Reductive leaching of manganese oxide ore in aqueous methanol sulphuric acid medium

The reductive leaching of manganese oxide ore in aqueous methanol-sulphuric acid was investigated. Studies were conducted at low (30 and 70 degrees C) and high (120-170 degrees C) temperatures, using different acid (0.005-0.30 M H2SO4) and methanol (0-50 vol%) concentrations. Results showed that satisfactory levels of manganese extraction could be achieved during autoclave digestion at temperatures between 150 and 170 degrees C with a reaction mixture containing 20-40 vol% methanol at relatively low sulphuric acid concentrations of between 0.1 and 0.20 M. Conditions for optimum manganese extraction are determined by the methanol and sulphuric acid concentrations as well as the reaction temperature. For example, manganese extraction of about 98% was reached at 160 degrees C with a methanol dosage of 40 vol% at 0.3 M sulphuric acid within a period of 2 h. Comparatively good extraction level of 86% could be attained at lower methanol and acid concentrations of 20 vol% and 0.092 M respectively, but at a longer reaction time of 3 h. Particle size seemed to have very little effect on extraction for sizes between 32 and 125 mu m An interesting feature of leaching in an aqueous methanol-sulphuric acid medium is the apparent suppression of iron dissolution from the ore in the presence of methanol. For example at 120 degrees C and 0.16 M sulphuric acid concentration iron extraction from the ore decreased from 58% at 0 vol% methanol addition to about 3.5% at 50 vol% methanol concentration. At 160 degrees C and 0.092 M acid concentration iron extraction was only 0.4% at 40 vol% methanol concentration. (C) 1999 Elsevier Science B.V. All rights reserved.