Ce travail concerne l’étude de la corrosion et du frottement du revêtement CrNi-9,5%C déposé par projection thermique sur l’acier SAE 1010. Les études ont été réalisées sur les revêtements bruts de déposition et après traitements thermiques à l’argon dans une gamme de températures variant entre 600 et 900 °C. Il a été trouvé que le revêtement était principalement constitué de Cr3C2 et NiCr en rapport avec la température de traitement. Il a été montré que la réponse du matériau revêtu au cours d’essais potentio-dynamiques dans une solution à 3.5% NaCl dépend fortement de l’épaisseur du revêtement et de l’évolution de la microstructure au cours des traitements thermiques. Il a été ainsi montré que le traitement réalisé à 900oC sur le revêtement de 450 mm d’épaisseur permettait de réduire de 97% la densité de courant de corrosion. Cela résulte d’un phénomène de diffusion à l’état solide qui conduit à une meilleure cohésion inter-lamellaire empêchant la solution de corrosion de pénétrer. Le principal mécanisme de corrosion est galvanique et résulte de la différence remarquable entre les propriétés électrochimiques de la matrice et de celles des carbures existants dans le revêtement. Durant les essais de frottement sous une charge de 5 N du matériau revêtu contre une bille d’alumine, on observe un changement progressif du mécanisme de frottement passant d’adhésif/abrasif à abrasif, principalement, lorsque la température du traitement augmente. Toutefois, les constantes de frottement sont du même ordre de grandeur, environ 10-6 mm3/N.m, ce qui indique un comportement satisfaisant du point de vue tribologique. / The present work has been devoted to the study of the corrosion and wear behaviors of CrNi-9.5%C coatings deposited onto a SAE 1010 steel substrate by a vacuum plasma thermal spray process. The studies were carried out with the coatings both in the as-deposited condition and after heat treatment in argon, at temperatures varying between 600° to 900oC. It has been found that the coatings contained mainly Cr3C2 and NiCr, irrespective to the heat treatment temperature. It has been shown that the response of the coated systems during the potentio-dynamic tests in a 3.5% NaCl solution depends strongly, besides the coating thickness, on the microstructural coating evolution that occurs during heat treatment. It has been found that the heat treatment performed at 900oC, for the 450 mm coating thickness, allowed the reduction of approximately 97% of the corrosion current density, as a result of a solid-state diffusion phenomenon, which produced a higher lamellar cohesion, impeding the penetration of the corrosive solution. The main corrosion mechanism has been attributed to the galvanic corrosion phenomenon, as a consequence of the remarkable difference between the electrochemical properties of the matrix and those of the existing carbides in the coating. During the sliding tests, the coated systems rubbed against alumina under a 5 N normal load, indicated a progressive change in the mechanism, from a mixed adhesive and abrasive, to a predominant abrasive as the heat treatment temperature increases. However, the wear constants were found to be of the order of approximately of 10-6 mm3/N.m, indicating that a satisfactory behavior from the tribological point of view. / En el presente trabajo se estudio el comportamiento ante la corrosión y el desgaste de recubrimientos de CrNi9,5%C depositados sobre un acero SAE 1010 usando la técnica de proyección térmica de plasma al vacío (VPS). Los estudios se realizaron para los recubrimientos tanto en condición de cómo depositados como tratados térmicamente, en atmósfera de argón, a temperaturas de recocido de 600°, 800° y 900°C. Se encontró que el recubrimiento tiene Cr3C2 y NiCr como fases mayoritarias, independiente de la temperatura del tratamiento. La respuesta de los sistemas recubiertos durante los ensayos potencio-dinamicos en solución acuosa de 3.5% NaCl indicó una significativa dependencia tanto del espesor, como de los cambios microestructurales producidos en función de la temperatura de tratamiento térmico. Se determinó que el tratamiento térmico realizado a 900oC, para un recubrimiento de 450mm de espesor, ha permitido una reducción de aproximadamente un 97% del valor de la densidad de corriente, como resultado del aumento en la cohesión interlamelar obtenida debido al fenómeno de difusión en estado sólido, lo cual impide la penetración de la solución agresiva. En este caso, el mecanismo principal de daño se debe al proceso de corrosión galvánica, como consecuencia a la diferencia apreciable existente entre la naturaleza electroquímica de la matriz de Ni con respecto a los carburos. La respuesta del sistema recubierto contra alumina durante los ensayos de desgaste deslizante bajo 5N de carga normal indica que tiene lugar un cambio progresivo del mecanismo combinado de desgaste adhesivo y abrasivo hacia un mecanismo mayormente abrasivo, a medida que la temperatura del tratamiento termico aumenta. Sin embargo, las constantes de desgaste determinadas para todos los ensayos llevados a cabo se encontraron del orden de 10-6 mm3/N.m, indicando un comportamiento satisfactorio desde el punto de vista tribologico.

