Electrochemical Aspects of the Nitric Acid Leaching of Lead Sulfide Concentrates: On the Way to a Highly Effective Method for Pb Recovery

摘要

Examination of the kinetics of hot nitric acid based leaching of a lead sulfide concentrate together with changes of potential of immersed Pt or PbS electrodes has revealed three stages of the leaching. The acidic decomposition of minerals that produces aqueous sulfide that is then oxidized by nitrate plays a major role in the first, slow leach stage. In the second stage, PbS oxidation is effectively accelerated by accumulated Fe{sup}(3+)/Fe{sup}(2+) ions, yielding largely elemental sulfur and making the process electrochemical in nature. The formation of predominant sulfate and the process impeding in the third stage seem to be due to oxidative action of nitrogenous species. It is proposed that leaching in practice is performed using cold ferric nitrate solution as this was found to be a surprisingly effective and selective oxidant for PbS. A process flowsheet for the treatment of the Gorevsky flotation lead concentrate was developed.