Liquidus temperatures and viscosities of FeO‐Fe2O3‐SiO2‐CaO‐MgO slags at compositions relevant to nickel matte smelting

Although the liquidus temperatures and viscosities of iron silicate slags are critical in the operation of many pyrometallurgical processes, there is relatively little published data relating to complex, multi‐component systems. In this study, liquidus temperatures and viscosities in the FeO‐Fe2O3‐SiO2‐CaO‐MgO slag system were determined at conditions relevant to base metal smelting processes. The classical quench technique was used to measure liquidus temperatures at Fe/SiO2 ratios of 1.3 to 1.8, CaO contents up to 9 wt%, MgO contents up to 12 wt% and at oxygen partial pressures of 10−11 and 10−8 atm. The addition of MgO was found to lead to large increases in liquidus temperature. The addition of CaO generally led to a moderate fall in liquidus temperature but the magnitude and direction of the change depended on the Fe/SiO2 ratio and MgO content. At CaO contents greater than about 3%, increasing the oxygen partial pressure of the system raised the liquidus temperature moderately and lowered the ability of CaO to depress the liquidus temperature. The viscosity of the slags was measured over similar composition ranges at iron saturation by means of a coaxial, cylindrical cup and bob arrangement. The slags were found to be Newtonian in behaviour above their liquidus temperatures. Viscosity decreased significantly as the Fe/SiO2 ratio was increased in the range 1.3 to 2.00. The addition of low levels of CaO or MgO lowered the viscosity but the addition of further MgO increased the viscosity. The MgO content at which the viscosity began to increase decreased with increased CaO content.