During ferrochrome (FeCr) production, three types of generic chromium (Cr) containing wastes are generated, i.e. slag, bag filter dust (BFD) and venturi sludge. The loss of these Cr units contributes significantly to the loss in revenue for FeCr producers. In this study, the liberation of Cr units was investigated utilising two case study waste materials, i.e. BFD from a semi-closed submerged arc furnace (SAF) operating on acid slag and the ultrafine fraction of slag (UFS) originating from a smelter operating with both open and closed SAFs on acid slag. A detailed material characterisation was conducted for both case study materials, which included particle size distribution, chemical composition, chemical surface composition and crystalline content. Cr liberation was achieved utilising two methods, i.e. aqueous ozonation and the advanced oxidation method. Various advanced oxidation processes could be applied. However, the advanced oxidation processes considered in this study was the use of gaseous ozone (O3) in combination with hydrogen peroxide (H2O2). Controlling parameters such as the influence of pH, ozonation contact time, waste material solid loading, gaseous O3 concentration and temperature on Cr liberation were investigated for the aqueous ozonation process. The influence of pH, volume H2O2 added and the method of H2O2 addition were considered for the advanced oxidation process. Results indicated that with aqueous ozonation, limited Cr liberation could be achieved. The maximum Cr liberation achieved was only 4.2% for BFD by varying the process controlling parameters. The Cr liberation for UFS was significantly lower than that of the BFD. The difference in the results for the two waste materials was attributed to the difference in characteristics of the materials. The Cr content in BFD was mostly related to chromite and/or altered chromite particles, while the Cr content of the UFS was mostly related to FeCr particles. It is possible that the Cr(III) present in the chromite and/or partially altered chromite might be more susceptible to oxidation to Cr(VI) than the metallic Cr(0) present in the FeCr. During ozonation, aqueous O3 spontaneously decomposes to form hydroxyl (OH•) radicals, which are very strong oxidants in water. The above-mentioned Cr liberation observed was related to the formation of the OH• radicals during the spontaneous decomposition of aqueous O3. This was indicated especially by enhanced Cr liberation at higher pH values, which was attributed to the acceleration of the spontaneous decomposition to OH• radicals at higher pH levels. The advanced oxidation method gave significantly higher Cr liberation results for both case study materials considered, achieving Cr liberations of more than 21%. The advance oxidation processes improve normal oxidation methods. In this study, the H2O2 used in combination with O3 enhanced the formation of the OH• radicals that are responsible for the oxidation of Cr. The Cr liberation levels achieved are possibly not high enough to be feasible for industrial purposes. However, a further investigation of the advanced oxidation process could optimise the process to yield even higher Cr liberation. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

During ferrochrome (FeCr) production, three types of generic chromium (Cr) containing wastes are generated, i.e. slag, bag filter dust (BFD) and venturi sludge. The loss of these Cr units contributes significantly to the loss in revenue for FeCr producers. In this study, the liberation of Cr units was investigated utilising two case study waste materials, i.e. BFD from a semi-closed submerged arc furnace (SAF) operating on acid slag and the ultrafine fraction of slag (UFS) originating from a smelter operating with both open and closed SAFs on acid slag. A detailed material characterisation was conducted for both case study materials, which included particle size distribution, chemical composition, chemical surface composition and crystalline content. Cr liberation was achieved utilising two methods, i.e. aqueous ozonation and the advanced oxidation method. Various advanced oxidation processes could be applied. However, the advanced oxidation processes considered in this study was the use of gaseous ozone (O3) in combination with hydrogen peroxide (H2O2). Controlling parameters such as the influence of pH, ozonation contact time, waste material