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.

A new effective method is proposed to prepare vanadium nitride (VN) via carbothermal reduction–nitridation (CRN) of the precursor, obtained by adding carbon black (C) to the stripping solution during the vanadium recovery from black shale. VN was successfully prepared at a low temperature of 1150 °C for only 1 h with a C/V₂O₅ mass ratio of 0.30 in N₂ atmosphere, but a temperature of 1300–1500 °C is required for several hours in the traditional CRN method. The low synthesis temperature and short period for the preparation of VN was due to the vanadium-coated carbon structure of the precursor, which enlarged the contact area between reactants significantly and provided more homogeneous chemical composition. In addition, the simultaneous direct reduction and indirect reduction of the interphase caused by the coating structure obviously accelerated the reaction. The phase evolution of the precursor was as follows: (NH₄)₂V₆O₁₆·1.5H₂O → V₂O₅ → V₆O₁₃ → VO₂ → V₄O₇ → V₂O₃ → VC → VN. The precursor converted to V₆O₁₃ and VO₂ completely after being calcined at 550 °C, indicating that the pre-reduction of V₂O₅ in the traditional CRN method can be omitted. This method combined the synthesis of VN with the vanadium extraction creatively, having the advantages of simple reaction conditions, low cost and short processing time.

During the acid leaching process of black shale, with the destruction of the aluminosilicate mineral structure, a large amount of aluminum (Al) is leached, accompanied by the release of vanadium (V). To separate aluminum from the vanadium-containing solution, the precipitation behavior of aluminum ions (Al³⁺) was investigated under hydrothermal conditions with the formation of alunite and natroalunite. In the solution environment, alunite and natroalunite are able to form stably by the Al³⁺ hydrolysis precipitation process at a temperature of 200 °C, a pH value of 0.4 and a reaction time of 5 h. When Al³⁺ was precipitated at a K/Al molar ratio of 1, the aluminum precipitation efficiency and the vanadium precipitation efficiency were 64.77% and 1.72%, respectively. However, when Al³⁺ was precipitated at a Na/Al molar ratio of 1, the precipitation efficiency of the aluminum decreased to 48.71% and the vanadium precipitation efficiency increased to 4.36%. The thermodynamics and kinetics results showed that alunite forms more easily than natroalunite, and the reaction rate increases with increasing temperature, and the precipitation is controlled by the chemical reaction. Vanadium loss increases as the pH value increases. It can be deduced that the ion state of tetravalent vanadium (VO²⁺) was transformed into the ion state of pentavalent vanadium (VO₂⁺) in the hydrothermal environment. The VO₂⁺ can be adsorbed on the alunite or natroalunite as a result of their negative surface charges, ultimately leading to vanadium loss.

The conventional V₂O₅ preparation processes include ion exchange, chemical precipitation, solvent extraction, and other processes. Given the long process and complex operation nature of traditional V₂O₅ production methods, we herein developed a short-process, low-temperature, and convenient operation method of isolating vanadium (in the form of V₂O₅) from shale acid leaching solution. The acid leaching solution was oxidized with NaClO₃ and pH-adjusted with NaOH to form a vanadium-containing precipitate, which was mixed with AlCl₃ (V:AlCl₃ = 1:5, mol/mol) and roasted for 120 min at 170 °C to afford vanadium oxytrichloride (VOCl₃) with a purity of 99.59%. In addition, the vanadium-containing precipitate was mixed with AlCl₃ and NaCl (V:AlCl₃:NaCl = 3:12:8, mol/mol/mol) and roasted for 120 min at 170 °C to afford VOCl₃ with a purity of 99.94%. VOCl₃ (purity of 99.94%) was dissolved in ultrapure water, and the solution (32 g_vanadium/L) was treated with NH₃·H₂O (NH₃:V = 1.34, mol/mol) at 50 °C for 120 min. The obtained precipitate (vanadium precipitation rate = 99.28%) was roasted at 550 °C for 3 h to afford high-purity vanadium pentoxide (V₂O₅) with a purity of 99.86%. Compared with the traditional hydrometallurgical method of V₂O₅ preparation, our method avoided solvent extraction and other undesired processes and the overall process flow is greatly shortened, thus having high practical value.

The method of carbonizing biomass using di-(2-Ethylhexyl) phosphoric acid and tributyl phosphate impregnation (SICB) was studied in this research. SICB combines the benefits of an extractant and an ion exchange resin. The adsorption and desorption properties of vanadium were investigated, and the adsorption mechanism was analyzed. The results showed that the carrier was first prepared at a temperature of 1073.15 K using sawdust as a biomass substitute and then cooled to room temperature. The best adsorption performance was obtained by impregnating the carriers with di-(2-Ethylhexyl) phosphoric acid and tributyl phosphate for 60 min. The vanadium adsorption rate of 98.12% was achieved using the biomass at an initial V(IV) solution concentration of 1.1 g/L, a pH value of 1.6, and a solid-to-liquid ratio of 1:20 g·mL for 24 h. Using 25 wt.% sulfuric acid solution as desorbent, the desorption rate of vanadium was as high as 98.36%. The analysis showed that the adsorption of vanadium by SICB was chemisorption, and the adsorption process was more consistent with the proposed second-order kinetic equation. Therefore, SICB has high selectivity and high saturation capacity because of the mesopores and micropores produced by carbonization.