Galvanic interaction between sulfide minerals and pyrolusite

Abstract

Galvanic interaction between manganese dioxide and sulfide mineral (FeS2, CuFeS2, ZnS and PbS) galvanic couples were investigated through polarization measurements and leaching studies. The sulfide minerals, being less noble than MnO2, form the anode in each couple, with MnO2 the cathode. Both sulfide minerals and MnO2 dissolve at an enhanced rate under the influence of the potential difference between the electrodes of the couple acting as the driving force. Polarization studies provided information on the individual half-cell reactions as well as the galvanic interactions. The kinetics and mechanism of the performance of these galvanic couples were examined by applying electrochemical principles. Hydrogen ions were found to have a prominent effect on the galvanic current observed for the MnO2-FeS2 and MnO2-CuFeS2 couples, which was less for the MnO2-ZnS couple and became totally ineffective in the case of the MnO2-PbS couple. The interaction occurred in the Tafel regions of each of the half-cell reactions of the first three couples, whereas it occurred in the Tafel-limiting current regions of the last couple. The cathodic reduction of MnO2 was found to be slower and rate controlling in the case of the MnO2-FeS2 couple, whereas the diffusion-controlled anodic oxidation of galena was rate controlling for the MnO2-PbS couple. The other two couples were under mixed control. These trends in the mode of operation of these four galvanic couples were as per the change in the noble character of the four sulfide minerals. The effect of the solid/liquid ratio and the sulfide/MnO2 ratio on the galvanic interaction during particulate leaching was also investigated.