Innovative application of two-stage sulfuric acid leaching for efficient recovery of Ti from titanium-bearing electric furnace slag

Abstract

A two-stage sulfuric acid leaching process was developed to efficiently recover Ti from a titanium-bearing electric furnace slag (TEFS) made from V-Ti magnetite, which has a high content of impurities and low Ti content. The efficiency of the recovery mechanism was investigated. Anosovite and gangue minerals in the TEFS reacted with sulfuric acid and generated several solid substances such as TiOSO4, CaSO4, sulfates of Mg and Al, and silicate in the first-stage of the acidolysis, which formed the product layer and hindered the diffusion of sulfuric acid. Moreover, a high content of the impurities caused the gangue minerals to closely wrap around the anosovite, which hindered the acidolysis. By adopting a two-stage acid-leaching process, soluble sulfates, which are the most abundant product of acidolysis, were dissolved in water during the first-stage of the water leaching, which exposed the unreacted anosovite, diopside, and spinel. Accordingly, sulfuric acid completely reacted with the unreacted minerals during the second-stage acidolysis. The Si- and Ca-containing products of the acidolysis mainly existed in the form of silicate and CaSO4 and were later converted to silica gel and gypsum, respectively, after the second-stage water leaching. With this innovative process, the leaching rate of Ti improved significantly, achieving a 99.33% total leaching rate. Moreover, lowering the initial sulfuric acid concentration to 48% still yielded a total leaching rate of 98.04%, with the Ti grade of the final residue dropped to 3.14%.