Metal extraction

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  • When do you use carbon monoxide and when do you use carbon to reduce ores?
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  • Because aluminium is more reactive than carbon, so the reaction wont work.
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  • 'Why cant we use carbon to get pure aluminium from aluminium oxide??'
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Metal extraction

  1. 1. Metal Extraction<br />
  2. 2. Metal Ores<br />Metals are usually found in ores containing minerals<br />They are combined with oxygen or sulfur to form oxides or sulfides<br />Sulfide ores are converted to oxides by heating them in the air, which is called ‘roasting’, e.g. zinc sulfide to zinc oxide<br />ZnS(s) + 1½O2(g)ZnO(s) + SO2(g)<br />zinc sulfide<br />oxygen<br />zinc oxide<br />sulfur dioxide<br />
  3. 3. Environmental Problems<br />When roasting sulfide ores, sulfur dioxide is produced as a waste product<br />This is a contributor to acid rain if it is allowed to escape into the atmosphere as it reacts in the air to form sulfuric acid<br />However it can be converted to sulfuric acid in controlled conditions which can then be sold for a variety of purposes<br />SO2(g) + H2O(g) + ½O2(g)H2SO4(l)<br />sulfur dioxide<br />sulfuric acid<br />oxygen<br />water<br />
  4. 4. Extraction of Metals<br />To obtain the metal its ore, a reducing agent is used to remove the oxygen, in a reduction reaction.<br />Examples of some reducing agents; <br />Coke (an impure form of carbon)<br />Hydrogen (made from methane and water)<br />A more reactive metal may be used.<br />Electrolysis can also be used for more reactive metals.<br />
  5. 5. Reduction of Metal Ores<br />For the extraction of iron, manganese and copper the reducing agents are carbon and carbon monoxide.<br />These are cheap because coke can be used which is cheaply produced by heating coal in the absence of air.<br />The extraction of iron is done in a blast furnace which reaches temperatures of 2000K.<br />Fe2O3(s) + 3CO(g) 2Fe(l) + 3CO2(g)<br />Carbon Monoxide<br />Carbon Dioxide<br />Haematite<br />Iron<br />
  6. 6. Reduction of Metals<br />Manganese is produced by the reduction of its oxide with carbon. <br />2MnO(s) + C(s) 2Mn(l) + CO2(g)<br />Copper used to be produced this way but nowadays some ores are converted in to solutions containing Cu2+ ions. The copper is extracted by reducing with scrap iron.<br />Cu2+(aq) + Fe(s) Cu(s) + Fe2+(aq)<br />This is ‘greener’ as no CO2 is produced and scrap iron is cheap and readily available. <br />Also, the solution can be made from low grade ore so it is readily available<br />
  7. 7. Extracting Other Metals<br />Some metals can’t be extracted using carbon reduction, such as aluminium, titanium and tungsten.<br />Aluminium can’t because it is more reactive than carbon.<br />Titanium and tungsten can’t because it would form a metal carbide which would make the metal brittle.<br />
  8. 8. Extraction of Aluminium <br />Aluminium is extracted from purified bauxite ore (mainly Al2O3)<br />The oxide is dissolved in molten cryolite, which forms a solution which melts at around 1240K (Al2O3 melts at 2435K therefore less energy is required<br />The solution is electrolysed so the main cost of the process is electricity which makes economic sense where cheap electricity is available<br />
  9. 9. Extraction of Aluminium <br />Aluminium is produced at negative electrode<br />2Al3+ +6e- 2Al<br />Oxygen is produced at the positive electrode<br />3O2- 1½O2 + 6e-<br />This gives an overall equation of:<br />Al2O3(l) 2Al(l) + 1½O2(g)<br />
  10. 10. Extraction of Titanium<br />As titanium can’t be reduced with carbon, it is reduced by sodium or magnesium<br />This is an expensive process as the titanium oxide is first converted to titanium chloride by reacting it with coke and chlorine at 1173K<br />TiO2(s) + 2C(s) + 2Cl2(g) TiCl4(l) + 2CO(g)<br />The titanium chloride is then reduced by sodium or magnesium into titanium under an inert argon atmosphere at 1300K<br />TiCl4(l) + 4Na(l) Ti(l) + 4NaCl(l) <br />
  11. 11. Extraction of Tungsten<br />Tungsten is extracted from its oxide, WO3, by reduction with hydrogen at high temperatures<br />WO3 + 3H2 W + 3H2O<br />However, there is some risk as hydrogen is a flammable gas, so using it as a reducing agent is a last resort.<br />
  12. 12. Effects on the Environment<br />Recycling scrap metals has many environmental and economic advantages<br />It reduces the amount of scrap metal in landfill and it has already been extracted from its ore so energy isn’t required again<br />Melting the scrap metal does not in itself produce carbon dioxide unlike extracting metals from their ores however the energy needed to melt the metal will<br />

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