Recycling and life cycle assessment

Humans use the Earth's resources to provide warmth, shelter, food and transport. Natural resources, supplemented by agriculture, provide food, timber, clothing and fuels. Finite resources from the Earth, oceans and atmosphere are processed to provide energy and materials.

Chemistry plays an important role in improving agricultural and industrial processes to provide new products, and in sustainable development — development that meets the needs of current generations without compromising the ability of future generations to meet their own needs.

You should be able to state examples of natural products that are supplemented or replaced by agricultural and synthetic products, and distinguish between finite and renewable resources given appropriate information.

The distinction to make: a finite resource is one being used up faster than it is replaced, so supplies will eventually run out — crude oil, metal ores, and the fossil fuels. A renewable resource is one that is replaced at the same rate or faster than it is used, so it can be maintained — timber from replanted forests, and crops.

You should also be able to extract and interpret information about resources from charts, graphs and tables, and use orders of magnitude to evaluate the significance of data. When a table gives reserves and annual use, dividing one by the other gives the number of years remaining — and it is the order of magnitude of that answer, tens of years or thousands, that decides whether the figure matters.

The reduction in use, reuse and recycling of materials by end users reduces the use of limited resources, use of energy sources, waste and environmental impacts.

Metals, glass, building materials, clay ceramics and most plastics are produced from limited raw materials. Much of the energy for the processes comes from limited resources. Obtaining raw materials from the Earth by quarrying and mining causes environmental impacts.

Some products, such as glass bottles, can be reused. Glass bottles can be crushed and melted to make different glass products. Other products cannot be reused and so are recycled for a different use.

Metals can be recycled by melting and recasting or reforming into different products. The amount of separation required for recycling depends on the material and the properties required of the final product. For example, some scrap steel can be added to iron from a blast furnace to reduce the amount of iron that needs to be extracted from iron ore.

You should be able to evaluate ways of reducing the use of limited resources, given appropriate information.

The arguments for recycling metals are strong and worth having ready: it uses much less energy than extracting the metal from its ore, it conserves a limited supply of ore, it avoids the environmental impact of quarrying and mining, and it reduces the amount sent to landfill. Against it: the material has to be collected, transported and sorted, which costs money and energy, and for some products the separation needed is expensive.

Notice how the scrap steel example answers the separation question. Steel added to a blast furnace does not need to be sorted precisely, because the furnace is producing steel anyway — the required properties of the final product decide how much separation is worth doing.

Life cycle assessments (LCAs) are carried out to assess the environmental impact of products in each of these stages:

• extracting and processing raw materials • manufacturing and packaging • use and operation during its lifetime • disposal at the end of its useful life,

including transport and distribution at each stage.

That last clause is easy to miss and often carries a mark: transport counts at every stage, not just once.

Use of water, resources, energy sources and production of some wastes can be fairly easily quantified. Allocating numerical values to pollutant effects is less straightforward and requires value judgements, so LCA is not a purely objective process.

That is the key limitation. You can count the litres of water and the kilowatt-hours of energy, but deciding how many units of damage a given amount of pollution is worth — and how that compares with using more water — is a judgement, and different people judge differently.

Selective or abbreviated LCAs can be devised to evaluate a product, but these can be misused to reach pre-determined conclusions, for example in support of claims for advertising purposes. An LCA that counts only the stages where a product does well is evidence of nothing.

You should be able to carry out simple comparative LCAs for shopping bags made from plastic and paper, and to interpret LCAs of materials or products given appropriate information.