L'arsenic est un élément toxique présent naturellement dans l'environnement. Parfois en fortes concentrations dans les eaux souterraines, utilisées comme eaux de boisson, il est responsable d'une des plus grandes mortalités au monde. Il est donc important de mieux comprendre les interactions de l'As avec l'environnement et son mode de transfert jusqu'aux aquifères. Cette thèse a pour objectif de comprendre les mécanismes de complexation direct et indirect de l'As(III) par la matière organique (MO) en milieu anoxique, notamment via les groupements thiols de la MO et sous forme de complexes ternaires faisant intervenir le Fe ionique. La première partie de ce travail a été consacrée à la complexation de l'As(III) par les groupements thiols de la MO. Des expériences de complexation d'As(III) par un acide humique (AH) naturel greffé ou non en sites thiols ont été réalisées. L'As(III) se complexe à la MO directement mais les concentrations complexées sont faibles et dépendantes de la densité en site thiol. La modélisation à l'aide de PHREEQC-Model VI modifié afin de tenir compte des sites thiols, a mis en évidence que l'As était complexé à la MO sous forme de complexes monodentates. Il existe, un autre mécanisme qui propose une complexation indirecte via la formation d'un pont cationique. Nous nous sommes intéressés ici, en conditions anoxiques, à la possibilité que ce pont soit un pont de Fe(II). Il n'existe cependant que très peu d'information sur la complexation du Fe(II) par la MO. Des expériences de complexation du Fe(II) par des substances humiques (SH) ont donc été réalisées. Les résultats expérimentaux ont montré que le Fe(II) est faiblement complexé aux SH lorsque le pH était acide et les groupements fonctionnels protonés. Au contraire à pH neutre à basique, 100% du Fe(II) est complexé aux SH. La modélisation a montré que le Fe(II) forme majoritairement des complexes bidentates carboxyliques à pH acides et des complexes bidentates carboxy-phénoliques et phénoliques à pH basiques. Dans la dernière partie, la complexation de l'As(III) par des complexes ternaires As(III)-Fe(II, III) ionique-MO a été testée. Les résultats expérimentaux ont montré que des complexes ternaires As(III)-Fe(II)-MO pouvaient se former en milieu anoxique. La modélisation a permis de tester différentes conformations structurales de complexes ternaires. Le complexe le plus probable est un complexe bidentate mononucléaire d'As(III) sur un complexe bidentate de Fe(II)-AH. Cependant, PHREEQC-Model VI doit être amélioré car la distribution des sites bidentate n'est pas réaliste en comparaison des données spectroscopiques. Au contraire pour de faibles concentrations en Fe(III), l'As(III) ne forme pas de complexes ternaires As(III)-Fe(III) ionique-MO. La spéciation de l'As et du Fe est particulièrement importante dans l'étude du transfert de l'As. Si l'As(III) est complexée à la MO, son transfert dépendra totalement des mécanismes de transfert de la MO. / Arsenic occurs naturally in groundwater used as drinking water. It is thus responsible of a great mortality in the world. Understand the As interactions with its environment and its transfer mode to the aquifers is therefore crucial. This work was focused on the direct and indirect binding mechanisms of As(III) by organic matter (OM) in anoxic environments, in particular via OM thiol groups and as ternary complexes involving ionic Fe. The first part of this work was dedicated to the complexation of As(III) by the OM thiol. Binding experiments of As(III) by a humic acid (HA) grafted or not by thiol were thus performed. Grafted or not OM were able to bind As(III) but bound As(III) concentrations were low and dependant on the thiol site density. Modeling with PHREEQC-Model VI modified to take into account thiol site demonstrated that As(III) was bound as monodentate complexes to OM thiol sites. Another indirect binding mechanism involving ternary complex via cationic bridge was however described to explain larger binding of As(III, V) to natural OM. Here under anoxic conditions, we speculated that this bridge was an ionic Fe(II) bridge. However, little information exists about the binding of Fe(II) by OM. Complexation experiments of Fe(II) by humic substances (HS) were thus conducted. The experimental results showed that Fe(II) was weakly complexed to HS at acidic pH, when the functional groups were protonated. By contrast, at basic pH, 100% of Fe(II) were complexed to HS. Modeling calculations demonstrated that Fe(II) formed mainly carboxylic bidentate at acidic pH and carboxy-phenolic and phenolic bidentate at basic pH. In the last part, the complexation