solid loading, gaseous O3 concentration and temperature on Cr liberation were investigated for the aqueous ozonation process. The influence of pH, volume H2O2 added and the method of H2O2 addition were considered for the advanced oxidation process. Results indicated that with aqueous ozonation, limited Cr liberation could be achieved. The maximum Cr liberation achieved was only 4.2% for BFD by varying the process controlling parameters. The Cr liberation for UFS was significantly lower than that of the BFD. The difference in the results for the two waste materials was attributed to the difference in characteristics of the materials. The Cr content in BFD was mostly related to chromite and/or altered chromite particles, while the Cr content of the UFS was mostly related to FeCr particles. It is possible that the Cr(III) present in the chromite and/or partially altered chromite might be more susceptible to oxidation to Cr(VI) than the metallic Cr(0) present in the FeCr. During ozonation, aqueous O3 spontaneously decomposes to form hydroxyl (OH•) radicals, which are very strong oxidants in water. The above-mentioned Cr liberation observed was related to the formation of the OH• radicals during the spontaneous decomposition of aqueous O3. This was indicated especially by enhanced Cr liberation at higher pH values, which was attributed to the acceleration of the spontaneous decomposition to OH• radicals at higher pH levels. The advanced oxidation method gave significantly higher Cr liberation results for both case study materials considered, achieving Cr liberations of more than 21%. The advance oxidation processes improve normal oxidation methods. In this study, the H2O2 used in combination with O3 enhanced the formation of the OH• radicals that are responsible for the oxidation of Cr. The Cr liberation levels achieved are possibly not high enough to be feasible for industrial purposes. However, a further investigation of the advanced oxidation process could optimise the process to yield even higher Cr liberation. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Research Report Submitted in Partial Fulfilment of the Requirements for the Degree of Master of Science in Environmental Sciences Date: May 2016 / This study assesses the water quality status of the Hex River downstream of Kroondal Mine (KMS15, sampling point located downstream of Kroondal Mine) and the effects of mining activities (Kroondal Chrome Mine) on the water quality of the Hex River in Rustenburg, which is in the North West Province of South Africa. Potential pollutants were identified, quantified and their distribution was determined over seven years (2007 to 2013) along different sampling points upstream and downstream to the mine. Water quality-monitoring data was obtained from the mine. The surface and underground water was sampled on a monthly basis and analysed by Aquatico, (a water quality service provider of Kroondal Chrome Mine) at SANAS Accredited Testing Laboratory (No T0374). Data was collected for the Hex River and its tributary; the nearby discharge from Crocodile Farm and Farm Dam; as well as mine containment dams, slimes dams, run-off from the processing plant and water dams within the mine. Descriptive statistics (mean/average, minimum and Maximum) and box plots are used to explain the water quality at all sampling points. Water quality from sampling location points was compared against the Total Water Quality Guideline Range (TWQGR) for irrigation, livestock watering, ideal domestic use, aquatic ecosystem limits and the exemption permit issued to the Kroondal Chrome Mine by the Department of Water Affairs and Forestry (DWAF) in 2007, now Department of Water and Sanitation (DWS). The water quality of the Hex River, downstream of Kroondal, was described as neutral, alkaline, saline and very hard with a high pH, and a high concentration of Electric conductivity (EC), Total Dissolve Solids (TDS), Chlorine (Cl), Sulphate (SO4), Nitrate (NO3), Ammonium (NH3), Hardness (CaCO3) and Orthophosphate (PO4). Pollution sources and pathways were identified using the study area layout and by conducting an impact pathway analysis using annual descriptive statistical (annual mean or average values) of water quality tables generated by SAS enterprise 6.1 (a software used to analysed descriptive statistics of the mine water quality data) for a period 2007 until 2013, and box