Dissertations / Theses on the topic 'Dissolution and precipitation processes'

La précipitation et la dissolution de la calcite sont des processus primordiaux dans les roches carbonatées et le fait de pouvoir les surveiller in situ est un enjeu majeur. Les méthodes hydrogéophysiques sont fondées sur le développement de techniques géophysiques appropriées pour le suivi des processus hydrologiques et biogéochimiques de manière non-intrusive et à faible coût. Parmi les techniques existantes, les méthodes électriques ont déjà prouvé leur capacité à surveiller de tels processus. Pour cette raison, les méthodes du potentiel spontané (PS) et de la polarisation provoquée spectrale (PPS) ont été choisies pour investiguer les processus de dissolution et de précipitation de la calcite. La PS est une technique passive consistant à mesurer le champ électrique naturel généré par les flux d’eau et les gradients de concentration, tandis que la PPS est une méthode active mesurant la conductivité électrique complexe aux basses fréquences (mHz-kHz). Ses composantes réelle et imaginaire peuvent être reliées respectivement à la microstructure et à l’état de surface des minéraux le constituant. Cette thèse présente des développements expérimentaux et théoriques afin d'améliorer l’interprétation des méthodes PS et PPS. Un nouveau modèle de conductivité électrique est développé et montre un bon ajustement avec les résultats numériques de dissolution et de précipitation. Des données PS remarquables ont été obtenues et ont pu être reliées quantitativement grâce à de la modélisation de transport réactif. Les résultats PPS nourrissent la réflexion sur les mécanismes responsables des variations de polarisation engendrés par la réactivité de la calcite
Precipitation and dissolution of calcite are key processes in carbonate rocks and being able to monitor them in situ is a major issue. Hydrogeophysical methods are based on the development of appropriate geophysical techniques for monitoring hydrological and biogeochemical processes in a non-intrusive and low-cost manner. Among the existing techniques, electrical methods have already proven their ability to monitor such processes. For this reason, the methods of self-potential (SP) and spectral induced polarization (SIP) were chosen to investigate the processes of dissolution and precipitation of calcite. SP is a passive technique consisting in measuring the natural electric field generated by water flows and concentration gradients, while SIP is an active method measuring the complex electrical conductivity at low frequencies (mHz-kHz). Its real and imaginary components can be related respectively to the microstructure and surface state of the minerals constituting it. This thesis presents experimental and theoretical developments in order to improve the interpretation of SP and SIP methods. A new electrical conductivity model is developed and shows a good fit with the numerical results of dissolution and precipitation. Remarkable SP data have been obtained and could be quantitatively linked through reactive transport modeling. The SIP results provide further insights into the mechanisms responsible for the polarization variations caused by the reactivity of calcite

Abstract A pulp suspension consists of water, fibres, fines, fillers and chemicals, but air or other gases are also present in practically all pulping processes either in dissolved form or as bubbles. Dissolved gases seldom disturb the processes, but they are readily converted to gaseous form when conditions change. The gas bubbles affect the properties of the pulp suspension, reduce the accuracy of certain measurements, interfere with the runability of the papermachine and detract from the quality of the end-product. Gases are removed from the process by either mechanical or chemical means, resulting in increased investments and operational costs. The aim of this work was to study the behaviour of gas in pulp and papermaking processes with laboratory, pilot-scale and mill-scale experiments. Five main areas of the research can be identified: 1. Occurrence of gases in pulp and paper mill processes, 2. Dissolution, precipitation and hold-up of gases in the pulp suspension and mill water, 3. Effects of gases on certain consistency measurements, centrifugal pumping and operation of the hydrocyclone. 4. Measurement of the gas content of the pulp suspension by compression, radiometric, microwave and sonar methods and 5. Removal of gases with a centrifugal pump equipped with vacuum pump or hydrocyclone equipped light reject removal. The results show that the dissolution and precipitation of gas is strongly dependent on the pulp and water properties. Dissolved and colloidal material reduces the solubility potential of gas, but also accelerates the precipitation of dissolved gases in gaseous form. The hold-up of precipitated gas bubbles was found to be much more pronounced in hydrophobic mechanical pulps than in lignin-free chemical pulps. The accuracy of consistency measurements was affected by free gas in the pulp suspension, requiring special attention when assessing the results. The operation of pressure screens and hydrocyclones was affected only at high volumes of free gas in the feed suspension. According to the experiments, a reliable gas content measurement can be achieved by in-line radiometric, microwave or sonar methods, and also by the off-line compression method if a representative sample is obtained. A centrifugal pump equipped with a gas removing unit is designed mainly to ensure undisturbed pumping, whereas its gas removal efficiency remains quite low, especially with small bubbles and at a low gas content. The gas removal efficiency of a hydrocyclone equipped with light reject removal is good, but decreases with small precipitated bubbles. These results offer new information of the behaviour of the gas in pulp suspensions and white water and underline the importance of the bubble generation mechanism in this context.

Thesis (Ph. D.)--West Virginia University, 2010.
Title from document title page. Document formatted into pages; contains viii, 159 p. Includes abstract. Includes bibliographical references (p. 108-125).

This thesis concerns the scale-up of precipitation processes aimed at predicting product particle characteristics. Although precipitation is widely used in the chemical and pharmaceutical industry, successful scale-up is difficult due to the absence of a validated methodology. It is found that none of the conventional scale-up criteria reported in the literature (equal power input per unit mass, equal tip speed, equal stirring rate) is capable of predicting the experimentally observed effects of the mixing conditions on kinetic rates and particle characteristics. As a result of high gradients in the supersaturation field during precipitation, particularly in the feed zone, high local gradients in the nucleation rate are to be expected. In this thesis, a compartmental mixing model (Segregated Feed Model SFM) linked to the population balance is proposed for scaling up both continuous and semibatch precipitation processes, and is validated with experiments on different scales. Experiments were carried out using two chemical systems (calcium oxalate CaC₂O₄ and calcium carbonate CaCO₃), varying the residence time/feed time, feed concentration, feed point position, impeller type, feed tube diameter and stirring rate in geometrically similar reactors ranging from 0.3 to 301. A new procedure is introduced in order to solve the inverse problem for determination of the kinetic parameters for nucleation, growth, disruption and agglomeration from the particle size distributions obtained in the continuous laboratory-scale experiments. This method, where the kinetic rates were extracted separately and sequentially from the particle size distribution, was found to be a reliable alternative to the conventional simultaneous estimation of all kinetic parameters from the distribution. Using the kinetic parameters extracted from the laboratory-scale experiments, the population balance is solved within the Segregated Feed Model. The local mixing parameters also required for solving the SFM are obtained from a sliding mesh Computational Fluid Dynamics (CFD) model. These are used to specify the different micromixing and mesomixing conditions in the feed and bulk zones of the reactor. The model accurately predicts the mean size, coefficient of variation and nucleation rate on different scales for different process and mixing conditions in both continuous and semibatch mode of operation. Furthermore, the model confirms the observed greater effect of mixing on product particle characteristics in semibatch than in continuous operation. This is thought to be due to direct mixing of the feed solution in semibatch operation with the other component already present in the reactor. The methodology proposed here for the scale-up of precipitation processes is very versatile and computationally efficient. It combines the advantages of both a CFD and a population balance approach without having to solve the equations together, which is currently still impracticable due to the excessive computational demand and simulation time required.

