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Spent NdFeB permanent magnets secondary resource

Discarded neodymium-iron-boron permanent-magnet material considered as a secondary resource, distinct from the neodymium element, a fixed-purity Nd2Fe14B compound, all rare-earth magnets, and the broader commodity grouping of raw materials for permanent magnets. Actual feeds can contain other rare earths, alloying elements, coatings and impurities; no universal composition is assigned. Riano and Binnemans document an end-of-life NdFeB feed. The microbial-origin biomass assay curated here instead used chemically prepared hard-disk-magnet leachate; its precise device history and waste collection provenance were not reported. This is the same Kucuker experiment represented under neodymium, not an independent replication or a criticality designation inherited from its constituent elements.

Microbial & Biochemical Mechanisms (1)

Nd depletion during contact of magnet-derived leachate with dried algae

biosorption Microbial

Associated Organisms: Chlorella vulgaris (NCBITaxon:3077)

Dried Chlorella vulgaris SAG 211-12 biomass was associated with removal of dissolved Nd from a selectively prepared hard-disk-magnet leachate. The reported uptake was calculated from filtered solution depletion, not measured as isolated Nd product. Thermal and nitric-acid steps dissolved the magnet before the biomass assay; the experiment does not demonstrate microbial dissolution of the intact alloy, metabolic uptake, a unique binding pathway or industrial magnet recycling.

Experimental Context & Analytical Limits:
The laboratory feed comprised crushed and milled NdFeB hard-disk magnets sieved below 250 micrometres, roasted at 950 degrees C for 7 h, then leached using 5 mL 65% HNO3 and 10 mL water per 15 g roasted sample at 80 +/- 2 degrees C for 72 h with stirring. Centrifugation at 3000 rpm for 10 min and sequential filter paper/0.45 micrometre filtration preceded preparation of 1000 mg Nd/L stock and diluted assay feeds. The biosorbent was cultured in outdoor photobioreactors, then dried at 90 degrees C for 24 h; its reported particle size was 250 micrometres. Pilot-scale biomass cultivation does not establish pilot-scale recovery. Batch assays used 0.2 L solution in 500 mL flasks at 300 rpm for 90 min, 50-250 mg Nd/L, 0.5-3 g dry biomass/L, pH 3-5 and 21, 35 or 50 degrees C. HCl/NaOH maintained pH within +/- 0.2. The curated endpoint is pH 5, 35 degrees C, 250 mg Nd/L and 0.5 g biomass/L. Filtered time-point samples were measured by ICP-OES; reported values average duplicate experiments. The source does not describe a matched biomass-free time-course blank in these Methods. NCBI identifies the species, whereas SAG and the paper establish the strain; catalogue axenity is not independent verification of the outdoor-grown assay biomass.
Curated Evidence Points:
Methods pp.2-4, Eq.1, Figure 2 and Conclusion p.10 support the stated preparation, inactive biomass and endpoint. At the scoped condition, the authors report 157.40 mg Nd/g dry biomass, calculated as solution volume times initial-minus-final concentration divided by dry biomass mass. This is a source-reported depletion-derived uptake per biomass, not a percent of original-magnet Nd recovered. Figure 1's combustion route is not accompanied by an isolated-metal or metal-rich-ash product yield in the inspected results. Table 1 separately gives a fitted Langmuir capacity of 188.68 mg/g, which is not the measured endpoint.
Tabelle1's merged condition cells A83:C86 specify 35 degrees C, pH 5 and 0.5 g/L; D86 gives 250 mg Nd/L and E86 gives experimental uptake 157.3984 mg/g when rounded to four decimal places. J86 is a separate fitted pseudo-second-order uptake of about 161.29 mg/g, which does not replace the reported endpoint.
Results pp.6-8 report Fe, B, Dy and Co below detection after selective preparation, without numerical detection limits; they are not established measured zeros. The assay therefore does not verify selectivity in an untreated multimetal waste. The source asserts no Nd hydroxide precipitation below pH 7 but also proposes precipitation at 50 degrees C, and gives differing 50-degree uptake values across abstract and Results. These statements are not silently reconciled or used to replace the scoped 35-degree endpoint. Missing matched blanks and phase/localization measurements leave precipitation, nonspecific loss and specific binding contributions unresolved. The resource's complete collection-to-product mass balance, biomass regeneration and industrial operation were not demonstrated.
Kinetic model fit does not prove a molecular mechanism or rate-limiting chemical reaction. S1 contains pseudo-second-order R-squared values below the paper's broad greater-than-0.99 wording, including K100 (about 0.7203) and K121 (about 0.9635), for other assay conditions. No universal kinetic fit or unique carboxyl-group mechanism is asserted.

Sources & References

  1. riano2015: Riano and Binnemans (2015). Extraction and separation of neodymium and dysprosium from used NdFeB magnets: an application of ionic liquids in solvent extraction towards the recycling of magnets. Green Chemistry 17:2931-2942. DOI 10.1039/C5GC00230C; pp.2932-2933, end-of-life feed, Selective leaching and direct magnet dissolution, and Table 1. Used for material/feed context, not microbial evidence.
    https://doi.org/10.1039/C5GC00230C (accessed 2026-10-11)
  2. kucuker2017: Kucuker et al. (2017). Biosorption of neodymium on Chlorella vulgaris in aqueous solution obtained from hard disk drive magnets. PLOS ONE 12(4):e0175255. DOI 10.1371/journal.pone.0175255; Methods pp.2-4, Figures 1-3, Table 1 and Results/Conclusion pp.5-10.
    https://doi.org/10.1371/journal.pone.0175255 (accessed 2026-10-11)
  3. kucuker2017_s1: Kucuker et al. (2017), S1 Table, Results of the kinetic analysis. Publisher XLSX; Tabelle1 merged A83:A86/B83:B86/C83:C86 and D86/E86/J86; selected experimental and fitted uptake values are different quantities.
    https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0175255.s001&type=supplementary (accessed 2026-10-11)
  4. ncbi_chlorella: NCBI Taxonomy 3077 - Chlorella vulgaris; species-level identifier
    https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=taxonomy&id=3077&retmode=xml (accessed 2026-10-11)
  5. sag21112: SAG culture catalogue, strain 211-12, Chlorella vulgaris
    https://sagdb.uni-goettingen.de/detailedList.php?str_number=211-12 (accessed 2026-10-11)

Curation History

Timestamp Curator Action Summary
2026-10-11T09:26:30.112393+00:00 Codex (GPT-6; Codex) CREATE Created a distinct magnet-waste resource identity and a source-scoped inactive-algal biosorption assay after thermal/acid pretreatment. Verified primary methods, figures, supplementary cells and organism authorities; retained uncertainties and distinguished reused evidence from replication.

Record source: data/records/spent-ndfeb-magnets.yaml