Indium element Critical Material
The element In, distinct from indium ions, salts, indium tin oxide and indium-bearing minerals or waste streams. The dated US designation concerns the named indium mineral commodity. The mechanism describes laboratory biosorption from synthetic solutions by prepared mixed microalgal biomass; it does not establish treatment of an actual indium waste stream or recovery of an isolated indium product.
Identifiers & Classification
| System | Identifier | Label |
|---|---|---|
| CHEBI |
CHEBI:30430
|
indium atom |
Criticality Designations
| Jurisdiction | List Name | Edition / Document | Classification | Source |
|---|---|---|---|---|
| United States of America | USGS Final List of Critical Minerals | 2025; Federal Register 90:50494-50497, 7 November 2025 | critical |
usgs2025
|
Microbial & Biochemical Mechanisms (1)
Indium biosorption by prepared mixed microalgal biomass
biosorption
Microbial
Washed, freeze-dried and subsequently oven-dried mixed microalgal biomass removed indium from synthetic aqueous InCl3 solutions under acidic conditions. This is sorption by prepared inactive microbial biomass, not demonstrated metabolism. Surface-group titration and marginal FTIR changes are consistent with binding but do not resolve one molecular mechanism or the contribution of any community member.
Experimental Context & Analytical Limits:
Biomass was harvested in June 2017 from a 0.5 m3 outdoor pilot algal pond treating municipal wastewater at Universitat Politecnica de Catalunya. The authors report Chlorella sp. and diatoms, mostly Nitzschia sp. and Navicula sp., with ciliate and flagellate grazers; this mixed biomass has no resolved strain or single-organism attribution. It was thickened at 4 degrees C for 24 h, centrifuged, frozen at -80 degrees C overnight, lyophilized for 24 h, repeatedly washed with ultrapure water, dried at 50 degrees C for 24 h and ground below 1 mm. Duplicate laboratory batch assays used 100 mg biomass in 10 mL synthetic solution in polypropylene tubes at room temperature and 115 rpm. The pH experiment used 0.15 mM initial In, initial pH 1-2 and 24 h contact; initial pH 2 was selected for subsequent assays, with final pH around 2.4. Initial and final concentrations, the latter after 0.45 micrometre filtration and ICP-MS, define removal and uptake per biomass mass. Section 2.6 reports precipitation-control experiments placing In(OH)3 precipitation onset near pH 2.7, but the cited supplementary Figure S2 was not accessible during this curation, so its control protocol and values were not independently inspected. Biomass production at pilot scale does not make these sorption assays pilot-scale indium recovery; only synthetic indium feeds were tested.
Biomass was harvested in June 2017 from a 0.5 m3 outdoor pilot algal pond treating municipal wastewater at Universitat Politecnica de Catalunya. The authors report Chlorella sp. and diatoms, mostly Nitzschia sp. and Navicula sp., with ciliate and flagellate grazers; this mixed biomass has no resolved strain or single-organism attribution. It was thickened at 4 degrees C for 24 h, centrifuged, frozen at -80 degrees C overnight, lyophilized for 24 h, repeatedly washed with ultrapure water, dried at 50 degrees C for 24 h and ground below 1 mm. Duplicate laboratory batch assays used 100 mg biomass in 10 mL synthetic solution in polypropylene tubes at room temperature and 115 rpm. The pH experiment used 0.15 mM initial In, initial pH 1-2 and 24 h contact; initial pH 2 was selected for subsequent assays, with final pH around 2.4. Initial and final concentrations, the latter after 0.45 micrometre filtration and ICP-MS, define removal and uptake per biomass mass. Section 2.6 reports precipitation-control experiments placing In(OH)3 precipitation onset near pH 2.7, but the cited supplementary Figure S2 was not accessible during this curation, so its control protocol and values were not independently inspected. Biomass production at pilot scale does not make these sorption assays pilot-scale indium recovery; only synthetic indium feeds were tested.
Curated Evidence Points:
Support
Source:
nicomel2020
Sections 2.1-2.2, 2.6-2.8 and 3.4-3.5 (accepted manuscript pages 5-9 and 13-16) and Figures 2-3 support the preparation, assay and pH-dependent indium depletion. At 0.15 mM initial In, 100 mL/g liquid/solid ratio and room temperature, the pH series reports 94.7% removal after 24 h at initial pH 2; the separate kinetics series reports about 80% after 30 min. These are aqueous-phase removal percentages relative to initial In, not isolated-product yields. The elemental root does not identify the InCl3 feed.
Partial
Source:
nicomel2020
Section 3.6 and Table 2 identify 0.14 mmol/g as a fitted Langmuir maximum from the 0.05-10 mM concentration series; the Freundlich model fits better, so this is not an observed maximum uptake. Sections 2.9 and 3.7 and Figure 5 show a substantial selectivity limit: with 1 mM initial In and 10 mM competing Fe(III), initial pH 2, 100 mL/g and 24 h contact, In removal fell from 67% without a competing ion to 5%. The reported Sn(II) removal in a separate binary solution was predominantly precipitation. Uninspected supplementary controls and the mixed biomass limit attribution of all solution loss to a specific microbial surface interaction.
Partial
Source:
nicomel2020
Sections 2.10 and 3.8-3.9 and Figures 6-9 distinguish desorption from recovery of a product. In the desorbent screen, 0.1 M HCl released about 80% of previously adsorbed In at 100 mL/g after 24 h. The reuse protocol instead used 0.1 M HCl at 60 mL/g for 30 min, with washing and drying between cycles. Over five cycles adsorption removal fell from 91.3% to 60.7%; these percentages refer to initial In in each adsorption step. Regeneration did not maintain initial performance. The reported concentration ratio was only about 1.5, and burning loaded biomass to obtain In-rich ash was proposed, not demonstrated. No isolated metal yield or industrial deployment follows from these assays.
Sources & References
-
chebi_indium: ChEBI CHEBI:30430 - indium atom; formula In, net charge 0
https://www.ebi.ac.uk/chebi/CHEBI:30430 (accessed 2026-10-11) -
usgs2025: USGS (2025). Final 2025 List of Critical Minerals. Federal Register 90:50494-50497, document 2025-19813; indium row on page 50496.
https://www.govinfo.gov/content/pkg/FR-2025-11-07/html/2025-19813.htm (accessed 2026-10-11) -
nicomel2020: Nicomel et al. (2020). Microalgae: a sustainable adsorbent with high potential for upconcentration of indium(III) from liquid process and waste streams. Green Chemistry 22:1985-1995, DOI 10.1039/C9GC03073E; accepted manuscript, Sections 2-3, Figures 2-9 and Table 2.
https://upcommons.upc.edu/server/api/core/bitstreams/e2c160fc-f3c7-4279-8931-d298426d9b78/content (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T05:39:22Z |
Codex (GPT-6; Codex) | CREATE | Added verified elemental identity, dated US designation and bounded mixed-microalgal biosorption evidence, preserving analytical basis, control-access limits, Fe competition and declining reuse performance; scientific review is separate. |
Record source: data/records/indium.yaml