Electrochemical aspects of metal sulfide bioleaching and biocorrosion.

摘要

The present study has investigated the electrochemical reactions involved in (a) the biooxidation of metal sulfides, such as pyrite (in relation to desulfurization of coal, extraction of uranium and gold from pyritic ores), copper from a chalcopyrite and zinc from a zinc sulfide flotation concentrate; and (b) the biocorrosion of stainless steel samples. Using cyclic voltammetry and carbon-paste-MS (metal sulfide) working electrodes, it was found that the oxidation of metal sulfides involved a large number of intermediate electrochemical reactions and/or the formation of non-stoichiometric compounds in the presence and absence of bacteria. The bacterial leaching processes were found to be solid-state diffusion controlled as suggested by the chronoamperometric and chronopotentiometric measurements. The activation energies associated with the solid-state diffusion of pyrite, chalcopyrite and zinc sulfide leachings were determined by the Sand's approach to be 22.4 kJ, 20.5 kJ and 21.3 kJ, respectively. These activation energies are in the order of magnitude of energies, which are typical for solid-state diffusion controlled reactions of semiconductor metal sulfides. The reaction mechanism of biooxidation of semiconductor metal sulfides was explained in terms of solid-state properties (energy density states) of metal sulfides and redox leach system.; The biocorrosion of stainless steel samples (304, 316 and 416 SS) indicated that the 416 SS sample containing the highest amount of sulfur (0.32%S) was the most corroded. In terms of initial rest potentials, it was found that the order of bacterial corrosion of SS samples: 416 SS {dollar}>{dollar} 304 SS {dollar}>{dollar} 316 SS was inversely proportional to their rest potentials {dollar}-{dollar}605 mV {dollar}<{dollar} {dollar}-{dollar}404 mV {dollar}<{dollar} {dollar}-{dollar}354 mV, respectively. For the stainless steel weldment samples, the percentage (%) of elongation (strain) and UTS (ultimate tensile strength) were found to be decreased, but their YS (yield strength) increased, as compared with the as received (no weldment) samples. After 5 days of biocorrosion, the 416 SS showed a significant decrease in the elongation, YS, and UTS.