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This dissertation includes theoretical and applied components that address the effect of coatings on rates of mineral reactions that occur in acid mine drainage (AMD) environments. The two major projects investigated how diffusion-limited transport of reactants through pore spaces in coatings on mineral grains affects the reaction rate of the underlying mineral. The first project considered the growth of gypsum coatings on the surface of dissolving limestone in anoxic limestone drains (ALD), which reduces the neutralization rate of the dissolving limestone and the subsequent effectiveness of this treatment. The second project investigated the conditions where iron oxyhydroxide coatings form on oxidizing pyrite and the potential strategies to prevent "runaway" AMD by reducing the rate of acid production to the point that the acid can be neutralized by the surrounding rocks. In both studies, experiments were conducted to measure reaction rates for the underlying minerals, as coatings grew thicker. These experimental data were fit to a diffusion model to estimate diffusion coefficients of reactants through pore spaces in coatings. These models are extrapolated to longer times to predict the behavior of the coated grains under field conditions. The experimental results indicate that management practices can be improved for ALDs and mine waste piles. For example, supersaturation with respect to gypsum, leading to coating formation, can be avoided by diluting the ALD feed solution or by replacing limestone with dolomite. AMD can be prevented if the rate of alkalinity addition to mine waste piles is faster than acid is produced by pyrite oxidation. The diffusion model developed in this study predicts when iron oxyhydroxide coatings will become thick enough that alkalinity from the surroundings is sufficient to neutralize acid produced by coated pyrite oxidation and additional alkalinity is no longer required. / Ph. D.

Les amas de pyrite de Niccioleta sont encaissés dans des lentilles d'anhydrite interstratifiées dans des micaschistes probablement Siluro-Devoniens. Certains caractères chimiques du milieu évaporitique (Mg et B) sont bien conservés par le métamorphisme épizonal (400-450°C, 2-3 kbar). Les minéralisations et les skarns, certains dérivant de l'anhydrite, ont pour origine une intense métasomatose de percolation par des solutions ferrifères à environ 475°C et 1 kbar. Ces phénomènes hydrothermaux sont liés à l'alimentation par des solutions salines, d'origine marine, d'un système géothermique (anté-Larderello) au Miocène supérieur Les conditions physicochimiques, les mécanismes des transformations et les compositions des solutions ont été précisés et quantifiés à l'aide d'une modélisation faisant appel aux données thermodynamiques disponibles pour les solutions salines à haute température et à haute pression. Le modèle représente une contribution à la connaissance des minéralisations hydrothermales et métasomatiques, et à celle des mécanismes minéralisateurs induits par les circulations de solutions aqueuses chlorurées.

The ability of RNA bases to self-assemble into larger structures is an important research area relevant to the origins of life. In the RNA helix the bases are arranged on a sugar-phosphate carcass but it has been suggested that the initial ordering could form on a flat surface. This thesis is an attempt to establish experimentally whether the complementary RNA bases, adenine and uracil, have the ability to self-assemble into large ordered structures when adsorbed on metal and mineral surfaces. The Au (111) surface was chosen as a preferred substrate as it is flat, relatively free of defects, chemically inert and reconstructs in a characteristic pattern of corrugation lines, which provide a reference for crystallographic directions. Six of the molecular phases shown were observed for the first time with molecular resolution and the possible two-dimensional arrangements of adenine and uracil molecules for these phases are proposed. The pure adenine and pure uracil structures have chiral unit cells and in the case of pure uracil alternating monochiral domains within the polychiral islands are created. Well-ordered intricate uracil-adenine bimolecular networks were also observed. The self-assembly of both uracil and adenine appears to be weakly influenced by the surface crystallography. The (100) surface of the mineral pyrite (FeS₂) was chosen as the alternative substrate as it is the most common face that occurs naturally in pyrite crystals. The experiments show the formation of small adenine and uracil crystals at the terrace edges. Neither uracil nor adenine were observed to form a monolayer on the surface of the terraces. The results of the experiments described in this thesis are very interesting in terms of establishing the possible mechanisms for creating regular chiral molecular networks and provide a useful insight into the role of surfaces in the processes of self-assembly of RNA bases.

