The weathering of apatite is the foundation of the phosphorus cycle and essential to life, yet little is known about the nanoscale mechanisms driving apatite weathering. Deciphering nanoscale dissolution in apatite is a significant step to understand phosphate weathering behavior, that was key to the development of life. Determining what controls apatite weathering can impact many areas of environmental and medical mineralogy such as dentistry, contaminant scavenging, geochronology, and paleoenvironment studies. The aim of this study was to characterize apatite dissolution across scales with an emphasis on the nanoscale mechanisms. Recent research on the weathering of silicate minerals at the nanoscale has provided telling evidence of a relatively new chemical weathering model referred to as coupled interfacial dissolution-precipitation (CIDR) mechanism. We hypothesize that this mechanism could be broadened to phosphate minerals. To investigate crystals of Durango fluorapatite (FAP) and hydroxyl-chlorapatite (HAP) were hydrolyzed in flow-through devices with pH 3 HNO3 solutions. Apatites used in the study were chemically and structurally characterized via Single Crystal-XRD, with particular emphasis on the anion composition and atomic arrangement. Determination of the mechanisms of dissolution was carried at multiple scales using ICP-OES chemical analysis (macroscale), SEM (microscale) and STEM-HAADF-EDS/EELS on FIB liftouts (nanoscale). At the macroscale, The anionic composition of the apatite controlled its weathering rate. As expected, HAP dissolution occurred at faster rates compared to FAP. SEM characterization of the crystal surfaces pre- and post-dissolution revealed the development of etch pits during dissolution, however, more pronounced for FAP than HAP. Observation of the mineral/solution interface at the nanoscale using STEM-HAADF revealed the development of a nanometric amorphous layer likely depleted in Ca compared to P. The observation of a sharp crystalline/amorphous transition and 5 to 15 nanometers thick amorphous surface altered layer, associated with a depletion in Ca suggests that similar to silicate, apatite is subject to a coupled interfacial dissolution-reprecipitation mechanism. This potential discovery could transform our understanding of phosphate behavior in medical and environmental mineralogy fields.

Mineral dissolution is an inherent chemo-hydro-mechanical coupled diagenetic process in sediments. This ubiquitous geological phenomenon affects all properties in sediments, however, its engineering impact remains largely unknown. This research centers on the effects of mineral dissolution on sediment behavior with emphasis on dissolution modes in nature and their engineering implications. Five different dissolution modes are identified: homogeneous, pressure-dependent, and localized dissolution, and the dissolution of shallow and deep dissolvable inclusions. The consequences of each dissolution mode are investigated through experiments and discrete element methods. While each dissolution mode triggers unique consequences, it is observed that in all cases 1) significant displacement takes places during dissolution, 2) there is a pronounced effect of internal friction and the extent of dissolution on the evolution of the sediment, 3) the sediment has higher compressibility and exhibits a more contractive tendency after dissolution, 4) a porous honeycomb-shaped internal fabric develops accompanied by contact force concentration along dissolved inclusions, and 5) horizontal stress reduction takes place during dissolution and shear localization may develop under zero lateral strain conditions. Mineral dissolution has important engineering implications, from soil characterization to slope stability and shallow foundations. Pre- and post-dissolution CPT studies show that dissolution decreases the tip resistance proportional to the extent of dissolution. Dissolution in sloping ground induces global settlement as the prevailing deformation pattern, and prominent lateral movements near the slope surface; sudden undrained shear failure may take place during otherwise quasi-static dissolution. While footings experience larger settlements during post-dissolution loading, subsequent dissolution beneath a previously loaded footing causes displacements that are greater than the sum of dissolution-induced and load-induced settlements.

