CMMMech
CMMMech > Element > Niobium

Niobium element Critical Material

The element Nb, also called columbium, distinct from niobium ions, oxides, host minerals, alloys and niobium-bearing furnace wastes. The United States 2025 list's Niobium entry is mapped to this element; it does not automatically designate a waste feed as critical. The curated experiment reports condition-dependent niobium release in an activated-sludge-derived culture, with unresolved controls and analytical preparation limiting causal inference.

Identifiers & Classification

System Identifier Label
CHEBI CHEBI:33344 niobium 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)

Condition-dependent niobium release in sludge-derived leaching cultures

bioleaching Microbial

An adapted, living mixed culture derived from municipal activated sludge was associated with greater reported niobium release from municipal-waste incineration ash in a shaken 24 degrees C assay than in the paper's averaged control. Compressed-air aeration instead gave a reported null niobium result in that ash, and sewage-sludge ash responded much less. These are assay-specific release observations, not demonstrated niobium redox chemistry, a resolved microbial pathway or isolated-metal recovery.

Experimental Context & Analytical Limits:
The community's taxa, strains and source treatment plant are not resolved. Activated sludge and distilled water were mixed 1:1 with 1% powdered sulfur; the percent basis was not specified. Adaptation at 24 degrees C, 120 rpm continued until pH below 3 and the reported sulfur-oxidizer index reached 10^-6. Each 300 mL flask then held 150 mL culture and 10 g ash for five days. Ash A came from municipal-waste thermal processing and ash B from sewage-sludge thermal processing; their reported initial Nb contents were 33.6 and 15.3 mg/kg waste. Feed mineralogy, particle size, sterilization and detailed provenance were not reported. Table 2's variants were 24 degrees C/120 rpm without compressed air, 24 degrees C with compressed-air mixing, and 37 degrees C/50 rpm without compressed air. Starting culture pH was below 3; final A pH was 10, 6 and 10, respectively, and B pH was 9, 8 and 9. This is a small laboratory flask experiment.
Curated Evidence Points:
Figure 3 reports ash-A Nb release of 100.0%, 0.0% and 6.7% in variants 1-3, versus 2.3% for the averaged control; Table 4 reports 33.6, 0.0 and 2.3 mg Nb released per kg initial ash. Figure 7 reports ash-B values of 14.6%, 14.5% and 14.7%, versus 5.9% control. These are the authors' values, without uncertainty intervals. The p.74 formula divides metal concentration in leaching culture times culture volume by initial ash mass times initial metal content. A reported 100% release is therefore relative to the measured initial ash inventory, not a purified Nb product yield or an independently closed mass balance.
Methods state that three corresponding control variants gave similar results and were averaged, but do not specify their composition, sterilization, inoculum exclusion or matched pH. ICP-OES is named, but filtration/centrifugation, digestion of the leaching sample, culture-background subtraction and Nb detection limits are not specified. Thus dissolved Nb cannot be separated confidently from colloidal or particulate Nb, and sludge chemistry or abiotic effects are not isolated. Three instrument exposures do not establish biological replication; independent replicate counts and statistical tests are not supplied. The reported 0.0% is retained as source wording, without interpreting it as an analytically proven zero.
Tables 2 and 4 disagree on variant-3 speed: 50 versus 120 rpm. Figures and running text agree with Table 2's 50 rpm, but the discrepancy remains unresolved. Increased sulfate and sulfur-oxidizer counts occurred under aeration, whereas ash-A Nb release was highest without that aeration and at final pH 10. This does not demonstrate sulfur oxidation or acid production as the cause of Nb release. The contrasting ash-B results prevent a general claim of complete Nb extraction from furnace wastes. No phase-specific dissolution, metal separation, product purity or industrial deployment was tested.

Sources & References

  1. chebi_niobium: ChEBI:33344 - niobium atom; formula Nb, net charge 0
    https://www.ebi.ac.uk/chebi/CHEBI:33344 (accessed 2026-10-11)
  2. 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; Niobium row on page 50496.
    https://www.govinfo.gov/content/pkg/FR-2025-11-07/html/2025-19813.htm (accessed 2026-10-11)
  3. andrzejewska_gorecka_2019: Andrzejewska-Gorecka et al. (2019). Release of critical metals from furnace wastes using the process of bioleaching in various variants. Archives of Environmental Protection 45(3):72-78. DOI 10.24425/aep.2019.128643. Research methods pp.73-74, Tables 1-4, Figures 3 and 7, Results pp.75-76.
    https://doi.org/10.24425/aep.2019.128643 (accessed 2026-10-11)

Curation History

Timestamp Curator Action Summary
2026-10-11T07:24:30.324752+00:00 Codex (GPT-6; Codex) CREATE Created element identity, US 2025 criticality and condition-dependent sludge-culture ash release, retaining nulls and unresolved controls, analytical fractions, replication and source discrepancies.

Record source: data/records/niobium.yaml