Chromite beneficiation tailings secondary resource
Mixed residual mineral solids from physical beneficiation of chromite-bearing ore. The curated 2018 case is fresh superficial tailings collected in May 2017 at a beneficiation plant in Sukinda valley, Odisha, India, with a separate stockpiled-tailings core used for chemical extraction comparisons. The source describes comminution, desliming and gravity concentration, rather than chromate manufacture. These solids are distinct from the chromite mineral species, unprocessed ore, lateritic overburden, the plant's chromite concentrate and chemically processed chromite ore residues. Reported XRD phases include chromite, goethite, hematite, gibbsite and chlorite; Cr also occurs in nonchromite phases. Table 1 reports 56.7 wt% Fe2O3 and 18.1 wt% Cr2O3 on an XRF oxide-equivalent basis, not quantitative mineral fractions. A separate 2025 fungal study uses two Eti Krom enrichment-tailings feeds labelled olivine and serpentine; both are mixed mineral materials, distinct from the Odisha samples and from pure olivine or serpentine minerals. Neither constituent criticality nor industrial microbial processing is inferred from these feeds' compositions or industrial origins.
Microbial & Biochemical Mechanisms (3)
Sulfur-fed culture-associated acidification and element release
bioleaching
Microbial
Associated Organisms:
Acidithiobacillus thiooxidans (NCBITaxon:930)
Living source-labelled A. thiooxidans DSM 9463 cultures maintained acidic conditions and were associated with release of Fe, Ni, Mn and Al from the mixed fresh tailings. Sulfur oxidation and resulting acid production are the proposed principal explanation. This is not evidence of selective chromite destruction, direct microbial iron oxidation or an isolated chromium recovery product. Initial Cr mobilization also occurred without inoculation and is associated with medium phosphate.
Experimental Context & Analytical Limits:
Laboratory duplicate batches at 5, 10 and 30 g tailings/L, in cotton-plugged 500 mL reactors at 30 degrees C and 190 rpm, with 1% v/v pregrown culture. Material was autoclaved at 121 degrees C for 20 min. The medium contained, per litre, 2 g (NH4)2SO4, 0.25 g MgSO4.7H2O, 0.1 g K2HPO4 and 0.1 g KCl, with elemental sulfur printed as 11% wt/v; that unusual reported dose is retained without correction. The medium was initially adjusted to pH 3.5; inoculated reactors subsequently shown in Figure 3 average about pH 1.6, whereas uninoculated medium controls have higher, loading-dependent pH. Controls contained sterile tailings and medium, and blanks sterile tailings and distilled water; both received sodium azide. Separate chemical comparisons used acidified water at initial pH 2 and 30 g/L. Each 20 mL sample withdrawal was replaced with fresh sterile medium. Filtered 0.45 micrometre leachates were acidified with 16 N HNO3 reagent and analyzed by ICP-AES/HR-ICP-MS; final acid concentration is not given. Fe speciation used ferrozine. Reported errors are standard deviations of duplicate experiments. Methods list sampling through day 30, whereas results and supplementary tables use day 34; exact scheduling remains inconsistent. Working liquid volume, tested particle-size distribution and cumulative withdrawal/replacement correction are not established. Reported mg element/kg tailings quantities are extraction-normalized results, not recovery yields or leachate mg/L.
