Metal extraction

S t udents name & pen no. Sr no.NameEnrollment number 1Kakadiya Rajan Vasoya Parth Dangariya Milan Godhani digjay Dhudhat Mayur Beladiya rakesh Guide by :- Amish B. Patel Guide by :- Amish B. Patel

Contents :- 1. Principles of metal extraction 2. Reactivity series 3.Electrochemical series 4.Method of metal extraction 5.Extraction of Iron 6.Extraction of Aluminium

Principles of Metal extraction Most elements do not occur as separate substances but exist naturally as compounds. Metals tend to exist as metal oxides as part of ores which are excavated from the earth. To recover the metal from it’s oxide the metal ion is split from the oxygen ion. Metals high up on the activity series have more stable oxides than those lower down and due to this are more difficult to split up than those lower down.

The Reactivity Series. The Reactivity Series is a list of metals arranged in order of reactivity. Potassium is the most reactive metal and thus is on top of the series. Hydrogen is a non-metal but is placed in this series to show that the metals below it do not react with acids to produce Hydrogen gas. Metal Potassium Sodium Calcium Magnesium Aluminium Zinc Iron Lead Hydrogen Copper Mercury Silver Gold Symbol K Na Ca Mg Al Zn Fe Pb H Cu Hg Ag Au

The Electrochemical Series. The electrochemical series is a listing that places ions in order of ease of electrical discharge. The lower an element is in the series then the easier it is to discharge. Cations K + Ca 2+ Na + Al 3+ Zn 2+ Fe 2+ Pb 2+ H + Cu 2+ Ag + Au + Anions SO 4 2- NO 3 - Cl - Br - I - OH -

Methods of metal extraction 1.Electrolyis 2. Reduction with carbon(carbon monoxide) 3. Heating of the ore.

Electrolysis : this entails the immersing of a positively and negatively charged electrical poles to a molten or aqueous solution of a substance. The passage of the current causes positively charged ions to be attracted to the negative pole and negatively charged ions to be attracted to the positively charged pole. While at the Negative pole, positively charged ions gain electrons to become neutral atoms and are deposited on the negative pole or fall to the bottom as a precipitate. The same occurs to positively charged ionsat the negative pole. The overall effect is that the constituents of the substance are separated and usually are deposited on the Positive Pole or Anode and the Negative pole or Cathode or it may sink to the bottom of the container as a precipitate

1.Electrolyis: Most powerful means of extraction. most expensive. Can only be used where electricity is abundant. 2. Reduction with carbon(carbon monoxide) Cheaper to operate than electrolysis. Labor intensive. Expensive to startup as large industrial equipment is used. 3. Heating of the ore. Cheap Can only be used on the most unreactive of metals(Mercury,gold,silver,etc.)

Extraction of Iron The extraction of Iron is a reductive process whereby oxygen is removed from the iron oxide by carbon monoxide. The process occurs within a Steel blast furnace lined with refractive(fire) bricks at temperatures from 800C upto 1900C. The Chamber is kept hot by jets of hot air at over 800C, giving it the name “Blast” furnace.

Start materials: –Iron Ore or Hematite –Lime or Calcium carbonate CaCO3 –Coke a carbonaceous ashy substance Iron Ore Lime Coke

Extraction of Iron: Step1 Burning of Lime Iron ore, limestone(CaCO3) and coke are delivered to the top of the blast furnace, where the temperature is around 800C. The lime stone burns at 800C yielding calcium oxide(CaO) and Carbon Dioxide(CO2). CaCO3 -> CaO + CO2 The Calcium oxide causes impurities which are present with the ore to fall as a precipitate near to the bottom producing a layer of “slag”.

Extraction of Iron: Step 2 Production of Carbon monoxide Coke

Extraction of Iron: Step 3 Reduction of Iron The Carbon monoxide yielded from the reaction of Carbon dioxide and lime removes the oxygen from Iron oxide. Each Carbon monoxide molecule is capable of binding a single oxygen so 3 are used to completely remove all oxygen from the iron oxide. Fe2O3 + 3 CO -> 2Fe(s) + 3 CO2 The molten iron sinks to the bottom lowest level of the furnace, where it can be tapped off. The iron produced by this process is called pig iron and is 95% pure.

Extraction of Iron: overview Production of iron from it’s ore uses Carbon monoxide to reduce Iron oxide to iron atoms. 1.Lime burns CaCO3----> CaO + CO2 2. CO2 reduced by coke to CO CO2 + C-----> 2 CO 3. Iron oxide reduced by CO Fe2O3 + 3CO----> 2Fe + 3CO2 Removes impuritiies : slag production

Extraction Of Aluminium Aluminium is very abundant in the earth’s crust, but is never found in its free state. Aluminium is found mainly in the form of aluminosilicates, of which bauxite (Al 2 O 3 ) is the chief source. The crude/mined bauxite is either: heated to 3000 o C to produce calcined bauxite Converted to pure alumina (Al 2 O 3 )

The process for extracting aluminium from aluminia is electrolysis. Electrolysis is the process by which the passage of an electric current through a substance causes it to decompose. In the current process of extracting aluminium from bauxite, an electrolytic cell made of steel using graphite electrodes is used. The current used is 100,000A and the temperature is 1,223K. Electrolysis of Aluminium

Pure aluminia (aluminium oxide) which melts at 2050 o C is dissolved in molten cryolite (sodium aluminium fluoride), Na 2 AlF 6. The addition of the cryolite lowers the temperature to 950 o C, because the presence of an impurity lowers the melting point of a substance. The presence of the cryolite also gives the melt better conducting properties and, in addition, it does not mix with the aluminium metal formed in the electrolysis.

