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The essence behind metal solvent extraction is the interaction between metal species and organic extractants. Aqueous metal species tuning at the molecular level is critical to improve the extraction efficiency and selectivity of the target metal. Herein, we demonstrate a quantitative metal species tuning strategy which is capable of extracting the most critical metals (e.g., V, W, and Mo) in extraction systems constructed by amines. We reveal the superior activities of V 4 and V 10 species among various V and Cr species by calculations and experiments. In addition, the contribution of various V n species was quantitatively evaluated via Ion Species Contribution Evaluation (ISCE). Our tuning strategy is rationally designed by bridging species characteristics and routine aqueous conditions with extraction activities. Consequently, a three-dimensional model of V and Cr solvent extraction is established for the prediction of reaction regions, and the reactivities of nearly 20 kinds of typical metal species are compared and predicted. Our strategy serves for industrial solvent extraction, and may provide inspiration for the traditional hydrometallurgical revolutionary., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Abstract: The stability of the interfacial crud produced during the extraction and separation of vanadium and chromium was studied in this paper. Thermodynamic stability, particle size distribution, setting time and clarifying curve of the emulsion droplet were investigated. From the results, the percentage of the crud produced decreases with the increasing setting time and after 30min it shows less change. The coalescence rate is relatively smaller than the rising rate, and the phase separation time is determined by the coalescence behavior of the droplet. The crud is considered to have thermodynamic instability, kinetic stability. The demulsifying mechanism was also put forward. New extraction system using n-hexane instead of kerosene as diluent with larger surface energy can prevent the emulsion formation. [Copyright &y& Elsevier]

Abstract: In this study, the interfacial crud produced during the extraction of vanadium and chromium by primary amine N1923 was investigated from the leaching solution containing heavy metals. Effect of pH values of the leaching solution on the percentage of the crud produced and the emulsion type of the crud were studied. X-Ray Fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FT-IR) and X-Ray Diffraction (XRD) and Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) have been employed for the physiochemical characterizations of the crud. Our results indicate that the percentage of the crud produced is greatly affected by the pH value of the real leaching solution, and the crud is more stable in the acidic solution. The crud is an oil-in-water emulsion with many fine solid particles in the water phase. The particles, which are from the real leaching solution, have been proved to be the main cause for the crud formation. Particles in the cruds are normally composed of a large number of the crystals of Na2SO4, a few SiO2 and oxides or hydroxids of Fe and Al. However, component proportions of the solids are dependent on the pH values. Possible mechanism of the crud formation is put forward. The solids present in the real leaching solution exert a stabilizing effect on the emulsion, based on which Na2SO4 crystallizes at the interface of the emulsion. Furthermore, the Na2SO4 crystals strengthen the stability of the emulsion, and thereafter the interfacial crud forms. Three effective methods to prevent the crud formation are proposed, i.e. clearing the real leaching solution by membrane filtration, increasing of the amount of the modifier, and applying of hexane as the diluent. [Copyright &y& Elsevier]

Graphical abstract Highlights • An available method was developed for characterization of vanadate species combined with ESI-TOF-MS and thermodynamics. • Evolutions of four characteristic vanadium species were comprehensively studied in acidic and neutral conditions. • The thermodynamic models were established and phase diagram was visualized for vanadium chemical speciation. • The semi-quantitative method is supposed to be effective for understanding of vanadium speciation in environmental fields. Abstract Identification the polymerization nature of vanadium bearing solution is difficult, yet it is of great environmental concern due to the possible carcinogenic effects as well as high-value sustainable necessities. Thus, seeking for simple and efficient characterization methods of tracking vanadium species is in urgent demand. In this work, high-resolution electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) coupled with thermodynamic calculations was employed to measure vanadium-containing samples. Evolutions of four characteristic vanadium species, H 2 VO 4 − (0–1%), V 2 species (0–1%), V 4 species (1–20%), and V 10 species (60–95%), were comprehensively studied from acidic to neutral conditions, based on which thermodynamic model and vanadium phase diagram were established to visualize transformation pathways. More than 30 types of aqueous vanadium species could be semi-quantitatively detected by employing this method with less than 5% relative error, and the corresponding existing forms and concentration of these vanadium species could be well predicted. The vanadium species identified in MS results were confirmed by NMR. This method can be widely used for the understanding of vanadium speciation in practical examples, especially involving V(V), Cr(VI) ions or organic complexes. [ABSTRACT FROM AUTHOR]

