Valorization of electric arc furnace slag via carbothermic reduction followed by acid baking – water leaching

Abstract

The current study is focused on developing a two-step pyro-hydrometallurgical process for the recovery of valuable components of electric arc furnace (EAF) slag produced by the steelmaking industry. The first step (hot step) involves carbothermic reduction of the EAF slag to recover iron along with niobium, chromium, and manganese in a metallic phase and titanium, magnesium, and aluminum in an iron-depleted slag phase. The second step (cold step) involves acid baking – water leaching of the iron-depleted smelting slag to recover these metals in an iron-depleted slag phase. Fractional factorial design of experiment and response surface methodology were utilized to find the optimum operating parameters of the two steps, respectively. The optimum operating conditions were determined to be smelting temperature of 1600 ºC, carbon to slag mass ratio of 0.12 g/gEAFS, and no flux addition for carbothermic reduction and baking temperature of 185 ºC, acid to smelting slag mass ratio of 2.03, baking time of 69.8 min, and water to acid-baked slag ratio of 5.83 for acid baking – water leaching. The metallic phase obtained in the smelting process contains 70.2 wt% iron, 17.3 wt% manganese, 7.0 wt% chromium, and 0.2 wt% niobium. The developed extraction process results in 86.4% titanium and 100% aluminum and magnesium extraction. We expect the findings of this study to help enable the EAF slag valorization using the two-step (hot and cold) pyro-hydrometallurgical process, contributing to sustainable recycling and circular economy.