Laboratory duplicate batches at 5, 10 and 30 g tailings/L, in cotton-plugged 500 mL reactors at 30 degrees C and 190 rpm, with 1% v/v pregrown culture. Material was autoclaved at 121 degrees C for 20 min. The medium contained, per litre, 2 g (NH4)2SO4, 0.25 g MgSO4.7H2O, 0.1 g K2HPO4 and 0.1 g KCl, with elemental sulfur printed as 11% wt/v; that unusual reported dose is retained without correction. The medium was initially adjusted to pH 3.5; inoculated reactors subsequently shown in Figure 3 average about pH 1.6, whereas uninoculated medium controls have higher, loading-dependent pH. Controls contained sterile tailings and medium, and blanks sterile tailings and distilled water; both received sodium azide. Separate chemical comparisons used acidified water at initial pH 2 and 30 g/L. Each 20 mL sample withdrawal was replaced with fresh sterile medium. Filtered 0.45 micrometre leachates were acidified with 16 N HNO3 reagent and analyzed by ICP-AES/HR-ICP-MS; final acid concentration is not given. Fe speciation used ferrozine. Reported errors are standard deviations of duplicate experiments. Methods list sampling through day 30, whereas results and supplementary tables use day 34; exact scheduling remains inconsistent. Working liquid volume, tested particle-size distribution and cumulative withdrawal/replacement correction are not established. Reported mg element/kg tailings quantities are extraction-normalized results, not recovery yields or leachate mg/L.
Curated Evidence Points:
Support
Source:
bolanos2018
Sections 2.2-2.4 and 3.2-3.3, Figures 3-8, support acidic culture-associated element release and its loading dependence. For 5 g/L, the Results report Fe increasing from 421 to 1234 mg/kg tailings over the plotted experiment. The uninoculated medium controls release less Fe, Ni, Mn and Al but do not match the inoculated pH trajectory. This supports association with the sulfur-fed culture, not an effect independent of acidity.
Partial
Source:
bolanos2018_supplement
Figure S3 and main Section 4.2 preserve counterevidence at 30 g/L: the authors compare 479 mg Fe/kg after approximately 11 days with acidified water against 213 mg/kg with the inoculated culture. Thus microbial enhancement is not universal. The separate acid arm has different medium chemistry and no documented matching pH trajectory; inhibition by released metals is a hypothesis. Figure S2 shows Fe(II)/Fe(III) evolution without bacteria. Its Fe axis is mg/L, whereas Figure S3 is mg/kg tailings, and their quantities are not reconciled here. The main paper's attribution of Fe(II) oxidation to A. thiooxidans is not independently demonstrated; its cited comparison concerns A. ferrooxidans.
Partial
Source:
bolanos2018
Figure 5 shows early Cr release in both medium controls and inoculated reactors, followed by declining aqueous Cr. The separate one-hour chemical extraction in Section 2.3 and Table 2 used 1 g solids with 25 mL water or 0.1 M KH2PO4 and a 0.22 micrometre filtrate. Fresh-tailings phosphate extraction reports 223 mg Cr(VI)/kg and 240 mg total Cr/kg, compared with 63 mg Cr(VI)/kg using water. These are operational exchangeable pools, not microbial yields. Table 2 labels bulk total Cr as 96 g/kg while the adjacent prose says 96 mg/kg; Table 1's oxide-equivalent assay is not converted to resolve this conflict. Old-tailings depth comparisons are separate chemical extractions, not evidence of microbial remediation in a stockpile.
Partial
Source:
bolanos2018_supplement
Figures S3 and S5 show lower Cr release from the separate concentrate than from fresh tailings, consistent with contributions from other phases. The main text's approximately threefold comparison is not imposed as a matched-time ratio because the plotted tailings and concentrate trajectories differ. Neither the concentrate nor the tailings is pure chromite. Tables S1-S3 model dissolved complexes and possible precipitation; they do not measure solid products or prove Cr(VI) reduction. Reduction by ferrous iron, sulfur intermediates and biomass, adsorption and precipitation remain alternative contributions to solution loss.
Alkalinizing WCS358 culture-associated element redistribution
bioleaching
Microbial
Associated Organisms:
Pseudomonas capeferrum (NCBITaxon:1495066)
The culture called Pseudomonas putida WCS 358 in the paper was associated with increasing pH, a CAS-reactive siderophore signal, transient iron mobilization and declining filtered chromium after initial release. The identifier follows NCBI's current P. capeferrum species entry, which includes WCS358 and explicitly marks the name effectively but not validly published. It is not genetic authentication of the experimental culture. Siderophore-specific mineral attack and direct enzymatic chromium reduction were not established.
