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Ponded mixed coal ash secondary resource

Mixed fly and bottom ash deposited in coal-combustion ash ponds, represented here by a sample from a Philippine circulating-fluidized-bed power plant burning local and imported coal. The mixture is a distinct secondary resource from separately collected coal fly ash, pure coal bottom ash and coal-gasification slag. Its fly-to-bottom ratio, residence time and plant identity are unreported. A laboratory mixed-culture study supports qualified metal mobilization from the mixed feed; it does not resolve either ash component's individual response or establish an isolated metal product, criticality designation or industrial deployment.

Microbial & Biochemical Mechanisms (1)

Culture-associated metal mobilization from mixed pond ash

bioleaching Microbial

Associated Organisms: Acidithiobacillus albertensis (NCBITaxon:119978), Acidithiobacillus thiooxidans (NCBITaxon:930)

Pangayao and colleagues measured zinc, manganese, chromium, iron and copper in filtered liquors following 15-day contact of the mixed ash with source-designated A. albertensis ATCC 35403 and A. thiooxidans ATCC 19377 cultures. Lower final pH and reported metal solubilization are consistent with culture-associated acid leaching. Added sulfuric acid and the absence of matched uninoculated controls prevent assignment of the full response to microbial sulfur oxidation or to either organism separately. No isolated recovered metal was demonstrated.

Experimental Context & Analytical Limits:
The pond ash was dried at 105 degrees C for 24 hours and sieved using a stated number-200 mesh; the paper's accompanying 0.075-micrometre value is inconsistent and is not accepted as a verified particle cutoff. The source reports DSMZ-supplied cultures under ATCC designations; catalogue correspondence does not authenticate the experimental stocks or their mixing ratio, which is unreported. Cultures were incubated for 10 days at 30 degrees C and 160 rpm in a medium containing ammonium sulfate, magnesium sulfate, calcium chloride, potassium dihydrogen phosphate and 10 g/L elemental sulfur. Leaching used 250 mL flasks containing 100 mL medium, 1-5 g ash, 1-5 mL inoculum and 1-3 g added sulfur, at 30 degrees C and 160 rpm. Ash/medium were autoclaved at 121 degrees C for 15 minutes and adjusted with 1 M sulfuric acid from pH 6.5-8 to pH 2 before sulfur and inoculum addition. The 17-run Box-Behnken design includes repeated central settings; duplicate runs are reported. After 15 days, 0.45-micrometre cellulose-acetate-filtered liquor was nitric-acid-preserved for ICP-OES. No acid-only, uninoculated or no-sulfur series is displayed, and no sulfur balance or direct organism-specific growth assay is supplied. This is a flask experiment with industrial-origin feed, not an industrial treatment demonstration.
Curated Evidence Points:
Sections 2.2-2.5 and 3.1-3.3, Figures 1-2 and Tables 1-3 support the mixed-feed identity, treatment and filtered-liquor assays. Table 3 reports run-specific maxima of 56.69% Zn and 69.32% Cu in run 13, 70.68% Mn in run 15, and 79.86% Cr and 70.74% Fe in run 17; these are not one combined optimum or isolated product yields. Figure 2 and Section 3.2 show final pH approximately 0.61-1.39 after the initial chemical adjustment to pH 2.
The paper labels Table 3 values as percent metal leached but does not give the calculation equation, initial-feed digestion procedure, blank corrections, raw liquor concentrations or complete solution/residue mass balance. Its reported total feed concentrations in Section 3.1 therefore do not independently validate the percentage denominator. Added chemical acid, unquantified inoculum chemistry and missing matched controls limit microbial attribution; pH decline alone does not establish growth or sulfur-oxidation causality. Neither species contribution nor fly-ash/bottom-ash-specific extraction is resolved.
Section 3.3 states 59.69% maximal Zn whereas Table 3, abstract and conclusion give 56.69%. Table 5 is numerical model optimization, not a separately described validation experiment; its Zn prediction 56.88% conflicts with abstract 56.38%, and its 1 g sulfur settings for Zn/Mn contradict the conclusion's general 3 g optimum. The inoculum main effect is reported nonsignificant. Table 4 gives Fe/Cu lack-of-fit p-values 0.0417/0.0416 despite broad model-adequacy wording. These source inconsistencies and statistical limitations prevent a validated optimum, universal enhancement or scale-up performance claim.
The catalogue corroborates the source's ATCC 35403 species designation and DSM 14366 correspondence. It does not establish purity, growth or the strain's separate causal contribution in the mixed-culture experiment.
The catalogue corroborates ATCC 19377 as A. thiooxidans and lists DSM 14887. This is culture-identity context, not an independent ash-leaching experiment.

Sources & References

  1. pangayao_2015: Pangayao, van Hullebusch, Gallardo and Bacani (2015). Bioleaching of trace metals from coal ash using mixed culture of Acidithiobacillus albertensis and Acidithiobacillus thiooxidans. Journal of Engineering Science and Technology, Special Issue on SOMCHE 2014 and RSCE 2014 Conference, 36-45. Sections 2.1-2.5, Figures 1-2, Tables 1-5 and Sections 3.1-3.5; complete 10-page original.
    https://jestec.taylors.edu.my/Special%20Issue%208_SOMCHE_2014/SOMCHE%202014_8_2015_036_045.pdf (accessed 2026-10-15)
  2. ncbi_albertensis: NCBI Taxonomy 119978: Acidithiobacillus albertensis, species.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=119978 (accessed 2026-10-15)
  3. ncbi_thiooxidans: NCBI Taxonomy 930: Acidithiobacillus thiooxidans, species.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=930 (accessed 2026-10-15)
  4. atcc_albertensis: ATCC 35403 culture catalogue: Acidithiobacillus albertensis; lists DSM 14366.
    https://www.atcc.org/products/35403 (accessed 2026-10-15)
  5. atcc_thiooxidans: ATCC 19377 culture catalogue: Acidithiobacillus thiooxidans; lists DSM 14887.
    https://www.atcc.org/products/19377 (accessed 2026-10-15)

Curation History

Timestamp Curator Action Summary
2026-10-15T16:16:05.719620+00:00 Codex (GPT-6; Codex) CREATE Created the distinct mixed pond-ash secondary-resource owner with primary culture-associated solubilization evidence, verified species identifiers and explicit control, denominator, source-conflict and scale limits.

Record source: data/records/ponded-coal-ash.yaml