This diploma thesis deals with influence of modifying additives on achieved properties of anhydrite binders. The first part is focused on funamentals of anhydrite binders. Ist second part introduces anhydrite under-layments and their standard requirements. The experimental part is dedicated to anhydrite binders modyfyied by plasticizers, while their final properties are compared.

La dissolution de cavités karstiques appelle à une description multi-échelle. A partir d'une discussion des hypothèses les plus fréquemment utilisées, un modèle à l'échelle du pore (ou micro-échelle) est développé pour des schémas réactifs géochimiques simples. L'impact du choix de conditions aux limites réactives ou équilibre thermodynamique est discuté. Ce modèle à l'échelle du pore est ensuite utilisé pour le développement de modèles aux échelles supérieures. Le premier problème traité considère le transport sur une surface chimiquement hétérogène et rugueuse, caractérisée par une condition mixte pour le transfert de masse. Le modèle résultant est un modèle de surface effective (ESCM). Le concept de surface effective est développé à l'aide d'une méthode de décomposition de domaine. Dans ce contexte, vitesse, pression et concentration à la petite échelle près de la surface sont estimées par une méthode de développement asymptotique par rapport aux champs loin de la surface. Des problèmes de fermeture sont alors obtenus qui sont utilisés pour définir la position de la surface effective et les conditions aux limites effectives associées. L'effet sur les propriétés effectives de la position de la surface, des nombres sans dimension est étudié. Une comparaison entre des résultats numériques à petite échelle avec ceux obtenus par le modèle effectif montre un bon accord. Dans le cas du transport dans un milieu poreux, le deuxième problème de changement d'échelle étudié, une méthode de changement d'échelle basée sur la prise de moyenne spatiale est proposée (PMM) à partir du problème à l'échelle du pore avec des conditions aux limites d'équilibre thermodynamique ou réactives non-linéaires. Une expression générale du modèle macroscopique est obtenue impliquant plusieurs propriétés effectives qui sont données par la résolution de problèmes de fermeture à l'échelle du pore. Pour une cellule unitaire représentative stratifiée, les paramètres effectifs sont obtenus analytiquement ou numériquement, alors que les propriétés pour des cellules plus complexes 2D/3D sont obtenus numériquement. L'impact sur les paramètres effectifs des propriétés physiques à l'échelle du pore (en terme de nombre de Péclet, Damköhler et ordre de la réaction) est étudié pour des cellules unitaires 1D, 2D ou 3D. Un exemple d'application du modèle macroscopique est présentée en mettant l'accent sur l'apport potentiel des termes additionnels non-classiques sur la précision des prédictions. Le modèle macroscopique de dissolution de milieu poreux est aussi utilisé comme un modèle à interface diffuse (DIM) pour décrire la dissolution d'une cavité à grande échelle, une cavité de gypse dans l'illustration traitée dans la thèse. Le modèle est basé sur l'approximation de pseudo-constituant, avec une condition d'équilibre à l'échelle du pore sur l'interface fluide-solide. Une méthodologie numérique est proposée pour choisir correctement les paramètres effectifs du DIM de façon à reproduire avec suffisamment de précision les flux et la vitesse de récession de l'interface. Une étude spécifique est effectuée sur l'impact du choix du modèle de bilan de quantité de mouvement macroscopique. De manière intéressante, les résultats numériques ne suggèrent pas un impact très important de ce choix dans le cas des problèmes aux limites traités. Des calculs ont aussi été effectués, dans le cadre d'une approximation de Boussinesq, pour évaluer l'impact éventuel de mouvements de convection naturelle. Le potentiel de la méthode est illustré dans deux cas: un correspondant à une lentille de gypse dans un aquifère, l'autre au cas d'un pilier isolé dans une carrière souterraine. Les conséquences de la dissolution sur la stabilité mécanique sont étudiées à l'aide d'un modèle géomécanique simplifié. Enfin, un cas test est étudié montrant la possibilité d'utiliser le modèle dans le cas de dissolution d'une cavité saline, matériau plus soluble que le gypse. / The karstic cavity dissolution problems are often studied from a hierarchical point of view. Based on a discussion of the frequently adopted assumptions, a pore-scale model is first developed for a simple geochemistry scheme. The impact of implementing reactive or thermodynamic equilibrium