Zeitschriftenartikel: „Dissolution and precipitation processes“

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Jordan, Guntram, Thomas Lohkämper, Martin Schellewald und Wolfgang W. Schmahl. „Investigation of loaded halite-SiO2 interfaces undergoing dissolution-precipitation processes“. European Journal of Mineralogy 17, Nr. 3 (14.06.2005): 399–409. http://dx.doi.org/10.1127/0935-1221/2005/0017-0399.

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Aurian-Blajeni, Benedict, Michael Kramer und Micha Tomkiewicz. „Computer simulation of dissolution-precipitation processes“. Journal of Physical Chemistry 91, Nr. 3 (Januar 1987): 600–605. http://dx.doi.org/10.1021/j100287a023.

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3

Hanschmann, Benedikt. „Precipitation of Polypropylene and Polyethylene Terephthalate Powders Using Green Solvents via Temperature and Antisolvent-Induced Phase Separation“. Advances in Polymer Technology 2023 (30.11.2023): 1–11. http://dx.doi.org/10.1155/2023/7651796.

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Polymer dissolution and precipitation are two common processes for the production of polymer powders, especially for cases where usual means of comminution are not applicable. I investigated six dissolution–precipitation processes based on high-boiling sustainable green organic solvents and antisolvents for the polypropylene and polyethylene terephthalate with respect to apparent particle morphology for a closed loop production scheme. Of the investigated processes two are considered antisolvent-induced precipitations whereas the other four can be considered temperature induced. The applied solvents included p-cymene, dibutoxymethane, ethylbenzoate, γ-valerolactone, ethanol, and hexanol. All processes yielded powders consisting of agglomerated primary particles at a powder dry substance of less than 25% by weight. The produced powders consist in all cases of agglomerates of smaller primary particles.

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Sadd, Matthew, Salvatore De Angelis, Sofie Colding‐Jørgensen, Didier Blanchard, Rune E. Johnsen, Simone Sanna, Elena Borisova, Aleksandar Matic und Jacob R. Bowen. „Visualization of Dissolution‐Precipitation Processes in Lithium–Sulfur Batteries“. Advanced Energy Materials 12, Nr. 10 (22.01.2022): 2103126. http://dx.doi.org/10.1002/aenm.202103126.

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Wu, Gang, und M. M. Sharma. „Model for precipitation and dissolution processes with precipitate migration“. AIChE Journal 35, Nr. 8 (August 1989): 1385–90. http://dx.doi.org/10.1002/aic.690350819.

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6

Ahmed, Anwar Qasim, Dániel Olasz, Elena V. Bobruk, Ruslan Z. Valiev und Nguyen Q. Chinh. „Effect of the Equal Channel Angular Pressing on the Microstructure and Phase Composition of a 7xxx Series Al-Zn-Mg-Zr Alloy“. Materials 16, Nr. 19 (07.10.2023): 6593. http://dx.doi.org/10.3390/ma16196593.

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A supersaturated Al-4.8%Zn-1.2%Mg-0.14%Zr (wt%) alloy was processed by the equal-channel angular pressing (ECAP) technique at room temperature in order to obtain an ultrafine-grained (UFG) microstructure having an average grain size of about 260 nm. The hardness and microstructural characteristics, such as the phase composition and precipitations of this UFG microstructure were studied using depth-sensing indentation (DSI), transmission electron microscopy (TEM), as well as non-isothermal scanning of differential scanning calorimetry (DSC), and compared to the properties of the un-deformed sample. Emphasis was placed on the effect of the UFG microstructure on the subsequent thermal processes in DSC measurements. It has been shown that the ECAP process resulted in not only an ultrafine-grained but also a strongly precipitated microstructure, leading to a hardness (2115 MPa) two and a half times higher than the initial hardness of the freshly quenched sample. Because of the significant changes in microstructure, ECAP has also a strong effect on the dissolution (endothermic) and precipitation (exothermic) processes during DSC measurements, where the dissolution and precipitation processes were quantitatively characterized by using experimentally determined specific enthalpies, ΔH and activation energies, Q.

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Meakin, Paul, und Bjørn Jamtveit. „Geological pattern formation by growth and dissolution in aqueous systems“. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 466, Nr. 2115 (26.11.2009): 659–94. http://dx.doi.org/10.1098/rspa.2009.0189.

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Progress towards the development of a better understanding of the formation of geological patterns in wet systems due to precipitation and dissolution is reviewed. Emphasis is placed on the formation of terraces, stalactites, stalagmites and other carbonate patterns due to precipitation from flowing supersaturated solutions and the formation of scallops by dissolution in undersaturated turbulent fluids. In addition, the formation of spherulites, dendrites and very large, essentially euhedral, crystals is discussed. In most cases, the formation of very similar patterns as a result of the freezing/melting of ice and the precipitation/dissolution of minerals strongly suggests that complexity associated with aqueous chemistry, interfacial chemistry and biological processes has only a secondary effect on these pattern formation processes.

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Dubinina, Elena O., und Leonid Z. Lakshtanov. „A kinetic model of isotopic exchange in dissolution-precipitation processes“. Geochimica et Cosmochimica Acta 61, Nr. 11 (Juni 1997): 2265–73. http://dx.doi.org/10.1016/s0016-7037(97)00076-8.

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Turpault, Marie-Pierre, Gilles Berger und Alain Meunier. „Dissolution-precipitation processes induced by hot water in a fractured granite Part 1: Wall-rock alteration and vein deposition processes“. European Journal of Mineralogy 4, Nr. 6 (15.12.1992): 1457–76. http://dx.doi.org/10.1127/ejm/4/6/1457.

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Slimani, Rabia, Abdelhamid Guendouz, Fabienne Trolard, Adnane Souffi Moulla, Belhadj Hamdi-Aïssa und Guilhem Bourrié. „Identification of dominant hydrogeochemical processes for groundwaters in the Algerian Sahara supported by inverse modeling of chemical and isotopic data“. Hydrology and Earth System Sciences 21, Nr. 3 (21.03.2017): 1669–91. http://dx.doi.org/10.5194/hess-21-1669-2017.

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Abstract. Unpublished chemical and isotopic data taken in November 1992 from the three major Saharan aquifers, namely the Continental Intercalaire (CI), the Complexe Terminal (CT) and the phreatic aquifer (Phr), were integrated with original samples in order to chemically and isotopically characterize the largest Saharan aquifer system and investigate the processes through which groundwaters acquire their mineralization. Instead of classical Debye–Hückel extended law, a specific interaction theory (SIT) model, recently incorporated in PHREEQC 3.0, was used. Inverse modeling of hydrochemical data constrained by isotopic data was used here to quantitatively assess the influence of geochemical processes: at depth, the dissolution of salts from the geological formations during upward leakage without evaporation explains the transitions from CI to CT and to a first end member, a cluster of Phr (cluster I); near the surface, the dissolution of salts from sabkhas by rainwater explains another cluster of Phr (cluster II). In every case, secondary precipitation of calcite occurs during dissolution. All Phr waters result from the mixing of these two clusters together with calcite precipitation and ion exchange processes. These processes are quantitatively assessed by the PHREEQC model. Globally, gypsum dissolution and calcite precipitation were found to act as a carbon sink.

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Cuadros, J. „Clay crystal-chemical adaptability and transformation mechanisms“. Clay Minerals 47, Nr. 2 (Juni 2012): 147–64. http://dx.doi.org/10.1180/claymin.2012.047.2.01.

