Selective extraction of rare earth elements from red mud using oxalic and sulfuric acids

Red mud is an alkaline industrial solid waste discharged from alumina production via the Bayer process and can be considered a kind of potential resource of rare earth elements (REEs). Many valuable metals such as iron, aluminum, and titanium also exist in red mud. A multi-stage extraction method was proposed in this study by taking full account of the REEs’ occurrence in red mud. Firstly, the pretreatments of oxalic acid leaching, roasting, and dilute hydrochloric acid leaching were employed to recover iron and enrich REEs in the residue. Subsequently, sulfuric acid leaching was used to selectively dissolve REEs into the leaching solution. Finally, the effects of sulfuric acid concentration, liquid-solid ratio, reaction temperature, and reaction time on the leaching efficiency of REEs were then investigated. The results show that the maximum extraction of the REEs reached 80% and less than 4% of Fe, Na, Ca, Ti and Al were extracted under the experimental conditions of 1 mol/L H 2 SO 4 , 3 h, 95 °C, and the liquid-solid ratio of 5:1 mL/g. The practicable approach by multi-stage extraction of acid leaching and roasting can split iron and REEs from red mud. • Oxalic acid was introduced to dissolve iron and to enrich REEs in form as oxalates. • Calcium was removed by roasting and HCl leaching to further enrich REEs. • Effects of H 2 SO 4 leaching condition on REEs leaching efficiency were investigated. • Approximately 80% Sc and less than 4% of Fe, Na, Ca, Ti and Al were extracted.