boundary condition at the dissolving surface is discussed. Such a pore-scale model is subsequently used as a basis for developing models at higher scale levels. The first problem deals with transport from a heterogeneous and rough surface characterized by a mixed boundary condition. The resulting macro-scale model takes the form of an effective surface theory. In the homogenized model developed with the effective surface concept (denote ESCM), the original rough surface is replaced locally by a homogeneous and smooth surface, where effective boundary conditions are prescribed. To develop the concept of effective surface, a multi-domain decomposition approach is applied. In this framework the velocity, pressure and concentration are estimated at the micro-scale with an asymptotic expansion of deviation terms with respect to macro-scale velocity and concentration fields. Closure problems for the deviations are obtained and used to define the effective surface position and the corresponding boundary conditions. The evolution of some effective properties and the impact of surface geometry and some dimensionless numbers are investigated. A comparison between the numerical results obtained with this effective model and those from direct numerical simulations with the original rough surface shows good agreements. In the case corresponding to mass transport in porous media, upscaling is carried out with the method of volume averaging to develop a macro-scale porous medium model (denote PMM), starting from a pore-scale transport problem involving thermodynamic equilibrium or nonlinear reactive boundary conditions. A general expression to describe the macro-scale mass transport is obtained involving several effective parameters which are given by specific closure problems. The impact on the effective parameters of the fluid properties, in terms of pore-scale Péclet number (Pe), and the process chemical properties, in terms of pore-scale Damköhler number (Da) and reaction order (n), is studied for periodic stratified, 2D and 3D unit cells. An example of the application of the macro-scale model is presented with the emphasis on the potential impact of additional, non-traditional effective parameters appearing in the theoretical development on the improvement of the accuracy of the macro-scale model. The above developed PMM is also used as a Diffuse Interface Model (DIM) to describe the evolution of a gypsum cavity formation induced by dissolution. The method is based upon the assumption of a pseudo-component dissolving with a thermodynamic equilibrium boundary condition. A methodology is proposed in order to choose suitable parameters for the DIM model and hence predict the correct dissolution fluxes and surface recession velocity. Additional simulations are performed to check which type of momentum balance equation should be used. Calculations with a variable density and Boussinesq approximation were also performed to evaluate the potential for natural convection. The results showed that the impact of density driven flows were negligible in the cases under investigation. The potential of the methodology is illustrated on two large-scale configurations: one corresponding to a gypsum lens contained within a porous rock layer and the other to an isolated pillar in a flooded gypsum quarry. Geomechanical consequences of the dissolution in terms of mechanical stability is evaluated with the help of a simplified geomechanical model. A final case is also studied in which gypsum is replaced by salt to show the applicability of the proposed methodology to a rapidly dissolving material

Synthesebedingt fällt die DTPMP als dunkelbraune, zähflüssige Lösung mit zahlreichen Verunreinigungen an. Diese Arbeit beschäftigt sich mit der Herstellung einer hochreinen, festen DTPMP. Hierfür wurden zwei unterschiedliche Reinigungsmethoden untersucht. Durch Umkristallisation und anschließendes Rühren in Ethanol konnte mit 95 % eine höhere Reinheit als bisher veröffentlicht erzielt werden. Eine alternative Reinigungsmethode stellt die Ausfällung als Erdalkali-DTPMP-Salz und anschließende Auflösung in Schwefelsäure und Abtrennung des entstehenden Erdalkalisulfats dar, wobei eine Reinheit > 99 % erzielt wurde. Zur strukturellen Charakterisierung wurden zahlreiche Kristallisationsexperimente zur Züchtung von Kristallen der DTPMP als Säure und deren Alkali- und Erdalkalisalzen durchgeführt. Weiterhin wurde das thermische Verhalten der DTPMP und deren Salzen charakterisiert. Unter den zahlreichen möglichen Anwendungen der DTPMP wurde beispielhaft die Wirksamkeit auf die Gipskristallisation untersucht.

