The effect of Na2O on dephosphorization by CaO-based steelmaking slags

Abstract

The effect of Na2O on the equilibrium phosphorous distribution ratio between slag and iron or iron alloys, LP, has been measured for CaO-SiO2, CaO-FeOr-SiO2 (CaO or 2CaO·SiO2 saturated), and CaO-Al2-SiO2 slags. The addition of Na2O to CaO-SiO2 slags significantly increases LP and the phosphate capacity. A 25 pct CaO-25 pct Na2O-SiO2 slag has a distribution ratio nearly two orders of magnitude greater than a comparable binary 50 pct CaO-SiO2 slag. For the CaO-saturated slags containing 40 wt pct FeOT, the addition of 6 wt pct Na2O increases LP by a factor of 5. For the 2CaO·SiO2-saturated CaO-FeOT-SiO2 slag, there is an optimum FeOr content (20 wt pct) for dephosphorization, and 10 wt pct Na2O increases LP by a factor of 2. For reducing slags typically used in ladle metallurgy for Al-killed steels (50 pct CaO-40 pct Al2O3-10 pct SiO2), as little as 3 wt pct Na2O increases LP by a factor of 100. The present results indicate that small additions of Na2O to conventional steelmaking slags can greatly improve dephosphorization.