How to Improve Metal Recovery in Aluminum Scrap Melting

Metal recovery in aluminium scrap melting is not one number. It is the result of everything you do — or fail to do — from the moment scrap enters the furnace until the last ingot is stacked. I have spent 25 years chasing that number in foundries across China, Southeast Asia, India, Europe, and North America. The best plants recover 93–95% of the metal they charge. The worst recover 82–85%. The difference is not the furnace. It is the process.

In 2019, I stood on the shop floor of a recycling plant in Binh Duong, Vietnam, watching a furnace operator skim dross every fifteen minutes. The dross was thick and grey, and it glistened with trapped aluminium. I asked him why he skimmed so often. He said, “Because the boss told me to keep the furnace clean.” He was doing what he was told. But every skim was throwing away metal. That plant was recovering 84% of its charge. They were losing over $2 million a year in metal they had already paid for.

This article is about how to fix that. Not with a new furnace. With discipline, measurement, and a few changes that cost almost nothing.

What Metal Recovery Really Means

Metal recovery is the percentage of aluminium you charge that ends up as saleable product. If you charge 100 tonnes of scrap and produce 88 tonnes of ingots, your recovery is 88%. The other 12 tonnes went to dross, salt slag, oxidation, or dust.

In secondary aluminium melting, typical recovery rates range from 82% to 95%. The variation depends on:

• Scrap quality and contamination level

• Furnace type and condition

• Melt temperature and atmosphere

• Fluxing and skimming practice

• Dross processing method

• Operator training and discipline

A well-run 9.5-tonne reverberatory furnace can achieve 8–10% melt loss. A poorly run one loses 14–18%. On a plant melting 30 tonnes per day, that difference is 1.8–2.4 tonnes of metal every day. At $2,500 per tonne, it is $4,500–$6,000 per day. Over a year, it is millions.

I wrote about how to reduce metal loss in secondary aluminium melting for ingot production. That article focused on the mechanisms. This one focuses on the practical steps — and the people who make them work.

The First Step: Measure What You Lose

You cannot improve what you do not measure. Most foundries I visit do not measure metal recovery at all. They know how much they charge and how much they sell. But they do not track recovery per shift, per furnace, or per scrap type.

The first thing I do on site is set up a simple measurement system:

Once you have this data, you can calculate recovery per tonne. You can see which shifts are better. You can see which scrap types lose more metal. You can see the effect of a process change.

I remember a plant manager in Malaysia who told me his recovery was “about 90%.” When we measured it properly for two weeks, it was 84%. He was shocked. But he was also motivated. Once he saw the number, he wanted to fix it.

Step 1: Control Melt Temperature

Every 10°C above the minimum required melting temperature increases oxidation loss. I have seen plants run at 780°C because “it melts faster.” Yes, it melts faster. It also oxidises faster.

For secondary aluminium ingot production, the melt temperature should be 700–730°C. For ADC12, 720°C is a good target. For pure aluminium, 680–700°C is sufficient.

A foundry in Thailand ran their gas-fired furnace at 780°C. Oxidation loss was 4.2%. We lowered the setpoint to 730°C and adjusted the burner. Melt time increased by 8 minutes. But oxidation loss dropped to 2.1%. The net saving was over $2,000 per month.

The fix: Set the furnace to the lowest temperature that achieves the required melt rate. Measure the actual metal temperature, not just the controller display.

Step 2: Reduce Contact Between Molten Aluminium and Air

Oxidation happens at the surface. The more surface you expose, and the longer you expose it, the more metal you lose.

Keep the furnace door closed. Every time the door opens, cold air rushes in and hot air escapes. The surface oxidises.

Use a cover flux. A cover flux creates a barrier between the melt and the atmosphere. For secondary aluminium, a chloride-based flux works well. It melts and forms a protective layer.

Charge below the surface. When adding scrap to a molten bath, submerge it quickly. Do not let it float on the surface where it oxidises.

Reduce melt surface area. A deep, narrow bath exposes less surface than a wide, shallow one.

I once saw a foundry in Vietnam that kept the furnace door open all day for “convenience.” They lost 2% of their metal to oxidation alone. We installed a simple door closer. The loss dropped to 0.8%.

Step 3: Optimise Charging Practice

How you charge the furnace affects how much metal you lose.

Pre-treat your scrap. Crushing, de-oiling, and drying reduce surface area and moisture content. Scrap with paint, oil, or moisture loses significantly more metal during melting.

Use the right charge mix. Research on melting efficiency found that specific charge make-ups reduced melt loss compared to mixed or contaminated charges.

Charge continuously, not in large batches. Continuous melting keeps the bath temperature stable and reduces the time molten metal sits exposed to air.

Avoid overcharging. Filling the furnace beyond 80–85% of capacity reduces freeboard and increases turbulence. The burner cannot melt efficiently. Oxidation increases.

A foundry in Indonesia was charging 1.5 tonnes into a 1-tonne furnace. The furnace could not reach temperature. The burner ran constantly. Metal loss was 5%. We reduced the charge to 900 kg. The furnace reached temperature in half the time. Metal loss dropped to 2.5%.

Step 4: Use Flux Correctly

Flux is not a cost. It is an investment. Used correctly, it pays for itself many times over in recovered metal.

Cover flux. Applied to the melt surface during holding, it creates a barrier against oxidation.

Remelting flux. For heavily contaminated scrap, a remelting flux helps separate metal from oxide.

Salt flux for chips and fines. Machining chips have a high surface-to-volume ratio and are prone to intense oxidation. Research on salt flux recycling of chips achieved over 99.5% clean aluminium collection in a short period.