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AbstractChemical and mineralogical transformations of phyllosilicates are among the most important in diagenetic environments in all types of rocks because they can exert a large control on the processes taking place in such environments and/or provide constraints for the conditions in which phyllosilicate transformation occurred. Dissolution-precipitation and solid-state transformation are usually the two mechanisms proposed for such reactions depending on the crystal-chemical and morphological similarities between parent and neoformed phases together with knowledge of the environmental conditions. These two mechanisms, however, may be at both ends of the spectrum of those operating and many transformations may take place through a mixture of the two mechanisms, generating observable elements that are characteristic of one or the other. In the present literature, the boundaries between the two mechanisms are not clear, mainly because dissolution-precipitation is sometimes defined at nearly atomic scale. It is proposed here that such small-scale processes are considered as a solid-state transformation, and that dissolution-precipitation requires dissolution of entire mineral particles and their dissolved species to pass into the bulk of the solution. Understanding the reaction mechanisms of diagenetic transformations is an important issue because they impinge on geochemical conditions and variables such as cation mobility, rock volume, fabric changes, rock permeability, stable isotope signature and phyllosilicate crystal-chemistry.I propose that, in the lower range temperatures at which clay mineral transformations take place, energy considerations favour solid-state transformation, or reactions that involve the breaking of a limited number of bonds, over dissolution of entire grains and precipitation of crystals of the new phase. Large morphological changes are frequently invoked as evidence for a dissolution-precipitation mechanism but changes in particle shape and size may be achieved by particle rupture, particle welding or by hybrid processes in which dissolution-precipitation plays a minor role.Past and recent studies of phyllosilicate transformations show chemical and structural intermediates indicating a large crystal-chemical versatility, greater than is commonly recognized. These intermediates include tetrahedral sheets of different composition within TOT units (termed polar layers), dioctahedral and trioctahedral domains in the same layer, and 2:1 and 1:1 domains also within the same layers. The existence of such intermediate structures suggests that the reaction mechanisms that generated them are within the realm of the solid-state transformation processes.

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Wierszyłłowski, Ignacy, und Sebastian Wieczorek. „Ageing Kinetics of Al.-4.7 % Cu Alloy. Dilatometric and DTA Studies“. Defect and Diffusion Forum 237-240 (April 2005): 768–73. http://dx.doi.org/10.4028/www.scientific.net/ddf.237-240.768.

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Studies of transformation kinetics during ageing of Al-4.7 % Cu were performed with use of dilatometric and DTA methods. The dilatometric method was used for studies of isothermal ageing, DTA for studies of ageing during isochronal heating. In order to determine isothermal transformation kinetics the JMA (Johnson – Mehl – Avrami) equation was applied, for isochronal heating transformation kinetics Kissinger method was used. Ageing of Al- Cu alloys consist of precipitation processes and dissolution processes that overlap each other. These processes, during isothermal ageing were distinguished with help of the time exponent n of JMA equation that is very sensitive to change of the transformation mechanism. During isochronal ageing, precipitation processes produce heat, dissolution processes consume heat. That helps to distinguish them. Results obtained during isothermal studies were in agreement with isochronal heating studies. Activation energies for precipitation processes 324-530 K temperature range varied from about 50 kJ/mol to about 100 kJ/mole and complied with the values obtained before. For precipitation processes at 650- 735 K temperature range, activation energies varied from 226 to 300 kJ/mole. The results obtained were discussed with literature data.

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Giuntoli, Francesco, Luca Menegon und Clare J. Warren. „Replacement reactions and deformation by dissolution and precipitation processes in amphibolites“. Journal of Metamorphic Geology 36, Nr. 9 (19.09.2018): 1263–86. http://dx.doi.org/10.1111/jmg.12445.

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Kasza, Angela Maria, Gabriel Katona, Monica Dan, Cezara Voica, Oana Grad, Maria Miheț, Tibor Dezso, Ruben Nagy, Tihamer Bots und Mihaela Diana Lazăr. „Platinum Recovery From Used Auto Catalysts: Dissolution and Precipitation Studies“. Studia Universitatis Babeș-Bolyai Ambientum 66, Nr. 1-2 (30.11.2022): 33–43. http://dx.doi.org/10.24193/subbambientum.2021.03.

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"Noble metals are used in a plethora of applications, from electronic and communication equipments, to aerospacial engines, mobile phones and catalytic convertors. Currently, there is a continuous interest in the recovery of noble metals from waste, as their natural reserves are limited. Herein, the paper presents studies on the recovery of platinum from spent automotive catalysts. The process involves two steps - dissolving of platinum, followed by its precipitation into a hexacloroplatinum complex. The optimum reaction conditions for dissolving Pt from the spent automotive catalyst use a mixture of H2O2 + HCl (1:5.5 molar ratio) at 30°C, for 8 h. For the full recovery of platinum from the solution, the volumetric ratio of 4:1 between the platinum solution and the precipitating ammonium chloride solution is optimum. In addition, studies regarding the precipitation time and temperature have also been performed. All the obtained precipitates were analyzed by X-ray powder diffraction and showed the structure of the hexachloroplatinic (NH4)2[PtCl6] complex, with high purity. Upscaling of the processes for technological transfer show promising results in the recovery of platinum from spent automotive catalysts. Keywords. Spent automotive catalyst, Pt recovery, (HCl + H2O2) leaching, precipitation. "

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Kula, Piotr, Emilia Wołowiec, Robert Pietrasik, Konrad Dybowski und Leszek Klimek. „The Precipitation and Dissolution of Alloy Iron Carbides in Vacuum Carburization Processes for Automotive and Aircraft Applications - Part I“. Advanced Materials Research 486 (März 2012): 297–302. http://dx.doi.org/10.4028/www.scientific.net/amr.486.297.

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The article is dedicated to the experiments and tests on the phenomena of precipitation and dissolution of alloy iron carbides in vacuum carburization processes. This researches was done in order to evaluate to the possibility of using artificial neural networks to predict the speed of the processes examined (it is described in the part II). In the section below, we are presenting the precipitation phenomena taking place in vacuum carburization processes and the experiments that were conducted.

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Berger, Gilles, Marie-Pierre Turpault und Alain Meunier. „Dissolution-precipitation processes induced by hot water in a fractured granite. Part 2: Modelling of water-rock interaction“. European Journal of Mineralogy 4, Nr. 6 (15.12.1992): 1477–88. http://dx.doi.org/10.1127/ejm/4/6/1477.

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Johnston, Vanessa, Andrea Martín-Pérez, Sara Skok und Janez Mulec. „Microbially-mediated carbonate dissolution and precipitation; towards a protocol for ex-situ, cave-analogue cultivation experiments“. International Journal of Speleology 50, Nr. 2 (April 2021): 137–55. http://dx.doi.org/10.5038/1827-806x.50.2.2372.

