The oxidation of refractory gold concentrates containing arsenopyrite and pyrite and the simultaneous dissolution of gold in aerated alkaline solutions at ambient temperatures and pressures without the addition of cyanide has been studied. It involves the following aspects: the chemistry of the oxidation of pure arsenopyrite and pyrite minerals in aerated alkaline solutions; the kinetics of oxidation of arsenopyrite and the simultaneous dissolution of gold in such solutions; the kinetics of simultaneous dissolution of gold during the alkaline oxidation of refractory gold concentrates; the electrochemistry of gold in alkaline solutions containing thiosulfate or monothioarsenate; the effect of copper on the leaching of gold in alkaline thiosulfate solutions; and the leaching of gold in alkaline solutions with thioarsenites. The nature and proportions of the products of the oxidation of arsenopyrite in aerated alkaline solutions have been studied using high pressure ion chromatography techniques that have shown that thiosulfate and a new species, monothioarsenate, are the main oxidation products of arsenopyrite apart from arsenate and sulfite. The alkaline oxidation of pyrite primarily yields thiosulfate and sulfite. A kinetic investigation of the oxidation of arsenopyrite with air or oxygen has shown that the initial rate of arsenopyrite oxidation is proportional to the concentration of dissolved oxygen. A reaction mechanism for the oxidation of arsenopyrite has been proposed, which involves an anodic oxidation of the mineral involving hydroxyl ions coupled to a cathodic process for oxygen reduction which is partially controlled by mass transfer of dissolved oxygen to the mineral surface. Detailed studies of the dissolution behaviour of gold in aerated alkaline solutions in the presence of thiosulfate or monothioarsenate by electrochemical and leaching methods have demonstrated that the dissolution rate is very low as compared to that of gold in alkaline cyanide or ammoniacal thiosulfate solutions. It has been found that copper ions catalyze the dissolution of gold in the thiosulfate solutions in the absence of ammonia. The leaching experiments also have shown that gold may dissolve in alkaline thioarsenite solutions, which provides a possible new process option for the leaching of gold. The oxidation of refractory arsenical gold concentrates in aerated alkaline solutions results in the formation of thiosulfate, arsenate and sulfate as well as the dissolution of gold, copper and iron. It appears that the dissolution of gold is due to the complex reactions of gold with thiosulfate ions promoted by the catalytic effect of copper ions. Up to 80% of the gold may be extracted during the oxidation of selected refractory arsenical

La lignine est un des polymères naturels les plus abondants et le seul constituant de la biomasse basé sur des unités aromatiques et, à ce titre, représente une ressource renouvelable prometteuse pour la production durable de molécules organiques plus complexes. Les travaux de cette thèse portent sur le développement de matériaux catalytiques capables de transformer sélectivement la lignine en molécules fonctionnelles de base, hautement oxygénées, et l'étude de leur mise en oeuvre en condition alcaline oxydante en utilisant le peroxyde d'hydrogène comme donneur d'oxygène. Différentes familles de matériaux hybrides de type SBA-15 à base de titane, Au/titane, Ag/titane et Fe(TAML) ont tout d'abord été synthétisées et entièrement caractérisées. Des études catalytiques comparatives ont ensuite été réalisées afin d'évaluer leurs performances en termes de degré de dépolymérisation et distribution de produits. Le catalyseur présentant le plus fort potentiel, le matériau TiO2 supporté sur SBA-15, a ensuite été soumis à des études de réactivité plus poussées afin d'optimiser les différents paramètres réactionnels (température, temps de réaction et quantité d'oxydant) permettant d'atteindre en présence d'un excès d'oxydant jusqu'à 90 %pds de conversion de la lignine et à 80°C un rendement en bio-huile de 50%pds constituée principalement d'acides carboxyliques et molécules aromatiques potentiellement valorisables / Lignin is one of the most abundant natural polymers and the only biomass constituent based on aromatic units and as such represents a promising renewable resource for the sustainable production of complex organic molecules. This dissertation reports on the development of catalytic materials capable of selectively transform lignin into basic functional molecules with high oxygen content and the study of their performance under alkaline oxidative conditions, using hydrogen peroxide as oxygen donner. Different families of hybrid materials based on the SBA-15 scaffold were first synthesized by incorporation of titanium, Au/titanium, Ag/titanium and Fe-TAML and completely characterized. Comparative catalytic studies were then accomplished in order to evaluate their performance in terms of degree of depolymerization and product distribution. The catalyst with the highest potential, the TiO2 based SBA-15 material, was then submitted to further reactivity studies in order to optimize the different reaction parameters (temperature, reaction time and quantity of oxidant). In the presence of an excess of oxidant, conversions up to 90 wt. % were obtained, whereas a temperature of 80 °C allowed to obtain a yield in bio-oil of 50 wt. %, which is mainly composed of carboxylic acids and aromatic molecules with potential to be further valorized