Industrial materials and environmental conservation
Every material has a life cycle: extraction (mining, drilling, farming) → manufacture → use → disposal. At each stage there is an effect on the environment.
- Extraction: land is dug up, forests are cleared, water gets polluted.
- Manufacture: energy is burnt, which gives carbon dioxide (CO₂) and smoke; some factories release harmful chemicals into air and water.
- Use: some products use energy all their life (cars, bulbs).
- Disposal: waste fills landfills, plastics reach rivers and seas, and heavy metals such as lead can leak into soil.
How we protect the environment:
- The 5 R's: Refuse what you do not need, Reduce use, Reuse, Recycle, and Recover energy from what remains.
- Eco-design: make products light, long-lasting, easy to repair and easy to take apart.
- Cleaner factories: filters for smoke, treatment of waste water, saving heat and electricity.
- Safer materials: replace harmful ones, for example lead-free solder.
- Rules and checks: laws and standards make factories control waste and emissions.
Recycling industrial materials
Recycling turns used material into raw material for new products. The steps are always similar: collect → sort → clean or shred → melt or reshape → make a new product.
- Metals: a magnet separates steel from other waste. The scrap is melted and cast again. Metals can be recycled again and again. Recycled aluminium needs only about 5% of the energy of making it from ore; recycled steel saves roughly half or more.
- Glass: crushed glass (cullet) melts at a lower temperature than fresh sand, so it saves fuel. Colours are sorted.
- Plastics: sorted by the resin code (a number inside a triangle), shredded, washed, melted and made into pellets. Thermoplastics can be melted again; thermosets cannot. Often the new plastic is of lower quality (downcycling).
- Paper: pulped, cleaned of ink and pressed again; fibres get shorter each time.
- Electronic waste: phones and computers hold gold, copper and rare metals that can be recovered, but they must be handled safely.
- Composites: fibres and resin are stuck together, so they are hard to separate and recycle.
Closed loop means the new product is the same as the old (can to can). Downcycling means a lower-grade product. Recycling rate = recycled mass ÷ total mass × 100.
Try it: for one week, collect the waste at home in four boxes: paper, metal, glass, plastic. Weigh each and find the recycling rate if everything in them were recycled.
Key formulas and definitions
- Recycling rate % = recycled mass ÷ total mass × 100
- Waste to landfill = total mass − recycled mass
- Energy saved = (energy from ore − energy from scrap) × mass
- Aluminium: scrap uses about 5% of the energy needed from ore
Worked examples
1. A factory collects 80 kg of scrap metal and 60 kg is recycled. Find the recycling rate.
60 ÷ 80 × 100 = 75%.
2. A product weighs 10 kg and 40% of the material is recycled. How many kg go to landfill?
Recycled = 0.4 × 10 = 4 kg. Landfill = 10 − 4 = 6 kg.
3. Making 1 kg of aluminium from ore needs 200 MJ; from scrap, 10 MJ. How much energy is saved on 30 kg?
Saved per kg = 200 − 10 = 190 MJ. For 30 kg = 190 × 30 = 5700 MJ.
4. Each plastic bottle weighs 25 g. How many kg of plastic are in 400 bottles?
25 × 400 = 10 000 g = 10 kg.
5. A plant makes 500 kg of waste and recycles 70% of it. How much is not recycled?
Recycled = 0.7 × 500 = 350 kg. Not recycled = 500 − 350 = 150 kg.
Common mistakes
- Thinking recycling is the best step. Refusing and reducing come first, because they make no waste at all.
- Believing all plastics can be recycled the same way. Different types need sorting, and thermosets cannot be re-melted.
- Forgetting that recycling also needs energy and transport. It is just much less than making from raw material.
- Throwing mixed waste in one bin. Sorting is what makes recycling possible.