Spent nickel-metal-hydride batteries secondary resource
End-of-life nickel-metal-hydride batteries, represented by mixed battery powder supplied by a recycler. This secondary resource is distinct from lithium-ion battery black mass, pure electrode compounds, and its constituent elements. Battery formulations and upstream recycling steps are not fully specified for the selected feed. No constituent-element criticality status is inherited by this waste resource.
Microbial & Biochemical Mechanisms (1)
Conditional metal solubilization by heterotrophic culture metabolites
bioleaching
Microbial
Associated Organisms:
Gluconobacter oxydans (NCBITaxon:442), Streptomyces pilosus (NCBITaxon:28893)
Gluconobacter oxydans DSM 3503 produced a gluconic-acid-containing culture liquid associated with metal solubilization from spent NiMH battery powder in two-step and spent-medium assays. Simultaneous inoculation and powder addition failed under the tested conditions. Streptomyces pilosus DSM 40097 treatments also lacked appreciable leaching. These observations concern filtered-liquid metals in laboratory flasks, not isolated products or industrial recovery. The spent-medium arm used microbial metabolites after cell removal rather than requiring live cells during dissolution.
Experimental Context & Analytical Limits:
Rasoulnia et al. used actual spent NiMH battery powder from AkkuSer Oy, Finland, homogenized and screened through 630-micrometre mesh. The powder was autoclaved for one hour at 121 degrees C under nitrogen; unchanged mineralogy after sterilization was not independently demonstrated. Assays used 1% w/v powder in 250-mL Erlenmeyer flasks with 100-mL initial working volume, 1% v/v inoculum, 27 +/- 1 degrees C and 150 rpm. Modified PVK medium contained 10 g/L glucose and either 2.7 mM K2HPO4 for G. oxydans or 27 mM for S. pilosus; insoluble calcium phosphate was replaced and 0.3 mM CaCl2 was supplied. Thus the two species were tested in different media. One-step addition was simultaneous; Methods and Figure 3 specify powder addition after one day for G. oxydans and two for S. pilosus in two-step assays. Spent medium was obtained after six days of growth by centrifugation at 10000 rpm for ten minutes, described as cell-free by the authors; residual viable cells were not independently quantified. Methods specify a 14-day leaching phase, while Table 3 labels the G. oxydans two-step treatment as two days of growth plus fourteen days of leaching, inconsistent with the one-day addition described elsewhere. All bioleaching experiments were triplicate. Controls included respective sterile media with and without powder and cultures without powder. Aliquots were filtered at 0.2 micrometres for ICP-MS total-element analysis; organic acids were analyzed by HPLC. No matched pure-gluconic-acid or pH-trajectory control isolated a unique molecular dissolution pathway.
Rasoulnia et al. used actual spent NiMH battery powder from AkkuSer Oy, Finland, homogenized and screened through 630-micrometre mesh. The powder was autoclaved for one hour at 121 degrees C under nitrogen; unchanged mineralogy after sterilization was not independently demonstrated. Assays used 1% w/v powder in 250-mL Erlenmeyer flasks with 100-mL initial working volume, 1% v/v inoculum, 27 +/- 1 degrees C and 150 rpm. Modified PVK medium contained 10 g/L glucose and either 2.7 mM K2HPO4 for G. oxydans or 27 mM for S. pilosus; insoluble calcium phosphate was replaced and 0.3 mM CaCl2 was supplied. Thus the two species were tested in different media. One-step addition was simultaneous; Methods and Figure 3 specify powder addition after one day for G. oxydans and two for S. pilosus in two-step assays. Spent medium was obtained after six days of growth by centrifugation at 10000 rpm for ten minutes, described as cell-free by the authors; residual viable cells were not independently quantified. Methods specify a 14-day leaching phase, while Table 3 labels the G. oxydans two-step treatment as two days of growth plus fourteen days of leaching, inconsistent with the one-day addition described elsewhere. All bioleaching experiments were triplicate. Controls included respective sterile media with and without powder and cultures without powder. Aliquots were filtered at 0.2 micrometres for ICP-MS total-element analysis; organic acids were analyzed by HPLC. No matched pure-gluconic-acid or pH-trajectory control isolated a unique molecular dissolution pathway.