Experimental Context & Analytical Limits:
The same fresh-tailings batch design used 5, 10 and 30 g/L, 1% v/v pregrown culture, 30 degrees C, 190 rpm, duplicate reactors and 20 mL sampling with replacement. WCS 358 was supplied by Peter Bakker, University of Utrecht. Iron-free succinate medium contained, per litre, 6 g K2HPO4, 3 g KH2PO4, 0.2 g MgSO4.7H2O, 1 g (NH4)2SO4 and 4 g succinic acid, initially pH 7. Figure 3 shows inoculated pH rising to approximately 9 while uninoculated medium controls remain near 7. Sodium-azide medium controls and water blanks, and a separate initial-pH-9 water comparison at 30 g/L, were used. Culture-associated protein and CAS response were assayed in supernatant; these are proxies rather than direct viable-cell counts or identified siderophore concentrations. The sampling-time and mass-accounting limits of the acidophile arm also apply. This is laboratory mobilization/redistribution, not isolated metal recovery or demonstrated field remediation.
The same fresh-tailings batch design used 5, 10 and 30 g/L, 1% v/v pregrown culture, 30 degrees C, 190 rpm, duplicate reactors and 20 mL sampling with replacement. WCS 358 was supplied by Peter Bakker, University of Utrecht. Iron-free succinate medium contained, per litre, 6 g K2HPO4, 3 g KH2PO4, 0.2 g MgSO4.7H2O, 1 g (NH4)2SO4 and 4 g succinic acid, initially pH 7. Figure 3 shows inoculated pH rising to approximately 9 while uninoculated medium controls remain near 7. Sodium-azide medium controls and water blanks, and a separate initial-pH-9 water comparison at 30 g/L, were used. Culture-associated protein and CAS response were assayed in supernatant; these are proxies rather than direct viable-cell counts or identified siderophore concentrations. The sampling-time and mass-accounting limits of the acidophile arm also apply. This is laboratory mobilization/redistribution, not isolated metal recovery or demonstrated field remediation.
Curated Evidence Points:
Support
Source:
bolanos2018
Sections 2.2.1, 2.4.3-2.4.4, 3.2-3.3 and 4.2 and Figures 3-8 support the stated pH and element trajectories. Culture-associated Cr depletion is greater than in the phosphate-rich medium controls, but both start with substantial Cr release. Total filtered elemental concentrations alone do not separate microbial reduction from adsorption, precipitation or sampling losses. The paper itself describes the P. putida influence on Cr leaching as negligible when discussing the alkaline-water comparison.
Partial
Source:
bolanos2018_supplement
Figure S4 shows transient, loading-dependent CAS and protein signals, not monotonic growth or molecular identification. Figures S1 and S3 document evolving dissolved oxygen and a separate alkaline-water arm; they do not provide matched cell-free culture-metabolite or siderophore-deficient controls. Tables S1-S3 are equilibrium simulations without adsorption parameters, not a measured Cr(III)/Cr(VI) time course or identified precipitate. Proposed biosorption, sulfur-mediated reduction, ferrous-iron reduction and enzymatic processes are not resolved quantitatively. No recovered-metal mass balance was demonstrated.
Metal release during OG2 fungal treatment of mixed silicate-rich tailings
bioleaching
Microbial
Associated Organisms:
Trametes versicolor (NCBITaxon:5325)
Nickel, iron, magnesium and silicon were reported in leachates during laboratory treatment with source-labelled living T. versicolor OG2. Organic-acid-mediated release is proposed; oxalic acid was detected in one treated filtrate. Absent uninoculated leaching controls prevent assigning an incremental microbial effect. Neither selective chromite dissolution nor isolated nickel recovery is demonstrated, and the source's percentage calculation is not accepted as a verified yield.
