In this paper, a novel K2SO4/KCl composite roasting additive was used to extract vanadium from vanadium–titanium magnetite concentrate. Further, the mechanism of K2SO4/KCl for extracting vanadium was studied. The results indicate that the vanadium leaching efficiency reached 82.04%, an increase of 7.43% compared to that of single K2SO4 and 10.05% compared to single KCl under the following conditions: a total dosage of K2SO4/KCl of 7 wt % with a mass ratio of 6/4, a roasting temperature of 950 °C, a roasting time of 1 h, a leaching temperature of 95 °C, a sulfuric acid concentration of 10% (v/v: volume percentage), and a leaching time of 1.5 h with a liquid-to-solid ratio of 3 mL/g. Moreover, crystal chemistry analyses indicated that the essence of the vanadium extraction with roasting was the conversion of cubic crystal systemic vanadium-bearing magnetite (FeO(Fe,V)2O3) to trigonal crystal systemic hematite (α-Fe2O3), and as most Fe(V)–O bonds were broken with the reconstructed conversion, the dissociation of V(III) occurred. Furthermore, the main decomposition products of K2SO4/KCl were K2O, SO2, and Cl2. X-ray diffraction (XRD) and related SEM-EDS analyses indicated that there were mainly three aspects in the mechanism of K2SO4/KCl for extracting vanadium. Firstly, activated K2O could combine with vanadium to generate soluble KVO3 rather insoluble Ca(VO3)2; secondly, SO2 could react with CaO to form CaSO4 to prevent the generation of acid-consuming Ca(VO3)2, which was beneficial to the dissolution of vanadium-bearing sphene (Ca(Ti,V)SiO4O); thirdly, Cl2 could destroy the structure of hematite (Fe2O3) to reduce its wrapping extent to KVO3.
Mechanism of Novel K2SO4/KCl Composite Roasting Additive for Strengthening Vanadium Extraction from Vanadium–Titanium Magnetite Concentrate
