A large number of unexploited low-grade vanadium-titanium magnetite deposits have been found in the Chao-yang area of China in recent years. The reserves are estimated at more than 20 billion tons. A mineralogical study of raw sample indicated that it was a typical low-grade vanadium-titanium magnetite ore with weathering. Most of vanadium-titanium magnetite was replaced by martite and sphene, which would affect the recovery of valuable elements. The intergrowth relationship between vanadium-titanium magnetite and sphene was very complex, and the grain size of sphene was generally fine, and could not be completely liberated even by fine grinding, whereas the content of vanadium and titanium in sphene was higher than that in vanadium-titanium magnetite, resulting in vanadium-titanium magnetite concentrates with characteristics of high vanadium and titanium content. A magnetic separation process was investigated for the pre-concentration of low-grade vanadium-titanium magnetite ore. The results showed that 73.52% of feed ore were directly discarded for reducing the processing capacity of follow-up processing. A vanadium-titanium magnetite concentrate with 1.14% V₂O₅, 22.22% TiO₂, 42.51% Fe and a rough concentrate of ilmenite with 16.05% TiO₂, 20.77% Fe were obtained from low-grade vanadium-titanium magnetite ore which contains 0.050% V₂O₅, 1.67% TiO₂ and 8.53% Fe.

In this paper, potassium salt roasting additives were applied to extract vanadium from vanadium–titanium magnetite concentrate. Meanwhile, the mechanisms of potassium salt roasting and acid leaching kinetics were investigated. The results indicate that potassium salt roasting additives are more efficient than sodium and calcium salt and that K₂SO₄ works best. Under certain conditions (a dosage of K₂SO₄ of 4 wt %, a roasting temperature of 900 °C, a roasting time of 1 h, a leaching temperature of 95 °C, a sulfuric acid concentration of 10% (v/v), and a leaching time of 1.5 h with a liquid to solid ratio of 3 mL/g) the vanadium leaching efficiency reached 71.37%, an increase of 30.20% compared to that of blank roasting. Additionally, XRD and related SEM-EDS analyses indicated that K₂SO₄ fully destroyed the structure of vanadium-bearing minerals such as magnetite, and promoted the generation of soluble KVO₃ to inhibit the formation of insoluble Ca(VO₃)₂ in the roasting process. Furthermore, it promoted the dissolution of sphene and the release of its vanadium in the leaching process, which increased the vanadium leaching efficiency significantly. Meanwhile, leaching kinetics analyses showed that the leaching process was controlled by internal diffusion; the apparent activation energy decreased from 37.43 kJ/mol with blank roasting to 26.31 kJ/mol with potassium salt roasting. The reaction order, with regards to the sulfuric acid concentration, decreased from 0.6588 to 0.5799. Therefore, potassium salt roasting could improve mineral activity, accelerating the leaching process and reducing the dependence on high temperature and high acidity.

Vanadium-bearing muscovite is the most valuable component of stone coal, which is a unique source of vanadium manufacture in China. Numbers of experimental studies have been carried out to destroy the carrier muscovite’s structure for efficient extraction of vanadium. Hence, the vanadium location is necessary for exploring the essence of vanadium extraction. Although most infer that vanadium may substitute for trivalent aluminium (Al) as the isomorphism in muscovite for the similar atomic radius, there is not enough experimental evidence and theoretical supports to accurately locate the vanadium site in muscovite. In this study, the muscovite model and optimal location of vanadium were calculated by density functional theory (DFT). We find that the vanadium prefers to substitute for the hexa-coordinated aluminum of muscovite for less deformation and lower substitution energy. Furthermore, the local geometry and relative electronic properties were calculated in detail. The basal theoretical research of muscovite contained with vanadium are reported for the first time. It will make a further influence on the technology development of vanadium extraction from stone coal.

