Dans cette thèse, nous avons déterminé les mécanismes qui régissent l'efficacité des particules de fer zérovalent (ZVI) dans la dépollution des sols et des eaux souterraines. Dans les milieux contaminés par des polluants accepteurs d'électrons, le ZVI est injecté in situ sous forme de suspensions de particules micro et/ou nanométriques. La première étude a porté sur la caractérisation de poudres industrielles et de particules synthétisées au laboratoire à partir de thé vert. Afin de comparer la réactivité de l'ensemble des particules, un test en milieu fermé a été mis en oeuvre avec une solution de nitrate. Ce test a permis de différencier les particules en mettant en évidence des mécanismes réactionnels et des cinétiques de réduction qui dépendent du type de poudre utilisé. La seconde étude a porté sur la dégradation du chrome hexavalent (dans une matrice sol et eau) en combinant le ZVI à du thiosulfate de sodium. Les résultats ont été probants et ont mené au dimensionnement d'un pilote sur un site de Soléo Services. Enfin, deux cas de remédiation de sites pollués aux solvants chlorés ont été étudiés. Des expériences de laboratoire ont été menées pour expliquer l'impact des conditions opératoires sur l'efficacité du traitement / This thesis aims at a better understanding of mechanisms governing the efficiency of zerovalent iron (ZVI) particles in soil and groundwater remediation. In these processes ZVI is injected in situ as micro and/or nanoparticles slurry in areas contaminated by electron acceptor pollutants. At first, we characterized industrial powders and particles synthetized with green tea in the laboratory. In order to compare the reactivity of all the particles, a batch test has been carried out with nitrate solution. Differences in pathways and kinetic reduction have been exhibited. Secondly, we combined ZVI with sodium thiosulfate to investigate hexavalent chromium degradation (soil and water matrices). The results are conclusive and were used to design a pilot on a Soléo Services site.Finally, remediation cases of sites contaminated by chlorinated solvents have been investigated. Lab experiments have been run to explain the influence of operating conditions on the treatment efficacy

Au cours des dernières décennies, un contexte alarmant de déclin des paramètres du sperme etd’accroissement constant des pathologies génitales masculines a été décrit dans de nombreuxpays industrialisés.Notre travail évalue dans un premier temps l’évolution des paramètres spermatiques chez11 330 hommes ayant consulté pour infertilité conjugale au Centre de ProcréationMédicalement Assistée du CHU de Marseille entre 1988 et 2007. Les données ont étérecueillies de manière rétrospective et analysées par régression linéaire multi-variée afin detenir compte de l’effet lié à l’âge. Nous montrons une diminution significative des principauxparamètres du sperme: concentration en spermatozoïdes (-1.4% par an), numération totale enspermatozoïdes (-1.5% par an), mobilité progressive rapide (-5.6% par an) et morphologienormale (-1.9% par an). Les possibles biais de selection ont été discutés. L’effet del’environnement sur notre fonction de reproduction est l’une des hypothèses principalesévoquées pour expliquer ce phénomène.Nous montrons ensuite comment un modèle de culture de tubes séminifères de rat en chambrebicamérale, couplé à des techniques d’étude de la méiose en immunocytochimie peut êtreutilisé comme nouvel outil de reprotoxicologie. Nous décrivons tout d’abord avec l’anticorpsanti-SCP3 la prophase de première division méiotique chez le rat in-vivo et nous validons lemodèle de culture par comparaison entre les résultats des cellules obtenues in vivo et ceux descellules obtenues ex-vivo. Nous montrons ensuite grâce à ce système l’impact du ChromeHexavalent et du Cadmium sur la méiose du rat. Ces 2 métaux lourds, largement présent dansnotre environnement, peuvent être responsables d’atteintes importantes des cellulesméiotiques, y compris à de faibles doses pouvant correspondre à celles retrouvées chez desindividus exposés dans leur vie quotidienne et/ou professionnelle. / In recent decades, an alarming decline of sperm parameters and a constant increase in malegenital diseases has been described in many industrialized countries.In a first time, our study evaluates the evolution of sperm parameters