Extraction of Metals

GENERAL PRINCIPLES General principles 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

GENERAL PRINCIPLES General principles 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

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.

Reactivity Series 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.

Specific methods to learn • 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

IRON

EXTRACTION OF IRON high temperature process continuous 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

RAW MATERIALS HAEMATITE - Fe2O3 a source of iron COKE fuel / reducing agent CHEAP AND PLENTIFUL LIMESTONE conversion of silica into slag (calcium silicate) – USED IN THE CONSTRUCTION INDUSTRY AIR source of oxygen for combustion

G A C D B B E F THE BLAST FURNACE 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

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

HOT AIR IS BLOWN IN NEAR THE BOTTOM 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. CARBON + OXYGEN CARBON + HEAT DIOXIDE C + O2 CO2 B B Now move the cursor away from the tower

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

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

CALCIUM SILICATE (SLAG) IS PRODUCED MOLTEN SLAG IS RUN OFF AND COOLED 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 CaCO3 CaO + CO2 CaO + SiO2 CaSiO3 E Now move the cursor away from the tower

F 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

HOT WASTE GASES ARE RECYCLED TO AVOID POLLUTION AND SAVE ENERGY THE BLAST FURNACE G HOT WASTE GASES ARE RECYCLED TO AVOID POLLUTION AND SAVE ENERGY CARBON MONOXIDE - POISONOUS SULPHUR DIOXIDE - ACIDIC RAIN CARBON DIOXIDE - GREENHOUSE GAS RECAP

Waste gases and pollution SULPHUR DIOXIDE • sulfur is found in the coke; sulfides occur in the iron ore • burning sulfur and sulfides S + O2 ——> SO2 produces sulfur dioxide • sulfur dioxide gives SO2 + H2O ——> H2SO3 rise to acid rain sulfurous acid CARBON DIOXIDE • burning fossil fuels increases the amount of this greenhouse gas

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

Exam Questions – Q7a Q7. This question is about the extraction of metals. (a) Coke is mainly carbon and is a raw material used in the extraction of iron from iron(III) oxide. (i) Write an equation for the formation of carbon monoxide from carbon. ............................................................................................................. (1) (ii) Write an equation for the reduction of iron(III) oxide to iron by carbon monoxide. (iii) The Earth’s resources of iron(III) oxide are very large and commercial ores have a high iron content. Give one economic and one environmental reason for recycling scrap iron and steel. Economic reason ................................................................................ Environmental reason ......................................................................... (2)

Q7 Answer M7. (a) (i) 2C + O2 → 2CO OR C + CO2 → 2CO 1 (iii) Economic: • Scrap iron/steel has higher iron content. • Recycling involves lower energy consumption • Blast furnace not required Ignore cost 1 Environmental: • Reduces greenhouse gas / CO2/ SO2 emission. • Reduces acid rain • Reduces mining • Reduces landfill • Removes an eyesore M7. (a) (i) 2C + O2 → 2CO OR C + CO2 → 2CO 1 (ii) Fe2O3 + 3CO → 2Fe + 3CO2 1

Exam Questions – Q9 a and b Iron is extracted from iron(III) oxide in a continuous process, whereas titanium is extracted from titanium(IV) oxide in a batch process. (a) Suggest why a high-temperature batch process is less energy-efficient than a high temperature continuous process. ...................................................................................................................... (2) (b) Write an overall equation for the reduction of iron(III) oxide in the Blast Furnace.

Q9 Answer M9. (a) Batch process involves stopping and starting (1) Energy lost when cools down after stopping or energy needed to heat up each time (1) (b) Fe2O3+ 3C → 2Fe + 3CO use of C or CO (1) balance (1) or Fe2O3 + 3CO → 2Fe + 3CO2 or 2Fe2O3+ 3C → 4Fe + 3CO2

Exam Questions – Q12 a Q12. (a) When iron(III) oxide is reduced in the Blast Furnace, both carbon and carbon monoxide act as reducing agents. (i) Write an equation to illustrate how carbon monoxide is formed in the Blast Furnace. ............................................................................................................. (ii) Write an equation to illustrate how carbon monoxide reduces iron(III) oxide. (iii) Suggest in terms of collisions why, in the Blast Furnace, carbon monoxide reacts more rapidly with iron(III) oxide than does carbon. (4)

Answer Q12 M12. (a) (i) C + CO2 → 2CO (or 2C + O2 → 2CO, or carbon reduction of an iron oxide) 1 (ii) 3CO + Fe2O3 →3CO2 + 2Fe (iii) CO is gaseous (or C is solid) CO has more collisions (or C has very few collisions)

Exam Questions –Q15 a Q15. (a) Iron is extracted in a Blast Furnace by a continuous reduction process. Identify two reducing agents present in the Blast Furnace. In each case, write an equation to show how the reducing agent reacts in the formation of iron. Reducing agent 1 ......................................................................................... Equation ....................................................................................................... Reducing agent 2 .........................................................................................

