction processes were studied on aggregates of calcite and bioclastic carbonate sands. Experimental compaction showed that compaction of carbonates sands should be modelled as a function of both mechanical and chemical compaction also at relatively shallow depth and low temperature. In all cases, the nature of the fluid, the initial grain packing, and the grain size represent important control parameters of the final strain and the strain rates at a given stress. Samples saturated with non, reactive fluids, e. G. Air or decane, show less strain than samples saturated with reactive fluids at the same effective stress since the compaction was only mechanical. During the loading phase, chemical compaction occurs by pressure solution creep which is enhanced by the presence of cracks at the grain, to, grain contacts. This is also supported by the identification of compaction related microstructures in thin, sections. During creep tests, the samples compressibility is controlled by, in order of importance, grain size, stress, and water saturation. Low ultrasonic velocities are especially observed in samples saturated with reactive fluids. Dissolution and transport affecting the grain, to, grain contacts geometry and crack propagation are likely to be the reason for such velocity alteration. In conclusion, porosity loss in carbonate sediments is mostly due to chemical compaction and very little to mechanical compaction. Chemical compaction processes are pressure solution and pressure solution enhanced by subcritical crack growth. The predominance of one or the other mechanism is to be related to the fluid in presence and to the nature of the grains

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Nesta dissertação, investiga-se a reação de dissolução ácida de rochas silicatos brasileiras visando a aplicação em um processo de captura e sequestro de carbono denominado por Carbonatação Mineral. Na carbonatação mineral pela rota indireta utiliza-se ácidos, bases ou sais de amônia para a extração do magnésio, principalmente, presente na rocha silicato a fim de a formar carbonatos estáveis. Destaca-se que a etapa de dissolução ácida é uma fase limitante para o processo de carbonatação mineral, principalmente por apresentar baixa taxa de reação. O objetivo deste trabalho é utilizar o ácido clorídrico (HCl) e dois serpentinitos oriundos do estado de Goiás e Minas Gerais para avaliar o processo de dissolução ácida. Os serpentinitos foram preparados, selecionados e caracterizados para determinar a composição elementar. Aplicou-se o planejamento experimental e arranjo L9 de Taguchi na avaliação dos fatores que influenciam o processo de dissolução, tais como, temperatura do processo, concentração do HCl, tamanho médio das partículas da matéria prima e excesso de ácido. Os 9 ensaios previstos na matriz de planejamento para cada serpentinito foram executados de forma aleatória e em duplicata. Os produtos finais, resíduo sólido retido no papel filtro e solução contendo os elementos de interesse, foram analisados obtendo-se a composição elementar das soluções. Considerando-se os testes previstos na matriz de planejamento, a condição de melhor ajuste para extração de Mg foi utilizando-se a granulometria média de 69 µm, temperatura de 70°C, HCl 2 M com quatro vezes a quantidade estequiométrica. Nas soluções foram obtidas as concentrações de 29 % e 76 % de Mg para as amostras de serpentinito de Minas Gerais e de Goiás, respectivamente. Foram também avaliadas as melhores condições para extração de Fe e Ca e menor extração de Si, uma vez que o Si diminui a conversão no processo. Na análise estatística verificou-se que para a amostra de Minas Gerais todos os fatores apresentaram significância. No caso da a amostra de Goiás a temperatura no nível alto (70°C) apresentou maior significância.
In this dissertation, acid dissolution reaction of Brazilian silicate rocks was investigated aiming the implementation in a Carbon Capture and Storage process named Mineral Carbonation. In the mineral carbonation by indirect route, acids, bases or salts of ammonia are used for magnesium extraction, mainly, present in the silicate rock in order to form stable carbonates. It is noteworthy that the acid dissolution step is a limiting step in the process of mineral carbonation, mainly because of its low reaction rate. The objective of this study was to use hydrochloric acid (HCl) and two serpentinites from Goiás and Minas Gerais states to evaluate the acid dissolution process. The serpentinites were prepared, selected, and characterized to determine the elemental composition. The L9 experimental design and Taguchi arrangement were applied to evaluate the factors that influence in the dissolution process, such as process temperature, HCl concentration, average particle size of material and acid excess. The nine tests prescribed in planning matrix for each serpentinite were performed at random and in duplicate. The end products, solid residue retained on the filter paper and the solution containing the elements of interest were analyzed obtaining the elemental composition of the solutions. Considering the prevised tests on planning matrix, the best adjust condition for Mg extraction was using the average particle size of 69 µm temperature of 70°C, 2 M HCl with four times the stoichiometric amount. In the solutions, the concentrations obtained were 29 % and 76 % Mg for samples of serpentinite from Minas Gerais and Goiás, respectively. The best conditions for the extraction of Fe and Ca and lower extraction of Si were evaluated, since Si decreases the conversion in the process. In the statistical analysis was found that in Minas Gerais sample all factors were significant. In the case of Goiás sample, the temperature at the high level (70°C) showed greater significance.

Etude de la reactivite de sept varietes differentes de fumees de silice condensees (csf). L'activite pouzzolanique depend de la nature et de la teneur des impuretes qua'ellesrenferment. On montre que: le carbone imbrule retarde le phenomene pouzzolanique; le carbone imbrule, en forte teneur, peut provoquer un important retard d'hydratation du ciment portland; l'incorporation de csf a un ciment portland permet d'obtenir un ciment ayant une resistance en compression comparable ou superieur a celle d'un ciment portland mitral, toutefois des impuretes dans une csf peut conduire a rejeter son utilisation.

Les aciers de construction sont sensibles à la corrosion sous contrainte (CSC) dans des milieux basiques tels que les carbonates. Des études par traction lente ont permis d'observer le comportement de deux nuances (A42 / E26 / et XC38) dans de telles conditions à pH 9. Le domaine des potentiels de susceptibilité à la CSC a été déterminé, et une fissuration inter et transgranulaire a été mise en évidence et mesurée par des méthodes micrographiques. La vitesse de fissuration a été étudiée en fonction des vitesses de déformation imposées : une vitesse expérimentale a été ainsi comparée à des valeurs calculées à partir de méthodes précédemment proposées, et de méthodes élaborées au cours de ce travail. Ces dernières donnent une meilleure idée de la fissuration observées dans notre cas. L'emploi d'un inhibiteur passivant (ions chromate) a permis de diminuer le risque de l'attaque fissurante, et d'annuler la vitesse de fissuration même dans les conditions préalablement sensibles.