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Subterranean calcite dissolution and precipitation are often considered as strictly geochemical processes. The active involvement of microbes in these processes is commonly underestimated in the literature due to general oligotrophic conditions in caves, except in particular cave conditions, such as sulfidic caves and moonmilk deposits, where the presence of microbes likely plays a key role in mineral deposition. Here, we study the possible involvement of microbes from Postojna Cave, Slovenia, in carbonate dissolution (litholysis) and precipitation (lithogenesis). Microbes were sampled from small pools below hydrologically diverse drip sites and incubated on polished limestone tablets at 10 and 20°C for 2 and 14 weeks under cave-analogue conditions. The tablets were then observed under scanning electron microscope to investigate microbe–rock interactions. Our experiments showed the presence of various microbial morphotypes, often associated with extracellular polymeric substances, firmly attached on the surfaces. Unfortunately, our surface sterilization method using 96% and 70% ethanol could not establish the complete aseptic conditions in deep natural cracks in the experimental limestone tablets. Nonetheless, our results emulate the interaction of environmental microbes with limestone rock. Conspicuous calcite dissolution and precipitation were observed in association with these microbes. Furthermore, we show evidence of entombment of microbes in a Si-rich precipitate during nutrient-depleted growth conditions and we suggest that microbial involvement in silica mobilization under ambient conditions may be a widespread and often overlooked phenomenon. Our findings have important implications for microbial-mediation of cave carbonate dissolution and precipitation, including the preservation of past climate proxy signals in speleothems and prehistoric cave art. Improvements to the methodology and further work are suggested to enable more robust ex-situ cultivation experiments in the future, facilitating better and more detailed research into this topic.

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Koutsoukos, Petros G., Aikaterini N. Kofina und Dimitra G. Kanellopoulou. „Solubility of salts in water: Key issue for crystal growth and dissolution processes“. Pure and Applied Chemistry 79, Nr. 5 (01.01.2007): 825–50. http://dx.doi.org/10.1351/pac200779050825.

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The formation of sparingly soluble salts from aqueous solutions and their dissolution has attracted broad research interest. Of particular importance is the formation and transformation of minerals exhibiting polymorphism or encountered in more than one crystalline phase as, for example, in the case of calcium phosphates, formed in biological mineralization and in industrial-scale deposits. Understanding of these processes depends primarily on the equilibrium between the mineral phases considered and the aqueous medium in contact. Precipitation takes place in supersaturated solutions with rates depending on the solution supersaturation. The experimental investigation may reveal mechanistic details if done at sustained supersaturation. The kinetics of crystal growth depends either on surface diffusion or on bulk diffusion, which in turn is controlled by the medium fluid dynamics. In the case of magnesium ammonium phosphate (struvite), the presence of water-soluble organic compounds is responsible for the retardation both of the time needed for the onset of precipitation and for the kinetics of growth of the supercritical nuclei. Dissolution processes are controlled by the same mechanisms. In the case of calcitic marble, the dissolution in alkaline solutions is controlled by surface diffusion. Compounds active at the marble/water interface may in this case be used as protective agents.

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Grosdidier, T., A. Hazotte und A. Simon. „Precipitation and dissolution processes in γ / γ ′ single crystal nickel-based superalloys“. Materials Science and Engineering: A 256, Nr. 1-2 (November 1998): 183–96. http://dx.doi.org/10.1016/s0921-5093(98)00795-3.

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Edery, Yaniv, Martin Stolar, Giovanni Porta und Alberto Guadagnini. „Feedback mechanisms between precipitation and dissolution reactions across randomly heterogeneous conductivity fields“. Hydrology and Earth System Sciences 25, Nr. 11 (11.11.2021): 5905–15. http://dx.doi.org/10.5194/hess-25-5905-2021.

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Abstract. Our study investigates interplays between dissolution, precipitation, and transport processes taking place across randomly heterogeneous conductivity domains and the ensuing spatial distribution of preferential pathways. We do so by relying on a collection of computational analyses of reactive transport performed in two-dimensional systems where the (natural) logarithm of conductivity is characterized by various degrees of spatial heterogeneity. Our results document that precipitation and dissolution jointly take place in the system, with the latter mainly occurring along preferential flow paths associated with the conductivity field and the former being observed at locations close to and clearly separated from these. High conductivity values associated with the preferential flow paths tend to further increase in time, giving rise to a self-sustained feedback between transport and reaction processes. The clear separation between regions where dissolution or precipitation takes place is imprinted onto the sample distributions of conductivity which tend to become visibly left skewed with time (with the appearance of a bimodal behavior at some times). The link between conductivity changes and reaction-driven processes promotes the emergence of non-Fickian effective transport features. The latter can be captured through a continuous-time random-walk model where solute travel times are approximated with a truncated power law probability distribution. The parameters of such a model shift towards values associated with increasingly high non-Fickian effective transport behavior as time progresses.

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de Ruiter, Lisa, Anette Eleonora Gunnæs, Dag Kristian Dysthe und Håkon Austrheim. „Quartz dissolution associated with magnesium silicate hydrate cement precipitation“. Solid Earth 12, Nr. 2 (18.02.2021): 389–404. http://dx.doi.org/10.5194/se-12-389-2021.

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Abstract. Quartz has been replaced by magnesium silicate hydrate cement at the Feragen ultramafic body in south-east Norway. This occurs in deformed and recrystallized quartz grains deposited as glacial till covering part of the ultramafic body. Where the ultramafic body is exposed, weathering leads to high-pH (∼ 10), Mg-rich fluids. The dissolution rate of the quartz is about 3 orders of magnitude higher than experimentally derived rate equations suggest under the prevailing conditions. Quartz dissolution and cement precipitation start at intergranular grain boundaries that act as fluid pathways through the recrystallized quartz. Etch pits are also extensively present at the quartz surfaces as a result of preferential dissolution at dislocation sites. Transmission electron microscopy revealed an amorphous silica layer with a thickness of 100–200 nm around weathered quartz grains. We suggest that the amorphous silica is a product of interface-coupled dissolution–precipitation and that the amorphous silica subsequently reacts with the Mg-rich, high-pH bulk fluid to precipitate magnesium silicate hydrate cement, allowing for further quartz dissolution and locally a complete replacement of quartz by cement. The cement is the natural equivalent of magnesium silicate hydrate cement (M-S-H), which is currently of interest for nuclear waste encapsulation and for environmentally friendly building cement, but it has not yet been developed for commercial use. This study provides new insights that could potentially contribute to the further development of M-S-H cement.

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Povar, Igor, und Oxana Spinu. „Correlation between global thermodynamic functions and experimental data in multicomponent heterogeneous systems“. Canadian Journal of Chemistry 94, Nr. 2 (Februar 2016): 113–19. http://dx.doi.org/10.1139/cjc-2015-0411.

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The correlation between global thermodynamic functions and such experimental data, which quantitatively characterize the precipitation–dissolution processes of sparingly soluble compounds, as the degree of precipitation and residual concentrations of the solid-phase components in saturated solutions under real conditions, taking into account the complex formation reactions, has been deducted. The paper intends also to introduce widely formal thermodynamic methods for forecasting the conditions of mutual transformation of solid phases through chemical synthesis by precipitation methods, optimization of coprecipitation methods, fractional precipitation from homogeneous solutions, and separation and analysis of chemical compounds. Within the method of residual concentrations, the thermodynamic parameters of the process of precipitating cadmium ions with potassium decanoate from acid and alkaline solutions for different temperatures were investigated. On the basis of the experimentally determined degree of precipitation and its dependence on temperature, the temperature coefficients and overall thermodynamic characteristics of the precipitation process ([Formula: see text], [Formula: see text], and [Formula: see text]) were determined. The optimum conditions of the investigated process of precipitation have been established.

