Kaolin mine waste secondary resource
Kaolin-bearing material discarded into mine waste dumps because iron impurities prevented commercialization, represented by high- and low-iron samples supplied by Caobar SA from Poveda de la Sierra, Guadalajara, Spain. The source describes waste from beds not exploited for sale; it does not establish that this is processing tailings. The mixed kaolinite-rich feed is distinct from a kaolinite mineral species, natural kaolin resource, elemental iron or an isolated recovered product. Secondary-resource scope follows its mine-discard status, not the source's conflicting descriptions of primary versus secondary geological origin. No criticality designation is inferred from constituents.
Microbial & Biochemical Mechanisms (2)
Limited culture-associated iron leaching in EDTA-containing medium
bioleaching
Microbial
Associated Organisms:
Bacillus thuringiensis (NCBITaxon:1428)
A living wastewater-derived Bacillus isolate was tested for removal of iron impurities from sterilized kaolin mine waste. Inoculated high-iron samples showed more dissolved iron than the corresponding uninoculated medium in the displayed assays, but the medium itself leached iron and the paper reported less than 1 percent elimination. Organic-acid and redox observations support a possible microbial contribution without demonstrating a specific respiratory pathway or separating all chemical and microbial effects. This is laboratory evidence of poor beneficiation performance, not a validated industrial recovery process.
Experimental Context & Analytical Limits:
Methods pp388-390 describe Caobar mine-dump samples from iron-rich beds. Table 2 gives 92.20 and 97.00 mass percent kaolinite in high- and low-iron feeds, respectively, with quartz and muscovite. Table 3 reports 3.06 and 0.34 mass percent Fe2O3, not elemental Fe percentages. Samples were autoclaved at 121 degrees C for 20 minutes. Isolate no. 91 came from a wastewater-treatment biological reactor in Madrid; the authors identify it as Bacillus thuringiensis EB63 according to GenBank but provide no sequence accession or independent strain-level verification. Isolate no. 37, identified as Bacillus cereus AH-2, was discarded before the leaching experiments. Reactivation and mass culture used LB agar at 30 degrees C for 24 hours; that temperature is not an unambiguous specification of the subsequent leaching incubation. Each inoculated assay contained 12.5 g feed, 250 mL medium and 1 mL inoculum. The inoculum suspension in 0.9 percent saline had OD 0.1, approximately 5 x 10^4 CFU/mL before dilution into the assay; bacterial clumps made aliquots comparable but not identical. Medium per litre contained 2 g K2HPO4, 1 g ammonium sulfate, 0.1 g CaCl2, 0.75 g disodium EDTA, 0.2 g NaCl, 0.085 g NaNO3, 0.2 g urea, 0.1 g yeast extract and 20 g glucose. Methods state initial pH adjustment to 7.5, while plotted initial values are near 6.8. Independently prepared duplicate cultures D1 and D2 covered high-iron feed with bacteria, low-iron feed with bacteria, and high-iron feed without bacteria. There was no displayed low-iron abiotic arm, pH-matched control or EDTA-free control. Assays lasted 14 days. Methods list sampling on days 0, 3, 7 and 14, whereas Figures 7-12 also show day 10 and Conclusions list days 3, 7, 10 and 14. Dissolved oxygen fell to approximately 0.4 mg/L or lower from day 3 in all arms, including controls. Successive 0.45- and 0.22-micrometre filtrates were assayed by AAS for total Fe, phenanthroline colorimetry for Fe(II), and subtraction for Fe(III); lauric-acid evidence used derivatization and GC-MS. No isolated iron product, commercial-quality kaolin or industrial deployment was established.
