Spent vanadium-flow-battery electrolyte secondary resource
Sulfuric-acid electrolyte containing dissolved vanadium in multiple oxidation states after use in all-vanadium redox flow batteries. This use-derived liquid resource is distinct from elemental vanadium, fresh electrolyte products, spent vanadium catalysts, and solid battery scrap. The two studies below concern different feeds: company-supplied failed positive/negative electrolytes and electrolyte deliberately cycled to capacity loss in a laboratory cell. Their outcomes are not interchangeable. No constituent criticality designation or microbial mechanism is inherited.
Microbial & Biochemical Mechanisms (2)
Abiotic oxidation and ammonium-salt precipitation from failed electrolyte
recovery
Sodium chlorate oxidation followed by alkaline ammonium-sulfate treatment produced a filtered solid described as ammonium metavanadate. Separate laboratory oxidation trials used positive and negative electrolyte; a reported pilot batch used positive electrolyte. The harvested product amount is distinct from the laboratory liquid-concentration-based precipitation percentages. This is a chemical process, with no microbial involvement tested.
Experimental Context & Analytical Limits:
Yang2016 Sections 1.1–2.2 and Table 1 identify failed electrolyte supplied by Hunan Huifeng New Energy. Positive feed contained total V 1.28 mol/L, V(V) 0.76 mol/L, V(IV) 0.52 mol/L and H2SO4 1.75 mol/L; negative feed contained total V and V(III) 1.53 mol/L and H2SO4 1.82 mol/L. Battery service history and failure criteria are not supplied. Separate 500-mL oxidation trials at room temperature varied NaClO3, with selected V(IV):oxidant and V(III):oxidant molar ratios 1:0.20 and 1:0.40. Methods describe dilution or concentration, NaOH adjustment to pH 8.0–8.5, ammonium sulfate addition at 50–60 degrees C, 100–120 min stirring, filtration and vacuum drying at 65 degrees C for 4 h. Total-V titration and ICP-AES impurity assays are named. Replicate numbers, uncertainty estimates, oxidation duration and a complete feed/product/filtrate balance are not supplied.
Yang2016 Sections 1.1–2.2 and Table 1 identify failed electrolyte supplied by Hunan Huifeng New Energy. Positive feed contained total V 1.28 mol/L, V(V) 0.76 mol/L, V(IV) 0.52 mol/L and H2SO4 1.75 mol/L; negative feed contained total V and V(III) 1.53 mol/L and H2SO4 1.82 mol/L. Battery service history and failure criteria are not supplied. Separate 500-mL oxidation trials at room temperature varied NaClO3, with selected V(IV):oxidant and V(III):oxidant molar ratios 1:0.20 and 1:0.40. Methods describe dilution or concentration, NaOH adjustment to pH 8.0–8.5, ammonium sulfate addition at 50–60 degrees C, 100–120 min stirring, filtration and vacuum drying at 65 degrees C for 4 h. Total-V titration and ICP-AES impurity assays are named. Replicate numbers, uncertainty estimates, oxidation duration and a complete feed/product/filtrate balance are not supplied.
Curated Evidence Points:
Support
Source:
yang2016
Section 3 and Table 5 report treating 1 m3 of Table 1 positive electrolyte in the company's pilot apparatus and obtaining 148.30 kg of white powder labelled NH4VO3, with 99.58% NH4VO3 on a dry basis and separately listed impurities. This supports a reported isolated product from that pilot batch, not continuous industrial operation, independently verified specification compliance or a directly measured overall vanadium recovery percentage. No diffraction pattern or explicit product NH4VO3 assay procedure is supplied; do not infer crystallographic purity from the product label.
Support
Source:
yang2016
Section 2.3.5 and Table 4 describe the time series at nominal initial concentration 26.35 g/L, pH 8.0, 50 degrees C and ammonium coefficient K=1.2. K is the mass ratio of added (NH4)2SO4 to solution V expressed as V2O5. At 120 and 140 min, Table 4 gives residual 0.26 g/L and precipitation 99.01%; at 80 min it gives 0.65 g/L and 97.53%. These percentages match a residual/initial concentration calculation, not an isolated product mass balance. Figure 2 labels the concentration axis V2O5 g/L and the text describes residual V on a V2O5 basis; generic prose calls it vanadium concentration. Preserve that analytical basis rather than silently treating the values as elemental-V g/L. Tables 2–3 print zero residual low-valent V at selected oxidation doses without detection limits; those cells do not prove literal absence.
Partial
Source:
yang2016
Conclusion item 2 specifies pH 2.0–2.5, whereas methods, Section 2.3.2, Figure 3 and both abstracts specify alkaline pH 8.0–8.5. This conflict is unresolved. Methods use 100–120 min precipitation while the abstract and conclusion give 80–120 min; the distinct Table 4 endpoints must not be collapsed into a universal 99% yield. Figure 2's concentration bases and the unreported assay/detection and replicate details limit quantitative transfer. Historical cost and environmental-benefit assertions were not independently validated and are not adopted as current economic or discharge claims.
Abiotic electrochemical regeneration of laboratory-aged electrolyte
recycling
Electrochemical rebalancing improved discharge capacity of previously cycled electrolyte relative to its untreated aged state. The four protocols regenerate electrolyte function; their capacity percentages and coulombic efficiencies are not vanadium extraction, product-purity or recovered-metal yields. None establishes microbial catalysis or complete restoration of every treated compartment.
