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Ion-adsorption rare-earth leach residue secondary resource

A processed, mixed mineral residue remaining after ammonium-sulfate extraction of ion-exchangeable rare earths from weathered ion-adsorption ore. Zhang and colleagues (2024) prepared the studied material in the laboratory from Guangdong, China ore; this is not evidence of sampling an industrial tailings deposit. It is distinct from the natural ion-adsorption rare-earth clay feed, individual mineral species and isolated rare-earth products. The preparation included repeated salt leaching, rinsing, 60-mesh sieving, drying and crushing. The authors' ion-unexchangeable designation is operational, referring to the rare earths remaining after that pretreatment. It does not mean resistance to every subsequent extractant. The experimental feed contains mainly kaolinite, quartz, orthoclase and muscovite, with minor Fe-bearing and rare-earth-bearing phases. Its composition is not a universal tailings specification, and no criticality designation is inherited from its constituent elements.

Microbial & Biochemical Mechanisms (1)

Fungal culture and metabolite-filtrate-associated rare-earth leaching

bioleaching Microbial

Associated Organisms: Aspergillus niger (NCBITaxon:5061)

Aspergillus niger culture and a separately produced culture filtrate were used to mobilize rare earths remaining in the pretreated residue. Measured organic acids and acidification support an acid-associated leaching interpretation. The proposed contributions of proton attack, carboxylate complexation and Fe-bearing phase dissolution are not individually established by matched biological controls. Chemical citric-acid experiments provide separate mechanistic context; they are not an independent microbial replication. Solution release and post-leach salt desorption do not establish an isolated rare-earth product or industrial recovery.

Experimental Context & Analytical Limits:
The source reports A. niger CGMCC3.739 supplied through BJMCC, without strain sequence authentication. Freeze-dried material was grown on PDA at 301 K for six days; a second generation was grown in PDB for five days as inoculum. Five mL fungal suspension was added to 150 mL PDB containing 20 g/L dextrose, 5 g/L potato powder and 0.1 g/L chloromycetin, initially pH 5.8-6.2. The one-step arm combined fungal cultivation and solid leaching at 301 K and 220 rpm. The two-step arm first cultivated the fungus until nutrient depletion and minimum pH, then used the filtrate for leaching; filtration cutoff and verified absence of cells are not stated. The text reports leaching outcomes after 20 days, while the separate Figure 4a pH trajectory is plotted in hours and does not span that entire duration. Solid loading and leachant volume are not clearly specified for the biological arms separately; chemical-batch loadings must not be transferred to them. A sterile PDB control without a sample is described, which is not a matched uninoculated medium-plus-solid control. Replicate counts and the meaning of the plotted error bars are not stated.
Curated Evidence Points:
Methods 2.2.1 and Results 3.1 establish the processed feed: 2.5 wt% ammonium sulfate column leaching twice at a reported liquid-to-solid ratio of 5:1, then stirred leaching at 10 mL/g, followed by rinsing and 60-mesh separation. The reported 610.5 mg/kg total rare earths and 261.8 mg/kg exchangeable fraction concern the source's 60-mesh sieve substrate, not unsieved bulk ore or a regional resource estimate.
Table S3 lists a residual-feed total of 348.7 mg/kg, whereas its displayed individual rare-earth entries sum to 348.8 mg/kg; rounding could account for the difference. Its heading says tailings without ion-unexchangeable REEs, contrary to the main preparation and residual-feed interpretation. This wording conflict is preserved rather than treated as a different feed. Figure S2 supports a heterogeneous multiphase material; mineral classifications and local elemental maps do not establish phase-specific extraction yields.
Section 3.4 and Figure 4 report one-step and two-step leaching ranges of 15.8-24.1% and 18.1-31.4%, respectively, after 20 days. The Figure 4b total bars are below the upper endpoints and have overlapping error bars. The headline 31.4% is therefore retained as the upper extent of the reported range, not asserted as a mean, a statistically established improvement or a percentage of original untreated ore recovered as product. Methods 2.2.3 also describe ammonium-sulfate desorption after leaching; separate liquid, re-adsorbed and final-solid inventories are insufficient to reconstruct a closed rare-earth mass balance.
Table S5 reports citric acid at 46.65 g/L in the bioleaching metabolite mixture, alongside oxalic, malic, tartaric, succinic and acetic acids. HPLC identification and the Figure 4a pH decrease in the main paper support organic-acid production. The mixture measurement does not show that citric acid alone caused the fungal-arm result or close a carbon balance for the stated cultivation medium.
Figures 2-3 compare chemical acid conditions, and Figure 5 explicitly characterizes citric-acid leaching by sequential extraction and XPS. These chemical results support a possible acid/ligand explanation but cannot be assigned wholesale to the microbial arm. Sequential extraction fractions are defined by reagents, not unique mineral species. Table 1 compares different local particle spots before and after treatment; their concentrations are not a paired whole-feed mass balance. Cluster-model DFT in Section 3.5 is a proposed explanation, not direct evidence of selective microbial attack on goethite.
Figure S1 labels the treated solid after A. niger leaching, whereas main Figure 5 specifies citric-acid treatment. The source's phase interpretation therefore retains arm boundaries. Table S1 reports Fe2O3-equivalent XRF fractions of 4.93 and 1.72 wt%, although the main discussion calls these iron content. They are oxide-equivalent relative compositions, not measured elemental Fe removal fractions. XPS fitted peak areas and DFT model clusters do not quantify bulk goethite abundance.
Context_only Source: zhang2024
The study is a laboratory investigation of one prepared feed. It supplies neither a fully matched abiotic leaching trajectory nor a purified product, pilot operation, environmental life-cycle assessment or industrial deployment. Claims of general process superiority or transfer to other tailings remain unsupported.

