The Effect of MgO on Gas–Slag–Matte–Tridymite Equilibria in Fayalite-Based Copper Smelting Slags at 1473 K (1200 °C) and 1573 K (1300 °C), and P(SO2) = 0.25 atm

Understanding the significance of magnesia as a common component in copper processing slags is essential for optimisation of the industrial copper production. Fundamental experimental studies have been undertaken to determine the effect of MgO on the equilibria between the gas phase (CO-CO2-SO2-Ar) and slag-matte-tridymite phases in the Cu-Fe-O-S-Si-Mg system at 1473 K (1200 °C) and 1573 K (1300 °C), and P(SO2) = 0.25 atm. The experimental methodology used was based on equilibration, quenching and microanalysis. New experimental data have been obtained for the four-phase gas–slag–matte–tridymite equilibria system for a range of MgO concentrations up to 3.1 wt pct in the slag phase as a function of matte grade, including the concentrations of dissolved sulphur and copper in slag, and Fe/SiO2 ratios in slag. The results are also used to analyse the effect of temperature on phase equilibria in the range investigated. The results obtained showed that dissolution of sulphur, copper and “FeO” in slag decreases with increase of MgO in slag while it has no detectable effect on concentration of sulphur in matte. Also, dissolved copper and sulphur in slag increases when temperature increases while the Fe/SiO2 ratio in slag is greater at 1473 K (1200 °C) than 1573 K (1300 °C). The new data provided in the present study are of direct relevance to the pyrometallurgical processing of copper and will be used as an input for optimization of the FactSage thermodynamic database for the copper-containing multi-component multi-phase system.