Dans la plupart des alliages metalliques, la composition de la surface differe de celle du volume. Ce phenomene, appele segregation superficielle, a fait l'objet jusqu'a present de beaucoup d'etudes, principalement sur des alliages ayant atteint l'equilibre thermodynamique dans le domaine de la solution solide. Le sujet de la these a ete centre autour de l'etude par simulations numeriques du phenomene de segregation lors des cinetiques de dissolution et de precipitation. Ce travail est illustre par l'etude du systeme fe-cu. A l'aide d'un modele de diffusion a l'echelle atomique couple a deux approches statistiques complementaires nous avons etudie, d'une part les modes de dissolution de depots, et d'autre part l'influence de la surface sur les cinetiques de demixtion. Tout d'abord, les cinetiques de dissolution de depots fe/cu et cu/fe ont ete abordees a l'aide de l'approximation de champ moyen. Lorsque l'energie de surface de l'element depose est superieure a celle du substrat (cas des depots fe/cu), l'element du substrat remonte en surface et forme une couche flottant sur le depot. Dans le cas des depots epais, une alternance entre deux modes de dissolution du precipite donne lieu a une grande variete de comportements pilotes par la temperature et l'epaisseur du depot. Nous avons montre que les differentes configurations observees au cours de la cinetique sont a l'equilibre local, ceci expliquant la persistance de configurations, et meme les transitions abruptes pouvant intervenir entre certaines d'entre elles. La seconde partie de ce travail a concerne les cinetiques de demixtion en couche mince. Des simulations monte-carlo ont permis de suivre l'evolution des configurations au cours du temps, pour differentes compositions du systeme et differentes epaisseurs de couche mince. Nous avons mis en evidence une decomposition pilotee par la surface avec la creation d'une couche mouillante de cuivre, progressant vers le coeur de la couche au cours du temps. Ce processus est couple a la formation de domaines au sein de la couche, menant a des comportements varies et complexes, suivant la concentration moyenne et l'epaisseur de la couche.

Struvite is a salt that is formed out of  Mg2+,NH4+ and PO43- and it crystallizes in form of MgNH4PO4.6H2O. Struvite‟s (magnesium ammonium phosphate or MAP) precipitation has recently been regarded as an interesting technique to remove phosphate and ammonium from waste water. The high elimination rates and the possibility of recycling the struvite as a direct slow release fertilizer make this process feasible and appealing. However, the costs due to the raw chemicals needed are drawbacks that leave aside the application of the process in some facilities. The MAP biological dissolution makes possible a recycling of magnesium and phosphate, a fact that reduces the process‟s costs and will help making it even more feasible and environmentally friend. This thesis goes also through the parameters, reactions and different techniques that optimize the struvite precipitation process.

2014 - 2015
In the last decade, the application of microparticles, nanoparticles and composite microparticles involved several industrial fields. Conventional micronization techniques, such as jet milling, spray drying, liquid antisolvent precipitation and solvent evaporation are sometimes not suitable, since the produced particles are irregular, with broad size distribution, could be degraded due to mechanical or thermal stresses and polluted with organic solvents or other toxic substances. In this context, supercritical fluids (SCFs) based techniques have been proposed as an alternative to traditional processes thanks to the specific characteristics of SCFs, mainly solvent power and liquid-like densities with gas-like transport properties, that can be tuned varying pressure and temperature. Among supercritical assisted micronization techniques, Supercritical Antisolvent (SAS) precipitation has been successfully used to obtain microparticles and nanoparticles of several kinds of compounds, such as pharmaceuticals, coloring matters, polymers and biopolymers. In this process carbon dioxide (CO2) is used as an antisolvent at supercritical conditions: a solution containing the product to be micronized is injected into the precipitation chamber, saturated with supercritical carbon dioxide under the chosen conditions of temperature and pressure. CO2, in contact with the solution, forms a mixture in which the product is insoluble, causing the precipitation... [edited by author]
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L'objectif de ce travail de these est de produire des nanoagregats par dissolution sous faisceau d'un film metallique enterre dans une matrice dielectrique. L'observation par microscopie electronique en transmission de l'evolution des echantillons lors de l'irradiation a revele une succession de processus complexes. Deux etapes principales ont ete mises en evidence : i) un demouillage du film metallique sous irradiation et la formation de grains isoles ; ii) la dissolution des atomes des grains et la formation de precipites metalliques. L'analyse de l'evolution morphologique des grains a montre qu'ils s'allongent dans la direction du faisceau d'ions. Cette elongation a ete interpretee en terme de fluage nabarro du a une contrainte de cisaillement (normale a la direction du faisceau) creee dans la silice lors de l'irradiation. Comme la technique rbs s'adapte mal a l'analyse d'un systeme granulaire, nous avons developpe un modele analytique pour interpreter les resultats des cinetiques de melange ionique. Le phenomene de la precipitation sous irradiation a egalement ete etudie. La mise en evidence de l'inversion, sous certaines conditions d'irradiation, de la loi de gibbs-thomson (murissement d'ostwald inverse) a ete interpretee sur la base d'un modele analytique propose par heinig. Nos resultats experimentaux ont ete compares aux previsions du modele de heinig en ayant recours a des simulations numeriques a l'aide du code de calcul k3dlmc. Ce travail constitue une premiere etape dans la comprehension de phenomenes aussi complexes que l'evolution de systemes non-miscibles sous irradiation.

