CHEMICAL AND MORPHOLOGICAL-CHANGES OF THE PYRITE INDUCED BY LEACHING AND BIOLEACHING PROCESSES IN THE PRESENCE OF CATALYTIC AG IONS

The chemical and morphological changes induced in the pyrite surface b y the leaching and bioleaching processes in the presence of catalytic Ag ions have been comparatively studied by means of X-ray photoemissio n spectroscopy, atomic force microscopy, and scanning electron microsc opy. Core level photoemission spectra of the S(2p) and Fe(2p) peaks ha ve revealed the formation of different oxides in the leaching and biol eaching processes. Bioleaching leads to the formation of higher valenc e oxides (jarosites) than those formed in the leaching process. These chemical changes are directly reflected in the surface morphology and particularly as an important increase of the surface roughness. Moreov er, the inclusion of catalytic Ag ions in the leaching medium does not produce substantial modification of the topography, and the Ag is inc orporated in little grains (similar to 0.1 mu m wide) which are spread along the surface. However, the presence of Ag in the bioleaching med ium inhibits the formation of high valence oxides and leads to a diffe rent oxidation mechanism. The roughening of the surface due to the cat alytic bioleaching is also significantly slowed down by the presence o f Ag ions in the solution.