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) was found to disserve mostly through reduction by ferrous ions generated by the oxidation of pyrite by ferric ions which was considered to take place through 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% and 80%, respectively, but in terms of electron involvement the participation of the former is insignificant, The dissolution rates obtained from leaching studies were analysed based on the kinetic expressions derived previously and were found to confirm the theoretical basis. The kinetics and mechanism vary depending on whether or not sufficient acid is present. In the presence of sufficient acid the expression {[Fe3+]/(Rate)(2) = K-3[Fe2+]+K-4} is 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 Elsevier Science Ltd. All rights reserved.