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Rutile mineral

Rutile is the mineral species with IMA-approved formula TiO2. The September 2026 IMA list gives grandfathered status G and original description year 1803; the year is not an IMA approval identifier. This mineral is distinct from elemental titanium, traded titanium products, rutile-bearing concentrates and other TiO2 polymorphs or manufactured TiO2 nanoparticles. The curated primary experiment calls its electrode coating natural rutile and reports an average mineral diameter of 40 micrometres, but does not supply a specimen locality, bulk chemical purity or diffraction-based phase-purity determination for that coating. Its observed role is light-assisted electron transfer supporting microbial iron cycling in a laboratory reactor, not demonstrated transformation of rutile or recovery of titanium. No criticality designation is inherited from a constituent element.

Microbial & Biochemical Mechanisms (1)

Natural-rutile photocatalysis associated with microbial iron cycling

other Microbial

Associated Organisms: Acidithiobacillus ferrooxidans (NCBITaxon:920)

Illuminated rutile on a graphite electrode supplied electrons through an external circuit to a separate chamber containing growing Acidithiobacillus ferrooxidans and an iron-rich medium. Ferrous-iron, electrical-current and cell-count observations support the authors' interpretation that photoelectrons regenerate Fe(II) from Fe(III), supporting further microbial Fe(II) oxidation and growth. Rutile is the photocatalytic component, not the iron feed, and the bacteria are spatially separated from the mineral coating. This is a coupled abiotic-photochemical and microbial process; it does not establish microbial Ti redox chemistry, rutile dissolution, a specific enzyme pathway, isolated-metal recovery or industrial deployment.

Experimental Context & Analytical Limits:
The source identifies the isolate by a nearly full-length 16S sequence with 100% reported similarity to A. ferrooxidans and accession HQ603786. NCBITaxon:920 maps the species only. The paper's Shanxi acid-pit-water origin and the accession's soil field are retained without harmonization. Two glass chambers of 350 mL each were separated by a proton-exchange membrane and connected by a wire through a 1000 ohm resistor. The mineral electrode was prepared from 0.54 g powder and 0.06 g acetylene black with approximately 0.3 mL polytetrafluoroethylene and ethanol, spread on a 5 by 7 cm graphite electrode and air-dried for 12 h. The photocatalytic chamber contained 12.5 g/L ascorbic acid as a chemical hole scavenger and 2.5 g/L KCl. Thus neither light nor rutile was the sole supplied source of reducing equivalents. The cell chamber contained modified 9K medium with 41.7 g/L FeSO4·7H2O and a final inoculum of 3.5e5 cells/mL at 10% v/v. Isolation used medium adjusted to pH 2.2 plus or minus 0.02, but a reactor pH trajectory is not supplied. The magnetically stirred reactor was maintained near 30 degrees C; 150 rpm in the supplement refers to culture enrichment, not an established reactor stirring speed. Figure 2 follows four days under 380-760 nm light at approximately 13.5 mW/cm2. Figure 4 separately varies wavelength or intensity. Cells were counted directly by microscopy, not by the CFU procedure used for another species in this paper. Exact replicate numbers and error-bar definitions for these rutile curves are not supplied.
Curated Evidence Points:
Support Source: lu2012
Figures 1-2 and Methods support sustained cell growth and iron cycling in the illuminated, rutile-containing circuit. Dark and rutile-free comparisons also grow initially using medium iron; the illuminated rutile arm continues growing later. Figure 2b reports a positive association of net cell growth with transferred charge, without identifying a molecular electron-transfer pathway. Figure 4 shows a wavelength-dependent response and an intensity response that is not monotonic: growth rises between 2 and 8 mW/cm2 at 420 nm, then falls at 16 mW/cm2. These observations support the conditional reactor association, not a universal growth benefit of rutile.
Partial Source: lu2012
Figure 2 labels the comparison rutile-free and open circuit, whereas Methods list a mineral-free anode without explicitly specifying its circuit state. Separate effects of removing mineral and opening the circuit therefore cannot be cleanly assigned from this arm. Its caption's about-fivefold growth statement lacks a specified time-point denominator and is not adopted as a quantitative enhancement factor. The no-cell control additionally replaces ferrous sulfate with 6.1 g/L ferric chloride, so it is not a same-initial-iron-speciation sterile counterpart. Supplementary Figure S2 shows additional rutile-free and dark cell-free curves, but its plotted axis says Fe(III) although the accompanying reduction experiment is discussed in terms of Fe(II) generation. These source limits prevent treating all control curves as interchangeable assays.
Partial Source: lu2012
The Results' 2.1 micrograms/L soluble Ti(IV) value is calculated from solubility assumptions, not a measured titanium-release endpoint. Photon-to-biomass efficiencies are model-based estimates using assumed biomass and energy conversions, not measured titanium recovery. The supplementary calculation contains conflicting oxidation/reduction wording, although its displayed equation does multiply the oxygen-consumption rate by 60 h; no missing time conversion is inferred. Figure 4 and the supplement also differ in their current-density area/unit descriptions. No numerical conversion efficiency or mineral extraction yield is adopted here. The separate sphalerite, goethite, A. faecalis and electrically biased soil-community experiments are not pooled with this rutile/A. ferrooxidans arm.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Rutile row on PDF page 189; column definitions on page 1 and distribution terms on page 2.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-12)
  2. lu2012: Lu A, Li Y, Jin S and colleagues (2012). Growth of non-phototrophic microorganisms using solar energy through mineral photocatalysis. Nature Communications 3:768. DOI 10.1038/ncomms1768. Complete original eight-page article, especially Figures 1, 2 and 4, Results on pages 2-5 and Methods on pages 6-7; original twelve-page Supplementary Information, especially Figure S2 and pages 5-11.
    https://doi.org/10.1038/ncomms1768 (accessed 2026-10-12)
  3. ncbi_ferrooxidans: NCBI Taxonomy 920, Acidithiobacillus ferrooxidans, species. Species identity only; not an experimental strain identifier.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=920 (accessed 2026-10-12)
  4. genbank_hq603786: NCBI GenBank HQ603786.1, Acidithiobacillus ferrooxidans strain HZ-PKU-1 partial 16S ribosomal RNA gene, 1495 bp. The accession cited by Lu et al. supplies a strain label, not functional-gene evidence. Its isolation-source field says soil, whereas the article describes acid-pit water; that discrepancy remains unresolved.
    https://www.ncbi.nlm.nih.gov/nuccore/HQ603786.1 (accessed 2026-10-12)

Curation History

Timestamp Curator Action Summary
2026-10-12T05:58:37Z codex (GPT-6; codex) CREATE Added the distinct IMA-grounded rutile mineral with a qualified natural-mineral photocatalysis and microbial iron-cycling association after full primary and supplement inspection; retained control, provenance and quantitative limits without claiming Ti recovery.

Record source: data/records/rutile.yaml