Slag Chemistry and Partitioning of Trace Elements in Direct-to-Blister Copper Smelting Conditions

A one-step direct-to-blister (DtoB) copper smelting process is an attractive route for sulfidic copper concentrates with high copper or low iron concentrations. It provides high recovery of copper and other valuable metals, while it requires no converting step. The process generates only one high-strength SO₂ stream to the acid plant and provides high recovery of sulfur. However, the literature data regarding the phase equilibria and trace element deportments in these smelting conditions are scarce. In the present work, we analyze recent experimental data on phase equilibria in the DtoB smelting conditions at 1250 °C and 0.25 atm pSO₂ as a function of sulfur concentration in blister copper at magnetite saturation. A complex iron silicate slag modified with fixed concentrations of alumina, potassia, and magnesia and fluxed with lime at two concentrations, 5 and 10 wt%, was used as the reference system for the previous data. Experimental data on chemical solubility of copper in slag were evaluated and discussed comparing to the DtoB copper smelting industrial practice. In addition, partitioning of minor elements was assessed. Their distribution coefficients were estimated as a function of oxygen partial pressure within the narrow range of interest (10^–6.5 to 10^–5.5 atm pO₂) from matte saturation to blister copper at low sulfur concentration. The prevailing oxidation degrees of the trace elements in slag and in DtoB conditions were discussed. The blister copper-slag distribution coefficients indicated a good agreement with most literature observations in sulfur-free iron silicate slag-copper systems at similar oxygen partial pressures.