This thesis is concerned with the development and application of novel theoretical and experimental methodologies to study crystal dissolution processes across multiple lengthscales. In particular, it presents a versatile in situ multimicroscopy approach, comprising atomic force microscopy (AFM), scanning ion-conductance microscopy (SICM), and optical microscopy (OM) that is readily combined with finite element method (FEM) simulations. The methodology permits the quantitative 3D visualization of microcrystal morphology during dissolution with well-defined, high mass transport rates, enabling both the measurement of face-dependent dissolution rates and the elucidation of the dissolution mechanism. The approach also allows the determination of interfacial concentrations and concentration gradients, as well as the separation of kinetic and mass transport limiting regimes. The high resolving power and versatility of this new methodology is demonstrated on four different crystalline compounds with very different characteristics. First, the dissolution kinetics of individual faces of single furosemide microcrystals are investigated by OM-SICM and FEM modeling. It is found that the (001) face is strongly influenced by surface kinetics, while the (010) and (101) faces are dominated by mass transport. Dissolution rates are shown to vary greatly between crystals, with a strong dependence on crystal morphology and surface properties. A similar approach is then used to investigate changes in both crystal morphology and surface processes during the dissolution of bicalutamide single crystals, achieving high resolution with in situ AFM. It is shown that dissolution involves roughening and pit formation on all dissolving surfaces, and that this has a strong influence on the overall dissolution rate. FEM simulations determine that mass transport contributions increase as dissolution proceeds due to a continuous increase of the intrinsic dissolution rate constant, promoted by the exposure of high index microfacets. The methodology is further developed to show that kinetic data obtained from OMSICM and AFM, which provide differing measures of kinetic parameters, are in good agreement when the different mass transport regimes of the two experimental configurations are accounted for. The robustness of the methodology is verified via studies of L-cystine crystals, while also providing insights into the dissolution mechanism by visualizing hexagonal spirals descending along screw dislocations. Finally, the ability of the methodology to characterize processes with fast surface kinetics is demonstrated by the study of the proton-promoted dissolution of calcite single crystals. The approach allows the accurate determination of the near-interface concentration of all species during dissolution, as well as the intrinsic dissolution rate constant of the {104} faces, showing that surface kinetics play an important role in the dissolution process. Overall, this methodology provides a significant advance in the analysis and understanding of dissolution processes at a single crystal level, revealing the intrinsic properties of crystal faces and providing a powerful platform from which future studies can be developed.

The aim of this thesis is twofold with both elements related to industrially relevant crystal systems and processes. The first element utilized a combined scanning electrochemical cell microscope (SECCM) and atomic force microscopy (AFM) method to study the dissolution of enamel surfaces with controlled proton flux to the surface. This was then extended to investigate the effect of both known surface treatments, fluoride and zinc ions, but also a novel treatment of calcium silicate and its methods of action. The second element investigated the use of a nanopipette to investigate the early nucleation and initial growth of calcium carbonate crystals. For the dissolution of enamel, an SECCM probe to selectively etch a surface for a defined period of time with a high spatial resolution was used. The extent of the etching in the resultant pits was then monitored through AFM to measure the volume of material removed along with other pit dimensions. The method allowed for multiple independent measurements on a single sample, which could be selectively treated to eliminate comparability issues associated with measurements on multiple samples. The system could be modelled via finite element method (FEM) to calculate an intrinsic rate of reaction for the proton induced dissolution of enamel. A proton induced rate constant of dissolution of k0= 0.099 ± 0.008 cm s-1 for bare untreated enamel was established, whereas treatment with 1000 ppm sodium fluoride (NaF) and/or zinc chloride (ZnCl2) decreased this rate constant. The work also characterised the use of calcium silicate as a novel additive in toothpaste and to determine its effect as both a remineralising agent and as a dissolution inhibitor. The release of Ca2+ ions into solution was measured which acts to promote the remineralisation of tooth enamel. The addition of phosphate buffer into this solution combined with micro-Raman spectroscopy was then used to confirm the formation of hydroxyapatite (HAP (Ca10(PO4)6(OH)2)) material. The extent of adhesion of calcium silicate onto rough and polished samples was also observed, showing the preference of particles to adhere to rough surfaces, and was quantified by investigating the effect of infilling of etch pits formed via the SECCM method above, which showed an average pit volume reduction of 77±12%. The second element of the thesis involved investigation into the initial phase of nucleation, nanoprecipitation and growth of calcium carbonate crystals using voltage driven ion migration within a nanopipette (~50 nm opening) geometry to control the mixing of constituent ions to selectively control and induce the nucleation and dissolution of crystals and monitor their growth. This was achieved using oppositely charged CO32- and Ca2+ ions, inside and outside the pipette respectively, which could be either driven together or apart depending on the applied polarity. This process was modelled using FEM to give quantitative information about the growth rate and nanocrystal size during growth as well as analysis of the saturation levels within the probe geometry. The nanocrystals formed were studied in situ using micro-Raman spectroscopy to give information about the polymorph of calcite produced. The effect of the driving bias was demonstrated and rationalised through simulation along with the effect of constituent ion concentration. This method was used to assess the effect of maleic acid as an inhibitor to the formation of calcium carbonate. Its potent effect was shown by the significantly larger time taken to block the pipette by crystal growth. This also provided evidence for the mechanism of crystal growth inhibition by comparison with ion concentrations expected as a result of a pure chelation effect.

Amorphous solids (glasses) are a class of materials that lack the traditional long-range order found in crystals, and are primarily formed by rapid cooling of a liquid to bypass crystal nucleation. Their lack of crystallinity and associated defects gives them useful electromagnetic and mechanical properties. However, the affinity of a material to vitrification is only loosely understood, and structural detail is difficult to obtain via traditional methods. This thesis firstly investigates the promotion of glass formation via crystal inhibition. Molecular dynamics simulations of binary alloys are used to show crystal frustration via specific interactions of interaction range and particle softness, resulting in a lower enthalpic drive and complex crystal structures. Secondly, a facilitated kinetic Ising model is used to investigate the dynamics of organic glasses in solution. Glass dissolution is shown to have a non-linear dependence on the effective temperature of the solute, switching between a front-like dissolution at low temperatures, and a diffuse interface at higher temperatures. Also shown is a method of preparing an enhanced glass via precipitation from a solution, capable of creating a much lower energy glass than simple bulk cooling.

