Föreläsning 6 - metals and sustainability Flashcards
What are the main resources used for metal production?
- Mineral containing the metal.
- Energy (coal, oil, electricity)
In which parts of the metal production process is energy used?
- Energy for reducing mineral to metal - natural constant- energy bound in the metal
- Other energy - Manufacturing and forming, transport, use- can be reduced, heat can be reused
In what ways do metal production have environmental impact?
- Interventions in nature
- CO_2 emissions
- Other emissions and pollutants
CO_2 can be used as a measure of environmental impact (carbon footprint)
Why do we recycle metals?
- Scrap metal is an excellent raw material for metal production.
- Requires less energy than production from ore: 1/10 for Al and 1/3 for steel.
- Less environmental impact.
- Metal made from scrap has the same characteristics as metal made from minerals.
What are some problems you may encounter in metal recycling?
- Alloys must be controlled - problems with mixed scrap and metal pollution.
- Copper and tin destroy steel.
- Fe makes Al brittle
- Lead, cadmium and mercury are often unwanted in alloys.
- The scrap must be collected, transported and sorted
Why is aluminium suitable for recyclable products?
- Most common element in the earth’s crust
- Production of primary aluminium requires a lot of energy
- Much less energy is required for recycling
=> Suitable for recyclable products, less suitable for non-recyclable products
What are some problems with recycling of aluminium?
- Casting alloys contain a lot of Si, 8-14%
- Other alloys (forging alloys) contain small amounts of Si
=> Mixed scrap can only be used in limited quantities for recycling for forging alloys
=> Polluted by Fe
What are some properties of steel?
- Good access in earth’s crust
- Relatively low environmental impact
- High strength in relation to environmental impact
- Corrodes, often requires surface treatment
- High strength steels can be used in lightweight structures
What are some properties of stainless steel?
- Alloy with iron, Cr, Ni, maybe Mo
- The avaliability of alloy substance in the earth’s crust is relatively small
- The alloy substances can be unhealthy and allergenic in free form. Usually not bound in stainless steel.
- Good corrosion resistance and longevity. Should be recycled
What are some widely available materials? What are some strategic or critical materials?
- The most common metals are widely found in the earth’s crust: Fe, Al, Mg, Ti
- Some alloying substances are avaliable in limited quantity in the earth’s crust
- 69 elements are considered strategic or critical: rare earth elements, platnium group, fission substance (U, Th, Pu), E, Ta, Nb, Ga, In
What type of scrap is most useful?
- When re-using scrap, the control of alloying substance is a problem
- Excess alloying and polluting metals may or may not be uneconomic to remove
- Sorted scrap is more useful and has higher value
What is CO_2 footprint?
- Amount CO_2 formed during the production of 1 kg of material.
- For metals:
- CO_2 formed in the production of energy
- CO_2 from chemical reactions when reducing the ore to metal
What is embodied energy?
The energy required to produce 1 kg of the material.
For metals:
- Energy required for the reduction reaction
- Transport, heating, processes
How do we create a material index for CO_2 footprint or embedded energy?
Determine load case: beam in bending, single axe-pull, widespread load on plate
Find material indexes for light and rigidity, light and durable…
Replace density in the material index with
- density * CO_2 footprint
- density * embedded energy