Depuis une dizaine d'années, une volonté internationale de réduction des émissions de gaz à effet de serre s'est développée, afin de limiter leur concentration dans l'atmosphère. Ainsi, il est envisagé de récupérer le CO₂ issu d'activités humaines fortement émettrices afin de le réinjecter dans le sous-sol à l'état supercritique. Hors du panache de CO₂ supercritique, ce gaz se dissout dans la saumure et l'acidifie. Deux phénomènes ont alors lieu. Ils constituent la base des études menées au cours de cette thèse : (i) le devenir des espèces chimiques mobilisées par la dissolution des minéraux, et (ii) les variations des propriétés d'écoulements induites par la réactivité de la roche encaissante. Pour étudier ces phénomènes, des expériences ont été menées sur les carbonates de Lavoux et de St-Emilion. Ces deux échantillons naturels ont été sélectionnés pour leur composition minérale modèle qui assure une forte réactivité dans le contexte de l'étude, et l'absence d'argile et de matière organique qui limite la complexité du système géochimique. Les expériences menées sont de deux types. En autoclave, la compétition entre dissolution et sorption des éléments traces est mise en avant et permet d'investiguer des conditions variant de celles de la surface (20°C – 1 atm) à celles d'un site de stockage (40°C – 90 bar de CO₂) en passant par des intermédiaires de pression (30 et 60 bar). Les effets de la salinité de la saumure, de la concentration initiale en cations divalents ainsi que de l'état de l'échantillon solide (poudre, plug) sont étudiés. D'autre part, un dispositif expérimental a été développé au cours de cette thèse. Il permet d'étudier les propriétés de diffusion d'éléments traces à travers une carotte dans des conditions représentatives de celles d'un réservoir de stockage de CO₂. Les résultats expérimentaux obtenus mettent en évidence à la fois l'impact de la dissolution sur la mobilisation des espèces chimiques, la compétition entre différents cations pour la sorption et les conséquences de cette sélectivité sur le transport et la disponibilité des espèces chimiques. L'étude pétrophysique des échantillons réagis met en évidence une augmentation de la porosité, et une tendance à l'uniformisation du réseau de pore. Les données obtenues dans les expériences en batch permettent d'obtenir par simulation les paramètres de sorption du système pour les différents éléments traces, en fonction des conditions de pression. Grâce à ces différents résultats, la surveillance de sites de stockage géologique de CO₂ est possible dans différentes formations, et permet un suivi à la fois des flux des espèces chimiques et des propriétés d'écoulement
Over the last decade, an international will to reduce the emissions of greenhouse gases in the atmosphere developed, in order to limit their atmospheric concentration. Thus, to deal with the large amounts of CO₂ produced by human activities, this gas is to be injected under supercritical state in the underground. Outside the CO₂ plume, this gas dissolves within brine and acidifies it. Two phenomena occurs then. They are the main subject of this work: (i) the fate of chemical species mobilized by mineral dissolution, and (ii) the evolution of flooding properties induced by mineral reactivity. To study those phenomena, experiments were carried out on the Lavoux and the Saint-Emilion carbonates. Those two natural samples were selected because their mineralogical composition ensures a high reactivity and limits the complexity of the geochemical system, as they contain neither clays nor organic matter. Two types of experiments were carried out. Competition between dissolution and sorption was studied in batch reactors, from conditions similar to those of the surface (20°C – 1 atm) to those of a storage site (40°C – 90 bar of CO₂), passing by intermediate pressures (30 and 60 bar). The parameters investigated are salinity, initial concentration of divalent cations, and the state of solid samples (powder, core). On the other hand, an experimental setting was developed during the thesis project. It allows the study of trace elements diffusion through a core in CO₂ geological storage conditions. The experimental results evidence the impact of dissolution on chemical species mobilization, competition between those species regarding sorption and consequences of this selectivity on transport and availability of those chemical species. The petrophysical study of reacted samples evidence a porosity increase and the homogenization of the porous network. The data resulting from the batch experiments are used as input data for simulations, in order to estimate sorption parameters of trace elements in the systems investigated. Thanks to those results, the monitoring of CO₂ geological storage sites is possible within several different geological formations, and allows to track both flux of chemical species and flooding properties evolution

Les échanges entre le carbone de l'atmosphère et les autres réservoirs (océan, biosphère terrestre...) étaient équilibrés jusqu'à l'ère industrielle. Depuis 1850, les activités anthropiques telles que la déforestation, l'élevage intensif et surtout la combustion d'énergies fossiles émettent en grande quantité CO2 et CH4 dans l'atmosphère. L'équilibre rompu provoque une augmentation de la teneur en carbone dans l'atmosphère. Cette augmentation devrait être plus importante mais il semble qu'une partie du carbone rejeté par la combustion de combustibles fossiles est absorbée par certaines régions de l'océan, des zones « puits ».
Les échanges de CO2 entre océan et atmosphère sont régis par les lois physicochimiques et répondent à des besoins biologiques. Les processus physicochimiques vont faire tendre les teneurs en carbone de l'océan et de l'atmosphère vers un équilibre variant selon la température et la surface de mélange qui est liée à l'intensité du vent. Des processus biologiques interviennent aussi dans les échanges de carbone entre l'océan et l'atmosphère. La couche de surface océanique reste sous-saturée en carbone car les floraisons algales consomment une partie du carbone dissous, par photosynthèse. Une partie de cette biomasse sédimente et emporte ainsi du carbone vers les couches océaniques profondes. A l'issue de la sédimentation une partie du carbone est séquestrée dans les eaux profondes et une moyenne de 0.3 % du carbone produit en surface est intégrée aux sédiments. C'est le principe de la pompe biologique qui augmente le transfert de CO2 vers l'océan profond.
Certaines algues unicellulaires favorisent plus que d'autres la sédimentation du carbone. Ces microalgues peuvent être lestées par des minéraux ou s'intégrer à des particules plus grosses qui sédimentent rapidement. Il existe deux types de ballasts biogéniques, la silice biogénique (BSiO2) principalement formée par les diatomées et le carbonate de calcium (CaCO3) formé majoritairement par les coccolithophoridés. La domination de la production primaire océanique par les diatomées, leur capacité à intégrer de grosses particules ainsi que leur position à la base d'une chaîne alimentaire saine, semblent faire des diatomées le participant majeur de la pompe biologique de carbone. Ceci est en contradiction avec les récentes exploitations des bases de données de flux de particules dans l'océan qui attribuent ce transfert aux coccolithophoridés. Cette incertitude a, en grande partie, motivé le présent travail.
Les diatomées ont besoin de l'acide orthosilicique (DSi) pour construire leur frustule, or, la disponibilité de la DSi dans l'océan global dépend essentiellement de la profondeur de recyclage de la BSiO2. A la fin d'un bloom, de nombreuses diatomées sédimentent sous la forme d'agrégats. L'agrégation des diatomées influence non seulement le recyclage de la BSiO2 dans les eaux océaniques de surface, mais aussi la sédimentation et la préservation de la BSiO2 sur le plancher océanique. Les diatomées agrégées sédimentent en effet rapidement le long de la colonne d'eau, ce qui laisse peu de temps à la dissolution. Les expériences en laboratoire présentées dans cette étude, ont exploré l'influence de l'agrégation sur la vitesse de dissolution de la BSiO2. Des agrégats monospécifiques ont été formés à partir de trois espèces différentes de diatomées, des Chaetoceros decipiens, des Skeletonema costatum, et des Thalassiosira weissflogii. Les vitesses de dissolution de la BSiO2 des cellules de diatomées de la même culture ont été mesurées pour des cellules agrégées et libres, puis comparées. Les vitesses de dissolution initiales des frustules de diatomées étaient significativement plus faibles pour les cellules agrégées (4.6 an-1) que pour les cellules libres (14 an-1). Les vitesses de dissolution plus lentes de la BSiO2 des agrégats ont été attribuées (1) aux concentrations élevées en DSi dans les agrégats (entre 9 et 230 µM) comparativement au milieu environnant les cellules libres, (2) à une plus forte viabilité des cellules agrégées et (3) à un nombre de bactéries par diatomées plus faible dans les agrégats. Les variations des vitesses de dissolution entre les différents agrégats semblent s'expliquer par des concentrations en TEP variables selon les agrégats.
Les processus biogéochimiques internes des agrégats sont fort peu connus. La diminution de la vitesse de sédimentation observée dans les expériences de laboratoire, pourrait n'être qu'apparente si seule la diffusion de l'acide orthosilicique (DSi) depuis l'intérieur vers l'extérieur de l'agrégat était ralentie. En effet de fortes concentrations en DSi ont été mesurées à l'intérieur des agrégats. Nous présentons un modèle qui décrit la dissolution de la BSiO2 dans un agrégat ainsi que la diffusion de la DSi depuis l'intérieur de l'agrégat vers le milieu environnant. Ce modèle simule l'évolution des concentrations internes en DSi et BSiO2, ainsi que l'accumulation de DSi dans le milieu environnant l'agrégat. La vitesse de dissolution est dépendante de l'écart à l'équilibre, qui décroît avec le temps à mesure que la concentration interne en DSi augmente suite au processus de dissolution, ainsi que de la viabilité des cellules, puisque seules les cellules mortes se dissolvent. Ce modèle permet de montrer que seule la combinaison d'une dissolution réellement ralentie et d'une diffusion également ralentie, permet de reproduire les concentrations internes et externes en DSi. Il est suggéré que le ralentissement de la diffusion pourrait être dû à une association étroite entre la DSi et les TEP. Le ralentissement de la dissolution est quant à lui, attribué pour 16 – 33% à la forte teneur en DSi au sein de l'agrégat et pour 33-66%, à une viabilité plus longue des diatomées agrégées.
Au vu de l'importance des diatomées dans les processus de sédimentation de la matière organique (carbone et BSiO2), nous avons utilisé les résultats précédents dans le but d'établir un modèle simplifié des flux de BSiO2 dans la colonne d'eau. Le flux de sédimentation est décrit comme étant majoritairement composé d'agrégats, mais aussi de cellules libres et de pelotes fécales, les résultats expérimentaux de mesures de vitesses de dissolution de la BSiO2 dans les cellules libres, les agrégats et les pelotes fécales sont ainsi combinés avec des mesures in situ de production de BSiO2 et de flux de BSiO2 dans les eaux profondes de neuf provinces biogéochimiques de l'océan. La comparaison des sorties du modèle et des mesures in situ permet de déterminer la composition du flux de sédimentation en qualité (vitesse de sédimentation) et en quantité (répartition de la BSiO2 entre les cellules libres et les grosses particules). Nous déterminons ainsi que 40% à 90% de la BSiO2 produite en surface, se dissout avant la profondeur maximale de la couche de mélange. Le recyclage domine dans tous les sites quelle que soit la vitesse de sédimentation calculée. L'intensité du recyclage en surface est attribuée à la capacité des cellules à rester libres. Indépendamment de leurs ballasts (BSiO2), les diatomées qui ne sédimentent pas sous la forme d'agrégats ou de pelotes fécales de gros brouteurs vont se dissoudre à de faibles profondeurs. Le modèle permet d'obtenir des informations sur la dynamique des particules puisque nous avons pu déterminer que 200 m est une profondeur maximum optimale pour la couche de mélange, à laquelle les processus de terminaison des blooms tels que l'agrégation et le broutage semblent favorisés.
Notre aptitude à comprendre et à prévoir le rôle de l'océan dans le cycle global du carbone et sa réponse aux changements climatiques, dépend fortement de notre capacité à modéliser le fonctionnement de la pompe biologique à l'échelle globale. En dépit des nombreux progrès réalisés, les mystères entourant la pompe biologique de carbone sont loin d'être éclaircis. Dans cette thèse, la pompe biologique correspond à l'ensemble des mécanismes qui assurent le transfert d'une partie de la production primaire marine vers des profondeurs excédant la profondeur de la couche de mélange hivernale, de sorte que le carbone ne sera plus échangé avec l'atmosphère avant quelques décennies ou quelques siècles, c'est-à-dire sur des échelles de temps relevant de celle associée au changement climatique.
La profondeur de la couche de mélange hivernale se situe, selon les régions, entre 50 et 500 mètres avec quelques pointes vers 800 m (Levitus, 1994). Il s'agit là des profondeurs correspondant à la zone mesopélagique dont nous savons peu de choses puisque les flux de matière in situ sont étudiés à l'aide des pièges à particules qui fonctionnent très mal dans cette zone. Ces incertitudes dans les estimations des flux se reflètent dans les hypothèses sur les mécanismes de la pompe biologique et sur ses variations spatio-temporelles, comme le montre notre démonstration fondée sur les concepts d'export hors de la couche de mélange et d'efficacité de transfert à travers la zone mesopélagique.
Dans cette étude, nous avons voulu évaluer le véritable rôle des diatomées dans la pompe biologique de carbone. Toute la question est de savoir à quelle profondeur le carbone transporté par les diatomées est reminéralisé : au dessus ou au dessous de la couche hivernale de mélange ?
Récemment, les modèles globaux ont incorporé une description plus mécanistique des flux, en remplaçant les exponentielles décroissantes par une compétition entre la vitesse de chute des particules et leur vitesse de reminéralisation. Nous présentons dans cette thèse, une approche dans laquelle les flux de carbone au bas de la couche hivernale de mélange ont été calculés à partir de la reconstitution des flux de BSiO2 présentée précédemment et d'une relation empirique décrivant l'évolution du rapport Si:C avec la profondeur dans différentes provinces biogéochimiques. En combinant les flux de BSiO2 avec cette équation, il est possible de reconstruire les flux de carbone à n'importe quelle profondeur et de calculer des efficacités d'export ou de transfert à travers la zone mesopélagique. L'idée est simple : l'utilisation des flux de Si comme traceur des flux de C permet de s'affranchir des difficultés liées à la chimie complexe à laquelle est soumis le C. Par ailleurs, s'il s'avère impossible de reconstruire les flux de C à partir des flux de Si dans l'océan moderne, l'utilisation de la BSiO2 des sédiments comme paleotraceur de la productivité passée sera d'autant plus compromise.
Les flux reconstruits à partir de cette approche semi-mécanistique sont plus faibles que ceux dérivés des algorithmes précédemment publiés et la proportion de carbone exporté diminue lorsque la productivité augmente. Cette reconstruction rappelle l'importance de la saisonnalité. Elle a des implications pour notre compréhension du fonctionnement de la pompe biologique dans l'océan actuel et pour nos interprétations des enregistrements paléocéanographiques sur son fonctionnement dans l'océan passé. Le rôle attribué aux diatomées ou aux coccolithophoridés dans l'export ou le transfert plus profond de carbone, est fortement dépendant de la façon avec laquelle l'export hors de la couche de surface est estimé.

