EXTRACTION OF METALS An aide for A level understudies - PowerPoint PPT Presentation

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EXTRACTION OF METALS An aide for A level understudies

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  1. EXTRACTION OF METALS A guide for A level students KNOCKHARDY PUBLISHING

  2. KNOCKHARDY PUBLISHING EXTRACTION OF METALS INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... www.knockhardy.org.uk/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard

  3. EXTRACTION OF METALS • CONTENTS • Theory of extraction • Extraction of iron • Conversion of iron into steel • Extraction of aluminium • Extraction of titanium • Extraction of chromium • Extraction of sodium • Recycling

  4. EXTRACTION OF METALS • Before you start it would be helpful to… • Recall the layout of the reactivity series • Recall definitions of reduction, oxidation and redox

  5. GENERAL PRINCIPLES OCCURRENCE • ores of some metals are very common (iron, aluminium) • others occur only in limited quantities in selected areas • high grade ores are cheaper to process because, ores need to be purified before being reduced to the metal

  6. GENERAL PRINCIPLES THEORY The method used to extract metals depends on the . . . • purity required • energy requirements • cost of the reducing agent • position of the metal in the reactivity series

  7. GENERAL PRINCIPLES REACTIVITY SERIES K Na Ca Mg Al C Zn Fe H Cu Ag • lists metals in descending reactivity • hydrogen and carbon are often added • the more reactive a metal the less likely it will be found in its pure, or native, state • consequently, it will be harder to convert it back to the metal.

  8. GENERAL PRINCIPLES METHODS - GENERAL Low in series occur native or Cu, Ag extracted by roasting an ore Middle of series metals below carbon are extracted by reduction Zn, Fe of the oxide with carbon or carbon monoxide High in series reactive metals are extracted using electrolysis Na, Al - an expensive method due to energy costs Variations can occur due to special properties of the metal.

  9. GENERAL PRINCIPLES METHODS - SPECIFIC • reduction of metal oxides with carbon IRON • reduction of metal halides with a metal TITANIUM • reduction of metal oxides by electrolysis ALUMINIUM • reduction of metal oxides with a metal CHROMIUM

  10. IRON

  11. EXTRACTION OF IRON GENERAL PROCESS • occurs in the BLAST FURNACE • high temperature process • continuous • iron ores are REDUCED by carbon / carbon monoxide • is possible because iron is below carbon in the reactivity series

  12. EXTRACTION OF IRON RAW MATERIALS HAEMATITE - Fe2O3a sourceofiron COKEfuel / reducing agent CHEAP AND PLENTIFUL LIMESTONE conversion of silica into slag (calcium silicate) – USED IN THE CONSTRUCTION INDUSTRY AIRsource ofoxygen for combustion

  13. THE BLAST FURNACE G IN THE BLAST FURNACE IRON ORE IS REDUCED TO IRON. THE REACTION IS POSSIBLE BECAUSE CARBON IS ABOVE IRON IN THE REACTIVITY SERIES Click on the letters to see what is taking place A C D B B E F

  14. THE BLAST FURNACE COKE, LIMESTONE AND IRON ORE ARE ADDED AT THE TOP Now move the cursor away from the tower A

  15. C + O2 CO2 CARBON + OXYGEN CARBON + HEAT DIOXIDE THE BLAST FURNACE HOT AIR IS BLOWN IN NEAR THE BOTTOM OXYGEN IN THE AIR REACTS WITH CARBON IN THE COKE. THE REACTION IS HIGHLY EXOTHERMIC AND GIVES OUT HEAT. B B Now move the cursor away from the tower

  16. C + CO2 2CO THE BLAST FURNACE THE CARBON DIOXIDE PRODUCED REACTS WITH MORE CARBON TO PRODUCE CARBON MONOXIDE Now move the cursor away from the tower C CARBON + CARBON CARBON DIOXIDE MONOXIDE

  17. 3CO + Fe2O3 3CO2 + 2Fe THE BLAST FURNACE THE CARBON MONOXIDE REDUCES THE IRON OXIDE CARBON + IRON CARBON + IRON MONOXIDE OXIDE DIOXIDE Now move the cursor away from the tower D REDUCTION INVOLVES REMOVING OXYGEN

  18. CaO + SiO2 CaSiO3 CaCO3 CaO + CO2 THE BLAST FURNACE SILICA IN THE IRON ORE IS REMOVED BY REACTING WITH LIME PRODUCED FROM THE THERMAL DECOMPOSITION OF LIMESTONE CALCIUM SILICATE (SLAG) IS PRODUCED MOLTEN SLAG IS RUN OFF AND COOLED E Now move the cursor away from the tower

