Recovery of TiO<sub>2</sub> from spent SCR catalyst by acidolysis and additional crystal seeds-hydrolysis method

Abstract

In this study, a rapid and efficient method of recovering TiO<sub>2</sub> from spent SCR (selective catalytic reduction) catalyst supplied by a coal-fired power plant in Shanghai was developed. The acid leaching and sodium roasting-water leaching residues (titanium slag) from spent SCR catalyst were employed as the raw material. First, titanium slag was dissolved into H2SO4 solution under different conditions. The optimal acidolysis conditions were 85 wt% H<sub>2</sub>SO<sub>4</sub>, 5.0 g/g acid-residues ratio, 90℃ acidolysis temperature and 2.0 h acidolysis time. Simultaneously, the highest acidolysis efficiency can reach 92.02%. The acidolysis solution was collected and concentrated to 200 g/L (measured by TiO<sub>2</sub> concentration). Then, acidolysis solution was adjusted to pH 0.52-9.15, followed by adding 0-40 mL additional crystal seeds and reacting under certain conditions to obtain the hydrolysis product. The optimal hydrolysis conditions were 25 mL additional crystal seeds, pH 7.46, 120℃ hydrolysis temperature and 3.0 h hydrolysis time. Finally, the recovered product was obtained by roasting hydrolysis product at 700℃ for 2.0 h. The results of hydrolysis stability test indicated that this method can make the hydrolysis efficiency of acidolysis solution stabilize at approximately 90% under optimal conditions. The main component of recovered product was anatase TiO<sub>2</sub> with the purity of 86.88%.