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Kula, Piotr, Emilia Wołowiec, Robert Pietrasik, Konrad Dybowski und Leszek Klimek. „The Precipitation and Dissolution of Alloy Iron Carbides in Vacuum Carburization Processes for Automotive and Aircraft Applications - Part II“. Advanced Materials Research 486 (März 2012): 303–8. http://dx.doi.org/10.4028/www.scientific.net/amr.486.303.

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The article is dedicated to the experiments and tests on the phenomena of precipitation and dissolution of alloy iron carbides in vacuum carburization processes. Special attention has been paid to the possibility of using artificial neural networks to predict the speed of the processes examined. In the section below, we are presenting the precipitation phenomena taking place in vacuum carburization processes and the experiments that were conducted. Moreover, a qualitative and metallographic analysis of carbide phenomena was described together with the method of numerical modelling and predicting the processes with the use of artificial neural networks.

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Rembert, Flore, Damien Jougnot, Linda Luquot und Roger Guérin. „Interpreting Self-Potential Signal during Reactive Transport: Application to Calcite Dissolution and Precipitation“. Water 14, Nr. 10 (19.05.2022): 1632. http://dx.doi.org/10.3390/w14101632.

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Geochemistry and reactive transport play a critical role in many fields. In particular, calcite dissolution and precipitation are chemical processes occurring ubiquitously in the Earth’s subsurface. Therefore, understanding and quantifying them are necessary for various applications (e.g., water resources, reservoirs, geo-engineering). These fundamental geochemical processes can be monitored using the self-potential (SP) method, which is sensitive to pore space changes, water mineralization, and mineral–solution interactions. However, there is a lack of physics-based models linking geochemical processes to the SP response. Thus, in this study, we develop the first geochemical–geophysical fully coupled multi-species numerical workflow to predict the SP electrochemical response. This workflow is based on reactive transport simulation and the computation of a new expression for the electro-diffusive coupling for multiple ionic species. We apply this workflow to calcite dissolution and precipitation experiments, performed for this study and focused on SP monitoring alternating with sample electrical conductivity (EC) measurements. We carried out this experimental part on a column packed with calcite grains, equipped for multichannel SP and EC monitoring and subjected to alternating dissolution or precipitation conditions. From this combined experimental investigation and numerical analysis, the SP method shows clear responses related to ionic concentration gradients, well reproduced with electro-diffusive simulation, and no measurable electrokinetic coupling. This novel coupled approach allows us to determine and predict the location of the reactive zone. The workflow developed for this study opens new perspectives for SP applications to characterize biogeochemical processes in reactive porous media.

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Yang, Leilei, Linjiao Yu, Donghua Chen, Keyu Liu, Peng Yang und Xinwei Li. „Effects of Dolomitization on Porosity during Various Sedimentation-Diagenesis Processes in Carbonate Reservoirs“. Minerals 10, Nr. 6 (25.06.2020): 574. http://dx.doi.org/10.3390/min10060574.

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Carbonate reservoirs, especially dolomite reservoirs, contain large reserves of oil and gas. The complex diagenesis is quite challenging to document the dolomite reservoirs formation and evolution mechanism. Porosity development and evolution in dolomite reservoirs primarily reflect the comprehensive effect of mineral dissolution/precipitation during dolomitization. In this study, multicomponent multiphase flow and solute transport simulation was employed to investigate dolomitization in the deep carbonate strata of the Tarim Basin, Northwest China, where active exploration is currently under way. One- and two-dimensional numerical models with various temperatures, fluid compositions and hydrodynamic characteristics were established to quantificationally study dolomitization and its effect on porosity. After determining the main control factors, detailed petrologic characteristics in the studied area were also analyzed to establish four corresponding diagenetic numerical models under different sedimentary environments. These models enabled a systematic analysis of mineral dissolution/precipitation and a quantitative recovery of porosity evolution during various sedimentation-diagenesis processes. The results allowed for a quantitative evaluation and prediction of reservoir porosity, which would provide a basis for further oil and gas exploration in deep carbonate reservoirs.

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Yang, Y. F., H. Y. Wang, J. G. Wang, R. Y. Zhao und Q. C. Jiang. „Ignition and reaction mechanisms of thermal explosion reaction in the Ni-Ti-C system under air and Ar“. Journal of Materials Research 24, Nr. 10 (Oktober 2009): 3197–205. http://dx.doi.org/10.1557/jmr.2009.0370.

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The ignition and reaction mechanisms of the thermal explosion reaction in the Ni-Ti-C system under air and Ar conditions were investigated. The reaction for the formation of TiC can be initiated at a low temperature under air. The ignition temperature under air is much lower than that under Ar. Under Ar, both the ignition and reaction mechanisms consist of dissolution, reaction, and precipitation. Under air, the ignition mechanism is confirmed to be the chemical oven mechanism, and the reaction mechanism is dissolution, reaction, and precipitation. The mechanism of gas transport plays a much more minor role in the ignition and reaction processes under air.

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Ebert, William L. „Glass Degradation in Performance Assessment Models1“. MRS Proceedings 1744 (2015): 163–72. http://dx.doi.org/10.1557/opl.2015.333.

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ABSTRACTThe interface with reactive transport models used in performance assessment calculations is described to identify aspects of the glass waste form degradation model important to long-term predictions. These are primarily the conditions that trigger the change from the residual rate to the Stage 3 rate and the values of those rates. Although the processes triggering the change and controlling the Stage 3 rate are not yet understood mechanistically, neither appears related to an intrinsic property of the glass. The sudden and usually significant increase in the glass dissolution rate suggests the processes that trigger the increase are different than the processes controlling glass dissolution prior to that change. Application of a simple expression that was derived for mineral transformation to represent the kinetics of coupled glass dissolution and secondary phase precipitation reactions is shown to be consistent with experimental observations of Stage 3 and useful for modeling long-term glass dissolution in a complex disposal environment.

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Lafay, Romain, German Montes-Hernandez, François Renard und Pierre Vonlanthen. „Intracrystalline Reaction-Induced Cracking in Olivine Evidenced by Hydration and Carbonation Experiments“. Minerals 8, Nr. 9 (18.09.2018): 412. http://dx.doi.org/10.3390/min8090412.

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In order to better understand the microtextural changes associated with serpentinization reactions, natural millimeter-sized olivine grains were experimentally reacted with alkaline NaOH and NaHCO3 solutions at a temperature of 200 °C and for durations of 3 to 12 months. During hydration experiments, dissolution and precipitation were intimately correlated in time and space, with reaction products growing in situ, either as layered veins or as nearly continuous surface cover. In contrast, carbonation experiments showed a strong decoupling between both processes leading to essentially delocalized precipitation of the reaction products away from dissolution sites. Textural analyses of the samples using scanning electron microscopy, Raman spectroscopy, and X-ray synchrotron microtomography provided experimental evidence for a cause-and-effect relationship between in situ precipitation and intracrystalline reaction-induced cracking in olivine. Juvenile cracks typically nucleated at the tip of dissolution notches or on diamond-shaped pores filled with reaction products, and propagated through the olivine crystal lattice during the course of the reaction. The occurrence of new cracks at the tip of diamond-shaped pores, but also of tiny subspherical pores lining up along microcracks, indicated that fracturation and porosity networks were mutually driven, making serpentinization an extremely efficient alteration process over time. Alternatively, our data suggested that some form of porosity also developed in absence of fracturation, thus further highlighting the remarkable efficiency and versatility of serpentinization processes.

