Intensification of carbonate scandium leaching from red mud (bauxite residue)

Bauxite residue (red mud) is a promising anthropogenic source of scandium because only at the aluminum plants of Ural region (Russia) nearly 150 tons of this trace metal appears in the waste dumps annually. This work describes a method of red mud carbonization by carbon dioxide that results on the one hand to scandium leaching and on the other hand decrease of toxicity of the red mud due to conversion of hydroxides to carbonates and decrease of pH value from 12 to less than 9. The ways of increase of scandium leaching degrees based on ultrasonic treatment and mechanical activation were evaluated. It was supposed that carbonated red mud had high sorption activity being the main cause of secondary loss of scandium in the carbonate treatment process.