Effects of Reductive Roasting with Sodium Salts on Leaching Behavior of Non-ferrous Elements in Bauxite Ore Residue

In our previous study, TiO2 was enriched through stepwise removal of SiO2 and Al2O3 via H3PO4 and NaOH leaching from non-magnetic material, which was derived from reductive roasting of bauxite ore residues with sodium salts followed by magnetic separation. In this research, to elucidate the corresponding mechanism, the effects of reductive roasting with sodium salts on leaching behaviors of non-ferrous elements in bauxite ore residues were further investigated. The logC-pH figures have shown the separation between SiO2 and Al2O3 can be achieved through H3PO4 leaching, and the leaching results proved the difference of leaching ratio between SiO2 and Al2O3 in bauxite ore residues was promoted from 30 to 60% after reductive roasting with sodium salts under the optimal H3PO4 concentration of 1.0 mol/L. TiO2 was found not dissolved after reductive roasting as the leaching ratio changed from 53.9% to be less than 3%, which was due to the insoluble perovskite (CaTiO3) generated in the roasting process. In the NaOH leaching process, the difference between the leaching ratio of Al2O3 and SiO2 in bauxite residue changed from 27.1% to about 60% after reductive roasting under the conditions of maximum Al2O3 extraction ratio with 50.wt% NaOH. The above results have indicated that reductive roasting process with sodium salts was not only favorable to the subsequent separation between SiO2 and Al2O3 as well as the enrichment of TiO2 in H3PO4 leaching process, but also beneficial to extraction of Al2O3 and the separation between Al2O3 and SiO2 in NaOH leaching process.