L’objectif de cette thèse était d’utiliser les propriétés magnétiques des roches (paléomagnétisme, anisotropie de la susceptibilité magnétique (ASM) et différentes techniques d’analyse de la minéralogie magnétique), complété par d’autres méthodes classiques (microscopie pétrographique et électronique, goniométrie de texture, spectroscopie Raman, statistiques d’orientation préférentielle de forme et cathodoluminescence) pour aborder des thématiques récurrentes relatives à la formation des gisements métalliques. Cette approche a été appliquée à deux problèmes métallogéniques : (i) le traçage de la circulation du fluide ayant produit la métasomatose ferrifère des carbonates de La Florida (Cantabrie, Nord de l’Espagne) et la mise en place des minéralisations à Pb–Zn associées (MVT) ; et (ii) l’étude de la structuration des gossans et le décryptage de l’histoire de l'altération des amas sulfurés de la Ceinture Pyriteuse Sud Ibérique (CPSI, Andalousie, Sud de l’Espagne). Dans le premier cas, nous avons pu démontrer expérimentalement que la circulation des fluides produit une anisotropie de forme dont on peut retrouver l’empreinte dans le signal de l’ASM. Cette propriété nous a permis de définir une direction NE–SW de circulation du fluide métasomatique à La Florida. Dans le deuxième cas, le couplage entre l’ASM et le paléomagnétisme nous a permis de définir deux fabriques magnétiques dans les gossans primaires ; (i) une fabrique, d’âge ancien, de « compaction », caractéristique des parties supérieures des gossans, probablement associé au réchauffement de l’Oligocène supérieur et (ii) une fabrique de « mélange », plus récente, localisée dans les parties inférieures des gossans, formée probablement lors de l’événement messinien. La fabrique de « compaction » refléterait donc une altération plus mâture comparée à la fabrique de « mélange ». Par ailleurs, l’analyse de la minéralogie magnétique des gossans et des terrasses de la CPSI a révélé la présence « inhabituelle » de la pyrrhotite, une présence que nous avons attribué à l’activité de bactéries sulfato-réductrices dans des microdomaines réducteurs, disséminés dans un environnement globalement oxydant et très acide. / The purpose of this PhD thesis was to use the magnetic properties of rocks (paleomagnetism, anisotropy of the magnetic susceptibility (ASM) and various techniques of magnetic mineralogy analysis), supplemented by some traditional methods (petrographic and electronic microscopy, texture goniometry, Raman spectroscopy, shape preferential orientation statistics and cathodoluminescence) to study the formation of metal deposits. This approach was applied to two metallogenic studies: (i) the track of fluid circulation that produced the iron-bearing metasomatism of the carbonates of La Florida mining district (Cantabria, Northern Spain), and the Pb–Zn mineralization deposits (MVT); and (ii) the study of the internal structures of the gossans and the alteration history of the massive sulphides of the Iberian Pyrite Belt (IPB, Andalusia, Southern Spain). In the first case, we showed experimentally that the fluid circulation produces a shape anisotropy, recorded in the form of a magnetic anisotropy. This property enabled us to define a NE–SW direction of the circulation of the metasomatic fluid in the La Florida district mining. In the second case, the coupling of AMS and paleomagnetism enabled us to define two magnetic fabrics in the primary gossans; (i) a “compaction” fabric in the upper parts of the gossans, associated to an old age, and probably caused by the Late Oligocene Warming Event, and (ii) a “mixture” fabric, more recent, located in the lower parts of the gossans and probably formed during the Messinian Salinity Crisis. The “compaction” fabric would reflect an alteration stage more mature than the “mixture” fabric. In addition, the magnetic mineralogical analysis of the gossans and the associated terraces of the CPSI revealed the “curious” occurrence of the pyrrhotite, which was attributed to the sulfato-reducing bacteria activity in some reducing microdomains, disseminated in an environment globally oxidant and highly acid.

