Chemistry - Using resources

what is potable water

water that has been treated or is naturally safe for humans to drink

why is potable water not pure

it contains dissolved substances

potable water production method for fresh water

1. goes through screening (filtration method) - wire mesh to remove insoluble things like sticks, stones etc.

2. sterilization - to kill any microbes. You could use O₃ (ozone),UV, Cl³ (Chlorine Gas)

potable water production method for sewage water

1. Screening - wire mesh to get rid of insoluble things

2. sedimentation in a settlement tank - heavier suspended solids sink to the bottom to produce sludge, lighter effluent goes to the top

3. effluent is removed and treated by biological aerobic digestion (air pumped through the water to encourage aerobic bacteria to break down any organic matter)

4. sludge from the bottom of the tank is also removed and transferred into large tanks. Goes through anaerobic digestion (breaks down the organic matter in the sludge, releasing methane gas in the process. Can be turned into sludge cakes to burn, get energy or used as fertiliser

5. Sterilisation using Ozone, UV light or chlorine gas

sea water potable water production method

desalination:

1. distillation - but requires high energy and is expensive

2. reverse osmosis - requires high energy, is expensive and membrane needs to be replaced

waste water

comes from lots of things at home - having a bath, going to the toilet, showers, sinks. when it is flushed away it goes to the sewers and towards sewage treatment plants. Agricultural systems also produce a lot of waste water including nutrient run off from fields and slurry from animals.

sewage from both of these places has to be treated to remove organic matter and any harmful microbes before it can be put back inot fresh water sources like lakes and rivers.

phytomining

1. plants are grown in soil that contains low grade ore

2. the plants absorb metal ions through their roots and concentrate these ions in their cells

3. the plants are harvested and burnt

4. the ash left behind contains metal compounds

phytomining/phytoextraction pros and cons

cons - slow

pros - reduces the need to obtain new ore by mining, conserves limited supplies of high grade ores, reduces the amount of rock waste that must be disposed of after traditional mining

bioleaching

certain bacteria can break down low grade ores to produce an acidic solution containing copper ions. the solution is called a leachate and the process in called bioleaching.

bioleaching negatives

it produces toxic substances such as sulfuric acid, which damage the environment

processing the metal compounds from phytomining and bioleaching

using displacement reactions or electroysis

corrosion

the destruction of materials by chemical reactions with substances in the environment

example of corrosion

rusting - both air and water are necessary for iron to rust

how can corrosion be prevented

by applying a coating that acts as a barrier - e.g. greasing, painting, coating with plastic or sacrificial protection (galvanising)

sacrificial protection (galvanising)

iron can be protected from rusting if it is in contact with a more reactive metal, such as zinc. The more reactive metal oxidises more readily than iron, so it sacrifices itself while the iron does not rust

properties of steels and aluminium alloys

high carbon - strong but brittle

low carbon - softer and more easily shaped

steels containing chromium and nickel (stainless steels) are hard and resistant to corrosion.

aluminium alloys are low denisty