A remineralização é uma prática antiga que está associada a aplicação de pós de rocha no solo visando a melhoria das propriedades edáficas e por fim o aumento da produtividade, associado também a redução dos custos de produção, uma vez que os remineralizadores possuem menor preço comparado com fertilizantes sintéticos solúveis. Porém ainda existem divergências nos resultados obtidos com o uso de remineralizadores, por vezes associados a dificuldade na descrição e controle dos fatores que podem interferir no processo, como clima, características do solo e do remineralizador empregado. Esta tese tem por objetivo investigar a dissolução de um remineralizador em experimentos em diferentes níveis de complexidade e avaliar as alterações mineralógicas correspondentes, inclusive com ênfase na possibilidade de neoformação de minerais. No experimento in vitro foi possível identificar os efeitos do tamanho das partículas e dos diferentes solventes na dissolução dos minerais do remineralizador. Aumentando o nível de complexidade, no experimento em colunas contendo solo, foi possível identificar principalmente um incremento nos teores de Ca+2, Mg+2, K+ trocáveis no solo, além do Na+, Fe e Si no tratamento com a aplicação do remineralizador. Também houve aumento dos teores de Fe e Al extraídos em solução de ditionito-citrato-bicarbonato e oxalato de amônio e, em concordância com os diagramas de estabilidade termodinâmica dos minerais, foi constatada a precipitação de óxidos de baixa cristalinidade no tratamento com remineralizador. No experimento em vasos, a presença das plantas atuou como um dreno, mas mesmo assim com aumento principalmente dos teores de Ca+2 e Mg+2 trocáveis, mas sem ser constatada a precipitação de óxidos amorfos. Por fim, o experimento de campo reafirma o que foi observado nos dois experimentos anteriores, no qual houve aumento dos teores de Ca+2, Mg+2, Na+ e Si trocáveis. Em todos os níveis de experimentos, de forma geral, foi possível observar a maior contribuição de plagioclásios cálcio-sódicos e clinopiroxênios no fornecimento de Ca+2 e Mg+2, principalmente, além de Na+, ferro e silício. / The remineralization is an ancient practice of application of rock powders into the soil in order to improve the soil properties and increase productivity. It is also associated with the reduction of production costs, since remineralizers are cheaper as compared to soluble synthetic fertilizers. Contradiction among the results obtained from the use of remineralizadores frequently be associated with difficulty to describe and control of the factors that may affect the results, such as climate, soil characteristics and characterization of the remineralizers used. This thesis aims to investigate the dissolution of remineralizers in experiments with increasing levels of complexity and evaluate the mineralogical changes, emphasing the possibility of neoformation minerals. In the in vitro experiment, it was possible to identify the effects of particle size and different solvents in the dissolution of the mineral presents in the remineralizer. The rock powder when applied in columns containing soil allowed to identify an increase in Ca+2, Mg+2, K+ exchangeable, including Na+, Fe and Si. Also increased the levels of Fe and Al extracted solution of sodium dithionite-citrate-bicarbonate, ammonium oxalate and in accordance with the thermodynamic stability diagrams of minerals, the precipitation of low crystallinity oxide in remineralizer treatment. In the pot experiment, the presence of plants acted as a drain, but there was still an increase of Ca+2 and Mg+2 exchangeable, specially, but without was observed precipitation of amorphous oxides. Finally, field experiment confirms what was observed in the two previous experiments in which there was an increase in Ca+ 2, Mg+ 2, Na+ and Si exchangeable. At all experiments, in general, we observed the greatest contribution of plagioclase and clinopyroxenes in providing of Ca+2 and Mg+2 in large amount, as well as Na+, Fe and Si in minor quantity.

A remineralização é uma prática antiga que está associada a aplicação de pós de rocha no solo visando a melhoria das propriedades edáficas e por fim o aumento da produtividade, associado também a redução dos custos de produção, uma vez que os remineralizadores possuem menor preço comparado com fertilizantes sintéticos solúveis. Porém ainda existem divergências nos resultados obtidos com o uso de remineralizadores, por vezes associados a dificuldade na descrição e controle dos fatores que podem interferir no processo, como clima, características do solo e do remineralizador empregado. Esta tese tem por objetivo investigar a dissolução de um remineralizador em experimentos em diferentes níveis de complexidade e avaliar as alterações mineralógicas correspondentes, inclusive com ênfase na possibilidade de neoformação de minerais. No experimento in vitro foi possível identificar os efeitos do tamanho das partículas e dos diferentes solventes na dissolução dos minerais do remineralizador. Aumentando o nível de complexidade, no experimento em colunas contendo solo, foi possível identificar principalmente um incremento nos teores de Ca+2, Mg+2, K+ trocáveis no solo, além do Na+, Fe e Si no tratamento com a aplicação do remineralizador. Também houve aumento dos teores de Fe e Al extraídos em solução de ditionito-citrato-bicarbonato e oxalato de amônio e, em concordância com os diagramas de estabilidade termodinâmica dos minerais, foi constatada a precipitação de óxidos de baixa cristalinidade no tratamento com remineralizador. No experimento em vasos, a presença das plantas atuou como um dreno, mas mesmo assim com aumento principalmente dos teores de Ca+2 e Mg+2 trocáveis, mas sem ser constatada a precipitação de óxidos amorfos. Por fim, o experimento de campo reafirma o que foi observado nos dois experimentos anteriores, no qual houve aumento dos teores de Ca+2, Mg+2, Na+ e Si trocáveis. Em todos os níveis de experimentos, de forma geral, foi possível observar a maior contribuição de plagioclásios cálcio-sódicos e clinopiroxênios no fornecimento de Ca+2 e Mg+2, principalmente, além de Na+, ferro e silício. / The remineralization is an ancient practice of application of rock powders into the soil in order to improve the soil properties and increase productivity. It is also associated with the reduction of production costs, since remineralizers are cheaper as compared to soluble synthetic fertilizers. Contradiction among the results obtained from the use of remineralizadores frequently be associated with difficulty to describe and control of the factors that may affect the results, such as climate, soil characteristics and characterization of the remineralizers used. This thesis aims to investigate the dissolution of remineralizers in experiments with increasing levels of complexity and evaluate the mineralogical changes, emphasing the possibility of neoformation minerals. In the in vitro experiment, it was possible to identify the effects of particle size and different solvents in the dissolution of the mineral presents in the remineralizer. The rock powder when applied in columns containing soil allowed to identify an increase in Ca+2, Mg+2, K+ exchangeable, including Na+, Fe and Si. Also increased the levels of Fe and Al extracted solution of sodium dithionite-citrate-bicarbonate, ammonium oxalate and in accordance with the thermodynamic stability diagrams of minerals, the precipitation of low crystallinity oxide in remineralizer treatment. In the pot experiment, the presence of plants acted as a drain, but there was still an increase of Ca+2 and Mg+2 exchangeable, specially, but without was observed precipitation of amorphous oxides. Finally, field experiment confirms what was observed in the two previous experiments in which there was an increase in Ca+ 2, Mg+ 2, Na+ and Si exchangeable. At all experiments, in general, we observed the greatest contribution of plagioclase and clinopyroxenes in providing of Ca+2 and Mg+2 in large amount, as well as Na+, Fe and Si in minor quantity.

