Titanium Extraction from Spent Selective Catalytic Reduction Catalysts in a NaOH Molten-Salt System: Thermodynamic, Experimental, and Kinetic Studies

Abstract

In this study, sodium hydroxide was used as an alkali reagent in roasting spent selective catalytic reduction (SCR) catalysts for titanium extraction. The thermodynamic analysis of the roasting process is discussed in terms of process design. The effects of various roasting parameters, such as the mass ratio of NaOH-to-SCR, temperature, and time, on the extraction efficiency of titanium were investigated; under the optimum parameters of 1.8:1, 550 °C, and 10 minutes, the titanium extraction yield reached 97.8 pct. The roasting kinetics of titanium extraction were also studied. The kinetics of titanium extraction follow the Avrami model, which is expressed as follows: $$ - \ln \left( {1 - x} \right) = K_{0} C_{{m_{\text{NaOH}} /m_{\text{SCR}} }}^{ - 2.012} \exp \left( { - \frac{4120}{8.314T}} \right)t $$ , and the overall roasting process is controlled by diffusion in the solid state, with an activation energy (Ea) of 4.12 kJ/mol.