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Nickel smelter slag secondary resource

Mixed solid residue from pyrometallurgical smelting in nickel extraction, distinct from nickel ore, flotation concentrate, flotation tailings and an individual constituent mineral. The curated case is the flash-furnace slag supplied by Votorantim Metais from its Serra de Fortaleza-MG nickel extraction operation in Brazil for a 2010 doctoral thesis. The source reports original particles of 100-500 micrometres and a dominant fayalite/forsterite-type iron-magnesium silicate diffraction pattern; that assignment does not make the bulk slag a pure mineral. Table 7 reports total Ni 0.26%, Cu 0.27% and Co 0.06%, versus aqua-regia-soluble Ni 0.07%, Cu 0.06% and Co 0.06%. The latter is an operational digestion fraction, not water solubility. These feed-specific assays do not define every nickel slag. No constituent criticality status or industrial microbial deployment is inferred.

Microbial & Biochemical Mechanisms (1)

Acidophile inoculation during slag leaching with little nickel advantage

bioleaching Microbial

Associated Organisms: Acidithiobacillus ferrooxidans (NCBITaxon:920)

Acidic leaching of slag was tested with source-labelled A. ferrooxidans LR, an isolate reported from acidic uranium-ore leachate at Lagoa Real, Bahia. Inoculation generally sustained a higher redox potential, but nickel release was similar to the corresponding uninoculated controls. The record documents microbial involvement in the assay and its limited metal-leaching benefit, not an established microbial enhancement of nickel recovery. Iron oxidation and secondary jarosite formation are consistent with the redox and diffraction observations; adsorption, passivation and the location of nickel within the silicate matrix remain proposed explanations for limited extraction. Dissolved metal was measured, without isolation of a nickel product.

Experimental Context & Analytical Limits:
Laboratory duplicate 250 mL Erlenmeyer flasks contained 150 mL T&K medium, 5% w/v original-size slag and 5% v/v inoculum, incubated at 30 degrees C and 150 rpm for 14 days. The nominally no-added-iron medium and the medium with 120 mmol/L Fe(II) each had an uninoculated counterpart. A third pair used previously grown culture containing approximately 120 mmol/L Fe(III), compared with culture described as sterile. T&K preculture medium was pH 1.8; experimental pH drifted upward and was corrected with sulfuric acid, as indicated in Figure 7, rather than remaining on an identical trajectory in all arms. Solution Ni and Cu used flame atomic absorption; redox used a platinum electrode against Ag/AgCl with saturated KCl. Total-feed assays used HF/microwave digestion, whereas the separate soluble fraction used aqua regia. The washed cells described for separate Warburg respirometry are not stated to have been used in these leaching flasks: inoculum carryover is not blank-corrected, and no added iron is not proof of no iron. No LR strain accession or independent authentication is supplied.
Curated Evidence Points:
Pages 33 and 36-39, Tables 1-2 and Figures 4 and 7-9 establish feed provenance, culture and flask treatment. Table 9 on page 56 reports day-14 Ni extraction relative to total feed Ni as inoculated/control pairs of 13/13%, 12/12% and 11/10% for the no-added-iron, ferrous and grown-ferric-culture treatments, respectively. Corresponding total-Cu percentages are 8/5%, 8/7% and 4/4%. These source-reported values indicate a small or absent treatment difference under this design; they are not a statistically demonstrated equivalence or general impossibility of biological slag leaching. Percentages against the smaller aqua-regia-soluble fraction in the adjacent columns must not be presented as total-metal recovery.
Figures 7-9 show elevated redox in inoculated arms, persistent dominant silicate peaks and minor peaks assigned to jarosite. These observations do not prove a unique nickel-release pathway or quantify secondary-phase mass. Separate respirometry on page 52 used washed cells, pH 2.2 glycine buffer and different loading; its oxygen consumption is not evidence of enhanced nickel release in the 14-day flasks. Duplicate assays are stated, but plotted dispersion, statistical tests, a complete metal mass balance and a killed-cell or inoculum-broth control are not provided for the leaching results.
Table 8 reports greater Ni extraction in a separate 48-hour chemical acid test at pH 0.5 than in the microbial flasks. Its loading, pH control and duration differ, so this is not a matched test of microbial efficiency. Static acid-curing experiments later in the thesis contain concentration-unit and total-versus-soluble reporting inconsistencies; their numerical yields are not assigned to this mechanism. Neither industrial origin of the feed nor proposed static processing establishes industrial bioleaching deployment.

Sources & References

  1. munoz_blandon2010: Nury Alexandra Munoz Blandon (2010). Recuperacao de niquel e outros metais a partir de diferentes fontes (rejeitos minerais de processo industrial e pentlandita (Ni,Fe)9S8) por lixiviacao bacteriana e acida. Doctoral thesis, UNESP, Instituto de Quimica, Araraquara. Official repository handle 11449/100745, issued 15 July 2010; repository accession in 2014 is not the experiment's publication year. Original 125-page PDF; source pp. 33, 36-39 and 50-58, Tables 1-2 and 7-9, Figures 4-9. Repository title wording differs slightly from the thesis front matter.
    https://hdl.handle.net/11449/100745 (accessed 2026-10-14)
  2. ncbi_ferrooxidans: NCBI Taxonomy 920, Acidithiobacillus ferrooxidans, species entry. Resolves the source species name; it does not authenticate the experimental LR isolate or identify it with the listed type strain.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=920&mode=info (accessed 2026-10-14)

Curation History

Timestamp Curator Action Summary
2026-10-14T05:35:29.026392+00:00 codex (GPT-6; codex) CREATE Created a process-defined nickel slag resource with source-labelled LR leaching assays, preserving negligible nickel advantage, analytical fractions and laboratory scope.

Record source: data/records/nickel-smelter-slag.yaml