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

Abstract

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 5–7 M HCl solution were preserved at 274–313 K 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 1 mg/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.