Preparation of synthetic rutile by hydrochloric acid leaching of mechanically activated Panzhihua ilmenite

Dissolution of mechanically activated Panzhihua ilmenite in hydrochloric acid for the preparation of synthetic rutile was investigated. Both the dissolution and its coupled titanium hydrolysis were greatly enhanced by the mechanical pretreatment. Increases in the lattice strain and surface area of ilmenite induced by energetic ball milling were responsible for the enhanced dissolution. The rapid hydrolysis led to formation of quantities of the nanosized primary particles, giving rise to a solid/liquid separation problem. The 15 min milled ilmenite, however, yielded an easy-to-filter hydrolysate due to formation of porous, micron-sized, secondary particles during the dissolution. The crystallization and aggregation behaviour of the primary particles were probably related to both the surface property of the un-reacted solid and the ferric ion concentration in solution. The technology for preparation of synthetic rutile was systematically investigated. The optimum milling and dissolution conditions were as follows: milling in air for 15 min, hydrochloric acid concentration 20%, initial reaction temperature 100 °C, ilmenite/20% acid mass ratio 1 g:5.5 g, reaction time ≥ 6 h. The synthetic rutile prepared under the optimum conditions contained 92% TiO₂ and 2.1% Fe₂O₃ as well as combined CaO and MgO of 0.28%. The results demonstrate that the mechanical pretreatment can take the place of the traditional high temperature pretreatment of ilmenite and avoid the dissolution being conducted under pressurized condition.