Using Resources
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Natural resources and sustainability
Natural resources come from the Earth's atmosphere, hydrosphere and lithosphere. Some are supplemented by agriculture and synthetic products.
Sustainability underpins every resource-use decision in this topic.
Natural resources and sustainability — Key Knowledge
- Natural resources from atmosphere, water and crust
- Sustainable development meeting present needs without compromising future generations
Potable water
Potable water is safe to drink but is not chemically pure — it contains dissolved substances that are not harmful.
Pure water in chemistry means a single substance with nothing dissolved — tap water does not meet this definition.
Potable water — Key Knowledge
- Potable water safe to drink, not pure
- Fresh water treatment sedimentation, then sand filtration, then sterilisation
- Sterilisation methods chlorine, ozone or UV light
Desalination
Desalination produces potable water from salty or sea water. It is energy-intensive and expensive.
Used in countries with limited fresh water supplies, such as parts of the Middle East.
Desalination — Key Knowledge
- Distillation boil and condense to remove salt
- Reverse osmosis water forced through a membrane that traps salt
Waste water treatment
Waste water from homes and industry is treated in several stages before being released back into the environment.
The treated effluent must be clean enough to release safely into rivers.
Waste water treatment — Key Knowledge
- Screening removes large debris
- Sedimentation solids settle to form sludge
- Biological treatment aerobic bacteria break down organic matter
- Anaerobic digestion of sludge produces biogas
Life cycle assessment
A life cycle assessment (LCA) evaluates the environmental impact of a product across its entire lifespan.
LCAs are useful but involve value judgements — they are not fully objective.
Life cycle assessment — Key Knowledge
- Four stages extracting raw materials, manufacturing and packaging, use during lifetime, disposal at end of life
- Disposal options landfill, recycling, incineration
- Subjectivity some impacts are hard to quantify, e.g. biodiversity loss
Reduce, reuse, recycle
Resource use can be reduced by using less material, reusing products without reprocessing, and recycling materials into new products.
Recycling still requires energy for collection, transport and reprocessing — but generally less than starting from raw materials.
Reduce, reuse, recycle — Key Knowledge
- Reduce use less
- Reuse use again without reprocessing
- Recycle reprocess into new products
- Recycling metals less energy than extraction from ores, conserves finite reserves
Corrosion and rusting
Corrosion is the destruction of materials by chemical reactions with substances in the environment. Rusting of iron requires both water and oxygen.
If either water or oxygen is removed, iron will not rust.
Corrosion and rusting — Key Knowledge
- Rusting conditions water and oxygen both needed
- Barrier methods painting, oiling, greasing — block water and oxygen
- Galvanising coating with zinc
- Sacrificial protection more reactive metal corrodes instead of the iron
Alloys and materials
Alloys are mixtures of a metal with one or more other elements. Different-sized atoms disrupt the regular lattice, preventing layers from sliding, making alloys harder than pure metals.
Materials are chosen and designed for specific purposes based on their properties.
Alloys and materials — Key Knowledge
- Alloys mixtures not compounds, harder than pure metals
- Ceramics hard, brittle, good insulators, high melting points
- Polymers properties depend on monomers and polymerisation conditions
- Composites two or more materials combined for improved properties, e.g. fibreglass, reinforced concrete
The Haber process
The Haber process combines nitrogen from the air with hydrogen from natural gas to produce ammonia. The reaction is reversible.
N2 + 3H2 reversible 2NH3
The conditions balance yield, rate and cost — a key example of industrial compromise.
The Haber process — Key Knowledge
- Reactants nitrogen from air, hydrogen from natural gas
- Conditions about 450 degrees C, about 200 atmospheres, iron catalyst
- Compromise lower temperature gives more yield but too slow; higher pressure gives more yield but expensive and dangerous
- Recycling unreacted N2 and H2 passed back through the reactor
NPK fertilisers
Plants need nitrogen, phosphorus and potassium for healthy growth. NPK fertilisers supply these essential elements.
Ammonia from the Haber process is the starting point for most nitrogen-based fertilisers.
NPK fertilisers — Key Knowledge
- N — nitrogen for protein and chlorophyll
- P — phosphorus for root growth and energy transfer
- K — potassium for disease resistance and enzyme function
- Ammonium nitrate nitrogen fertiliser made from Haber process ammonia