Le jaunissement des horizons superficiels de sols rouges tropicaux est étudié sur des échantillons des llanos de Colombie ou ce phénomène est actuel. Dans ces sols, le nombre de bactéries ferri-réductrices est corrélé au stock de carbone organique. La réduction bactérienne du fer est obtenue par simple incubation du sol avec de l'eau distillée. Le facteur limitant son développement est la source de carbone. La réduction du fer se produit dans l'horizon rouge profond, très pauvre en bactéries ferri-réductrices, lorsqu'on ajoute aux incubations du glucose en faible concentration, simulant les conditions naturelles. La réduction conduit au jaunissement de cet horizon rouge par dissolution de la totalité de l'hématite et la résistance d'une partie de la goethite. Cette résistance provient d'une accumulation relative, à la surface du minéral, de l'aluminium substitué au fer. Les atomes de fer ne sont alors plus accessibles aux agents réducteurs. Le fer III disponible pour la réduction serait utilisé par les bactéries comme puits d'électrons produits au cours de la fermentation. Pour une souche, la consommation de glucose est corrélée à la réduction du fer. Dans ce cas, le fer III serait un accepteur d'électrons obligatoire au cours de la fermentation. Les caractéristiques de la solution d'incubation (eh et ph) sont les conséquences de la fermentation et de la réduction. Mais les acides organiques produits pourraient intervenir dans le passage en solution du fer II

En vue de contrôler les émissions de gaz à effet de serre, il est envisagé d’injecter du CO2 dans des réservoirs géologiques. Or le CO2 n'est pas un gaz inerte. En modifiant la composition chimique de l'eau in situ, il est à l'origine d'interactions roche/fluide. Ces réactions géochimiques impactent les propriétés d'écoulement. Aussi, pour s'assurer de la viabilité et de la pérennité du stockage, les opérateurs ont besoin de simulations tenant compte de ces écoulements réactifs. Cependant les paramètres de l'équation macroscopique de transport utilisée sont affectés par les réactions surfaciques. Or, ces spécificités dues au transfert de masse ne sont pas prises en compte actuellement. De même, la loi perméabilité-porosité (K-F) n’est estimée que semi-empiriquement. Le but de cette thèse a été de développer une méthode pour obtenir les coefficients macroscopiques précédents et les relations K-F, en résolvant les équations gouvernant les phénomènes à l'échelle du pore. Pour ce faire, nous avons utilisé l'approche réseau de pores. L'avantage du modèle réseau est qu'il prend en compte explicitement la structure tout en conceptualisant cette dernière à un ensemble de pores et de canaux à la morphologie simplifiée (sphères, cylindres). L'étude est basée sur deux changements d'échelles successifs : du local au pore, puis du pore à la carotte. Le problème de transport réactif est résolu pour des éléments basiques, analytiquement ou numériquement. Puis, en faisant appel aux solutions précédemment trouvées, le transport réactif est traité sur l'ensemble du réseau. Notre model fut validé par des observations sur micromodèles, puis à l'aide d'une expérience d'altération acide
The geological storage of CO2 is considered as an attractive option to reduce the greenhouse gas emissions in the atmosphere. CO2 is not an inert gas, however. Its dissolution in brine forms a weak acid that has the potential to react with the host rock formation. The induced pores structure modification impacts the flow properties. Thus, to ensure the viability and sustainability of CO2 storage, operators need simulations that take into account the specificities of reactive transport. However, the macroscopic coefficients of the reactive transport equation are modified from the values of an inert tracer by surface reactions. These specificities due to mass transfer are currently not considered. Similarly, the permeability-porosity (K-F) relationship is only estimated semi-empirically. The aim of this thesis was to develop a method to obtain the macroscopic coefficients and the K-F laws, by solving the equations governing the pore-scale phenomena. To do this, we used the Pore Network Modelling approach (PNM). The advantage of the PNM is that it explicitly takes into account the pore structure, while conceptualizing the latter to a set of pores and throats whose morphology is simplified into spheres or cylinders for instance. The study is based into two successive upscalings: from local-scale to pore-scale, then from pore-scale to core-scale. The reactive transport problem is solved for basic elements, analytically or numerically. Then, using the solutions previously found at the pore scale, the reactive transport phenomena are treated throughout the network. Our model was validated by observations on micromodels and by a comparison with an acid-induced alteration experiment