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 aim of this thesis was to investigate crystal nucleation, growth and dissolution processes, focussing particularly on the behaviour of the crystal surface. To facilitate this various methods of microscopy were used, as well as electrochemical techniques, with the goal to separate mass transport towards the crystal surface and the processes which occur close to the crystal surface, and measure intrinsic growth/dissolution rates. In order to do this, crystal systems were screened for their relevance to applications in industrial processes, and those chosen were related to pharmaceutical crystallization and scale formation in o↵ shore oil wells. For each system, different methods of electrochemical measurement and microscopy were investigated to chose a technique which works best for the problem in hand. Further to the experimental data produced, these were supported by mass transfer models, with the aim of finding out more quantitative information about the surface behaviour of the crystal systems observed. Firstly, salicylic acid micro-crystals were observed in aqueous solution by optical microscopy to visualise growth/dissolution rates of individual faces. It was found from finite element method (FEM) simulations that the most active (001) face was strongly mass transport controlled, and that the (110) and ( ¯ 110) were closer to the surface controlled regime. Salicylic acid crystals were further analysed by scanning electrochemical microscopy (SECM) using 3 dimensional (3D) scans containing a series of approaches to the surface. By inducing dissolution on the crystal surface, and measuring a change in ultramicroelectrode (UME) current, the dissolution rate constant of the (110) face of salicylic acid was determined for this heterogeneous surface. Barite nucleation and growth was observed by optical microscopy, using a flow cell with hydrodynamic flow. High supersaturations were used and the crystals were deposited onto foreign surfaces with differing surface charge. It was found that the flux of material, once initial nucleation was achieved, matched closely to simulated mass transport fluxes. Finally, nanoprecipitation was induced at the opening of a nanopipette (ca. 100 nm) diameter and an ion current was applied to induce the early stages of barite nucleation. It was possible to observe nucleation and blockage of the nanopipette from the current transient produced. This process was used to test the effectiveness of different phosphonate inhibitors.

Hydrocalumite is a calcium/aluminium-based layered double hydroxide. This material has a wide range of applications, such as polymer additives, basic catalysts and water treatment agents. There are a variety of synthesis methods available of which co-precipitation is most widely used. The negative aspects of using most of the developed methods are use of high cost metal salts as reagents. These materials are not only high in cost but are highly corrosive and result in damage of production equipment. A salt containing effluent is produced in these processes that can be harmful to the environment, thus requires treatment before disposal. As the interest in the use of hydrocalumite has increased, there is a need for environmentally friendly and more cost effective synthesis procedures. The aim of this study was to explore different reagents, time and temperature reaction conditions for the dissolution-precipitation synthesis of carbonate-containing hydrocalumite. In this method metal oxides/hydroxides reagents are used which are less corrosive and do not lead to harsh effluent production. This method has two distinct steps namely precursor formation followed by intercalation. In the precursor formation step, it was found that for the reaction between calcium oxide and aluminium hydroxide the conversion of both the calcium and aluminium sources increase as reaction time and temperature increase. It was confirmed that the dissolution of aluminium hydroxide is the limiting step. An aluminium conversion of ~90 % is reached at 80 oC at 6 h reaction time. A further increase in temperature reduces the reaction time immensely, with ~90 % aluminium conversion reached within 30 min at 100 oC and 120 oC. Extending the reaction times beyond these points does not have a significant influence on the conversion of aluminium as it remains constant at ~90 %. Of the various carbonate sources tested for intercalation, sodium carbonate showed the most crystalline hydrocalumite samples. Using sodium bicarbonate as a carbonate source renders similar conversion results to sodium carbonate. When reacting these carbonate sources with the precursor, the conversion to hydrocalumite increased with increasing reaction time and temperature. There is a significant spike in the intensity of the primary hydrocalumite diffraction peak of the sodium carbonate samples at 60 oC and 70 oC for 10 h reaction time; resulting in the highest yield of hydrocalumite. Use of air, CO2 (g), calcite and dry ice CO2 (s) as carbonate sources resulted in poor formation of hydrocalumite. Considering the results of the precursor formation and intercalation, the most promising synthesis conditions is to react calcium oxide and aluminium hydroxide at a temperature of 100 oC for 30 min, where after sodium carbonate should be added to the mixture and reacted for a further 10 h between 60 oC and 70 oC.
Dissertation (MEng)--University of Pretoria, 2015.
tm2016
Chemical Engineering
MEng
Unrestricted

The large-scale production of nanomaterials with fine control over their shape, size and properties remains a major obstacle towards their further use in a wide range of industrial applications. Therefore, the aim of the present PhD thesis is to assess the manufacturing of metal oxide NPs at large-scale using a membrane emulsification (ME)-precipitation process. In the project, flat and ring-shaped anodic alumina membranes (AAMS) were fabricated and their synthesis conditions optimised to obtain membranes with a narrow pore size distribution. Flat AAMs were used to produce oil-in-water nanoemulsions (NEs) in a dead-end stirred cell ME setup for the first time. Results show the regular pore structure and narrow pore size distribution of the AAMs enabled the formation of NEs with narrow droplet size distributions. The results demonstrated that rotational speed and membrane pore size were the key parameters in controlling the droplet size, with droplets as small as 144 ± 18 nm obtained, when Dpore = 58 ± 6 nm. Low proportionality values, Ddroplet/Dpore, ranging from 1.8 to 3.5, were obtained. Ring-shaped AAMs (Dp = 77 ± 9 nm) were synthetized for the first time with the purpose of producing oil-in-water NEs using a commercial stirred ME setup operating in a dead-end configuration. A systematic investigation of process parameters showed that narrow NEs were produced, obtaining proportionality constant values, as small as 2.8. Then, it was first reported the production of metal oxide NPs using an oil-in-water ME-precipitation process that can be easily scaled-up. For instance, we synthesized hematite NPs in a commercial dead-end ME setup fitted with a ring-shaped AAM and operating in a semi-continuous mode. The average primary particle size was 4.2 ± 0.5 nm and 18 ± 4 nm for the as-synthetized and calcined hematite NPs, respectively. Nevertheless, drying and calcination of the NPs leads to the formation of clusters in the micrometre range. Calculations of the emulsion production rate demonstrate the potential of the ME setup to produce up to 1.4 kg of per hour per metre square of membrane. Then, TiO2 NPs were synthesized in a continuous ME setup operating in a crossflow configuration, with the intention to produce NPs in a larger scale, with an average primary particle size ranging from 9.7 to 13.4 nm. The results show this manufacturing method can produce up to 2.8 kg NPs per hour per metre square of membrane. Non-metal doping was investigated, the results demonstrated the successful incorporation of interstitial nitrogen and carbon in the TiO2 lattice and showing a reduction of 1.05 eV in the band gap, which results in the formation of TiO2 NPs with photocatalytic response in the visible light spectrum.

