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Schwertmannite mineral

Schwertmannite is an iron(III) oxyhydroxysulfate mineral listed as approved under IMA 1990-006 in the September 2026 IMA compilation. It is distinct from elemental iron, dissolved ferrous sulfate, jarosite and an unspecified iron precipitate. The evidence below concerns laboratory synthesis from dissolved reagents and subsequent testing of the collected material, not extraction from a natural ore or industrial mineral recovery. No criticality designation is inherited from a constituent element.

Microbial & Biochemical Mechanisms (2)

Resting-cell iron oxidation associated with schwertmannite precipitation

biomineralization Microbial

Associated Organisms: Acidithiobacillus ferrooxidans (NCBITaxon:920)

Washed resting cells of source-reported A. ferrooxidans LX5 oxidized dissolved Fe(II) in acidic ferrous sulfate solution while an iron precipitate formed and was assigned to schwertmannite by powder X-ray diffraction. A cell-free hydrogen-peroxide comparator also formed the phase. Biological total-iron precipitation was lower than the chemical comparator at 60 hours despite higher subsequent arsenic uptake by the collected biological material. The study supports microbial participation in reagent-based mineral formation, not a requirement for living cells in every schwertmannite synthesis or superior biological recovery yield.

Experimental Context & Analytical Limits:
Song et al. report obtaining LX5 as CGMCC No. 0727. The asserted taxon identifier verifies the species, not that strain accession. Cells grown in modified 9K medium containing 44.48 g/L FeSO4.7H2O were collected at the end of exponential growth, filtered to remove precipitate, centrifuged, washed three times in pH 1.5 sulfuric acid and resuspended at pH 2.5. The formation assay used 225 mL solution containing 11.12 g FeSO4.7H2O in 500 mL flasks, with 10% v/v resting-cell inoculum and reported density 6.0 x 10^6 cells/mL. Initial pH was adjusted to 3.0 with sulfuric acid; incubation was at 28 degrees C and 180 rpm, with triplicate treatments. The chemical arm used 11.12 g FeSO4.7H2O in 250 mL effective volume, with approximately 6 mL of 30% H2O2 added by pump at a constant rate selected to approximate the average biological Fe(II) oxidation rate. Periodic samples were filtered at 0.22 micrometers before Fe(II) and total-Fe measurement. Section 2.2.1 says collection followed complete Fe(II) oxidation, reported at 60 hours, whereas Figures 1-3 captions describe 72 hours. The 60-hour solution comparison is retained separately from that unresolved collection-time discrepancy. These are laboratory flask experiments with reagent substrates, not industrial deployment.
Curated Evidence Points:
Sections 3.1-3.2 and Figures 1-3 show Fe(II) oxidation and precipitate formation in both arms. Broad XRD features were assigned to the schwertmannite reference pattern 47-1775; the authors report no other characteristic peaks. This supports the stated phase assignment but does not quantify amorphous impurities or establish absolute product purity. Biological material had a rough, spiny aggregate morphology, contrasting with smoother chemical particles.
Section 3.1 and Figure 1 report total-Fe precipitation of 35.0% in the biological arm and 47.9% in the chemical arm after 60 hours. These percentages quantify dissolved total-Fe loss relative to initial dissolved total Fe; they are not isolated mineral-mass or elemental-metal recovery yields. Matching the average oxidation rate did not match every time point: at 12 hours Fe(II) oxidation was 11.0% biologically and 18.4% chemically. The H2O2 comparator changes oxidant chemistry and does not isolate an exclusive enzymatic or extracellular-polymer cause of precipitation.
Context_only Source: song2018
Sections 2.2.2 and 3.3 and Figure 4 test a downstream property of the collected materials: 25 mg solid in 100 mL solution initially containing 0-30 mg/L As(III), adjusted to pH 7.5, at 28 degrees C and 180 rpm for four hours, in triplicate. The authors report saturation uptake of 117 mg/g for biological and 87 mg/g for chemical material. These are source-reported mass-normalized uptake values under this assay, not microbial arsenic extraction or universal capacities. Section 2.3 specifies total-As analysis of filtrates, so the experiment does not independently resolve arsenic redox speciation. It demonstrates neither isolated arsenic recovery nor a living-cell adsorption mechanism.
The current authority resolves the asserted species name and identifier. LX5 and CGMCC No. 0727 remain primary-source strain labels; the species node is not evidence of a strain-specific mechanism.