Ce travail entre dans le cadre de l’étude des interactions eau-roche dans le cas du stockage du CO2 en milieu géologique. Un intérêt particulier est accordé aux hétérogénéités des paramètres associés aux phénomènes géochimiques. Ces hétérogénéités peuvent s’observer à différentes échelles: celle des grains (les minéraux présentent des défauts de cristallinité et des impuretés), et l’échelle centimétrique/pluri-décamétrique. En particulier, les paramètres thermodynamiques (logK) et de cinétique chimique (dans ce travail nous avons considéré le produit de la constante cinétique k par la surface spécifique S soit kS comme "paramètre de cinétique chimique") sont connus à partir des expériences de laboratoire pour des échantillons de quelques centimètres de dimension, alors que l’on s’intéresse aux réactions minéralogiques à l’échelle des réservoirs.Nous avons évalué les caractéristiques géostatistiques de la variabilité spatiale après réaction à travers des simulations de transport réactif dans lesquelles différents paramètres (logK et kS) sont perturbés avec une première variabilité imposée. Une combinaison de deux approches est ainsi abordée : déterministe et géostatistique. Le code du transport-réactif COORES (IFP-EN et Ecole nationale supérieure des mines de Saint-Etienne) a été utilisé pour les simulations déterministes et le système géochimique étudié concerne la dissolution du diopside avec précipitation de minéraux secondaires comme la calcite et la magnésite.Après analyse par la méthode des plans d’expériences, les résultats montrent qu’une corrélation spatiale élevée combinée avec une grande variance de dispersion des minéraux favorise une réactivité importante des minéraux lorsqu’on perturbe le paramètre de cinétique chimique kS. Par ailleurs une vitesse d’injection élevée accélère le processus de dissolution du minéral étudié. La variabilité spatiale du paramètre thermodynamique n’a cependant pas d’effet significatif sur les résultats, le système se comporte comme dans le cas homogène. Du point de vue de l’homogénéisation du paramètre kS, on retrouve l’influence de l’historique de dissolution
The present work is based on the study of water-rock interactions in the case of CO2 storage in geological media. Particular attention is devoted to heterogeneities at different observation scales geochemical phenomena. These heterogeneities can be observed at different scales: the grain (mineral crystallinity present defects and impurities), and the centimeter scale / multi- decametric (rocks are heterogeneous at different scales). In particular, the thermodynamic parameters logK and chemical kinetics kS (in this work we considered the product of the rate constant k by the specific surface area S is kS as "chemical kinetics parameter") are known from laboratory experiments to a few centimeters in size, while we are interested in mineralogical reactions across tanks.We propose to evaluate the geostatistical characteristics of the local variability after reaction through simulations of reactive transport on a small scale in which various parameters (logK and kS) are perturbed with a first spatial variability imposed. A combination of both approaches is discussed: deterministic and geostatistical for the study of geochemical problems at different scales. The reactive transport code - COORES (IFP - EN and Ecole nationale supérieure des mines de Saint -Etienne) was used for deterministic simulations and the geochemical system studied concerns the dissolution of diopside with precipitation of secondary minerals such as calcite and magnesite.After analysis by the method of design of experiments, the results show that high spatial correlation variance combined with high dispersion of minerals promotes a high reactivity when minerals chemically disturbing is the kinetic parameter kS. In addition, a high velocity injection accelerates the dissolution of the mineral studied. However, the effect of spatial variability of the thermodynamic parameter, did not significantly affect the results, the system behaves as in the homogeneous case. From the standpoint of homogenizing the parameter kS, include the influence of the history of dissolution

Les dangers potentiels liés à l'augmentation de la teneur en CO2 de l'atmosphère, tels que les changements climatiques ou l'élévation du niveau des mers, ont provoqué un grand intérêt pour la séquestration du gaz carbonique dans les formations géologiques. Le moyen thermodynamiquement le plus sûr pour stocker le carbone est sous la forme de minéraux carbonatés, mais il exige une source de cations divalents qui ne soit pas carbonatée. Les roches basaltiques qui présentent de fortes teneurs en calcium, magnésium et fer peuvent être une de ces sources et la possibilité de former des minéraux carbonatés par injection de CO2 dans les roches basaltiques est en cours d'investigation en Islande et dans d'autres endroits du monde. Dans ce cadre, l'objectif de cette thèse est de contribuer à l'optimisation de la précipitation des carbonates dans les basaltes lors de l'injection de CO2 grâce à une série d'études de terrain et de laboratoire complémentaires. Une étude détaillée de la composition chimique des eaux souterraines au pied du volcan Mont Hekla, dans le sud de l'Islande, a d'abord été menée afin d'évaluer l'évolution chimique des fluides et la mobilité des métaux toxiques lors des interactions entre basalte et fluides riches en CO2. Ces fluides fournissent un analogue naturel pour estimer les conséquences de la séquestration du CO2 dans les basaltes. La teneur de ces fluides en carbone inorganique dissous diminue de 3,88 à 0,746 mmole/kg avec l'augmentation de la mise en solution du basalte tandis que le pH passe de 6,9 à 9,2. Ces observations fournissent une preuve directe du potentiel qu'offre la dissolution du basalte pour séquestrer le CO2. Les concentrations des métaux toxiques dans ces eaux sont faibles et la modélisation des chemins réactionnels suggère que la calcite et les (oxy)hydroxydes de fer piègent ces métaux, suite à l'alcalinisation des fluides induite par la dissolution continue du basalte. On sait que ce sont les cations divalents libérés par la dissolution du verre basaltique qui contrôlent la minéralisation du gaz carbonique dans les basaltes. La vitesse de dissolution du verre basaltique peut être accrue par l'addition de ligands qui se complexent avec Al3+. L'ion SO42- fait partie de ces ligands et l'étude de son impact sur la vitesse de dissolution du verre basaltique a été conduite dans des réacteurs de type 'mixed flow' à 50°C et 3 < pH < 10. .
The potential dangers with increased concentration of CO2 in the atmosphere, such as climate changes and sea level rise, have lead to an interest in CO2 sequestration in geological formations. The thermodynamically most stable way to store carbon is as carbonate minerals. Carbonate mineral formation, however, requires divalent cations originating from a non-carbonate source. One such source is basaltic rocks which contain high concentrations of Ca2+, Mg2+ and Fe2+. The potential for forming carbonate minerals through the injection of CO2 into basalt is under investigation in Iceland and several other places around the world. The aim of this thesis is to help optimize carbonate mineral precipitation in basalts during CO2 injection through a series of related field and laboratory studies. A detailed study of the chemical composition of the groundwater surrounding the Mt. Hekla volcano in south Iceland was performed to assess fluid evolution and toxic metal mobility during CO2-rich fluid basalt interaction. These fluids provide a natural analogue for evaluating the consequences of CO2 sequestration in basalt. The concentration of dissolved inorganic carbon in these groundwaters decreases from 3. 88 to 0. 746 mmol/kg with increasing basalt dissolution while the pH increases from 6. 9 to 9. 2. This observation provides direct evidence of the potential for basalt dissolution to sequester CO2. The concentrations of toxic metals in these waters are low and reaction path modeling suggests that calcite and Fe(III) (oxy)hydroxides scavenge these metals as the fluid phase is neutralized by further basalt dissolution. The rate limiting step for mineralization of CO2 in basalt is thought to be the release of divalent cations to solution through basaltic glass dissolution. .