in 11 330 menconsulting for infertility of their couple in the Reproduction Biology Laboratory of anUniversity Hospital in Marseilles between 1988 and 2007. Data were collected retrospectivelyand analyzed by multivariate linear regression to take into account the effect related to age.We show a significant decrease of the main sperm parameters: sperm concentration (-1.4%per year), total sperm count (-1.5% per year), rapid progressive motility (-5.6% per year) andnormal morphology (-1.9 % per year). Possible selection bias were discussed. The effect ofenvironment on our reproductive function is one of the main hypothesis to explain thisphenomenon.Secondly, we show how a rat seminiferous tubule culture in a bicameral chamber system,coupled with study of meiosis by immunocytochemistry can be used as a new tool ofreprotoxicology. We first describe with an anti-SCP3 antibody the first prophase of ratmeiosis and we validate the model of culture by comparing the results obtained on cellsobtained after in vivo spermatogenesis and those of cells obtained ex-vivo. Then, we showusing this system, the impact of hexavalent chromium and cadmium on rat meiosis. These twoheavy metals, widely present in our environment, may cause substantial impairment ofmeiotic cells, including low doses which can fit with those found in individuals exposed intheir personnal life and / or occupational training.

L’utilisation du chrome hexavalent pour le traitement de surface des matériaux de l’aéronautique est en passe d’être interdite par la réglementation REACH. Dans l’objectif de trouver une solution alternative, PROTEC industrie et le CEA travaillent en collaboration sur le développement d’une nouvelle solution sans-chrome permettant de remplacer les revêtements classiquement utilisés. Le travail de thèse présenté dans ce manuscrit s’inscrit dans le cadre du laboratoire commun MESTREL financé par le programme ANR Labcom, réunissant les deux entités citées ci-dessus. La solution proposée est basée sur le greffage d’un revêtement organique inspiré de la chimie des sels de diazoniums à la surface de l’Al2024-T3, alliage de référence du secteur aéronautique. Cette thèse vise initialement à déterminer les conditions pour lesquelles les propriétés du film greffé se rapprochent le plus de celles de son prédécesseur. Pour cela, des caractérisations spectroscopiques et électrochimiques des films greffés ont été réalisées. Les protocoles de microscopies électrochimiques développés ont notamment permis de sonder le niveau de passivation de la couche. La haute porosité du film greffé, nous a ainsi permis d’imaginer et de développer un système bicouche innovant combinant les propriétés anticorrosion des solutions actuelles aux hautes propriétés d’adhérence du film organique fonctionnalisé. En parallèle, une méthode de dépôt hors-cuve a été développée pour générer un gain économique important et faciliter le traitement de pièces de grandes dimensions. / The use of hexavalent chromium for anticorrosion surface treatments in aeronautics field will soon be banned by the REACH reglementation. Looking for an innovative solution, PROTEC industry and the CEA research center work in collaboration with the aim of developing a chromium free replacement treatment, which can substitute current solution and give competitive results both in adhesion and corrosion protection. The thesis project presented in this manuscript is part of a common laboratory named MESTREL, including the two entities. The proposed solution is based on the grafting of a polymeric film inspired by the diazonium chemistry on an Al2024-T3 surface, reference alloy in the aeronautic field. The principal objective of the thesis is to determinate the best conditions of grafting, -giving similar properties to chromium treatment. To this end, spectroscopic and electrochemical characterizations have been performed. Electrochemical Microscopy protocols are developed to assess the passivation properties of the film The high porosity of the film has allowed to develop a new innovative bilayer process combining anticorrosive properties of current solution and adhesion properties of the functionnal coating. At the same time, an out-of-tank deposition technique is developed. The goal is to enable economic benefits and facilitate treatment of very large aeronautic pieces.

