How Smelters Process Scrap Metal

TL;DR — Smelting turns sorted scrap back into usable metal. The process varies by metal — electric arc furnaces (EAF) for steel, reverberatory or induction furnaces for copper and brass, rotary or tilting furnaces for aluminium. Each involves pre-processing (sorting, shredding, magnetic separation), charging, melting, refining to remove contaminants, alloying to spec, and casting into ingots, billets, or slabs. Most Singapore scrap is shipped to smelters in Malaysia, Thailand, Vietnam, Taiwan, South Korea, India, and China.

Stage 1: Sorting and Pre-Processing

Before any metal hits a furnace, it passes through a preparation line. The quality of this stage determines everything downstream — a smelter’s yield, energy cost, and final product purity.

Typical pre-processing steps:

• Visual and manual sorting — separating ferrous from non-ferrous; further separating copper, aluminium, brass, stainless.
• Magnetic separation — overhead magnets pulling ferrous from mixed streams.
• Eddy current separation — a rotating magnetic field that repels non-ferrous metals, separating them from plastic, rubber, and inert material.
• Shredding — heavy hammer mills or shear shredders reducing bulky scrap (car bodies, appliances, structural steel) into fist-sized fragments suitable for furnace charging.
• Density separation — heavy media or air classification to separate metals by density (e.g., separating zinc from aluminium in mixed non-ferrous shred).
• Cleaning — removing paint, oil, rubber, plastic, and attachments that would burn off as pollutants or contaminate the melt.

Much of this sorting is what NEA-licensed dealers do locally before export. The cleaner the scrap leaves Singapore, the higher the price the smelter pays. That’s why clean vs dirty scrap grading affects your payout directly.

Stage 2: Steel — Electric Arc Furnace (EAF)

Most recycled steel worldwide is processed in an Electric Arc Furnace. The process:

1. Charging — 80–150 tonnes of shredded steel scrap are dumped into the furnace shell from above using a clamshell bucket.
2. Arc striking — three graphite electrodes lower into the charge. Electricity arcs between the electrodes and the scrap, generating temperatures around 1,800°C.
3. Melting — the charge melts into a pool of molten steel. Oxygen is injected to accelerate melting and oxidise contaminants.
4. Refining — slag forms on top from lime additions, pulling out phosphorus, sulfur, silicon, and other non-iron elements. Samples are taken and composition is adjusted by adding alloying elements (carbon, manganese, chromium for stainless, etc.).
5. Tapping — the furnace tilts and pours the refined steel into a ladle, which transfers it to a continuous caster. The caster solidifies the steel into billets, blooms, or slabs.

A typical EAF heat takes 45–90 minutes. Energy use is roughly 350–500 kWh per tonne of steel — versus around 1,400 kWh per tonne for primary steel from iron ore via blast furnace. This is why HMS scrap and other ferrous grades have sustained global demand.

Stage 3: Copper — Fire Refining and Electrolysis

Copper smelting from scrap is a two-stage process for high-grade output:

1. Fire refining — copper scrap is melted in a reverberatory, rotary, or induction furnace around 1,100°C. Air is blown through the melt to oxidise impurities (iron, zinc, tin, lead) which report to the slag. This produces “blister copper” at roughly 98–99% purity.
2. Electrolytic refining — blister copper is cast into anodes, placed in an electrolytic cell with copper sulfate solution, and dissolved. Pure copper plates out on cathodes at 99.99%+ purity. Impurities including silver, gold, and platinum collect as “anode slime” and are recovered separately — these trace precious metals help finance the process.

Clean copper scrap — bare bright wire, Cu #1 — can skip the electrolytic step and be direct-melted for many applications, fetching premium prices at the smelter gate.

Stage 4: Aluminium — Lower Temperature, Higher Yield

Aluminium is the poster child of recycling efficiency. Secondary aluminium smelting runs at around 660–750°C, a fraction of the temperatures used for steel or copper. Process:

• Delacquering — heating painted or coated aluminium (e.g., used beverage cans) to burn off organic coatings before melting.
• Melting in a tilting rotary, reverberatory, or induction furnace under a protective salt flux that absorbs oxides and impurities.
• Alloying — adding silicon, magnesium, copper, or manganese to hit a specific alloy grade (e.g., 6061 for structural, 356 for castings).
• Degassing — injecting argon or nitrogen to remove dissolved hydrogen, which would otherwise cause porosity in the finished casting.
• Casting into ingots, T-bars, or sows for resale to mills and foundries.

Recycled aluminium uses about 5% of the energy of primary aluminium from bauxite — the largest energy saving of any commonly recycled material.

Stage 5: Other Non-Ferrous Metals

Brass, bronze, zinc, and lead follow broadly similar patterns — pre-sorting, melting in an appropriate furnace, skimming slag, alloying, and casting. Key variations:

• Brass melts around 900–940°C. Zinc loss during melting must be managed with fluxes or slight zinc over-additions.
• Stainless steel is recycled through EAFs similar to carbon steel but with tighter alloy control — chromium and nickel must be balanced against input scrap composition.
• Lead is one of the simplest to smelt (327°C) and one of the most regulated due to toxicity. Battery smelting is tightly controlled under hazardous-waste rules.

If you’re unsure which category your scrap falls into, check the Singapore scrap metal glossary.

Where Singapore Scrap Goes

Singapore has almost no primary smelting capacity — no blast furnaces, no major integrated steel mills. So virtually all locally collected scrap is exported for processing. Typical destinations:

• Malaysia, Thailand, Vietnam — regional EAF steel mills producing rebar, billet, structural sections.
• Taiwan, South Korea — stainless and specialty alloy smelting.
• India — large EAF and induction-furnace base; major destination for HMS.
• China — when import policy allows, for higher-grade shred and non-ferrous.
• Japan — specific non-ferrous and specialty feed.

Prices paid to Singapore dealers track the LME plus or minus regional freight and grade premiums. This is why LME moves ripple into our scale-weight quotes within days.

Related Reading

• Ferrous vs Non-Ferrous Identification Guide
• Scrap Metal Glossary — Singapore Terms
• HMS Scrap (Heavy Melting Steel)
• LME — London Metal Exchange Guide for Singapore Scrap

Recycled steel uses a third of the energy of virgin steel. Recycled aluminium uses 5%. Every tonne of scrap you sell is a tonne of ore that stays in the ground.

Molten Steel Pte Ltd — NEA-licensed scrap metal dealer, Singapore