Extraction

Extraction

1. LEARNING OBJECTIVES

   • evaluate the possible social, economic and environmental impacts of mining ores
   • explain why we recycle metals
   • explain why some rare metals were discovered before more common metals
   • explain why more-reactive metals such as aluminium are much more difficult and expensive to extract than less-reactive metals
   • describe how iron is extracted from its ore
   • explain why copper is easier to get from good quality ores
   • explain why new methods of copper extraction are being developed

2. electrolysis

   • extraction by electrolysis
     • metals that are more reactive than carbon have to be extracted using electrolysis of molten compounds i.e. aluminium
     • uses a lot of energy and is therefore more expensive
     • 1)metal ore is heated up and melted into molten 2)liquid conducts electricity (called the electrolyte) as it has free ions 3)electrons are taken away by the positive anode and given away by the negative anode 4)as ions gain or lose electrons they become atoms or molecules and are released
   • THE BREAKING DOWN OF A SUBSTANCE USING ELECTRICITY
   • electrolysis can be used to purify compounds by separating them from their ore
   • aluminium has to be extracted this way, making it much more expensive than other metals i.e. iron

3. reduction with carbon

   • OXYGEN IN THE SUBSTANCE IS REMOVED
   • position in the periodic table determines whether the metal can be extracted by reduction with carbon
     • metals higher than carbon have to be extracted using electrolysis (expensive)
     • metals lower than carbon can be extracted using reduction
   • if carbon is more reactive than other metals it can push the metal out of its compound and take its place

4. oxidation

   • when the ore is reacted with carbon, the carbon combines with the ore to form carbon dioxide-the carbon is oxidised
   • reduction follows oxidation-the two always go together

5. displacement

   • if you put a reactive metal into a solution of a dissolved metal compound, the reactive metal will replace the less reactive metal in the compound
     • this is because the more reactive metal bonds more strongly to the non-metal bit of the compound and pushes out the less reactive metal

6. iron

   • most common metal
   • large production makes it cheap
   • to extract it by reduction, much more energy is needed
   • iron ore is called iron oxide
   • in a blast furnace, air is pumped through the burning coke, raising the temperature to more than 1600ºC to reduce the ore and melt the iron

7. copper

   • usually found as copper sulphide crystals scattered around the ore body
   • separating out the copper by reduction is too expensive
   • acid is sprayed onto the rock causing soluble copper compounds to dissolve out of the rock (leachate) which is collected. copper is removed from the leachate by electrolysis. (copper forms positive ions in the solution which will move towards the negative electrode

8. recycling metals

   • there are only a few major copper mines in the world as copper is so hard to fine
   • large amounts of copper are used for things like water pipes and electrical wiring
   • scientists are now trying to find other ways to extract copper from ores that contain small amounts of copper of from waste
     • bioleaching
       • bacteria is used to separate copper from copper sulphide
         • the bacteria gets energry from the bond between copper and sulphur which separates copper from the ore-this produces leachate
           • the copper in the leachate can be extracted by process such as filtering
     • phytomining
       • plants are grown in soil that contains copper
         • plants can't use copper so it builds up in the leaves
           • plants are harvested, dried and burned in a furnace
             • the copper is collected from the ash left in the furnace
       • this helps to reclaim spoilt land as a lot of plants won't grow on soils that are contaminated with metals, therefore phytomining is a more environmentally friendly way to extract copper and it also reclaims spoilt land
   • importance
     • recycling metals uses a fraction of the energy needed to mine and extract new metals
     • saving energy saves money
     • recycling conserves ressources as metals are finite
     • cuts down on rubbish that gets sent to landfills which take up space and pollute the surroundings
   • impacts of extraction and mining
     • rich countries will often buy poor countries' resources as developed countries often use up their own resources-they are cheaper because LEDC have lower labour wages
       • benefit-provides jobs in the LEDCs
       • drawback-poor working conditions
     • same as those with quarrying
     • provides jobs
     • brings money to the area
       • services such as transport and health can be improved
   • environmental impacts
     • extraction uses a lot of energy and is bad for the environment
     • the energy comes from burning fossil fuels which contributes to acid rain, global dimming and climate change
     • causes noise
     • ruins the landscape
     • destroys animal habitats
     • mine shafts can be dangerous after they are abandoned
     • rainwater will naturally leach these mines which will carry toxic metal salts into surrounding rivers
   • recycling costs money
     • waste material contains a lot of different materials mixed together which means recycling is only do-able for metals that are easy to separate
   • reduces pollution
   • prolongs resource use
   • reduces energy consumption