Regular Article

Study of CO₂ injection on the desulfurization of low-titanium slag

¹ School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, PR China
² HBIS Company Limited Chengde Branch, Chengde 067102, Hebei, PR China
³ National Engineering and Research Center of Continuous Casting Technology, Central Iron and Steel Research Institute, Beijing 100081, PR China

^* e-mail: zhangmingbo45@163.com

Received: 9 April 2018
Accepted: 29 October 2018

Abstract

A new idea that the low-titanium slag (LTS) used in the steelmaking process after CO₂ injection desulfurization is proposed in this paper. The CO₂ injection process mainly involves the grinding of low-titanium slag, mixing of slag and water, CO₂ injection, filtration, and then obtains the low sulfur and low titanium slag. The effects of cooling rates (water cooling, air cooling, crucible cooling, and furnace cooling) and CO₂ injection on the desulfurization of LTS were studied by both experimental and thermodynamic calculations. The results showed that sulfite and sulfate ions couldn’t be removed from LTS using this method, and the main removal substance in slag was sulfide ion S²⁻. The desulfurization mechanism with CO₂ injection was that the CO₂ injection reacted with H₂O to form H₂CO₃, and then the H⁺ disrupted from H₂CO₃ reacted with the S²⁻ in the slag to achieve desulfurization. During the desulfurization process, the desulfurization reaction was mainly determined by S²⁻ + CO₂ (aq) + H₂O (l) = CO₃²⁻ + H₂S(g) within the first 5 min, and then the main desulfurization reaction was S²⁻ + 2CO₂ (aq) + 2H₂O(l) = 2HCO₃⁻ + H₂S(g). As the cooling rate decreasing, the desulfurization rate of LTS increased. The desulfurization effect of furnace-cooled slag is the highest in four kinds of slag. The desulfurization rate of furnace-cooled slag reaches 72.28%, which is 4.34, 1.75 and 1.15 times than that of water-cooled slag, air-cooled slag and crucible-cooled slag, respectively. The optimal rate of desulfurization is 80.0%.