of As(III) as As(III)-ionic Fe(II, III)-OM ternary complexes was tested. Experimental results showed that As(III)-Fe(II)-OM ternary complexes could form in anoxic environments. Modeling allowed to test several ternary complexes conformations. The most potential was the binding of As(III) as mononuclear bidentate complex onto a bidentate Fe(II)-AH complex. However, another definition of the model that should be constrained by XAS data is required. By contrast, at low concentrations of Fe (III), when the oxidizing and reduced species coexist, As(III) does not form As(III)-ionic Fe(III)-OM ternary complexes. Speciation of As and Fe is particularly important in the study of the As(III) transfer. When As(III) is bound to OM as ternary complexes, its transfer is entirely controlled by the own OM transfer mechanisms. Here, we calculated, however, that much of As(III) remains as labile species and can therefore reach underlying aquifers as long as anoxic conditions exist.

<p>The primary aim of these coal fired industries for co-disposing fly ash and brine was to use the fly ash as a sustainable salt sink. It is therefore important to study the interaction chemistry of the fly ash-brine systems to fully understand the leaching and mobility of the contaminant species, and to determine the possibility of capturing the salts from the brine solution when fly ash and brine are co-disposed. In order to achieve the aims and objectives of this study, several leaching procedures such as batch reaction tests, long-term fly ash-brine interaction tests, acid neutralization capacity (ANC) tests, up-flow percolation tests and sequential extraction tests were employed. The geochemical modeling software was applied to predict the formation of secondary mineral phases controlling the release of species in the fly ash-brine systems. Several analytical techniques such as x-ray diffraction (XRD), x-ray fluorescence (XRF), scanning electron microscopy-energy dispersion spectroscopy (SEM-EDS), inductively coupled plasma-mass spectroscopy (ICP-MS) and ion chromatography (IC) were applied to characterize the fresh fly ashes, solid residues recovered from the fly ash-brine interaction tests, the brine sample used in this study and the leachate samples in order to determine the chemical and mineralogical compositions and speciation of the waste materials.</p>

The objective of the work described in this thesis was to understand sorption reactions of uranium occurring at the water-clay mineral interfaces in the presence and absence of arsenic and other inorganic ligands. Uranium(VI) removal by clay minerals is influenced by a large number of factors including: type of clay mineral, pH, ionic strength, partial pressure of CO2, load of the sorbent, total amount of U present, and the presence of arsenate and other inorganic ligands such as sulfate, carbonate, and phosphate. Both sulfate and carbonate reduced uranium sorption onto IBECO bentonite due to the competition between SO42- or CO32- ions and the uranyl ion for sorption sites, or the formation of uranyl-sulfate or uranyl-carbonate complexes. Phosphate is a successful ligand to promote U(VI) removal from the aqueous solution through formation of ternary surface complexes with a surface site of bentonite. In terms of the type of clay mineral used, KGa-1b and KGa-2 kaolinites showed much greater uranium sorption than the other clay minerals (STx-1b, SWy-2, and IBECO montmorillonites) due to more aluminol sites available, which have higher affinity toward uranium than silanol sites. Sorption of uranium on montmorillonites showed a distinct dependency on sodium concentrations because of the effective competition between uranyl and sodium ions, whereas less significant differences in sorption were found for kaolinite. A multisite layer surface complexation model was able to account for U uptake on different clay minerals under a wide range of experimental conditions. The model involved eight surface reactions binding to aluminol and silanol edge sites of montmorillonite and to aluminol and titanol surface sites of kaolinite, respectively. The sorption constants were determined from the experimental data by using the parameter estimation code PEST together with PHREEQC. The PEST- PHREEQC approach indicated an extremely powerful tool compared to FITEQL. In column experiments, U(VI) was also significantly retarded due to adsorptive interaction with the porous media, requiring hundreds of pore volumes to achieve breakthrough. Concerning the U(VI) desorption, columns packed with STx-1b and SWy-2 exhibited irreversible sorption, whereas columns packed