  19. THE BLAST FURNACE MOLTEN IRON RUNS TO THE BOTTOM OF THE FURNACE. IT IS TAKEN OUT (CAST) AT REGULAR INTERVALS CAST IRON - cheap and easily moulded - used for drainpipes, engine blocks F Now move the cursor away from the tower

  20. THE BLAST FURNACE G HOT WASTE GASES ARE RECYCLED TO AVOID POLLUTION AND SAVE ENERGY CARBON MONOXIDE - POISONOUS SULPHURDIOXIDE - ACIDICRAIN CARBONDIOXIDE - GREENHOUSEGAS RECAP

  21. SLAG PRODUCTION • silica (sand) is found with the iron ore • it is removed by reacting it with limestone • calcium silicate (SLAG) is produced • molten slag is run off and cooled • it is used for building blocks and road foundations

  22. SLAG PRODUCTION • silica (sand) is found with the iron ore • it is removed by reacting it with limestone • calcium silicate (SLAG) is produced • molten slag is run off and cooled • it is used for building blocks and road foundations EQUATIONS limestone decomposes on heating CaCO3 —> CaO + CO2 calcium oxide combines with silica CaO + SiO2 —> CaSiO3 overall CaCO3 + SiO2 —> CaSiO3 + CO2

  23. WASTE GASES AND POLLUTION SULPHURDIOXIDE • sulphur is found in the coke; sulphides occur in the iron ore • burning sulphur and sulphides S + O2 ——> SO2 produces sulphur dioxide •sulphur dioxide gives SO2 + H2O ——> H2SO3 rise to acid rain sulphurous acid CARBONDIOXIDE • burning fossil fuels increases the amount of this greenhouse gas

  24. LIMITATIONS OF CARBON REDUCTION Theoretically, several other important metals can be extracted this way but are not because they combine with the carbon to form a carbide e.g. Molybdenum, Titanium, Vanadium, Tungsten

  25. STEEL MAKING Iron produced in the blast furnace is very brittle due to the high amount of carbon it contains. In the Basic Oxygen Process, the excess carbon is burnt off in a converter and the correct amount of carbon added to make steel. Other metals (e.g. chromium) can be added to make specialist steels. Removal of impurities SILICA add calcium oxide CaO + SiO2 ——> CaSiO3 CARBON add oxygen C + O2 ——> CO2 PHOSPHORUS add oxygen 2P + 5O2 ——> P4O10 SULPHUR add magnesium Mg + S ——> MgS

  26. TYPES OF STEEL MILD easily pressed into shape chains and pylons LOW CARBON soft, easily shaped HIGH CARBON strong but brittle chisels, razor blades, saws STAINLESS hard, resistant to corrosion tools, sinks, cutlery (contains chromium and nickel) COBALT can take a sharp edge highspeedcuttingtools can be magnetised permanentmagnets MANGANESE increased strength pointsinrailwaytracks NICKEL resists heat and acids industrialplant, cutlery TUNGSTEN stays hard at high temps highspeedcuttingtools

  27. TITANIUM

  28. EXTRACTION OF TITANIUM • titanium ores (titanium(IV) oxide - TiO2) are very common • titanium however is not used extensively as its extraction is difficult using conventional methods • the oxide can be reduced by carbon but the titanium produced reacts with the carbon to give titanium carbide • the extraction is a batch process so there is much time wasted and heat lost; this makes it even more expensive

  29. EXTRACTION OF TITANIUM • the oxide is first converted to the chloride TiO2(s) + 2C(s) + 2Cl2(g) ——> TiCl4(l) + 2CO(g) •which is then reduced with sodium. TiCl4(l) + 4Na(s) ——> Ti(s) + 4NaCl(s) The reduction of TiCl4 is carried out in an atmosphere of argon because the titanium reacts with oxygen at high temperatures.

  30. EXTRACTION OF TITANIUM • the oxide is first converted to the chloride TiO2(s) + 2C(s) + 2Cl2(g) ——> TiCl4(l) + 2CO(g) •which is then reduced with sodium. TiCl4(l) + 4Na(s) ——> Ti(s) + 4NaCl(s) The reduction of TiCl4 is carried out in an atmosphere of argon because the titanium reacts with oxygen at high temperatures. Titanium is STRONG and RESISTANT TO CORROSION so is used in making ARTIFICIAL JOINTS.