Experimental Context & Analytical Limits:
Eti Krom supplied final chromite-enrichment tailings called olivine and serpentine. XRD identifies multiple silicates and spinels in both; Table 1 reports 2.91 and 29.91 wt% Cr2O3 equivalents, respectively, not chromite phase fractions. Table 2 reports solid-feed Ni at 3246.61 and 1457.18 ppm. The as-received feeds were not ground; Figure 1 documents different size distributions. Ataturk University supplied OG2. The paper states ITS identification and assigned GenBank accessions but prints no accession value, so strain identity remains source-reported. Cultures were reactivated on potato dextrose agar at 30 degrees C for 5-11 days, then washed with pH-7.2 PBS and 0.01% Tween 80. Each 20 g solid suspension in 500 mL water was autoclaved at 121 degrees C for 15 min, received 80 mL medium prepared with 2 g/L glucose, 0.5 g/L peptone and 0.5 g/L yeast extract plus 1 mL spore suspension, and was brought to 1000 mL. These medium concentrations are for the prepared aliquot; final nutrient concentrations are not assumed. Treatments used initial pH 4.5, 5.0, 5.5 or 6.3, 20 degrees C and 3 or 7 days. The methods conflict between 150 and 200 rpm and give spore density approximately 10^7 without a unit. They call loading 2% by weight; the explicit mass and volume correspond to 20 g/L. Solids were separated at 6000 rpm, dried at 60 degrees C for two days, and supernatants stored at 4 degrees C for ICP-MS analysis. No leach replicate number, uncertainty, final pH trajectory, uninoculated control, matched-acid control or recovered-product mass balance is reported. The control in Table 3 belongs to a separate fungal growth-tolerance plate assay and does not control the leaching.
Eti Krom supplied final chromite-enrichment tailings called olivine and serpentine. XRD identifies multiple silicates and spinels in both; Table 1 reports 2.91 and 29.91 wt% Cr2O3 equivalents, respectively, not chromite phase fractions. Table 2 reports solid-feed Ni at 3246.61 and 1457.18 ppm. The as-received feeds were not ground; Figure 1 documents different size distributions. Ataturk University supplied OG2. The paper states ITS identification and assigned GenBank accessions but prints no accession value, so strain identity remains source-reported. Cultures were reactivated on potato dextrose agar at 30 degrees C for 5-11 days, then washed with pH-7.2 PBS and 0.01% Tween 80. Each 20 g solid suspension in 500 mL water was autoclaved at 121 degrees C for 15 min, received 80 mL medium prepared with 2 g/L glucose, 0.5 g/L peptone and 0.5 g/L yeast extract plus 1 mL spore suspension, and was brought to 1000 mL. These medium concentrations are for the prepared aliquot; final nutrient concentrations are not assumed. Treatments used initial pH 4.5, 5.0, 5.5 or 6.3, 20 degrees C and 3 or 7 days. The methods conflict between 150 and 200 rpm and give spore density approximately 10^7 without a unit. They call loading 2% by weight; the explicit mass and volume correspond to 20 g/L. Solids were separated at 6000 rpm, dried at 60 degrees C for two days, and supernatants stored at 4 degrees C for ICP-MS analysis. No leach replicate number, uncertainty, final pH trajectory, uninoculated control, matched-acid control or recovered-product mass balance is reported. The control in Table 3 belongs to a separate fungal growth-tolerance plate assay and does not control the leaching.
Curated Evidence Points:
Support
Source:
acar2025
Experimental and Results, pages 2528-2536, support feed identity, inoculated treatment and detected metal release. Figures 5 and 7 label their highest Ni dissolution indices as 41.82% and 30.97% at initial pH 5 after seven days for the olivine-labelled and serpentine-labelled feeds. These are author-reported indices, retained only to identify the experimental observations. Equation 1 divides solution ppm by solid-sample ppm without an explicit solid-mass/liquid-volume conversion. Under the stated 20 g/L loading this expression alone does not establish a feed-mass extraction fraction. Original solution values and normalization calculations are not supplied, so no corrected yield is inferred. Figures 6 and 8 use ratios of these dissolution indices for selectivity, not product purity or isolated-metal yield.
