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°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 = ∼15 kJ mol^-1) and a second, chemically controlled stage (E_a = ∼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 1 h at 120°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.