Sodium-oxide fluxed aluminothermic reduction of manganese ore for a circular economy : Cr collector metal application

Abstract

Aluminothermic reduction is gaining renewed interest as an alternative processing route for the circular economy. Aluminium is produced electrochemically in the Hall–Héroult process with minimal CO2 emissions if electricity is sourced from non-fossil fuel energy sources. The Al2O3 product from the aluminothermic reduction process can be recycled via hydrometallurgy, with leaching as the first step. NaAlO2 is a water-leachable compound that forms a pathway for recycling Al2O3 with hydrometallurgy. In this work, a suitable slag formulation is applied in the aluminothermic reduction of manganese ore to form a Na2O-based slag of high Al2O3 solubility to effect good alloy–slag separation. The synergistic effect of added chromium metal as a collector metal is illustrated with an increased alloy yield at 68%, from 43% without added Cr. The addition of small amounts of carbon reductant to MnO2-containing ore ensures rapid pre-reduction to MnO. This approach negates the need for a pre-roasting step. The alloy and slag chemical analyses are compared to the thermochemistry-predicted phase chemistry. The alloy consists of 57% Mn, 18% Cr, 18% Fe, 3.4% Si, 1.5% Al, and 2.2% C. The formulated slag exhibits high Al2O3 solubility, enabling effective alloy–slag separation, even at an Al2O3 content of 55%.