High Vanadium Research Articles

In-situ electrochemical etching of V4AlC3 MAX to V2O5/C composite as Zn-ion storage host

Although V2O5 is considered as promising cathode for aqueous Zn-ion batteries (AZIBs), the poor intrinsic conductivity and unstable structure can significantly hamper its electrochemical energy storage capability. In this work, an in-situ formation strategy of V2O5/C composite nanosheets-derived from V4AlC3 MAX is reported, as an efficient Zn2+ storage host via electrochemically etching-induced phase transition strategy. And the mechanism behind the V4AlC3 MAX electrode conversion were systematically studied. The results revealed that the V-Al bond and Al 1s peak of V4AlC3 were gradually disappearing at prolonged cycling, meanwhile the high valence state vanadium was formed simultaneously as the V2O5/C composite. Benefiting from the efficient reaction kinetics endowed by the V2O5/C nanosheets, such V4AlC3 MAX derived electrode can deliver a high specific capacity of 102 mA h g−1 (20 A/g) at the cut-off voltage of 2.0 V, Furthermore, discharge capacity of 158 mA h g−1 after 3000 cycles at 10 A/g can be retained, confirming it a superior rate capability and cycling stability. The work demonstrates an effective strategy for green and advanced cathode material design and high-performance AZIBs.

Process mineralogy approach to optimize curing-leaching in vanadium-bearing stone coal processing plants

The purpose of this study is to apply process mineralogy as a practical tool to further understand and analyze the reasons for low leaching rates in the curing-leaching process of vanadium-bearing stone coal and to find a solution or improvement to optimize the leaching index. Using vanadium-bearing stone coal with the V2O5 mass fraction of 0.88% as the research object, the effects of particle size, mineral composition, and sulfuric acid curing on the feed, intermediate, and final products of curing-leaching were analyzed. The main vanadium-bearing minerals in the feed samples included sericite/illite, montmorillonite, kaolinite, limonite, and schreyerite. Through the penetration depth analysis of sulfuric acid, the reason for the high vanadium content in the coarse leaching residue (0.205% V2O5) was found, mainly due to the poor curing effect and incomplete washing after screening. Therefore, thorough washing after sieving and further optimizing the curing process are necessary. The vanadium content of the fine leaching residue (0.078%) was low and the curing-leaching effect was good. However, the vanadium content in the thickened residue (0.296%) exceeded that in the fine leaching residue, which was attributed to the neutralization reaction in the #1 thickener. To solve this problem, the neutralization and thickening processes should be performed in separate equipment. The analysis and detection of key products is helpful for identifying problems and improving the curing-leaching circuit process.

Phosphate synergism activation strategy for amorphous vanadium oxide cathode materials of high-performance aqueous zinc ion batteries

Durability of V-based cathode materials at low current density is a key factor for application of aqueous zinc ion batteries (AZIBs). An isotropy high entropy amorphous vanadium oxide material (VO-PO@C) is obtained by in-situ electrochemical oxidation activation strategy. Larger phosphate cluster radius not only offers abundant defect active sites but also improves the solid-state solubility and transfer kinetics of Zn2+. For the in-situ electrochemical oxidation activation strategy, phosphate can prevent the structural reorganization which is caused by excessive oxidation. In addition, Zn|Zn(CF3SO3)2|VO-PO@C exhibits a specific capacity of 247.8 m h g−1 at 0.5 A g−1, and an excellent cyclic performance up to 300 cycles at 1.0 A g−1 with a capacity retention of 94.2% and coulombic efficiency of 100% without any phase transformation. Phosphate is beneficial to activate amorphous vanadium oxide and increase ions diffusion contribution of reversible capacity for high-performance AZIBs cathode materials. This work provides a universality design strategy for efficient V-based cathode electrodes of AZIBs.

