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.

High-chromium vanadium residue (HCVR (HCVR: high-chromium vanadium residue)) is an important secondary resource of valuable metals such as vanadium (V), chromium (Cr), and molybdenum (Mo). The mainstream technology for the utilization of HCVR, the Na₂CO₃-assisted-roasting–water-leaching method, usually requires roasting temperatures of more than 800 °C and results in the synchronous leaching of Cr with V and Mo. This makes the subsequent separation of V, Mo, and Cr in the aqueous system difficult. In this study, an efficient and clean process for the selective separation of Cr and stepped recoveries of V and Mo from HCVR is proposed via K₂CO₃-mediated carbonation conversion. Using this process, the roasting temperature can be reduced from more than 800 °C to 200 °C, and 83.14%, 99.94%, and 0.33% of V, Mo, and Cr, respectively, can be leached. Further, using the weakly alkaline ammonium-salt and sulfide precipitation methods, 98.28% pure V₂O₅ and 98.65% pure MoS₂ can be obtained and the recoveries of V and Mo can reach 82.47% and 98.88%, respectively. While almost all Mo can be recovered from the HCVR, Cr and some V might be present as a stable ferrochrome spinel in the tailing, which may be returned to the main process for the extraction of V and Cr from vanadium slag. Thus, K₂CO₃ might be a more effective alternative to Na₂CO₃ for the separation and recovery of V and Mo from HCVR and, hence, may enable its more efficient utilization.

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.

During pressure acid leaching process of black shale-hosted vanadium, increasing the reaction interface of muscovite dissolution can enhance the vanadium release. In this paper, calcium sulfate (CaSO₄) deposition behavior and its effect on muscovite under K₂SO₄ assistance were focused on for demonstrating the function of CaSO₄ on vanadium leaching from the black shale. Results showed that as K₂SO₄ mediated, the apparent activation energy of vanadium leaching and the apparent reaction order of sulfuric acid decreased from 24.37 kJ/mol to 16.63 kJ/mol and 2.7 to 1.9, respectively. The leaching rate and dependence on pH value were modified. The vanadium leaching acceleration owed to CaSO₄ deposition on muscovite in the black shale. The ion absorption stimulations found that Ca²⁺ is confirmed to be easily absorbed on the six-membered ring cavity of silicon-oxygen tetrahedrons in muscovite structure prior to K⁺ and Na⁺. Meanwhile, SO₄²⁻ provides two oxygen atoms to bond with Ca²⁺ absorbed on muscovite (001) surface. The continuous absorption and bonding create CaSO₄ deposition on muscovite (001) surface which also involves the load transmitting. The stress load transmitting correlates to pore formation in muscovite particles. It was proved that massive micropores initiated and proliferated in the existing pores under K₂SO₄ assistance. The porosity caused by CaSO₄ deposition greatly increased the reaction interface of muscovite dissolution and accelerate internal diffusion of H⁺ to the reaction interface, which can significantly weaken the vanadium leaching dependence on acid.

Capacitive deionization (CDI) based on LSC-957 resin/carbon composite electrodes was used to remove Fe impurity ions from a spent vanadium electrolyte, which enabled simple and efficient regeneration of the electrolyte. The experiments conducted in this study demonstrated that 3:1 was the optimal mass ratio of LSC-957 resin to activated carbon for the preparation of the composite electrodes, and the optimal operating voltage and operating time were 0.9 V and 6 h, respectively. After five stages of CDI tandem treatment, the adsorption rate of Fe impurity ions was 86.84% and the loss rate of V was only 3.8%. The energy efficiency of the regenerated electrolyte was 84.49%, and its performance was significantly improved compared to the spent vanadium electrolyte. The adsorption process of composite electrodes was analyzed by kinetic and isothermal models’ fit, SEM-EDS, and FTIR. This work has provided an effective and novel method for removing impurity ions from a spent electrolyte.