5.10.1.4Alternative methods of extracting metals (HT only)
AQA GCSE Combined Science (8464), Higher tier · Chemistry › Using resources › Using the Earth's resources and obtaining potable water
Practise Alternative methods of extracting metals (HT only). 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Higher tier only. Why new ways of extracting copper from low-grade ores are needed, how phytomining and bioleaching work, and how copper is obtained from the compounds they produce. Expect 'describe' questions, 'evaluate' questions based on given information and sometimes equations or calculations on Paper 2.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
5
Explain why new extraction methods are neededMetal ores are limited and copper ores are becoming scarce, so low-grade ores must be used.
5
Describe how phytomining worksPlants absorb metal compounds; they are harvested and burned, and the ash contains the metal compounds.
6
Describe how bioleaching worksBacteria are used to produce leachate solutions that contain metal compounds.
6
Name ways to get copper from solutionsDisplacement using scrap iron, or electrolysis.
7
Explain displacement and electrolysis of copper compoundsIron is more reactive than copper; at the negative electrode Cu2+ + 2e− → Cu.
8
Evaluate biological extraction methods using given dataWeigh up using low-grade ores without digging up rock against slow rates, small yields and possible pollution.
Notes
Why new methods are needed
The Earth's resources of metal ores are limited. Copper ores are becoming scarce.
Low-grade ores contain only a small percentage of copper. Mining them in the traditional way would mean digging up, moving and disposing of huge amounts of rock for very little copper.
Phytomining and bioleaching extract copper from low-grade ores and avoid most of this digging, moving and disposing of rock.
Phytomining and bioleaching
Phytomining: plants are grown on land containing low-grade ore. The plants absorb metal compounds from the soil.
The plants are harvested and burned. The ash contains the metal compounds.
Bioleaching: bacteria are used to produce leachate solutions that contain metal compounds.
Both methods are slow, and the metal compounds they produce still have to be processed to obtain the metal.
Getting copper metal from its compounds
Displacement: scrap iron is added to a solution of a copper compound. Iron is more reactive than copper, so it displaces the copper: iron + copper sulfate → iron sulfate + copper.
Ionic equation: Fe + Cu2+ → Fe2+ + Cu. Iron atoms lose electrons (oxidised); copper ions gain electrons (reduced). grade 7+
Electrolysis of a solution of the copper compound: copper metal forms at the negative electrode (cathode).
Half equation at the cathode: Cu2+ + 2e− → Cu (reduction). grade 7+
Evaluating the biological methods
For: they can use low-grade ores and old mine waste; they avoid digging, moving and disposing of large amounts of rock; there is less damage to the landscape; they help conserve a limited resource.
Against: they are slow (crops take time to grow; bioleaching can take months or years); they produce only small amounts of copper; leachate solutions could pollute soil and water if they escape; further processing is needed.
Cheatsheet
Copper ores are becoming scarce, so copper is extracted from low-grade ores
Phytomining: plants absorb metal compounds → harvest → burn → ash contains metal compounds
Bioleaching: bacteria produce leachate solutions containing metal compounds
Both avoid digging, moving and disposing of large amounts of rock
Copper from solution: displacement using scrap iron, or electrolysis
iron + copper sulfate → iron sulfate + copper
Fe + Cu2+ → Fe2+ + Cu grade 7+
Cathode: Cu2+ + 2e− → Cu grade 7+
How to answer each type of question
Describe how phytomining or bioleaching works
2 to 3 marks5
Phytomining: plants absorb metal compounds, are harvested, then burned; the ash contains the metal compounds.
Bioleaching: bacteria produce leachate solutions that contain metal compounds.
If there is a further mark, say the compounds are then processed to obtain the metal.
Example. Describe how phytomining is used to obtain copper compounds from land containing low-grade copper ore. (3 marks)
Show the model answer
Plants are grown on the land and absorb copper compounds (1). The plants are harvested and burned (1). The ash produced contains the copper compounds (1).
Explain how copper is obtained from a solution
2 to 4 marks7
Name the method: displacement using scrap iron, or electrolysis.
For displacement, give the reason: iron is more reactive than copper.
Write an equation if asked; in half equations, balance the charges with electrons.
Say which species is oxidised or reduced, in terms of electrons.
Example. A solution produced by bioleaching contains copper(II) sulfate. Scrap iron is added to the solution. (a) Explain why copper is produced. (1 mark) (b) Write an ionic equation for the reaction. Iron(II) ions are formed. (1 mark) (c) Which substance is reduced? Explain your answer. (2 marks)
Show the model answer
(a) Iron is more reactive than copper, so it displaces copper from the solution (1). (b) Fe + Cu2+ → Fe2+ + Cu (1) (c) The copper(II) ions (1), because they gain electrons (1).