Methods pp388-390 describe Caobar mine-dump samples from iron-rich beds. Table 2 gives 92.20 and 97.00 mass percent kaolinite in high- and low-iron feeds, respectively, with quartz and muscovite. Table 3 reports 3.06 and 0.34 mass percent Fe2O3, not elemental Fe percentages. Samples were autoclaved at 121 degrees C for 20 minutes. Isolate no. 91 came from a wastewater-treatment biological reactor in Madrid; the authors identify it as Bacillus thuringiensis EB63 according to GenBank but provide no sequence accession or independent strain-level verification. Isolate no. 37, identified as Bacillus cereus AH-2, was discarded before the leaching experiments. Reactivation and mass culture used LB agar at 30 degrees C for 24 hours; that temperature is not an unambiguous specification of the subsequent leaching incubation. Each inoculated assay contained 12.5 g feed, 250 mL medium and 1 mL inoculum. The inoculum suspension in 0.9 percent saline had OD 0.1, approximately 5 x 10^4 CFU/mL before dilution into the assay; bacterial clumps made aliquots comparable but not identical. Medium per litre contained 2 g K2HPO4, 1 g ammonium sulfate, 0.1 g CaCl2, 0.75 g disodium EDTA, 0.2 g NaCl, 0.085 g NaNO3, 0.2 g urea, 0.1 g yeast extract and 20 g glucose. Methods state initial pH adjustment to 7.5, while plotted initial values are near 6.8. Independently prepared duplicate cultures D1 and D2 covered high-iron feed with bacteria, low-iron feed with bacteria, and high-iron feed without bacteria. There was no displayed low-iron abiotic arm, pH-matched control or EDTA-free control. Assays lasted 14 days. Methods list sampling on days 0, 3, 7 and 14, whereas Figures 7-12 also show day 10 and Conclusions list days 3, 7, 10 and 14. Dissolved oxygen fell to approximately 0.4 mg/L or lower from day 3 in all arms, including controls. Successive 0.45- and 0.22-micrometre filtrates were assayed by AAS for total Fe, phenanthroline colorimetry for Fe(II), and subtraction for Fe(III); lauric-acid evidence used derivatization and GC-MS. No isolated iron product, commercial-quality kaolin or industrial deployment was established.
Curated Evidence Points:
Support
Source:
sanchez_palencia_2022
Figures 7-12 and Results pp394-402 support limited culture-associated iron mobilization with substantial abiotic-medium leaching. High-iron inoculated bars exceed the matched high-iron control bars, but D1 day-14 values are close and no quantitative significance test of that difference is supplied. Low-iron cultures lack their own abiotic comparison. The authors explicitly identify EDTA complexation as a plausible source of the uninoculated leaching. Their reported maximum 0.83 percent iron elimination is retained as a source-reported gross assay result, not an abiotic-subtracted bacterial yield or verified closed mass balance; the exact arm/time and calculation are not provided with that percentage.
Partial
Source:
sanchez_palencia_2022
Quantitative and plotting limits prevent reconstructing a precise recovery yield. Figure 9 caption specifies 14.9 mg/L total Fe for the high-iron D2 day-7 sample and Figure 11 shows a large Fe(III) peak, whereas Figure 10 clips that total-Fe bar at its 6 mg/L axis limit. The D2 peak then decreases, contrary to a universal reading of the prose's steadily increasing trend. The stated 0.83 percent is not transparently reconciled with the feed's Fe2O3 basis and this peak. The paper initially says analytical determinations were triplicate, but the biological Results describe duplicate analyses; D1 and D2 are retained separately, without inferred standard errors or pooled extraction estimates.
Partial
Source:
sanchez_palencia_2022
Figure 12 reports lauric acid as chromatographic percentage area, not an absolute mass concentration or molar secretion rate. Its curves are not universally monotonic, and the low-iron D1 day-10 bar exceeds the high-iron bar. Culture-associated acid signals and the D2 day-7 low pH are consistent with a microbial influence but do not establish that lauric acid caused iron dissolution. Figure 9 is a calculated equilibrium diagram, not direct identification of the iron host or an iron-respiration assay; its headings say 25 degrees C while the caption says approximately 22 degrees C. The precise leaching temperature and control of oxygen transfer remain unclear.
ESM geological text and Figures S1-S2 describe kaolin beds in the fluvial/deltaic Utrillas Sandstone Formation and call the kaolin secondary in origin through feldspar hydrolysis. The main Introduction instead describes the studied deposit as primary and in place from granite alteration. This source conflict is not resolved by renaming the waste as a mineral species or processing residue; the record's resource kind rests on the independently explicit mine-dump origin.
Context_only
Source:
ncbi_thuringiensis
Resolves the species label used by the paper within the Bacillus cereus group. The taxon link does not verify isolate no. 91 as the reference EB63 strain, identify its sequence, or prove its metabolic role beyond the actual inoculation experiment.
Chemical acid leaching comparator and failed long-duration validation
other
Oxalic/citric acid assays chemically removed a fraction of the iron impurities from high-iron mine waste. The chemical comparator performed better than the bacterial assays under different conditions, but a longer validation did not produce the predicted complete elimination. No microbial attribution applies to these acid-only experiments.
