A mining company wants to extract copper from an old spoil heap. The spoil heap contains only 0.2% copper by mass.
The table compares three extraction methods.
| Feature | Mining and smelting | Bioleaching | Phytoextraction |
|---|---|---|---|
| lowest copper content of ore that can be used economically | 0.5% | 0.1% | 0.01% |
| energy needed per tonne of copper / GJ | 100 | 40 | 20 |
| time to produce 1 tonne of copper | weeks | months | years |
| main waste produced | sulfur dioxide gas and large amounts of waste rock | acidic solutions that may contain toxic metal ions | carbon dioxide from burning plants and ash |
Calculate the percentage reduction in energy needed per tonne of copper when phytoextraction is used instead of mining and smelting.
A phytoextraction site produces 50 tonnes of plant ash each year. The ash contains 12% copper by mass. Calculate the mass of copper in the ash produced each year.
Explain why biological methods of extraction are becoming more important.
Evaluate the use of the three methods for extracting copper from this spoil heap.
45 exam-style questions on Edexcel GCSE Chemistry 5.1 Obtaining and using metals, covering 5.1.1 The reactivity series of metals, 5.1.2 Displacement reactions as redox reactions, 5.1.3 Extracting metals from ores by reduction, 5.1.4 Biological methods of metal extraction, 5.1.5 Resistance to oxidation and recycling metals, and 5.1.6 Life cycle assessment. Each one has a worked solution and a mark scheme showing where the marks go.