Abstract The recovery of polyoxovanadate acid compounds has got increasing attention because of both sustainable necessities and material applications. In this paper, we proposed a recovery strategy of ammonium substituted polyoxovanadate acid compounds (ASPOVC) by solvent extraction from leaching/aqueous solution. It is noted that the state of the compound (solid or liquid) is possibly controllable by the type of amines (branched or linear amine chains), enlarging application fields of these compounds. Subsequently, the compounds were characterized by comprehensive techniques, from which the molecular structures with hydrogen bonds were described. The solubility parameters were calculated, and solid ASPOVC was the biggest among the four compounds, explaining formation reasons of different states. The amine extractants performed well-efficiency (more than 98.5%) for reutilization. This approach is believed to be promised for a sustainable recovery for high-value vanadium materials from waste water. Graphical abstract Image Highlights • A recovery strategy of ASPOVC was developed by solvent extraction. • The state of the compound was controllable by the type of primary amine. • The hydrogen bond extraction mechanism was verified by NMR and FTIR. • The solubility parameters were calculated, of which solid state compound was the biggest. [ABSTRACT FROM AUTHOR]

This paper deals with a systematic thermodynamic study on the liquid–liquid extraction of vanadium from aqueous solution (0.001–0.1 mol/kg) using primary amine N1923 (0.004–0.3 mol/kg). Suitable and practical thermodynamic models (Pitzer–Pitzer and Pitzer–Margules) were improved and verified for the first time. Firstly, the Pitzer parameters were correlated based on solid–liquid equilibrium data, and then employed as the initial values in regression progress. Finally, all the interaction parameters ( β aq 0 , β aq 1 , β RV , RV org , β R , RV org , β R , R org , A RV , R org , A tol , RV org and A tol , R org ) were regressed. Liquid–liquid equilibrium data were predicted using those parameters and compared to the experimental results, which confirmed the reliability and suitability of these models for the present system. Furthermore, these models provided excellent predictions of the effect of the initial amine molality and pH value on the extraction, showing great promise for industrial applications. [ABSTRACT FROM AUTHOR]

For the purpose of the recovery of the high-purity vanadium product in leaching solution, solvent extraction has been considered as a promising approach. However, the vanadium species varied in different concentrations and pH values in aqueous solution, thus affecting the extraction yield or the reaction product in the process. In this paper, the main species of vanadium in solutions were determined with the equilibrium constants. The extraction reactions were determined based on determined species, then the hydrogen bond association mechanism of the reaction as well as the possible structures of the vanadium complexes were proposed and discussed in detail. This study established a systematic methodology for understanding the transition metal speciation in aqueous solutions as well as the extraction reactions, and envisaged the insights into the mechanism of the transition metal solvent extraction by primary amines. [ABSTRACT FROM AUTHOR]

In this report the extraction of V(V) and Cr(VI) from a synthetic feed solution and real leaching solution of the chromium-bearing vanadium slag (V–Cr slag) using primary amine LK-N21 was studied. Detailed fundamental research work was conducted to investigate the primary amine extracting V(V) and Cr(VI). The mechanism and the difference between the two metals of extraction were studied and the experimental results were compared with previously published data. The optimum technological parameters for the separation of two metals were determined including: pH value in feed solution, phase ratio, mixing time, as well as others. The results showed that primary amine LK-N21 can extract V(V) selectively by hydrogen bonding association. Cr(VI) competed V(V) to combine with the primary amine, and the concentration of Cr(VI) decided the percentage extraction of V(V) and Cr(VI). Primary amine LK-N21 extracted more than 90% of V(V) which resulted in over 90% of Cr(VI) left in the leaching solution of the V–Cr slag in the optimal conditions. Based on the results of experiments, V(V) and Cr(VI) can be separated with a high degree of selectivity. [ABSTRACT FROM AUTHOR]

