Statistical modeling and optimization of ultrasound-assisted sulfuric acid leaching of TiO2 from red mud

Ultrasound has proven to be a very effective tool for enhancing reaction rates by inducing a number of chemical and mechanical effects on the reaction medium. In this study, the effect of ultrasound power on the sulfuric acid leaching of Ti from red mud has been investigated by statistically designed experiments. The effects of five parameters, ultrasound power, temperature, leaching time, acid concentration and solid to liquid ratio, on the leaching of TiO2, Al2O3 and Fe2O3 have been investigated. First-order models have been obtained by using 25−1 fractional factorial design. Auxiliary experiments for second-order models have been conducted according to an orthogonal central composite design. These second-order models have been used in a constrained optimization study which showed that both high and selective yields of TiO2 may be obtained under suitable process conditions. The major factors influencing TiO2 leaching were acid concentration and temperature, the other variables had comparatively small effects. The use of ultrasound resulted in a 20% increase in TiO2 leaching compared to identical conditions without ultrasound.