Utilization of Scrap Metals as Reductants for Improved Ni and Cu Recoveries in Copper Smelting

Abstract

This study investigated a novel approach of using Al and Al–Mg scrap as heat providers and reductants that do not cause direct carbon-containing emissions in pyrometallurgical copper processing. Aluminum and magnesium are typical elements in metal wastes, such as WEEE, and they oxide easily under copper smelting conditions. In the reduction experiments, a copper- and nickel-rich industrial slag was equilibrated under Ar gas atmosphere at 1300 °C, after which a reductant metal piece was dropped on top of the slag. The slag-reductant samples were drop quenched in brine after 2–128 min of reduction. Thermodynamic calculations were executed with MTDATA to evaluate the phase equilibria and thermochemistry of the copper slag in metallothermic reduction. All the results proved that Al and Al-5wt% Mg alloys can be used as reductants in copper processes to enhance the recoveries of nickel and copper in metal/matte. Cu concentration in slag decreased from 2 to 1.2 wt% and Ni from 1.7 to 1.2 wt% in 30 min in aluminothermic reduction experiments, despite an immediate formation of a solid alumina layer on the surface of the reductant, hindering the reduction kinetics. The heat produced was calculated as 31 kWh/ton slag or 2.1 kWh/kg added Al or Al–Mg. Graphical Abstract