This thesis aims at providing new knowledge on the, otherwise poorly known, molecular-scale mechanisms that operate during hydration of cement phases and dissolution of their hydrates. In order to pursue this objective, a novel approach has been followed, including the development of a new procedure to synthesize thin films of calcium silicates, real time characterization of grain growth and dissolution with liquid-cell atomic force microscopy, and monitoring of their chemical evolution by X-ray photoelectron spectroscopy of thin films hydrated in-situ, avoiding atmospheric contamination. Nanometer-sized films of clinker phases have been prepared using electron-beam evaporation methods. After deposition on silicon substrates, film thicknesses and mineralogical composition were characterized by atomic force microscopy (AFM) or mechanical profilometry and grazing-angle X-ray diffraction (GAXRD), respectively. Chemical composition was determined by X-ray photoelectron spectroscopy (XPS). Results from the GAXRD and XPS analysis show that aluminates phases are not suitable to be evaporated by electron beam technique. However quantitative analysis of calcium silicates samples shows that the Ca:Si ratio of the deposited film is the same as in the bulk starting material, confirming the suitability of the technique for the synthesis of these materials. Calcium silicate thin films with different thicknesses were submitted to hydration in different ways. XPS results describe clear chemical changes when samples are exposed to water vapor by shifts on the silicon peak, broadening on the calcium peak and decreasing on the Ca:Si ratio, related to the silicon polymerization due to the C-S-H formation. In situ hydration in fluid cell followed by AFM in water and calcium hydroxide saturated solution allows observing the formation of C-S-H particles, that happens very fast in C3S, which is dissolved later, and slower in C2S. Finally, Scanning transmission X-ray microscopy (STXM) of samples hydrated in situ with water allows observing the formation of particles with different concentration of calcium and silicon, and different chemical state at some point. The development of this technique of synthesis and the results obtained on the hydration allow improving the knowledge of early stage clinker phase hydration at the molecular level and to better understand the behavior of these materials, shedding some additional light on the complex problem of the hydration mechanisms of cementitious materials.
Aquesta tesi té per objectiu proporcionar nous coneixements sobre els mecanismes, abans poc coneguts, que operen durant la hidratació de les fases de ciment i la dissolució dels seus hidrats a escala molecular. Per tal d'aconseguir aquest objectiu, un nou enfocament ha estat seguit amb l'elaboració d'un nou procediment per sintetitzar pel·lícules primes de silicats de calci, la seva caracterització en temps real del creixement del gra i de la dissolució amb les cel·les de líquid al microscopi de forces atòmiques i el seguiment de l'evolució de la seva composició química per espectroscòpia de fotoelectrons de raigs X de pel·lícules primes hidratades in-situ, evitant la seva contaminació atmosfèrica. S'han preparat pel·lícules nanomètriques de les fases del clínquer utilitzant l'evaporació per feix d'electrons. Després de la deposició en substrats de silici, es van caracteritzar el gruix mitjançant la microscòpia de forces atòmiques (AFM) i la perfilometria mecànica i la composició mineralògica amb la difracció de raigs X d'angle rasant (GAXRD). La composició química es va determinar per espectroscòpia fotoelectrònica de raigs X (XPS). Els resultats del GAXRD i d'XPS mostren que els aluminats no són adequats per a ser evaporats utilitzant l'evaporació assistida amb feix d'electrons. No obstant això, anàlisis quantitatives de les mostres de silicats de calci mostren que la relació Ca:Si de la pel·lícula dipositada és la mateixa que en el material de partida, el que confirma la idoneïtat de la tècnica per a la síntesi d'aquests materials. Les pel·lícules primes de silicat càlcic de gruixos diferents van ser sotmeses a hidratació de diferents maneres. Els resultats d`XPS descriuen canvis químics clars quan les mostres estan exposades al vapor d'aigua com s'infereix dels canvis en el pic del silici, l'eixamplament del pic del calci i la disminució en la relació Ca:Si, que es relaciona amb la polimerització del silici degut ala formació de C-S-H. La hidratació in situ en aigua o solució saturada d'hidròxid de calci a la cel·la de fluid de l'AFM permet observar la formació de partícules de C-S-H. La hidratació ocorre molt ràpidament en el C3S, que després es dissol, i és més lenta en el C2S. Finalment, la microscòpia de transmissió i escaneig de raigs X (STXM) de les mostres hidratades in situ amb aigua permet observar la formació de partícules amb diferents concentracions de calci i silici i, en alguns casos, la variació de l'estat químic . El desenvolupament d'aquesta tècnica de síntesi i els resultats obtinguts en la hidratació permeten millorar el coneixement de la hidratació de les fases del clínquer en estadis inicials a nivell molecular i entendre millor el comportament d'aquests materials, ajudant a aclarir el complex problema dels mecanismes d'hidratació dels materials del ciment

Precipitated surface films form when metal cations are produced faster than they can move away from the dissolving interface. This build up of cations results in supersaturation conditions, which cause a solid to precipitate. The precipitated solid affects ion transport and thus the dissolution kinetics, which ultimately control the two systems studied here. X-ray diffraction, small angle X-ray scattering and fast radiography were chosen to study the metal/solution interface in-situ, using synchrotron radiation. The AC electrograining system is a widely used industrial process whereby an alternating current is applied to aluminium plates to form a pitted surface. During this process, an Al(OH)3 surface gel (smut) forms within seconds whilst electrograining continues for several minutes in its presence. Although smut formation has been investigated previously, how the smut affects metal dissolution is currently unknown and is the primary goal of this project. The second system is a nickel “artificial pit,” which is commonly used to simulate pit propagation. In this system, a salt film is precipitated by imposing a large overpotential whilst restricting transport through a 1-D pit. Interfacial phenomena that occur during salt film formation are investigated towards an understanding of how the salt film forms.

