Natural kaolin feed primary resource
Naturally occurring kaolinite-bearing clay feed, represented here by a mixed ore from Bilecik-Söğüt, Turkey. XRD identified kaolinite, quartz and microcline as major phases. This resource is distinct from the mineral species kaolinite, discarded kaolin mine waste and a refined alumina or traded purity-defined product. Table 1 reports 0.82 wt% Fe2O3, 21.79 wt% Al2O3 and 66.83 wt% SiO2 as bulk XRF oxide equivalents, not mineral fractions or proof of a particular iron phase. The record does not inherit a criticality designation from aluminium or another constituent.
Microbial & Biochemical Mechanisms (1)
Fungal culture-associated iron removal from natural kaolin
bioleaching
Microbial
Associated Organisms:
Aspergillus niger (NCBITaxon:5061)
Living Aspergillus niger cultures were associated with acidification and greater reported iron removal from the tested natural kaolin than no-fungus medium controls. The authors propose organic-acid-mediated leaching, but did not quantify those acids or establish a unique molecular mechanism. The experiment demonstrates conditional laboratory iron mobilization, not isolated iron recovery or industrial deployment.
Experimental Context & Analytical Limits:
The study used a supplied pure culture without a reported strain name, culture-collection accession or molecular identification. Approximately 40 kg of representative Bilecik-Söğüt feed was crushed and ground in an alumina ball mill to below 106 micrometres, with d80 of 65 and d50 of 25 micrometres. Shake-flask assays used 500 mL vessels, 247.5 mL sterile nutrient medium and 2.5 mL inoculum, at 30 degrees C and 125 rpm. Solid loading was 1-10% w/v and sucrose 5-20% w/v across separate experiments. Controls omitted fungus. Samples of 5 mL were taken every three days, centrifuged at 4100 rpm for 10 minutes and the clarified liquid analyzed for Fe by AAS or ICP-OES; pH and fungal dry biomass were also followed. Reported Fe2O3 removal percentages are retained as author-reported results, not as verified yields of a mineral phase. The paper does not give an explicit yield equation, serial-withdrawal correction, full mass balance, replicate number, statistical test or uncertainty bars for these trajectories. Initial inoculum and final biomass do not establish a specific strain's molecular activity. No isolated iron product, standardized final whiteness measurement or demonstrated industrial process is reported.
The study used a supplied pure culture without a reported strain name, culture-collection accession or molecular identification. Approximately 40 kg of representative Bilecik-Söğüt feed was crushed and ground in an alumina ball mill to below 106 micrometres, with d80 of 65 and d50 of 25 micrometres. Shake-flask assays used 500 mL vessels, 247.5 mL sterile nutrient medium and 2.5 mL inoculum, at 30 degrees C and 125 rpm. Solid loading was 1-10% w/v and sucrose 5-20% w/v across separate experiments. Controls omitted fungus. Samples of 5 mL were taken every three days, centrifuged at 4100 rpm for 10 minutes and the clarified liquid analyzed for Fe by AAS or ICP-OES; pH and fungal dry biomass were also followed. Reported Fe2O3 removal percentages are retained as author-reported results, not as verified yields of a mineral phase. The paper does not give an explicit yield equation, serial-withdrawal correction, full mass balance, replicate number, statistical test or uncertainty bars for these trajectories. Initial inoculum and final biomass do not establish a specific strain's molecular activity. No isolated iron product, standardized final whiteness measurement or demonstrated industrial process is reported.
Curated Evidence Points:
Support
Source:
kale2020
Sections 2 and 3.1, Table 1 and Figures 4-6 support the material, assay and loading-dependent outcome. At 1% w/v solids and 10% w/v sucrose with ore present from inoculation, reported Fe2O3 removal was 52.47% after 336 hours, versus 6.22% in the no-fungus control. At 10% solids it was 18.51%. The lower endpoint pH in the 1% culture (3.75 versus 5.88 in its control) supports association with culture acidification; controls were not held at the same pH. These results do not separate proton action from other culture-derived effects.
Partial
Source:
kale2020
Section 3.2 and Figures 7-9 show that the sucrose response at 5% solids was nonmonotonic: 10% sucrose gave the highest reported removal, 34.66% at 336 hours, while 5%, 15% and 20% gave less. The abstract's broad statement that increasing sucrose decreases removal is therefore not applied across the whole tested range. The 5%-solids experiment is not the 1%-solids comparison above.
Partial
Source:
kale2020
Section 3.3 and Figures 10-13 report 61.09% removal for 1% solids and 10% sucrose when ore was added after 240 hours of fungal growth. Figure 10 places that endpoint at 504 hours of total culture time, corresponding to 264 hours of mineral contact. It is not a 14-day simultaneous-inoculation result or a matched elapsed-time comparison with the 52.47% endpoint. A matched no-fungus control at 504 hours is not displayed. Delayed addition may avoid early feed effects on growth, but that causal explanation was not isolated experimentally.
Partial
Source:
kale2020
Sections 2-4 measure Fe, pH and biomass rather than organic-acid concentrations, Fe oxidation-state changes, enzyme activity or particular iron-mineral dissolution. Citric, oxalic and other acid mechanisms are discussed using background literature. Figures 1-2 describe general industry uses and processing, not commercial operation of this fungal assay. Neither this one ore batch nor its unaccessioned fungal culture supports a universal kaolin outcome.
Sources & References
-
kale2020: Kale and Çiftçi (2020). Kaolen Cevherinden Demirin Aspergillus niger ile Uzaklaştırılması / Removal of Iron from Kaolin Ore by Aspergillus niger. Teknik Bilimler Dergisi 10, 16-22. DOI 10.35354/tbed.592519. Complete seven-page primary PDF inspected, including Table 1 and Figures 1-13; Turkish methods/results with English abstract. The official page and Crossref identify the publication as 20 February 2020.
https://doi.org/10.35354/tbed.592519 (accessed 2026-10-11) -
ncbi_niger: NCBI Taxonomy 5061, Aspergillus niger, current species-level entry. This resolves the reported species name, not the identity of the study's unaccessioned culture.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=5061&mode=Info (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T19:10:21.186278+00:00 |
codex (GPT-6; codex) | CREATE | Created a natural-kaolin resource from complete primary fungal bioleaching evidence, with explicit controls, unequal timing, unresolved mass accounting and no inherited criticality claim. |
Record source: data/records/kaolin.yaml