Partial
Source:
acar2025
Figure 4 and pages 2530-2534 report oxalic acid at 9.562 mg/L in the seven-day olivine-treatment filtrate chromatogram. The methods describe a 100-fold dilution without clarifying the reported concentration's back-correction; it is not converted here. Citric acid, laccase-driven release, specific metal-organic complexes and ferric/ferrous reaction pathways are discussed rather than measured in this experiment. No abiotic filtrate comparison establishes the increment attributable to fungal acid production. The proposed Cr(VI)-toxicity explanation for differences between feeds lacks a leaching-stage Cr(VI) assay; chromite abundance is not evidence that hexavalent chromium was present. Different mineralogy and particle size also confound feed comparisons. The graphical nickel-product depiction and proposed downstream separation are not demonstrated recovery operations or industrial deployment.
Sources & References
-
bolanos2018: Bolaños-Benítez, van Hullebusch, Lens, Quantin, van de Vossenberg, Subramanian and Sivry (2018). (Bio)leaching Behavior of Chromite Tailings. Minerals 8(6):261, published 20 June 2018. DOI 10.3390/min8060261. Complete 23-page primary; Sections 2-4, Tables 1-2 and Figures 1-8.
https://doi.org/10.3390/min8060261 (accessed 2026-10-11) -
bolanos2018_supplement: Supplementary Materials to Bolaños-Benítez et al. (2018), (Bio)leaching Behavior of Chromite Tailings. Original seven-page publisher PDF, final page blank; Figures S1-S5 and Tables S1-S3. Tables S1-S3 are visual MINTEQ calculations, not measured product speciation or mineral recovery.
https://mdpi-res.com/minerals/minerals-08-00261/article_deploy/minerals-08-00261-s001.pdf (accessed 2026-10-11) -
dsm9463: DSMZ culture catalogue. Acidithiobacillus thiooxidans DSM 9463, strain designation B-S2, isolated from an Australian bioleaching reactor. Catalogue identity does not authenticate the experimental stock.
https://www.dsmz.de/collection/catalogue/details/culture/DSM-9463 (accessed 2026-10-11) -
ncbi_thiooxidans: NCBI Taxonomy 930, Acidithiobacillus thiooxidans, species-level entry.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=930 (accessed 2026-10-11) -
ncbi_wcs358: NCBI Taxonomy 1495066, current species label Pseudomonas capeferrum, listing WCS358 as its type strain and Pseudomonas sp. WCS358 as included. NCBI marks the name effectively but not validly published. This resolves the source's WCS 358 label without asserting stock authentication.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=1495066 (accessed 2026-10-11) -
acar2025: Acar, Gulmez, Baris and Basman (2025). Sustainable Nickel Extraction from Low-Grade Ores via Trametes versicolor: A Bioleaching Case Study on Olivine and Serpentine. Journal of Sustainable Metallurgy 11:2527-2540; published online 4 June 2025. DOI 10.1007/s40831-025-01123-1. Complete 14-page publisher PDF; Experimental, Results and Discussion, Tables 1-3 and Figures 1-8.
https://doi.org/10.1007/s40831-025-01123-1 (accessed 2026-10-11) -
ncbi_versicolor: NCBI Taxonomy 5325, Trametes versicolor, species-level entry. This mapping does not independently authenticate isolate OG2.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=5325&mode=Info (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T19:07:31.421425+00:00 |
codex (GPT-6; codex) | CREATE | Created a mixed chromite-beneficiation-tailings resource with two qualified culture-associated laboratory observations, verified organism mappings and explicit phosphate, control, speciation, unit and mass-accounting limits. |
2026-10-11T19:47:38.292106+00:00 |
codex (GPT-6; codex) | EDIT | Added a separately scoped 2025 OG2 fungal-treatment observation for two Eti Krom chromite-enrichment tailings, with control, strain, recipe, mass-normalization and mechanism limits. Retained the preceding 2018 observations and their provenance. |
Record source: data/records/chromite-beneficiation-tailings.yaml