Answer Q15 Reducing agent 1: C(1) (or coke) Not coal Equation: 3C + Fe2O3 → 3CO + 2Fe (1) or + 2Fe2O3 → 3CO2+ 4Fe C + O2 → CO2 C + ½ O2 →CO CO2 + C → 2CO penalise Fe2 (allow Fe3O4 and FeO) Reducing agent 2: CO (1) Equation: 3CO + Fe2O3 → 3CO2+ 2Fe (1) (again allow Fe3O4, FeO) Equation mark depends on correct reducing agent

TITANIUM

Titanium extraction TiO2 (s) + 3C (s) TiC (s) + 2CO (g) • 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 TiO2 (s) + 3C (s) TiC (s) + 2CO (g) • the extraction is a batch process so there is much time wasted and heat lost; this makes it even more expensive

The titanium oxide is first converted to titanium chloride by heating it with carbon in a stream of chlorine gas TiO2(s) + 2C(s) + 2Cl2(g) ——> TiCl4(l) + 2CO(g) The titanium chloride is then purified using fractional distillation under an inert atmosphere of argon or nitrogen The titanium chloride is then reduced in a furnace using either sodium or magnesium TiCl4(l) + 4Na(s) ——> Ti(s) + 4NaCl(s) TiCl4(l) + 2Mg(s) ——> Ti(s) + 2MgCl(s) The reduction of TiCl4 is carried out in an atmosphere of argon because the titanium reacts with oxygen at high temperatures.

Exam Questions – Q1 Q1. Metals can be extracted by different methods. (a) Give one reason why titanium cannot be extracted directly from titanium(IV) oxide using carbon. ........................................................................................................................ (1) (b) Titanium steel is an alloy of titanium and iron. Titanium steel is extracted from the mineral ilmenite (FeTiO3) in a two-stage process. Purified FeTiO3 is first converted into a mixture of two metal chlorides. These two metal chlorides are then reduced simultaneously using sodium. (i) Write an equation for the reaction of FeTiO3 with chlorine and carbon to produce iron(III) chloride (FeCl3), titanium(IV) chloride and carbon monoxide. ............................................................................................................... (ii) Write an equation for the simultaneous reduction of the mixture of iron(III) chloride and titanium(IV) chloride to iron and titanium using sodium.

Answer Q1 M1. (a) Ti is not produced OR TiC / carbide is produced OR titanium reacts with carbon Product is brittle (b) (i) FeTiO3+ 3½Cl2+ 3C FeCl3+ TiCl4+ 3CO (ii) FeCl3+ TiCl4 + 7Na 7NaCl + Fe + Ti 2FeCl3+ TiCl4 + 10Na 10NaCl + 2Fe + Ti Ignore state symbols Credit multiples including

Exam Question – 5d 5(d) Magnesium is used in the extraction of titanium. (i) Write an equation for the conversion of titanium(IV) oxide into titanium(IV) chloride. ............................................................................................................. (2) (ii) Write an equation for the extraction of titanium from titanium(IV) chloride using magnesium. (1) (iii) State the role of magnesium in this extraction.

Answer 5d (ii) TiCl4+ 2Mg Ti + 2MgCl2 Or multiples (d) (i) M1 use of Cl2 and C M2 balanced equation consequential on correct reactants TiO2+ 2Cl2+ 2C TiCl4+ 2CO OR TiO2 + 2Cl2 + C TiCl4 + CO2 (ii) TiCl4+ 2Mg Ti + 2MgCl2 Or multiples Ignore state symbols 1 (iii) Reducing agent OR reduces TiCl4 OR Electron donor Credit “reduction” or “reductant” Penalise “electron pair donor”

Exam Question – 7b 7(b) Pure titanium is extracted by the reduction of titanium(IV) chloride, but not by the direct reduction of titanium(IV) oxide using carbon. (i) Write an equation for the conversion of titanium(IV) oxide into titanium(IV) chloride. ............................................................................................................. (2) (ii) Write an equation for the extraction of titanium from titanium(IV) chloride. (iii) State why titanium is not extracted directly from titanium(IV) oxide using carbon. (1)

Answer 7b (b) (i) M1 Use of Cl2 and C M2 Balanced equation consequential on correct reactants EITHER TiO2+ 2Cl2+ 2C → TiCl4 + 2CO OR TiO2 + 2Cl2 + C → TiCl4 + CO2 (ii) M1 Use of Na OR Mg TiCl4+ 4Na → Ti + 4NaCl TiCl4 + 2Mg → Ti + 2MgCl2 (iii) One from • TiC / carbide is produced • Product is brittle • Product is a poor engineering material

Exam Question – 11c 11(c) Identify a reducing agent used to obtain titanium metal from titanium(IV) chloride. In addition to a high temperature, state a condition that is used for this reaction and explain why this condition is necessary. Reducing agent ........................................................................................... Condition ..................................................................................................... Explanation ..........................................................................................................