Proper understanding and evaluation of a metal production process is crucial for its further optimization. Economic evaluation is frequently used to estimate the practicality of a specific process based on the product life cycle assessment. However, it encounters difficulties to identify the importance of materials efficiency coupling with pollution control during evaluation on the effectiveness of process optimization. In this research, a factor defining the material recirculation is introduced to economic evaluation. Typical vanadium oxide production processes in China were evaluated by the economic evaluation model considering the whole production process, through defining a range of parameters, i.e., the materials cost, water cost, energy cost, waste treatment cost and auxiliary cost. Three V 2 O 5 production processes are analyzed and compared to each other. The production process of high purity V 2 O 5 has the best cost-effective products with high purity, the simplest production, the highest materials efficiency and the lowest cost for waste treatment. It is noticed that materials efficiency tends to be inversely proportional to waste treatment cost. Under comprehensive environmental assessment, proper pollutant control improves material recirculation percentage and reduces the expense for waste treatment which is an important aspect of economic evaluation. With this research, an optimization scheme is illustrated for the economic evaluation of typical metal production process which may provide guidance to industrial factories to optimize relevant production processes. Image 1 • A material recirculation factor is introduced to economic evaluation model. • Typical vanadium oxide production processes were evaluated. • Comprehensive environmental assessment analyzed environmental impact of the waste. • The high recirculation percentage can effectively decrease the total cost. [ABSTRACT FROM AUTHOR]

Hierarchically nanostructured carbon hybrids with highly exposed active sites and specific surface area have been widely researched in high-performed electrochemical capacitors. Inspired from the synergistic effect of uniformly distributed active components and stable carbon substrate, combining with green solvent extraction process, we explored a facile strategy to prepare vanadium nitride quantum dots/nitrogen-doped hierarchical carbon nanocomposites (VNQD/NDHCs) from vanadium aqueous solution, which can provide large pseudocapacitance and excellent electrochemical stability. Vanadate is selective recovered from aqueous solution in form of vanadium-organic compounds (VAORCs) as precursor. Primary amines favor not only the selective metal-polymer coordination, but also the formation of cross-linked carbon matrix. Then, during chemical molecules vapor deposition (CMVD), the vanadate is in-situ nitrided along with the formation of hierarchical carbon. The prepared VNQD/NDHCs-800 exhibits exceptional capacitance (318.3 F g−1 at 1 A g−1) and retains 89.7% of the initial capacities after 12000 cycles. SEM and TEM images confirm that a large amount of quantum dots are well embedded in a graphitic carbon matrix, which provides abundant electroactive sites and fast ion diffusion for capacitive storage. This work indicates that it is feasible to directly recovery valuable metals from aqueous solutions to prepare high-performance electrode materials. Image 1 • Vanadium-based carbon hybrids contain abundant vanadium nitride active sites • Vanadium in aqueous solution is almost completely recycled. • Scalable fabrication of the products based on green solvent extraction process. • The products exhibits exceptional capacitance and excellent cycling stability. [ABSTRACT FROM AUTHOR]