L'altération chimique des roches primaires et des minéraux dans les systèmes naturels a un impact majeur sur la formation des sols et leur composition. L'altération chimique est largement pilotée par la dissolution des minéraux. Les éléments chimiques libérés dans les eaux souterraines par la dissolution des minéraux réagissent facilement pour former des minéraux secondaires comme les argiles, zéolites et carbonates. Les carbonates se forment par réaction des cations divalents (Ca, Fe et Mg) avec CO2 dissous tandis que la formation des kaolins et de la gibbsite est attribuée à l'altération des minéraux riches en aluminium, le plus souvent les feldspaths. Le projet Carbfix à Hellisheiði (sud-ouest de l'Islande) a pour but d'utiliser les processus d'altération naturelle pour former des minéraux carbonatés par réinjection dans les roches basaltiques environnantes de CO2 provenant d'une centrale géothermique. Ce processus trouve son origine dans la dissolution des roches basaltiques riches en cations divalents (Ca, Fe et Mg) qui se combinent au CO2 injecté pour former des minéraux carbonatés. Cette thèse est centrée sur la dissolution du basalte cristallin de Stapafell qui est composé essentiellement de trois phases minérales (plagioclase, pyroxène et olivine) et qui est riche en cations divalents. La vitesse de libération des éléments du basalte à l'état stationnaire et loin de l'équilibre a été mesurée dans des réacteurs à circulation à des pH de 2 à 12 et des températures de 5 à 75°C. Les vitesses de libération de Si et Ca à l'état stationnaire présentent une variation en fonction du pH en forme de U avec une diminution des vitesses lorsque le pH augmente en conditions acides et une augmentation avec le pH en conditions alcalines. Les vitesses de libération du silicium par le basalte cristallin sont comparables à celles par le verre basaltique de même composition chimique aux faibles pH et aux températures = 25°C mais elles sont plus lentes aux pH alcalins et aux températures = 50°C. Par contre, les vitesses de libération de Mg et Fe diminuent de manière monotone avec l'accroissement du pH à toutes les températures. Ce comportement a pour cause les variations contrastées, en fonction du pH, des vitesses de dissolution des trois minéraux constitutifs du basalte: plagioclase, olivine et pyroxène. Les vitesses de libération des éléments déduites de la somme des vitesses de dissolution du plagioclase, pyroxène et olivine normalisées à la fraction volumique de ces minéraux sont, à un ordre de grandeur près, les mêmes que celles mesurées dans cette étude. En outre, les résultats expérimentaux montrent que, durant l'injection d'eaux chargées en CO2 de pH proche de 3. 6, le basalte cristallin libère préférentiellement Mg et Fe en solution par rapport à Ca. L'injection de fluides acides chargés en CO2 dans des roches cristallines basaltiques peut donc favoriser la formation de carbonates de Mg et Fe aux dépends de la calcite aux conditions de pH acides à neutres. Le plagioclase, qui est la phase la plus abondante du basalte, influence fortement la réactivité de ce dernier. La vitesse de dissolution du plagioclase, basée sur la libération de la silice, présente une variation en forme de U en fonction du pH, diminuant lorsque le pH augmente aux conditions acides mais augmentant avec le pH aux conditions alcalines. En accord avec les données de la littérature, la vitesse de dissolution du plagioclase à pH constant, en conditions acides, augmente avec sa teneur en anorthite. L'interprétation et le fit des données obtenues suggèrent que la vitesse de dissolution du plagioclase est contrôlée par la décomposition d'un complexe activé riche en silice, formé par le départ de Al de la structure du minéral. Le plus remarquable, par comparaison aux hypothèses antérieures, est que la vitesse de dissolution du plagioclase en conditions alcalines est indépendante de sa teneur en anorthite - e. G. Les vitesses de dissolution des plagioclases riches en anorthite augmentent avec le pH aux conditions alcalines. A ces conditions, il est probable que la vitesse de dissolution rapide du plagioclase domine, en raison de sa forte teneur en Ca, la libération vers la phase fluide des cations divalents du basalte cristallin. La gibbsite est généralement le premier minéral qui précipite lors de la dissolution du plagioclase. C'est un hydroxyde d'aluminium que l'on trouve dans divers sols et qui est aussi la phase principale des minerais de bauxite. Les vitesses de précipitation de la gibbsite ont été mesurées dans des réacteurs fermés, en conditions alcalines à 25 et 80°C, en fonction de l'état de saturation du fluide. Les analyses des solides après réaction ont démontré que la précipitation de gibbsite s'est produite dans toutes les expériences. L'interprétation de l'évolution dans le temps de la chimie du fluide réactif fournit des vitesses de précipitation de la gibbsite qui sont près des vitesses de dissolution du plagioclase. En plus, des vitesses de précipitation de la gibbsite diminuent plus rapidement que des vitesses de dissolution du plagioclase quand le pH descende. Ceci suggère que l'étape limitant de l'altération du plagioclase sur la surface de la terre est plutôt la consommation d'Al par formation de la gibbsite que la dissolution même du plagioclase. La kaolinite est en général le second minéral formé après la gibbsite lors de la dissolution du plagioclase à basse température. Les vitesses de précipitation de la kaolinite ont été mesurées dans des réacteurs à circulation à pH = 4 et t = 25°C, en fonction de l'état de saturation du fluide. Au total, 8 expériences de précipitation de longues durées ont été réalisées dans des fluides légèrement supersaturés par rapport à la kaolinite, en utilisant comme germes pour la précipitation une quantité connue de de kaolinite de Géorgie (KGa-1b) contenant peu de défauts et préalablement nettoyée. Les vitesses de précipitation de kaolinite mesurées sont relativement lentes comparées aux vitesses de dissolution du plagioclase. Cette observation suggère que la formation de kaolinite lors de l'altération est limitée par sa vitesse de précipitation plutôt que par que la disponibilité en Al et Si issus de la dissolution du plagioclase. L'ensemble des résultats de cette étude fournit un certain nombre de principes scientifiques de base nécessaires à la prédiction des vitesses et des conséquences de la dissolution du basalte cristallin et du plagioclase à la surface de la Terre et lors de l'injection du CO2 à proximité de la surface dans le cadre des efforts de stockage du carbone. Les résultats obtenus indiquent, bien que les vitesses de précipitation de la gibbsite soient relativement rapides, que la vitesse de précipitation relativement lente de la kaolinite peut être le processus contrôlant la formation de ce minéral à la surface de la Terre. Cette observation souligne la nécessité de poursuivre la quantification de la précipitation de ce minéral secondaire aux conditions typiques de la surface de la Terre. En outre, comme les proportions des différents métaux divalents libérés par les basaltes cristallins varient sensiblement avec le pH, la carbonatation des basaltes doit produire un changement systématique de l'identité des minéraux carbonatés et des zéolites précipités en fonction de la distance au puits d'injection. Cette dernière conclusion pourra être directement testée dans le cadre du projet CarbFix actuellement conduit à Hellisheiði en Islande
The chemical weathering of primary rocks and minerals in natural systems has a major impact on soil development and its composition. Chemical weathering is driven to a large extent by mineral dissolution. Through mineral dissolution, elements are released into groundwater and can readily react to precipitate secondary minerals such as clays, zeolites, and carbonates. Carbonates form from divalent cations (e. G. Ca, Fe and Mg) and CO2, and kaolin clay and gibbsite formation is attributed to the weathering of aluminium- rich minerals, most notably the feldspars. The CarbFix Project in Hellisheiði SW-Iceland aims to use natural weathering processes to form carbonate minerals by the re-injection of CO2 from a geothermal power plant back into surrounding basaltic rocks. This process is driven by the dissolution of basaltic rocks, rich in divalent cations, which can combine with injected CO2 to form and precipitate carbonates. This thesis focuses on the dissolution behaviour of Stapafell crystalline basalt, which consists of three major phases (plagioclase, pyroxene, and olivine) and is rich in divalent cations. Steady-state element release rates from crystalline basalt at far-from-equilibrium conditions were measured at pH from 2 to 11 and temperatures from 5° to 75° C in mixed-flow reactors. Steady-state Si and Ca release rates exhibit a U-shaped variation with pH, where rates decrease with increasing pH at acid condition but increase with increasing pH at alkaline conditions. Silicon release rates from crystalline basalt are comparable to Si release rates from basaltic glass of the same chemical composition at low pH and temperatures =25°C but slower at alkaline pH and temperatures =50°C. In contrast, Mg and Fe release rates decrease continuously with increasing pH at all temperatures. This behaviour is interpreted to stem from the contrasting dissolution behaviours of the three major minerals comprising the basalt: plagioclase, pyroxene, and olivine. Element release rates estimated from the sum of the volume fraction normalized dissolution rates of plagioclase, pyroxene, and olivine are within one order of magnitude of those measured in this study. In addition, these experimental results show that during injection of CO2-charged waters with pH close to 3. 6, crystalline basalt preferentially releases Mg and Fe relative to Ca to the fluid phase. The injection of acidic CO2-charged fluids into crystalline basaltic rocks may therefore favour the formation of Mg and Fe carbonates rather than calcite at acidic to neutral conditions. Plagioclase is the most abundant phase in crystalline basalts and thus influences strongly its reactivity. Plagioclase dissolution rates based on Si release show a common U-shaped behaviour as a function of pH where rates decrease with increasing pH at acid condition but increase with increasing pH at alkaline conditions. Constant pH plagioclase dissolution rates increase with increasing anorthite content at acid conditions, in agreement with literature findings. Interpretation and data fitting suggests that plagioclase dissolution rates are consistent with their control by the detachment of Si-rich activated complexes formed by the removal of Al from the mineral framework. Most notably, compared with previous assumptions, plagioclase dissolution rates are independent of plagioclase composition at alkaline conditions, e. G. Anorthite-rich plagioclase dissolution rates increase with increasing pH at alkaline conditions. At such conditions rapid plagioclase dissolution rates likely dominate divalent metal release from crystalline basalts to the fluids phase due to its high Ca content. Gibbsite is commonly the first mineral formed during low temperature dissolution of plagioclase. Gibbsite is an aluminium-hydroxide that is found in various soils as well as the dominant phase in many bauxite ores. Gibbsite precipitation rates were measured in closed system reactors at alkaline condition, both at 25 °C and 80 °C as a function of fluid saturation state. Analyses of the solids demonstrate that gibbsite precipitation occurred in all experiments. The comparison of gibbsite precipitation to the dissolution rates of plagioclase at pH 11 shows that the rates are close to equal. The precipitation rates of gibbsite, however, decrease faster with decreasing pH than plagioclase dissolution rates. As such it seem likely that plagioclase dissolution is faster than gibbsite precipitation at near to neutral pH, and the relatively slow rate of gibbsite precipitation influences plagioclase weathering in many Earth surface systems. Kaolinite is commonly the second secondary mineral formed during low temperature dissolution of plagioclase. Kaolinite precipitation rates were measured in mixed flow reactors as a function of fluid saturation state at pH=4 and 25 °C. In total eight long-term precipitation experiments were performed in fluids mildly supersaturated with respect to kaolinite, together with a known quantity of cleaned low defect Georgia Kaolinite as seeds. Measured kaolinite precipitation rates are relatively slow compared with plagioclase dissolution rates. This observation suggests that kaolinite formation during weathering is limited by its precipitation rates rather than by the availability of aqueous species sourced from plagioclase dissolution. Taken together the results of this study provide some of the fundamental scientific basic for predicting the rates and consequences of crystalline basalt and plagioclase dissolution at both the Earth's surface and during the near surface injection of CO2 as part of carbon storage efforts. Results indicate that although gibbsite precipitation rates are relatively rapid, the relatively slow precipitation rates of kaolinite may be the process controlling the formation of this mineral at the Earth's surface. This observation highlights the need to further quantify this secondary mineral precipitation rates at conditions typical at the Earth's surface. Moreover, as the composition of divalent metals released from crystalline basalts varies significantly with pH, CO2 carbonation in basalt should yield a systematic variation in the identity of carbonate and zeolite minerals precipitated with distance from the injection site. This latter conclusion can be tested directly as part of the currently on-going CarbFix project in Hellisheiði, Iceland

