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Ferrochrome slag secondary resource

Mixed slag generated during smelting of chromite-bearing feed to produce ferrochrome alloy. The curated experiment used waste supplied by Zimasco at Kwekwe, Zimbabwe. This processing-derived resource is distinct from chromite ore, physical beneficiation tailings, chromite ore processing residue from chemical chromium extraction, the ferrochrome alloy product and individual slag mineral phases. Composition varies with feed and process; the selected sample is not a universal specification. No constituent criticality designation or mineral identifier is inherited.

Microbial & Biochemical Mechanisms (1)

Hydrochloric-acid extraction of magnesium into solution

separation

Hydrochloric acid solubilized magnesium from prepared ferrochrome slag in laboratory stirred-vessel experiments. The measured endpoint is magnesium in filtered solution relative to magnesium in the feed, not isolated metallic magnesium or a characterized fertilizer product. Shrinking-core fits do not independently prove a unique rate-controlling molecular mechanism.

Experimental Context & Analytical Limits:
Sections 2.1-2.2 describe Zimasco slag pulverized and sieved to 80% passing 75 micrometres, a 1 L vessel in a water bath, 500 mL of 5 or 6 M HCl, nominal solid:liquid 1:10 and 250 rpm, with 5 mL samples withdrawn over 30-180 minutes, diluted, filtered and analyzed by atomic absorption spectroscopy. Duplicate experiments were averaged. The source does not specify ratio units explicitly or establish error bars, a full magnesium mass balance, a no-acid control or isolated product purity. Table 1 labels its analysis mineralogy and Section 2.1 names X-ray diffraction, but the reported entries are oxide composition percentages, including MgO 26.4%, SiO2 31.4%, Al2O3 18.0% and Cr2O3 14.3%. These are not accepted as mineral phase fractions or elemental magnesium concentration. The generic method and individual optimization arms differ as retained below.
Curated Evidence Points:
Sections 2.2 and 3.1-3.4, Equation 1 and Figures 1-4 support laboratory magnesium extraction into the liquid phase, with response to mixing, liquid:solid ratio, duration and temperature. The abstract reports 88.2% extraction after 150 minutes at the authors' selected 5 M HCl, 70 degrees C, 250 rpm and solid:liquid 1:10 conditions; Section 3.3 separately reports 88.2% after 150 minutes. This number is retained as an author-reported, internally unreconciled result, not an independently validated optimum or recovered-product yield.
Figure 3 approaches the stated 88.2% at 150 minutes, whereas Figure 4 plots visibly lower extraction at 70 degrees C for its stated 150-minute temperature series. No exact values are digitized or silently reconciled. Section 3.1 uses liquid:solid 14:1, 6 M HCl, 80 degrees C and 180 minutes; it then says 250 rpm was used in all future trials, but Section 3.2 specifies 350 rpm. Section 3.3 calls the interval from 150 to 180 minutes an additional 15 minutes. These unresolved arm and reporting inconsistencies limit confidence in the numerical optimum.
Sections 3.5-3.6 and Figures 5-8 compare fitted shrinking-core and Arrhenius models. The abstract gives chemical-reaction activation energy 41.45 kJ/mol; Section 3.6 gives 52.05 kJ/mol and diffusion 95.44 kJ/mol. The conclusion instead assigns 95.44 kJ/mol to chemical reaction and 52.04 kJ/mol to diffusion. Figure 8 labels the steeper fitted line diffusion. No single activation energy or uniquely demonstrated chemical-control mechanism is adopted. Gel formation at 80 degrees C was observed, while silica precipitation and magnesium adsorption are proposed interpretations, not independently characterized causes in this experiment.
Sections 3.7-3.8 and Table 2 discuss possible use of the impure leachate in struvite production and a reagent-cost calculation that assumes free slag and excludes transport and capital. This study does not demonstrate struvite production, full process economics, acid regeneration, industrial deployment or complete selective magnesium recovery. The industrial origin of the feed does not change the laboratory scale of the extraction.
Despite its simulated-slag title, Sections 2.1-2.3 and 3.1-3.4 describe K2CrO4 in basal mineral medium, glucose and iron salts with a wastewater-derived bacterial culture; they do not establish treatment of an actual ferrochrome-slag solid or its leachate. Its chromate-removal results are not transferred to this material, and no microbial mechanism is assigned from that study.

Sources & References

  1. moyo2022: Moyo, L. B.; Simate, G. S.; Mamvura, T. A. (2022). Magnesium recovery from ferrochrome slag: kinetics and possible use in a circular economy. Heliyon 8(12):e12176. DOI 10.1016/j.heliyon.2022.e12176; PMID 36578389; PMCID PMC9791875. Complete original XML/HTML, Sections 2-4, Tables 1-2 and all eight original figures inspected.
    https://doi.org/10.1016/j.heliyon.2022.e12176 (accessed 2026-10-16)
  2. bansal2017_context: Bansal, N.; Coetzee, J. J.; Chirwa, E. M. N. (2017). In Situ Bioremediation of Chromium (VI) In a Simulated Ferrochrome Slag. Chemical Engineering Transactions 61:55-60. DOI 10.3303/CET1761007. Complete six-page publisher original; Sections 2.1-2.3 and 3.1-3.4 establish synthetic chromate solution rather than an actual solid slag feed.
    https://doi.org/10.3303/CET1761007 (accessed 2026-10-16)

Curation History

Timestamp Curator Action Summary
2026-10-16T00:38:41.465095+00:00 Codex (GPT-6; Codex) CREATE Created a distinct smelting-derived ferrochrome slag resource with qualified laboratory acid extraction, explicit source contradictions, and exclusion of synthetic-solution microbial extrapolation.
2026-10-16T00:43:35.378131+00:00 Codex (GPT-6; Codex) EDIT Corrected two primary-source section locators identified by independent review while preserving all scientific claims and limitations.

Record source: data/records/ferrochrome-slag.yaml