The Utilization of Bauxite Residue with a Calcite-Rich Bauxite Ore in the Pedersen Process for Iron and Alumina Extraction

Metallurgical grade alumina is produced worldwide through the well-known Bayer process, which unavoidably generates bauxite residue (BR, also known as red mud) in almost equal amounts to alumina. This study aims the valorization of BR through a smelting-reduction process to obtain calcium aluminate slags that can be a proper feed for alumina recovery via the Pedersen process. It investigates the thermodynamics and characteristics of the slags and pig iron produced from mixtures of BR, a bauxite beneficiation byproduct, and lime. In this context, the evolution of the different phases in the slags is studied with advanced analytical techniques and thermodynamic calculations. According to the results, a CaO/Al2O3 mass ratio within 1.3 to 1.4 in the slags can yield more Al2O3-containing leachable phases, such as CaO·Al2O3 and 12CaO·7Al2O3. The cooling dictates the amount and the characteristics of these phases, and the slower cooling rate yields improved slag characteristics. The distribution of the elements between the slag and metal phases shows that iron is separated, and the majority of the P, Cr, Ni, and V are distributed in the produced pig iron, while S, Ti, and Si are mostly concentrated in the slags.

The effect of NaOH on the direct calcification–carbonation method for processing of Bayer process red mud

The Bayer red mud generated from the alumina industry is a hazardous solid waste. In our team, a green calcification–carbonation process is proposed for its disposal. Red mud is treated with lime to convert the silicon phase in solution into hydrogarnet, which is then decomposed by CO2 to recover alumina. In order to simplify the process flow, the direct carbonation process is employed, in which the NaOH-containing solution resulting from calcification is sent directly to carbonation without prior liquid–solid separation. The discrete and direct carbonation processes gave 34.9% and 35.5% alumina recoveries, respectively, with Na2O contents in the final red muds of 0.15%wt and 0.21%wt, respectively. The optimum NaOH concentration in the whole calcification–carbonation process liquor was 40 g/l. Under this alkali condition, alumina recovery reached 40.5% and the Na2O content in the processed red mud was reduced to <1 %wt.