Purification of pigment grade titanium dioxide by processing in molten salts

An alternative method of purifying the mineral rutile (TiO2) is reported. This offers potential savings in process energy and reduced waste when compared with current technology. The work reported here focused on refining rutile sand (95% TiO2) containing transition metal oxides (Fe2O3, SiO2, ZrO2, Cr2O3, V2O5 and Al2O3), which impart a strong colour to the mineral concentrate. The objective was to remove the colour giving oxides to produce rutile of over 99% purity (which is white in colour). Complete dissolution in molten salt (alkali chloride-fluoride) at 750 degrees C allowed electroseparation of the transition metals between a graphite anode and a stainless steel cathode. The voltage maintained across the cell ensured removal of transition metal ions from the solution, with minimal loss of titanium. In this process, dissolution of TiO2 was enhanced by partial replacement of chloride by fluoride in the melt to allow the complex ion TiF(6)(2-)dominate the titanium speciation. This had the additional advantage of minimising losses of Ti as volatile TiCl4.