The production of ferrochrome (FeCr) from chromite ore is a reducing process, whereby the Cr(III) and Fe(II) in the ore are reduced to metallic chromium (Cr) and iron (Fe) in the final product. FeCr is mostly used for the production of stainless steel, which is a vital alloy in modern society. It is, however, impossible to exclude oxygen completely from all the high temperature steps during the production process and very small amounts of Cr(VI) are therefore formed, although not intended. The formed Cr(VI) is mostly associated with the off-gas of the high temperature processes, which are cleaned before it is released into the atmosphere by means of venturi scrubbers or bag filter systems. Certain Cr(VI) species are regarded as carcinogenic, with specifically airborne exposure to these Cr(VI) species being associated with cancer of the respiratory system. FeCr smelter facilities generate three main types of waste materials, i.e. slag, venturi sludge and bag filter dust (BFD). Most of the Cr in the waste materials consists mostly of Cr(III). However, BFD generated during the cleaning of the off-gas of open/semi-closed furnaces, could contain more significant levels of Cr(VI) than the slag and sludge. The aim of this study was to determine the solubility of different Cr(VI) species present in BFDs. This would allow that the Cr(VI) in BFD is categorised as water soluble Cr(VI), sparingly soluble and insoluble Cr(VI). These solubility categories can then be related to groups of Cr(VI) compounds, therefore taking the first step in better characterisation of Cr(VI) present in BFD. Four different BFD samples from FeCr producers in South Africa were characterised in detail. Analytical methods such as scanning electron microscope (SEM), SEM with energy-dispersive X-ray spectroscopy (SEM-EDS), particle size analysis, trace metal analysis with inductively coupled plasma with a mass spectrometer detector (ICP-MS) and Cr(VI) analysis with ion chromatography (IC) were utilised in order to characterise and categorise the samples. The results indicated that more Cr(VI) leached with an increase in pH. This was in contrast with the trend for most heavy metals. This was also an indication that not only soluble, but also sparingly- and insoluble Cr(VI) compounds occur in the BFD samples evaluated. Further analysis showed that approximately one third of the Cr(VI) species was insoluble and the remainder consisted of sparingly insoluble and soluble Cr(VI) compounds. The most significant finding was that the current leaching procedures applied by FeCr producers, prior to the chemical reduction of Cr(VI), do not effectively extract the sparingly water insoluble compounds. This results in Cr(VI) leaching from waste facilities at later stages, even if seemingly effective Cr(VI) treatment was applied. Therefore, it should be considered as an extremely important future perspective to develop economically feasible Cr(VI) extraction procedures that will ensure complete extraction of sparing water soluble Cr(VI) compounds together with the water soluble fraction, prior to chemical reduction of Cr(VI) and subsequent storage of the residue on a waste facility. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2015

The production of ferrochrome (FeCr) from chromite ore is a reducing process, whereby the Cr(III) and Fe(II) in the ore are reduced to metallic chromium (Cr) and iron (Fe) in the final product. FeCr is mostly used for the production of stainless steel, which is a vital alloy in modern society. It is, however, impossible to exclude oxygen completely from all the high temperature steps during the production process and very small amounts of Cr(VI) are therefore formed, although not intended. The formed Cr(VI) is mostly associated with the off-gas of the high temperature processes, which are cleaned before it is released into the atmosphere by means of venturi scrubbers or bag filter systems. Certain Cr(VI) species are regarded as carcinogenic, with specifically airborne exposure to these Cr(VI) species being associated with cancer of the respiratory system. FeCr smelter facilities generate three main types of waste materials, i.e. slag, venturi sludge and bag filter dust (BFD). Most of the Cr in the waste materials consists mostly of Cr(III). However, BFD