Extraction of alumina and sodium oxide from red mud by a mild hydro-chemical process

A mild hydro-chemical process to extract Al2O3 in red mud to produce sodium aluminate hydrate was investigated, and the optimum conditions of Al2O3 extraction were verified by experiments as leaching in 45% NaOH solution with CaO-to-red mud mass ratio of 0.25 and liquid-to-solid ratio of 0.9. under 0.8 MPa at 200 degrees C for 3.5 h. Subsequent process of extracting Na2O from the residue of Al2O3 extraction was carried out in 7% NaOH solution with liquid-to-solid ratio of 3.8 under 0.9 MPa at 170 degrees C for 2 h. Overall, 87.8% of Al2O3 and 96.4% of Na2O were extracted from red mud. The final residues with less than 1% Na2O could be utilized as feedstock in construction materials. The chemical reactions taking place in both Al2O3 and Na2O extractions from red mud are proposed. (C) 2009 Elsevier B.V. All rights reserved.