Ruthenium element Critical Material
Ruthenium (Ru). This element record is distinct from the dissolved Ru(III) chloride feed, cell-associated oxidized ruthenium material, and Pd/Ru catalyst preparations in the curated laboratory study. The US 2025 list names the ruthenium commodity individually; this maps to the element without extending criticality to every ruthenium compound, mineral or waste. The evidence supports biomass-associated deposition, without demonstrating elemental Ru recovery, a microbial enzyme requirement or industrial operation.
Identifiers & Classification
| System | Identifier | Label |
|---|---|---|
| CHEBI |
CHEBI:30682
|
ruthenium 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
|
Microbial & Biochemical Mechanisms (1)
Biomass-associated deposition of oxidized ruthenium from a chloride feed
other
Microbial
Associated Organisms:
Bacillus benzoevorans (NCBITaxon:1456)
Washed Bacillus benzoevorans NCIMB 12555 biomass, reported as B. benzeovorans, acquired Ru-containing deposits after exposure to a synthetic Ru(III) chloride solution under hydrogen, with or without prior Pd deposition. Microscopy and spectroscopy support association with oxidized Ru material. The study does not demonstrate Ru(0), a Pd-Ru metallic alloy or a necessary metabolic contribution. Microbial involvement denotes the biomass scaffold; sustained cell viability during acidic exposure and subsequent processing was not established.
Experimental Context & Analytical Limits:
Laboratory batches used biomass grown aerobically at 30 degrees C and 180 rpm in beef extract, yeast extract, peptone and 15 g/L NaCl medium at pH 7.3; harvested at OD600 0.7-1.0, washed three times in 20 mM MOPS-NaOH pH 7 and stored concentrated overnight at 4 degrees C. The Ru-only preparation used 2 mM Ru(III), supplied as RuCl3.2H2O at pH 2, for 30 minutes at 30 degrees C, then hydrogen bubbling for about 1 h and 96 h in sealed hydrogen-saturated bottles at 30 degrees C and 180 rpm. The separate sequential Pd/Ru preparation first deposited Pd from 2 mM Pd(II) under hydrogen for 30 minutes, washed the biomass twice with water, and then added a 1 mM Ru(III) solution for a 96 h hydrogen stage; its final mixed-suspension pH and exact liquid volumes are not specified. Nominal metal loadings are relative to cell dry weight. Table 1 reports inferred actual Ru loadings of 14.2 wt% for nominal 20 wt% Ru-only material, 6.0 wt% Ru with 9.7 wt% Pd for nominal 10/10 wt% Pd/Ru, and 2.0 wt% Ru with 2.4 wt% Pd for nominal 2.5/2.5 wt% Pd/Ru. These are calculated by solution difference using a stannous chloride colorimetric assay, not direct solid-element recovery yields. The text reports incomplete removal, with about 40% Ru remaining after about 96 h; this approximate statement is not identical to every Table 1 loading ratio. Collected catalyst preparations were washed three times with water and once with acetone, air-dried and ground before analysis.
Laboratory batches used biomass grown aerobically at 30 degrees C and 180 rpm in beef extract, yeast extract, peptone and 15 g/L NaCl medium at pH 7.3; harvested at OD600 0.7-1.0, washed three times in 20 mM MOPS-NaOH pH 7 and stored concentrated overnight at 4 degrees C. The Ru-only preparation used 2 mM Ru(III), supplied as RuCl3.2H2O at pH 2, for 30 minutes at 30 degrees C, then hydrogen bubbling for about 1 h and 96 h in sealed hydrogen-saturated bottles at 30 degrees C and 180 rpm. The separate sequential Pd/Ru preparation first deposited Pd from 2 mM Pd(II) under hydrogen for 30 minutes, washed the biomass twice with water, and then added a 1 mM Ru(III) solution for a 96 h hydrogen stage; its final mixed-suspension pH and exact liquid volumes are not specified. Nominal metal loadings are relative to cell dry weight. Table 1 reports inferred actual Ru loadings of 14.2 wt% for nominal 20 wt% Ru-only material, 6.0 wt% Ru with 9.7 wt% Pd for nominal 10/10 wt% Pd/Ru, and 2.0 wt% Ru with 2.4 wt% Pd for nominal 2.5/2.5 wt% Pd/Ru. These are calculated by solution difference using a stannous chloride colorimetric assay, not direct solid-element recovery yields. The text reports incomplete removal, with about 40% Ru remaining after about 96 h; this approximate statement is not identical to every Table 1 loading ratio. Collected catalyst preparations were washed three times with water and once with acetone, air-dried and ground before analysis.
Curated Evidence Points:
Support
Source:
omajali_2019
Results on deposition, Figure 1 and supplementary Figures S3-S5 support Ru association with the cell surface in Ru-only material and Pd/Ru co-localization in some intracellular deposits after Pd seeding. Cells without added metal lack the comparable electron-dense deposits. This is a no-metal imaging comparison, not a cell-free Ru precipitation control or evidence of a defined uptake pathway.