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Maharaj, Bikash Chandra, Maria Rosaria Mattei, Luigi Frunzo, Eric D. van Hullebusch und Giovanni Esposito. „ADM1 based mathematical model of trace element precipitation/dissolution in anaerobic digestion processes“. Bioresource Technology 267 (November 2018): 666–76. http://dx.doi.org/10.1016/j.biortech.2018.06.099.

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An, Tianxia, Bingsong Yu, Yongshi Wang, Zhuang Ruan, Wei Meng und Yuelin Feng. „Water-rock interactions and origin of formation water in the Bohai Bay Basin: A case study of the Cenozoic Formation in Bonan Sag“. Interpretation 9, Nr. 2 (07.04.2021): T475—T493. http://dx.doi.org/10.1190/int-2020-0181.1.

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The faulted lacustrine Bohai Basin in eastern China contains abundant hydrocarbon resources. In these reservoirs, understanding the sandstone diagenesis and the resulting formation water provides a means to unravel the evolution processes in the basin. In most cases, the lack of isotopic and trace element analysis tests in this type of basin limits the research on the origin and evolution of formation water in this area. We have used multivariate statistical methods to classify the geochemical characteristics of the formation water for the Cenozoic Formation of Bonan Sag in the Bohai Bay Basin. Analysis of correlations among the evolution processes of different ions in different types of formation water provides an understanding of the primary factors influencing the ion content. We also evaluate the water-rock interactions of different types of formation water to evaluate their geologic significance, and we find three types. Type I formation water includes a mixture of river water, lake water, and atmospheric precipitation and exhibits weak water-rock interactions. Type II formation water contains primitive freshwater and brackish lake water that has undergone an evolution process similar to that of type I formation water, but that was followed by evaporation and concentration, the dissolution and precipitation of calcite and iron calcite, and feldspar dissolution. Type III formation water, which is a product of rock reconstruction, originates from saline lake sediment water. After undergoing evolution processes similar to those of types I and II, type III formation water is also affected by dissolution of evaporite, albite, dolomite, and iron dolomite. Thus, type III formation water is the product of water-rock interactions such as precipitation, SO42− reduction, and pyrite precipitation in which the water-rock reaction controls the development mechanism and characteristics of the reservoir space.

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Butts, Susan H. „Silicification“. Paleontological Society Papers 20 (Oktober 2014): 15–34. http://dx.doi.org/10.1017/s1089332600002783.

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Silicification is the replacement of original skeletal material accomplished through the concurrent dissolution of calcium carbonate and precipitation of silica. The processes is aided by the nucleation of silica to organic matter which surrounds the mineral crystallites within the shell. Factors that control silicification are those that influence the dissolution/precipitation process: shell mineralogy, shell ultrastructure (and, therefore, surface area), the amount and location of organic matter, and the character of the enclosing matrix. Silicification, like all types of fossilization, can produce taphonomic biases: it is far more common in Paleozoic than younger deposits, is more likely to occur in organisms with low-magnesium calcite shells, in carbonate sediments, and in environments with elevated dissolved silica.

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Rowolt, Christian, Benjamin Milkereit, Jette Broer, Armin Springer und Olaf Kessler. „Continuous Heating Dissolution and Continuous Cooling Precipitation Diagrams of a Nickel-Titanium Shape Memory Alloy“. Shape Memory and Superelasticity 7, Nr. 4 (23.11.2021): 541–49. http://dx.doi.org/10.1007/s40830-021-00356-9.

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AbstractBinary NiTi alloys are the most common shape memory alloys in medical applications, combining good mechanical properties and high biocompatibility. In NiTi alloys, the shape memory effect is caused by the transformation of an austenite phase to a martensite phase and the reverse process. Transformation temperatures are strongly influenced by the exact chemical composition of the NiTi phase and the presence of precipitates in the microstructure induced by thermo-mechanical treatment, especially solution annealing and ageing. Isothermal time–temperature precipitation diagrams can be found in the literature. Cooling is frequently not considered, as water quenching is typically assumed to be sufficient. To the best of our knowledge, continuous heating dissolution (CHD) and continuous cooling precipitation (CCP) diagrams do not exist. Differential scanning calorimetry (DSC) is a common method to analyse the austenite/martensite transformation in shape memory alloys, but it has not yet been used to analyse precipitation processes during continuous temperature changes. We have enabled DSC to analyse dissolution and precipitation processes in situ during heating as well as during cooling from the solution annealing temperature. Results are presented as CHD and CCP diagrams, including information from microstructure analysis and the associated changes in the austenite/martensite transformation temperatures.

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NG, Felix, und Bernard Hallet. „Patterning mechanisms in subglacial carbonate dissolution and deposition“. Journal of Glaciology 48, Nr. 162 (2002): 386–400. http://dx.doi.org/10.3189/172756502781831214.

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AbstractDeglaciated bedrock surfaces in limestone areas often exhibit extensive patterning by solutional furrows and carbonate deposits that occur in close association with undulations in the bed topography. These features clearly result from subglacial dissolution and precipitation of calcite on the bed — induced, for instance, by melting and freezing in a regelation water film — but little is known about the observed morphology. In particular, it is intriguing that (i) the solutional furrows, whose formation requires explanation, are collectively organized into arcuate patterns, with characteristic spacing, and (ii) a fluted or “spiculed” surface texture is ubiquitous on the calcite deposits. Herein, we propose specific mechanisms for such patterning based on a theory where chemical processes in the water film are coupled to regelation physics. Solutional furrows reflect locally enhanced dissolution along stoss surfaces, where CO2-rich bubbles advected in the ice from up-glacier come into contact with the bed. The bubbles form as CO2 is exsolved from freezing film water at the lee of bed bumps. The flutings on the deposit are inherently the manifestation of a spatial instability at the interface where calcite precipitation occurs. Complex interactions underlie some of the striking glacier-bed features shaped by subglacial chemical processes.

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Unwin, P. R., J. V. Macpherson, M. A. Beeston, N. J. Evans, D. Littlewood und N. P. Hughes. „New Electrochemical Techniques for Probing Phase Transfer Dynamics at Dental Interfaces in Vitro“. Advances in Dental Research 11, Nr. 4 (November 1997): 548–59. http://dx.doi.org/10.1177/08959374970110042401.

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Phase transfer reactions such as dissolution, precipitation, sorption, and desorption are important in a wide range of processes on dental hard tissue surfaces. An overview is provided of several new complementary electrochemical techniques which are capable of probing the dynamics of such processes at solid/liquid interfaces from millimeter- to nanometer-length scales, with a variable time resolution down to the sub-millisecond level. Techniques considered include channel flow methods with electrochemical detection, which allow reactions at solid/liquid interfaces to be studied under well-defined and calculable mass transport regimes. Scanning electrochemical microscopy allows the chemical activity of interfaces to be mapped at higher spatial and temporal resolutions. This technique, which utilizes a scanning ultramicroelectrode, has been used extensively for the study of dissolution processes of ionic crystals, as well as in imaging the action of fluid-flow-blocking agents on dentin surfaces, which act via precipitation. So that interfaces at the nanometer level can be probed, an integrated electrochemical-atomic force microscope has been developed which enables the local solution conditions to be controlled electrochemically while topographical changes are mapped simultaneously.