Evaluate a biological method using given information
4 to 6 marks8
Use the information given: quote figures such as the percentage of metal or the time taken.
Give advantages: uses low-grade ore, avoids digging, moving and disposing of rock.
Give disadvantages: slow, small amounts, possible pollution, further processing needed.
Finish with a justified conclusion.
Example. A company owns a heap of waste rock left from an old copper mine. The rock contains 0.2% copper by mass. (a) Calculate the mass of copper in 50 000 tonnes of the waste rock. (1 mark) (b) The company plans to use bioleaching to extract copper from the heap. Evaluate this plan. (4 marks)
Show the model answer
(a) 50 000 × 0.2 ÷ 100 = 100 tonnes (1) (b) Any four, with at least one advantage and one disadvantage: the rock has already been dug up, so no further digging, moving or disposing of rock is needed (1); bioleaching can use low-grade material like this, which is too poor for traditional methods (1); it recovers copper, a limited resource, from waste (1); but bioleaching is slow, taking months or years (1); the leachate could escape and pollute soil or water (1); the copper compounds still need to be processed by displacement or electrolysis (1).
Shortcuts and memory tricks
PHYTO means plants (as in photosynthesis); BIO-leaching uses bacteria to leach the metal out.
Phytomining in three verbs: grow, harvest, burn.
Scrap iron works because iron is above copper in the reactivity series, and it is cheap.
OIL RIG: iron atoms lose electrons (oxidised); copper ions gain electrons (reduced).
Where marks are lost
Saying the plants 'make' copper. They absorb copper compounds that are already in the soil.
Forgetting that the plants are burned and that the ash contains the metal compounds.
Saying phytomining or bioleaching produces copper metal directly. They produce copper compounds, which still need displacement or electrolysis.
Writing that bacteria 'eat' the copper. The bacteria produce leachate solutions that contain copper compounds.
Writing Fe3+ in the displacement equation when told iron(II) ions form, or leaving the charges unbalanced.
Exam technique
In 'evaluate' questions, give advantages and disadvantages, use figures from the information, and end with a conclusion.
The key phrase for the main advantage: these methods avoid digging, moving and disposing of large amounts of rock.
If asked why scrap iron is used, give both ideas: iron is more reactive than copper, and scrap iron is cheap.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
New ways of extracting copper from low-grade ores include phytomining and bioleaching. What does phytomining use to absorb metal compounds?
plants
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy3 marks
New ways of extracting copper from low-grade ores include phytomining and bioleaching.
(a) Why are new ways of extracting copper being developed? Tick (✓) one box.[1]
Copper ores are becoming scarce
Copper is no longer used in electrical wiring
Copper is more reactive than iron
Copper cannot be extracted by electrolysis
(b) What does phytomining use to absorb metal compounds?[1]
(c) What does bioleaching use to produce solutions of metal compounds?[1]
Show the answer and mark scheme
(a)Answer: Copper ores are becoming scarce
(b)Answer: plants
plants
(c)Answer: bacteria
bacteria
Question 2Medium6 marks
Phytomining can be used to obtain copper from land containing low-grade copper ore.
(a) Describe how phytomining is used to obtain copper compounds.[3]
(b) Copper can be obtained from a solution of copper compounds by adding scrap iron. Explain why iron can displace copper.[1]
(c) Give one other method of obtaining copper from a solution of a copper compound.[1]
(d) Give one advantage of phytomining compared with traditional mining.[1]
Show the answer and mark scheme
(a)
plants are grown on land containing (low-grade) copper ore
the plants absorb copper compounds and are harvested
the plants are burned to produce ash that contains copper compounds
(b)
iron is more reactive than copper
(c)
electrolysis
(d)
it avoids digging, moving and disposing of large amounts of rock / it can use low-grade ores / less damage to the landscape
Question 3Hard6 marks
Bioleaching produces a solution containing copper(II) ions. Copper metal can be obtained from the solution by displacement using scrap iron, or by electrolysis.
(a) Write the ionic equation for the reaction between iron and copper(II) ions. Iron(II) ions are formed.[1]
(b) Explain which species is oxidised in this reaction.[2]
(c) Write the half equation for the reaction at the negative electrode when copper is obtained by electrolysis.[1]
(d) Calculate the mass of iron needed to displace 1.0 tonne of copper. Relative atomic masses (Ar): Fe = 56 Cu = 63.5[2]
Show the answer and mark scheme
(a)Answer: Fe + Cu2+ → Fe2+ + Cu
Fe + Cu2+ → Fe2+ + Cu
(b)
iron (atoms) are oxidised
because they lose electrons
(c)Answer: Cu2+ + 2e− → Cu
Cu2+ + 2e− → Cu
(d)Answer: 0.88 tonnes
1 mole of iron displaces 1 mole of copper / 1.0 × 56 ÷ 63.5