pots graphs showing monthly water-quality data for pH, EC, TDS, Cl, SO4, NO3, NH3, CaCO3 and PO4 at 15 monitoring localities between Kroondal Chrome Mine, the Hex River and its tributaries (Kroondal tributary and Sandspruit) over seven years. It was concluded that the surface/groundwater of the Kroondal Chrome Mine process – such as seepage from slimes dams, plant run-off and the vent shaft underground water dam – had an influence on the water quality of Hex River with regard to the discharge of pH modifying pollutants, EC, TDS, Cl, SO4, NO3, NH3, CaCO3 and PO4. Other pollution sources were discharge from Crocodile Farm and Hex River, as well as the Sandspruit upstream sources such as mining (platinum and chrome), industries’ municipal sewage treatment works, agricultural activities and informal settlements activities. Mine pollutants or constituents were identified as a unique example of the compound impact of weathering, hydrologic and anthropogenic processes such as the increased use of explosives containing NO3 and NH3 underground. The chemical compositions of surface water in the mine sampling location were strongly influenced by rock water in tractions, dissolution and dilution, as well as anthropogenic inputs. Key insights drawn from the study is that, cumulative impacts in the Hex River catchment present different issues, roles and responsibilities for industries, government/ regulators and community stakeholders. Practical and cooperative management of cumulative impacts by catchment stakeholders can benefit regional environments and communities of Rustenburg and the North West Province at large. This study demonstrates the usefulness of descriptive statistical techniques for analysis and interpretation of complex data sets, water quality status of the Hex River catchment, influence of the Kroondal Chrome Mine (KCM) waste water to the Hex River catchment, pollution sources and pathways from different activities around Hex River catchment. Best practice water management was recommended to form part of the Kroondal Chrome Mine environmental objects, target and management plan as well as the mine risk profile. Cumulative management dimensions, approaches and/or methods were recommended for all Hex River catchment stakeholders including Department of Water and Sanitation (DWS), mines, farmers, industries and disadvantage communities along the catchment.

Na área de Química, uma das linhas mais tradicionais de pesquisa envolve o estudo de formação de complexos. Estes trabalhos são realizados de modo sistemático em nossos laboratórios, geralmente envolvendo cátions de metais de transição com vários ligantes (haletos, pseudo-haletos e carboxilatos). A intensa coloração desenvolvida pela maioria dessas reações de complexação, entre um metal e um pseudo-haleto, tem motivado o desenvolvimento de novos métodos espectrofotométricos para a determinação de íons em amostras reais. Espera-se que o crômio(III), da mesma forma que outros metais de transição, como o ferro, níquel e cobalto, forme complexos com o pseudo-haleto denominado azida ou azoteto (N3-). Desta forma, dando continuidade a esta linha de pesquisa, este trabalho teve como objetivo otimizar as condições experimentais para o sistema crômio(III)/azoteto. Diversos parâmetros como acidez, concentração de ligante, natureza e concentração de solvente, bem como o efeito da temperatura, foram investigados. Reunidas as melhores condições (otimização), montou-se o método analítico que possibilita a determinação do metal. As condições ideais empregadas foram: concentração analítica de ligante e ácido perclórico de 493 e 12,0 mmol L-1, respectivamente, numa temperatura de 25ºC, em meio aquoso. Para a determinação no ultravioleta, o tempo de espera para cada medida foi de 1 hora, enquanto que na região do visível, foi de apenas 30 minutos. Os máximos de absorção ocorreram em torno de 646, 480 e 287 nm, com coeficientes de absortividade molar médios de 184±1, 157±1 e (1,481±0,008) 104 L mol-1 cm-1, respectivamente. As condições estabelecidas foram promissoras, permitindo uma boa repetitividade nas regiões do visível e ultravioleta. Para o método desenvolvido, os íons mais interferentes na região do visível foram: Fe3+, Co2+ e Cu2+ e, na região do ultravioleta, foram HC8H4O4-, Fe3+, Cu2+ e Hg2+. Por meio de um sistema com duas equações, a determinação simultânea de crômio e ferro mostrou-se possível