Selective separation of aluminum, silicon, and titanium from red mud using oxalic acid leaching, iron precipitation and pH adjustments with calcium carbonate

Abstract

Red mud discharged from alumina production is a valuable metal resource of great importance in the context of the requirement to reduce the impact of mining on the environment and resource consumption. The efficient dissolution of iron from red mud by oxalic acid has been reported. Although the concentrations of aluminum, silicon, and titanium were also high in the red mud-oxalic acid leachate after iron precipitation, they have received little attention. The present study aims to recover aluminum, silicon, and titanium from red mud-oxalic acid leachate after the precipitation of iron. The leaching efficiencies of aluminum, silicon, and titanium in 1.0 mol/L oxalic acid at 80 °C, reached 63–75% after 2 h. Sodium hydroxide, calcium oxide, and calcium carbonate were chosen to adjust the pH of the oxalic acid leachate, and the effective separation of silicon and titanium from the oxalic acid leachate could be achieved at pH 4.0 by stepwise separation using calcium carbonate. A silicon dioxide primary product with a purity of 70.8% was obtained in addition to the aluminum hydroxide primary product. The stepwise selective separation of aluminum, silicon, and titanium from red mud-oxalic acid leachate could assist the values recovery and simultaneously minimize environmental hazards of the acidic leachate.