generated during the cleaning of the off-gas of open/semi-closed furnaces, could contain more significant levels of Cr(VI) than the slag and sludge. The aim of this study was to determine the solubility of different Cr(VI) species present in BFDs. This would allow that the Cr(VI) in BFD is categorised as water soluble Cr(VI), sparingly soluble and insoluble Cr(VI). These solubility categories can then be related to groups of Cr(VI) compounds, therefore taking the first step in better characterisation of Cr(VI) present in BFD. Four different BFD samples from FeCr producers in South Africa were characterised in detail. Analytical methods such as scanning electron microscope (SEM), SEM with energy-dispersive X-ray spectroscopy (SEM-EDS), particle size analysis, trace metal analysis with inductively coupled plasma with a mass spectrometer detector (ICP-MS) and Cr(VI) analysis with ion chromatography (IC) were utilised in order to characterise and categorise the samples. The results indicated that more Cr(VI) leached with an increase in pH. This was in contrast with the trend for most heavy metals. This was also an indication that not only soluble, but also sparingly- and insoluble Cr(VI) compounds occur in the BFD samples evaluated. Further analysis showed that approximately one third of the Cr(VI) species was insoluble and the remainder consisted of sparingly insoluble and soluble Cr(VI) compounds. The most significant finding was that the current leaching procedures applied by FeCr producers, prior to the chemical reduction of Cr(VI), do not effectively extract the sparingly water insoluble compounds. This results in Cr(VI) leaching from waste facilities at later stages, even if seemingly effective Cr(VI) treatment was applied. Therefore, it should be considered as an extremely important future perspective to develop economically feasible Cr(VI) extraction procedures that will ensure complete extraction of sparing water soluble Cr(VI) compounds together with the water soluble fraction, prior to chemical reduction of Cr(VI) and subsequent storage of the residue on a waste facility. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2015

Esta tese apresenta um estudo original das propriedades estruturais e eletrônicas dos nanotubos de carbono de parede simples (NTCPS) por meio de complexos de titânio e a possibilidade de adsorção e redução do cromo hexavalente Cr (VI) utilizando a teoria da densidade funcional. Cr (VI) é um dos principais poluentes ambientais, sua remoção apresenta várias dificuldades, e resulta em poluição ambiental, causando problemas de saúde. A adsorção de Cr (VI) foi investigada a partir das moléculas de cromato e dicromato no semicondutor NTCPS funcionalizado com complexos de TiO2, TiO4H4 e Ti2O6H4. Os resultados sugerem que os NTCPS funcionalizados são grandes candidatos à adsorção de Cr (VI). Além disso, as estruturas de banda eletrônica mudaram na região próxima à energia de Fermi das bandas de valência e de condução para os NTCPS pristino e funcionalizados com sistemas de cromo. Após adsorção de Cr (VI) nos sistemas, observa-se a formação de moléculas com menor toxicidade e atividade carcinogênica o que não ocorreu sem a presença dos nanotubos. / This thesis presents an original study of the structural and electronic properties of doped single-walled carbon nanotubes (SWCNT) through titanium complexes and the possibility of adsorption and reduction of hexavalent chromium Cr(VI) using density functional theory. Cr(VI) is one of the major environment pollutants, its removal presents several difficulties, and it results in industrial pollution, causing health problems. The adsorption of Cr(VI) was investigated from the chromate and dichromate molecules in semiconductor SWCNT functionalized with TiO2, TiO4H4 and Ti2O6H4 complexes. The results suggest that the functionalized SWCNT are great candidates to adsorb Cr(VI). In addition, the electronic band structures changed in the region near the Fermi energy of the valence and conduction bands for the pristine and functionalized SWCNT with chromium systems. After adsorption of Cr(VI) in the systems, the formation of molecules with less toxicity and carcinogenic activity is observed, which did not occur without the presence of the nanotubes.nanotubes.

