A hydrometallurgical process for the selective removal of silicon from titanium-vanadium slag by alkaline leaching was investigated. X-ray diffraction, scanning electron microscopy and electron dispersive spectroscopy were used to characterize the samples. The results show that anosovite, pyroxene and metallic iron are the major components of the titanium-vanadium slag. Anosovite is presented in granular and plate shapes, and pyroxene is distributed in the anosovite crystals. Metallic iron is spheroidal and wrapped in anosovite. Silicon is mainly in the pyroxene, and titanium and vanadium are mainly in the anosovite. The effects of agitation speed, leaching temperature, leaching time, sodium hydroxide concentration and liquid-solid （L/S） mass ratio on the leaching behavior of silica from titanium-vanadium slag were investigated. The leaching temperature and L/S mass ratio played considerable role in the desilication process. Under the optimal conditions, 88.2% silicon, 66.3% aluminum, 27.3% manganese, and only 1.2% vanadium were leached out. The desilication kinetics of the titanium-vanadium slag was described by the chemical control model. The apparent activation enerffv of the desilication orocess was found to be 46.3 kJ/mol.
A method was proposed for removing zirconium （Zr） from hydrous titanium dioxide （HTD） by the NaF solution. The effects of main parameters, i.e. pH values, NaF dosage, temperature and retention time, on the removal of zirconium were stud- ied. The optimal conditions were found as the following： pH value, 〈5.5; molar ratio of NaF to TiQ, 0.6; retention time, 80 min and temperature, 80℃. The removal rate of Zr under the optimized conditions was above 87.7%. The adsorption energy of the preferential absorption of hydrofluoric acid for Zr（OH）2SOt（OH2） on the （001） crystal surface of HTD was determined by theo- retical calculation. The possible mechanism of the removal process was also discussed.
