Phase equilibria of silicate slags relevant to the copper smelting/converting operations have been systemically investigated in the temperature range 1200 to 1300 °C and oxygen partial pressures between 10-5 and 10-9 atm. The experimental procedures include high temperature equilibration, quenching and accurate measurements of phase compositions using electron probe X-ray microanalysis (EPMA). The effects of CaO, Al2O3, MgO and Po2 on the phase equilibria of the fayalite slags have been systematically investigated.
It was found that spinel and tridymite (SiO2) are major primary phases in the composition range related to copper smelting/converting slags. In addition, olivine, diopside and pyroxene may also appear at certain conditions. The presence of up to 20 wt% CaO, up to 10 wt% MgO and 10 wt% Al2O3 in the slag increases the spinel liquidus and decreases the tridymite liquidus. Liquidus temperatures in tridymite primary phase field are not sensitive to Po2; Liquidus temperatures in spinel primary phase field increase significantly with increasing Po2. Addition of the same weight of Al2O3 or MgO in slag shows the same effect on the liquidus temperatures in spinel and tridymite primary phase fields. The trends in the effects of Al2O3 or MgO on liquidus temperatura are similar for both copper smelting and converting slags.