Carbide Characteristics of High Vanadium High-speed Steel Manufactured by Electroslag Remelting

Carbide Characteristics of High Vanadium High-speed Steel Manufactured by Electroslag Remelting

An Advanced Composite Membrane for the All-Vanadium Redox Flow Battery

Redox flow batteries (RFBs) are a promising technology for grid scale stationary energy storage to complement renewable energy systems. These batteries have a relatively low energy density; however, they offer important advantages, including: long life-time; decoupled energy (arbitrarily large electrolyte volume) and power (electrode area); high round-trip efficiency; scalability and design flexibility; fast response; and low environmental impacts. These advantages make them superior to many energy storage technologies for stationary applications [1-4]. Among the various types of RFBs, vanadium RFBs (VRFBs) are an emerging technology for grid scale energy storage and the integration of renewable energy generation [5]. The membrane is a key component of a VRFB that separates the two half-cell electrolytes and prevents cross-mixing, while allowing the transport of ions during charge-discharge cycles [6]. The VRFB membrane should exhibit low vanadium ion permeability to minimize self-discharge, low cost, and long‐term chemical stability under normal operating conditions. A high proton conductivity and low vanadium ion crossover are known to improve the efficiency of VRFBs [6-7]. In this study, we present a novel composite Nafion based membrane that results in a significant increase in the VRFB performance. The composite membrane has been characterized for its chemical, structural, and thermal properties using appropriate analytical techniques. The battery performance was evaluated in a flow cell using a ‘zero-gap’ design with an electrode area of 5 cm2. The electrolytic solution, 1.6 M VOSO4 in 3 M H2SO4, was circulated through the cell. Thermally treated carbon papers were used as the cathode and anode electrodes. For charge-discharge experiments, a constant current density (10 to 80 mA cm−2) was applied with upper and lower voltage cut-offs of 1.65 and 0.8 V, respectively. The stability of the battery using the composite membrane was evaluated over 100 cycles. Figures 1 and 2 show the energy efficiency and capacity retention during 100 charge-discharge cycles. The results reveal that the energy efficiency was improved from 51% to 63% by using the composite membrane. In addition, the charge-discharge capacity and capacity retention improved by around 200% and 25%, respectively. This improvement can be attributed to a higher proton conductivity and lower vanadium permeability of the composite membrane.

(Digital Presentation) High-Temperature Ammonia Treatment for Carbon Felt Electrodes in All-Vanadium Redox Flow Batteries

Ammonia gas treatments of varying temperature were performed on carbon felt electrodes in this study. Their physical and electrochemical properties were investigated.Carbon felt electrodes are often used in vanadium redox flow batteries (VRFBs). Without processing, carbon felt has poor wettability which frustrates electrochemical activity. This material must be modified to improve performance, which has been historically accomplished with thermal treatments ostensibly to promote oxygen functional groups, although this has been the subject of debate as morphological impacts have also been observed. [1-3] Many attempts have been made to improve performance of carbon felt in VRFBs, but some of the more successful modifications have resulted in an increase in the specific surface area. [4-6] Previous research at the University of Tennessee Knoxville suggests edge sites play a role in improving performance. Preliminary experiments on carbon felt performed by this lab with ammonia at high temperatures have shown promising results. Additional experiments were performed at 900°C by varying length of treatment time, finding four hours to be optimal. [3] New experiments have been done to investigate the kinetic effects of temperature.For these experiments, commercially available carbon felts (SIGRACELL® GFD3 by SGL Carbon, Meitingen, Germany) were modified by exposure to flowing ammonia gas through a furnace at (500°C, 700°C, 900°C, and 1100°C) varying temperatures for four hours. The samples were tested in a single-cell flow battery using cyclic voltammetry (CV), polarization curves, and electrochemical impedance spectroscopy (EIS). This treatment results in a significant increase in electrochemical surface area and performance.The physical properties were characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and Raman spectroscopy. This was done to study the mechanism and kinetic effects of ammonia on the carbon felt material as temperature increases during the treatment itself. Samples treated at the highest temperatures exhibited a notable loss of mass, which is observed in the SEM images in Figure 1. This resulted in a significant increase in edge sites and active surface area, along with a substantial increase in cell performance, which was achieved with the ammonia-modified carbon felts described in this work, with over three times the current density at 80% voltage efficiency compared to untreated felt. Sun, B. and M. Skyllas-Kazacos, Modification of graphite electrode materials for vanadium redox flow battery application—I. Thermal treatment.Electrochimica Acta, 1992. 37(7): p. 1253-1260.Pezeshki, A.M., "Impedance-Resolved Performance and Durability in Redox Flow Batteries. " PhD diss., University of Tennessee, 2016.Gass, K., High Performance Vanadium Redox Flow Battery Electrodes. [manuscript under submission], 2021.Lu, W., et al., High-performance porous uncharged membranes for vanadium flow battery applications created by tuning cohesive and swelling forces.Energy & Environmental Science, 2016. 9(7): p. 2319-2325.Zhou, X.L., et al., A high-performance dual-scale porous electrode for vanadium redox flow batteries.Journal of Power Sources, 2016. 325: p. 329-336.Wei, L., et al., Highly catalytic hollow Ti3C2Tx MXene spheres decorated graphite felt electrode for vanadium redox flow batteries.Energy Storage Materials, 2020. 25: p. 885-892. Figure 1. SEM images at 30,000X magnification of carbon felt electrodes: a) untreated, b) 4 hours NH3 treated at 500°C, c) 4 hours NH3 treated at 700°C, d) 4 hours NH3 treated at 1100°C. Scale was identical for all micrographs Figure 1