Experimental Context & Analytical Limits:
Tables 1 and 4 describe ten RSM runs, including duplicate centre-point experiment 9, with nominal acid levels 20, 60 and 100 mM, 1, 4 and 7 g kaolin per 100 mL, and 7, 30 or 60 days. Methods mix 50 mL each of citric and oxalic acid solutions; they do not clearly distinguish the tabulated concentrations from the pre-mixing stock concentrations. Suspensions were hand-shaken initially and for one minute daily. AAS measured solution iron. The separate long validation used 14 g feed in 200 mL of 20 mM oxalic acid for 218 days with occasional stirring. These are laboratory chemical assays, not matched-pH or matched-time controls for the 14-day microbial experiment.
Tables 1 and 4 describe ten RSM runs, including duplicate centre-point experiment 9, with nominal acid levels 20, 60 and 100 mM, 1, 4 and 7 g kaolin per 100 mL, and 7, 30 or 60 days. Methods mix 50 mL each of citric and oxalic acid solutions; they do not clearly distinguish the tabulated concentrations from the pre-mixing stock concentrations. Suspensions were hand-shaken initially and for one minute daily. AAS measured solution iron. The separate long validation used 14 g feed in 200 mL of 20 mM oxalic acid for 218 days with occasional stirring. These are laboratory chemical assays, not matched-pH or matched-time controls for the 14-day microbial experiment.
Curated Evidence Points:
Support
Source:
sanchez_palencia_2022
Table 4 reports 32.21 percent Fe removed for experiment 4 at nominal 100 mM each acid, 1 g/100 mL, 60 days and final pH 0.74; experiment 7 gave 31.7 percent. Equation 1 uses the phrase Fe reduced for an iron-removal calculation, not proof of Fe(III)-to-Fe(II) conversion. Post-treatment Fe2O3 percentages in Table 3 are solid-composition values, not directly interchangeable with Table 4 extraction yields; an independently closed solid/liquid mass balance is not supplied.
Partial
Source:
sanchez_palencia_2022
Figures 4-5 and Equation 2 describe fitted relationships, including percent removal = 0.48 x days, rather than a validated prediction of complete removal at arbitrary duration. The 218-day validation ended with only traces of solution Fe and 3.42 mass percent Fe2O3 in the residue versus 3.06 initially. The authors attribute this to reprecipitation during a final cold week below approximately 5 degrees C. Similar major XRD phases in Figure 6 do not independently identify a new iron precipitate or isolate temperature causality. The prose asserts that iron leaching increased linearly with time in a repeated 218-day experiment, without supplying the corresponding numerical dataset. The source explicitly considers the demonstrated removal inadequate for industrial use.
Context_only
Source:
sanchez_palencia_2022_esm
Figure S3 photographs the yellow suspension about halfway through the long chemical assay. It establishes neither a final iron yield nor an independently quantified precipitate or recovered product.
Sources & References
-
sanchez_palencia_2022: Sanchez-Palencia et al. (2022). Iron Removal from Kaolin Waste Dumps by Chemical (Oxalic and Citric Acids) and Biological (Bacillus Strain) Leaching. Clays and Clay Minerals 70(3):386-404. DOI 10.1007/s42860-022-00192-7. Original Springer version published 7 July 2022; complete 19-page PDF, Tables 1-4 and Figures 1-12 inspected. The later Cambridge/Crossref online date is not a separate experiment.
https://doi.org/10.1007/s42860-022-00192-7 (accessed 2026-10-11) -
sanchez_palencia_2022_esm: Sanchez-Palencia et al. (2022), original ESM 1 DOCX. Complete geological description and original images for Figures S1-S3 inspected; S3 is a photograph partway through the 218-day chemical experiment, not a final recovery measurement.
https://media.springernature.com/original/springer-static/esm/art%3A10.1007%2Fs42860-022-00192-7/MediaObjects/42860_2022_192_MOESM1_ESM.docx (accessed 2026-10-11) -
ncbi_thuringiensis: NCBI Taxonomy 1428, Bacillus thuringiensis, species-level identifier and current label inspected 11 October 2026. This resolves the published species name, not the experimental isolate or an EB63 culture accession.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=1428&mode=Info (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T19:12:40Z |
codex (GPT-6) | CREATE | Added a distinct kaolin mine-discard resource using complete primary evidence and original supplementary figures. Preserved poor microbial performance, chemical-medium confounding, unresolved source discrepancies and the absence of demonstrated industrial recovery; independent review remains a separate observation. |
2026-10-11T19:17:41Z |
codex (GPT-6) | EDIT | Corrected independent-review finding F1 and issue 110 by removing an unsupported characterization of the undocumented repeated chemical assay as successful. The record now states only the source's assertion of linear iron-leaching increase and the missing numerical dataset. |
Record source: data/records/kaolin-mine-waste.yaml