Curated Evidence Points:
Support
Source:
rasoulnia_2021
Results, Bioleaching of REEs and Base Metals, and Figure 4 report G. oxydans two-step leaching of 34% Mn, 88% Fe, 41.5% Co, 18.5% Ni, 21% Cu, 12% Zn and 6.5% total REEs. Spent-medium values are 35%, 68%, 35.5%, 16.5%, 20%, 9% and 9%, respectively. These are source-reported feed-relative aqueous extraction percentages at the reported endpoint, not isolated-product recovery. Figure 4 error bars represent standard deviations of triplicate experiments. Individual REE yields differ; the total must not be assigned to every REE.
Partial
Source:
rasoulnia_2021
The abstract gives 6.0% total REEs for two-step treatment whereas main Results and Table 3 give 6.5%; this discrepancy and the two-step timing conflict remain unresolved. Figure 3 supports gluconate accumulation before powder addition and subsequent rising pH. The spent-medium result supports activity of culture liquid after cell removal, but different culture ages and solution histories prevent attribution of yield differences solely to the presence of cells. Proposed REE adsorption onto cells and phosphate precipitation were not closed by independent partition measurements or a complete mass balance in this study.
Refute
Source:
rasoulnia_2021
The tested conditions refute an unconditional claim that either culture or any inoculation schedule efficiently leaches this powder. Results and Figures 3-4 report no metal leaching for one-step G. oxydans and no appreciable leaching for S. pilosus in any tested mode, even with pyruvate in its spent medium. These are reported null outcomes rather than exact analytical zeros. Different phosphate concentrations, buffering, initial pH and metabolites prevent a general ranking of intrinsic species capability; toxicity and precipitation are proposed contributors rather than isolated causal tests.
Partial
Source:
rasoulnia_2021
Figure 5 shows selected particle surfaces, cross-sections and elemental maps before and after treatment. It does not establish phase-specific metal flux, identify every REE precipitate or prove selective recovery. Table 1 characterizes this mixed powder, not a universal NiMH composition. No recovered metal product, complete process balance, technoeconomic demonstration or industrial deployment was established.
Context_only
Source:
rasoulnia_2021_supplement
Medium-selection experiments compare acid production, pH and available growth measurements in PVK and GYM before the selected battery assays. These support the culture-medium context, not an independent battery leaching replicate or a molecular pathway assignment.
Sources & References
-
rasoulnia_2021: Rasoulnia, Barthen, Valtonen and Lakaniemi (2021). Impacts of Phosphorous Source on Organic Acid Production and Heterotrophic Bioleaching of Rare Earth Elements and Base Metals from Spent Nickel-Metal-Hydride Batteries. Waste and Biomass Valorization 12:5545-5559. DOI 10.1007/s12649-021-01398-x; Materials and Methods, Results and Discussion, Tables 1-3 and Figures 1-5.
https://doi.org/10.1007/s12649-021-01398-x (accessed 2026-10-11) -
rasoulnia_2021_supplement: Online Resource 1 to Rasoulnia et al. (2021), DOI 10.1007/s12649-021-01398-x. Medium-selection text and Figure ESM 1; DOCX text, chart labels, cached series and error values inspected. Original Word page rendering was not available.
https://media.springernature.com/original/springer-static/esm/art%3A10.1007%2Fs12649-021-01398-x/MediaObjects/12649_2021_1398_MOESM1_ESM.docx (accessed 2026-10-11) -
dsm3503: DSMZ catalogue, Gluconobacter oxydans DSM 3503, strain I. Collection identity does not independently authenticate the experimental stock.
https://www.dsmz.de/collection/catalogue/details/culture/DSM-3503 (accessed 2026-10-11) -
dsm40097: DSMZ catalogue, Streptomyces pilosus DSM 40097.
https://www.dsmz.de/collection/catalogue/details/culture/DSM-40097 (accessed 2026-10-11) -
ncbi_oxydans: NCBI Taxonomy 442, Gluconobacter oxydans, species-level identity.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=442&mode=Info (accessed 2026-10-11) -
ncbi_pilosus: NCBI Taxonomy 28893, Streptomyces pilosus, species-level identity.
https://www.ncbi.nlm.nih.gov/taxonomy/28893 (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T14:24:36.953625+00:00 |
Codex (GPT-6; Codex) | CREATE | Curated conditional NiMH battery-powder bioleaching from primary evidence, retaining null treatments, yield and timing conflicts, and laboratory limits. |
Record source: data/records/spent-nickel-metal-hydride-batteries.yaml