Le stockage géologique du dioxyde de carbone (CO2) est une des options envisagées à moyen terme pour limiter les émissions de gaz à effet de serre. Or, le CO2 n'est pas un gaz inerte et aura tendance à acidifier l'eau en place dans les sites de stockage. Cette acidification de l'eau est alors susceptible de modifier la structure de cette roche ainsi que les propriétés de transport des espèces chimiques. Le but de cette étude est de quantifier l'impact du transport réactif sur la répartition d'une espèce chimique et sur la modification de la structure du milieu poreux de l'échelle du pore à celle du réservoir. Nous nous sommes focalisés dans cette étude sur le transport réactif monophasique d'une espèce dissoute aux temps longs. Pour ce faire, nous avons opté pour une approche multi-échelles considérant successi- vement (i) l'échelle locale, où les phénomènes d'écoulement, de réaction et de transport sont connus ; (ii) l'échelle du pore, où le transport réactif est représenté par des équations issues de l'écriture moyennée des équations locales ; (iii) l'échelle de Darcy (ou échelle de la carotte), où la structure de la roche est retranscrite par un réseau tridimensionnel de pores interconnectés par des canaux ; et (iv) l'échelle du réservoir, où les phénomènes physiques, au sein de chaque maille constituant le modèle réservoir, sont pris en compte par l'introduction de coefficients macroscopiques issus de l'étude de ces même phénomènes à l'échelle de Darcy, comme par exemple la perméabilité, la vitesse de réaction apparente, la vitesse apparente du soluté et sa dispersion.

碩士
國立中山大學
機械與機電工程學系研究所
103
In this study, a numerical model is built to investigate the factors on carbon dissolution rate and develop a lump system for carbon particle dissolution in hot liquid metal. We assume the carbon particles dissolve in the molten iron is a quasi-steady process. Therefore, the steady state model has been developed. The simulation data shows the distribution of mass dissolution rate at the particle surface is significantly affected by the flow circulation behind a particle as a relative flow velocity is applied. The lump system has been developed by the correlation of Reynolds number and Schmidt number, which can predict the carbon particles dissolve at times of different state. The correlation of mass/heat transfer are as following: Sh=2.81+0.52 Re^0.52 Sc^0.38 Nu=0.53+0.27 〖Re〗^034 Pr^0.16 The study also established a transient model, and compare the time of dissolution between two models. Simulation results of transient model show that when the Reynolds number is smaller, the dissolution rate of carbon particles goes to be slightly longer.in addition this study also building a two dimension injection model through the simulation result of different model confirm the reliability of lump system

Carbon sequestration is a method of capturing and storing excess anthropogenic CO₂ in the subsurface. When CO₂ is injected, the temperature and pressure at depth turn it into a supercritical (SC) fluid, where density is that of a liquid, but viscosity and compressibility resemble a gas. Ultimately the SC CO₂ is trapped at depth either by low permeability sealing layers, by reactions with minerals, or by dissolving into fluids. The injected CO₂ is buoyant and initially exists as a non-aqueous hydrophobic layer floating on top of the subsurface brine, up against the upper sealing formation, but over time it will dissolve into the brine and potentially react with minerals. The details of that initial dissolution reaction, however, are only poorly understood, and I address three basic questions for this research: What is the fundamental kinetics of SC CO₂ dissolution into water? How fast does dissolved CO₂ diffuse away from the source point? And what geochemical conditions influence the dissolution rate? To answer these questions I employed a high pressure flow-through approach using a column packed with coarse quartz sand. The system was both pressure and temperature controlled to have either liquid or SC CO₂ present, and was typically run at 100 Bar, 0.5 to 2.5 mls/min, and 28-60°C. After establishing the hydraulic parameters for the column using two conservative tracers (Br, As), injections (5 and 20 [mu]l) were made either as aqueous solutions equilibrated to high pressure CO₂, or as pure liquid or SC CO₂ into 0.1 mmol NaOH. For all experiments the pH of the system was monitored, and [CO₂] over time was calculated from those data. For injections of brine with dissolved CO₂, transport was conservative and was nearly identical to the conservative tracers. The CO₂ quickly mixes in the column and does not react with the quartz. The liquid and SC CO₂ injections, however, do not act conservatively, and have a very long tailing breakthrough curve that extends to tens of pore volumes. I hypothesize that the SC CO₂ is becoming trapped as a droplet or many droplets in the pore spaces, and the long breakthrough tail is related either to the rate of dissolution into the aqueous phase, the diffusion of dissolved CO₂ away from the phase boundary, or the reaction with the NaOH, limited to the narrow contact zones in the pore throats. Because of the speed at which acid-base reactions occur (nanosecond kinetics), I infer that the rate limiting step is either surface dissolution or diffusion. From plots of ln[CO₂] v. time I obtained values for k, the specific rate of the dissolution reaction R=-k[CO₂]. No trend for k was seen with respect to changes in temperature, but k did show a trend with respect to changing flow rate. k increased from an average value of 3.05x10⁻³ at 0.5 ml/min to an average value of 3.38x10⁻³ at 1.6 ml/min, and then held constant at the higher flow rates, up to 2.5 ml/min. I interpret these data to show that at low flow rates, the reaction is diffusion limited; the fluid nearest the contact zone becomes saturated with dissolved CO₂. At higher flow rates, the fluid is moving fast enough that saturation cannot occur, and the kinetics of the dissolution reaction dominate. Simple geometric models indicate that the CO₂/water interface is shaped like a spherical cap, indicating that the snapped-off CO₂ is forming a meniscus in the pore throat, limiting the surface area across which dissolution can occur.
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The need for more efficient blast furnaces is even greater now that there are stricter environmental regulations on greenhouse gas (GHG) emissions. Coke within the blast furnace not only supports the furnace bed and allows gas flow, it also carburises liquid iron. The carburisation of iron is one of the most important reactions and must be better understood if the ironmaking process in the blast furnace is to be made more sustainable. By understanding what coke properties influence the rate at which coke dissolves in iron we can predict a coke?s performance and use it to determine its quality. As carbon dissolution rates have only been determined for a few cokes, a systematic and comprehensive study was conducted on the dissolution of carbon from nine Australian cokes into liquid iron. The kinetics of carbon dissolution from Cokes A to I was measured and a range of experimental techniques were used to elucidate the dominant rate influencing factors. The role of coke structure, coke inorganic matter composition and yield and temperature were investigated. Furthermore, the influence of interfacial products and dynamic wettability studies were also conducted. The carburiser cover method was used to measure carbon pick-up as a function of time over the temperature range of 1450-1550 ??C. Fundamental data on the apparent carbon dissolution rate constant (K) in molten iron at 1550 ??C for Cokes A to I were obtained and ranged from K (x 103 s-1) = 0.47 to K (x 103 s-1) = 14.7. The wide variation in K showed that not all cokes dissolve at similar rates. In fact one of the nine cokes in this investigation dissolved at a rate comparable to graphite dissolution rates. The apparent carbon dissolution activation energy, Ea, for two of the nine cokes plus synthetic graphite (SG) was also determined. The Ea obtained for SG (Ea = 54 kJ / mol) was in agreement with literature values and was consistent with a diffusion controlled mechanism. The observed Ea values for Cokes D and F (313 kJ / mol and 479 kJ / mol respectively) are an order of magnitude larger than the Ea obtained for SG. The difference in Ea between cokes and SG does not appear to be solely due to differences in the structure of the carbon source. The difference in Ea between the cokes was attributed to differences in their inorganic matter composition. The interfacial contact area is a function of inorganic matter yield and composition, which in turn is a function of temperature. Therefore, as temperature decreases the slag / ash layer produced at the carbon / iron interface can increase in area and viscosity and thus hinder carbon dissolution and transfer, and increasing the apparent activation energy for carbon dissolution. Thus, the differences in viscosity and melting temperature of the interfacial product play a key role. Wettability experiments were carried out using the sessile drop technique. The wettability of Cokes D, F and G with liquid iron at 1550 ??C was measured as a function of time. All three coke samples showed non-wetting behaviour with contact angles ranging between 123-129?? in the initial stages and between 109-114?? after two hours of contact. The differences in the wettability of the three coke samples could not explain the large differences in dissolution rates observed between these cokes. Thus, the wettability of these coke samples was not considered a dominant factor in influencing the rate of carbon dissolution. The sessile drop technique was also used to study the interfacial products formed at the coke / iron interface. The interfacial products formed on the underside of the iron droplet after contact with Cokes F and G were initially different in regards to the morphology and chemical composition. The interfacial product formed with Coke G had a network or mesh like structure that seemed to wet the iron droplet much better than the interfacial product formed with Coke F. In contrast, Fe globules and discrete interfacial products were observed in Coke F. It was suggested that this was due to differences in inorganic matter content, especially in calcium (Ca) and sulfur (S) content in the coke. Formation of interfacial products containing sulfides, such as calcium sulfide (CaS) and manganese sulfide (MnS), were observed on the iron side of the interface of both Cokes F and G. As a result, the interfacial products can act as a physical barrier blocking iron and coke contact, thus reducing the contact area for carbon dissolution and decreasing the rate of carbon dissolution. The presence of MnS may act to lower the liquidus temperature of the interfacial product, which in turn can affect the overall viscosity of the interfacial layer. Thus, the deposition of reaction products at the interfacial region can have a significant effect on carbon dissolution rates. The mineral pyrrhotite was also identified as a significant factor in influencing the rate of carbon dissolution. Electron dispersive X-ray analyses of Coke F identified iron to be in close association with sulfur. These Fe / S species have atomic ratio similar to pyrrhotite (Fe1-xS) or troilite (FeS). Pyrrhotite in coke can decompose to release gaseous sulfur and metallic iron, which can be carburised by carbon in the surrounding area to form Fe-C particles. Thus, carburisation of liquid iron can occur via Fe-C particles. There was little difference in structure between the nine coke samples and therefore the high dissolution rates of Coke F, cannot be explained on the basis of crystallite size or anisotropic carbon content. Inorganic matter yield and composition were identified as the dominant rate influencing factors on carbon dissolution. More specifically: - High content of iron phases, such as iron oxides and pyrrhotite, can lead to an increase in carbon dissolution rates. This maybe due to increased amounts of Fe-C particles that are formed upon the reduction of magnetite and decomposition of pyrrhotite, and carried through the slag layer to carburise the bulk liquid iron. - High aluminium oxide content can lead to a decrease in carbon dissolution rates. This maybe due to higher ash fusion / melting temperature or decrease in wettability, both of which lead to a decrease in carbon / iron contact area. - Formation of interfacial products, such as CaS and MnS, can lead to a decrease in carbon dissolution rates. Such products can act as a physical barrier blocking iron and coke contact, thus reducing the contact area for carbon dissolution. However, the presence of MnS may act to lower the liquidus temperature of the interfacial product. - An increase in temperature increases the rate of carbon dissolution. This dependence is predominantly due to the composition of the inorganic matter present in cokes, which influences the viscosity and melting point of the interfacial product formed and hence contact area between coke and iron.