with KGa-1b and KGa-2 demonstrated slow, but complete desorption. Furthermore, most phenomena observed in batch experiments were recognized in the column experiments, too. The affinity of uranium to clay minerals was higher than that of arsenate. In systems containing uranium and arsenate, the period required to achieve the breakthrough in all columns was significantly longer when the solution was adjusted to pH 6, due to the formation of the uranyl-arsenate complex. In contrast, when pH was adjusted to 3, competitive sorption for U(VI) and As(V) accelerated the breakthrough for both elements. Finally, experiments without sorbing material conducted for higher concentrations of uranium and arsenic showed no loss of total arsenic and uranium in non-filtered samples. In contrast, significant loss was observed after filtration probably indicating the precipitation of a U/As 1:1 phase.

<p>The primary aim of these coal fired industries for co-disposing fly ash and brine was to use the fly ash as a sustainable salt sink. It is therefore important to study the interaction chemistry of the fly ash-brine systems to fully understand the leaching and mobility of the contaminant species, and to determine the possibility of capturing the salts from the brine solution when fly ash and brine are co-disposed. In order to achieve the aims and objectives of this study, several leaching procedures such as batch reaction tests, long-term fly ash-brine interaction tests, acid neutralization capacity (ANC) tests, up-flow percolation tests and sequential extraction tests were employed. The geochemical modeling software was applied to predict the formation of secondary mineral phases controlling the release of species in the fly ash-brine systems. Several analytical techniques such as x-ray diffraction (XRD), x-ray fluorescence (XRF), scanning electron microscopy-energy dispersion spectroscopy (SEM-EDS), inductively coupled plasma-mass spectroscopy (ICP-MS) and ion chromatography (IC) were applied to characterize the fresh fly ashes, solid residues recovered from the fly ash-brine interaction tests, the brine sample used in this study and the leachate samples in order to determine the chemical and mineralogical compositions and speciation of the waste materials.</p>

L'arsenic est un metalloïde toxique et cancérigène. Ubiquiste dans la pedosphere, il est très sensibleaux fluctuations des conditions redox du sol, ce qui influe significativement sa toxicité et mobilité. Nousétudions le cycle biogéochimique global de l'arsenic, en tenant compte de l'usage croissant des ressources, etpassons en revue l'importance respective de l'arsenic geogénique et anthropogénique dans l'environnement.La contamination à l'arsenic est souvent diffuse dans les bassins sédimentaires de l'Europe. Cependant, desconcentrations dans l'eau interstitielle du sol peuvent être élevées lors de périodes de saturation du solcausées par la monté des eaux souterraines ou les inondations, prévues d'augmenter dû aux changementsclimatiques. La spectrométrie de fluorescence X quantitative et sans standard a été utilisée pour analyserl'arsenic dans des sols relativement contaminés de la plaine alluviale de la Saône au moyen de protocoles depréparation d'échantillons conçus pour optimiser la précision d'analyse et l'exactitude in situ aux bassesconcentrations d'arsenic. L'arsenic dans ces sols est associe aux (hydr)oxydes du fer et de manganèse de lataille d'argile colloïdale. Ceux-ci subissent une dissolution réductrice par les microorganismes lors desinondations, libérant une importante concentration d'arsenic dans la phase aqueuse. Si, par la suite, l'arsenicdégagé n'est pas éliminé avec l'eau de crue évacuée, il est ré-immobilisé pendant l'oxydation du sol et lareprécipitation des oxydes métalliques. Grâce à une combinaison novatrice d'analyses chimiques par voiehumide, d'écologie microbienne, de spectroscopie ainsi que de modélisation thermodynamique et cinétique,nous démontrons que les cycles d'oxydo-réduction séquentiels entraînent une atténuation d'arsenic aqueuxdans des conditions réductrices dû à la coprécipitation croissante, et a une diminution de l'activitémicrobienne causée par l'appauvrissement en matière organique labile. Des processus d'atténuationsimilaires sont observés en l'absence d'activité microbienne pour Cr et As dans des argiles pyriteuses lorsquecelles-ci sont exposés aux oscillations redox provoquées par l'ajout de substances humiques réduites. Ainsi,nous montrons que les effets cumulatifs de cycles redox successifs sont extrêmement importants pour lamobilité de divers contaminants dans l'environnement.