Novel ether-free membranes based on poly(p-terphenylene methylimidazole) for vanadium redox flow battery applications

The fabrication of low-cost and high-performance membranes is one of the most critical issues for vanadium redox flow batteries (VRFBs). Herein, a novel ether-free poly(p-terphenylene methylimidazole) (PTMIm) is synthesized by a facile one-pot Friedel-Crafts polyhydroxyalkylation of p-terphenyl and 1-methyl-2-imidazolecarboxaldehyde. The PTMIm has excellent organic solubility and good chemical stability towards high valence vanadium ions. Meanwhile, due to the present pendant imidazole groups, the PTMIm membrane exhibits a high sulfonic acid absorption capability, achieving a suitable area resistance (AR). In order to further enhance the performance of the PTMIm membrane, side-chain quaternization is carried out by using 1-bromopropane, 3-bromo-N,N,N-trimethylpropan-1-aminium bromide and 3-chloro-2-hydroxypropyltrimethyl ammonium chloride as quaternized reagents. Comparing with pure PTMIm membrane and propyl group grafted membrane (i.e. PTMIm-C3), terminal quaternary ammonium side chain grafted membranes of PTM-C3-QA and PTMIm-C3-OH-QA possess lower AR and better vanadium ion resistance simultaneously. Consequently, the ion selectivity value of the PTMIm-C3-QA membrane is 8.7 × 105 S min cm−3, which is approximately 130 times higher than that of Nafion 115 (6.6 × 103 S min cm−3), mainly resulting from its low AR (0.68 Ω cm2) and ultralow vanadium ion permeability (9.5 × 10−9 cm2 min−1). Meanwhile, both PTMIm and its grafted membranes exhibit excellent chemical stabilities within 400 h chemical stability test. Owing to the superior restriction on vanadium migration, the single cell with PTMIm-C3-QA displays an excellent self-discharge duration of 500 h, which is greatly longer than that of Nafion 115 (58 h). In the range of 40–160 mA cm−2, the PTMIm-C3-QA based cell expresses higher coulombic efficiencies (>99.5%) and larger energy efficiencies than the cell with Nafion 115. For the cycling test of VRFB during 500 cycles, the PTMIm-C3-QA based cell displays excellent cycle stability and good discharge capacity retention, indicating a great application potentiality of the PTMIm-C3-QA membrane for VRFBs.

