Promote Alumina Leaching Through Re-Pelleting: Effects of Directional Coating of Calcite on Silicate Grains

The contents of Fe and SiO2 in ferric bauxite are much higher than that in regular bauxite, and the leaching yield of Al2O3 from ferric bauxite cannot reach the general level of ordinary ores, even under optimal conditions. This paper introduces a pretreatment method to enhance sintering before leaching. First, mixing followed by grinding was found to be more efficient than grinding followed by mixing as a pretreatment method by forming a directional coating structure of CaCO3 on the SiO2 surface. Second, leaching yields increased grinding fineness because CaCO3 grain uniformity could be improved with the latter method. Finally, the leaching yields were increased by pulp consistency under certain conditions, as evidenced by improvements in CaCO3 uniformity, bulk density, and Al2O3 grain size, which parameters were beneficial to enhance leaching. The leaching yield of Al2O3 was increased from 75.2% to 87.15% by using the proposed mixing–grinding method with the leaching agent of water.