e com erros dentro dos limites analiticamente aceitáveis. Sem a utilização do sistema de equações, verificou-se ainda a possibilidade de se determinar crômio diretamente, mesmo na presença de ferro, no comprimento de onda de 646,5 nm, com um erro menor que 5%, desde que a concentração de ferro não ultrapasse 4 mg L-1. Aplicações analíticas para o método proposto foram testadas em dois suplementos alimentares contendo crômio. Os resultados foram comparados e mostraram-se concordantes com os da técnica de espectrometria de absorção atômica, para o suplemento contendo crômio quelato. Para o suplemento alimentar contendo picolinato de crômio, houve uma discordância dos resultados, indicando a existência de interferentes da matriz que não puderam ser eliminados. Um teste com uma amostra sintética de crômio mostrou um erro de cerca de 1,0% para o método proposto. Em condições ideais, e com um controle dos interferentes presentes, o método proposto mostra-se preciso, simples e barato. Considerando valores de absorbância entre 0,2 e 0,8 (faixa ideal), pode-se determinar o metal nos intervalos de 1,27 a 5,09 mmol L-1 a 480,5 nm, de 1,09 a 4,35 mmol L-1 a 646,5 nm e, finalmente, entre 0,702 a 2,81 mg L-1 no ultravioleta (287 nm). / In Chemistry, the study of complexes formation is one of the most traditional research lines. These studies are done under systematic manners in our laboratories, usually involving metallic transition cations with several ligands (halides, pseudohalides and carboxylates). The intense coloration developed by the major part of those complexation reactions, between a metal and a pseudohalide, has encouraged the development of new spectrophotometric methods for determination of ions in real samples. Conforming others transition metals, (iron, nickel and cobalt), which form complexes with the pseudohalide azide (N3-), we tried to observe the same behavior to chromium(III). Continuing this research line, this work had as principal objectives optimizes the experimental conditions for the chromium(III)/azide system. Several parameters were investigated as acidity, ligand concentration, nature and solvent concentration, as well as temperature effect for optimization of experimental conditions. Gathering all these conditions, the analytical methods were tested for the metal determination. The ideal conditions employed were: analytical ligand concentration and perchloric acid of 493 and 12.0 mmol L-l respectively, at 25 °C, in aqueous medium. For the studies in the ultraviolet region, the contact time before the measures was one hour, while for studies in the visible band measures were made after 30 minutes. The wavelengths of maximum absorption were encountered at 646, 480 and 287 nm, with molar absorptivity coefficients (mean) of 184±1, 157±1 and (1.481±0,008) 104 L mol-1 cm-1, respectively. The established conditions were promising, allowing a good precision in the visible and ultraviolet region. For the developed method, the more interfering ions on visible band were: Fe3+, Co2+ and Cu2+ and, on the ultraviolet band, were HC8H4O4-, Fe3+, Cu2+ and Hg2+. Through a system of two equations, the simultaneous determination of chromium and iron ions was possible with errors within the tolerance range. Without the simultaneous equations system, it was verified directly the possibility of chromium determination in the presence of iron, at a wavelength of 646.5 nm, with an error smaller than 5%, since the concentration of iron doesn’t exceed 4 mg L-l. In this proposed method, analytical applications were tested for two alimentary supplements containing chromium. The results were compared, being concordant with those of atomic absorption technique for the supplement containing chromium chelate, while for the alimentary supplement containing chromium picolinate, the results were in disagreement with the results, indicating the existence of matrix interferences which could not be eliminated. A test with a synthetic sample of chromium had an error of about 1.0% for the proposed method. Under ideal conditions, and with some control of possible interfering, the proposed method can be precise, accurate, simple and cheap. Considering the absorbance values between 0.2 and 0.8 (ideal range), the metal can be determined from 1.27 to 5.09 mmol L-l in 480 nm; 1.09 to 4.35 mmol L-l in 646 nm and, finally, from 0.702 to 2.81 mg L-l at 287 nm (ultraviolet).