The general preparation method for V₂O₅ is ammonium salt vanadium precipitation, which inevitably produces large amounts of ammonia nitrogen wastewater. In this paper, we propose an environmentally friendly method for preparing high-purity V₂O₅ with low ammonium consumption. The purity of the V₂O₅ product reaches more than 99% while reducing the level of ammonium consumption. The vanadium precipitation efficiency reaches 99.23% and the V₂O₅ purity of the product reaches 99.05% under the following conditions: precipitation time of 1.5 h, precipitation temperature of 98 °C, initial precipitation pH of 2, ammonium addition coefficient of 2, purification time of 5 min with purification performed twice, purification temperature of 65 °C. In this study, compared with the use of ammonia spirit for vanadium precipitation and ammonium salt vanadium precipitation, the ammonia consumption levels are reduced by 79.80% and 80.00%, and the purity levels are increased by 0.70% and 1.01%, respectively. The compositions of the precipitated (NaV₃O₈∙xH₂O) and purified ((NH₄)₂V₆O₁₆·1.5H₂O) hydrolysis products are characterized via XRD. The TGA results show that NaV₃O₈∙xH₂O contains 1.5 times the amount of crystal water. The FTIR results explain that the two V₃O₈⁻ layers are combined end-to-end to form a V₆O₁₆²⁻ layer. The change of the product image indicates that the purification process includes three stages. Firstly, heating and NH₄⁺ attack expand the V₃O₈⁻ layer. NH4⁺ diffuses more easily into the V₃O₈⁻ layer. Secondly, NH₄⁺ destroys the electrostatic interaction between Na⁺ with the V₃O₈⁻ layer and replacing Na⁺. Finally, V₃O₈⁻ is polymerized into V₆O₁₆²⁻ to keep the crystal structure stable.

Process mineralogy shows that most vanadium in mica-type black shale exists in the octahedral sites of muscovite. The extraction of vanadium mainly occurs in the acid leaching process with participation of H ions. In this work, we firstly analyzed the dissolution rules of elements in acid leaching of muscovite, then adopted the density functional theory (DFT) calculation to accurately visualize the primary process of the surface corrosion of muscovite by H ions. The experimental results show that K releases the fastest and the release of Al is consistent with K. The simulation results find that the H preferentially shifts to the unsaturated structured O of the tetrahedron to form a strong 001 surface hydroxyl after replacing K, as well as relaxing the near Al(Si)–O bonds for the further removal of structural oxygen. Then, the 001 surface hydroxyls more likely participate in the dehydroxylation reaction through the reverse-path mechanism to remove the structural oxygen and break the hexagonal rings of the tetrahedral sheets. Remarkably, the formation and removal of structural water are overall endoergic, meaning that the disintegration of muscovite requires a sustained supply of heat. Further, the octahedral sheets where vanadium exists can be exposed to the acid environment for overall destruction. This detailed atomic migration process in acid leaching of black shale is visualized, which not only illuminates the reaction mechanism of H ions with the muscovite, but also provides guidance for vanadium extraction from black shale and a new concept for the destruction of other minerals.

In this paper, the extraction of vanadium from stone coal by roasting with MgO and leaching with sulfuric acid has been investigated, and the mechanism analysis of stone coal roasting with MgO was studied. The results indicated that under the conditions that the mass fraction of the particles with grain size of 0–0.074 mm in raw ore was 75%, the roasting temperature was 500 °C, the roasting time was 1 h, MgO addition was 3 wt %, the sulfuric acid concentration was 20 vol %, the liquid-to-solid ratio was 1.5 mL/g, the leaching temperature was 95 °C, and leaching time was 2 h, resulting in a vanadium leaching efficiency of 86.63%, which increased by 7.73% compared with that of blank roasting. The mechanism analysis showed that the degree of calcite decomposition was low and, thus, magnesium vanadate was more easily formed than calcium vanadate below 500 °C. Moreover, magnesium vanadate was easier to dissolve than calcium vanadate during the sulfuric acid leaching process. Thus, the vanadium leaching efficiency was enhanced by using MgO as a roasting additive below 500 °C. Additionally, at high temperature the formation of tremolite would consume calcium oxide produced from the decomposition of calcite, thus, the formation of calcium vanadate was hindered, and V₂O₅ would react with MgO to form magnesium vanadate. Therefore, the vanadium leaching efficiency of roasting with MgO was higher than that of blank roasting at high temperature.