Philosophiae Doctor - PhD / The primary aim of these coal fired industries for co-disposing fly ash and brine was to use the fly ash as a sustainable salt sink. It is therefore important to study the interaction chemistry of the fly ash-brine systems to fully understand the leaching and mobility of the contaminant species, and to determine the possibility of capturing the salts from the brine solution when fly ash and brine are co-disposed. In order to achieve the aims and objectives of this study, several leaching procedures such as batch reaction tests, long-term fly ash-brine interaction tests, acid neutralization capacity (ANC) tests, up-flow percolation tests and sequential extraction tests were employed. The geochemical modeling software was applied to predict the formation of secondary mineral phases controlling the release of species in the fly ash-brine systems. Several analytical techniques such as x-ray diffraction (XRD), x-ray fluorescence (XRF), scanning electron microscopy-energy dispersion spectroscopy (SEM-EDS), inductively coupled plasma-mass spectroscopy (ICP-MS) and ion chromatography (IC) were applied to characterize the fresh fly ashes, solid residues recovered from the fly ash-brine interaction tests, the brine sample used in this study and the leachate samples in order to determine the chemical and mineralogical compositions and speciation of the waste materials. / South Africa

Irrigation of the municipal cemetery in Brigham City, Utah resulted in stained headstones in 2001 and 2002. The water used in the irrigation came from Mantua reservoir, a medium sized impoundment situated near the mouth of Box Elder Canyon. In order for Brigham City to establish a city wide secondary pressurized irrigation system using water from Mantua reservoir, the cause and the source of staining problem must be determined. Previous research (Wallace 2006) determined that the source of the staining was the reduction of iron found in Mantua Reservoir sediments that occurred when seasonal variations in the reservoir caused anaerobic conditions. The reduced iron then dissolved in the water and was used in the irrigation system, causing re-oxidation of the iron. The oxidized iron then precipitated out on the headstones causing the staining. The purpose of this investigation is to determine the iron oxidation kinetics after the re-aeration of the water which will help determine appropriate mitigation methods. A secondary purpose is to confirm the Mantua reservoir's capacity to become anaerobic, resulting in the conditions which cause staining. Using laboratory investigations and computer modeling, I determined that on re-aeration, fifty percent of the dissolved iron in the water precipitates in five hours. Using first-order kinetics to model this process, I found the rate constant of the kinetic reaction to be 0.0029 min-1. Fitting a geochemical computer model of the iron oxidation kinetics in Mantua reservoir, which uses a higher-order kinetics model to better model this process, to experimental kinetic data yielded a rate constant of 4x1013 /atm x min. I also recreated the staining process in the laboratory using concrete. This was successful and provided visual evidence that the iron precipitates out of the water and stained the concrete within a couple of hours of application. Field data collected from Mantua reservoir showed that the dissolved oxygen concentration in the reservoir drops regularly below levels consistent with equilibrium to the atmosphere. While my field measurements did not record anaerobic conditions, based on the patterns shown, this study shows that it would be possible for anaerobic conditions to occur during warmer weather.