Les systèmes ultramafiques sont souvent synonymes de fortes teneurs en chrome (Cr) dans des roches, qui est naturellement lixivié vers les eaux de surface et souterraines. En raison de cet enrichissement naturel, les zones ultramafiques font souvent l’objet d’extractions massives. Le processus minier inclut l'exploitation et les activités d'enrichissement, dans lesquelles la grande quantité de résidus produits riches en métaux, tels que les gangues et les terrils, sont stockés à l’air libre. Ces processus peuvent considérablement augmenter les teneurs en Cr trivalent (Cr (III)) et hexavalent (Cr (VI)) disséminé dans l'environnement. Ce dernier (Cr (VI)), est connu pour être fortement soluble dans l'eau, biodisponible et toxique. Ce travail de thèse a porté sur i) la zone d’exploitation minière du nickel de Barro Alto (BA, Etat du Goiás, Brésil); ii) la zone d'exploitation minière historique de chromite de Cromínia (CA, Etat du Goiás, Brésil) et iii) une exploitation minière actuelle dans la vallée de Sukinda (Odisha, l'Inde). Le principal objectif de ces travaux est l'identification de l'impact d'activités minières (extraction du nickel et du chrome) sur la mobilité de Cr et sa disponibilité dans des zones ultramafiques, à l'aide des techniques isotopiques. Les compartiments chimiquement et isotopiquement échangeables de Cr(VI) (ECr (VI)) les plus hauts ont été mesurés dans des échantillons de minerai à BA, où l'enrichissement en isotopes légers de Cr (-0.76 à -0.16 ‰) a été attribué à la perte de Cr isotopiquement lourd et échangeable Cr(VI) pendant l’altération. Des valeurs étonnamment lourdes de δ53Cr ont été aussi trouvées dans des minerais saprolitiques à BA et dans des sols affectés par l’extraction à CA, jusqu’à +3.9 ‰ alors qu’ils étaient fortement enrichis en Cr(III). Les causes principales ont été attribuées à l'existence de chromite hydrothermale à CA et/ou à l’altération naturelle suivie par la réduction de Cr(VI), induisant la reprécipitation de Cr mobile et isotopiquement lourd. Le chrome était présent dans les lixiviats des échantillons de minerais saprolitiques et lateritiques de BA, sous la forme de Cr(VI) isotopiquement lourd (jusqu’à +4.84 ‰), en cohérence avec le Cr échangeable (ECr(VI)) (jusqu’à +4.37 ‰). Ces valeurs étaient dans la même gamme de compositions isotopiques que celles mesurées dans les eaux douces de surface (ruisseaux et réservoirs) situés dans la zone ultramafique. Ces résultats impliquent que Cr est principalement disséminé sous sa forme toxique Cr(VI), dont la disponibilité augmente depuis i) le profil de sol ii) les minerais et iii) les résidus miniers. Lors de tests de bioaltération réalisés sur les terrils avec Acidithiobacillus thiooxidans (pH~2) ou Pseudomonas putida (pH~9), Cr a été initialement extrait sous sa forme Cr(VI) puis réduit en Cr (III). Dans les expériences avec A. thiooxidans, la réduction du chrome est dû à l’important pouvoir réducteur d'une série de composés soufrés, tandis que P. putida utilise probablement pour la réduction des chromates une variété d'accepteurs d’électrons. Ces mécanismes, de même que l’augmentation de la concentration en matière organique et la carbonatation minérale, pourraient expliquer la plus faible concentration en Cr(VI) échangeable dans les terrils âgés par rapport aux terrils récents. Par la technique d’échange isotopique, la contribution des SPM au transport du chrome échangeable, ainsi que l’impact des colloïdes contenant des phases porteuses de Cr sur la mesure de ce compartiment échangeable associé aux SPM (EWCr) a été mise en évidence. Les plus grosses particules (> 0.2 µm) jouent un rôle prépondérant dans la zone impactée par l’activité minière, tandis que le chrome est principalement associé aux colloïdes (1 kDa-500 kDa) dans la zone vierge. La présence de colloïdes organiques et inorganiques contenant du chrome non-échangeable induit une surestimation de la valeur de EWCr, qui peut être corrigée par le biais d’un scénario du pire / Ultramafic systems are often synonym of high chromium (Cr) content in rocks, which is naturally leached to surface and groundwater. Due to this natural enrichment, ultramafic areas are massively mined. The mining process includes exploitation and beneficiation activities, in which large amount of metal-rich residues, such as overburden, waste rock and tailings, stored in open air, are produced. These processes may considerably increase the amount of both trivalent (Cr(III)) and hexavalent chromium (Cr(VI)) released to the environment. The later (Cr(VI)), known to be highly soluble in water, bioavailable and toxic. Within these mining residues, many chemical and biological processes may take place, which will control Cr speciation, mobility and availability. The present work was conducted on i) the nickel exploitation and metallurgic area of Barro Alto (BA, Goiás state, Brazil); ii) the antique chromite exploitation area of Cromínia (CA, Goiás State, Brazil) and iii) the current chromite mine in the Sukinda valley (Odisha, India). The