  31. ALUMINIUM

  32. EXTRACTION OF ALUMINIUM Aluminium is above carbon in the series so it cannot be extracted from its ores in the same way as carbon. Electrolysis of molten aluminium ore (alumina) must be used As energy is required to melt the alumina and electrolyse it, a large amount of energy is required.

  33. EXTRACTION OF ALUMINIUM RAW MATERIALS BAUXITE aluminium ore Bauxite contains alumina (Al2O3 aluminium oxide) plus impurities such as iron oxide – it is purified before use.

  34. EXTRACTION OF ALUMINIUM RAW MATERIALS BAUXITE aluminium ore Bauxite contains alumina (Al2O3 aluminium oxide) plus impurities such as iron oxide – it is purified before use. CRYOLITEAluminiumoxidehasavery high melting point. Adding cryolite lowers the melting point and saves energy.

  35. EXTRACTION OF ALUMINIUM ELECTROLYSIS Unlike iron, aluminium cannot be extracted using carbon. (Aluminium is above carbon in the reactivity series)

  36. EXTRACTION OF ALUMINIUM ELECTROLYSIS Unlike iron, aluminium cannot be extracted using carbon. (Aluminium is above carbon in the reactivity series) Reactive metals are extracted using electrolysis

  37. EXTRACTION OF ALUMINIUM ELECTROLYSIS Unlike iron, aluminium cannot be extracted using carbon. (Aluminium is above carbon in the reactivity series) Reactive metals are extracted using electrolysis Electrolysis is expensive - it requires a lot of energy… - ore must be molten (have high melting points) - electricity is needed for the electrolysis process

  38. EXTRACTION OF ALUMINIUM ELECTROLYSIS SOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITY THIS IS BECAUSE THE IONS ARE NOT FREE TO MOVE

  39. EXTRACTION OF ALUMINIUM ELECTROLYSIS SOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITY THIS IS BECAUSE THE IONS ARE NOT FREE TO MOVE DISSOLVING IN WATER or… MELTING ALLOWS THE IONS TO MOVE FREELY

  40. EXTRACTION OF ALUMINIUM ELECTROLYSIS SOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITY THIS IS BECAUSE THE IONS ARE NOT FREE TO MOVE DISSOLVING IN WATER or… MELTING ALLOWS THE IONS TO MOVE FREELY POSITIVE IONS MOVE TO THE NEGATIVE ELECTRODE NEGATIVE IONS MOVE TO THE POSITIVE ELECTRODE

  41. EXTRACTION OF ALUMINIUM

  42. EXTRACTION OF ALUMINIUM CARBON ANODE THE CELL CONSISTS OF A CARBON ANODE

  43. EXTRACTION OF ALUMINIUM STEEL CATHODE CARBON LINING THE CELL CONSISTS OF A CARBON LINED STEEL CATHODE

  44. EXTRACTION OF ALUMINIUM MOLTEN ALUMINA and CRYOLITE ALUMINA IS DISSOLVED IN MOLTEN CRYOLITE Na3AlF6 SAVES ENERGY - the mixture melts at a lower temperature

  45. EXTRACTION OF ALUMINIUM MOLTEN ALUMINA and CRYOLITE ALUMINA IS DISSOLVED IN MOLTEN CRYOLITE Na3AlF6 aluminium and oxide ions are now free to move

  46. Al3+ + 3e- Al EXTRACTION OF ALUMINIUM POSITIVE ALUMINIUM IONS ARE ATTRACTED TO THE NEGATIVE CATHODE CARBON CATHODE EACH ION PICKS UP 3 ELECTRONS AND IS DISCHARGED

  47. O2- O + 2e- EXTRACTION OF ALUMINIUM NEGATIVE OXIDE IONS ARE ATTRACTED TO THE POSITIVE ANODE CARBON ANODE EACH ION GIVES UP 2 ELECTRONS AND IS DISCHARGED

  48. EXTRACTION OF ALUMINIUM ELECTRONS CARBON ANODE CARBON CATHODE

  49. EXTRACTION OF ALUMINIUM ELECTRONS OXIDATION (LOSS OF ELECTRONS) TAKES PLACE AT THE ANODE CARBON ANODE ANODE 3O2- 1½O2 + 6e-OXIDATION

  50. EXTRACTION OF ALUMINIUM ELECTRONS OXIDATION (LOSS OF ELECTRONS) TAKES PLACE AT THE ANODE REDUCTION (GAIN OF ELECTRONS) TAKES PLACE AT THE CATHODE CARBON CATHODE ANODE 3O2- 1½O2 + 6e- OXIDATION CATHODE 2Al3+ + 6e- 2Al REDUCTION