Support
Source:
omajali_2019
Figure 2 lattice imaging, Figure 3 XPS, Figure 4 EXAFS and supplementary Figure S11 XANES support oxidized rather than metallic Ru in the analyzed preparations. The authors assign RuO2-like lattice fringes in Pd/Ru particles and Ru-O coordination in EXAFS. The record retains that qualitative interpretation without claiming a single pure phase, complete Ru mass balance or independent spectral refitting.
Partial
Source:
omajali_2019
Surface XPS is interpreted in the text and Table 2 as Ru(III)/Ru(VI), whereas bulk XANES is interpreted as Ru(III)/Ru(IV); samples were not protected from air. Figure 3 and supplementary Figure S8 also label RuCl3 and Ru(OH)3 components. The differing assignments and analysis depths preclude one definitive whole-sample valence distribution. The EXAFS text claims absence of Ru-Ru peaks immediately after describing a Ru-Ru shell that is also fitted in Table 3. That internal tension prevents repeating the stronger claim of exclusively atomically dispersed Ru; it does not establish metallic Ru.
Partial
Source:
omajali_2019
The inspected study and supplement do not report matched cell-free, killed-cell or hydrogen-free Ru deposition outcomes, nor a replication count for the Ru-removal assay. Cell scaffolding, sorption, hydrolysis, air oxidation and Pd-assisted chemistry are not experimentally separated. Supplementary Figure S6 is interpreted as no Pd-lattice shift or alloying, but its high-loading curve is labelled 20% Ru/5% Pd, unlike Table 1's nominal 10% Pd/10% Ru material; precise sample matching remains unresolved. No particular microbial enzyme is assigned.
Context_only
Source:
omajali_2019
The later 5-hydroxymethylfurfural catalytic tests use dried catalyst, 260 degrees C, 50 bar hydrogen and a 2 h reaction. Their conversion and dimethylfuran yields concern organic-substrate catalysis, not Ru extraction or recovered-metal yield, and do not demonstrate living-cell catalysis or industrial deployment.
Context_only
Source:
gomez_bolivar_2019
A related study with Escherichia coli MC4100 describes predominantly oxidized Ru but allows a low metallic-Ru contribution in bulk XANES/EXAFS interpretations. Its organism, Pd/Ru loadings and sample preparation differ, so this is neither proof of Ru(0) in NCIMB 12555 nor a direct refutation of the narrower Bacillus observation. It prevents generalizing the Bacillus phase interpretation to all microbial Ru preparations; it is not an independent replication of the same assay.
Sources & References
-
chebi_ruthenium: ChEBI:30682 - ruthenium atom; Ru, charge 0
https://www.ebi.ac.uk/chebi/CHEBI:30682 (accessed 2026-10-11) -
usgs_2025: U.S. Geological Survey (2025). Final 2025 List of Critical Minerals. Federal Register 90 FR 50494-50497, November 7, 2025; final commodity table, Ruthenium row on page 50497.
https://www.govinfo.gov/content/pkg/FR-2025-11-07/html/2025-19813.htm (accessed 2026-10-11) -
omajali_2019: Omajali et al. (2019). Novel catalytically active Pd/Ru bimetallic nanoparticles synthesized by Bacillus benzeovorans. Scientific Reports 9, 4715; published March 18, 2019. DOI 10.1038/s41598-019-40312-3. Methods, Tables 1-3, Figures 1-4 and supplementary Figures S3-S11.
https://www.nature.com/articles/s41598-019-40312-3 (accessed 2026-10-11) -
gomez_bolivar_2019: Gomez-Bolivar et al. (2019). Synthesis of Pd/Ru Bimetallic Nanoparticles by Escherichia coli and Potential as a Catalyst for Upgrading 5-Hydroxymethyl Furfural Into Liquid Fuel Precursors. Frontiers in Microbiology 10, 1276. DOI 10.3389/fmicb.2019.01276; XANES and EXAFS Results, Table 3. Used as organism-specific interpretive context.
https://doi.org/10.3389/fmicb.2019.01276 (accessed 2026-10-11) -
ncbi_benzoevorans: NCBI Taxonomy 1456, Bacillus benzoevorans, species; NCIMB 12555 is listed among its type-strain collection identifiers. The paper spells the organism Bacillus benzeovorans.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=1456&mode=info (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T06:51:17Z |
Codex (GPT-6; Codex) | create | Created the ruthenium element record from verified identity, dated US criticality and primary laboratory evidence. Preserved assay boundaries, controls, phase uncertainties and deployment limits; attached canonical CREATE history. Independent scientific review is separate. |
Record source: data/records/ruthenium.yaml