main focus of this research is the identification of the impact of mining activities (nickel and chromium mining) on Cr mobility and availability in ultramafic environments, through the use of isotopic techniques. The chemically and isotopically exchangeable pools of Cr(VI) (ECr(VI)) were higher in BA ore samples, where the enrichment in light chromium isotopes (-0.76 to -0.16‰) was attributed to the loose of isotopically heavy and exchangeable Cr(VI) during weathering. Astonishingly, heavy δ53Cr values were also found in saprolitic ores in BA and in mining-affected soils in CA up to +3.9‰, strongly enriched in Cr(III). The main causes have been attributed to the existence of hydrothermal chromite in CA and/or to natural weathering followed by Cr(VI) reduction that induces reprecipitation of mobile and isotopically heavy Cr. In such a mining context, the accelerated weathering would play an important role in this process. Chromium in the leachate, of BA lateritic and saprolitic ores samples, was present as Cr(VI) isotopically enriched in heavy isotopes (up to +4.84‰), consistently with the exchangeable Cr (ECr(VI)) (up to +4.37‰). These values were in the same range as isotopic compositions measured in the fresh waters (streams and ponds) in the ultramafic area. These results imply that Cr is mainly released as the toxic Cr(VI) specie, which availability increases from i) the soil profile to ii) the ores and iii) the mining residues. This also suggests that δ53Cr could be used as a tracer of Cr leaching in environmental studies in the dissolved phase.In bioleaching tests on tailings with Acidithiobacillus thiooxidans (pH ~ 2) or Pseudomonas putida (pH ~ 9), Cr was initially extracted as Cr(VI) and later reduced to Cr(III). In the experiments with A. thiooxidans the Cr reduction is due to the production of a series of sulfur compounds with high reducing power, while for P. putida probably uses a variety of electron acceptor for chromate reduction, enhanced by the presence of extracellular polymeric substances. Those mechanisms together with the increase of natural organic matter (NOM) and mineral carbonation, could explain the lower exchangeable pool of Cr(VI) in stockpiled chromite tailings compared to fresh tailings. Through the use of isotopic exchange, the contribution of SPM to the transport of exchangeable chromium and the impact of colloids containing Cr-bearing phases on the determination of the exchangeable pool of Cr associated to SPM (EWCr) was highlighted. Larger particles (>0.2 μm) were dominant in the impacted area, while chromium was mainly associated with colloids (1 kDa–500 kDa) in the pristine area. The presence of organic and inorganic colloids containing non-exchangeable chromium induces an overestimation of the EWCr values, which can be over-come thanks to a worst-case scenario correction

Les effets du dichromate et de l'aluminium sur le transport d'électrons photosynthétique et les mécanismes de dissipation d'énergie des Photosystèmes II et l ont été évalués quand différentes espèces d'algues ont été exposées aux métaux. Les propriétés structurelles du photosystème II ont été étudiées par immunobuvardage de type Western blot et par chromatographie liquide à haute performance. Les propriétés fonctionnelles des Photosystème II et l ont été déterminées par la mesure de la cinétique de fluorescence chlorophylienne et les changements d'absorbance à 830 nm, respectivement. Pour l'étude des effets du dichromate, l'algue verte Chlamydomonas reinhardtii et des mutants de C. reinhardtii déficients du cycle des xanthophylles ont été utilisés comme modèle biologique. Pour l'aluminium, l'étude des effets de la forme ionique libre A1³⁺ a été effectuée dans un milieu acide (pH 3,0) en utilisant deux espèces d'algues tolérantes à de bas pH, Euglena gracilis et Chlamydomonas acidophila. Nous avons conclu que les rendements photochimiques maximals des Photosystèmes II et l sont diminués par les effets du dichromate. L'inhibition de la photochimie par le dichromate cause une diminution de la dissipation d'énergie par la voie photochimique du Photosystème II et une augmentation de la dissipation d'énergie sous forme non-photochimique non-régulée. L'absence d'un cycle des xanthophylles fonctionnel rend l'appareil photosynthétique plus sensible à la photoinhibition induite par la toxicité du dichromate. Pour les effets de l'aluminium sur la photochimie du Photosystème II, la dissipation d'énergie par les voies photochimiques et non-photochimiques est affectée différemment chez des espèces d'algues présentant des résistances différentes aux effets des métaux. Cette inhibition va entrainer une diminution de la production d'ATP et de NADPH menant à une diminution de la production de biomasse chez les algues sensible à l'aluminium. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Algues, Aluminium, Chlamydomonas acidophila, Chlamydomonas reinhardtii, Dichromate, Euglena gracilis, Métaux, Photosynthèse, Photosystème l, Photosystème II, Toxicologie.

