Most high-grade copper ores have now been used up.
A mining company has 50 000 tonnes of a low-grade ore. The ore contains 0.30% copper by mass.
The company compares three methods of extracting the copper.
Smelting: the ore is crushed, concentrated and then heated strongly in a furnace.
Bioleaching: bacteria are added to heaps of the ore. The bacteria produce a solution, called a leachate, that contains copper ions. Copper is then obtained from the leachate. The leachate is acidic and can pollute rivers if it leaks.
Phytoextraction: plants are grown on the ore. The plants absorb copper compounds through their roots. The plants are harvested and burned. Copper is obtained from the ash.
The table shows information about the three methods.
| Method | Time taken to extract the copper | Percentage of the copper recovered (%) | Relative energy used per tonne of copper |
|---|---|---|---|
| smelting | a few weeks | 90 | 100 |
| bioleaching | about 2 years | 80 | 30 |
| phytoextraction | about 10 years | 40 | 10 |
Calculate the mass of copper that the company would obtain from the 50 000 tonnes of ore by bioleaching.
Mass of copper = ...... tonnes
The leachate contains copper ions, Cu2+\mathrm{Cu^{2+}}Cu2+.
Scrap iron is added to the leachate. Copper metal forms.
Explain why.
Copper can also be obtained from the leachate by electrolysis.
Write the half equation for the reaction at the cathode.
Evaluate the use of bioleaching and phytoextraction to extract copper from this ore, compared with smelting.
Use the information above.
61 exam-style questions on OCR GCSE Chemistry 6.1 Improving processes and products, covering 6.1.1 Extracting metals industrially and by electrolysis, 6.1.2 Life cycle assessment and recycling, 6.1.3 Biological methods of metal extraction, 6.1.4 The Haber process and the production of fertilisers, 6.1.5 Alloys and their uses, 6.1.6 Corrosion and its prevention, 6.1.7 Comparing and selecting materials, and 6.1.8 Industrial conditions, rate and position of equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.