Palladium element Critical Material
Palladium (Pd), chemical element with atomic number 46. This record concerns laboratory reduction of dissolved Pd(II) to cell-associated elemental Pd(0), not extraction from a palladium mineral or an industrial recovery operation.
Identifiers & Classification
| System | Identifier | Label |
|---|---|---|
| CHEBI |
CHEBI:33363
|
palladium atom |
Criticality Designations
| Jurisdiction | List Name | Edition / Document | Classification | Source |
|---|---|---|---|---|
| United States of America | U.S. Department of the Interior Final List of Critical Minerals | 2025 (published November 7, 2025; 90 FR 50494-50497) | critical |
usgs_2025
|
| European Union | Regulation (EU) 2024/1252, Annex II, Section 1(aa), platinum group metals (palladium membership documented in ec2017_groups) | 2024 original act; OJ L 2024/1252, 3 May 2024 | critical |
eu2024
|
Microbial & Biochemical Mechanisms (1)
Resting-cell reduction of dissolved Pd(II) to elemental palladium
redox transformation
Microbial
Associated Organisms:
Desulfovibrio desulfuricans (NCBITaxon:876)
Desulfovibrio desulfuricans ATCC 29577 resting cells reduced soluble Pd(II) to cell-associated Pd(0) with an electron donor. Hydrogenase involvement was inferred, not established by a specific genetic test.
Experimental Context & Analytical Limits:
Laboratory anaerobic batch assay using washed, nongrowing ATCC 29577 cells (0.5 g/L; 2.5 mL in sealed 12 mL serum bottles) in 20 mM MOPS-NaOH, pH 7, at 30 degrees C. The substrate was 0.5 mM Pd(II) supplied as the palladium ammine chloride salt reported by Lloyd et al.; hydrogen replaced nitrogen in the headspace. The reported 100% dissolved-Pd(II) depletion after 24 h is an assay result, not a purified metal yield. Pd(0) identity was supported by X-ray diffraction and cell-associated deposits by electron microscopy and elemental analysis. This experiment does not establish performance in mixed waste leachates, ore extraction, or industrial deployment.
Laboratory anaerobic batch assay using washed, nongrowing ATCC 29577 cells (0.5 g/L; 2.5 mL in sealed 12 mL serum bottles) in 20 mM MOPS-NaOH, pH 7, at 30 degrees C. The substrate was 0.5 mM Pd(II) supplied as the palladium ammine chloride salt reported by Lloyd et al.; hydrogen replaced nitrogen in the headspace. The reported 100% dissolved-Pd(II) depletion after 24 h is an assay result, not a purified metal yield. Pd(0) identity was supported by X-ray diffraction and cell-associated deposits by electron microscopy and elemental analysis. This experiment does not establish performance in mixed waste leachates, ore extraction, or industrial deployment.
Curated Evidence Points:
Support
Source:
lloyd_1998
Methods and results preceding Figure 1, and Figure 1A-C: the reported outcome was absent in cell-free, heat-killed, and electron-donor-free controls. These controls and solid-phase characterization support microbial Pd(II) reduction under the stated conditions in this strain.
Partial
Source:
lloyd_1998
Hydrogen-supported reduction and inhibition following copper pretreatment implicate hydrogenase activity, but do not identify a unique enzyme or establish its necessity genetically.
Context_only
Source:
mikheenko_2008
The introduction cautions that copper is not a specific hydrogenase inhibitor. The mutant experiments concern D. fructosivorans, a different species, and cannot establish enzyme necessity in ATCC 29577. This narrows the 1998 mechanistic inference without refuting its observed Pd reduction.
Sources & References
-
lloyd_1998: Lloyd, Yong and Macaskie (1998). Enzymatic Recovery of Elemental Palladium by Using Sulfate-Reducing Bacteria. Applied and Environmental Microbiology 64(11), 4607-4609. DOI 10.1128/AEM.64.11.4607-4609.1998.
https://journals.asm.org/doi/10.1128/AEM.64.11.4607-4609.1998 (accessed 2026-10-06) -
mikheenko_2008: Mikheenko et al. (2008). Bioaccumulation of Palladium by Desulfovibrio fructosivorans Wild-Type and Hydrogenase-Deficient Strains. Applied and Environmental Microbiology. DOI 10.1128/AEM.02538-07.
https://journals.asm.org/doi/10.1128/AEM.02538-07 (accessed 2026-10-06) -
usgs_2025: U.S. Geological Survey (2025). Final 2025 List of Critical Minerals. Federal Register 90 FR 50494-50497, November 7, 2025.
https://www.govinfo.gov/content/pkg/FR-2025-11-07/html/2025-19813.htm (accessed 2026-10-06) -
chebi_palladium: ChEBI:33363 - palladium atom
https://www.ebi.ac.uk/chebi/CHEBI:33363 (accessed 2026-10-06) -
ncbi_desulfuricans: NCBI Taxonomy: Desulfovibrio desulfuricans (Taxonomy ID 876)
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=876&mode=Info (accessed 2026-10-06) -
eu2024: Regulation (EU) 2024/1252 of 11 April 2024. Original Official Journal text, 3 May 2024; Annex II, Section 1(aa), platinum group metals, page 58 of 67.
https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=OJ:L_202401252 (accessed 2026-10-09) -
ec2017_groups: European Commission COM(2017) 490 final, on the 2017 list of Critical Raw Materials for the EU. Annex 1, page 4, footnote 13 explicitly includes palladium in platinum group metals. Used for group membership only.
https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52017DC0490 (accessed 2026-10-09)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-08T02:36:12Z |
Codex (GPT-6; Codex) | provenance_adoption | Appended canonical history reference and this present adoption event. Earlier scientific review artifacts remain linked in the sidecar; scientific content is unchanged and was not reassessed. |
2026-10-09T05:51:45Z |
Codex (GPT-6; Codex) | criticality_extension | Added the historical EU 2024 Annex II designation through its named platinum group metals entry, with source and mapping scope documented. Preserved existing scientific evidence; independent review is separate. |
Record source: data/records/palladium.yaml