Reproduction de : Thèse de doctorat : Science et génie des matériaux : Toulouse, INPT : 2004. / Titre provenant de l'écran-titre. Bibliogr. 207 réf.

Thèse de doctorat : Sciences et ingénierie des matériaux : Vandoeuvre-les-Nancy, INPL : 2006. / Titre provenant de l'écran-titre. Bibliogr.

Este trabalho tem por objetivo analisar a produção do adubo obtido a partir do resíduo da raspa do couro bovino, curtido ao cromo (III), bem como avaliar a viabilidade de ganhos ambientais e energéticos que ao adubo se atribui. A metodologia usada foi estabelecida a partir de uma revisão bibliográfica sobre as alternativas para o gerenciamento de resíduo sólido da indústria de beneficiamento do couro e no estudo do efeito do cromo no meio ambiente, fundamentada na teoria das restrições no aspecto ambiental e energético. Para a implementação da parte experimental e produção do adubo da raspa do couro bovino hidrolisado foi montado um protótipo composto de três componentes: caldeira, autoclave e secador, considerando-se os parâmetros termodinâmicos: temperatura de 403 a 433 K e a pressão de 700 a 800 kPa. No decorrer desse processo automaticamente controlado, calcularam-se as incertezas das medidas efetuadas nos parâmetros do adubo e do solo, da pressão e a produção de vapor gerado pela caldeira, bem como nas medições dos equipamentos, autoclave e secador com suas respectivas densidades, obtendo-se a relação de massa e volume. As amostras foram analisadas para verificar os teores máximos e mínimos dos macro e micronutrientes, assim como seus elementos de maior relevância. Foram avaliadas as características fisico-químicas e agronômicas do produto, o balanço de massa e a energia da produção do adubo. A experiência aplicada com o adubo na cultura do milho foi realizada em casa de vegetação, com delineamento inteiramente casualizado com quatro repetições. Os tratamentos constituíram-se a partir da utilização de dois tipos de adubo de apara de couro (resíduo italiano e resíduo brasileiro) e sulfato de amônio como fonte de nitrogênio em três doses. Foram utilizados dois tipos de solo: Latossolo Férrico e Latossolo Vermelho Amarelo. A produção desse adubo será implantada industrialmente para a redução do impacto ambiental provocado pelas indústrias de beneficiamento do couro e também para a agricultura, uma vez que esse adubo é um produto rico em nitrogênio. / The purpose of this study is to analyze the production of fertilizer obtained from cow leather shavings cured with Chrome (III), as well as the viability for this fertilizer to contribute for environmental and energetic gains. The methodology was based on a review of bibliographic material of the alternatives for management of solid waste from the leather industry and on a study of the effect of chrome on the environment based on the theory of restrictions, with concern for environmental and energy factors. The experimental portion of the study involved the assemblage of a prototype composed of three pieces of equipment: a boiler, an autoclave and a dryer, for the production of fertilizer from hydrolyzed cow leather shavings. In relation to the thermodynamic process, the temperature was maintained at 403 and 430 K and pressure at 700 and 800 kPa. During this automatically controlled process, the uncertainties in the measurements conducted in the parameters of fertilizer and soil were calculated of pressure and production of steam generated by the boiler and the readings of the autoclave and dryer equipment were calculated in addition to their respective densities, to obtain the ratio of mass and volume. The samples were analyzed to determine the maximum and minimum amounts of the macro and micro nutrients and their most important elements. The physical-chemical and agronomic characteristics of the product were evaluated as well as the balance of mass and energy of the fertilizer production. The experiment conducted with fertilizer from cow leather applied to a corn crop, was conducted in a vegetable greenhouse, with completely arbitrary delineation and four repetitions. The treatment involved the use of two types of fertilizer made from leather shavings (Italian residue and Brazilian residue) and ammonia sulfate as a nitrogen source in three doses. Two types of soil were used: Ferric Latosol and Red-Yellow Latosol. The fertilizer can be produced industrially to reduce the environmental impact caused by leather manufacturing companies and to agriculture because it is rich in nitrogen.