Geological carbon dioxide (CO₂) capture and storage in geological formations has the potential to reduce anthropogenic emissions. The viability of technology depends on the long-term security of the geological CO₂ storage. Dissolution of CO₂ into the brine, resulting in stable stratification, has been identified as the key to long-term storage security. The dissolution rate determined by convection in the brine is driven by the increase of brine density with CO₂ saturation. Here we present a new analog laboratory experiment system to characterize convective dissolution in homogeneous porous medium. By understanding the relationship between dissolution and the Rayleigh number in homogeneous porous media, we can evaluate if convective dissolution occurs in the field and, in turn, to estimate the security of geological CO₂ storage fields. The large experimental assembly will allow us to quantify the relationship between convective dynamics and the Rayleigh number of the system, which could be essential to trapping process at Bravo Dome. A series of pictures with high resolution are taken to show the existence and movement of fingers of analog fluid. Also, these pictures are processed, clearly showed the concentration of analog fluid, which is essential to analyze the convective dissolution in detail. We measured the reduction in the convective flux due to hydraulic dispersion effect compared to that in homogeneous media, to determine if convective dissolution is an important trapping process at Bravo Dome.
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Here, we present a dissolution study of exposed hydrate from outcrops at Barkley Canyon. Previously, a field experiment on synthetic methane hydrate samples showed that mass transfer controlled dissolution in under-saturated seawater. However, seafloor hydrate outcrops have been shown to have significant longevity compared to expected dissolution rates based upon convective boundary layer diffusion calculations. To help resolve this apparent disconnect between the dissolution rates of synthetic and natural hydrate, an in situ dissolution experiment was performed on two distinct natural hydrate fabrics. A hydrate mound at Barkley Canyon was observed to contain a “yellow” hydrate fabric overlying a “white” hydrate fabric. The yellow hydrate fabric was associated with a light condensate phase and was hard to core. The white hydrate fabric was more porous and relatively easier to core. Cores from both fabrics were inserted to a mesh chamber within a few meters of the hydrate mound. Time-lapse photography monitored the dissolution of the hydrate cores over a two day period. The diameter shrinkage rate for the yellow hydrate was 45.5 nm/s corresponding to a retreat rate of 0.7 m/yr for an exposed surface. The white hydrate dissolved faster at 67.7 nm/s yielding a retreat rate of 1.1 m/yr. It is possible these hydrate mounds were exposed due to the fishing trawler incident in 2001. If these dissolution experiments give a correct simulation, then the exposed faces should have retreated ~ 3.5 m and 5.5 m, respectively, from 2001 to this expedition in August 2006. While the appearance of the hydrate mounds appeared quite similar to photographs taken in 2002, these dissolution experiments show natural hydrate dissolves rapidly in ambient seawater. The natural hydrate dissolution rate is on the same order as the synthetic dissolution experiment strongly implying another control for the dissolution rates of natural hydrate outcrops. Several factors could contribute to the apparent longevity of these exposed mounds from upward flux of methane-rich fluid to protective bacterial coatings.

This study geochemically characterized a proposed Carbon Capture and Storage project in northeast British Columbia, and presents new dissolution kinetics data for the proposed saline aquifer storage reservoir, the Keg River Formation. The Keg River Formation is a carbonate reservoir (89-93% Dolomite, 5-8% Calcite) at approximately 2200 m depth, at a pressure of 190 bar, and temperature of 105 °C. The Keg River brine is composed of Na, Cl, Ca, K, Mg, S, Si, and HCO3 and is of approximately 0.4 M ionic strength. Fluid analysis found the Keg River brine to be relatively fresh compared with waters of the Keg River formation in Alberta, and to also be distinct from waters in overlying units. These findings along with the physical conditions of the reservoir make the Keg River Formation a strong candidate for CO2 storage. Further work measured the dissolution rates of Keg River rock that will occur within the Keg River formation. This was performed in a new experimental apparatus at 105 °C, and 50 bar pCO2 with brine and rock sampled directly from the reservoir. Dissolution rate constants (mol!m-2s-1) for Keg River rock were found to be Log KMg 9.80 ±.02 and Log KCa -9.29 ±.04 for the Keg River formation. These values were found to be significantly lower compared to rate constants generated from experiments involving synthetic brines with values of Log KMg -9.43 ±.09, and Log KCa -9.23 ±.21. Differences in rates were posited as due to influences of other element interactions with the >MgOH hydration site, which was tested through experiments with brines spiked with SrCl2 and ZnCl2. Results for the SrCl2 spiked solution showed little impact on dissolution rates with rate constants of Log KMg -9.43 ±.09, and Log KCa -9.15 ±.21, however the ZnCl2 spiked solution did show some inhibition with rate constants of Log KMg -9.67 ±.04, and Log KCa -9.30 ±.04. Rate constants generated in this work are among the first presented which can actually be tested by full-scale injection of CO2.
Graduate