Que ce soit à des fins spéculatives ou pour financer des conflits armés, une grande opacité entoure les filières des concentrés de matières premières minérales dont la demande ne cesse d'augmenter. Compte-tenu de l'éloignement entre les sites primaires d'extraction et les sites de production de produits finis, il est difficile d'identifier l'origine de ces produits. Dans un souci de traçabilité des concentrés, l'établissement d'une carte d'identité du minerai permettrait le contrôle des échanges dans l'industrie minérale. Le problème peut être posé en termes d'inversion: remonter au minerai d'origine en étudiant le produit vendu. Deux stades doivent être distingués: 1) la caractérisation du minerai brut et 2) la « perte de mémoire » des caractéristiques du tout-venant au cours du traitement minéralurgique. Les paramètres retenus sont la composition minéralogique, l'identification de microfaciès caractéristiques des minéraux cibles, la pseudo-succession paragénétique, le contenu et la distribution en éléments mineurs de minéraux cibles. Les minéraux cibles retenus sont la pyrite pour son ubiquité, la sphalérite car elle est susceptible d'incorporer une grande variété d'éléments mineurs, éventuellement valorisants ainsi que la chalcopyrite car elle est souvent liée aux deux autres minéraux. La comparaison de la composition chimique des phases minérales est effectuée en calculant la distance de Kolmogorov-Smirnov et de Colin-White. Des tests ont été réalisés sur les gîtes de type amas sulfuré volcanogène. Ils ont montré que les caractéristiques retenues permettaient de distinguer les pyrites, les sphalérites et les chalcopyrites de deux gisements de la province Sud-Ibérique (IPB), de sept gisements de la province d’Oural et du fumeur noir actuel de Rainbow. Les cartes d’identité obtenues permettent de discriminer les différents sites (IPB, Oural et Rainbow) et les gisements d’une même province. Les paramètres minéralogiques et microtexturaux ont également été suivis au cours du traitement minéralurgique de la mine de Neves Corvo. Pour une chaîne de traitement donnée, le paramètre « perte de mémoire » est une estimation de l'erreur commise lors de l'inversion, mais aussi une façon de caractériser une succession d'opérations minéralurgiques. / The demand in mineral resources is increasing rapidly, but there is a lack of transparency in the trade of concentrated raw mineral materials because of speculation and involvement in the financing of armed conflicts. Because of the distance between the primary extraction and the final production sites it is difficult to check the origin of such products. An identity card is required for minerals which would permit trading in the mineral industry to be verified and ensure traceability of concentrates. This problem may be considered as an inversion process: studying the products sold to identify the original ore. Two steps may be distinguished: 1) the characterization of the raw ore and 2) the “memory loss” of the crude ore characteristics during its mineral processing. The discriminant parameters are mineralogical composition, identification of textural microfacies of the target minerals, pseudo-paragenetic sequence, and the contents and distribution of minor elements of target minerals. The selected target minerals are pyrite, for its ubiquity, sphalerite for its ability to host numerous discriminant and potentially valuable minor elements in its lattice and chalcopyrite for its proximity with the two others minerals. The Kolmogorov-Smirnov distance and the Colin-White test are used to compare the chemical composition of the three target minerals. The application to Volcanic Massive Sulfide ore deposit showed that the selected characteristics permit to distinguish pyrite, sphalerite and chalcopyrite between two ore deposits in the Iberian Pyrite Belt province, seven ore deposits from the Urals province and a currently active Rainbow blacksmoker. From the established identity cards ore deposits from different provinces may be discriminated. Identity cards can also distinguish different deposits in the same province. Evolution of mineralogical and microtextural parameters was studied during the mineral processing of the Neves Corvo mine. For a given processing chain, the “memory loss” parameter is an estimate of the errors introduced in the inversion from concentrate to the original ore and can be used to characterize a given processing flow.

