The bioleaching of different sulfide concentrates using thermophilic bacteria
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Sulfolobus) was studied. Since the use of this type of bacteria in leaching systems involves stirring and the control of temperature, the influence of the type of stirring and the pulp density on dissolution rates was studied in order to ascertain the optimum conditions for metal recovery. At low pulp densities, the dissolution kinetic was favored by pneumatic stirring, but for higher pulp densities, orbital stirring produced the best results. A comparative study of three differential concentrates, one mixed concentrate, and one global concentrate was made. Copper and iron extraction is directly influenced by bacterial activity, while zinc dissolution is basically due to an indirect mechanism that is activated in the presence of copper ions. Galvanic interactions between the different sulfides favors the selective bioleaching of some phases (sphalerite and chalcopyrite) and leads to high metal recovery rates. However, the formation of galvanic couples depends on the type of concentrate.
I.
INTRODUCTION
THE minerals known as "complex sulfides" or "complex pyrites" are an association of chalcopyrite (CuFeS2), galena (PbS), and sphalerite (ZnS) disseminated in a pyritic matrix. The world's reserves of the most common metals (Cu, Pb, and Zn) contained in complex sulfides are substantial. It has been calculated that if the average grade of the copper contained in these minerals was 1.35 pct, such reserves could represent 8 pct of the total reserves of copper, t'l In addition, the presence of lead, zinc, and other constituents, such as silver and gold, present in much smaller quantities, increases the value of these sulfides and justifies the enormous interest shown in their treatment. Flotation is the most suitable method that has been devised for separating the different sulfurated species that make up the complexes. Differential flotation is widely used on a industrial scale, though the resulting concentrates are impure and frequently totally uneconomical. For this reason, bulk flotation is an alternative, since a particle size of 50/~m is sufficient; it is simple, more economical, and gives greater yields of metal. The problem lies in the subsequent treatment of bulk concentrates since no satisfactory procedure exists for processing them, and the method is, therefore, still at the laboratory or pilot plant stage. The principal methods for treating these primary materials continue to be based on pyrometallurgical techniques, which are responsible for substantial SOz pollution. Hydrometallurgical processes are an alternative to conventional processes. They use simple and more economical installations, although they have the inconvenience of being slow and of giving lower recovery rates. Much research is being put into improving both parameters. F. TORRES, Graduate Student, M.L. BLAZQUEZ and F. GONZ/tLEZ, Associate Professors, A. BALLESTER, Professor, and J.L. MIER, Assistant Professor, are with the Department of Materials Science and Metallurgical Engineering, School of Chemistry, University Complutense, 28040 Madri
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