Electrochemical and microbial assisted dissolution of mineral sulfides in acidic and corrosive media for the recovery of value metals

摘要

In contrast to corrosion of technically used materials which has to be prevented for safety and functional reasons, the dissolution of mineral sulfides at very acidic and corrosive conditions is an economic relevant process which is intentionally induced at industrial scale. Thereby, slow kinetics is overcome by biological catalysis using iron- and sulfur- oxidising microorganisms. This kind of metal recovering bioprocess is described as biomining and applied at commercial scale for the recovery of metals like Cu, Ni, Zn, U, Co and Au from ores. However, the biological leaching of refractory ores like primary copper sulfides is still suffering from slow reaction rates. This is probably due to semi-conductive properties and/or formation of passive surface layers which hinder charge transfer. Therefore, further improvements in process engineering are required. As the corrosive dissolution of mineral sulfides is accomplished via redox reactions, electrochemical regulation of the leaching milieu is one approach of such an improvement. By using mineral electrodes we investigated the electrochemical properties of iron and copper containing minerals. Mineral dissolution was reduced after biotic and abiotic leaching due to passivation effects and less redox active surface species. Although bioleaching enables higher metal recovery, the passivation reached a higher state during bioleaching. For this reason we are working on electrochemical engineering techniques to further improve the bioleaching of mineral sulfides. By the implementation of an electrochemical bioreactor we investigated the controllability of redox conditions to accelerate mineral dissolution kinetics.