The vanadium precipitation liquor produced by the vanadium slag extraction process contains various valuable elements, which are not utilized at high value. In this paper, chromium is recovered through aluminum salt impurity removal - chemical reduction precipitation method. Moreover, the ammonia nitrogen and sodium sulfur in the vanadium precipitation liquor are recovered by stripping and crystallization, thereby achieving comprehensive resource recovery and utilization. The aluminum salt slag removal reduction chemical precipitation method is used to separate Cr from Si, Ca and V impurities. As a result, the obtained Cr2O3 product has a purity of 98.20%, the chromium recovery efficiency is 97.58%, and the silicon removal efficiency reaches 99.66%. The ammonia nitrogen was recovered by stripping, which would be reused to the vanadium precipitation process, with an ammonia nitrogen stripping efficiency of 98%. The purity of NH4Cl is 99.13% and meets the 99-level national standard. The Na2SO4 was recovered by evaporation concentration - crystallization method, which would be reused to the vanadium slag roasting process, with a Na2SO4 recovery efficiency of 88.38%. And the purity of Na2SO4 is 98.85%, which meets the industrial standard for Class II Na2SO4 products. The final solution after comprehensive recovery of valuable elements would be reused to the leaching process, thereby achieving water circulation. This process realizes the high-value utilization of chromium, ammonia, nitrogen, sodium and sulfur, and has no wastewater discharge and is an environment-friendly route.

Ionic liquid (IL)-based extraction is a promising and environmentally benign separation technology. Processes for quaternary ammonium-based IL extraction of vanadium have been extensively studied, but the vanadium extraction mechanism has not been accurately confirmed. This study investigated vanadium extraction from sulphuric acid leachate of shale by solvent extraction with tri-n-octylmethylammonium chloride (TOMAC/ CH3NClR3). The results indicated that 90.50 % of the vanadium extraction percentage comprised one stage under the optimal condition experiments. These experiments were carried out at pH 1.8; the IL phase consisted of 25 vol% TOMAC, 15 vol% TBP, and 60 vol% sulfonated kerosene; O/A phase ratio of 1:7.5; extraction time of 120 s. The forms of vanadium and impurities present were revealed by the solution chemistry, Medusa software simulation. The extraction mechanism of vanadium was investigated using ultraviolet spec-trophotometer (UV-Vis), fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), and hotometer matrix-assisted laser-resolved ionization time-of-flight mass spectra (MALDI-TOF-MS). Under extraction conditions at pH 1.8, vanadium was present as an anion in the form H2V10O4- 28 and HV10O5- 28. Since the extraction mechanism of TOMAC was anion exchange, the extracted vanadium was mainly present as the anionic complex [(CH3NR3)4 & sdot;H2V10O4- 28]/[(CH3NR3)5 & sdot;HV10O5- 28]. The ESP map of TOMAC and V (V) was calculated to confirm the reaction sites and was used to verify the anion exchange mechanism.

为积极响应国家"双碳"目标,开发高效选择性钒页岩酸浸液净化分离工艺对页岩提钒行业意义重大.在本研究中,从溶液pH值、杂质离子(铁、铝和镁)浓度和反萃剂 3 个因素对比了新型羟肟类萃取剂Mextral 984H和有机磷类萃取剂P204 的萃取行为.结果表明,Mextral 984H的最佳萃取pH值在0.5～1.5,P204 的最佳萃取pH值在1.5～2.4,相比于P204,Mextral 984H与钒形成的钒萃合物结构更稳定,钒氧键键长值更小,分子间隙更大,钒萃合物在酸性环境中更容易稳定存在.Fe(Ⅲ)、Al(Ⅲ)和Mg(Ⅱ)对Mextral 984H萃取V(Ⅴ)的影响较小,而在P204 中,Fe(Ⅲ)对V(Ⅳ)的萃取影响较大,将Al(Ⅲ)和Mg(Ⅱ)的浓度控制在10g/L以下,可降低Al(Ⅲ)和Mg(Ⅱ)的共萃率.碳酸钠和草酸对Mex-tral 984H负载有机相的单级反萃率均超过80％.

