Desilication of Highly Acidic Titanyl Chloride Solution for the Production of High-Purity Titania Pigment from a Spent Selective Catalytic Reduction Catalyst

An effective desilication method for a titanyl chloride (TiOCl2) solution obtained by dissolving sodium titanate using concentrated hydrochloric acid was investigated in order to increase the purity of titania pigment and the productivity of the process. When the TiOCl2 solution obtained by HCl leaching was used without desilication, clogging of the filtration system or precipitation of silica occurs. To overcome these disadvantages using a simple and efficient desilication method, the acidity, preservation temperature, and time elapsed after the preservation of TiOCl2 solution were controlled. In the experiments, TiOCl2 solutions produced using 5-7M HCl solution were preserved at 274-313K for 5 days. When the acidity, preservation temperature, and time elapsed after preservation were increased, the removal efficiency of silica increased. The conditions for the concentration of silica below 1mg/L and the removal of silica by gelation were determined. When the purified TiOCl2 solution was hydrolyzed at 363 K, titanium dioxide with a purity of 99.6-99.9% was obtained. Therefore, the results of this study demonstrated a straightforward and effective desilication method for highly acidic TiOCl2 solution.