This study was made to increase the understanding of how heavy metals in the aqueous phase are removed at low initial concentrations in different pH and Eh values. The reaction that has been studied is mainly hydroxide precipitation and adsorption in a condensate treatment. In the study, data from one of Vattenfalls waste incinerators was analysed and the results from the data were then compared to previous studies. To increase the understanding, modelling of the heavy metals behaviour in the given concentrations was then made with Medusa and PHREEQC. The heavy metals that were analysed were Sb, As, Pb, Zn, Cr, and Cd. The low initial concentration that vary between 36.1-23600 μg/l complicates the removal process because it corresponds in a low driving force and the results are hard to compare to other studies since the initial concentrations vary between 10-100 mg/l. From the modelling and the measurement data it can be seen that Pb, Zn, Cr, and Cd was removed by hydroxide precipitation at pH 10. According to the speciation calculations, the dominant species at this pH are Pb(OH) 2 , Cd(OH)2, Zn(OH)2 and Cr(OH)3. For arsenic a clear conclusion could not be drawn from the modelling and the measurement data because of low precision. Due to the limited thermodynamic parameters of antimony in comparison with other heavy metals in the database of Medusa and PHREEQC, the modelling of antimony behaviour in condensate treatment has relatively larger uncertainty is low. The modelling results show that the main species in acidic solutions for antimony is Sb(OH)3 and in basic solutions Sb(OH)-6. Further investigation for antimony in needed for a clear conclusions to be drawn

Uganda is well endowed with economic quantities of mineral salts present in the interstitial brines and evaporite deposits of Lake Katwe, a closed (endorheic) saline lake located in the western branch of the great East African rift valley. Currently, rudimentally and artisanal methods continue to be used for salt extraction from the lake raw materials. These have proved to be risky and unsustainable to the salt miners and the environment and they have a low productivity and poor product quality. This work involves the investigation of the salt raw materials that naturally occur in the brines and evaporites of Lake Katwe. The purpose is to propose strategies for the extraction of improved salt products for the domestic and commercial industry in Uganda. The literature concerning the occurrence of salt and the most common available technologies for salt extraction was documented. Also, field investigations were undertaken to characterize the salt lake deposits and to assess the salt processing methods and practices. The mineral salt raw materials (brines and evaporites) were characterized to assess their quality in terms of the physical, chemical, mineralogical, and morphological composition through field and laboratory analyses. An evaluation of the potential of future sustainable salt extraction from the lake deposits was done through field, experimental, and modeling methods. Moreover, the mineral solubilities in the lake brine systems and dissolution kinetics aspects were investigated. The results reveal that the salt lake raw materials contain substantial amounts of salt, which can be commercialized to enable an optimum production. The brines are highly alkaline and rich in Na+, K+, Cl-, SO42-, CO32-, and HCO3-. Moreover, they contain trace amounts of Mg2+, Ca2+, Br-, and F-. The lake is hydro-chemically of a carbonate type with the brines showing an intermediate transition between Na-Cl and Na-HCO3 water types. Also, the evaporation-crystallization is the main mechanism controlling the lake brine chemistry. These evaporites are composed of halite mixed with other salts such as hanksite, burkeite, trona etc, but with a composition that varies considerably within the same grades. The laboratory isothermal extraction experiments indicate that various types of economic salts such as thenardite, anhydrite, mirabilite, burkeite, hanksite, gypsum, trona, halite, nahcolite, soda ash, and thermonatrite exist in the brine of Lake Katwe. In addition, the salts were found to crystallize in the following the sequence: sulfates, chlorides, and carbonates. A combination of results from the Pitzer’s ion-interaction model in PHREEQC and experimental data provided a valuable insight into the thermodynamic conditions of the brine and the sequence of salt precipitation during an isothermal