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Hövelmann, Jörn, Christine Putnis und Liane Benning. „Metal Sequestration through Coupled Dissolution–Precipitation at the Brucite–Water Interface“. Minerals 8, Nr. 8 (10.08.2018): 346. http://dx.doi.org/10.3390/min8080346.

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The increasing release of potentially toxic metals from industrial processes can lead to highly elevated concentrations of these metals in soil, and ground- and surface-waters. Today, metal pollution is one of the most serious environmental problems and thus, the development of effective remediation strategies is of paramount importance. In this context, it is critical to understand how dissolved metals interact with mineral surfaces in soil–water environments. Here, we assessed the processes that govern the interactions between six common metals (Zn, Cd, Co, Ni, Cu, and Pb) with natural brucite (Mg(OH)2) surfaces. Using atomic force microscopy and a flow-through cell, we followed the coupled process of brucite dissolution and subsequent nucleation and growth of various metal bearing precipitates at a nanometer scale. Scanning electron microscopy and Raman spectroscopy allowed for the identification of the precipitates as metal hydroxide phases. Our observations and thermodynamic calculations indicate that this coupled dissolution–precipitation process is governed by a fluid boundary layer at the brucite–water interface. Importantly, this layer differs in composition and pH from the bulk solution. These results contribute to an improved mechanistic understanding of sorption reactions at mineral surfaces that control the mobility and fate of toxic metals in the environment.

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Klunk, Marcos Antonio, Leonardo Hax Damiani, Gustavo Feller, Rommulo Vieira Conceição, Mara Abel und Luiz Fernando De Ros. „Geochemical modeling of diagenetic reactions in Snorre Field reservoir sandstones: a comparative study of computer codes“. Brazilian Journal of Geology 45, suppl 1 (August 2015): 29–40. http://dx.doi.org/10.1590/2317-4889201530145.

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ABSTRACTDiagenetic reactions, characterized by the dissolution and precipitation of minerals at low temperatures, control the quality of sedimentary rocks as hydrocarbon reservoirs. Geochemical modeling, a tool used to understand diagenetic processes, is performed through computer codes based on thermodynamic and kinetic parameters. In a comparative study, we reproduced the diagenetic reactions observed in Snorre Field reservoir sandstones, Norwegian North Sea. These reactions had been previously modeled in the literature using DISSOL-THERMAL code. In this study, we modeled the diagenetic reactions in the reservoirs using Geochemist's Workbench (GWB) and TOUGHREACT software, based on a convective-diffusive-reactive model and on the thermodynamic and kinetic parameters compiled for each reaction. TOUGHREACT and DISSOL-THERMAL modeling showed dissolution of quartz, K-feldspar and plagioclase in a similar temperature range from 25 to 80°C. In contrast, GWB modeling showed dissolution of albite, plagioclase and illite, as well as precipitation of quartz, K-feldspar and kaolinite in the same temperature range. The modeling generated by the different software for temperatures of 100, 120 and 140°C showed similarly the dissolution of quartz, K-feldspar, plagioclase and kaolinite, but differed in the precipitation of albite and illite. At temperatures of 150 and 160°C, GWB and TOUGHREACT produced different results from the DISSOL-THERMAL, except for the dissolution of quartz, plagioclase and kaolinite. The comparative study allows choosing the numerical modeling software whose results are closer to the diagenetic reactions observed in the petrographic analysis of the modeled reservoirs.

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Ogawa, T., und K. Minato. „Dissolution and formation of nuclear materials in molten media“. Pure and Applied Chemistry 73, Nr. 5 (01.05.2001): 799–806. http://dx.doi.org/10.1351/pac200173050799.

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As innovative means to recover actinides from irradiated fuels, pyrochemical processes are proposed. In the Japan Atomic Energy Research Institute (JAERI), the feasibility of applying molten-salts processes to nitride fuels containing transuranium elements for transmutation is investigated. In the course of study, experiments and analyses have been made on the high-temperature chemistry of MNCl systems, the effects of oxygen impurities, and the implications of the divalent state along with the normal trivalent state of lanthanides and actinides. Thermodynamic calculation and the electrochemical measurements are compared in a few aspects of dissolution and precipitation of nuclear materials in molten halides.

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Ekіncі Şans, B., F. Esenlі, S. Kadir und W. C. Elliott. „Genesis of smectite in siliciclastics and pyroclastics of the Eocene İslambeyli Formation in the Lalapaşa region, NW Thrace, Turkey“. Clay Minerals 50, Nr. 4 (September 2015): 459–83. http://dx.doi.org/10.1180/claymin.2015.050.4.04.

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AbstractThe Eocene İslambeyli Formation in the Lalapaşa region (NW Thrace, Turkey) consists predominantly of siliciclastic clayey clastics at the bottom and of claystone, tuff and tuffaceous claystone/ sandstone/limestone in the middle and uppermost parts of this formation. Some tuff-tuffaceous beds of the middle–upper parts of the formation are economically viable bentonite depoits. The İslambeyli Formation exhibits vertical variations in the mineralogy, elemental compositions, and smectite-forming processes. Smectite was formed by weathering and diagenetic processes in the fluvial-shore environments in the lower part and by diagenetic alteration in a shallow-marine environment in the middle–upper parts of the formation. Ca-smectite flakes were formed by two processes: direct precipitation; and by means of a dissolution-precipitation mechanism from feldspar and mica. Dissolution-precipitation was most prevalent in the siliciclastic lower part of the formation. The amounts of Al, Fe, Mg and Ca required to form smectite and accessory illite were supplied mainly from the alteration of feldspars, mica and glass shards. The origin of smectite can also be explained by the inferred solution compositions given the parent phases in this formation, and the devitrification of glass shards in pyroclastic-rich middle–upper parts of the formation. In the upper beds, the observed decrease of K and Fe in the smectite structure coincided with both the increase in the amount of smectite and the increase in solution pH suggesting that precipitation of smectite developed over a prolonged period and under arid conditions.

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Hamdi, Ines, Zakaria Boumerzoug und Foued Chabane. „STUDY OF PRECIPITATION KINETICS OF AN AL-MG-SI ALLOY USING DIFFERENTIAL SCANNING CALORIMETRY“. Acta Metallurgica Slovaca 23, Nr. 2 (30.06.2017): 155. http://dx.doi.org/10.12776/ams.v23i2.908.

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<p class="AMSmaintext">This work has been carried out by differential scanning calorimetric (DSC) to study the precipitation kinetics in quenched and natural aging Al-Mg-Si alloy. DSC curves showed exothermic and endothermic peaks corresponding to the precipitation and the dissolution processes. The activation energy of the precipitation process has been calculated using Kissinger model. The results obtained showed a change in the activation energy values, the activation energy for the β″ and β determined for natural aging alloy were higher than that in the quenched alloy. </p>

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Moras, Charly A., Lennart T. Bach, Tyler Cyronak, Renaud Joannes-Boyau und Kai G. Schulz. „Ocean alkalinity enhancement – avoiding runaway CaCO₃ precipitation during quick and hydrated lime dissolution“. Biogeosciences 19, Nr. 15 (01.08.2022): 3537–57. http://dx.doi.org/10.5194/bg-19-3537-2022.