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Thesis advisor: Yvette D. Kuiper
Crystallographic Preferred Orientations (CPO) are common in deformed rocks, and usually result from crystal plastic deformation by dislocation creep. Whether deformation mechanisms that occur at lower differential stress and lower temperature than dislocation creep, such as Dissolution-Precipitation Creep (DPC), may result in the development of a CPO is less certain. DPC, a process also known as pressure-solution creep or dissolution creep, has caused substantial removal and reprecipitation of quartz within the Purgatory Conglomerate of Rhode Island. The conglomerate is exposed within the southeastern region of the Pennsylvanian Narragansett basin and experienced folding during the Alleghanian orogeny. Strain within the southeastern portion of the Narragansett basin increases from west to east and is associated with a metamorphic gradient from very low grade greenschist facies in the west to the lower biotite zone in the east. Within the Pugatory Conglomerate DPC has led to the dissolution of quartz along cobble surfaces perpendicular to the shortening direction, and to be precipitated as overgrowths at the ends of the cobbles (strain shadows), parallel to the maximum extension direction. This offers a unique opportunity to study the effects of dissolution and precipitation separately, because the quartz grains within the cobbles experienced dissolution only, while precipitation occurred in the strain shadows. Cathodoluminescence (CL) analysis was conducted on regions within the strain shadow in order to determine what amount of the quartz was formed authigenically. The results suggest that quartz-rich areas of the strain shadow were comprised primarily of authigenic quartz and formed channels or wedges. Electron Backscatter Diffraction (EBSD) analysis was used to test whether quartz dissolution processes within the cobbles and/or quartz precipitation within the strain shadows resulted in CPO development. Quartz grain c-axis orientations of various domains within the cobbles and strain shadows indicate that CPO patterns are absent in both domains of dissolution and of precipitation irrespective of the degree of strain or metamorphic grade. The existence of discrete mica selvages along the cobble margins suggests that quartz dissolution only occurred along the cobble surface and did not affect the grains, or result in a CPO, within the cobble's interior. Quartz precipitation within the strain shadows did not result in a CPO, probably because the strain shadows are truly localized regions of low strain with little to no differential stress, allowing quartz grain growth in random orientations
Thesis (MS) — Boston College, 2010
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Geology and Geophysics