Increased collected precipitate after extracellular-material removal

biomineralization Microbial

Associated Organisms: Acidithiobacillus ferrooxidans (NCBITaxon:920)

A separate experiment found more dried precipitate after centrifugation and removal of the cell supernatant than with conventional resting cells or centrifuged cells whose detached extracellular material was retained. This is evidence for a treatment-associated difference in biomineralization, with extracellular polymer inhibition proposed by the authors. It does not identify a specific polymer, enzyme or exclusive molecular cause.

Experimental Context & Analytical Limits:
Section 2.2.3 compared conventional LX5 resting cells, cells centrifuged at 20,000 g for 20 minutes at 4 degrees C then resuspended with their supernatant, and similarly centrifuged cells whose supernatant was removed and replaced by the same volume of deionized water. Each treatment used 25 mL cell suspension plus 225 mL solution containing 11.12 g FeSO4.7H2O, with reported cell density approximately 6.0 x 10^6 cells/mL and initial pH 3.0, at 28 degrees C and 180 rpm for 72 hours. Solids were filtered through Whatman No. 4 paper, washed once and dried at 60 degrees C to constant mass. This is a separate assay from the 60-hour solution comparison.
Curated Evidence Points:
Figures 5-7 and Table 1 report similar Fe(II) oxidation trajectories but collected dry masses of 0.89, 0.96 and 1.29 g for conventional, detached-but-retained, and detached-and-removed treatments, respectively. Table 1 reports BET areas of 68.23, 56.76 and 86.43 square meters/g for those arms. These are precipitate properties, not purity-corrected mineral yields or metal recovery percentages.
Supernatant removal also changes dissolved constituents and the handling treatment; there is no purified-polymer add-back or independent viability assay that isolates the proposed cause. Organic carbon was used as an extracellular-material proxy, and Figure 5a labels its concentration mg/L whereas Section 3.4 prints mg/mL; no reconciled concentration is adopted here. The hydroxyl coefficients in Table 1's calculated formulas also do not follow the article's stated Fe8O8(OH)8-2x(SO4)x relation. Those formulas are not used as mineral identity or stoichiometric proof.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Schwertmannite row, PDF page 195; introductory column definitions and distribution terms.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-11)
  2. song2018: Song, Liu and Wang (2018). Comparison of the Biological and Chemical Synthesis of Schwertmannite at a Consistent Fe2+ Oxidation Efficiency and the Effect of Extracellular Polymeric Substances of Acidithiobacillus ferrooxidans on Biomineralization. Materials 11(9):1739. Sections 2-3, Figures 1-7 and Table 1; complete 13-page primary article.
    https://doi.org/10.3390/ma11091739 (accessed 2026-10-11)
  3. ncbi_ferrooxidans: NCBI Taxonomy 920. Acidithiobacillus ferrooxidans, species node.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=920&mode=Info (accessed 2026-10-11)

Curation History

Timestamp Curator Action Summary
2026-10-11T21:46:33Z codex (GPT-6; codex) CREATE Added IMA-grounded schwertmannite with controlled LX5 formation evidence, a distinct extracellular-material perturbation and qualified downstream arsenic adsorption, preserving null comparisons and source discrepancies.
2026-10-11T21:50:53Z codex (GPT-6; codex) EDIT Corrected issue118 denominator wording: dissolved total-Fe loss is divided by initial dissolved total Fe, preserving the reported percentages and the source-specific interpretation.

Record source: data/records/schwertmannite.yaml