High-temperature reactors make use of tri-structural coated fuel particles as basic fuel components. These TRISO particles consist of fissionable uranium dioxide fuel kernels, about 0.5 mm in diameter, with each kernel individually encased in four distinct coating layers, starting with a porous carbon buffer, then an inner pyrolytic carbon (IPyC) layer, followed by a layer of ceramic silicon carbide (SiC) and finally an outer pyrolytic carbon layer (OPyC). Collectively, the coating layers provide the primary barrier that prevents release of fission products generated during burn up in the UO2 fuel kernel. It is crucial to understand how the fission products contained within the fuel interact with the coating layers and how they are distributed within the fuel. The first step commonly performed to obtain the information on distribution is removal of the coating layers. The purpose of this study was to investigate the possible use of wet chemical etching techniques with the aim of removing the coating layers of ZrO2 coated fuel particles in a controlled way and to establish experimental parameters for controlled dissolution of irradiated fuel particles. Stepwise dissolution of coated fuel particle coating layers, containing zirconia kernels has been investigated by chemical etching experiments with acidic solutions of different mixtures. The heating methods used include heating by conventional methods, hot plates and a muffle furnace, a reflux-heating system and microwave-assisted digestion. The etching mixtures were prepared from a number of oxidizing acids and other dehydrating agents. The capability of each reagent to etch the layer completely and in a controlled manner was examined. On etching the first layer, the OPyC, the reflux heating method gave the best results in removing the layer, its advantage being that the reaction can be carried out at temperatures of about 130 ºC for a long time without the loss of the acid. The experimental results demonstrated that a mixture composed of equal amounts of concentrated nitric and sulfuric acid mixed with chromium trioxide dissolves the OPyC layer completely. The most favourable experimental conditions for removal of OPyC from a single coated fuel particle were identified and found to depend on the etching solution composition and etching temperature. Light microscopy yielded first-hand information on the surface features of the samples. It allowed fast comparison of etched and untreated sample features. The outer surface of particles prior to chemical etching of the outer pyrolytic carbon layer appeared black in colour with an even surface compared to the etched surfaces which appeared to have an uneven metallic grey, shiny texture. The scanning electron microscope (SEM) examination of the chemically treated outer carbon layer samples gave information on the microstructure and it demonstrated that the outer pyrolytic carbon layer could be readily removed using a solution of HNO3/H2SO4/CrO3, leaving the exposed SiC layer. Complete removal of the layer was confirmed by energy dispersive X-ray spectroscopic (EDS) analysis of the particle surface. For etching the second layer, the silicon carbide layer, microwave-assisted chemical etching was the only heating technique found to be useful. However, experimental results demonstrated that this method has limited ability to digest the sample completely. Also common chemical etchants were found to be ineffective for dissolving this layer. Only fluoride containing substances showed the potential to etch the layer. The results show that a mixture consisting of equal amounts of concentrated hydrofluoric and nitric acid under microwave heating at 200 ºC yielded partial removal of the coating and localized attack of the underlying coating layers. The SEM analyses at different intervals of etching showed: partial removal of the layer, attack of the underlying layers and, in some instances, that attack started at grain boundaries and progressed to the intra-granular features. The SEM results provide evidence that etching of the silicon carbide layer is strongly influenced by its microstructure. From these findings, it is concluded that etching of the silicon carbide under the investigated experimental conditions yields undesirable results and that it does not provide complete removal of the layer. This method has the potential to etch the layer to some extent but has limitations. Copyright
Dissertation (MSc)--University of Pretoria, 2013.
Chemical Engineering
unrestricted

With increased attention on rising carbon dioxide levels, carbon capture and sequestration (CCS) has become a commonly proposed solution. CCS has been studied for several decades, but is being researched more and more seriously as to whether it may be a viable and economically feasible long-term solution to climate change. Research conducted for this project is for application at the site of a coal fired power facility in the Black Warrior Basin of Alabama, and was funded by the DOE Recovery Act. Despite the excitement regarding CCS, some major technical obstacles exist due to the nature of working with acidic solutions and carbonate formations. This project explores the dissolution of carbonate formations while exposed to an acidic brine solution. Dissolution kinetics, with and without inhibitors, are presented and compared with modeled expectations.

With the atmospheric concentration of carbon dioxide steadily increasing and little sign of a reduction in fossil fuel demand worldwide, there is a well-established need for an alternative strategy for dealing with carbon emissions from energy production. One possible solution is the accelerated weathering of ultramafic rocks. Accelerated weathering is an environmentally benign route to a thermodynamically and kinetically stable form of carbon. The chemistry is based on naturally occurring reactions and the raw materials are abundant across the earth's surface. However, the reactions are relatively slow, and achieving reaction rates sufficient to match the carbon dioxide production rate at an energy conversion facility is challenging. This work addresses a number of the challenges facing the integration of accelerated weathering with energy conversion, and presents one view of how the integration could be achieved. This work begins by developing a suite of tools necessary for investigating the dissolution and precipitation of minerals. Chapter 2 starts with a description of the minerals that will be evaluated, and then goes on to develop the techniques that will be used. The first is a differential bed reactor, which is used for measuring the dissolution rates of minerals under tightly controlled conditions. Next a bubble column reactor is developed for the investigating the adsorption of carbon dioxide and the precipitation of mineral carbonates in a single vessel. These techniques, together with a batch reactor for studying direct carbonation reactions, constitute a comprehensive set of tools for the investigation of accelerated mineral weathering. With the necessary techniques developed and proven, Chapter 3 addresses the first challenge faced by accelerated mineral weathering; the dissolution rate of magnesium from a silicate mineral. While the dissolution of this mineral is thermodynamically favorable, the kinetics are prohibitively slow. It is thought that this is because silica from the mineral tends to accumulate on the particle surface creating a passivation layer, which limits the reaction rate of the mineral. In this work, the effects of a combination of chemical chelating agents, catechol and oxalate, are evaluated for their ability to circumvent this passivation layer. The results indicate that catechol and oxalate modify the passivation layer as it forms, both accelerating the dissolution rate of the mineral and maintaining pore volume, leading to greater dissolution rates. This pore modification process is proposed as the primary mechanism by which catechol affects the passivation layer. The combination of catechol and oxalate under acidic conditions is also shown be effective when the ambient solution approaches the saturation point of silica. Finally, the chelating does not impede the precipitation of carbonate products, a critical hurdle for a carbon storage process. The chelating agent work is extended in Chapter 4, with a sensitivity study that evaluates the response of the dissolution rate to changes in both pH and the concentration of the chelating agents. Oxalate and pH are found to exhibit a strong influence on the mineral dissolution rate, while the effect of catechol is more apparent after significant dissolution has taken place. These observations are in agreement with the model of passivation layer modification proposed. In addition, some alternatives to the chelating agent catechol are evaluated. It is found that when used in combination with oxalate, these alternatives appeared equivalent to catechol, but alone they had only a minor effect. Catechol was also noted to have a significant effect on the dissolution rate of iron from the silicate mineral, and a mechanism for this effect was proposed. The direct adsorption of carbon dioxide and precipitation of solid carbonates in a single reaction step presents another challenge for accelerated mineral carbonation. In general, the magnesium carbonates formed at ambient pressure and moderate temperatures tend to be hydrated, and at times contain unused hydroxides, leading to inefficiencies in both transport and storage. It is shown in Chapter 5 that by seeding reaction vessels with the anhydrous form of magnesium carbonate, it is possible to grow this desired phase with minimal formation of the metastable hydrated phases. The formation of this phase is primarily limited by the precipitation rate, but in some situations, carbon dioxide hydration kinetics and magnesium hydroxide precipitation kinetics also play a role. In Chapter 6, these developments in both magnesium silicate dissolution and carbonate precipitation are combined into a proposed technology for the direct capture and storage of carbon dioxide. This application of accelerated mineral weathering is shown to significantly reduce the carbon emissions of an energy conversion technology through life cycle assessment. This novel approach to the mitigation of carbon emissions presents a compelling argument for the continued development of accelerated mineral weathering as a combined carbon capture and storage technology.