The high-efficient extraction of vanadium using primary amine and its application in the utilization of the chromium-bearing vanadium slag (V–Cr slag) were studied in this work. The extraction mechanism and the possible difficulties in the application were both considered. From the results, the extraction percentage of vanadium using free primary amine with the hydrogen bond association mechanism is higher than that in the acidic environment by primary amine salts. The inorganic ions and other impurities existing in the system were all considered to research for the continuous operation of the extraction. Furthermore, the viscosities of the fresh organic phase and the recycled organic phase were determined using the extractant not only N1923 but also LK-N21, where the viscosity of the latter system increased slightly during the recycled process of the extractant. Based on the above results, the pilot and the commercial experiment were carried out. In the large-scale experiment, the vanadium was extracted and the product of 99.5 wt.% vanadium pentoxide was obtained, and the mass loss of the extractant was only 0.1%. [ABSTRACT FROM AUTHOR]

In this work, a free-standing, flexible and highly conductive vanadium-carbon nanofiber composite has been fabricated as electrode for Supercapacitors. Vanadium monoxide (VO) coupled with amorphous vanadium covalent bonds (VO x ) are successfully incorporated into carbon nanofibers (VO/VO x /CNF) by electrospinning and heat treatment. A theoretical explanation is proposed for the formation of VO/VO x in CNF composites. The VO and VO x are respectively reduced and formed from vanadium precursors of vanadium dioxide (VO 2 ) and vanadyl (IV) acetylacetonate (VOA) by means of self-reduction method, in which carbon precursors (polyacrylonitrile and polyvinylpyrrolidone), small evolved gas molecules (CO, H 2 , HCN) and graphitized carbon act as self-reductants. No additional reductants is needed before or after heat treatment, avoiding the secondary contamination. The VO/VO x /CNF electrode has a specific capacitance of 325.7 F g −1 at a current density of 1 A g −1 and is capable of reserving 92% of its initial capacitance after 5000 cycles operating at a current density of 4 A g −1 in a symmetric two-electrode capacitor using 6 M KOH as an electrolyte. The superior electrochemical performance of VO/VO x /CNF may be attributed to two advantages. The first is the enhanced conductivity brought upon the incorporation of quasi-metallic VO (∼ 10 2 Ω −1 cm −1 ) and the network of nanowire, and the second is the rapid ion transfer rate caused by the rich vanadium redox couples VO/VO x and the well-developed pore structure. Notably, this work has also provided a facile method to obtain varaible low valence states from vanadium oxides through self-reduction, which may also be applied to synthesize other metal oxides-carbon nanofiber composites. [ABSTRACT FROM AUTHOR]

• A novel strategy of utilization of impurity in waste-derived V 2 O 5 was provided. • Recycled vanadium oxides show high surface areas, and low work function values. • The Cr-doped V2O5 delivers high capacities and excellent long cycle stability. To meet the urgent requirement of sustainable energy storage technologies, it is essential to incorporate efficient waste management into designing energy storage materials. Herein, we report an environmentally responsible pathway to utilize the recycled V 2 O 5 from V-Cr slag leaching solution. Because of the fact that trace Cr are existed in the recycled V 2 O 5 from initial leaching solution. Therefore, the Cr-doped V 2 O 5 with different content of Cr was successfully synthesized and the effect of Cr on the structure and electronic characteristics of V 2 O 5 was systematically investigated. The date arising from spectral analyses informs us that the trace Cr doping can result in an expansion of the V 2 O 5 lattice, and lead to the decreasing of the work function values, so aiding in enhancing the electrochemical performance. Owing to the trace Cr doped into V 2 O 5 lattice, the recycled V 2 O 5 shows a high specific capacity of 405.5 mAh g−1 and excellent cycling stability over 2000 cycles. A detailed electrochemical reaction mechanism of Cr-doped V 2 O 5 cathode is investigated through a series of in-depth analyses. Different from conventional recycled strategy, we use the impurity element Cr, which is very difficult to separate from V, and realize the enhancement of the electrochemical performance of the recycled V 2 O 5. Moreover, the practicability of recycled V 2 O 5 is exemplified by fabricating a flexible, quasi-solid-state zinc batteries, and the cell operates well upon deformation. This work provides a new strategy for recycling wasted materials into high value materials for sustainable battery systems. [ABSTRACT FROM AUTHOR]

