Mechanical enhancement of the dissolution of ilmenite

An ilmenite concentrate has been ball milled for up to 100 h in a laboratory mill without any evidence of a phase change. The particle size reached steady-state within 10 h of milling with a concomitant maximum in the BET surface area. There was considerable damage to the crystal lattice with a decrease in the crystallite size which was a function of log (milling time) and an increase in the lattice strain. The resultant powders were leached in sulphuric acid at up to 120 degrees C for up to 8 h. It was found that there were two stages of dissolution, a rapid stage which was mass transport controlled (E-a = similar to 15 kJ mol(-1)) and a second, chemically controlled stage (E-a = similar to 70 kJ mol(-1)). The fraction of dissolution during the initial stage increased with milling time until over 80 % of the ilmenite was solubilised within I h at 120 degrees C for 100 h milled powder. The enhanced dissolution was attributed to the exposure of planes along which preferential dissolution of ilmenite has been shown to occur. (C) 1998 Elsevier Science Ltd. All rights reserved.