This thesis examines sulfide oxidation in 4 physically and mineralogically diverse acid sulfate soil (ASS) materials collected from coastal floodplain sites in north-eastern New South Wales. The aim of this study is to gain further understanding of the process of sulfide oxidation in ASS materials, which will allow improved and more effective management strategies to be applied to these materials. The process of sulfide oxidation was examined using laboratory incubation experiments. The oxidation of pyrite was the primary cause of initial acidification of the ASS materials studied. Although the acid volatile sulfur fraction increased in concentration by an order of magnitude over the initial 8 days of incubation, the subsequent oxidation of this fraction did not result in substantial acidification. Sulfate (SO42-) was the dominant sulfur species produced from sulfide oxidation, however, water-soluble SO42- was a poor indicator of the extent of sulfide oxidation. The sulfoxyanion intermediates thiosulfate (S2O32-) and tetrathionate(S4O62-) were only detected in the early stages of incubation, and their relative abundance appeared to be pH dependent. The diminishing presence of these 2 sulfur species as oxidation progressed was indicative that ferric iron (Fe3+) and bacterial catalysis were driving the oxidation processes. The rate of sulfide oxidation, and consequent rate of acidification, was highly dependent on the soil pH and oxygen availability. Accelerated sulfide oxidation was only observed at low pH (i.e. pH < 4.0) when oxygen availability was not limited. The application of sub-optimal amounts of neutralising agents prevented severe soil acidification in the short-term (i.e. up to 2 months), but had little effect on decreasing the rate of sulfide oxidation and acidification in the long-term. Sub-optimal amounts of CaCO3 accelerated sulfide oxidation and acidification of the peaty marcasitic ASS material resulting in elevated soluble Fe and Al concentrations. For some of the ASS materials, sub-optimal applications of seawater-neutralised bauxite refinery residue (SNBRR) also resulted in elevated soluble Al concentrations. The response of partially-oxidised ASS materials to the exclusion of oxygen was variable. The rate of sulfide oxidation, acidification and the production of soluble oxidation products generally decreased markedly when subjected to anoxia. However, especially in highly acidic ASS materials (i.e. pH < 3.5), sulfide oxidation and acidification generally occurred (albeit at much slower rates), most probably due to oxidation by Fe3+. Rapid sulfide re-formation occurred in the peat ASS material that had been oxidised for 63 days, with 0.47% reduced inorganic sulfur (SCR) formed over 60 days of anoxia. Biogeochemical sulfide formation consumes acidity, however, sulfide re-formation was ineffective in reversing acidification under the conditions of this experiment. The peroxide oxidation methods examined were method dependent and substantially underestimated peroxide oxidisable sulfur, sulfidic acidity and net acidity. The precipitation of jarosite during peroxide oxidation was a major factor contributing to the underestimation in these ASS materials. Clay mineral dissolution may contribute towards the underestimation of both sulfidic and net acidity using peroxide oxidation methods. The atmospheric loss of sulfur and acidity was also identified as a possible additional interference. This study has shown that the initial pH of an ASS material is a useful indicator (additional to those already used) of the potential environmental hazard of an ASS material when oxygen is expected to be non-limiting, such as when ASS materials are excavated and stockpiled. The recommended action criteria need to be reassessed as the data indicate that the current criteria are conservative for alkaline and neutral ASS materials, but should be lowered for all acidic ASS materials (i.e. pH < 5.5) to 0.03% sulfide regardless of texture. Alternative strategies are necessary for the management of ASS materials that are subject to oxidation when the addition of optimal rates of neutralising materials cannot be ensured. The treatment of sites containing actual ASS materials by management strategies that rely on oxygen exclusion need to be accompanied by strategies that include either acid neutralisation or containment in order to reduce acid export from the site. The peroxide oxidation methods examined were subject to substantial interferences, and consequently are unable to reliably provide accurate measurements of the reduced inorganic sulfur fraction, sulfidic acidity, and net acidity in ASS materials.