Critical metal sustainability is a worldwide issue whose extraction relies on hydrometallurgy mostly. The significance of metal ion species evolution in critical metal hydrometallurgy-extraction has got more and more attention. Here, the importance of the metal ion species during the whole vanadium recycling process has been evaluated quantitatively for the first time. Metal ion species as the key parameter was investigated through efficiency, material and energy accounting, and emission accounting to illustrate the effect of the metal ion species, which donated as ion species contribution (ISC). Specifically, 7 types of vanadium ion species were assessed in the process of V 2 O 5 production from leachate, including H 2 VO 4 −, HV 2 O 6 −, V 4 O 12 4−, H 2 V 5 O 14 −, V 10 O 28 6−, HVO 4 2− and VO2+. The results demonstrated that different vanadium ion species were closely related to recovery efficiency and purity, and they impact separation section, materials and energy consumption mostly in whole process. Consequently, V 4 O 12 4− occupied the highest ISC which was 1.11 times than V 10 O 28 6−, 1.37 times than VO2+ and 4.85 times than H 2 VO 4 −. Correspondingly, control of V 4 O 12 4− as dominant species appeared to be the most potential in the vanadium extraction process, which showed the feasibility of whole process optimization. With this research, ISC can help to point out dominant ion species in holistic critical metals supply chain, thus promote sustainability of critical metals in a new perspective. • Evaluating in detail the contribution of ion species to the whole V 2 O 5 production. • Covering comprehensive indicators related to ion species evolution. • An effective method for ion species regulation in critical metal resources recovery. [ABSTRACT FROM AUTHOR]

The complete separation of vanadium (V) and chromium (Cr) from chrome vanadium slag is still challenging. Many studies focus on the activity of vanadium, while the effect of the other element chromium and their mutual interaction are ignored. Here, we found that proper concentration of chromium can promote the extraction efficiency of vanadium. The extraction of V and Cr with various mass ratios ranging from 8:1–4:3 at different initial pH values using primary amine N1923 were studied. The extraction efficiency of V reached nearly 100%, while none of Cr was extracted when the mass ratio of Cr and V is 0.5 under proper pH. Through the dynamic monitoring of species evolutions during extraction, the transformation of the two metals and advantage extracted species were analyzed. Cr would transfer H+ for the combination of V 3 O 9 3-/V 4 O 12 4-, providing a great contribution to the continuous extraction of V. The real leachate was applied and 99.9% vanadium pentoxide was produced at a scale of 50 L/h. This paper offers deep insights of the separation of similar metal elements, and guide sustainable vanadium recovery from hazardous waste. [Display omitted] • Promotive action of competitive chromium species was explored. • The extraction efficiency of vanadium increased under proper addition of chromium. • The transformation and advantage extracted species of V and Cr were discussed. • Chromium species contributed continuous extraction by offering acid. • This paper encourage people to focus on the metal species transformation. [ABSTRACT FROM AUTHOR]

Rechargeable aqueous zinc ion batteries have attracted significant attention for potential applications in large-scale energy storage. However, developing suitable cathode materials with both high capacity and rate performance remains a great challenge. Herein, we report an efficient method for functional materials via controlling the stage of hydrogen bond association extraction to fabricate well-structured vanadium oxynitride without adding extra templates, turning the waste to advanced materials towards high-performance zinc ion storage. Primary amines as highly efficient selective extractant are used in this work. They result in two different structures, from hollow microsphere to novel 0D-in-2D pillared lamellar structure, for the vanadium oxynitrides. Impressively, based on structural merits of abundant electrolyte-accessible sites and transfer pathways, the resulting products are found to be excellent cathode materials with a high reversible specific capacity and rate capability for rechargeable zinc ion batteries (ZIBs). Hence, this work introduces a new clue for designing unique nanostructure vanadium oxynitride to boost the electrochemical properties of aqueous ZIBs. [ABSTRACT FROM AUTHOR]