[resources] LCAs, recycling & metal extraction

[ https://www.bbc.co.uk/bitesize/guides/z96ydxs/revision/1 ]

Life Cycle Assessments (LCAs)

Assessments which are carried out to assess the impact of a product on the environment at every stage of its life.

Stages of a Life Cycle Assessment:

1. Extracting raw materials (Elephants)

2. Manufacturing and Packaging (Make)

3. Transportation (Tea)

4. Use of Product

5. Disposal of product (Drunk)

Peer Review

A process where scientists evaluate each other's work to ensure it is accurate, reliable, and free of bias.

Recycling

Reusing materials or reprocessing waste materials to produce new materials.

Recasting

Pouring melted metal into a mould.

Reforming

Heated metal is re-shaped.

Advantages of Recycling:

• fewer quarries & mines are needed to extract finite reserves of metal ores

• less crude oil needs to be extracted as a raw material for making plastics

• less energy is needed for recycling compared with making a new product from natural resources, so the emission of greenhouse gases is reduced

• the amount of waste that is disposed of in landfill is reduced

Disadvantages of Recycling:

• the collection and transport of used items needs organisation, workers, vehicles and fuel

• it can be difficult to sort different metals from one another

• the sorted metal may need to be transported to where it can be turned into ingots

Need for Alternative Methods of Copper Extraction:

The Earth's supply of metal ores is limited. For example, high-grade copper ores are becoming harder to find and mine, so scientists are researching way to extract low-grade copper.

Phytomining

Using plants to absorb metal compounds from the ground through their roots. The plants are then burned to produce an ash containing a high concentration of the metal compounds.

Stage 1 of Phytomining:

Plants are grown in soil that contains low levels of (low-grade) copper.

Stage 2 of Phytomining:

Plants absorb the copper and it builds up in their leaves.

Stage 3 of Phytomining:

The plants are then harvested and burned to produce ash that contains soluble metal compounds.

Stage 4 of Phytomining:

Copper is extracted from this ash either by electrolysis or a displacement reaction.

Advantages of Phytomining:

• removes ground minerals that shouldn’t be there

• carbon neutral

• less mining/quarrying so less environmental pollution

• reduces the amount of rock waste that must be disposed of after traditional mining

Disadvantages of Phytomining:

• slow process

• combustion → releases CO2

Bioleaching

The use of bacteria to convert copper compounds in the ore into soluble copper compounds. Certain bacteria can break down low-grade ores to produce an acidic solution (leachate) containing copper ions.

Leachate

The acidic solution which contains the copper ions. Copper is extracted by displacement using scrap iron OR by electrolysis.