Every card in Earth and atmosphere, Year 11: phytomining and life cycle assessment
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- A way of extracting metals in which plants absorb metal compounds from the ground and are then harvested and burned
Phytomining
HintThe name begins with the Greek for 'plant'.
WhyThe plants are grown on land that contains a low-grade ore. They take up metal compounds through their roots and concentrate them. The metal is recovered afterwards from what is left when the plants are burned.
- In bioleaching, which type of organism is used to produce a solution containing metal compounds? (one word)
Bacteria
HintThey are single-celled, and far too small to see.
WhyThe solution they produce is called a leachate. It contains the metal as dissolved compounds, so the metal still has to be obtained from it, by displacement or by electrolysis.
- In phytomining, why are the harvested plants burned?
To produce ash that contains the metal compounds
HintBurning removes most of the plant and leaves the useful part behind in a small residue.
WhyThe metal compounds are spread thinly through the living plant. Burning gets rid of the plant material and leaves them concentrated, ready to be processed to obtain the metal.
- Scrap iron is added to copper sulfate solution obtained by bioleaching. Write the balanced symbol equation for the reaction that produces copper.
Fe + CuSO4 → FeSO4 + Cu
HintIron is the more reactive metal, so it takes copper's place in the compound.
WhyIron displaces copper because it is more reactive, and scrap iron is cheap. The other way to obtain copper from the solution is electrolysis, in which copper forms at the negative electrode.
- Why are phytomining and bioleaching becoming useful as copper-rich ores run out?
They can extract copper from low-grade ores
HintThink about rock that holds too little metal to be worth digging up and smelting.
WhyThese methods also avoid digging up, moving and disposing of large amounts of rock, so they do less damage to the landscape. Their main drawback is that they are slow.
- A study of the environmental impact of a product at every stage, from obtaining the raw materials to final disposal
A life cycle assessment (LCA)
HintIts three-word name describes following the product from 'birth' to 'death'.
WhyIt lets two products that do the same job be compared stage by stage: for example how much energy and water each uses and how much waste each produces.
- An LCA looks at four stages: extracting and processing ____; manufacturing and packaging; use during the product's lifetime; and ____ at the end of its useful life.
raw materials; disposal
HintThe first is what the product is made from; the last is what happens when it is thrown away.
WhyTransport and distribution are counted at every stage. Looking at all four stops a product from seeming 'green' just because one stage, such as its use, causes little harm.
- Putting a number on the harm done by a pollutant requires what is called a ____ judgement (a decision about what matters most), which is why an LCA is not a purely objective process.
value
HintThe missing word also means what something is worth.
WhyThe use of water, energy and resources, and some wastes, can be measured fairly easily. Deciding how much a pollutant's effects count is not a measurement, so two fair assessors can reach different totals.
- How could a company misuse a life cycle assessment in its advertising?
By using a selective LCA that leaves out stages to reach the conclusion it wants
HintThink about what happens if only the flattering parts of the story are told.
WhyA shortened LCA can be useful, but it can also be designed so that a product looks better than a rival. A claim based on an LCA should say which stages and which impacts were included.
- In one life cycle assessment, a paper bag took more energy to make than a plastic bag. Give a reason why the paper bag may still have less impact at the disposal stage.
Paper rots quickly (it is biodegradable); plastic persists in landfill or as litter
HintThink about what happens to each material if it is left in the ground for a year.
WhyThe raw materials differ too: paper comes from trees, which are renewable, and plastic from crude oil, which is finite. Plastic bags are lighter and are often reused more. An LCA sets these stages side by side, and neither bag is better at all of them.
1★ GCSE-CHEM-EAR-0062
2★ GCSE-CHEM-EAR-0063
3★ GCSE-CHEM-EAR-0064
4★ GCSE-CHEM-EAR-0065
5★ GCSE-CHEM-EAR-0066
6★ GCSE-CHEM-EAR-0067
7★ GCSE-CHEM-EAR-0068
8★ GCSE-CHEM-EAR-0069
9★ GCSE-CHEM-EAR-0070
10★ GCSE-CHEM-EAR-0071
Keep what you learn
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