A new approach to the discovery of high absorbing semiconductors for solar cells was taken by working under a set of design principles and taking a systemic methodology. Three transition metal chalcogenides at varying states of development were evaluated within this framework. Iron pyrite (FeS���) is well known to demonstrate excellent absorption, but the coexistence with metallic iron sulfides was found to disrupt its semiconducting properties. Manganese diselenide (MnSe���), a material heavily researched for its magnetic properties, is proposed as a high absorbing alternative to iron pyrite that lacks destructive impurity phases. For the first time, a MnSe��� thin film was synthesized and the optical properties were characterized. Finally, CuTaS���, a known but never characterized material, is also proposed as a high absorbing semiconductor based on the design principles and experimental results. / Graduation date: 2013

Ce travail présente les résultats dune étude menée sur la dépollution des tailings de Kipushi (RD Congo) par la valorisation des métaux contenus. Ce sont les rejets anciens dun concentrateur. Ils contiennent de la pyrite et des sulfures résiduels de cuivre et de zinc. Du fait du stockage à lair libre pendant plus de 40 ans, ces sulfures sont partiellement oxydés. Ces tailings présentent une certaine instabilité physique et chimique qui est à la base de la dégradation des milieux environnants les plus proches (rivières naturelles, sols sous-jacents, nappes souterraines, etc.) suite à la migration et à la dispersion dETM (éléments traces métalliques) tels que larsenic, le cadmium, le cobalt, le cuivre, le plomb, le zinc, Linstabilité physique se manifeste par des phénomènes dérosion par les eaux de ruissellement pendant la saison des pluies et par des phénomènes dérosion éolienne pendant la saison sèche. Leur stockage en surface saccompagne dune lente oxydation des sulfures avec production deaux acides qui dans leur neutralisation par la dolomie présente dans les rejets et celle des formations géologiques sur lesquelles ils reposent, contribuent à laccroissement des réseaux karstiques, au durcissement des eaux des nappes et parfois provoquent des phénomènes daffaissements, voire même deffondrements de terrains. Pour réduire les impacts environnementaux majeurs de ces tailings, nous avons effectué ce travail en recherchant un traitement qui combinerait dune part la dépollution par la réduction des ETM et du soufre sulfure et dautre part la valorisation du cuivre et du zinc contenus. Les deux voies qui ont été testées commencent par une flottation globale de tous les sulfures (désulfuration environnementale). Les résultats de nos expérimentations montrent quon peut obtenir un nouveau rejet de flottation dans lequel une majeure partie des ETM facilement mobilisables dans lenvironnement est éliminée ainsi que presque tout le soufre (95 %), ce qui écarte donc tout risque de DMA. Nous avons démontré que pour atteindre ces résultats, il suffit de ne broyer que la fraction la moins libérée de dimension supérieure à 75 μm et dactiver par un prétraitement à pH 6 les sulfures dont la collection par le xanthate est sinon inhibée par laltération superficielle avec formation doxydes ou par les complexes cyanométalliques formés lors de la flottation avec dépression de la pyrite par les ions cyanures ayant produit les tailings étudiés. Nous avons tenté denrichir le concentré global de la désulfuration environnementale par une flottation différentielle avec dépression de la pyrite à pH 11. Cet enrichissement est difficile à réaliser à cause de la finesse des grains et des caractéristiques minéralogiques du concentré global qui contient beaucoup de grains mixtes. Les essais ont alors porté sur la lixiviation chimique acide oxydante (avec Fe3+) et la lixiviation bactérienne du concentré global après son enrichissement en cuivre et en zinc dans un circuit de flottation avec deux finissages. Une étude approfondie des paramètres qui influencent le mécanisme des biolixiviations a été effectuée et les conditions de leur mise en pratique industrielle ont été déterminées. La lixiviation chimique doit être réalisée à des températures élevées (98°C) pour fragiliser la couche de passivation de soufre élémentaire qui se forme à la surface des grains et qui tend à freiner la diffusion des réactifs et des produits de la réaction. Par contre, la biolixiviation donne de bons résultats à température modérée. Elle est techniquement applicable aux tailings de Kipushi. Nous proposons de réaliser la biolixiviation en deux étapes successives, la première avec des bactéries thermophiles modérées (55°C) à une densité de pulpe de 15 % (poids/volume) et la deuxième avec des bactéries mésophiles (33°C) sur des pulpes à 4 % de solides. Dans ces conditions, on réussit à produire deux solutions de lixiviation (PLS : pregnant leach solution), lune à 3 g/l de cuivre et 7 g/l de zinc et lautre à 0,2 g/l de cuivre et 7 g/l de zinc, quon purifie et concentre facilement dans un circuit