O homem cada vez mais interfere e contamina o meio ambiente. Acidentes envolvendo o derramamento de substâncias químicas no solo tem sido cada vez mais frequente, gerando preocupação aos órgãos ambientais, visto que essa contaminação promove riscos à saúde humana, o que torna necessário intervenções que impulsionam o aprimoramento de técnicas de remediação. Dentre essas técnicas, a utilização de nanopartículas, em especial as nanopartículas de ferro de valência zero, têm se destacado para uso em remediação devido ao baixo custo de produção, elevada reatividade para contaminantes orgânicos e inorgânicos e baixa toxicidade. Para contaminantes inorgânicos não se tem definidas as melhores relações de nano ferro em relação ao contaminante e também o comportamento no solo. Dessa forma o objetivo do trabalho foi avaliar o transporte e a aplicação de nanopartículas de ferro para remediação de um solo residual argiloso, contaminado com cromo hexavalente. O trabalho foi dividido em três fases, em que na primeira foi avaliado a melhor concentração, tipo de nano ferro e determinação do parâmetro de filtração através do uso do ensaio em coluna de parede flexível com corpos de prova indeformados. Na segunda fase, a partir dos resultados da primeira, foram realizados ensaios de remediação do solo contaminado em bancada para se definir as melhores relações entre o nano ferro e o contaminante. E na terceira fase foram realizados ensaios com corpos de prova deformados e contaminados (800mg/Kg de Cr(VI)), para se avaliar a influência da pressão de injeção na eficiência do processo de redução do Cr (VI) Para realização dos ensaios de coluna, foi utilizado um solo residual argiloso, moldando-se corpos de prova de 5 cm de diâmetro e 5 cm de altura, utilizados na fase 1 e 3. Para avaliação do transporte e determinação do parâmetro de mobilidade de filtração foram utilizados 3 tipos de nanopartículas de ferro com e sem estabilizantes, nas concentrações de (1g/L, 4g/L, 7g/L e 10g/L), avaliando mudança na condutividade hidráulica do solo e concentração retida no meio. O parâmetro de filtração foi determinado utilizando-se o modelo analítico proposto por Reddy et al., (2014). Os resultados demonstram que as nanopartículas apresentam uma alta reatividade, porém baixa mobilidade para concentrações mais elevadas, tendo influência também o uso de estabilizantes. Os melhores valores obtidos nesta fase foram para concentrações de 1g/L e 4g/L, tanto para a mobilidade, quanto para a mudança na condutividade do meio O parâmetro de filtração, variou de 10-3s-1, para o nano ferro com surfactante e 10-2s-1, para o nano ferro sem surfactante. Para a remediação do cromo hexavalente se observou uma eficiência de 87% para a relação de 1000mg de Fe° para 23 mg de Cr(VI). Utilizando 4g/L na referida relação agente redutor e contaminante, em coluna se observou que maiores valores de pressão aumentam a eficiência da redução, porém acabam favorecendo a colmatação dos vazios do solo pelas nanopartículas. Utilizando uma pressão de 100Kpa, se obteve um valor de redução máximo próximo de 50%, muito menor que aqueles em bancada. Assim o uso de nanopartículas de ferro é eficiente para remediação de um solo argiloso contaminado com cromo (VI) ex situ, pois o contato do contaminante com o agente redutor se torna mais fácil pela melhor homogeneização do solo. As nanopartículas com surfactante apresentam melhor movimentação no solo e menor valor de filtração, sendo indicado o uso de uma concentração de até 4 g/L para não alterar as características naturais do meio. / The human being is constantly interfering and contaminating the environment. Accidents evolving the spill of chemical and toxic substances in the soil has been more frequently nowadays. This topic became a concern to the environmental regulation departments around the world, since this contaminations promote risks to the human health. In this way the necessity for improvements in the remediation techniques is required. Among the techniques, the use of nanoparticles zero valent iron has being highlight for use in remediation process due it's low cost for production, low toxicity and high reactivity for organic and inorganic contaminants. For inorganic contaminants the best nanoiron/contaminant ration and also the behavior in the soil have not been defined. Thus, the objective of this work was to evaluate the transport and the application of iron nanoparticles for the remediation of residual clay soil contaminated with hexavalent chromium The work is divided in three phases: The first evaluated the best concentration, type of nanoiron and determination of the filtration parameter through the use of the flexible wall column test with undeformed specimens. In the second phase, from the results of the first phase remediation tests were carried out on the contaminated soil in the workbench to define the best relations between the nanoiron and the contaminant. In the third phase, tests with deformed and contaminated test specimens (800 mg / kg Cr (VI)) were carried out to evaluate the influence of the injection pressure on the Cr (VI) reduction efficiency. To perform the column tests, a residual clay soil was used, molding