Effective aluminum extraction using pressure leaching of bauxite reaction residue from coagulant industry and leaching kinetics study

During hydrochloric acid leaching of bauxite reaction residue (BRR) produced from coagulant industry, the effects of hydrochloric acid concentration, liquid solid ratio and silica remove on the extraction of aluminum were studied, at atmospheric pressure (85 °C). The aluminum dissolution rate under the optimal conditions (8 mol L−1, L S−1 5:1) was only 44.15 %. After the leached residue was treated by alkali to selectively remove silica and then leached with hydrochloric acid at the same conditions, the aluminum extraction rate rarely changes, even if the silica removal rate reaches 81.52 %. Direct leaching after mechanical activation for 10 h, resulted in the extraction rate increased by 5.05 %. However, compared with the optimal condition (8 mol L−1, 5:1, 10 h) under atmospheric pressure, the aluminum extraction rate was only 49.2 %, while up to 84.23 % of aluminum was extracted from BRR at high-pressure (210 °C). In addition, the leaching experiment and kinetics of aluminum were analyzed in-depth under high-pressure. The apparent activation energy of aluminum dissolution was found to be 20.82 kJ mol−1, and the dissolution process is determined by liquid diffusion. Obtained leachate has been well recycled without waste discharged, which provides a theoretical basis for the BRR utilization.