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Spent iron-molybdate oxidation catalyst secondary resource

Used iron-molybdate catalyst from methanol oxidation for formaldehyde production. This process-defined secondary resource contains iron molybdate and excess molybdenum oxide, with feed-specific impurities and amorphous material. It is distinct from molybdenite, elemental molybdenum, fresh catalyst and spent Ni/Co-Mo refinery catalysts. Two primary studies examine different spent feeds; their compositions and yields are not interchangeable. No mineral identifier or constituent-element criticality is assigned.

Microbial & Biochemical Mechanisms (3)

Abiotic tartaric-acid leaching of spent oxidation catalyst

separation

Tartaric acid obtained from winery-waste processing dissolved molybdenum and iron from a spent catalyst in laboratory tests. Acid provenance does not make the leaching microbial; the study did not establish selective molybdenum extraction or quantified isolated-product recovery.

Experimental Context & Analytical Limits:
Orim S.p.A. supplied the spent catalyst; Distillerie Mazzari S.p.A. supplied recovered tartaric acid used as received (99.90% purity). Total digestion/ICP-OES gave 58.01 +/-2.71 wt% Mo and 13.81 +/-0.54 wt% Fe; Table 1 instead contains EDX atomic percentages. Selected leaching used 1.3 M tartaric acid, 75 g/L solid loading, 25 degrees C, 60 minutes and 300 rpm in a 25 mL round-bottom flask with condenser. The 350-degree-C hotplate setting belongs to total digestion, not this leach or a measured liquid temperature.
Curated Evidence Points:
Experimental Section and Figures 4-5 report 87.36 +/-2.94% Mo leached under selected conditions; the Figure 5 caption describes analytical error, not a biological-replicate standard deviation. Iron followed a similar leaching trend, and the authors explicitly state that tartaric acid is not selective between Mo and Fe. Acid blanks had Mo/Fe below detection. Three total-digestion trials do not establish three replicates for every leaching arm.
Reported solid-loading ranges differ (33 versus 30 g/L lower bound), but the selected 75 g/L arm is consistent. The printed efficiency equation does not explicitly include feed mass in its denominator, so the published percentage is retained as reported, not independently reconstructed. Similar shrinking-core fits are model-based kinetic interpretations, not direct proof of a unique molecular mechanism. The described calcium-tartrate/ammonium-molybdate downstream route lacks a quantified isolated-product balance and purity assay; closed-loop acid reuse and industrial operation were not demonstrated.
Context_only Source: russo_2023_si
Figures S1-S5 characterize carbon/hydrogen, FTIR bands and heating-induced diffraction changes. They support a heterogeneous spent feed without identifying every organic component. The SI thermal-loss wording does not clearly match the plotted temperature interval, so no decomposition threshold or exact organic fraction is inferred.

Ammoniacal molybdenum leaching and iron settling

separation

A separate spent iron-molybdate feed underwent selective laboratory molybdenum leaching in an ammonia/ammonium-sulfate system, followed by iron settling. Reagent-ratio and yield inconsistencies prevent treating the reported optimum as an unambiguous transferable recipe.

Experimental Context & Analytical Limits:
An unnamed chemical-industry end-user supplied pellets, ground below 200 mesh. Duplicate digestions gave 52.59 +/-0.80 wt% Mo, 12.98 +/-0.43 wt% Fe and 0.07 +/-0.03 wt% Al. Leaching used 1.5 g feed in 15 mL solution, 30 mL capped vials, 20 degrees C, 300 rpm and 60 minutes; each condition was tested in duplicate. The subsequent 500 mL liquor was prepared at reported total NH3 2.0 mol/L and NH4OH-(NH4)2SO4 molar ratio 3:1, settled 12 hours and filtered.
Curated Evidence Points:
Experimental pp. 2-4 and Figures 2-4 distinguish water (about 11% Mo/8% Fe leached), ammonia alone (64-89% Mo over 1-5 mol/L; Fe below 1.5%) and the mixed system (above 91% Mo at 2 mol/L and nominal 1:1 contribution, with about 4.5% Fe). After settling, the liquor used for crystallization contained 48.2 g/L Mo and less than 7 mg/L Fe. Leaching uncertainty is described as deviation between duplicate experiments.
The ratio section reports about 95% Mo at ratios at least 3:1, whereas abstract/discussion summarize about 92%. NH4OH-to-(NH4)2SO4 and NH3-to-NH4+ are used interchangeably although the salt supplies two ammonium ions. No corrected recipe or combined yield is inferred. Iron settling is observed, but proposed pentaammine speciation is not directly measured; reaction equations are not treated as verified stoichiometric evidence. The 2023 acid experiment uses another feed and is not a matched control.