Chelating extractants have shown excellent selectivity in vanadium extraction. Nevertheless, the resulting extraction complex is stable, making the stripping of chelating extractant a challenge. The H2C2O4-H2SO4 system was proposed to stripping vanadium from the loaded organic phase of chelating extractant Mextral 984 H. The effects of process parameters of H2C2O4-H2SO4 system on the vanadium stripping percentage was investigated. The results show that the single-stage vanadium stripping percentage reached 93.12%, and the vanadium concentration in the single-stage stripping solution reached 13.44 g/L under optimum conditions: the H2SO4 concentration of 1.87 mol/L, the H2C2O4 concentration of 0.16 mol/L, the temperature of 80 degrees C, the time of 30 min, and phase ratio(O/A) of 4:1. In addition, the high extraction efficiency (>85%) was maintained after 10 cycles, indicating that the developed system can be used in the Mextral 984 H stripping system. The mechanism of stripping was also analysed using FT-IR and H-1 NMR combined with thermodynamic and quantum calculations. It was summarized that after H2C2O4 reduces V(V) to V(IV), H+ can replace V(IV), the free V(IV) in organic phase is more prone to coordinated with C2O42- and SO42- and then goes into aqueous phase. Thus the stripping and regeneration of the loaded organic phase of Mextral 984 H can be occurred simultaneously. Meanwhile, the introduction of H+ can speed up the stripping process. The innovative method of the reduction stripping of vanadium is proposed in the black shale extraction field.

The sulfuric acid leachate from vanadium-bearing shale (SALV) has high acidity with pH around 0.5, and contains several different elements. The chelating extractant Mextral 984H was proposed to extract vanadium from said leachate. In this study, the effects of pH, temperature, extraction time, phase ratio and Mextral 984H concentration on the vanadium extraction efficiency were investigated. Moreover, this has been appraised as well in regards to other impurities such as iron, aluminum, magnesium, potassium, phosphorus, and calcium. The results show that 99.55% of vanadium was extracted through a three-stage extraction, while concentration of extracted impurities was lower than 3%. These experiments were carried out at pH = 0.53, temperature of 25?, extraction time of 12 min, phase ratio (A/O) equal to 2:1, Mextral 984H concentration of 20 vol% and sulfonated kerosene as diluent. The extraction mechanism of vanadium was investigated using FT-IR, H-1 NMR, ESI and quantitative calculations. It has been observed that the O atom on the phenolic hydroxyl and the N atom on the oximido were coordinated with V(V) to form an extraction complex composed of a six-membered ring with 1:1 (metal:ligand) mole ratio; interestingly, the H atom on the phenolic hydroxyl was dissociated. According to the reported results, the Mextral 984H extraction system can be used to extract vanadium from the SALV with no need to adjust pH, which can simplify the extraction process and reduce the consumption of chemicals.

Aluminum speciation is complex in a solution where organic and inorganic ligands coexist, and aluminum can form different complexes with various ligands. In this paper, the coordination mechanism of aluminum with oxalate and fluoride in aluminum recovery from vanadium extraction wastewater was investigated. By comparing the process of recovering aluminum with oxalate and fluoride precipitation, oxalate crystallization is found to perform better with vanadium extraction wastewater. Under optimum conditions, the crystallization percentage of aluminum was 87.10%. K3Al(C2O4)(3)center dot 3H(2)O was obtained and characterized by XRD and FTIR, and the total recovery of aluminum was 80%. The coordination mechanism and migratory behavior of aluminum with oxalate and fluoride during crystallization were studied by thermodynamic simulation and quantum chemical calculation. Results showed that aluminum primarily exists as AlF2+, AlF2+, AlC2O4+, and Al(C2O4)(2) in vanadium extraction wastewater. With the addition of K2C2O4 and an increase in solution pH, these complexes were coordinated by C2O42- and formed Al (C2O4)(3)(3-) complex anions, which provided a saturated solution environment for K3Al(C2O4)(3)center dot 3H(2)O crystallization. The DFT simulation showed that the Gibbs free energies of the coordination reactions for Al (C2O4)(3)(3-) were negative, which indicates that these coordination reactions can proceed spontaneously. This study is important when enriching the coordination mechanism of aluminum and improving the comprehensive utilization rate of resources for vanadium-bearing shale. (C) 2021 Elsevier B.V. All rights reserved.

考察Mextral 984H螯合萃取体系下料液相pH、相比、萃取剂浓度、萃取时间对钒和杂质离子铁、铝、镁、钾、磷的萃取率的影响.结果 表明:在料液pH=1.0、萃取时间20 min、相比O/A=1/2、萃取剂浓度20％、稀释剂为磺化煤油的条件下,酸浸液中钒一级萃取率为79.43％,二级萃取率达到99.06％,且杂质铁、铝、镁、钾和磷的萃取率均低于2％.Mextral 984H通过羟基和肟基共同作用螯合萃取Ⅴ(Ⅴ),实现了高酸多杂页岩提钒浸出液中钒的高效分离提取.