The salt factor — the ratio of salt to scrap — matters. For a tilting rotary furnace, the salt factor can be as low as 0.4–0.8. For fixed-axis furnaces, it is typically 0.9–2.0. Lower salt factor means less salt consumption, lower cost, and less waste.

I have written about how to choose a secondary aluminium melting furnace for ingot production. Salt flux management is part of that selection.

Step 5: Improve Dross Management

Dross is not waste. It is metal you paid for and did not recover. Typical dross contains 15–80% metallic aluminium.

Skim less often. Every skim exposes fresh metal to the atmosphere. If you skim every 20 minutes, you are losing metal. Skim every 45 minutes, or when the dross layer reaches a thickness that interferes with melting.

Skim gently. Do not stir the melt. Use a skimming tool that drains metal back into the furnace. A perforated skimming tool works better than a solid rake.

Use a dross press. A dross press squeezes residual metal from the dross. This is standard practice in well-run secondary aluminium plants.

Process hot dross immediately. Hot dross oxidises rapidly. The longer it sits, the more metal you lose. Innovative techniques combining superimposed extrusion with supergravity separation have achieved 95.78% total metallic aluminium recovery from hot dross under optimised conditions.

I remember a plant in Guangdong that installed a dross press. The dross metal content dropped from 46% to 28%. That single change recovered 1.5 tonnes of metal per day. The press cost $12,000. It paid for itself in three weeks.

Step 6: Control the Furnace Atmosphere

The atmosphere inside your furnace matters. If it is rich in oxygen or moisture, oxidation increases.

Check for air leaks. A furnace door that does not seal properly draws in air. This is the most common atmosphere problem I find.

Tune the burner. Too much excess air increases oxygen in the furnace. Use a flue gas analyser to set O₂ at 2–4%.

Reduce moisture. Wet scrap, damp refractories, and humid air all increase oxidation. Pre-dry scrap before charging. Store under cover.

Consider inert gas blanketing. For high-value alloys, nitrogen or argon blanketing can reduce oxygen to below 1%. The cost is justified when the metal value is high.

I have written about how to optimise burner efficiency in gas-fired aluminium furnaces. The principles apply to atmosphere control as well.

Step 7: Train Operators and Change Habits

Most metal loss is caused by operator habits. Wet scrap. Overcharging. Excessive skimming. Running too hot. Leaving the door open.

Train operators on the relationship between their actions and the loss rate. Show them the monthly metal balance. When they see that skimming every 20 minutes costs the plant $50,000 per year, they change their behaviour.

I was in a plant in Malaysia where the night shift had 3% higher metal loss than the day shift. The night operators were charging wet scrap because the scrap pile was outdoors and it rained at night. We built a covered drying rack. The difference disappeared.

The fix: Train operators on the metal balance. Show them the numbers. Give them feedback. Celebrate improvement.

A Real Case from Vietnam

In 2019, I worked with a recycling plant in Binh Duong, Vietnam. They were melting 25 tonnes per day of mixed scrap in a 5-tonne tilting rotary furnace. Their metal recovery was 84%. They had no measurement system. They skimmed every 15 minutes. The furnace ran at 780°C. Scrap was stored outdoors and charged wet.

We made four changes:

1. Lowered the melt temperature from 780°C to 720°C.

2. Changed skimming frequency from every 15 minutes to every 45 minutes, with a dross press.

3. Built a covered drying rack for scrap. No more wet charging.

4. Added a cover flux during holding.

Results after one month:

The plant manager called me six months later. Recovery was holding at 92%. The furnace was running cleaner. The ingot surface quality had improved. And the scrap rate on downstream customers had dropped.

A Simple Checklist to Improve Metal Recovery

1. Measure metal recovery every shift. You cannot improve what you do not measure.

2. Set melt temperature to the minimum required. Do not run hot.

3. Keep the furnace door closed except when charging or skimming.

4. Pre-treat scrap: crush, de-oil, dry.

5. Use cover flux during holding.

6. Skim less often — every 45 minutes, not every 15.

7. Use a dross press to recover metal from dross.

8. Process hot dross immediately.

9. Check furnace door seals monthly.

10. Tune the burner every three months.

11. Train operators on the metal balance.

12. Record everything and review weekly.

When to Call an Expert

You can do much of this work yourself. But sometimes an experienced eye finds things you miss. The plant in Vietnam had a competent maintenance team. They had kept the furnace running for years. But they had never been trained on metal balance or dross processing. They did not know what they did not know.

My fee for the five-day audit and commissioning support was $11,000. The annual saving was $1.46 million. That is a 130x return.

If your metal recovery is below 88%, or your dross metal content is above 30%, call someone. Or use the checklists on this blog. Either way, do not wait.

Final Thoughts

Improving metal recovery in aluminium scrap melting is not about buying a new furnace. It is about controlling temperature, skimming practice, salt flux, and charge moisture. It is about measuring what you lose and training your people to lose less.

In my 25 years, I have seen plants recover millions by making small changes to their process. The furnace did not change. The people did.

If you run a recycling plant, start by measuring your metal recovery and dross metal content. If either is out of specification, fix it. You will see the difference in your profit.

About the Author: Hu Shenyue is a veteran aluminium melting furnace expert with 25 years of hands-on experience in China, Southeast Asia, India, the UK, Europe, and North America. He writes practical, experience-based content on furnace selection, maintenance, and optimisation at SmeltPro.

Internal links: How to Reduce Metal Loss in Secondary Aluminium Melting for Ingot Production, How to Choose a Secondary Aluminium Melting Furnace for Ingot Production, How to Optimize Burner Efficiency in Gas-Fired Aluminium Furnaces