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Bauxite residue (red mud) secondary resource

The heterogeneous residue from alkaline Bayer processing of bauxite for alumina production, commonly called red mud. It is distinct from bauxite ore, alumina commodity, aluminium element and any single mineral species. The curated assay used material collected from the Ajka spill site; its composition and treatment response do not define every bauxite residue. No criticality designation is inherited from constituent elements.

Microbial & Biochemical Mechanisms (1)

Aspergillus-associated aluminium mobilization from Ajka bauxite residue

bioleaching Microbial

Associated Organisms: Aspergillus niger (NCBITaxon:5061)

Growing isolate G-10 mobilized aluminium from an Ajka red-mud sample while acidifying the medium and accumulating organic acids. Synthetic acid mixtures also leached aluminium, supporting extracellular chemical contributions without demonstrating a requirement for living-cell contact, a specific enzyme, or a mineral-specific dissolution pathway.

Experimental Context & Analytical Limits:
Material collected in October 2010 was air-dried, disaggregated and sieved below 0.2 mm. The selected assay used 0.2 g dry residue in 45 mL Sabouraud dextrose broth plus 5 mL suspension of approximately 10^6 spores/mL in 250 mL flasks, cultured statically in darkness at 25 degrees C for seven days. Medium was autoclaved before inoculation. Each condition had triplicate parallel experiments. Isolate G-10 was assigned to Aspergillus niger by morphology and a 612-bp ITS sequence with 99% similarity; the species identifier does not authenticate the isolate independently. Table 1 reports 6.97% Al in the dry feed. XRD identified hematite, calcite and quartz; Al-host phases remained unresolved. The experiment does not establish recovery of alumina or aluminium metal, nor industrial deployment.
Curated Evidence Points:
Sections 2.3, 2.5 and 3.3 with Figure 3 report approximately 141 mg/L Al in 0.45-micrometre filtrate after seven days with G-10. ICP-OES measures filter-passing total Al, not free-ion speciation. No-fungus controls were reported undetected or below detection, without a numerical Al detection limit. Section 3.4 and Figure 7a report final pH 2.3 and oxalic/citric acid concentrations of 16.0/28.6 mmol/L. These are release and culture-chemistry outcomes, not a purified-product yield.
Sections 2.4 and 3.4 with Figure 8: synthetic mixture B, representing the day-five organic-acid profile, produced approximately 142 mg/L Al. These mixtures used sodium salts, HCl-adjusted pH, 0.2 g residue in 50 mL and two days at 25 degrees C. The differing media and incubation times prevent a matched kinetic comparison with growing fungi. Proton effects, complexation and other metabolites were not independently isolated. Section 3.1 reports calcite loss but warns that XRD does not resolve minor or amorphous phases; no particular Al-bearing mineral is assigned as the dissolved substrate.

Sources & References

  1. urik2015: Urik, Bujdos, Milova-Ziakova, Mikusova, Slovak and Matus (2015). Aluminium leaching from red mud by filamentous fungi. Journal of Inorganic Biochemistry 152:154-159. DOI 10.1016/j.jinorgbio.2015.08.022; Sections 2.1-2.5, 3.1 and 3.3-3.5, Table 1 and Figures 3, 7-8.
    https://doi.org/10.1016/j.jinorgbio.2015.08.022 (accessed 2026-10-11)
  2. urik2017_copy: Urik (2017). Interactions of toxic metals and metalloids with fungi, habilitation thesis; official Brno University of Technology copy, Attachment E, PDF pages 80-85 reproducing the 2015 article, journal pages 154-159. Same experiment, not independent replication.
    https://www.vut.cz/uredni-deska/habilitace?action=priloha&priloha=226417 (accessed 2026-10-11)
  3. ncbi_aspergillus: NCBI Taxonomy 5061 - Aspergillus niger; species
    https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=taxonomy&id=5061&retmode=xml (accessed 2026-10-11)

Curation History

Timestamp Curator Action Summary
2026-10-11T09:02:35.258572+00:00 Codex (GPT-6; Codex) CREATE Created bauxite-residue identity and source-specific fungal leaching evidence, retaining phase and chemical-control limitations.

Record source: data/records/bauxite-residue.yaml