Aluminium salt slag secondary resource
Salt-flux-bearing mixed slag from aluminium scrap remelting, containing process salts and oxide-rich solids. The accepted study sampled a rotary furnace batch from a Brazilian recycler using NaCl/KCl flux. This resource is defined by salt-flux remelting origin, distinct from the existing post-metal-recovery secondary aluminium dross specimen, generic smelting slag, bauxite residue, elemental aluminium or a single mineral. Laboratory water leaching and recovered salt crystals are documented; microbial action, inherited criticality and industrial deployment of this recipe are not.
Microbial & Biochemical Mechanisms (1)
Abiotic chloride-salt dissolution and evaporative crystallization
separation
Water dissolved chloride salts from crushed salt slag. Filtration and evaporation yielded NaCl/KCl-bearing crystals and a residue with lower salt content. The reported chloride-removal fraction is a head-assay normalized leachate measure, not aluminium recovery or the mass yield of saleable salt. Product characterization supports recovery of mixed salts with impurities. The paper reports a preliminary scaled solids and elemental balance; it does not measure an industrial throughput or a complete gas and water balance.
Experimental Context & Analytical Limits:
Section 2.1 sampled 481 kg comprising a rotary-furnace slag batch from a 14-tonne charge of manufacturing scrap, end-of-life scrap and primary aluminium dross, with reported NaCl:KCl flux ratio 3:1. After four days cooling, jaw crushing below 19 mm and staged homogenization/riffling, separate aliquots were roller crushed below 2.8 mm or ball milled below 0.5 mm. Section 2.2/Figures 2-3 used 70-160 g laboratory portions, distilled or tap water initially at pH 6.9-7.0, 25 degrees C and 55 rpm, with 20, 30 or 40 wt.% solids and sampling over two hours. The authors state duplicate tests; the listed 72 assays describe combinations, not 72 independent replicates of one condition. The selected arm used tap water, below-2.8-mm feed, 30 wt.% solids and 90 min. Filtered solids were dried at 50 degrees C for eight hours. The evaporation temperature is inconsistent: Section 2.2 specifies 85 degrees C for 24 h, while Figure 3 gives 50 degrees C for 24 h. No biological treatment was used.
Section 2.1 sampled 481 kg comprising a rotary-furnace slag batch from a 14-tonne charge of manufacturing scrap, end-of-life scrap and primary aluminium dross, with reported NaCl:KCl flux ratio 3:1. After four days cooling, jaw crushing below 19 mm and staged homogenization/riffling, separate aliquots were roller crushed below 2.8 mm or ball milled below 0.5 mm. Section 2.2/Figures 2-3 used 70-160 g laboratory portions, distilled or tap water initially at pH 6.9-7.0, 25 degrees C and 55 rpm, with 20, 30 or 40 wt.% solids and sampling over two hours. The authors state duplicate tests; the listed 72 assays describe combinations, not 72 independent replicates of one condition. The selected arm used tap water, below-2.8-mm feed, 30 wt.% solids and 90 min. Filtered solids were dried at 50 degrees C for eight hours. The evaporation temperature is inconsistent: Section 2.2 specifies 85 degrees C for 24 h, while Figure 3 gives 50 degrees C for 24 h. No biological treatment was used.
Curated Evidence Points:
Support
Source:
teixeira2022
Section 3.2/Figure 5b and page 9 report 91.2% chloride removal for the selected tap-water arm at 90 min; the same curve reaches 92.2% at 120 min. The abstract/conclusion greater-than-92% summary is therefore not accepted for the 90-minute selected condition. Equation 1 defines removal using normalized leachate/head-slag chloride concentrations. Figure 4 preserves a less favorable coarse-feed result: below-19-mm feed at 40 wt.% solids could not be agitated. Finer grinding offered limited improvement over roller crushing for more dilute pulps; those observations concern this feed only.
Support
Source:
teixeira2022
Section 3.3/Figures 8-11 identify NaCl and KCl in evaporated crystals and diminished salt peaks in the residual slag. Table 5 separately reports K, Na and Cl mass percentages of 8.78, 28.84 and 51.92 in recovered salts, and 0.24, 0.78 and 1.41 in residual slag. Thus salt-forming elements total about 90% in the crystals, with appreciable impurities; these percentages are composition, not recovery yield. The ED-XRF estimate of about 95.6% differs from titration/FAAS. The source proposes filtration/evaporation improvements and does not demonstrate remelting with this product.
Support
Source:
teixeira2022
Section 4/Figure 12 reports a preliminary balance scaled to the 481 kg furnace batch: 116.4 kg recovered salts and 364.6 kg leached residue, with 24.2% of feed mass dissolved. The authors estimate about 90% salt purity and 92% overall salt recovery using titration/FAAS analyses. Their elemental closure error is at most +0.15% for K using those assays, versus approximately -8% for K using ED-XRF. This reported solids/element balance is distinct from the Figure 5 chloride-removal measurement; it is not evidence that the laboratory recipe was operated on the entire 481 kg batch. The recovered NaCl:KCl ratio of 4.3:1 motivates proposed KCl addition before reuse, whose performance was not tested here.
Partial
Source:
teixeira2022
Tables 1 and 3 list high Al percentages in ED-XRF elemental compositions without oxygen; they do not quantify metallic-Al content, bulk alumina recovery or the aluminium mass balance. XRD phase non-detection does not demonstrate absence of hydrolyzable constituents or negligible gas emission: no direct gas balance is reported. Table 3's zero K entry is a non-detection, whereas Table 5 gives 0.24% K by another method, not evidence for zero potassium. Impurities below the stated approximately 5% XRD detection limit can remain despite only NaCl/KCl peaks in the recovered crystals. Figure 12 is a proposed flowsheet. Subsequent aluminium recovery, complete detoxification and industrial closed-loop flux reuse are outside the demonstrated experiment.
Sources & References
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teixeira2022: Teixeira, Ambros, Sampaio, Raposo, De Brum and Moncunill (2022). Optimization of Water Leaching of Chlorides from Aluminum Salt Slag. Minerals 12(9):1141. DOI 10.3390/min12091141. Complete 15-page original, Sections 2-5, Figures 1-12 and Tables 1-5; published 9 September 2022.
https://doi.org/10.3390/min12091141 (accessed 2026-10-16)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-16T05:57:40.805922+00:00 |
Codex GPT-6 | CREATE | Create a salt-flux remelting resource with chloride leaching, impure recovered crystals, and explicit analytical and protocol limits. |
2026-10-16T06:05:34.181400+00:00 |
Codex GPT-6 | EDIT | Address issue480: acknowledge the source-reported scaled solids and elemental balance while preserving the lack of demonstrated industrial throughput, gas/water balance and flux reuse. |
Record source: data/records/aluminium-salt-slag.yaml