Unraveling diverse survival strategies of microorganisms to vanadium stress in aquatic environments

Worldwide vanadium contamination is posing serious risks to ecosystems. Although abilities of microbial communities to cope with vanadium stress using specific survival strategies have been reported, little is known regarding their relative importance and the underlying detoxification/tolerance mechanisms. Herein, we investigated the potential survival strategies of microbial communities and associated pathways in aquatic environments based on geochemistry and molecular biology. High vanadium content was observed for both water (12.6 ± 1.15 mg/L) and sediment (1.18 × 103 ± 10.4 mg/kg) in the investigated polluted stream. Co-occurrence network investigation implied that microbial communities showed cooperative interactions to adapt to the vanadium-polluted condition. Vanadium was also characterized as one of the vital factors shaping the community structure via redundancy analysis and structural equation models. Based on the metagenomic technology, three survival strategies including denitrification pathway, electron transfer, and metal resistance in innate microbes under the vanadium stress were revealed, with comprehensively summarized vanadium detoxification/tolerance genes. Remarkable role of electron transfer genes and the prevalent existence of resistance genes during detoxifying vanadium were highlighted. Overall, these findings provide novel insights into survival strategies under the vanadium contamination in aquatic environments, which can be of great significance for the identification, isolation, and application of vanadium reducing bacteria in vanadium bioremediation.

Vanadium for Green Energy: Increasing Demand but With Health Implications in Volcanic Terrains.

The transition to a clean energy future may require a very substantial increase in resources of vanadium. This trend brings into focus the potential health issues related to vanadium in the environment. Most vanadium enters the Earth's crust through volcanic rocks; hence, vanadium levels in groundwaters in volcanic aquifers are higher than in other aquifers and can exceed local guidance limits. The biggest accumulation of volcanogenic sediment on the planet is downwind of the Andes and makes up much of Argentina. Consequently, groundwaters in Argentina have the highest vanadium contents and constitute a global vanadium anomaly. The high vanadium contents have given rise to health concerns. Vanadium could be extracted during remediation of domestic and other groundwater, and although the resultant resource is limited, it would be gained using low‐energy technology.

Chemical properties, sources and size-resolved hygroscopicity of submicron black-carbon-containing aerosols in urban Shanghai

Abstract. Refractory black carbon (rBC) aerosols play an important role in air quality and climate change, yet highly time-resolved and detailed investigations on the physicochemical properties of rBC and its associated coating are still scarce. In this work, we used a laser-only Aerodyne soot particle aerosol mass spectrometer (SP-AMS) to exclusively measure rBC-containing (rBCc) particles, and we compared their properties with those of the total nonrefractory submicron particles (NR-PM1) measured in parallel by a high-resolution AMS (HR-AMS) in Shanghai. Observations showed that, overall, rBC was thickly coated, with an average mass ratio of coating to rBC core (RBC) of ∼5.0 (±1.7). However, the ratio of the mass of the rBC-coating species to the mass of those species in NR-PM1 was only 19.1 (±4.9) %; sulfate tended to condense preferentially on non-rBC particles, so the ratio of the sulfate on rBC to the NR-PM1 sulfate was only 7.4 (±2.2) %, while the majority (72.7±21.0 %) of the primary organic aerosols (POA) were associated with rBC. Positive matrix factorization revealed that organics emitted from cooking did not coat rBC, and a portion of the organics that coated rBC was from biomass burning; such organics were unidentifiable in NR-PM1. Small rBCc particles were predominantly from traffic, while large-sized ones were often mixed with secondary components and typically had a thick coating. Sulfate and secondary organic aerosol (SOA) species were generated mainly through daytime photochemical oxidation (SOA formation, likely associated with in situ chemical conversion of traffic-related POA to SOA), while nocturnal heterogeneous formation was dominant for nitrate; we also estimated an average time of 5–19 h for those secondary species to coat rBC. During a short period that was affected by ship emissions, particles were characterized as having a high vanadium concentration (on average 6.3±3.1 ng m−3) and a mean vanadium/nickel mass ratio of 2.0 (±0.6). Furthermore, the size-resolved hygroscopicity parameter (κrBCc) of rBCc particles was obtained based on their full chemical characterization, and was parameterized as κrBCc(x)=0.29–0.14 × exp⁡(-0.006×x) (where x ranges from 150 to 1000 nm). Under critical supersaturations (SSC) of 0.1 % and 0.2 %, the D50 values were 166 (±16) and 110 (±5) nm, respectively, and 16 (±3) % and 59 (±4) %, respectively, of the rBCc particles by number could be activated into cloud condensation nuclei (CCN). Our findings are valuable for advancing the understanding of BC chemistry as well as the effective control of atmospheric BC pollution.