dextraction par solvant. Lextraction par solvant du cuivre est réalisée avec le LIX984N directement sans modifier le pH des PLS (1,7-1,9) et le zinc est extrait par le D2EHPA après précipitation dions Fe3+ du raffinat cuivre à des pH entre 3 et 3,5. On obtient ainsi des solutions aqueuses de cuivre et de zinc convenant aux installations délectrolyse industrielle. Nous avons proposé un schéma de traitement des tailings de Kipushi qui pourrait fonctionner pendant 20 ans avec les 36 684 600 tonnes sèches de rejets stockés à la digue 1 et 2. Le traitement produirait un nouveau rejet plus ou moins dépollué qui représente 66 % en poids des tailings traités, 80 950 tonnes de cuivre et 631 750 tonnes de zinc. The work present results from research study devoted to de-pollution of the stocked tailings in Kipushi (DR Congo) via valorization of the metals contained in the tailings. Pyrite and copper and zinc sulfides present the principal mineral composition of the laid down tailings from the concentrator. Due to the fact that the sulphides have been stocked during more than 40 years, they are partly oxidized. These tailings present a constant risk from physical instability and spillage, which reflects in the deterioration of the surrounding environment (rivers, soil, underground water table, etc). Moreover the migration and dispersion of TEM (trace metal elements) such as arsenic, cadmium, cobalt, copper, lead, zinc, is leading to erosion and mine run-off phenomena during wet season and generate air-borne particles during dry season. The stocking of the tailings is accompanied by slow oxidation of the sulfides with concomitant production of acidic waters which are neutralized by the dolomite present, which finally reflects in hardening of the underground waters and even provoke soil subsidence and ground collapses. In order to reduce the major environmental impacts from the tailings, we have performed a study for their post-treatment which encompasses the cleanup from one side and the reduction of TEMs and sulphur on the other side. Apart from this, the aim was to economically extract the remaining non-ferrous metals, notably Zn and Cu. The approach which has been chosen to accomplish this task has been to re-float by bulk flotation the majority of the sulphides and thus by elimination of the nearly total sulphur (95 %) to eliminate the risk of AMD generation and metals immobilization. We have shown that this is possible to be achieved via grinding the 75 μm oversize fraction in order to facilitate minerals liberation, following by subsequent activation at pH 6 before flotation. Without this pretreatment step, the flotation by use of xanthates is impossible, due to the surface coatings of the grains, which are either of oxide nature or are cyano-metallic complexes formed from the use of potassium cyanide as pyrite depressor in the flotation circuit practiced at the times when the concentrator was operational. The further attempts to produce monometallic flotation concentrates via selective flotation with depression of the pyrite at pH 11 have been unsuccessful due to reasons of complex mineralogy. Therefore chemical (Fe3+) and bacterial leaching of the bulk concentrate enriched in Cu and Zn via two cleaning flotation circuits have been envisaged. The technological parameters for the both leaching options have been studied and the mechanisms of the bioleaching taking place have been proposed in view industrial scale up of the process. It has been found that the chemical leaching should be conducted at very high temperatures (98°C) in order to breakdown the passivation coatings (sulphur). In contrast, the bioleaching has shown good results at moderate temperatures. It has been found that bioleaching is technically feasible to the tailings of Kipushi. We have suggested a bioleaching in two successive stages: the first one with moderate thermophilic microorganisms (55 °C) at pulp density 15 % (weight / volume) and the second one with mesophilic microorganisms (33 °C) at pulp density of 4 % (w/v). Under these conditions two principal PLSs (pregnant leach solution) can be obtained - a one with 3 g/l Cu and 7 g/ l Zn and other one in 0.2 g/l Cu and 7 g/l Zn. The both PLSs could be further processed via solvent extraction. The solvent extraction of Cu is accomplished with LIX984N without modifying the pH of the PLS (1.7 - 1.9), while Zn is extracted using a D2EHPA at pH between 3 and 3,5, after elimination of the iron from the copper raffinate. The aqueous solutions thus obtained are suitable for Cu and Zn electrowinning. Finally, a flow sheet for re-treatment of the Kipushi tailings which could operate during 20 years has been proposed. It could treat about 37 mln tones of dry tailings stocked in the tailing ponds 1 and 2. Preliminary calculations estimate that such treatment would produce new tailings with low environmental risk which will represent about 66 % in weight of the original treated tailings and will yield about 80 950 tons of Cu and 631 750 tons of Zn.