Vanadium nitride (VN) plays an important role in high-strength steel production due to the unique precipitation strengthening and grain refinement effects [1]. high-purity VN is widely used in the fields of advanced materials, batteries and catalysts since high electrical conductivity, high thermal conductivity and good chemical stability [2, 3]. The traditional method for preparing VN is the carbon thermal reduction method [4]. Nowadays, thermal processing precursor method is highly anticipated for preparing high-quality VN due to lower reaction temperature, simple process, and short production process [5]. This method includes two steps, which the precursors containing the shell of vanadium and core of carbon powders are formed and then the precursors are reduced and nitrided in the N₂ atmosphere to obtain VN.

However, carbon powders are difficult to disperse in the solution uniformly owing to the huge surface tension and adsorption properties, and the precursors prepared subsequently are agglomerate. This is the main reason that the reaction is insufficient during the nitrogen reduction process, which affects the quality of VN. 

In response to the above issue, Polyvinyl pyrrolidone (PVP) and the other two dispersants are used to optimize the structure of the precursors in order to prepare high quality VN. Under optimum condition of 1150 °C, the VN with nitrogen content of 17.94% is prepared by adding 5% PVP. When the reaction temperature exceeds 400 °C, the precursors of adding 5% PVP are easily converted to V₇O₁₃, V₃O₅, V₂O₃ and VN at the same temperature. The precursors of adding 5% PVP have lower E_a during reduction and nitration process, which are easier to be reduced and nitridated. In comparison with the process without adding dispersants, the addition of carbon powders is reduced by 9% and the nitriding time is decreased by 75%, which reduce CO₂ emission, the energy consumption for generation and the production cost.

Vanadium is a valuable and rare resource widely used in chemical manufacturing, military affairs, aerospace, metallurgical industry and other fields [1], and China is rich in vanadium resources, accounting for 34% of the world's total, ranking first in the world. Vanadium mainly in the form of vanadium-titanium magnetite and vanadium-bearing coal [2]. As a new type of energy storage technology, vanadium redox flow battery has been widely studied due to its advantages of environmental protection, long-life, safety and flexible power design [3]. Vanadium electrolyte is an important component of vanadium batteries, and it is directly related to the performance and cycle life of vanadium batteries [4]. Solvent extraction is widely used for the extraction of vanadium. It can prepare electrolyte from vanadium-containing solution, eliminating the steps of vanadium precipitation, impurity removal and dissolution, which meets the requirements of energy saving and environmental protection. Based on the above, we propose a clean and short process for the preparation of vanadium electrolyte from vanadium shale leaching solution by solvent extraction.

An oxidative stripping system, with the low concentrations of hydrogen peroxide and sodium hypochlorite was introduced to facilitate vanadium recovery and further separation of impurities from the leach solution. In order to investigate the mechanism, FTIR and Raman spectroscopy were used to investigate the changes in valence bonding before and after extraction and stripping. The concentration of vanadium and other impurities in the vanadium-rich liquid was investigated by ICP to determine whether it complied with national standards（GB/T 37204-2018）.

After reduction and enrichment, a high purity vanadium electrolyte with low concentration of impurities was prepared. The prepared electrolyte exhibits acceptable electrochemical and charge/discharge properties. The method saves a large amount of preparation cost than the traditional method and does not produce ammonia, nitrogen or harmful gases. The technology is economically reasonable and eco-friendly, and is expected to be applied to large-scale production and promote the development of vanadium redox flow battery and new energy.

 

The vanadium shale is a unique and valuable resource of vanadium, and its efficient development can significantly contribute to the expansion of the overall available vanadium resources. However, the distribution of vanadium shale resources is widespread, with varying ore properties and significantly regional extraction characteristics. Currently, the process mineralogy data of vanadium shale is intricate and indistinct, while gangue impurity elements also hinder the detection of vanadium traces within the lattice structure. In terms of technical reliability, replicating and popularizing advanced technology proves challenging due to the unclear mechanism behind vanadium extraction from shale. The crystal lattice characteristics and vanadium extraction rules of vanadium shales are investigated based on the analysis of vanadium shales in China, providing insights into the process of vanadium coordination transformation and migration within vanadium shale. With the aid of quantum chemistry and numerical simulation methods, significant advancements have been made in enhancing the mineral genetic information of vanadium shale, thereby unveiling the fundamental mechanisms underlying key strengthening technologies for efficient extraction of vanadium from shale. The primary objective of this study is to facilitate the sustainable development of highly effective and environmentally friendly extraction techniques for utilizing vanadium resources from shale.