Thermodynamic Behaviour of Chlorine in CaO-SiO2-MgO-Al2O3(-CaF2) Slags

Abstract

The solubility of chlorine in CaO-SiO2-Al2O3-MgO(-CaF2) slag was measured at 1673 -1823 K. By estimating the chloride capacity of slags, thermodynamic behaviour of chlorine in the molten slag was investigated. Chloride capacity increased with increasing CaO/SiO2 ratio (C/S). An increase in MgO content decreased chloride capacity at C/S≥1.0 because it lowered the activity of Ca2+ which seemed to have strong affinity with Cl− in molten slag. Also, the chloride capacity decreased with increasing Al2O3 content. The affinity between the Ca2+ and Cl− ions was confirmed by measuring the infrared spectra of slags. The dissolution reaction of chlorine into slag was exothermic and its molar enthalpy was evaluated from the experimental results at 1673 - 1823 K. Based on the result obtained in the present study, the quantitative prediction of chlorine distribution during the blast furnace process was performed. It was estimated that almost all chlorine in the blast furnace would be absorbed into molten slag even if the PCI ratio was increased or low quality coal with chlorine content less than 1.0 mass% was injected.