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Scorodite mineral

Scorodite is the ferric arsenate mineral FeAsO4.2H2O, listed as Fe3+(AsO4)(H2O)2 in the September 2026 IMA list. It is grandfathered, with original-description year 1818; that year is not an approval number. Scorodite is distinct from its dimorph parascorodite, amorphous ferric arsenate, elemental arsenic or iron, and mixed arsenic-bearing wastes. Laboratory culture-associated precipitation can transfer arsenic from solution into scorodite-bearing solids. The evidence below does not establish permanent environmental sequestration, a saleable recovery product or industrial deployment. No criticality designation is inherited from a constituent element.

Microbial & Biochemical Mechanisms (1)

Scorodite precipitation in Acidianus brierleyi cultures

biomineralization Microbial

Associated Organisms: Acidianus brierleyi (NCBITaxon:41673)

Living cultures reported as Acidianus brierleyi DSM 1651T produced scorodite-bearing precipitates from synthetic Fe(II)- and As(III)-containing acidic solutions. Culture-associated oxidation and precipitation provide a route for transferring arsenic into solids; the experiments do not establish an exclusive enzymatic pathway or prove that cells are necessary for every precipitation step. Scorodite made without added seeds was identified by original X-ray diffraction. Additional seeded cultures showed condition-dependent solution arsenic removal, with amorphous material or jarosite under other conditions.

Experimental Context & Analytical Limits:
Sections 2.1-2.2 describe unseeded production of bioscorodite seed material in 200 mL heterotrophic basal salts medium in 500 mL flasks, initially pH 1.5 with sulfuric acid, containing 18 mM Fe(II) as FeSO4.7H2O, 13 mM As(III) as NaAsO2 and 0.02% w/v yeast extract. Cultures were incubated for 14 days at 70 degrees C and 100 rpm. Subsequent crystallization experiments used the same flask volume, temperature and agitation, initial pH 1.5 or 1.2, 3.3-20 mM As(III), 4.5-28 mM Fe(II), an initial cell density of 1.0 x 10^7 cells/mL and 0.15% w/v bioscorodite or chemical scorodite seeds where indicated. Initial pH was specified, not maintained as a constant. Experiments were conducted in duplicate. Dissolved Fe(II), As(III), total soluble Fe and As, cell counts, pH and redox potential were monitored. Solid analyses included XRD, FTIR, thermogravimetry and electron microscopy. These are laboratory synthetic-solution experiments.
Curated Evidence Points:
Sections 2.1-2.2 explicitly state that production of the seed crystals did not involve seed feeding. Figure 1a shows XRD of the collected biogenic material assigned to scorodite using JCPDS 37-0468. This supplies direct phase evidence for material produced in the stated culture, without pre-existing scorodite seeds. Figure 2 shows its rounded, hollow particle aggregates; morphology alone is not the mineral identification.
Table 3 reports 3.3 mM initial As(III), 4.5 mM Fe(II), initial pH 1.5 and 24 days: without added seeds, 11% arsenic removal and amorphous material; with 0.15% w/v bioscorodite seeds, 95% arsenic removal and a scorodite assignment. These percentages concern disappearance of initial solution arsenic, not an isolated-product yield or a measured fraction of newly formed scorodite. Table 3 also reports jarosite and 59% arsenic removal at 3.3 mM As(III) with 13.5 or 20 mM Fe(II), demonstrating that solution removal does not by itself identify scorodite.
The chemical seed preparation is not a matched abiotic control: it starts with 267 mM As(V) and 358 mM Fe(II) in deionized water for seven days, rather than the culture medium, lower feed concentrations, As(III) and 14-day biogenic preparation. A matched uninoculated or killed-cell culture series is not reported. Seeded experiments contain pre-existing arsenic-bearing material; final phase identification and microscopy do not separately quantify seed and newly precipitated mineral masses. Original endpoint XRD patterns are not provided for every Table 3 arm. The 99% removal row at 13 mM As(III), 18 mM Fe(II) and 14 days is explicitly attributed there to Okibe et al. 2014 and is not treated as a new measurement of the 2018 experiment.
Figure 1b thermogravimetry gives inferred hydration values of 1.55 H2O for bioscorodite and 1.91 H2O for chemical scorodite, compared with the ideal mineral formula's two waters. FTIR and thermal results indicate associated organic material. Final products also have bulk Fe/As ratios above one under some conditions. These observations limit claims of pure, perfectly stoichiometric products; the proposed sulfate incorporation is not independently established by those bulk ratios.
Section 2.4 tests leachability in acetate buffer at pH 4.9, 5% w/v solids, 25 degrees C and 30 rpm for 18 hours, in duplicate. Table 2 reports 0.59 +/- 0.20 mg/L arsenic in the leachate of the final bioscorodite-seeded product grown at initial pH 1.5, whereas narrative text and the conclusion give 0.59 +/- 0.08 mg/L for that endpoint. The uncertainty discrepancy remains unresolved; no error statistic is inferred. These leachate concentrations are not reactor effluent concentrations, extraction yields or proof of long-term environmental stability. The source's proposed continuous treatment system is prospective, not demonstrated industrial deployment.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Scorodite row, PDF page 195; column definitions and distribution terms on pages 1-2. Original list freshly acquired and relevant pages visually inspected.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14)
  2. handbook_scorodite: Handbook of Mineralogy. Scorodite, one-page species entry. Formula, orthorhombic structure and dimorphism with parascorodite.
    https://handbookofmineralogy.org/pdfs/scorodite.pdf (accessed 2026-10-14)
  3. tanaka2018: Tanaka and Okibe (2018). Factors to Enable Crystallization of Environmentally Stable Bioscorodite from Dilute As(III)-Contaminated Waters. Minerals 8(1), 23. Complete original article, Sections 2-4, Figures 1-4, Tables 1-3 and Appendix A; the institutional PDF has one cover page followed by all 16 article pages.
    https://doi.org/10.3390/min8010023 (accessed 2026-10-14)
  4. tanaka2018_original: Kyushu University institutional copy of Tanaka and Okibe (2018), including original figures and tables. This is the same study as tanaka2018, not independent experimental evidence.
    https://catalog.lib.kyushu-u.ac.jp/opac_download_md/4737404/4737404.pdf (accessed 2026-10-14)
  5. ncbi_brierleyi: NCBI Taxonomy. Acidianus brierleyi, taxon 41673, species rank. Taxonomic grounding only, not an assay or strain-specific identifier.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=41673 (accessed 2026-10-14)
  6. dsm1651: DSMZ catalogue. Acidianus brierleyi DSM 1651, type strain. Catalogue identity supports the reported strain designation, not independent authentication of the experimental stock.
    https://www.dsmz.de/collection/catalogue/details/culture/DSM-1651 (accessed 2026-10-14)

Curation History

Timestamp Curator Action Summary
2026-10-14T05:33:20.718862+00:00 codex (GPT-6; codex) CREATE Created scorodite mineral identity and qualified laboratory culture-associated precipitation evidence, retaining phase, seed, control, composition and short-term leachability limitations without inherited criticality.

Record source: data/records/scorodite.yaml