Masters of Science / This study was conducted to investigate hydrogeochemical processes controlling the evolution of groundwater chemistry and their influence on water quality in the Heuningnes Catchment. The role or influence of hydrogeochemical processes in groundwater quality in aquifer systems remains poorly understood. One of the ways of improving such understanding is to employ different techniques to explore key processes that govern groundwater quality in aquifer systems. Therefore, the present study investigated hydrogeochemical processes of groundwater resources and identified key processes that explained its quality from a spatiotemporal perspective. The quantitative approach that provides the ability to assess relationships between variables both spatially and temporally was applied. Groundwater sampling was done on four occasions during July 2017, October 2017, March 2018, and July 2018. Identification of hydrogeochemical processes controlling the evolution of groundwater chemistry and quality was done using various complementary tools. These tools included classification of the main water types, evaluation of water-rock interaction by means of stoichiometry analysis and bivariate correlation plots, inverse geochemical modelling, and statistical analysis (hierarchical cluster analysis and factor analysis). Physical parameters were measured in situ, while water samples were collected from boreholes, piezometers, springs, and artesian boreholes for laboratory analysis for major ions analysis. Descriptive and bivariate statistical methods were used to summarise and evaluate the strength of the relationship between variables, while multivariate statistical methods were applied to group similar samples based on their chemical compositions. Tri linear Piper diagrams were generated to characterize water type based on double normalizing the proportions of cations and anions, while correlation and stoichiometric analysis were applied to identify hydrogeochemical processes influencing groundwater chemistry. The results generated from the trilinear Piper diagrams confirmed the dominance of sodium and chloride ions in waters of the Heuningnes Catchment. Groundwater of a Na/Cl type is typical for a coastal aquifer characterised by saline, deep ancient groundwater. The lower parts of the Catchment were characterised by saline groundwater. The results indicated that shallow groundwater samples within the study area were more mineralised as compared to deep groundwater with EC values ranging between 20.8 and 2990 mS/m, with waters within the Table Mountain Group region (TMG), recording the lowest values. Deep groundwater for boreholes and artesian boreholes located upstream in the Catchment was fresh and yielded some of the lowest EC values recorded with an EC value below 50 mS/m. Generally, EC values increased from the upper TMG region of the Catchment towards the Bokkeveld shale region downstream and were highest during the dry season of 2018. The results indicated strong geological influences on water chemistry. Bivariate correlation and stoichiometric analysis identified cation exchange, adsorption, evaporation, weathering of carbonates, sulphates and silicate minerals as processes influencing the chemistry of groundwater in the Heuningnes Catchment. The Saturation Index (SI) results showed a change of calcite, dolomite, aragonite, gypsum, anhydrite, halite, melantinterite, siderite and sylvite from being undersaturated to oversaturated at some areas for the different seasons along the flow path. The mass-balance modelling results indicated that ion exchange and reverse ion exchange processes were more dominant at low elevations along the same flow path during the dry periods. However, at high elevations along the flow path, silicate weathering was the dominant process taking place. The findings of this study demonstrated the influence of hydrogeochemical processes in changing the water chemistry along the flow paths. In conclusion, the study showed the value of utilising various assessment tools as complementary techniques to improve the understanding about hydrogeochemical processes, and its influence on evolution of groundwater chemistry and quality. Based on the findings of the study the following recommendations were made for future studies; the sample points or sample boreholes in the study Catchment should be increased; and to have more sampling trips to enable better comparison between the possible processes

The aim of this doctoral thesis is to verify, using previously developed laboratory instruments, the possibility of a complete or partial substitution of currently used dehydration solutions of sodium chloride and calcium chloride by potassium chloride solution extracted from chloride dusts coming from cement production, using non-pressure method to produce alpha gypsum.

No description available.

