Extraction of Vanadium from High-Chromium Vanadium-Bearing Titano-Magnetite Concentrate Pellets by Oxidizing and Na-Activation Roasting and Water Leaching

Abstract

The vanadium-bearing titanomagnetite concentrates (VTMCs) are a major raw material for vanadium extraction, but the existing process has some defects such as the low yield and long process flow. The leaching rate of vanadium is less than 65% by roasting and water leaching process using the VTMCs powders. In order to increase the leaching rate of vanadium, the VTMCs powders are mixed with sodium carbonate to form pellets by rolling forming process, and the oxidizing and Na-activation roasting and water leaching process were investigated. The high-chromium vanadium-bearing titanomagnetite concentrates (HCVTMCs) and sodium carbonate were mixed evenly according to a certain proportion, and then the mixture was formed pellet by rolling forming process. The green pellet was dried at 120 ℃ for 2 h to obtain the dry pellet in the electrothermal drier. The dry pellet was placed into a corundum crucible and was oxidation and Na-activation roasted in the box electric furnace when the temperature of electric furnace was 300 ℃. The time from 300 ℃ to set temperature was fixed at 2 h, and continue to roasting at the set temperature for 2 h. After reaction, the roasted pellets were rapidly taken out and cooled at room temperature, and crushed and ground to obtain roasted clinker powders. In a water leaching experiment, 50 g roasted clinker powder was used to extracting vanadium via a water leaching process, and the fixed leaching conditions as follows, the leaching temperature was 95 ℃, the leaching time was 90 min and the liquid-solid ratio was 6:1. Through analyzing the data of experiments, the conclusions were as follows: (1) The results of the thermodynamic analysis of oxidizing and Na-activation roasting processshowed that the order of reaction of main compounds in HCVTMCs was: FeTiO3>Fe2SiO4>FeV2O4> FeCr2O4> Fe3O4. FeV2O4 was easier to form the water-soluble sodium salt than Fe3O4 in thermodynamics, the oxidation reaction of FeV2O4 was occurred on the premise that the Fe3O4 structure must be destroyed due to the fact thatthe vanadiumwas embedded in Fe3O4 in the form of isomorphism. (2) X-ray diffraction (XRD) patterns of roasting clinkers indicated that the sodium carbonate ratio had a great influence on the phase composition of calcined clinkers, and the peak intensity of unoxidized Fe3O4 increased significantly with increasing the sodium carbonate ratio. The reaction of FeTiO3 with sodium carbonate was a simultaneous process of oxidation and Na-activation, and Na0.75Fe0.75Ti0.25O2 intermediates was formed when the reaction was not sufficient. (3) The results of extraction vanadium showed that increasing appropriately roasting temperature and sodium carbonate ratio were beneficial to improve the leaching rate of vanadium, but excessive roasting temperature and sodium carbonate ratio were led to the leaching rate of vanadium decreased significantly. The increase of calcination temperature and the ratio of sodium carbonate were beneficial to the formation of low melting point phases such as Na4TiO4, Na2SiO3 and NaAlSi3O8 in the roasting clinkers, and the chemical reaction of forming water soluble vanadate was hindered by the liquid phase. (4) The analysis results of X-ray photoelectron spectroscopy (XPS) showed that the vanadium was fully oxidized, and some iron and chromium were not oxidized to high valence state. There was no obvious peak position of vanadium and chromium in HCVTMCs, but the peak intensity of vanadium and chromium in roasted clinker was obvious. The atomic proportions of Cr6+ and Cr3+ in roasted clinkerwere 53.51% and 46.49%, respectively, and the atomic proportions of Fe3+ and Fe2+ were 77.30% and 22.70%, respectively. 5. Scanning electron microscope (SEM) images of the roasted clinker and leaching slag showed that the surface structure of roasted clinker was compact and had crystalline attachments, while the cracks and voids were evenly distributed on the surface of leaching slag. The soluble sodium salt was leached from the roasted clinker, resulting in cracks and voids were appeared on the surface of leaching slag. In addition, the roasting clinker and leaching residue particles had two kinds of morphology: dense and loose. The iron was more concentrated in the dense, while vanadium, titanium and sodium were concentrated in the loose. Based on the thermodynamic analysis of oxidizing and Na-activation roasting process, the effects of roasting temperature and sodium carbonate ratio on the roasting and water leaching process were investigated with HCVTMCs pellets as raw material. During the roasting process, the oxidation of Fe3O4 to Fe2O3, sodium oxidation of FeTiO3 to NaFeTiO4, and sodium oxidation of vanadium oxides to water-soluble sodium vanadate were realized simultaneously. After the roasting process, the water leaching process was used to dissolve the water-soluble sodium vanadate in the roasted clinker. Finally, the leaching rates of V2O5, Cr2O3 and TiO2 were 89.70%, 55.85% and 11.54%, respectively, under the condition of roasting temperature of 1100 ℃ with the sodium carbonate ratio of 15%. The oxidizing and Na-activation reaction of the larger particles in HCVTMCs were not sufficient. Reducing the particle size of HCVTMCs was helpful to improve the kinetic conditions of oxidizing and Na-activation reaction between HCVTMCs and sodium carbonate, and further increased the leaching rate of vanadium.