Answer 11c (c) Na (or Mg); Argon; Na (or Mg or TiCl4) reacts with air (or oxygen or water) ( or impurities of O or N in Ti);

Exam Question – 18b 18 (b) (i) State why carbon cannot be used to reduce titanium(IV) oxide directly to titanium. ............................................................................................................. (ii) Carbon is used in one of the steps in the batch process for titanium extraction. Write an equation for the reaction which occurs in this step and state a condition under which this reaction is carried out. Equation .............................................................................................. Condition ............................................................................................. (4)

Answer 18b (b) (i) (Titanium) carbide is formed (1) Allow C bonds / reacts with Ti ii) Equation: TiO2+ 2C (or C) + 2Cl2 → TiCl4+ 2CO (or CO2) (1) (1) All species correct (1) Balanced equation Condition: High temperature (1) or (700 – 1100°C) NOT “heat” Mark independently

ALUMINIUM

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.

Raw Materials BAUXITE aluminium ore Bauxite contains alumina (Al2O3 aluminium oxide) plus impurities such as iron oxide – it is purified before use.

Raw Materials BAUXITE aluminium ore Bauxite contains alumina (Al2O3 aluminium oxide) plus impurities such as iron oxide – it is purified before use. CRYOLITE Aluminium oxide has a very high melting point. Adding cryolite lowers the melting point and saves energy.

Electrolysis Unlike iron, aluminium cannot be extracted using carbon. (Aluminium is above carbon in the reactivity series)

Electroylsis Unlike iron, aluminium cannot be extracted using carbon. (Aluminium is above carbon in the reactivity series) Reactive metals are extracted using electrolysis

Electroylsis 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

Electrolysis THIS IS BECAUSE THE IONS ARE NOT FREE TO MOVE SOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITY THIS IS BECAUSE THE IONS ARE NOT FREE TO MOVE

THIS IS BECAUSE THE IONS ARE NOT FREE TO MOVE 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

THIS IS BECAUSE THE IONS ARE NOT FREE TO MOVE 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

EXTRACTION OF ALUMINIUM

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

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

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

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

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

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

EXTRACTION OF ALUMINIUM ELECTRONS CARBON ANODE CARBON CATHODE

EXTRACTION OF ALUMINIUM ELECTRONS OXIDATION (LOSS OF ELECTRONS) TAKES PLACE AT THE ANODE CARBON ANODE ANODE 2O2- O2 + 4e- OXIDATION

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 Al3+ + 3e- Al REDUCTION

EXTRACTION OF ALUMINIUM ELECTRONS OXIDATION (LOSS OF ELECTRONS) TAKES PLACE AT THE ANODE CARBON ANODE REDUCTION (GAIN OF ELECTRONS) TAKES PLACE AT THE CATHODE CARBON CATHODE ANODE 2O2- O2 + 4e- OXIDATION CATHODE Al3+ + 3e- Al REDUCTION

PROBLEM EXTRACTION OF ALUMINIUM CARBON DIOXIDE PROBLEM THE CARBON ANODES REACT WITH THE OXYGEN TO PRODUCE CARBON DIOXIDE CARBON ANODE

PROBLEM EXTRACTION OF ALUMINIUM CARBON DIOXIDE PROBLEM THE CARBON ANODES REACT WITH THE OXYGEN TO PRODUCE CARBON DIOXIDE CARBON ANODE THE ANODES HAVE TO BE REPLACED AT REGULAR INTERVALS, THUS ADDING TO THE COST OF THE EXTRACTION PROCESS

Properties of aluminium ALUMINIUM IS NOT AS REACTIVE AS ITS POSITION IN THE REACTIVITY SERIES SUGGESTS THIS IS BECAUSE A THIN LAYER OF ALUMINIUM OXIDE QUICKLY FORMS ON ITS SURFACE AND PREVENTS FURTHER REACTION TAKING PLACE THIN LAYER OF OXIDE ANODISING PUTS ON A CONTROLLED LAYER SO THAT THE METAL CAN BE USED FOR HOUSEHOLD ITEMS SUCH AS PANS AND ELECTRICAL GOODS

Exam Question – 7C 7(c) Aluminium is extracted by the electrolysis of a molten mixture containing aluminium oxide. (i) State why the electrolysis needs to be of a molten mixture. ............................................................................................................. (1) (ii) Write an equation for the reaction of oxide ions at the positive electrode during the electrolysis. (iii) State why the positive electrodes need frequent replacement. (iv) Give the major reason why it is less expensive to recycle aluminium than to extract it from aluminium oxide by electrolysis.

