Secondary aluminium remelting can create dross and salt-bearing slag containing recoverable metallic aluminium, sodium/potassium chloride flux salts, aluminium oxides and reactive compounds. Fresh residue may be hot, dusty and chemically reactive; uncontrolled contact with water can generate hydrogen, ammonia and heat. Recovery therefore needs a carefully sequenced hot-material, gas and brine system.
Canonical owner boundary. This article owns post-furnace aluminium dross/salt-slag recovery: receiving and cooling, metal separation, crushing, salt leaching/crystallisation, reactive-gas management, non-metallic product qualification, water, storage and closure. Aluminium scrap sorting/remelting, primary smelting, regional scrap policy, transport, finance, government and civilisation remain separate.
1. Distinguish dross, salt slag and salt cake
Residues differ in salt content, metal content, temperature, moisture and reactivity and should not share one acceptance rule.
2. Preserve furnace and alloy source
Alloy additions and flux practice can affect metal recovery, salts and final non-metallic product quality.
3. Treat hot dross as a thermal hazard
Fresh dross can continue reacting and oxidising. Dedicated refractory receiving and controlled cooling protect workers and recoverable metal.
4. Keep water away until deliberately introduced
Uncontrolled wetting of reactive aluminium compounds or metal fines can generate hydrogen, ammonia and heat.
5. Recover coarse metallic aluminium first
Screening and physical separation can return metal with less energy and less reactive surface area than grinding everything.
6. Control aluminium-bearing dust
Crushing and milling can create combustible metal dust and mineral fines. Enclosure, extraction and housekeeping must follow the actual particle hazard.
7. Treat leaching as a reactive-gas process
Adding water to salt slag can release ammonia and hydrogen. Gas detection, capture and ventilation belong in the core design.
8. Close the salt-water balance
Dissolution, filtration, evaporation, crystallisation and mother-liquor purge should reconcile so salt recovery does not create an uncontrolled saline wastewater stream.
9. Release recovered NaCl/KCl to a real furnace specification
Composition, moisture and particle condition determine whether salt can return as flux.
10. Keep off-spec salt segregated
Failed material belongs in rework or another lawful route and should not be diluted into compliant flux.
11. Qualify the alumina-rich non-metallic fraction separately
Cement, ceramic, refractory and mineral uses have different chloride, reactivity, leaching and fineness requirements.
12. Track reactive nitrides and residual metal
Aluminium nitride and residual metallic aluminium can continue generating gas when wet and should remain visible in product testing.
13. Close aluminium, salt and gas mass balances
Metal recovery, recovered flux, residual chloride and ammonia/hydrogen generation should all be measurable rather than hidden inside total diversion.
14. Separate hot incoming material from clean products
Vehicle routes and storage should prevent new hot loads from exposing recovered salt, product bags or combustible stock.
15. Size each process buffer to the next bottleneck
Hot bays, leach tanks, crystallisers and non-metallic product storage can fail independently. Upstream intake should slow before any buffer becomes emergency storage.
16. Retain contaminated firewater
Reactive events can mobilise salts, aluminium fines and alkaline/ammoniacal water. Isolation and retention belong in the emergency plan.
17. Treat new smelting or chemical production as material change
Adding remelting furnaces or higher-value chemical conversion changes emissions, energy, molten-metal and residual pathways and requires fresh review.
18. Plan closure around reactive residue and brine first
Hot/reactive fines, mother liquor and off-spec non-metallic residue are harder closure inventory than recovered aluminium and clean salt.
The deepest test
A strong hub recovers aluminium and salt without converting water into the new hazard. Water enters only inside controlled gas and brine systems, and every residual stays bounded when equipment or markets fail.
Sources and further reading
- EGA Leichtmetall — 2026 integrated salt-slag recovery investment.
- European Commission circularity initiatives for high-quality secondary raw materials.
- CORDIS AluSalt and current commercial aluminium salt-slag recycling practice.
- APA, UN-Habitat, World Bank and OECD circular-economy planning resources.
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