The demand for metals is great for the purpose of developing green technologies, and EU has listed 30 metals and minerals that are of critical importance for the maintenance and evolving of today’s society, so called critical materials. However, mining of raw materials generates mine waste which can have adverse effect on human health, ecosystems, and surrounding areas. To be able to prevent the release of toxic levels of elements from mine waste, an understanding of how different elements behave in the secondary environments is necessary in order to use the most successful methods for mining remediation. It is common that secondary minerals, such as gypsum and/or HFOs (hydrous ferric oxides), forms in mine waste or in downstream environments, depending on the geochemical conditions. From prior studies, it is well established that trace elements are sorbed by HFO. But studies are scares regarding co-precipitation of elements with secondary gypsum formation, and few studies investigates the possibility of critical elements to be captured by secondary minerals. In this study, a prior unknown white precipitation along with tailings material from the Smaltjärnen tailings beach in Yxsjöberg, Sweden, has been investigated by combining mineralogical studies (SEM-EDS and DXRD analysis) with sequential extraction. The aim with the study was to identify the precipitation and to examine if critical elements had co-precipitated with the precipitation and HFOs within the sample. From the results it was possible to prove that the white precipitation was gypsum (CaSO4*2H2O), and it was indicated that some of the critical elements (beryllium for instance) showed affinity for gypsum, and that bismuth, tungsten, and chromium were sorped by HFOs. The combining of chemical analysis with mineralogical studies was of great importance for determining in which mineral phases the leached elements were situated, and the study has shown that secondary gypsum formation can be an important sink for some critical elements. More studies should be performed within this field of research to further investigate the importance of secondary minerals for scavenging of elements, not only to prevent toxic levels to be leached, but also to capture these elements in the purpose of re-mining. / Idag är behovet av metaller stort inom användningsområden för att utveckla gröna teknologier. EU har därför listat 30 metaller och mineral (kritiska material) som anses vara kritiska för att underhålla och utveckla dagens samhälle. Men brytning av råmaterial resulterar i generering av gruvavfall där avfallet potentiellt kan utgöra en risk för att skada bland annat människors hälsa och ekosystem. För att kunna förhindra att giftiga halter av grundämnen släpps ut från gruvavfall så krävs en förståelse om hur olika ämnen beter sig i sekundära miljöer, för att på så sätt kunna tillämpa de mest framgångsrika metoderna för sanering och återställning av gruvområden. Det är vanligt förekommande att sekundära mineraler (såsom gips och järnhydroxider) fälls ut i gruvavfallet och/eller nedströms om gruvområdet beroende på de geokemiska förhållandena. Tidigare studier har visat att spårämnen kan binda till järnhydroxider, men endast ett fåtal studier undersöker samutfällning av olika spårämnen tillsammans med sekundärt gips. Hur specifikt kritiska metaller kan fångas upp av sekundära mineral är ännu inte välstuderat. I denna studie har en vit, tidigare okänd, utfällning provtagits från en av deponierna med anrikningssand i den historiska volframgruvan i Yxsjöberg. Utfällningen identifierades genom att kombinera mineralogiska studier (SEM-EDS och DXRD analys) med kemiska lakvattenanalyser från en sekventiell lakning. Målet med studien var att mineralogiskt karaktärisera den okända utfällningen och att undersöka om kritiska ämnen möjligen samutfällts tillsammans med de sekundära mineralen. Studien visade att utfällningen var sekundärt gips (CaSO4*2H2O) och det kunde påvisas att vissa kritiska metaller visade affinitet för gipset (exempelvis beryllium) och att andra kritiska metaller samutfällts/adsorberats av järnhydroxider. Att kombinera dom olika metoderna visade sig att vara till stor nytta för att kunna påvisa vilka mineral dom olika grundämnena var bundna till, och studien har även visat att sekundärt gips kan vara en sänka för vissa kritiska metaller. Mer studier bör utföras inom detta forskningsområde i framtiden för att vidare undersöka hur sekundära mineral kan binda kritiska metaller, inte endast för att förhindra att giftiga halter av metaller släpps ut, utan också för att undersöka möjligheten att återvinna gruvavfallet för utvinning av kritiska metaller.

