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Heazlewoodite mineral

Heazlewoodite is the Ni3S2 mineral species listed with grandfathered status G and original-description year 1897 in the September 2026 IMA compilation. The year is not an approval identifier. The Handbook gives space group R32 in a hexagonal setting. This species is distinct from millerite, pentlandite, elemental nickel and mixed nickel ores. The accepted experiment concerns a source-characterized synthetic analogue, not a natural ore or demonstrated absolutely pure endmember. No constituent-element criticality is inherited.

Microbial & Biochemical Mechanisms (1)

Ferric-mediated leaching with no demonstrated microbial enhancement

bioleaching Microbial

A living mixed culture maintained iron oxidation during laboratory dissolution of synthetic heazlewoodite-bearing material. A paired source-labelled sterile system used hydrogen peroxide to approximately follow the inoculated system's redox potential. Nickel entered solution in both systems; later dissolution was greater in the sterile comparison. The experiment supports microbial participation in the iron cycle and a conditional null result for enhancement, without isolating a direct mineral-attack pathway, proving a specific inhibitory product or demonstrating recovered nickel product.

Experimental Context & Analytical Limits:
Appendix A.2.3 describes an unresolved mixed nickel-resistant bacterial culture transferred onto synthetic Ni7S6/Ni3S2 and subsequently maintained semicontinuously on Ni3S2 in diluted 9K medium. No resolved strain, sequence or member-specific causal contribution is assigned. The assay solid was made by sulfide precipitation followed by repeated melting, recrystallization, sulfuric-acid tarnish removal and final heating to 1350 degrees C; it was then vibratory-milled and size-characterized. Source mineralogy assigned the final almost-pure material to alpha-Ni3S2. Main Type C tests used paired 2-L stirred vessels, initially 1.50 L of one-tenth-strength 9K nutrients with 9 g/L ferrous iron, nominal pH 1.6, 37 degrees C, 300 rpm and about 0.9 L/min air. After initial iron oxidation, 20 g of solid was added. The control received 0.05 g HgCl2 and redox-controlled hydrogen peroxide, initially 30% by mass and later diluted threefold. Sulfuric acid adjusted pH; evaporation was replenished and daily 30-mL slurry samples removed. C1-C5 were tests of differing duration and evolving technique, not five identical biological replicates. Mineral was not sterilized; the author used semi-aseptic handling and reported no suspended bacteria observed in sterile tests after one week. Inoculum volume and strain composition remain unresolved.
Curated Evidence Points:
Methods 3.1 and Appendix A.2.1.2, printed pages 28-29 and 111-115, describe synthesis through intermediate nickel-sulfide mixtures. A polished section before the final cleanup/heating was estimated at approximately 99% Ni3S2; the final material was described as almost pure and its X-ray pattern as typical of alpha-Ni3S2. Results 4.3.6, pages 63-67 and Figures 4.11-4.13 explicitly assign residual cores to heazlewoodite and porous rims to millerite by X-ray diffraction, with approximate composition checked by SEM. The phase assignment is more than nominal formula alone, but diffraction traces and a refined initial phase mass balance are not displayed. These source assignments do not establish absolute purity or transfer the result to natural mixed ores.
Results 4.3.1-4.3.4, Figures 4.4 and 4.7-4.9, and Appendix tables A.36 and A.39-A.43 document redox increase, declining ferrous iron, suspended cell counts and nitrogen-based estimates of attached biomass in the inoculated system. Ferric-mediated mineral dissolution with microbial iron reoxidation is supported within this mixed-culture assay. Nitrogen attribution and attachment estimates are operational proxies, not identification of a direct-attack enzyme or a causal individual taxon.
This evidence refutes enhancement under these particular test conditions, not microbial activity in every heazlewoodite system. Results 4.3.2, printed page 52 and Figures 4.5-4.6, report broadly similar early nickel concentrations, followed by greater sterile than inoculated dissolution. C5 extends to 330 hours in Table A.36; Tables A.39-A.40 provide the corresponding supernatant measurements. The figure's 100% recovery reference is 9.77 g/L nickel, an operational solution-concentration denominator, not isolated-metal yield. The five differing-duration comparisons do not supply an independently replicated effect size or uncertainty estimate.
Methods 3.6.3 and Appendix A.2.4-A.2.5 disclose nonidentical control chemistry, initial peroxide/redox overshoot and electrode fouling; C5 subsequently used manual pH adjustment after recalibration. Table A.36 records deviations from nominal conditions. Slurry sampling recovered approximately 80% of expected solids in preliminary checks (page 41), with larger particles presumed preferentially retained. HgCl2 and hydrogen peroxide can affect comparability, and no factorial control isolates their contributions. Type D peroxide-free sterile tests used different solid loading, ferric starting solution and no 9K nutrients, so they are not an otherwise identical microbial comparison.
Results 4.3.5-4.3.6 and Figures 4.10-4.13 associate lower acid demand and a compact residue rim with inoculation. Sulfur oxidation and possible rim-related inhibition are interpretations. The rim was too thin for conclusive microprobe composition and organic material was not demonstrated; jarosite and partly leached mineral also occurred. Discussion 5.3 and 6, pages 77-86 and Figures 5.5-5.6, acknowledges that the shrinking-core model did not describe later sterile leaching and omitted the millerite intermediate. Model agreement does not prove an exclusive pathway or a quantified biological inhibition mechanism. This is laboratory evidence, without product purification or industrial validation.

Sources & References

  1. ima_2026_09: IMA-CNMNC (September 2026). The New IMA List of Minerals. PDF page 91, Heazlewoodite row; page 1, status and year definitions.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-15)
  2. handbook_heazlewoodite: Handbook of Mineralogy. Heazlewoodite, Ni3S2. One-page entry, formula, space group, powder pattern and natural occurrences.
    https://www.handbookofmineralogy.org/pdfs/heazlewoodite.pdf (accessed 2026-10-15)
  3. huberts1986: Robert Huberts (1986). Application of electrochemical kinetics to elucidate the leaching mechanism in the bio-oxidation of a synthetic nickel sulphide. MSc Engineering dissertation, University of the Witwatersrand, Johannesburg. Original title page establishes 1986; repository 2015 date is deposit metadata. Complete ten-part original; methods 3.1-3.6, results 4.3-4.4, discussion 5.3 and 6, Appendices A.2.1-A.2.5 and A.3.3-A.3.5, including original figures and tables.
    https://hdl.handle.net/10539/16901 (accessed 2026-10-15)

Curation History

Timestamp Curator Action Summary
2026-10-15T07:22:48.039255+00:00 codex (GPT-6; codex) CREATE Created IMA-grounded heazlewoodite with complete Huberts1986 original evidence, source-assigned synthetic phase and mixed-culture ferric leaching; retained null enhancement, control and purity limitations.

Record source: data/records/heazlewoodite.yaml