SEM AND AES STUDIES OF A LEAD SULFIDE BIOLEACHING IN PRESENCE OF CATALYTIC IONS

Scanning electron microscopy (SEM) and Auger electron spectroscopy (AE S) were used to follow the surface changes occurring in galena when th e bioleaching medium contained Ag(I), Hg(II) and Bi(III) ions. The res ults showed that the catalyst ions Ag(I), Hg(II) and Bi(III) are incor porated into the surface irrespectively of the presence of bacteria, a nd different reactions take place on the surface of galena depending o n the cation added to the leaching medium. When the bioleaching proces s takes place without catalyst or with Bi(III) the galena is transform ed into PbSO4 and the growth of oxidation products is characterized by needles. Ag(I) and Hg(II) ions form a layer on the galena surface, wh ich prevents the transformation of such surface into PbSO4. The layer formed in this process can be like a silver sulphide and a mercury sul phide depending on the ion species. Microorganisms oxidize the surface sulphur of this layer and thus decrease the S/Ag and S/Hg ratios at t he surface.