Non-aqueous rechargeable calcium-ion batteries based on high voltage zirconium-doped ammonium vanadium oxide cathode

Calcium-ion batteries heed the research attention as a energy storage system due to the merits of natural abundance, low-cost, reduction potential (−2.87 V vs. SHE) similar to lithium (−3.04 V vs. SHE) and high theoretical working potential of calcium. However, the practical realization experiences a barrier due to the lack of suitable high-voltage positive electrodes to accommodate the large Ca 2+ with sufficiently fast ionic conduction. Herein, we investigate the zirconium-doped ammonium vanadium oxide (Zr–NH 4 V 4 O 10) as a high-voltage cathode for the rechargeable calcium-ion batteries for the first time at room temperature. It exhibited an initial discharge capacity of 78 mAh g −1 with an average discharge voltage of ∼3.0 V vs. Ca 2+ |Ca and delivered an initial energy density of 231 W h kg −1 in calcium triflate [Ca(CF 3 SO 3) 2 ] added in propylene carbonate electrolyte. Moreover, the Zr–NH 4 V 4 O 10 host presents a high-rate capability, excellent cycling stability (0.021% capacity decay per cycle) for 500 cycles with ∼89% capacity retention, maintaining ∼100% Coulombic efficiency. This is one of the first demonstrations of reversible Ca-ion storage with a high voltage (∼3.0 V) using a conventional electrolyte.

Effect of alloy element on microstructure and properties of heat-affected zone

In the present study, the influences of general composition (GC steel), magnesium deoxidation treatment (MT steel) and magnesium deoxidation treatment with high vanadium (MVT steel) content on the inclusions, microstructure and low-temperature toughness of the welding heat affected zone of EH36 steel were studied. The thermal cycle process of the heat-affected zone (HAZ) was simulated by a thermal simulator, and then microstructure and impact properties were tested and analyzed. Obtained results show that Magnesium deoxidation treatment and magnesium deoxidation treatment with higher vanadium content decrease the number and average size of inclusions. Compared with GC steel, the austenite grain size of MT and MVT steel reduces at high temperatures so that the nucleation temperature of acicular ferrite in HAZ microstructure increases. Compared with GC steel, the low-temperature impact toughness of HAZ by MT steel and MVT steel increases.

Pre-reduction of carbon-containing pellets of high chromium vanadium–titanium magnetite at different temperatures

Abstract The effect of temperature on phase transformation, metallization rate, carbon residue and agglomeration of metal Fe after the pre-reduction of carbon-containing pellets in high-chromium vanadium–titanium magnetite (HCVTM) was investigated. The results indicated that titanomagnetite was finally reduced to metal Fe and (Mg, Fe)Ti2O5 without low valence titanium oxide with increasing pre-reduction temperature from 950 to 1,250℃; Vanadium magnetite produces Fe, VO and VC0.88 without V, and chromite magnetite produces Fe, Cr2O3, CrC x and a small amount of Cr. With an increase in the pre-reduction temperature, the metallization rate in the metallized pellets gradually increases, while the content of the residual carbon gradually decreases. Meanwhile, the iron particles precipitated on the surface of ore particles begin to soften into strips and finally agglomerate to form spherical iron particles, which leads to the diameter of iron particles increasing from 8.23 to 182.35 μm. When the pre-reduction temperature is 1,250℃, the maximum metallization rate in the metallized pellets is 92.49 wt% and the minimum content of residual carbon is 10.37 wt%.