Discontinuous planes often develop in soils; examples include shear bands, desiccation cracks, polygonal faults, and hydraulic fractures. These discontinuities affect the mechanical behavior (stiffness and strength) and transport properties of sediments (fluid migration and diffusion). Contrary to discontinuities in solid materials, granular materials such as soils are already separated at the particle scale. Therefore, the fundamental understanding of the development of discontinuities in soils must recognize their inherent granular nature and effective-stress dependent behavior. This research focuses on particle-scale mechanisms involved in contraction-driven shear failure due to mineral dissolution, desiccation cracks, and hydraulic fractures. Complementary experimental, analytical and numerical methods are used to study three cases. Contraction-driven polygonal fault formation under the seabed. Shear failure planes are often found in sediments that formed under near horizontal burial conditions. Particle-scale volume contraction due to mineral dissolution causes a decrease in the state of stress from the insitu K0-condition to the active failure Ka stress field. Shear strain localization follows in sediment with post-peak strain softening response. Desiccation cracks in saturated fine soils. The formation of desiccation cracks in soils is often interpreted in terms of tensile strength, which contradicts the cohesionless, effective stress dependent frictional behavior of fine grained soils. Experimental results monitored using high resolution time lapse photography point to a proper effective stress-dependent mechanism centered on the invasion of the air-water interface membrane. Miscible and immiscible fluid-driven fracture formation. Hydraulic fracture in granular materials cause grain separation and the development of conduits for preferential fluid flow leading to fracture formation due to the forced invasion of either immiscible or miscible fluids. Capillary, seepage, and skeletal interparticle forces define particle scale mechanisms at the fracture tip. Numerical simulations confirm that the effective stress remains in compression everywhere throughout the granular medium in the three localization mechanisms.

No description available.

Silicate minerals are the most common mineral group in the earth's crust so it is not surprising that their weathering reactions dominate the chemistry of many earth surface processes. This project used forsterite as a model system to identify the important factors that affect silicate mineral dissolution rates and grain lifetimes in the weathering environment. I determined an empirical rate law for forsterite dissolution of forsterite in oxalic acid solutions: based on a series of 124 semi-batch reactor experiments over a pH range of 0 to 7 and total oxalate concentrations between 0 and 0.35 m at 25°C. These experiments show that oxalate-promoted dissolution rates depend upon both oxalate concentration and pH. I propose a reaction mechanism in which a hydrogen ion and an oxalate ion are simultaneously present in the activated complex for the reaction that releases H4SiO4 into solution. By analogy, I propose that water acts as a ligand in the absence of oxalate. I also ran 82 batch reactor experiments in magnesium and sodium sulfate and magnesium and potassium nitrate solutions. These experiments show that ionic strength up to 12 m, log mMg up to 4 m, and log mSO4 up to 3 m have no effect on forsterite dissolution rates. However, decreasing aH2O slows forsterite dissolution rates. The effect of decreasing dissolution rates with decreasing aH2O is consistent with the idea that water acts as a ligand that participates in the dissolution process.Forsterite dissolution rate data from previously published studies were combined with results from my experiments and regressed to produce rate laws at low and high pH. For pH < 5.05 or and for pH > 5.05 or I then developed a diagram that shows the effect rate-determining variables on the lifetime of olivine grains in weathering environments using these rate laws. / Ph. D.