test pieces 5 cm in diameter and 5 cm in height, used in phase 1 and 3. For evaluation of the transport and determination of the parameter of mobility of filtration (1 g / L, 4 g / L, 7 g / L and 10 g / L) were used, evaluating changes in soil hydraulic conductivity and the concentration retained in the system. The filtration parameter was determined using the analytical model proposed by Reddy et al., (2014).The results demonstrate that the nanoparticles have a high reactivity, but low mobility at higher concentrations, and also the use of stabilizers. The best values obtained in this phase were for concentrations of 1g/L and 4 g/L, both for mobility and for the change in conductivity of the system The filtration parameter ranged from 10-3s-1, for the nanoiron with surfactant and 10-2s-1, to the nanoiron without surfactant. For the remediation of the hexavalent chromium, an efficiency of 87% was observed for the ratio of 1000mg Fe ° to 23mg Cr (VI). By using 4g / L in the referred reducing agent and contaminant ratio, it was observed in column that higher pressure values increase the reduction efficiency, but they end up favoring the filling of the voids of the soil by the nanoparticles. Using a pressure of 100Kpa, a maximum reduction value of around 50% was obtained, much lower than those in bench. Thus, the use of iron nanoparticles is efficient for the remediation of a clay soil contaminated with chromium (VI) in deformed samples, since the contact of the contaminant with the reducing agent is made easier by better homogenization of the soil. The nanoparticles with surfactant present better a better movement in the soil and a lower filtration value, being indicated the use of a concentration of up to 4 g/l in order not to alter the natural characteristics of the system.

Avaliação ambiental, biológica e médica foram realizadas em 17 cromadores de 9 galvânicas do Estado de São Paulo, sendo cinco de cromo decorativo e quatro de cromo duro. O ar do ambiente de trabalho foi coletado individual e estacionariamente durante a semana de trabalho. Amostras de urina dos cromadores, foram coletadas no início e final do período de trabalho, encontrando-se uma correlação entre cromo urinário final e cromo no ar de 0,5. Usou-se a Absorção Atômica com Forno de Grafite GFAAS para determinar-se a concentração de cromo no ar ( Cr-ar) e cromo urinário ( Cr-U). O cromo hexavalente Cr (VI) foi extraído dos filtros de membrana de PVC com porosidade 5 µm com o tampão ácido acético/acetato de sódio, com a complexação do Cr (VI) feita por APDC. O complexo foi extraído com MIK. O limite de detecção foi de 1,1 µg/L. O Cr-U foi analisado diretamente por GFAAS com o limite de detecção 0,50 µg/L utilizando-se como modificador de matriz, nitrato de magnésio hexahidratado. Sem o modificador de matriz o limite de detecção foi de 0,14 µg/L. As concentrações de Cr (VI) no ar nas galvânicas de cromo decorativo variaram de 0,3 a 64,6 µg/m3 e nas de cromo duro variaram de 4,1 a 72,8 µg/m3 , mostrando a inadequação de alguns sistemas de exaustão. 60% dos cromadores das galvânicas de cromo duro tinham o septo nasal perfurado e todos os cromadores avaliados clinicamente tinham alterações nas vias aéreas superiores. O Cr-Uf que é utilizado como indicador biológico para compostos solúveis de cromo hexavalente, em muitos casos seus valores deram menores que o Cr-Ui, necessitando-se de estudos mais aprofundados quanto a esse aspecto, para evitar que o trabalhador possa ser prejudicado com resultados nem sempre condizentes com sua exposição. / Environmental, biological and medical evaluations was made in 17th workers of 9 chrome plating plants of the State of Sao Paulo, being 5 of decorative chrome plating and 4 of hard chrome plating. Environmental air samples were individual and stationarily collected during are week. Worker\'s urine samples were collected in the starting and in the end of the working period and it was obtained a correlation of 0,5 between the final urine chromium content and chromium air content. Graphite Furnace Atomic Absorption Spectrometry GFAAS was used for the determination of the chromium levels in the air (Cr-air) and in the urine(Cr-U). The Cr (VI) was extrated of the PVC membrane filters with an acetic acid/sodium acetate buffer and the Cr (VI) was isolated with APDC/MIBK. The detection limit obtained was 1,1 µg/L. The Cr-U was analised directly by GFAAS and the detection limit obtained was 0,50 µg/L, using magnesium Nitrate as matrix modifier and 0,14 µg/L without matrix modifier. The Cr (VI) concentration in the air was in the range of 0,3 to 64,6 µg/m3 in the decorative chrome plating and of 4,1 to 72,8 µg/m3 in the hard chrome plating, showing that the exhaust systems were inadequate. 60% of the workers of the hard chrome plating had perforation in the nasal cartilage and alI workers clinically evaluated presented alterations in the upper respiratory airway. The Cr-Uf that is used as biological indicator for the Cr(VI) soluble compounds, in many cases presented lower levels that the Cr-Ui showing that it is necessary more studies about this subject. In order to present inadequated results concerning the worker\'s exposition.

