New Process For The Extraction Of Iron, Titanium, Vanadium, And Chromium By Direct Reduction And Hydrometallurgical Routes From High-chromium Vanadium-bearing Titanomagnetite Concentrates

High-chromium vanadium-bearing titanomagnetite in Hongge District (SW China) exists as a giant iron-polymetallic deposit containing titanium, vanadium, chromium, and other valuable elements, with titanomagnetite reserves of 3.55 billion tons. The existing technologies are disadvantaged by low recoveries of the valuable metals, high energy consumption, and serious environmental pollution. Therefore, a new process for comprehensive utilization of the high-chromium vanadium-bearing titanomagnetite concentrates has been proposed. This process includes selective direct reduction, magnetic separation, and hydrochloric acid leaching processes, providing an alternative route for the efficient recovery of iron, titanium, vanadium, and chromium resources. The main points are listed as follows:(1) A systematic thermodynamics study for direct reduction of titanomagnetite concentrates indicate that titanium, vanadium, and chromium can be separated from iron by selective reduction. The grain growth study of metallic iron during the selective direct reduction indicates that the introduction of additives containing sodium or silicon helped to generate some new phases with low melting points, which could improve the diffusion of metallic iron and facilitate the grain growth of metallic iron.(2) Titanium, vanadium and chromium in the titanomagnetite concentrates have been efficiently separated from iron by coal-based selective reduction followed by magnetic separation. Further studies indicate that a little vanadium and chromium in the titanomagnetite concentrates had been reduced to carbides and dissolved in the y(fcc) phase by controlling the C/Fe molar ratio and the reduction temperature, so that vanadium and chromium could be concentrated in the phases where titanium was concentrated. Under the optimal conditions, the recoveries of iron, titanium, vanadium, and chromium were 88.3%,94.0%,90.0%, and 90.4%, respectively.(3) Atmospheric acid leaching of titanium slag containing V and Cr by hydrochloric acid has been systematically studied. Under optimal conditions, the recoveries of vanadium and chromium were 76.5% and 83.6%, respectively. This could be attributed to the fact that pseudobrookite in the slag cannot be efficiently decomposed by atmospheric acid leaching. The kinetic studies indicate that acid leaching of the slag could be well described by the unreacted shrinking core model. The leaching of vanadium and chromium were both controlled by mass diffusion in residual layer, and the apparent activation energies were 31.6 and 39.8 kJ/mol, respectively.(4) Vanadium and chromium in the titanium slag has been efficiently separated from titanium by pressure acid leaching. Further studies indicate that dissolution-reprecipitation mechanism was well suited for elucidating the acid leaching behaviors of titanium and silicon, and as such, compared to the pre-desilication-pressure acid leaching process, the pressure acid leaching-alkaline desilication process could realize more efficient silicon removal. Under the optimal conditions, the leaching of vanadium, chromium, and silicon were 90.9%,92.3%, and 94.3%, respectively, with titanium losses less than 1.5%. High titanium slag with purity of >91% was finally produced. The high titanium slag could be easily digested by concentrated sulfuric acid probably because of its decrease in the crystallite dimension, intracrystalline defects and oxygen nonstoichiometry.