<p>This dissertation studies the chemo-hygro-mechanical coupling involved in the process of crack propagation encountered both in natural and engineered context. Chemical processes are likely to affect the mechanical properties of geo-materials, resulting in possible weakening effect. The deformation and micro-cracking induced by material weakening in turn enhances the overall mass removal. In this study, several models within both elasticity and plasticity domain are developed for a better understanding of the enhanced crack propagation. A deformational plasticity model based on experimental observations is addressed. Rigid-plasticity models are applied to various boundary conditions. In the chemo-elasticity model, chemical dissolution is assumed to be a function of a comprehensive strain invariant. One-way coupling and two-way coupling models are discussed. In the two-way coupling model, volumetric strain coupling and deviatoric strain coupling are compared. A variety of loading modes are adopted to investigate the chemical enhancement of propagation of a single crack. The behavior of the material is either rigid-plastic, or elastic with the variable of mass removal enters the constitutive equation as a chemical strain. Comparison between the results from two models is presented and discussed.</p> / Dissertation

Les principaux objectifs étaient d'évaluer la stabilité de l'environnement des scories métallurgiques de Cu résultant de différentes périodes d'activités industrielles et de différentes technologies de fusion. Parmi les scories étudiées, on retrouve: les scories historiques cristallines (SH) ainsi que modernes: les scories de four vertical (SFS), les scories granulées (GS) et les scories de plomb (LS). Les différentes approches adoptées dans ce travail de thèse ont tenu compte de: i) la composition chimique et la phase minérale des scories, ii) la sensibilité à la lixiviation des scories sous l’exposition à différentes conditions de pH en mode statique, iii) l’altération des scories sous exposition aux acides organiques couramment trouvés dans l'environnement du sol, iv ) la bio-altération des scories par les bactéries (Pseudomonas aeruginosa) et v) l’application future de la récupération des métaux provenant des scories étudiées en mettant en œuvre la méthode de lixiviation biologique. Résultats cruciaux: Les résultats des tests de lixiviation dépendant du pH ont montré une libération de métal plus élevée dans des conditions fortement acides (pH 2 et 4), alors que la lixiviation dans des conditions alcalines (pH 10.5) était moins importante pour toutes les scories analysées. L'effet de l’altération par le sol a été démontré, la dissolution des scories est notamment sensible à la présence d'exsudats racinaires artificiels (ARE), d’acides humiques (HA) et d’acides fulviques (FA), la contribution des ARE étant la plus forte. Selon les données recueillies, la dissolution relative des scories est strictement liée à leurs caractéristiques (composition chimique et minéralogique) en fonction des différentes conditions étudiées. L'étude concernant l’effet de l’altération biologique a révélé que Pseudomonas aeruginosa améliore considérablement la libération des éléments majeurs (Si et Fe) et métalliques (Cu, Zn, Pb) par rapport aux effets des facteurs abiotiques, indépendamment de la chimie et de la structure des scories. En outre, une récupération élevée (jusqu'à 90%) des métaux (Cu, Zn, Fe) pourrait être obtenue grâce à la lixiviation avec Acidithiobacillus thiooxidans dans des conditions de laboratoire. Conclusions générales : La stabilité des scories dans l'environnement dépend à la fois des caractéristiques chimiques et de la minéralogie. Cependant, les phases minérales hébergeant les métaux sont les facteurs les plus déterminants concernant l'intensité de la lixiviation des métaux. Pour cette raison, l'examen individuel du comportement des scories est important pour empêcher la contamination de l'environnement et devrait être considéré comme une priorité pour la gestion durable des scories. L’optimisation des paramètres de fonctionnement pour le biolessivage et le développement de la technologie à l'échelle industrielle pourrait permettre une bien meilleure gestion (voir l’exploitation) des scories métallurgiques de Cu / Problem statement: Copper pyrometallurgical slags are inevitable waste by-products of Cu smelting operations. These waste are considered to be important due to their production volume and high residual metal content that are inefficiently recovered during industrial process. Due to the lack of sustainable practices in the past, tremendous volumes of Cu-slags have been disposed in many industrial districts, regardless of the weathering and associated environmental risk. Consequently, there are many areas where slags have been proven to be a source of metallic pollution for the surrounding environment. At the present time, the outstanding contradiction between the sustainable development and environmental pollution encourages to undertake the action regarding this aspect. For this reason, slags are currently being used as supplementary materials for civil engineering purposes (e.g. cement and concrete additives, road bed filling materials, hydraulic construction materials) rather than disposed. Additionally, modern-day management strategies require slags to be thoroughly evaluated with respect to their environmental stability prior undertaking any reuse action. Main objectives were to evaluate environmental stability of Cu-metallurgical slags resulting from different periods of industrial activities and different smelting technologies. Those included: historical crystalline slag (HS) as well as modern: shaft furnace slag (SFS), granulated slag (GS) and lead slag (LS). Different approaches undertaken in this PhD work considered: i) chemical and mineral phase compositions of slags, ii) leaching susceptibility of slags under exposure to different pH-stat conditions, iii) slags weathering under exposure to organic acids commonly found in soil environment, iv) bacterially (Pseudomonas aeruginosa) mediated weathering of slags and v) future application of studied slags for metal recovery by implementing the bioleaching method. Crucial results: The results of the pH-dependent leaching tests showed a higher metal release in strong acidic conditions (pH 2 and 4), whereas leachability at alkaline conditions (pH 10.5) revealed a lower importance for all the slags analyzed. The study considering soil weathering scenario demonstrated that Cu-slags are susceptible to dissolution in the presence of artificial root exudates (ARE), humic (HA) and fulvic acids (FA), whereby ARE were found to have stronger contribution than HA and FA. According to data collected, the different behavior of individual slags is strictly related to their characteristics (chemical and phase composition) reflecting various susceptibilities to dissolution under the investigated conditions. The study considering bio-weathering scenario revealed that Pseudomonas aeruginosa considerably enhances the release of major (Si and Fe) and metallic (Cu, Zn, Pb) elements compared to the effects of abiotic factors, regardless of the slags chemistry and structure. Furthermore, a high gain (up to 90%) of metals (Cu, Zn, Fe) could be credited to bioleaching with Acidithiobacillus thiooxidans under laboratory conditions. General conclusions: The environmental stability of slags depends on both, their bulk chemistry and mineralogy. However, mineral phases harbouring the metals are the key players in metal leachability intensity. For, this reason consideration of individual slags behaviour is important for preventing environmental contamination and should be regarded as priority branch of sustainable slag management. Optimization of operating parameters for bioleaching following development of industrial scale technology is an incentive scheme for future management of Cu-metallurgical slags