abstract: Mineral weathering and industrial activities cause elevated concentration of hexavalent chromium (Cr(VI)) in groundwater, and this poses potential health concern (>10 ppb) to southwestern USA. The conversion of Cr(VI) to Cr(III) – a fairly soluble and non-toxic form at typical pH of groundwater is an effective method to control the mobility and carcinogenic effects of Cr(VI). In-situ chemical reduction using SnCl2 was investigated to initiate this redox process using jar testing with buffered ultrapure water and native Arizona groundwater spiked with varying Cr(VI) concentrations. Cr(VI) transformation by SnCl2 is super rapid (<60 seconds) and depends upon the molar dosage of Sn(II) to Cr(VI). Cr(VI) removal improved significantly at higher pH while was independent on Cr(VI) initial concentration and dissolved oxygen (DO) level. Co-existing oxyanions (As and W) competed with Cr(VI) for SnCl2 oxidation and adsorption sites of formed precipitates, thus resulted in lower Cr(VI) removal in the challenge water. SnCl2 reagent grade and commercial grade behaved similarly when freshly prepared, but the reducing strength of the commercial product decreased by 50% over a week after exposing to atmosphere. Equilibrium modeling with Visual MINTEQ suggested redox potential < 400 mV to reach Cr(VI) treatment goal of 10 ppb. Kinetics of Cr(VI) reduction was simulated via the rate expression: r=-k[H+]-0.25[Sn2+]0.5[Cr2O72-]3 with k = 0.146 uM-2.25s-1, which correlated consistently with experimental data under different pH and SnCl2 doses. These results proved SnCl2 reductive treatment is a simple and highly effective method to treat Cr(VI) in groundwater. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2019

In this thesis work, a high grade chromite concentrate obtained from PinarbaSi, Kayseri region of Turkey was reacted with sulfuric acid solution to determine the optimum conditions of leaching of chromite ores. Conventional methods for producing chromium are still valid in industry. The main process in production includes soda melting and taking it into solution in the form of chemical compounds such as sodium dichromate. Three and six valence states of chromium have importance in production. Trivalent chromium, chrome ore or chromite have no harmful effects. However, compounds of hexavalent chromium show toxic, irritating and corrosive action to people and environment. In the mentioned conventional method, main products consist of hexavalent chromium compounds. In this study, only trivalent chromium remained in the leach solution and did not change to hexavalent state. Obtained product after leaching was chromium(III) sulfate. The maximum extraction of chromium in the absence of perchloric acid was 94.1 % under the conditions of 175 &deg / C, 6 hours and 84.6 wt % sulfuric acid. The maximum extraction of chromium in the presence of perchloric acid was 98.7 % under the conditions of 175 &deg / C, 2 hours, 84.6 wt % sulfuric acid and &frac12 / perchloric acid / chromite ratio. The latter one was also the highest recovery value obtained during the experiments. Moreover, in none of the analyzed samples, appreciable amounts of hexavalent chromium was found during analyses.