Experimental Context & Analytical Limits:
Peng2024 Sections 1.1–1.3 used purchased 1.7 M vanadium electrolyte with nominal average valence +3.5 and 3 M H2SO4, cycled in a 28-cm2 laboratory cell until actual capacity fell below 50% of rated capacity. The cell used 4.2-mm graphite felt and Nafion 212. The age in cycles, temperature, flow rate, replicate count and uncertainty estimates are not specified. New and aged electrolyte were compared by UV-visible analysis, cyclic voltammetry and cell tests at 50–300 mA/cm2. The four distinct arms are staged charging with compartment replacement; direct electrolysis of 100 mL aged electrolyte per compartment; electrolysis with 100 mL aged negative electrolyte and 100 mL 3 M sulfuric acid in the positive compartment; and asymmetric electrodes in aged electrolyte compared by a salt bridge with new electrolyte. In the last arm, 5 A was applied until the potential difference was below 0.01 V, requiring approximately 5 h for 100 mL.
Peng2024 Sections 1.1–1.3 used purchased 1.7 M vanadium electrolyte with nominal average valence +3.5 and 3 M H2SO4, cycled in a 28-cm2 laboratory cell until actual capacity fell below 50% of rated capacity. The cell used 4.2-mm graphite felt and Nafion 212. The age in cycles, temperature, flow rate, replicate count and uncertainty estimates are not specified. New and aged electrolyte were compared by UV-visible analysis, cyclic voltammetry and cell tests at 50–300 mA/cm2. The four distinct arms are staged charging with compartment replacement; direct electrolysis of 100 mL aged electrolyte per compartment; electrolysis with 100 mL aged negative electrolyte and 100 mL 3 M sulfuric acid in the positive compartment; and asymmetric electrodes in aged electrolyte compared by a salt bridge with new electrolyte. In the last arm, 5 A was applied until the potential difference was below 0.01 V, requiring approximately 5 h for 100 mL.
Curated Evidence Points:
Support
Source:
peng2024
Figures 3–7 compare untreated new, untreated aged and protocol-treated electrolytes. At 100 mA/cm2, Section 2.2.1 reports about 1200, 500 and 900 mAh for new, aged and proportionally regenerated electrolyte, respectively, supporting the reported approximately 75% capacity restoration for that arm. Other arms approach but do not equal the new-electrolyte curves. The plotted cycles are sequential measurements, not demonstrated independent replicates or long-term deployment. Coulombic efficiency remains high while energy and voltage efficiencies decline with increasing current; high coulombic efficiency alone does not establish retained energy capacity.
Partial
Source:
peng2024
Results Sections 2.2.2–2.2.3 assign 93% capacity restoration to direct electrolysis and 92% to sulfuric-acid electrolysis; the abstract and conclusion reverse those assignments. Section 2.2.4 also calls its asymmetric-arm 92% result sulfuric-acid electrolysis. The individual percentages cannot be unambiguously assigned from these conflicting statements, and no raw replicate data resolve them. Section 1.3.2 states a required charge of 1190 mAh but prescribes 2238 mA for 30 min, whose arithmetic product is 1119 mAh. This calculation mismatch is retained without guessing a corrected current or duration. UV-visible concentrations follow the stated 50-fold dilution; they are not undiluted feed concentrations or a complete vanadium inventory.
Partial
Source:
peng2024
Methods, Table 2 and the conclusion retain material limitations: direct electrolysis raises the positive compartment's valence while regenerating only the negative compartment; the sulfuric-acid arm evolves gas, corrodes positive collectors and requires their replacement and fresh graphite felt before testing; the asymmetric route is slow. Thus the reported comparisons do not use unchanged hardware in every arm or demonstrate whole-feed recovery. A 30-cycle, changing-current test is not evidence of prolonged capacity retention. Reuse is demonstrated only in these laboratory cells, independently of the different 2016 pilot precipitation feed.
Sources & References
-
yang2016: Yang, M. and Wang, Y. (2016). Study on the preparation technology of ammonium metavanadate with vanadium recycled from spent vanadium electrolyte solutions. Chemical Industry and Engineering Progress 35(9), 2982–2986. DOI 10.16085/j.issn.1000-6613.2016.09.047. Complete five-page publisher original, Figures 1–5 and Tables 1–5; especially methods 1.1–1.3, Table 4 precipitation endpoints and Section 3 pilot product. Chinese conclusion pH conflicts with methods, results and abstracts.
https://hgjz.cip.com.cn/EN/abstract/abstract4251.shtml (accessed 2026-10-15) -
peng2024: Peng, H., Xu, J., You, R., Zhao, L. and Hu, X. (2024). Recovery and regeneration of waste electrolyte from all-vanadium redox flow battery. Iron Steel Vanadium Titanium 45(3), 9–15. DOI 10.7513/j.issn.1004-7638.2024.03.002. Complete seven-page publisher original, Figures 1–7 and Tables 1–2; laboratory feed preparation, four regeneration arms and capacity comparisons. Direct/sulfuric-acid percentage assignments differ between results and abstract/conclusion.
https://doi.org/10.7513/j.issn.1004-7638.2024.03.002 (accessed 2026-10-15)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-15T21:17:44.858647+00:00 |
Codex (GPT-6; codex) | CREATE | Created a distinct used-electrolyte resource from two complete primary studies, separating chemical product recovery and electrochemical capacity regeneration. Preserved source discrepancies, experimental feed identity, analytical bases and laboratory/pilot limits. |
Record source: data/records/spent-vanadium-flow-battery-electrolyte.yaml