Organic ligand complexation reactions at the mineral-water interface play an important role in several environmental and geochemical processes such as adsorption, dissolution, precipitation, pollutant transport, nutrient cycling, and colloidal stability. Although organic ligand surface complexation reactions have been extensively studied, a molecular level understanding regarding the mechanisms underlying the adsorption of such compounds is still limited. The purpose of the current study was to investigate the interactions between some common naturally occurring organic ligands and a common aluminosilicate clay mineral, kaolinite, using a combination of macroscopic and microscopic experimental methods. Molecular level information regarding the structure and binding mode of adsorbed species was obtained using in situ MIR-FTIR spectroscopy. Other experimental techniques including adsorption experiments, surface titrations, and surface complexation modelling were also employed in order to quantify and describe the macroscopic adsorption properties of the organic ligands examined. Three low molecular weight organic acids (oxalic, salicylic, and phthalic acid) and humic acid were chosen as representative organic ligands. Spectroscopic evidence revealed that low molecular weight organic acids are able to form both inner and outer sphere complexes on kaolinite, and the relative concentrations of these surface complexes varies with solution chemistry. Inner sphere coordination modes inferred are a mononuclear bidentate for oxalate (five-membered chelate ring) and phthalate (seven-membered chelate ring); and a mononuclear monodenate (six-membered pseudochelate ring) for salicylic acid. Similar coordination modes were shown to form on simpler mineral (hyrd)oxides. Elucidation of the coordination chemistry of these ligands can provide insights into the dissolution mechanisms of silicate minerals In contrast to low molecular weight organic acids, there was no evidence of inner sphere complexation by humic acid acids on kaolinite or gibbsite. The combined spectroscopic and macroscopic adsorption results suggest that cation bridging and van der Waals interactions are the two most probable mechanisms for the adsorption of humic acid by these mineral substrates. This finding casts doubts over the use of low molecular weight organic acids as humic acid analogs.