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Abstract. Ocean alkalinity enhancement (OAE) is a method that can remove carbon dioxide (CO2) from the atmosphere and counteract ocean acidification through the dissolution of alkaline minerals. Currently, critical knowledge gaps exist regarding the dissolution of different minerals suitable for OAE in natural seawater. Of particular importance is to understand how much alkaline mineral can be dissolved before secondary precipitation of calcium carbonate (CaCO3) occurs, since secondary CaCO3 precipitation reduces the atmospheric CO2 uptake potential of OAE. Using two types of mineral proposed for OAE, quick lime (CaO) and hydrated lime (Ca(OH)2), we show that both (<63 µm of diameter) dissolved in seawater within a few hours. No CaCO3 precipitation occurred at a saturation state (ΩA) of ∼5, but CaCO3 precipitation in the form of aragonite occurred above an ΩA value of 7. This limit is lower than expected for typical pseudo-homogeneous precipitation, i.e. in the presence of colloids and organic matter. Secondary precipitation at low ΩA (∼ 7) was the result of heterogeneous precipitation onto mineral surfaces, most likely onto the added CaO and Ca(OH)2 particles. Most importantly, runaway CaCO3 precipitation was observed, a condition where significantly more total alkalinity (TA) was removed than initially added. Such runaway precipitation could reduce the OAE CO2 uptake efficiency from ∼ 0.8 mol of CO2 per mole of added TA down to 0.1 mol of CO2 per mole of TA. Runaway precipitation appears to be avoidable by dilution below the critical ΩA threshold of 5, ideally within hours of the mineral additions to minimise initial CaCO3 precipitation. Finally, OAE simulations suggest that for the same ΩA threshold, the amount of TA that can be added to seawater would be more than 3 times higher at 5 ∘C than at 30 ∘C. The maximum TA addition could also be increased by equilibrating the seawater to atmospheric CO2 levels (i.e. to a pCO2 of ∼ 416 µatm) during addition. This would allow for more TA to be added in seawater without inducing CaCO3 precipitation, using OAE at its CO2 removal potential.

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Shiraishi, Fumito, Yusaku Hanzawa, Jiro Asada, Leonardo Fadel Cury und Anelize Manuela Bahniuk. „Decompositional processes of microbial carbonates in Lagoa Vermelha, Brazil“. Journal of Sedimentary Research 93, Nr. 3 (30.03.2023): 202–11. http://dx.doi.org/10.2110/jsr.2022.053.

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ABSTRACT In Lagoa Vermelha, Brazil, a lagoonal stromatolite and a saltpan microbial mat are investigated to understand the influence of environmental changes on the decomposition of microbial carbonates. The lagoonal stromatolite, composed mainly of magnesian calcite and aragonite, is developed on a dolomite-containing carbonate crust. While most stromatolites are eroded to the water surface level, some smaller, green stromatolites below the water surface retain a domal shape. The domal stromatolite surface is dominated by endolithic cyanobacteria with conspicuous microborings. In addition, microbial aerobic respiration causes carbonate dissolution in darkness, and metazoans grazing the inner surface of the stromatolite excrete fecal pellets. This suggests that the formational stage of lagoonal stromatolites has ceased and they are now decomposing, most likely because of environmental changes in recent years. The microbial mat, which is about 3 cm thick, developed in a saltpan pond precipitating carbonate and gypsum, and it contains quartz, magnesian calcite, aragonite, and gypsum. At the time of the investigation, the population of oxygenic phototrophs is low at the mat surface, and carbonate dissolution, rather than precipitation, is occurring by microbial metabolism deeper in the mat. This suggests that the formation of carbonate in the mat has ceased and is decomposing, probably due to the progressive salinity increase in the salt pan. This examination of two carbonate deposits in Lagoa Vermelha suggests that microbial metabolism is an important process for decomposing microbial carbonates in addition to grazing and microboring, and that environmental changes may alter microbial compositions from carbonate-constructive to carbonate-destructive communities.

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Hansen, R. N. „Process network modelling of the geochemical reactions responsible for acid mine drainage emanating from the Witwatersrand tailings facilities“. South African Journal of Geology 123, Nr. 3 (01.09.2020): 357–68. http://dx.doi.org/10.25131/sajg.123.0024.

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ABSTRACT Acid mine drainage (AMD) and associated metal(loid) and SO42- pollution of soil, surface water and groundwater is ubiquitously associated with tailings material generated by Au mining in the Witwatersrand Basin in South Africa. The individual geochemical processes responsible for the AMD generation in this tailings material are relatively well understood. What is less clear are how these different processes interact as a network within the tailings system. Process network modelling (PNM) is a tool that can be used to study such interactive and complex networks of geochemical processes, especially when stochastic methods, e.g. Monte Carlo simulation, are included in the model development. Secondary mineral phase supersaturation requirements from classical nucleation theory are also built into the model. A PNM was developed for a tailings facility in the Witwatersrand gold basin focussing on pH, Fe(total) and SO42- concentrations in the tailings pore water and the relationship of these parameters to the dissolution of pyrite, O2 diffusion into the tailings, oxidation of Fe2+ and the precipitation of secondary minerals, specifically goethite and jarosite. The model indicated that AMD conditions develop fairly rapidly after the sulphidic material is exposed to the Earth’s oxygenated atmosphere. The concentration of H+, and hence the pH, in the tailings pore water is controlled by a number of feedbacks. The positive feedback, implying addition of H+, is the dissolution of pyrite and the precipitation of the secondary Fe3+-bearing minerals goethite and jarosite. Jarosite precipitation was shown to increase the median H+ addition rate by ~2%. The negative feedback, i.e. decrease in H+, is the oxidation of Fe2+ to Fe3+. This feedback loop produces a net excess of H+. Together with the buffer effect of goethite and jarosite precipitation, system steady-state conditions are eventually achieved with respect to pH. The pore water SO42- concentration is controlled by the positive and negative feedback of pyrite dissolution and jarosite precipitation. This feedback loop produces a large excess of SO42- and steady state conditions can only be achieved if SO42- is physically removed from the tailings system, e.g. seepage to groundwater. Oxidation of the Fe2+ produced by pyrite dissolution to Fe3+ is the only positive feedback for tailings pore water Fe3+ concentrations. The negative feedbacks are precipitation of goethite and jarosite and the oxidation of pyrite by Fe3+. The former effect is delayed as these phases first have to achieve a certain level of supersaturation in the tailings pore water solution before they can form. The precipitation of jarosite and goethite, by removing Fe3+ from solution, decreases the effect of Fe3+ pyrite oxidation causing O2 to remain the dominant oxidation mechanism. This feedback loop produces a small excess of Fe3+ over time, however, the model is very sensitive to other factors, e.g. O2 diffusion deeper into the tailings facility.

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Wang, Huiqi, Mingxia Guo, Yue Niu, Jiayu Dai, Qiuxiang Yin und Ling Zhou. „Study on Precipitation Processes and Phase Transformation Kinetics of Iron Phosphate Dihydrate“. Crystals 12, Nr. 10 (27.09.2022): 1369. http://dx.doi.org/10.3390/cryst12101369.

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The process of the phase transformation from amorphous to crystalline FePO4·2H2O was studied in this research. It was found that Fe and P are predominantly present as FeHPO4+ and FeH2PO42+ and an induction period exists during the transition from amorphous to monoclinic form. The induction period and the time required for phase transformation were shortened with the increased temperature. Phase transformation could be kinetically described by the Johnson–Mehl–Avrami (JMA) dynamics model. The dissolution rate of amorphous FePO4·2H2O is the rate-limiting step of this process. the activation energy of phase transformation is calculated to be 9.619 kJ/mol. The results in this study provided more guidelines for the regulation of FePO4·2H2O precursors by precipitation method.

