Study on Direct Alloying of Waste SCR Catalysts

TiO₂ in the waste SCR catalysts was reduced by aluminum, and the SiO₂-TiO₂-CaO-Al₂O₃-CaF₂-Na₂O slag system was selected. As the reduction process progresses, TiO₂ in the slag gradually decreases and Al₂O₃ gradually increases. The product titanium can transfer into the iron liquid to form the iron-titanium alloy, which can realize titanium recovery from the waste SCR catalysts. Calculated by the thermodynamic software Factsage 7.1 Equilb module, the slag compositions after completion of the reaction were 3% of SiO₂, 15% of CaO, 44% of CaF₂, 2% of Na₂O and 35% of Al₂O₃, with 2.5% of titanium content in the steel. In the phase diagram, the A, B, C, and D points were selected on the path of composition change. The viscosity of the slag in the reduction process was calculated by the viscosity module of Factsage 7.1. It is concluded that the slag viscosity is less than 0.03 Pa·s during the reduction process, indicating well liquidity. According to the experiment and analyses, the titanium content in the steel reached 1.67%, 67% of the calculated value. A large amount of TiO₂ in the slag was reduced into the steel, and the direct alloying of titanium from the waste SCR catalysts can be basically achieved.