Thermodynamic Behaviour of Chlorine in CaO-SiO sub(2)-MgO-Al sub(2)O sub(3)(-CaF sub(2)) Slags

The solubility of chlorine in CaO-SiO sub(2)-Al sub(2)O sub(3)-MgO(-CaF sub(2)) 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/SiO sub(2) ratio (C/S). An increase in MgO content decreased chloride capacity at C/S greater than or equal to 1.0 because it lowered the activity of Ca super(2+) which seemed to have strong affinity with Cl super(-) in molten slag. Also, the chloride capacity decreased with increasing Al sub(2)O sub(3) content. The affinity between the Ca super(2+) and Cl super(-) 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.