A novel sequential leaching process for titanium slag to increase TiO2 grade to prepare boiling chlorinated charges

Abstract

The efficient removal of calcium and magnesium impurities from titanium slag to prepare a boiling chlorinated charge is one of the technical bottlenecks in producing high-end titanium products from titanium resources in Panxi. This work proposes a novel process to prepare boiling chlorinated charges from the modified titanium slag, which includes sulfuric acid leaching, hydrochloric acid leaching, and removing silica from the hydrochloric acid leach residue. The transformation of phases, change in microstructure and the leaching efficiency of elements during the combined process were systematically investigated. The mixture of MxTi3-xO5 and diopside (CaMgSi2O6) can be decomposed by sulfuric acid into water-soluble sulfates (titanyl sulfate TiOSO4 and iron sulfates). The leaching efficiencies of Fe, Ca, Mg, V, and Si, respectively, were 85.9%, 48.6%, 93.0%, 95.9%, and 69.2% at the process parameters used: 250 °C, liquid/solid ratio of 1.7:1, leaching time of 2 h, and the particle size 74 μm. The sulfuric acid leach residue was washed and leached in hydrochloric acid. The hydrochloric acid leaching efficiencies of Fe, Ca, Mg, V and Si reached 72.0%, 75.4%, 70.4%, 67.9%, and 58.7%, respectively, in a 15% HClsolution at a liquid/solid ratio of 8, and leaching time of 2 h at 140 °C. The NH4HF2 leaching step is necessary to remove silica for the preparation of boiling chlorinated charges. The product obtained in this combined process contains TiO2 (98.8%), SiO2 (0.17%), and CaO and MgO (0.47%), which meets the requirements of the chemical compositions for boiling chlorinated charge.