Effect of Eco‐Friendly Minimum Quantity Lubrication in Hard Machining of Vanadis 10: A High Strength Steel

Vanadis 10 SuperClean is a high vanadium alloyed powder metallurgy tool steel offering a unique combination of an excellent abrasive wear resistance in combination with a good chipping resistance. In this study, the effects of the eco‐friendly (100% biodegradable plant‐based) Minimum Quantity Lubrication (MQL) system on the cutting temperature, cutting tool vibration amplitude, tool wear, average surface roughness, and tool life in the turning of Vanadis 10 steel (50 HRC) used in the automotive industry are investigated. In the experiments, TiCN/Al2O3/TiN‐coated cemented carbide tools are used. Experimental results showed that, compared to Dry machining, MQL produced remarkable improvements in terms of cutting temperature, cutting tool vibration amplitude, tool wear, and surface roughness. In addition, the Taguchi experimental design, ANOVA, and linear and quadratic regression analyses are applied to the experimental data. The statistical analysis found the most effective parameter on average surface roughness to be the cutting environment (86.31%). It is determined that the cutting speed was the most effective on vibration amplitude and tool wear (46.22% and 32.41%). The correlation coefficients for the linear and quadratic regression analysis were 0.9 and 0.95, respectively.

Zwitterionic interface engineering enables ultrathin composite membrane for high-rate vanadium flow battery

Thin membranes with high conductivity are of great importance for high power density vanadium flow batteries (VFBs), however, the trade-off between conductivity and ion selectivity limits their further development. Herein, an ultrathin composite membrane (∼10 μm) enabled by a zwitterionic interface between conductive polybenzimidazole (PBI) and porous polyethylene (PE) substrate is proposed to break the trade-off, and greatly enhance the power density of a VFB. The zwitterionic interface is engineered by the covalent reaction between polydopamine and zwitterionic sulfonated 3-dimethylaminopropylamine (DMAPAPS). The as-fabricated composite membrane features excellent mechanical properties and high dimensional stability. Furthermore, the zwitterionic interface facilitates proton transportation while blocking vanadium-ion permeation. More importantly, the ion selectivity of the ultrathin membrane is nearly three times higher than the pure PBI membrane (i.e., 2.71 × 104 vs. 1.09 × 104 S min cm−3). As a result, a VFB assembled with the ultrathin membrane demonstrates a superior energy efficiency of 78.7% at 300 mA cm−2, and achieves an excellent cycle stability over 500 cycles at 300 mA cm−2. Therefore, the engineering of zwitterionic interface provides a promising strategy in the development of ultrathin composite membrane for high power density VFBs.

Directed energy deposition and characterization of high‐speed steels with high vanadium content

• We produced defect-free builds of high vanadium high speed steels using DED. • We investigated the intricate microstructure imparted by the DED process, which contains fine metal carbides. • Our alloys exhibit high micro-hardness values ranging between 850 HV and 1000 HV. • Based on our results, we propose novel DED processing strategies to design HVHSS alloys for hard-facing applications. High vanadium high speed steels (HVHSSs) are alloys that are often employed for hard-facing applications owing to their excellent hardness and wear-resistance. These properties, however, make them difficult to machine into functional parts, even when employing energy-intensive processes. In this work, we employ directed energy deposition (DED) as an alternative manufacturing route to produce defect-free HVHSSs builds. We study the printability of two alloy compositions—namely Fe-10V-4.5Cr-2.5C (V10) and Fe-15V-13Cr-4.5C (V15)—and confirm their exceptionally high microhardness, which ranges from 850 HV to 1000 HV. We ascribe the differences in mechanical properties between the two HVHSSs to the size and volume fraction of vanadium carbides in the microstructure as well as the phase content, all of which vary as a function of the cooling rate imposed by DED. Our work inspires new strategies to design near-net-shape parts for hard-facing applications via additive manufacturing.

