INCORPORATION OF CHLORINE IN A SECONDARY STEELMAKING SLAG BASED ON THE CAO-AL2O3-SIO2 SYSTEM

CaO-Al2O3-SiO2 = 50-42-8% by weight (wt%) eutectic slags, similar in c omposition to a secondary steelmaking slag, containing 1-15 wt% CaCl2 were heated to 1798 K. DTA was performed and the system was cooled. Sa mples were characterized by electron microprobe and X-ray powder diffr action. Four main crystalline phases were present, CaO . Al2O3, 2CaO . Al2O3 . SiO2, beta-2CaO . SiO2 and 11CaO . 7Al(2)O(3) . CaCl2. The ch lorine phase was very similar to the mayenite phase (12CaO . 7Al(2)O(3 )). It formed first at 1321 (+/- 27) K and remained solid as a separat e phase because of its high melting point. The rest of the system, upo n cooling, crystallized according to the well-known CaO-Al2O3-SiO2 pha se diagram. It was seen that if chlorine is present in sufficient amou nts (greater than 4.9 wt%), the chlorine phase constitutes 92 wt% of t he final slag. Also when the chlorine phase was less than 92 wt% in th e final slag, the recovery of chlorine exceeded 90%. For comparison, C aO-Al2O3-SiO2 = 48-12-40 wt% representing an ironmaking slag, was mixe d with 10.0 wt% CaCl2 and also similarly heated and characterized afte r cooling. The phases observed were 2CaO . Al2O3 . SiO2 and two new ch lorine phases, all of which were glassy.