C14

Question 1

What is potable water ?

Answer 1

Water that is safe to drink.

Question 2

How is water from a reservoir treated to make it potable ?

Answer 2

• water from reservoir flows through filter of fine sand to remove particles of mud and grit
• water passed through metal screen to catch larger debris such as sticks
• 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

Question 3

How is desalination carried out and why ?

Answer 3

• 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)

Question 4

How is waste water treated ?

Answer 4

• 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)

Question 5

How is copper extracted from high-grade malachite ores ? (2 ways)

Answer 5

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

Question 6

What is bioleaching ?

Answer 6

• 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

Question 7

What is phytomining ?

Answer 7

• 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

Question 8

What are the five stages in a life cycle assessment (LCA) ?

Answer 8

raw material extraction -> manufacturing -> use/reuse -> maintenance -> recycling/waste management

Question 9

Should numerical values be used in LCAs ?

Answer 9

only for widely accepted data points.

Question 10

What are some drawbacks of LCAs ?

Answer 10

• no peer review (done from within the company)
• don’t account for differences in cost and performance
• largely no exact numerical values used

Question 11

Why is aluminium recycled ?

Answer 11

• conserves ore/resources
• saves energy in terms of not having to do electrolysis (still have to heat, but much less energy used)

Question 12

Which other metals are recycled ?

Answer 12

• copper
• steel
• tin