Effects of thermal preoxidation on reductive leaching of ilmenite

Abstract

This paper examines the effects of preoxidation on the removal of iron during ilmenite reductive leaching. Oxidation of ilmenite was carried out at temperatures of 700°C, 800°C, 900°C and 1050°C for 6h. The preoxidised ilmenite was leached using hydrochloric acid and iron powder as leaching and reductive agent, respectively.A test without iron powder was also conducted to determine the effect of iron. Ilmenite without oxidation was leached for comparison. Original ilmenite and solid products of both oxidation and leaching processes were characterised by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. Solutions obtained after leaching were analysed by atomic absorption and UV spectrophotometry for iron and titanium determination, respectively.Results indicated that preoxidation produced phase transformation of ilmenite that facilitated iron dissolution. Oxidation temperature affected the type and distribution of phases achieved. Hematite and rutile, with a layered configuration, were obtained at 700°C. This revealed to be the optimum condition to dissolve iron selectively. Randomly distributed pseudobrookite and rutile were obtained at 900°C and 1050°C. Leaching products obtained from ilmenite preoxidised under those conditions, appeared to be high crystallinity rutile. Nevertheless, the presence of pseudobrookite promotes titanium dissolution, although it could be recovered by precipitation. Reductive leaching at 105°C yield better results in terms of kinetic and iron extraction.