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Aluminium extraction by electrolysis needs about 170 GJ per tonne, compared with about 20 GJ for iron. Free notes with key terms and 11 questions answered.
Evaluating metal extraction processes is part of Reactivity of metals in GCSE AQA Higher Chemistry.
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Aluminium extraction by electrolysis needs about 170 GJ per tonne, compared with about 20 GJ for iron. Free notes with key terms and 11 questions answered.
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Use this lesson to stay inside Reactivity of metals while connecting the detail back to the wider Topic 4: Chemical changes topic.
Read the core explanations from Evaluating metal extraction processes before testing yourself from memory.
Every smartphone contains over 30 different metals. Your bike frame might be aluminium, your coins are copper alloy, and your car engine block is iron. But none of these metals exist pure in nature - they're locked up in rocks called ores.
The challenge? Different metals need completely different extraction methods. Get it wrong and you waste millions of pounds, destroy the environment, or end up with no metal at all. This is where evaluation skills become crucial - you need to weigh up costs, environmental impact, and practicality.
Think of metal extraction like a toolkit. You wouldn't use a sledgehammer to crack a nut, and you wouldn't use a nutcracker to demolish a wall. The reactivity series tells us which 'tool' to use for each metal.
When chemists choose an extraction method, they're like judges weighing evidence. They consider multiple factors, and sometimes there's no perfect answer - just the best compromise.
Worked example: Evaluating Iron Extraction vs Aluminium Extraction
Compare the extraction of iron (using carbon) with aluminium (using electrolysis). Which method is more sustainable?
Answer: Currently iron extraction is more sustainable due to lower energy requirements, but aluminium extraction could become more sustainable with renewable electricity sources.
Notice how the 'best' method depends on your priorities. If you prioritise immediate energy efficiency, choose iron extraction. If you prioritise future potential with renewable energy, aluminium extraction could win.
Textbook extraction looks simple, but real industrial processes face messy complications. Ores aren't pure compounds - they're mixtures. Environmental regulations change. Energy prices fluctuate. Let's see how professionals handle these challenges.
Consider titanium extraction. Titanium is incredibly useful - lightweight, strong, corrosion-resistant. Perfect for aircraft engines. But titanium sits above carbon in the reactivity series, so we can't use carbon reduction. Electrolysis of titanium compounds is technically possible but economically disastrous.
The solution? The Kroll process uses magnesium metal to reduce titanium chloride. It's expensive and complex, which is why titanium costs 10 times more than steel. This shows how extraction method directly affects the final product cost.
Every extraction method leaves an environmental footprint. The question isn't whether there's an impact - it's how big that impact is and whether it's justified by the benefits.
Carbon reduction produces carbon dioxide and carbon monoxide. One tonne of iron produces about 2 tonnes of CO₂. Electrolysis produces no direct emissions, but the electricity often comes from fossil fuel power stations, creating indirect emissions.
Then there's waste heat, water pollution from ore processing, and habitat destruction from mining. A complete evaluation must consider the entire lifecycle, not just the extraction step.
Money talks in industrial chemistry. Even if a method works scientifically, it must make economic sense. Companies evaluate several cost factors when choosing extraction methods.
Worked example: Economic Comparison: Carbon Reduction vs Electrolysis
A company can extract 1000 kg of metal using either carbon reduction (£500 energy cost) or electrolysis (£2000 energy cost). Carbon reduction produces 200 kg CO₂ (carbon tax £50 per tonne). Which is cheaper?
Answer: Carbon reduction is £1490 cheaper per 1000 kg of metal, making it the economically preferred method despite environmental costs.
This calculation shows why most metals below carbon in the reactivity series are still extracted using carbon reduction, despite environmental concerns. The cost difference is too large to ignore.
Evaluation questions are where students either excel or crash spectacularly. The difference? Understanding what examiners actually want. They're not looking for your opinion - they want systematic analysis using scientific evidence.
For 6-mark evaluation questions, use this structure: State your conclusion first, then present evidence for your view, acknowledge the counter-argument with evidence, and finish by explaining why your conclusion is stronger. This shows sophisticated thinking that examiners reward highly.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Titanium is extracted by the Kroll process, which uses magnesium metal to reduce titanium chloride. Titanium is more reactive than carbon and electrolysis of its compounds is economically disastrous, so the process is expensive and titanium costs 10 times more than steel.
Titanium is expensive because it is more reactive than carbon, so carbon reduction can't be used, and electrolysis is economically disastrous. The Kroll process, using magnesium to reduce titanium chloride, is expensive and complex, so titanium costs 10 times more than steel.
Metal extraction affects the environment because carbon reduction produces carbon dioxide and toxic carbon monoxide; one tonne of iron produces about 2 tonnes of CO₂. Electrolysis has no direct emissions, but the electricity often comes from fossil fuel power stations, and mining causes water pollution and habitat destruction.
Aluminium extraction costs more because it uses electrolysis, which requires massive amounts of electricity: about 170 GJ per tonne compared with about 20 GJ per tonne for iron extracted with carbon. Iron is less reactive than carbon, but aluminium is more reactive.
Iron extraction is currently more sustainable than aluminium extraction because it needs much less energy. However, aluminium extraction produces no direct emissions, so it could become more sustainable if the electricity came from renewable sources.
Carbon reduction is still used for metals less reactive than carbon because it is much cheaper than electrolysis, even with a carbon tax. In one example, carbon reduction cost £510 per 1000 kg of metal including carbon tax, compared with £2000 for electrolysis.
Extracting aluminium by electrolysis takes about 170 GJ per tonne, compared with about 20 GJ per tonne for extracting iron using carbon. Electrolysis requires massive amounts of electricity, which makes aluminium extraction far more energy-hungry.
One tonne of iron produces about 2 tonnes of CO₂. Carbon reduction produces carbon dioxide and toxic carbon monoxide, which is one of the main environmental costs of extracting iron.
Electrolysis produces no direct emissions, unlike carbon reduction, which produces carbon dioxide and carbon monoxide. However, the electricity often comes from fossil fuel power stations, creating indirect emissions, although it could be sustainable with renewable electricity.
Evaluating metal extraction methods means weighing costs, environmental impact and practicality. A good evaluation states the conclusion first, presents evidence for it, acknowledges the counter-argument with evidence, and finishes by explaining why the conclusion is stronger.
The choice of extraction method depends on how reactive the metal is, energy costs, environmental taxes such as carbon tax, emissions and practicality. Carbon reduction is still used for metals less reactive than carbon because it is much cheaper, even after carbon tax.