Ethanol-assisted molybdate crystallization from clarified leachate

recovery

Adding ethanol to clarified ammoniacal leachate produced crystals assigned by XRD to ammonium heptamolybdate tetrahydrate. Solution-depletion recovery and microscopic characterization support a laboratory precipitation step, with unresolved ratio and bulk-purity claims.

Experimental Context & Analytical Limits:
Experiments used 12 mL total aqueous/ethanol volume, 20 degrees C and ethanol added at zero time. The time-series maximum was reported at 45 minutes and 400 rpm, followed by 30 minutes settling, filtration, 5 mL ethanol wash and overnight drying at 30 degrees C. Figure 5 gives aqueous/organic ratio 1.5 for the time/speed/product arms; Results selects 2, and the abstract says 1:2. These conflicting ratios remain unresolved.
Curated Evidence Points:
Experimental pp. 3-4, equation 2 and Figure 5: the reported 95.3% maximum is removal from the crystallization feed liquor calculated using initial and mother-liquor Mo inventories. It is not 95.3% overall recovery from spent catalyst. Duplicate ASC experiments are presented as means with standard error. The separated product was examined by XRD and SEM-EDX.
The claimed purity above 99.9% is associated with SEM-EDX, without a separately quantified bulk purity balance in the inspected report. It is not adopted as an independently verified product specification. Conflicting aqueous/organic ratios prevent one exact optimized recipe. Ammonia/ethanol recycling, closed-loop performance, scale-up economics and industrial deployment were left for future work.

Sources & References

  1. russo_2023: Russo et al. (2023). Hydrometallurgical Molybdenum Recovery from Spent Catalyst Using Tartaric Acid Derived from Agrifood Waste. ACS Sustainable Chemistry & Engineering 11(43):15644-15650. DOI 10.1021/acssuschemeng.3c04318. Inspected institutional ACS-typeset early-online PDF pp. A-G, not final numbered pagination; Experimental Section, Figures 1-6 and Table 1.
    https://doi.org/10.1021/acssuschemeng.3c04318 (accessed 2026-10-15)
  2. russo_2023_si: Russo et al. (2023) Supporting Information, five pages; Figures S1-S5, elemental/FTIR/thermal/XRD characterization. Official ACS Figshare deposit 24315602 version 1, DOI 10.1021/acssuschemeng.3c04318.s001. Companion evidence, not an independent experiment.
    https://doi.org/10.1021/acssuschemeng.3c04318.s001 (accessed 2026-10-15)
  3. farhan_2026: Farhan, Srivastava and Ilyas (2026). Hydrometallurgical recovery of high-purity molybdenum from spent iron-molybdate catalysts via ammoniacal leaching and anti-solvent crystallization. Scientific Reports 16:12039. DOI 10.1038/s41598-026-47825-8; published 9 April, version of record 10 April 2026. Complete ten-page published PDF; Experimental, Results, Discussion, Table 1 and Figures 1-5.
    https://doi.org/10.1038/s41598-026-47825-8 (accessed 2026-10-15)

Curation History

Timestamp Curator Action Summary
2026-10-15T22:14:14.553938+00:00 Codex (GPT-6; Codex) CREATE Created a distinct spent-catalyst resource with source-scoped abiotic laboratory evidence and explicit yield, composition and scale limits.

Record source: data/records/spent-iron-molybdate-oxidation-catalyst.yaml