Carbon allotropes have taken central stage of nanotechnology in the last two decades. Today, fullerenes, carbon nanotubes (CNTs), and graphene are essential building blocks for nanotechnology. Their superlative electrical, thermal and mechanical properties make them desirable for a number of technological applications ranging from lightweight strong materials to electrical wires and support for catalysts. However, transferring the exceptional single molecule properties into macroscopic objects has presented major challenges. This thesis demonstrates that carbon nanotubes and graphite dissolve in superacids and these solution can processed into macroscopic objects. Chapter 2 reviews neat CNT fiber literature. Specifically, the two main processing methods —solid– state and solution spinning — are discussed. CNT aspect ratio and fibers structure are identified as the main variables affecting fiber properties. Chapter 3 shows that graphite can be exfoliated into single-layer graphene by spontaneous dissolution in chlorosulfonic acid. The dissolution is general and can be applied to various forms of graphite, including graphene nanoribbons. Dilute solutions of graphene can be used to form transparent conductive films. At high concentration, graphene and graphene nanoribbons in chlorosulfonic acid forms a liquid crystal and can be spun directly into continuous fibers. Chapter 4 describes a solution–based method to form a thin CNT network. This network is an ideal specimen support for electron microscopy. Imaging nanoparticles with atomic resolution and sample preparation from reactive fluids demonstrate the unique feature of solution–based CNT support compared to state–of–the–art TEM supports . Chapter 5 describes CNT liquid crystalline phase. Specifically, CNT nematic droplets shape and merging dynamics are analyzed. Despite nanotube liquid crystals having been reported in various CNT systems, a number of anomalies such as low order parameter and spaghetti–like, nematic droplets are reported. However, CNTs in chlorosulfonic acid show elongated, bipolar droplets typical of other rod–like molecules. Moreover, their large aspect ratio allows capturing the transition from homogeneous to bipolar transition expected from scaling arguments.The equilibrium shape and merging dynamics demonstrate the liquid nature of CNT liquid crystals. Chapter 6 describes the CNT/chlorosulfonic acid fiber spinning. The influence of starting material, spinning dope concentration, spin draw ratio and coagulation on fiber properties is discussed. The linear scaling of fiber strength with CNT aspect ratio is demonstrated experimentally, once the best properties from different batches are compared. Moreover, Successful multi–hole spinning demonstrates the intrinsic scalability of wet spinning to meet the typical production output of industrial–scale spinning. Chapter 7 compares acid–spun CNT fibers to other CNTs fibers as well as existing engineered materials. Acid–spun CNT fibers combine the typical specific strength of high–strength carbon fibers to the thermal and electrical conductivity of metals. These properties are obtained because of a highly aligned, dense structure. The combined strength and electrical conductivity allow acid-spun fibers to be used as structural as well as conducting wire while the combined electrical and thermal properties allow for exceptional field emission properties. In conclusion, we demonstrate that multifunctional properties of carbon nanotubes that have fuelled much of the research in the past 20 years, can be attained on a macroscopic level via rational design of fluid–phase processing.

碩士
國立臺灣科技大學
化學工程系
104
Element sulfur, with the advantages of low cost, environmental friendly, and high theoretical specific capacity (1675 mAh/g) has been seen as a promising choice of high energy density cathode material for rechargeable lithium batteries. Relative to the ordinary lithium sulfur battery cathodes, the sulfur/polyacrylonitrile, without the formation of high-order lithium polysulfides during the charge/discharge process, exhibits better electrochemical performance using commercial electrolyte (LiPF6 in EC: DEC). However, several drawbacks exist in the S/PAN such as the lower sulfur content leading to the lower capacity of the battery and poor electrical conductivity of sulfur at high charge/discharge rate. In order to overcome the problem as mentioned, in this study, dissolution/reprecipitation process was used to wrap the polyacrylonitrile onto conductive carbon (super P) and the polyacrylonitrile-carbon composite (rSP@PAN), with the higher surface area and uniform particle size, was obtained by adjusting the concentrations of the PAN/NMP solution and the ratio of PAN and the conductive carbon. Then, the sulfur was dissolved into CS2 solvent and mixed with rSP@PAN in which the uniformity can be improved via liquid-solid mixing, and the SCS2/rSP@PAN was obtained after the calcination. It was found that the contact area between PAN and S can be effectively increased by the higher surface area of rSP@PAN. After heat treatment with sulfur, the highest sulfur content of obtained SCS2/rSP@PAN reaches 54.5%, which is 66.5% sulfur content in only S/PAN compound, showing an obvious improvement in comparison to only 44.5% sulfur content in sulfur/commercial PAN compound. Moreover, the introduction of the conductive carbon can compensate the low conductivity of PAN and sulfur, which improves the reversible capacity at high charge/discharge rate. The result shows that SCS2/rSP@PAN can deliver a high reversible capacity of 511 mAh/gS at 10 C-rate, which is only 80 mAh/gS obtained in sulfur/commercial PAN compound. This reveals that the electrochemical performance can be improved by introducing the conductive carbon. In general, the sulfur content and the conductivity of material can be effectively enhanced by developed sulfur- polyacrylonitrile-carbon composite, leading a higher energy density and power density and providing a promising cathode material for lithium sulfur battery.

Underground injection of acid gas has been studied for several decades for oil field applications, such as enhanced oil recovery (EOR), but is now being studied as a solution to climate change. This research aims to simulate underground conditions at injection sites, such as the pilot scale injection site located near the site of a coal fired power facility in the Black Warrior Basin of Alabama. This proposed carbon capture and sequestration (CCS) location would involve injection of liquid CO2 into a carbonaceous saline aquifer. The objective of this study was to investigate carbonate surface treatments that alter the kinetics and mechanism of mineral dissolution resulting from the injection of an acid gas (CO2) into a geologic formation. A variety of mineral coatings were tested in an attempt to preserve mineral integrity under acidic conditions. Surface active chemicals were first tested, including scale inhibitors, followed by a novel acid induced surface treatment that precipitates an inorganic layer on the calcite to preserve the acid soluble mineral. These experiments are the first to investigate the use of scale inhibitors for mineral preservation, although were found ultimately to have little impact on dissolution kinetics. However, anions of moderate to strong acids induced surface coatings that were determined to effectively inhibit dissolution. Additionally, a novel, high pressure flow-through experimental apparatus was developed to simulate pressure and temperature conditions relevant to injection sites. Similar mineralogical studies in the literature have used pressurized, unstirred, batch systems to simulate mineral interactions. Solids with an acid induced surface coating were tested in the high pressure column and no calcium was found to leave the column.

碩士
國立清華大學
生醫工程與環境科學系
95
The dechlorination of carbon tetrachloride (CT) by biogenic iron species produced from the reductive dissolution of ferrihydrite by Geobacter sulfurreducens in aqueous solutions containing quinone compounds as electron mediators was investigated. The use of quinone compounds in the presence of G. sulfurreducens under iron-reductive conditions can effectively dechlorinate CT. The dechlorination of CT followed pseudo-first-order kinetics and the pseudo-first-order constants (kobs) for 10 �嵱 AQDS, LQ (lawson) and NQ (naphthoquinone) were correspond to 6.5, 5.1, and 2.5 times higher than that in control systems, respectively. The dechlorination of CT was related to the ferrous concentrations produced from the dissolution of ferrihydrite by G. sulfurreducens. The dechlorination of CT was obvious when the system amended with 100 �嵱 quinone compounds and contained no ferrihydrite in the presence of G. sulfurreducens under anaerobic conditions. Addition of ferrihydrite enhanced the efficiency and rate of CT dechlorination under iron-reducing conditions. This enhanced effect is attributed to the formation of active surface-bound iron species when ferrous adsorbed onto the surface of ferric oxides. In addition, the amendment of 10 �嵱 AQDS, LQ, or NQ produced the highest Fe(II) concentration in the presence of G. sulfurreducens. Addition of 0.2 mM NQ and BQ into media, however, inhibited the growth of G. sulfurreducens. Spectroscopic results including EPR and UV-Vis showed that the selected quinone compounds can form various active electron mediators for electron transfer. AQDS can be reduced to semiquinone, LQ can be converted to hydroquinone, while NQ could be produced to hydroquinone and trace amounts of semiquinone in the presence of G. sulfurreducens. Results obtained show that addition of quinone compounds can enhance the ferrous production, and subsequently formed surface-bound iron species to effectively dechlorinate chlorinated hydrocarbon for long-term remediation under iron-reducing conditions.

碩士
國立臺灣大學
材料科學與工程學研究所
92
The purpose in this research is to analyze the micro-structure and mechanism of the carbon nanotubes in the system of liquid surrounding. Our research focused on using DPG (Dissolution Precipitation Graphite) process to produce artificial graphite that dispersed some carbon nanotubes and nano-materials. Furthermore, the boron-triggering mechano-chemical effect, change of microstructure, and hydrochloric acid treatment, are the reasons inducing the formation of the carbon nanotubes. Also, the four-points-probe instrument was used in this research to determine electric conductivity, expecting to discuss the relationship with impedance and the number and the orientation of carbon nanotubes formatted by the different concentrations of chloride ion. On the other hand, the trend of the decreasing of graphitization degree as increasing chloride ion concentration is observed, which is analyzed by XRD with Rietveld refinement method. It implies that the carbon nanotubes formation has a strong relationship to chloride ion doping. This result could also prove that the mechano-chemical effect and HCl treatment are the driving forces of carbon nanotubes formation. These are the critical keys of the new unusual process. Then, on the application of the anodic material of the lithium secondary battery, the method to control the forming of SEI, reduce the first irreversible capacity, and improve the battery efficiency was also be find out by pre-treating powder with different concentration of chloride ion.