Tantalum element Critical Material
The element Ta, distinct from tantalum ions, oxides, mineral species, capacitor components and mixed electronic scrap. The United States 2025 list's Tantalum entry is mapped to this element; that designation is not inherited by every capacitor or waste feed. The curated primary study documents an unsuccessful acidophile leaching attempt for Ta under specified conditions, preserving a useful limitation rather than asserting recovery.
Identifiers & Classification
| System | Identifier | Label |
|---|---|---|
| CHEBI |
CHEBI:33348
|
tantalum atom |
Criticality Designations
| Jurisdiction | List Name | Edition / Document | Classification | Source |
|---|---|---|---|---|
| United States | Department of the Interior Final List of Critical Minerals | 2025 final list, published 7 November 2025 | critical |
us_2025
|
Microbial & Biochemical Mechanisms (1)
No detected tantalum mobilization in an acidophile capacitor-scrap assay
bioleaching
Microbial
A living mixed iron- and sulfur-oxidizing acidophile culture mobilized several base metals from tantalum capacitor scrap, but Ta was not detected in the reported leachate. This experiment limits claims that the tested culture directly solubilizes Ta from this feed. It does not demonstrate that all microbial Ta leaching is impossible or establish a recovered tantalum product from the remaining solids.
Experimental Context & Analytical Limits:
The paper names Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans in the mixed culture, without strain accessions, relative abundance or member-specific activity tests. No organism identifiers are assigned to this unresolved experimental mixture. Visually identified surface-mount capacitors from spent mobile phones were manually removed and ground to 0.5 and 0.75 mm fractions. Table 1 reports Ta at 292.5 g/kg (SD 2.32) after HF-containing microwave digestion for both fractions; this is bulk elemental composition, not a Ta phase determination. Laboratory trials used 250 mL Erlenmeyer flasks, 100 mL actively growing modified 9K culture, 2% w/v scrap, 30 degrees C and 150 rpm for 10 days, with pH maintained at 1.8 using 10% v/v sulfuric acid. Activation medium contained elemental sulfur and ferrous sulfate. The study varied initial iron in its PCB assays, but does not unambiguously specify the final ferrous concentration for the capacitor comparison. Medium sterilization is described at 121 degrees C for 30 min, with ferrous sulfate excluded. The sentence concerning sterilization of the samples is grammatically ambiguous, so feed sterility is not assumed. Experiments were triplicate with non-inoculated medium controls; 0.45 micrometre-filtered liquor was sampled every second day, with sterile water replacing sampling and evaporation losses.
The paper names Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans in the mixed culture, without strain accessions, relative abundance or member-specific activity tests. No organism identifiers are assigned to this unresolved experimental mixture. Visually identified surface-mount capacitors from spent mobile phones were manually removed and ground to 0.5 and 0.75 mm fractions. Table 1 reports Ta at 292.5 g/kg (SD 2.32) after HF-containing microwave digestion for both fractions; this is bulk elemental composition, not a Ta phase determination. Laboratory trials used 250 mL Erlenmeyer flasks, 100 mL actively growing modified 9K culture, 2% w/v scrap, 30 degrees C and 150 rpm for 10 days, with pH maintained at 1.8 using 10% v/v sulfuric acid. Activation medium contained elemental sulfur and ferrous sulfate. The study varied initial iron in its PCB assays, but does not unambiguously specify the final ferrous concentration for the capacitor comparison. Medium sterilization is described at 121 degrees C for 30 min, with ferrous sulfate excluded. The sentence concerning sterilization of the samples is grammatically ambiguous, so feed sterility is not assumed. Experiments were triplicate with non-inoculated medium controls; 0.45 micrometre-filtered liquor was sampled every second day, with sterile water replacing sampling and evaporation losses.
Curated Evidence Points:
Refute
Source:
sikander_2022
Refutes efficient direct Ta solubilization by this specific acidophile treatment, not all microbial Ta processing. Section 4.3 states that Ta was not detected in the leachate. Figure 12 shows no Ta mobilization bar for either capacitor particle fraction; supplementary Table S6 records Ta concentration as u and leached percentage as 0 for both Ta.Cap rows. The supplement does not define u or provide a numeric Ta detection limit. Those entries are therefore not curated as measured zero concentrations or a quantified recovery percentage.
Partial
Source:
sikander_2022
The microorganism-containing experiment and uninoculated controls test this laboratory protocol, but maintained acidity and added iron do not isolate each consortium member or prove an enzymatic mechanism. Removal of other metals is not itself a measured Ta enrichment factor, recovered mass, purity or mass balance. Supporting Table S1 is a composition table for digestion without HF, despite the Methods' reference to it as ICP-OES validation; it supplies no calibration or Ta detection-limit study. Table 1's HF digest and S1's non-HF digest cannot be treated as interchangeable estimates of total Ta. The study's broader upscaling discussion does not show industrial deployment, and the native insolubility or chemical form of the residual Ta was not resolved in this assay.
Sources & References
-
chebi_tantalum: ChEBI:33348 - tantalum atom; formula Ta, net charge 0
https://www.ebi.ac.uk/chebi/CHEBI:33348 (accessed 2026-10-11) -
us_2025: US Department of the Interior, Geological Survey. Final 2025 List of Critical Minerals, 7 November 2025, Federal Register 90:50494-50497, document 2025-19813; Tantalum row on page 50497.
https://www.govinfo.gov/content/pkg/FR-2025-11-07/html/2025-19813.htm (accessed 2026-10-11) -
sikander_2022: Sikander et al. (2022). Chemical and Microbial Leaching of Valuable Metals from PCBs and Tantalum Capacitors of Spent Mobile Phones. International Journal of Environmental Research and Public Health 19:10006. DOI 10.3390/ijerph191610006; PMC9408593. Sections 2.1-2.3.2 and 4.3, Table 1, Figure 12 and supplementary Table S6.
https://doi.org/10.3390/ijerph191610006 (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T07:24:30.325571+00:00 |
Codex (GPT-6; Codex) | CREATE | Created element identity, US 2025 criticality and a condition-specific unsuccessful acidophile leaching observation; preserved non-detection limits without claiming zero Ta or a recovered product. |
Record source: data/records/tantalum.yaml