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Tese (Doutoramento)
IPEN/T
Instituto de Quimica, Universidade de Sao Paulo - IQ/USP

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.
Includes bibliographical references (leaves 79-80).
A simulation study was performed to model the transient behavior of the dissolution of hexahydro-1, 3,5-trinitro-1, 3,5-triazine (RDX) in Composition B. Composition B, also referred to as CompB. CompB is made up of three parts: 54% RDX, 6% HMX and 40% TNT. A numerical simulation was employed to model the overall solute transport equation. The solute transport equation takes into account advection, dispersion, sorption, degradation, mobile-immobile sorption, and a mass transfer source term. Numerical code was developed and this model simulated the following: (1) flow rate, (2) initial mass loading, (3) particle size and (4) field oil. The simulation model results verified laboratory experiments provided by Phelan et. al. [2003] by applying the governing advection-dispersion equation with a linear-driving-force source term of the form kf (C, - C) . The variable k represents the lumped mass transfer coefficient [1/day], which implicitly incorporates specific surface area. The concentration denoted as C [mg/L], represents the effluent chemical concentration present in water at a given time while C, [mg/L] represents the concentration at equilibrium. The mass transfer source term was evaluated by correlating k to the modified Sherwood number. The modified Sherwood number was fitted with a least-squares method that approximated non-aqueous phase liquid (NAPL) dissolution [Miller et. al., 1990]. This study adjusted the constants developed with the obtained modified Sherwood number to model RDX. Modeling development used a modified Sherwood number in the form: ... The simulation code effectively modeled RDX effluent profiles.
by Joseph Vincent Romero.
S.M.

A series of local and bench scale laboratory experiments and bench and field scale numerical simulations were conducted to develop a better understanding of the interrelationship between nonwetting phase (NWP) source zones and downgradient aqueous phase concentrations in saturated porous media contaminated by immiscible organic liquids. Specific emphasis was placed on the factors governing the rate of NWP source zone evolution and the factors governing the rate of mass transfer from the NWP to the aqueous phase. Hysteretic NWP relative permeability-saturation (krN-SW) relationships were measured at the local scale for six sands to examine the relationship between krN-SW functions and porous media type. Parameterization of the measured constitutive relationships revealed a strong correlation between mean grain diameter and the maximum value of NWP relative permeability. The measured krN-SW relationships, were validated through a bench scale experiment involving the infiltration, redistribution, and immobilisation of NWP in an initially water saturated heterogeneous porous medium. This match of simulation to experiment represents the first validation of a multiphase flow model for transient, fixed volume NWP releases. Multiphase flow simulations of the bench scale experiment were only able to reproduce the experimental observations, in both time and space, when the measured krN-SW relationships were employed. Two-dimensional field scale simulations of a fixed volume NWP release into a heterogeneous aquifer demonstrate the influence of spatially variable krN-S relationships correlated to porous media type. Both the volume of the NWP invaded porous media, and the length of time during which NWP is migrating, will be under predicted if variable (correlated) kr,N is not accounted for in the numerical model iv formulation. This under prediction is exacerbated as the mean intrinsic permeability of the release location decreases. A new, thermodynamically-based interfacial area (IFA) model was developed for use in the single-boundary layer expression of mass transfer as an alternative to existing empirical correlation expressions. The IFA model considers consistency and continuity of constitutive relationships, energy losses, effective specific interfacial area for mass transfer, and dissolution of residual NWP. A bench scale experiment involving the release and dissolution of a transient NWP source zone in heterogeneous porous media was conducted to evaluate the appropriateness of the developed IFA model when utilised to predict NWP dissolution rates. Comparison of measured downgradient dissolved phase concentrations and source zone NWP saturations in time and space with those from numerical simulations of the experiment reveal that the proposed IFA model is superior to both a local equilibrium assumption and existing empirical correlation expressions. This represents the first mass transfer model validated for the dissolution of a complex NWP source zone. Twodimensional simulations at the field scale of multiphase flow and dissolution suggest that employing existing mass transfer expressions instead of the IFA model lead to incorrect predictions of the life spans of NWP source zones, downgradient dissolved phase concentrations, and the rate of mass flux through a downgradient boundary. The practical implication of this research is that accurate numerical predictions of the evolution of a transient NWP source in porous media require consideration of krN-S relationships and NWP / aqueous phase IFA, as these factors dictate the rates of the key subsurface contaminant processes of migration and dissolution, respectively.

Thesis (doctoral) - Delft University of Technology, Delft, 2002.
"Dissertation submitted in fulfillment of the requirements of the Board for Doctorates of Delft University of Technology and of the Academic Board of the International Institute for Infrastructural, Hydraulic and Environmental Engineering for the Degree of Doctor to be defended in public on Monday, 29 April 2002 at 13:30 hours in Delft, The Netherlands." Includes bibliographical references (p. [191]-199).

Experiments were conducted to precipitate dissolved copper, zinc, and lead from simulated wastewater solutions as solids which could then be separated by filtration. The precipitants used were hydrated lime, as a slurry and in powdered form, aqueous ammonium hydroxide, ferrous sulphide sludge, and carbon dioxide gas. These five different chemicals, singly or in combination, were used; at least one of which was highly successful in precipitating each of the metals, removing at least 99% of that originally present. Copper and zinc were very effectively precipitated as the hydroxides with lime, whereas lead was not. Considering lead to be the most difficult metal to remove, four other chemical conditions were attempted for lead; these were ferrous sulphide alone, lime with ferrous sulphide, lime with carbon dioxide, and lime with ozone. The precipitation of lead with ferrous sulphide alone, was only partially successful with only 95% removal. The other three combinations of chemicals precipitated more than 99% of the soluble lead, giving excellent results. Furthermore, because lead is usually difficult to remove from solution, it is considered that the three new chemical combinations show strong promise for the removal of other heavy metals from wastewater solutions. Experiments were also conducted to decompose the organic compounds, formaldehyde and pyridine, in simulated wastewater solutions in a mixed reactor, using ozone and UV radiation as oxidants. Although 200 ppm Total Organic Carbon content of each of those chemicals, and a mixture of both, were completely decomposed by ozone-UV oxidation, the time taken for these decompositions ranged from about three to four hours. Such prolonged reaction times are considered too long for most wastewater treating processes. However, low concentrations of organic matter might be successfully treated using ozone/UV processes.