Answer 7C (c) (i) One from To allow • ions to move • current to flow • it to conduct electricity (ii) 2O2– → O2 + 4e– (iii) Carbon / graphite / the electrodes oxidise OR Carbon / graphite / the electrodes burn in / react with the oxygen formed carbon dioxide / CO2 is formed (iv) Recycling involves lower electricity OR less energy consumption The converse for electrolysis Ignore references to raw materials The answer MUST show some evidence of comparison e.g. lower or less

Exam Question – 11D 11(d) (i) State two essential conditions used for the electrolytic extraction of aluminium from aluminium oxide. Condition 1 .......................................................................................... Condition 2 .......................................................................................... ............................................................................................................. (ii) Write an equation to illustrate how aluminium is formed from aluminium ions in this process. (3)

Answer 11D (d) (i) cryolite; 1 Molten (or liquid or solution); (ii) Al3+ + 3e– → Al;

CHROMIUM

Extraction of Chromium The method of extraction often depends on the purity required. IMPURE CHROMIUM The ore (chromite) is reduced by heating with carbon. ... FeCr2O4(s) + 4C(s) ——> Fe(s) + 2Cr(s) + 4CO(g)

Extraction of Chromium PURE CHROMIUM The chromite is converted to chromium(III) oxide which is then reduced using aluminium at high temperatures. This is known as ACTIVE METAL REDUCTION. Cr2O3(s) + 2Al(s) ——> 2Cr(s) + Al2O3(s)

Other Extractions needed

Tungsten The extraction of tungsten is carried out using Hydrogen It is expensive and explosive WO3 (s) + 3H2 (g) W (s) + 3H2O (l)

Sulfide Ores Lead Sulfide and Zinc sulfide Roast the sulfide in air to turn it into an oxide 2Zn (s) + 3O2 (g) 2ZnO (s) + 2SO2 (g) Bad – Releases sulfur dioxide (acid rain) Good – Can convert it into sulfuric acid The oxide can then be reduced to the metal

Molybdenum extraction 1st stage is to roast the ore in the air to remove sulfur MoS2 + 3 ½ O2 MoO3 + 2SO2 Pure molybdenum is then reduced using hydrogen MoO3 + 3H2 Mo + 3H2O

Other reductions that come up regularly in CHEM 2 Iron (III) oxide 2Fe2O3 + 3C 4Fe + 3CO2 Fe2O3 + 3CO 2Fe + 3CO2 Manganese dioxide (manganese (IV) oxide) MnO2 + C Mn + CO2 MnO2 + 2CO Mn + 2CO2

Copper carbonate heat directly with carbon 2CuCO3 + C 2Cu + 3CO2 Or Heat until it decomposes then reduce the oxide with carbon CuCO3 CuO + CO2 Then 2CuO + C 2Cu + CO2

Scrap iron and copper extraction Works with a low grade ore in solution Acidified water dissolves the copper compounds in the ore Scrap iron is added, the iron dissolves and reduces the copper (II) ions. The copper then precipitates out of the solution Slower and only a low yield produced but it is cheaper and it doesn’t need a high temp or produce CO2 Cu2+ (aq) + Fe (s) Cu (s) + Fe 2+ (aq)

(c) Scrap iron is used to extract copper from dilute aqueous solutions containing copper(II) ions. Explain, in terms of redox, what happens to the copper(II) ions in this extraction. ........................................................................................................... Either order Penalise reference to incorrect number of electrons in M1 M1 The Cu2+ / copper(II) ions / they have gained (two) electrons OR Cu2+ + 2e– Cu For M1, accept “copper” if supported by correct half-equation or simplest ionic equation OR oxidation state / number decreases (or specified from 2 to 0) Ignore charge on the electron M2 The Cu2+ / copper(II) ions / they have been reduced For M2 do not accept “copper” alone 2

Extraction of magnesium in sea water React Mg ions with hydroxide ions to form magnesium hydroxide Mg2+ + 2OH- Mg(OH)2 Next react with HCl to give magnesium chloride Mg(OH)2 + 2HCl MgCl2 + 2H2O Final step MgCl2 is electrolysed to form magnesium and chlorine

Recycling Problems • high cost of collection and sorting • unsightly plant • high energy process Benefits • less visible pollution of environment by waste • provides employment • reduces the amount of new mining required • maintains the use of valuable resources • strategic resources can be left underground