The effect of sulfur dioxide partial pressure on gas-slag-matte-tridymite equilibria in the Cu-Fe-O-S-Si system at 1200°C

The gas-slag-matte-tridymite equilibria in the Cu–Fe–O–S–Si system at 1200°C have been experimentally studied. An improved experimental technique was used, which includes high temperature equilibration of sulfide-oxide mixtures on silica substrates at p(SO₂) = 0.6 atm, preservation of the equilibrium phases by rapid quenching, and direct compositional analysis of the phases using microanalysis techniques. The new data have enabled the effects of sulfur dioxide partial pressure between 0.1 and 0.6 atm on the equilibria to be accurately determined. Whilst, for a given matte grade, the dissolved copper in slag is not sensitive to sulfur dioxide partial pressure, the Fe/SiO₂ in slag in equilibrium with tridymite was found to increase with increasing p(SO₂). This latter observation has implications for fluxing practice in industrial copper smelting operations.