Electrochemical phenomena in MnO2-FeS2 leaching in dilute HCl. Part 3: Manganese dissolution from Indian Ocean nodules

The present paper deals with the kinetics and mechanism of MnO2 dissolution from sea bed manganese nodules in the presence of pyrite. Manganese (iv) w as found to disserve mostly through reduction by ferrous ions generated by the oxidation of pyrite by ferric ions which was considered to take place t hrough two reactions, one producing S degrees and the other [SO42-]. These two reactions were found to take place at a mole proportion of about 20% an d 80%, respectively, but in terms of electron involvement the participation of the former is insignificant, The dissolution rates obtained from leachi ng studies were analysed based on the kinetic expressions derived previousl y and were found to confirm the theoretical basis. The kinetics and mechani sm vary depending on whether or not sufficient acid is present. In the pres ence of sufficient acid the expression {[Fe3+]/(Rate)(2) = K-3[Fe2+]+K-4} i s valid and in depleted acid conditions {rate = K-6[H+][Fe2+])(1/2)} holds good. (C) 1998 Canadian Institute of Mining and Metallurgy. Published by El sevier Science Ltd. All rights reserved.