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Crompton, Jeff W., Gwenn E. Flowers, Dirk Kirste, Birgit Hagedorn und Martin J. Sharp. „Clay mineral precipitation and low silica in glacier meltwaters explored through reaction-path modelling“. Journal of Glaciology 61, Nr. 230 (2015): 1061–78. http://dx.doi.org/10.3189/2015jog15j051.

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AbstractThe subglacial chemical weathering environment is largely controlled by low temperatures and the presence of freshly comminuted minerals with a high surface area. These characteristics are believed to promote dissolution processes that give rise to low silica and high Ca2+fluxes emanating from glacierized basins. We test an alternative hypothesis, that mineral precipitation reactions in the subglacial environment play an equally important role in controlling the water chemistry in glacierized basins. We analyze borehole and proglacial water chemistry from a subarctic polythermal glacier, complemented by mineral XRD analysis of suspended sediment, till and bedrock samples. In conjunction with a thermodynamic analysis of the water and mineral chemistry, we use reaction-path modelling to study the chemical enrichment of water through the glacier system. We find that the high pH of the subglacial environment is conducive to secondary mineral precipitation, and that it is not possible to balance the water chemistry using dissolution reactions alone. We show that low silica can be explained by standard weathering reactions without having to invoke mineral-leaching reactions. Our results suggest that subglacial weathering intensity may be significantly underestimated if the production of secondary minerals is not considered.

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Carter, B. R., J. R. Toggweiler, R. M. Key und J. L. Sarmiento. „Processes determining the marine alkalinity and carbonate saturation distributions“. Biogeosciences Discussions 11, Nr. 7 (21.07.2014): 11139–78. http://dx.doi.org/10.5194/bgd-11-11139-2014.

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Abstract. We introduce a composite tracer, Alk*, that has a global distribution primarily determined by CaCO3 precipitation and dissolution. Alk* also highlights riverine alkalinity plumes that are due to dissolved calcium carbonate from land. We estimate the Arctic receives approximately twice the riverine alkalinity per unit area as the Atlantic, and 8 times that of the other oceans. Riverine inputs broadly elevate Alk* in the Arctic surface and particularly near river mouths. Strong net carbonate precipitation lowers basin mean Indian and Atlantic Alk*, while upwelling of dissolved CaCO3 rich deep waters elevates Northern Pacific and Southern Ocean Alk*. We use the Alk* distribution to estimate the carbonate saturation variability resulting from CaCO3 cycling and other processes. We show regional variations in surface carbonate saturation are due to temperature changes driving CO2 fluxes and, to a lesser extent, freshwater cycling. Calcium carbonate cycling plays a tertiary role. Monitoring the Alk* distribution would allow us to isolate the impact of acidification on biological calcification and remineralization.

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Erdem, Mehmet, und Fikret Tümen. „A Study on Dissolution Properties of the Sludges from Cr(VI) Reduction–Precipitation Processes“. Journal of Environmental Science and Health, Part A 39, Nr. 1 (Januar 2004): 253–67. http://dx.doi.org/10.1081/ese-120027382.

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Missana, T., U. Alonso, A. C. Scheinost, N. Granizo und M. García-Gutiérrez. „Selenite retention by nanocrystalline magnetite: Role of adsorption, reduction and dissolution/co-precipitation processes“. Geochimica et Cosmochimica Acta 73, Nr. 20 (Oktober 2009): 6205–17. http://dx.doi.org/10.1016/j.gca.2009.07.005.

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Hiorth, A., E. Jettestuen, L. M. Cathles und M. V. Madland. „Precipitation, dissolution, and ion exchange processes coupled with a lattice Boltzmann advection diffusion solver“. Geochimica et Cosmochimica Acta 104 (März 2013): 99–110. http://dx.doi.org/10.1016/j.gca.2012.11.019.

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Sun, Zhongheng, Hongtao Zhu, Changgui Xu, Xianghua Yang, Xiaofeng Du, Qingbin Wang und Jinyang Qiao. „Pore Fluid Evolution Influenced by Volcanic Activities and Related Diagenetic Processes in a Rift Basin: Evidence from the Paleogene Medium-Deep Reservoirs of Huanghekou Sag, Bohai Bay Basin, China“. Geofluids 2017 (2017): 1–16. http://dx.doi.org/10.1155/2017/9732575.

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Volcanic activities exert a significant influence on pore fluid property and related diagenetic processes that substantially controlled reservoirs quality. Analysis of Paleogene medium-deep sandstones on the Huanghekou Sag provides insight into relating the diagenetic processes to pore fluid property evolution influenced by volcanic activities. Three distinct types of pore fluids were identified on the basis of an integrated and systematic analysis including core and thin section observation, XRD, SEM, CL, and trace element. Alkaline aqueous medium environment occurred in E2s1+2 where volcanic activities have insignificant influence on pore fluids, evidenced by typical alkaline diagenetic events such as K-feldspar albitization, quartz dissolution, feldspar dissolution, and carbonate cementation. During the deposition of E3d3, influx of terrestrial freshwater and alteration of ferromagnesian-rich pore water result in the formation of mixing aqueous medium environment through volcanic eruption dormancy causing zeolite dissolution, clay mineral transformation, and K-feldspar albitization. Ferromagnesian-rich aqueous medium environment developed resulting from the intensive hydrolysis of the unstable ferromagnesian minerals formed due to intense volcanic activities during E3d1+2 and corresponding predominant diagenetic processes were characterized by the precipitation and dissolution of low-silica zeolites. Therefore, the differential properties of pore fluids caused various diagenetic processes controlling reservoir quality.

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Chaparro, M. Carme, Nicolas Finck, Volker Metz und Horst Geckeis. „Reactive Transport Modelling of the Long-Term Interaction between Carbon Steel and MX-80 Bentonite at 25 °C“. Minerals 11, Nr. 11 (16.11.2021): 1272. http://dx.doi.org/10.3390/min11111272.

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The geological disposal in deep bedrock repositories is the preferred option for the management of high-level radioactive waste (HLW). In some of these concepts, carbon steel is considered as a potential canister material and bentonites are planned as backfill material to protect metallic waste containers. Therefore, a 1D radial reactive transport model has been developed in order to better understand the processes occurring during the long-term iron-bentonite interaction. The numerical model accounts for diffusion, aqueous complexation reactions, mineral dissolution/precipitation and cation exchange at a constant temperature of 25 °C under anoxic conditions. Our results suggest that Fe is sorbed at the montmorillonite surface via cation exchange in the short-term, and it is consumed by formation of the secondary phases in the long-term. The numerical model predicts precipitation of nontronite, magnetite and greenalite as corrosion products. Calcite precipitates due to cation exchange in the short-term and due to montmorillonite dissolution in the long-term. Results further reveal a significant increase in pH in the long-term, while dissolution/precipitation reactions result in limited variations of the porosity. A sensitivity analysis has also been performed to test the effect of selected parameters, such as corrosion rate, diffusion coefficient and composition of the bentonite porewater, on the corrosion processes. Overall, outcomes suggest that the predicted main corrosion products in the long-term are Fe-silicate minerals, such phases thus should deserve further attention as a chemical barrier in the diffusion of radionuclides to the repository far field.

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