A fundamental theoretical and experimental study on calcium sulphate scale formation in hydrometallurgical solutions containing various minerals was conducted. A new database for the Mixed Solvent Electrolyte (MSE) model of the OLI Systems® software was developed through fitting of existing literature data such as mean activity, heat capacity and solubility data in simple binary and ternary systems. Moreover, a number of experiments were conducted to investigate the chemistry of calcium sulphate hydrates in laterite pressure acid leach (PAL) solutions, containing Al2(SO4)3, MgSO4, NiSO4, H2SO4, and NaCl at 25–250ºC. The database developed, utilized by the MSE model, was shown to accurately predict the solubilities of all calcium sulphate hydrates (and hence, predict scaling potential) in various multicomponent hydrometallurgical solutions including neutralized zinc sulphate leach solutions, nickel sulphate–chloride solutions of the Voisey’s Bay plant, and laterite PAL solutions over a wide temperature range (25–250°C). The stability regions of CaSO4 hydrates (gypsum, hemihydrate and anhydrite) depend on solution conditions, i.e., temperature, pH and concentration of ions present. The transformation between CaSO4 hydrates is one of the common causes of scale formation. A systematic study was carried out to investigate the effect of various parameters including temperature, acidity, seeding, and presence of sulphate/chloride salts on the transformation kinetics. Based on the results obtained, a mechanism for the gypsum–anhydrite transformation below 100°C was proposed. A number of solutions for mitigating calcium sulphate scaling problems throughout the processing circuits were recommended: (1) operating autoclaves under slightly more acidic conditions (~0.3–0.5 M acid); (2) mixing recycled process solutions with seawater; and (3) mixing the recycling stream with carbonate compounds to reject calcium as calcium carbonate. Furthermore, aging process solutions, saturated with gypsum, with anhydrite seeds at moderate temperatures (~80°C) would decrease the calcium content, provided that the solution is slightly acidic.

Gypsum rich soils are found in many parts of the world, particularly in arid and semi-arid regions. Most gypsum occurs in the form of evaporites, which are minerals that precipitate out of water due to a high rate of evaporation and a high mineral concentration. Gypsum rich soils make good foundation material under dry conditions but pose major engineering hazards when exposed to water. Gypsum acts as a weak cementing material and has a moderate solubility of about 2.5 g/liter. The dissolution of gypsum causes the soils to undergo unpredictable collapse settlement leading to severe structural damages. The damages incur heavy financial losses every year. The objective of this research was to use geophysical methods such as free-free resonant column testing and electrical resistivity testing to characterize gypsum rich soils based on the shear wave velocity and electrical resistivity values. The geophysical testing methods could provide quick, non-intrusive and cost-effective methodologies to screen sites known to contain gypsum deposits. Reconstituted specimens of ground gypsum and quartz sand were prepared in the laboratory with varying amounts of gypsum and tested. Additionally geotechnical tests such as direct shear strength tests and consolidation tests were conducted to estimate the shear strength parameters (drained friction angle and cohesion) and the collapse potential of the soils. The effect of gypsum content on the geophysical and geotechnical parameters of soil was of particular interest. It was found that gypsum content had an influence on the shear wave velocity but had minimal effect on electrical resistivity. The collapsibility and friction angle of the soil increased with increase in gypsum. The information derived from the geophysical and geotechnical tests was used to develop statistical design equations and correlations to estimate gypsum content and soil collapse potential.

