Reductive leaching of ilmenite ore in hydrochloric acid for preparation of synthetic rutile

Abstract

The reactivity of ilmenite ore during leaching with hydrochloric acid can be greatly enhanced by reduction in solution using metallic iron. Addition of a particular amount of iron powder after a certain time of reaction will reduce all the dissolved Fe 3+ to Fe 2+ and reduce a portion of the dissolved Ti 4+ to Ti 3+. As the leaching continues, any further dissolved Fe 3+ will be simultaneously reduced by the action of the formed Ti 3+ to produce Fe 2+ and Ti 4+. As a result, dissolution of the iron and titanium contents from the ore will be improved. Meanwhile, the dissolved Ti 4+ will be hydrolysed and precipitated leaving mainly ferrous chloride in the solution. The hydrolysis is accompanied by fast dissolution of the unreacted ore. A reductive leaching process is proposed taking advantages of the recent advances in HCl regeneration from spent leach liquor. The different leaching parameters were optimised to obtain as little iron as possible in the titanium dioxide product. Synthetic rutile of about 90% TiO 2 and 0.8% Fe 2O 3 was obtained from an Egyptian medium-grade ilmenite ore of grain size 100%–75 μm using 20% HCl at boiling temperature (110 °C), with addition of 0.11 g iron powder/g ore for 5 h. The product has a low content of colouring elements (total MnO 2, Cr 2O 3 and V 2O 5=0.12%) and chlorine consuming elements (total CaO, MgO and Al 2O 3=0.08%) but contain high silica (SiO 2=5.8%). The process is applicable for higher grade ilmenite ores which will produce higher quality synthetic rutile.