ϕ–pH diagrams and kinetics of V2O3 prepared by solution-phase hydrogen reduction

Solution-phase hydrogen reduction (SpHR) was introduced into V2O3 preparation to overcome disadvantages of traditional reduction roasting, which include a long process, high energy consumption, and generation of pollution. The research mainly focuses on ϕ–pH diagrams and kinetics of SpHR. Thermodynamic analysis of ϕ–pH diagrams for the V–H2O system demonstrates that V2O3 preparation via SpHR requires a high temperature, a high vanadium concentration, and sufficient hydrogen in acidic solution. Kinetic analyses show that the activation energy of V2O3 preparation via SpHR is 38.0679 kJ/mol, indicating that the reduction is controlled by a combination of interfacial chemical reaction and internal diffusion. Effects of H2 partial pressure (slope K=0.05246) on the reaction rate is not as significant as the vanadium concentration (K=1.58872). V2O3 crystals with a purity of 99.59% and a vanadium precipitation rate of 99.83% were obtained under the following conditions: pH=5–6, c(V2O5)=0.5 mol/L, p(H2)=4 MPa, m(PdCl2)=10 mg, T=250 °C, and t=2.5 h.

Removing trace chromium from high concentration vanadium solution by photoreduction deposition with Ti–Zr solid solution

The preparation of ultrahigh-purity vanadium (>99.99 wt%) requires the removal of trace amounts of chromium, but economical vanadium purification is difficult to achieve using crude vanadium mother liquors (>98 wt%) because of the similar properties of V(V) and Cr(IV) ions. In this study, a Ti–Zr solid solution was used for the deep purification of high-concentration ammonium polyvanadate by removing trace chromium using photocatalytic reduction process. The results show that V(V) and Cr(VI) are competitively adsorbed and photoreduced, but V(V) adsorption is preferred and occurs more rapidly than that of Cr(VI). However, after the photoreduction product of V(V), V(IV) is desorbed, whereas after that of Cr(VI), Cr(III) is deposited on the photocatalyst, achieving the separation of vanadium and chromium. The 2 h removal efficiency of chromium exceeds 80%, and the chromium content in the obtained vanadium is less than 0.04 wt%. After precipitation, the chromium content in the obtained ammonium metavanadate is less than 0.001 wt%, and the purity of the final V2O5 product exceeds 99.99%, which meets the requirement for ultrahigh-purity vanadium products. The used photocatalyst can be regenerated and reused with stable performance. This work provides a reference method for ultrahigh-purity vanadium production and an example of the industrial application of the photoreduction process.

Effect of Cooling Rate on Carbide Characteristics of the High Vanadium High-speed Steel

Effect of Cooling Rate on Carbide Characteristics of the High Vanadium High-speed Steel

Extraction and separation of chromium from the solution after hydrolysis precipitation of vanadium

ABSTRACT The qualified chromium oxide product was prepared successfully using acidic chromium solution after hydrolysis precipitation of vanadium based on sodium salt roasting-water leaching process in high chromium vanadium slag. The reduction conditions of sodium thiosulfate were provided. The influences of various factors on the filtration performance of chromium hydroxide were discussed, including precipitation agents, precipitation modes and precipitation temperature. The effects of chromium hydroxide calcination conditions and washing mode on the quality of chromium oxide were investigated. The results indicated that Na2S2O3 can completely reduce the acidic chromium solution, the reduction pH was less than 4.0, and the mass ratio of Na2S2O3 to Cr(VI) in the solution was 3.1. When the temperature was higher than 60°C, chromium hydroxide obtained by parallel flow precipitation using sodium carbonate as precipitant performed much better in filtration. The washed chromium hydroxide was calcined at 1200°C for 2 h. The final product of Cr2O3 with a purity of 98.76% was obtained after grinding and washing appropriately.