PARTITION BEHAVIOR OF NIOBIUM BETWEEN CARBON SATURATED IRON AND SLAGS FROM THE CAO-AL2O3-SIO2-MGO SYSTEM

Equilibrium studies were conducted to further understand the partition behavior of niobium between carbon saturated iron and the lime-alumina-silica-magnesia slag system with change in basicity in the temperature range 1773- 1873K. The behavior of niobium in this range of slag composition is of interest to those who use ferroniobium to alloy steel during ladle metallurgy. Small variations in slag composition caused the activity coefficient for niobium pentoxide in the slag to change by over an order of magnitude and the activity coefficient of NbO2.5was found to be a strong function of optical basicity. The measured data were used, in conjunction with literature values for the activity of niobium in steel, to predict the niobium partition under secondary steelmaking conditions. This showed that niobium losses to the slag under these conditions may be significant and the erratic nature of industrial niobium recoveries may be explained by the strong sensitivity to slag composition. The temperature dependence of the activity coefficient of niobium pentoxide was found to be positive which requires an unusually large contribution from the entropy of mixing to justify the measured activity coefficient.