What is potable water ?
Water that is safe to drink.
How is water from a reservoir treated to make it potable ?
- water passed through metal screen to catch larger debris such as sticks
- water flows through filter of fine sand to remove particles of mud and grit
- water to settlement tank for any remaining sand, grit or dirt to settle out
- water to another fine sand and gravel filter to clean even more
- treated with ozone/UV/chlorine to kill bacteria
- water is pH treated then is ready for public
How is desalination carried out and why ?
- some countries don’t have fresh water supplies
- have to use sea water
- distillation is used to desalinate
- reverse osmosis is used to desalinate (water passed through membranes to separate salts + uses no heat so is low energy cost)
How is waste water treated ?
- sewage passed through screen to clear debris
- primary sedimentation tank for dirt etc. to settle out (resulting sludge sent to another tank for anaerobic bacterial treatment)
- water passed to biological treatment tank (bacteria used to kill harmful bacteria + organic material)
- secondary sedimentation (bacteria settle out + are returned to biological treatment tank)
- water treated w/chorine, ozone or UV then pH checked and released into environment or used to drink again
- sludge from first tank is digested anaerobically by bacteria and heated - can be used as fertiliser, biofuel etc. - gases released during digestion can be purified for use as natural gas (methane)
How is copper extracted from high-grade malachite ores ? (2 ways)
SMELTING:
- malachite ores contain copper carbonate
- heat
- thermal decomposition happens, leaving copper oxide
- copper oxide at anode, pure copper extracted at the cathode, sludge of precious metals below anode in solution w/copper ions
- produces the very purest copper
ELECTROLYSIS ONLY:
- dissolve malachite in sulfuric acid to give copper sulfate solution
- here, either scrap iron can be used to collect the copper, or electrolysis with carbon electrodes
What is bioleaching ?
- low grade copper ores are broken down by bacteria
- leachate with copper ions in it is left, purified by electrolysis
- 20% copper from bioleaching, takes a long time
What is phytomining ?
- plants grown on top of low grade copper ores
- plants absorb copper ions as they grow
- burn plants and obtain copper from copper compounds in the ash
- can be made leachate by adding sulfuric acid
- purified by electrolysis or with scrap metal
What are the five stages in a life cycle assessment (LCA) ?
raw material extraction -> manufacturing -> use/reuse -> maintenance -> recycling/waste management
Should numerical values be used in LCAs ?
only for widely accepted data points.
What are some drawbacks of LCAs ?
- no peer review (done from within the company)
- don’t account for differences in cost and performance
- largely no exact numerical values used
Why is aluminium recycled ?
- conserves ore/resources
- saves energy in terms of not having to do electrolysis (still have to heat, but much less energy used)
Which other metals are recycled ?
- copper
- steel
- tin
