STUDIES ON INITIAL DISSOLUTION KINETICS FROM POLARIZATION DATA .6. MANGANESE DISSOLUTION FROM INDIAN-OCEAN NODULES IN DILUTE HYDROCHLORIC-ACID IN THE PRESENCE OF PYRITE

Abstract

The present paper examines the kinetics and mechanism of MnO2 dissolution from sea bed manganese nodule in the presence of pyrite through the measurement of leaching as well as electrochemical parameters. Manganese (IV) was found to dissolve mostly through reduction by ferrous ion generated by the oxidation of pyrite by ferric ion which was considered to take place through two reactions, one producing S-0 and the other [SO42]. Both these reactions are slower and control the process. Manganese dissolution runs at the same rate as that of pyrite oxidation by maintaining ferrous ion concentration at a much lower level than that of ferric ion concentration. The dissolution rate is equal to K-1[Fe3+]/(K-2[Fe2+][H+]SO42] + K-3[Fe3+])(1/2) and K-4[Fe3+]/(K-5[Fe3+] + K-6[Fe2+])(1/2). The activation energy is 43.5 kJ mole(-1). Some extent of galvanic interaction between FeS2 and MnO2 is not ruled out.