Sources & References

  1. zhang2024: Zhang J, Li P, Guan X and colleagues (2024). Bioleaching ion-unexchangeable rare earth in ion-adsorption type rare earth waste tailing. Separation and Purification Technology 348, 127691. DOI 10.1016/j.seppur.2024.127691. Complete nine-page accepted manuscript supplied by OSTI record 2479444; Methods 2.2.1-2.2.6, Results 3.1-3.5, Figures 1-5 and Table 1 inspected.
    https://doi.org/10.1016/j.seppur.2024.127691 (accessed 2026-10-12)
  2. zhang2024_repository: OSTI 2479444 public accepted manuscript of Zhang and colleagues, matched by title, authors, DOI and publisher metadata. The OSTI April 2024 date and PNNL December 2024 posting differ from the journal's November 2024 issue; these do not identify new experiments.
    https://www.osti.gov/servlets/purl/2479444 (accessed 2026-10-12)
  3. zhang2024_supplement: Zhang and colleagues (2024), original Elsevier supplementary DOCX for PII S1383586624014308. Matching article title and all authors; Parts 1.1-1.3, Figures S1-S7 and Tables S1-S6 inspected through original XML, tables, embedded graphics and a local PDF rendering.
    https://ars.els-cdn.com/content/image/1-s2.0-S1383586624014308-mmc1.docx (accessed 2026-10-12)
  4. ncbi_aspergillus_niger: NCBI Taxonomy 5061, Aspergillus niger, current species-level identity. This does not authenticate the experimental CGMCC3.739 strain or establish its sequence identity.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=5061&mode=Info (accessed 2026-10-12)

Curation History

Timestamp Curator Action Summary
2026-10-12T10:38:56Z codex (GPT-6) CREATE Added a distinct laboratory-prepared leach residue with fungal culture and filtrate evidence, retaining source inconsistencies, control gaps, arm boundaries and the absence of product recovery.

Record source: data/records/ion-adsorption-rare-earth-leach-residue.yaml