Landfills: efficient method to deal with large volumes, filled land can be used for other purposes. However local residents may object to new sites, filled land needs time to settle and requires maintenance as methane is released.
Open dumping: Convenient and inexpensive. However causes air, ground and water pollution; health hazard and attracts pests, and unsightly.
Ocean dumping: Source of nutrients, convenient and inexpensive. However dangerous to marine animals, pollutes the sea.
Incineration:Reduce volume, requires minimal space, produces stable odourless residue, can be source of energy. However expensive to build/operate, cause pollutants if inefficiently burned, requires energy.
Recycling: provides a sustainable environment. However expensive, difficult to separate different materials (sometimes impossible).
E.8.2 Describe the recycling of metal, glass, plastic and paper products, and outline its benefits.
Metal: Mainly aluminium and steel. Sorted and melted, or re-used directly or added to purification stage of metals formed from their ores. Important for metals like aluminium (large amounts of energy needed to produce direct from ore).
Glass: Sorted by colour, washed, crushed and then melted and moulded into new products. Not degraded during the recycling process so can be recycled many times.
Plastic: Sorted (though this may be problematic), degraded to monomers by pyrolysis, hydrogenation, gasification and thermal cracking, then repolymerised. Recycling causes less pollutants and uses less energy than producing new plastics from crude oil.
Paper: Sorted into grades, washed to remove inks, made into a slurry to form new types of paper. High transportation costs- may be more efficient to compost.
E.8.3 Describe the characteristics and sources of different types of radioactive waste.
Two types of radioactive waste: High level waste and low level waste.
Low level waste is where activity is low and the half-lives of the radioactive isotopes are generally short lived. Such items include rubber gloves, paper towels and protective clothing that have been used to handle radioactive materials.
High level waste is where activity is high and the half-lives of the radioactive isotopes are generally long and so the waste remains active for a long period. Most high level waste comes from spent fuel rods or the reprocessing of spent nuclear rods.
E.8.4 Compare the storage and disposal methods for different types of radioactive waste.
Low level waste:
-is sometimes discharged straight into the sea, but this is now banned by many governments and so the following methods are used:
-produces heat during decay and so is stored in 'ponds' of cooled water where it loses much of its activity. Before discharge, it is filtered through an ion exchange resin which removes stronium and caesium (elements responsible for radioactivity).
-Storage of waste in steel containers inside concrete-lined vaults.
High level waste:
-96% uranium is recovered during reprocessing for reuse.
- 1% is plutonium (valuable fuel)
-3% is level liquid waste that is vitrified. The liquid waste is dried in a furnace and then fed into a melting pot together with glass making materials. This molten material is then poured into stainless steel tubes where it solidifies, with air flowing around the containers to keep them cool. High activity and long half-lives means that the waste will remain active for hundreds of years, and hence the solid matter should be buried in a geologically stable place such as disused mines or in granite rock. However there is concern that the radioactive material may eventually leach into the water table and then into drinking water.
No comments:
Post a Comment