Chapter 14 : The Earth's Resources (Finite and Renewable Resources…
Chapter 14 : The Earth's Resources
Finite and Renewable Resources
Natural resources, supplemented by agriculture, provide food, timber, clothing and materials.
Finite resources from the Earth, oceans and atmosphere are processed to provide energy and materials.
Humans use the Earth's resources to provide warmth, shelter, food and transport.
Chemistry plays an important role in providing agricultural and industrial processes to provide new products, and in sustainable development, which is development that meets the needs of current generations without compromising the ability of future generations to meet their own needs.
Some of these natural resources are finite - they will run out eventually if we continue to exploit them, e.g. fossil fuels.
Others are renewables - they can be replaced as we use them up, e.g. crops used to make biofuels.
We rely on the Earth's natural resources to make new products and provide us with energy.
Estimates of the time left before fossil fuels run out can only be rough estimates, because of the uncertainty involved in the calculations.
Water Safe to Drink
In the United Kingdom, rain water provides water with low levels of dissolved substances (fresh water) that collects in the ground and in lakes and rivers, and most potable water is produced by:
choosing an appropriate source of fresh water
passing the water through filter beds
Sterilising agents used for potable water include chroline, ozone or ultraviolet light.
The methods used to produce potable water depend on available supplies of water and local conditions.
If supplies of fresh water are limited, desalination of salty water or sea water may be required. Desalination can be done by distillation or by processes that use membranes such as reverse osmosis. These processes require large amounts of energy.
Water of appropriate quality is essential to life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. Water that is safe to drink is called potable water. Potable water is not pure water in the chemical sense because it contains dissolved substances.
Water can be purified by distillation, but this requires large amounts of energy, which makes it expensive.
Reverse osmosis uses membranes to separate dissolved salts from salty water, but this method of desalination also uses energy to make the high pressures needed.
Water is made fit to drink by passing it through filter beds to remove solids and adding chlorine, ozone, or by passing ultraviolet light through it (sterilising) to reduce microbes.
Treating Waste Water
Urban lifestyles and industrial processes produce large amounts of waste water that require treatment before being released into the environment. Sewage and agricultural waste water require removal of organic matter and harmful microbes. Industrial waste water may require removal of organic matter and harmful chemicals.
Sewage treatment includes:
screening and grit removal
sedimentation to produce sewage sludge and effluent
anaerobic digestion of sewage sludge
aerobic biological treatment of effluent
Waste water requires treatment at a sewage works before being released into the environment.
Sewage treatment involves the removal of organic matter and harmful microorganisms and chemicals.
The stages include screening to remove large solids and grit, sedimentation to produce sewage sludge, and aerobic biological treatment of the safe effluent released into the environment.
The sewage sludge is separated, broken down by anaerobic digestion and dried. It can provide us with fertiliser and a source of renewable energy.
Extracting Metals from Ores
Phytomining uses plants to absorb metal compounds. The plants are harvested and then burned to produce ash that contains metal compounds.
Bioleaching uses bacteria to produce leachate solutions that contain metal compounds.
Copper ores are becoming scarce and new ways of extracting copper from low-grade ores include phytomining, and bioleaching. These methods avoid traditional mining methods of digging, moving and disposing of large amounts of rock.
The metal compounds can be processed to obtain the metal. For example, copper can be obtained from solutions of copper compounds by displacement using scrap iron or by electrolysis.
The Earth's resources of metal ores are limited.
Copper can be extracted from solutions of copper compounds by electrolysis or by displacement using scrap iron. Electrolysis is also used to purify impure copper, e.g. the copper metal obtained from smelting.
Scientists are developing new ways to extract copper that use low-grade copper ores. Bacteria are used in bioleaching and plants in phytomining.
Most copper is extracted by smelting (roasting) copper-rich ores, although supplies of ores are becoming scarcer.
Life Cycle Assessments
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
Selective or abbreviated LCAs can be devised to evaluate a product but these can be misused to reach pre-determined conclusions, e.g. in support of claims for advertising purposes.
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
They analyse each of the stages of a life cycle, from extracting and processing raw material to disposal at the end of its useful life, including all transport and distribution at each stage.
Data is available for the use of energy, water, resources and production of some wastes.
Life Cycle Assessments (LCAs) are carried out to assess the environmental impact of products, processes or services.
However, assigning numerical values to the relative effects of pollutants involves subjective judgements, so LCAs using this approach must make this uncertainty clear.
Reduce, Reuse, and Recycle
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.
The reduction in use, reuse and recycling of materials by end users reduces the use of limited resources, use of energy resources, waste and environmental impacts.
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.
There are social, economic and environmental issues associated with exploiting the Earth's limited supplies of raw materials, such as metal ores.
Recycling metals saves energy and our limited, finite metal ores (and fossil fuels). The pollution caused by the mining and extraction of metals is also reduced by recycling.