Estudos experimentais realizados por alguns autores abordaram os mecanismos de deformação nas gipsitas, tais como o fluxo plástico e a dissolução por pressão. Ainda assim, é pequeno o conhecimento do comportamento mecânico das rochas de gipso. Nesta tese foram estudados os mecanismos de deformação lenta em gipsitas bandadas da Formação Santana da Chapada de Araripe com uso da técnica de emissão acústica. Adotou-se este procedimento como técnica indireta de detecção do processo de microfissuramento, para evitar mudanças que ocorrem na microestrutura durante seu descarregamento e preparação de amostras para sua observação por técnicas diretas. Realizaram-se ensaios de fluência de curto e longo prazo numa prensa hidráulica servocontrolada MTS 815 e em conjunto modulares (torres individuais) em um laboratório de fluência especialmente equipado. Encontrou-se que o mecanismo do microfissuramento está fortemente influenciado por processos de cicatrização durante ensaios de fluência de longo prazo. Devido ao processo de cicatrização da microfissura, a fluência terciaria nunca foi alcançada, mesmo em corpos de prova carregados com até 95% da resistência à compressão uniaxial. Nesta tese outros resultados importantes foram alcançados como: identificar que o fenômeno de microfissuramento para a rocha em questão é detectado por fenômenos de emissão acústica de freqüências intermediárias (de 100 a 400 kHz) e constatar que o efeito Kaiser se manifesta neste tipo de rochas de modo inequívoco para solicitações rápidas, enquanto após ensaios de fluência de longa duração, não mais se manifesta, por causa da cicatrização. Ou seja, corpos de prova submetidos mais uma vez à compressão uniaxial após o descarregamento, voltam a apresentar eventos de emissão acústica e, conseqüentemente, a geração de novas microfissuras. Este fato somente pode ser explicado por um processo de cicatrização da microfissura durante a fluência de longo prazo. Esta cicatrização, devido a fenômenos físico-químicos, apresentou outros indícios como um aumento no módulo de elasticidade após ensaios de fluência, quando comparado aos valores antes do ensaio, e mesmo um endurecimento (aumento da resistência à compressão uniaxial) também após a fluência. Esclareceu-se também de modo inequívoco que o descarregamento provoca o progresso do microfissuramento. Além dos sinais característicos do microfissuramento, constatou-se que o módulo de elasticidade, medido nos mesmos níveis de tensão, é mais alto antes que depois do descarregamento. O decréscimo de rigidez é indício do processo de dano por microfissuramento. / Experimental studies by several authors have shown some of the key deformation mechanisms in gypsum, such as plastic flow and pressure dissolution. Even so, there is still sparse knowledge about the mechanical behavior of natural gypsum rocks. Creep mechanisms of the banded gypsum rock of Santana Formation from the Chapada do Araripe (Santana Formation) in creep tests were studied with acoustic emission technique correlating the stress levels related to microcracking to the energy release associated with these mechanisms. This procedure was adopted as an indirect technique of detection of the microcracking process, to prevent changes that occur in the microstructure during unloading and in sample preparation for its observations with direct techniques. Short and long-term creep tests were carried out in an MTS 815 servo-controlled testing system and in modular sets (single towers) in a specially equipped creep laboratory. It was found that the microcrack mechanism is strongly influenced by healing processes during long-term creep. Due to the microcrack healing process, tertiary creep was never reached, even in specimens loaded with up to 95% of the uniaxial compressive strength. In this thesis other important results were reached as: to identify that the microcracking phenomenon for the rock in question is detected by acoustic emission phenomena of intermediate frequencies (from 100 to 400 kHz) and to evidence that the Kaiser effect unequivocally manifests in this type of rock when subjected to quick loads, while after long-term creep tests, it is no longer evidenced on account of healing. In other words, the specimens subjected once again to uniaxial compression after unloading, again show acoustic emission events and therefore the generation of new microcracks. This fact can only be explained by a microcrack healing process during long-term creep. This healing, due to physical-chemical phenomena, presented other indications as an increase in the modulus of elasticity after creep tests, when compared to the values before the test, and even a hardening (increase of the uniaxial compressive strength) also after the creep. It was also clarified in unequivocal way that the unloading provokes microcracking progress. In addition to the microcracking characteristic indications, it was found that the modulus of elasticity, when measured at the same stress levels, is higher before unloading than after the unloading. The stiffness decrease is indication of the microcracking damage process.