evaporation. A good agreement between the theoretical and experimental results of the mineral solubilities in the lake brine systems was observed with an average deviation ranging between 8-28%. The understanding of the mineral solubility and sequence of salt precipitation from the brine helps to control its evolution during concentration. Hence, it will lead to an improved operating design scheme of the current extraction processes. The dissolution rate of the salt raw materials was found to increase with an increased temperature, agitation speed and to decrease with an increased particle size and solid-to-liquid ratio. Moreover, the Avrami model provided the best agreement with the obtained experimental data (R2 = 0.9127-0.9731). In addition, the dissolution process was found to be controlled by a diffusion mechanism, with an activation energy of 33.3 kJ/mol. Under natural field conditions, the evaporative-crystallization process at Lake Katwe is influenced by in-situ weather conditions. Especially, the depth of the brine layer in the salt pans and the temperature play a significant role on the brine evaporation rates. With the optimal use of solar energy, it was established that the brine evaporation flux can be speeded up in the salt pans, which could increase the production rates. Moreover, recrystallization can be a viable technique to improve the salt product purity. Overall, it is believed that the current work provides useful information on how to exploit the mineral salts from the salt lake resources in the future. / <p>QC 20151217</p>

Variable groundwater quality in complex aquifer-aquitard systems presents a challenge for sustainable groundwater development. In the Lower Murrumbidgee alluvial fan of the Murray-Darling Basin in semi arid inland Australia, shallow groundwater is saline (12000 &micro S/cm) and locally contaminated by nitrate. Deep fresh aquifers (150 &micro S/cm), developed as an irrigation water supply, were thought to be protected from downwards leakage by laterally extensive aquitards. However, hydrochemical sampling, augmented by historic data, revealed that aquifer salinisation (400 to 4000 &micro S/cm) had occurred at some sites to 50 m depth since the mid 1980s. Aquitard windows, landscape depositional features at a scale of 10s to 100s of metres which are rarely detected by conventional investigations, were proposed as conduits for rapid downwards leakage in stressed systems. Intensive research was conducted at the Tubbo site where downhole geophysical logging and minimally disturbed cores were used to describe a saline clayey silt to 15m depth, an indurated clayey sand and 2 deep deposits of hard clayey silt. Fracturing was inferred by the scale dependency of aquitard permeability (Kv 10E-11 to 10E-6 m/s). Lithological variation near the surface was delineated by electrical imaging which revealed a 40m wide aquitard window beneath a veneer of smectite clay. Intensive monitoring of groundwater pressures in six piezometers (23-96 m depth) near the Tubbo irrigation bore and two other peizometers upgradient, indicated that the indurated clayey sand formed an effective hydraulic barrier but the deep silty deposits were spatially discontinuous. Groundwater samples were collected before, three times during, and after the 1998-99 irrigation season. A large, but delayed TDS increase occurred in the shallow aquifer and small pulses of saline water were sustained in the middle aquifer but shortlived in the deep aquifer. Hydrochemical and isotopic data dC-13, dH-2, dO-18, C-14 and H-3) showed the middle aquifer mixing with the deep aquifer, though retaining the signature of a palaeowater. Hydrochemical changes were accounted for with PHREEQC inverse mass balance models for the shallow aquifer. Mixing of aquifer water with 20-70% saline porewater from the upper aquitard occurred, together with ion exchange and NaCl dissolution. Based on an axisymmetric radial FEFLOW model, 5-30% of the volume pumped was accounted for by vertical leakage from the middle aquifer. Leakage from the shallow aquifer was small but significant, as it allowed high salinity water to migrate. Permeability and compressible storage measurements (Ss 10E-5 to 10E-4 /m) were used to constrain model calibration, and to show that direct mixing occurred mainly via aquitard windows at depth, and between the shallow and middle aquifers via leaky boreholes. Fracture flow and aquifer-aquitard interaction by diffusion were of secondary importance.