Aluminium is discharged at the graphite cathode, which lines the chamber. The product is 99% pure, the chief impurities being silicon and iron. Liquid aluminium is tapped off at the end of the cell. Al 3+ (l) + 3e - Al (l) Oxygen is the other product that is produced at the anode. 2O 2- (l) - 4e - O 2(g)

Electrolysis of Aluminium.

Alumina - Bauxite is the most important aluminous ore for the production of alumina. Bauxite occurs close to the surface in seams varying from one meter to nine meters, formed as small reddish pebbles (pisolites). Bauxite contains 40 to 60 mass% alumina combined with smaller amounts of silica, titania and iron oxide. Alumina is mainly extracted from bauxite using Bayer Process. Bayer process

The Bayer process dissolves the aluminium component of bauxite ore in sodium hydroxide (caustic soda); removes impurities from the solution; and precipitates alumina tri hydrate, which is then calcined to aluminium oxide. A Bayer Process plant is principally a device for heating and cooling a large re circulating stream of caustic soda solution. Bauxite is added at the high temperature point, red mud is separated at an intermediate temperature, and alumina is precipitated at the low temperature point in the cycle. Alumina (aluminium oxide Al2O3) obtained is a fine white material similar in appearance to salt. Alumina is also used in abrasive, ceramics and refectory industries.

THE BAUXITE PURIFICATION PROCESS To produce metal of high quality it is essential to start with alumina of high purity and to strictly control the reduction process. The process consists of two parts: 1.Chemical purification of raw materials to form a high purity alumina. 2. Reduction of alumina. The major raw materials used in the manufacture of aluminium Other raw materials include oil for manufacture of electrode blocks and the metals for alloying with pure aluminium.

Step 1 - Purification of Raw Materials The bauxite is open cast mined, crushed and washed before shipping around Cape York and then south down the Queensland coast to Gladstone, which is at the southern end of the Barrier Reef. There it is purified to alumina using the Bayer process which is based on the fact that silica is an acidic oxide, alumina is amphoteric and both iron oxide and titania are basic. The crushed ore is mixed with caustic soda (NaOH) solution and heated. This dissolves the alumina and some reactive crystalline forms of silica but has no effect on the iron oxide, the titania, or most of the silica which is already combined with other elements. These can then be filtered off.

Al2O3 + 6NaOH + 3H2O → 2Na3Al(OH)6 SiO2 + 4NaOH → Na4SiO4 + 2H2O When the solution of alumina and silica is cooled, a complex aluminosilicate "sand" is first precipitated out before altering process conditions allows pure aluminium hydroxide to crystallise out. This is speeded up by initially adding a small quantity of pure crystalline aluminium hydroxide to act as sites for crystal growth. Na3Al(OH)6 + 2H2O → 3NaOH + Al(OH)3.3H2O The pure crystals of aluminium hydroxide Al (OH)3.3H2O are heated to 1100oC, causing them to decompose to alumina (Al2O3) and water. 2Al(OH)3.3H2O + heat → Al2O3 + 9H2O

Step 2 - Reduction of Alumina (Hall- Heroult process ) Aluminium metal is not produced directly by the electrochemical reduction of alumina: 2Al2O3 → 4Al + 3O2 Rather, it is reduced by a combination of chemical and electrical energy according to the following two reactions in parallel: Al2O3 + 3C → 2Al + 3CO 2Al2O3 + 3C → 4Al + 2CO2 This use of a consumable carbon anode lowers the required voltage by 1.0 V at the operating temperature of oC.

Alumina is a covalently bonded oxide so it can only be electrolysed when the aluminium is in an ionic form. It is dissolved in molten cryolite, Na3AlF6 (an electrolyte, i.e. an ionic compound), and forms conducting complex anionic oxyfluorides. The electrolysis requires a large amount of energy because aluminium's affinity for oxygen makes the reaction 4Al + 3O2 → 2Al2O3 highly exothermic. The enthalpy of formation of Al2O3 is kJ mol-1. The electrolysis is carried out in an electric furnace using carbon electrodes. Figure shows a cross section of a cell or electric furnace, and Figure is a photograph of one of the four pot-rooms.

Each cell is four metres wide and ten metres long, and shaped like a shallow bath. The base is lined with carbon and forms the cathode on which aluminium is deposited. Suspended above the bath and dipping into the molten alumina-cryolite mix are 18 carbon blocks (the anodes) which are electrochemically oxidised using the oxide ions. Each carbon block has enough material to last 24 to 28 days in the cell. A current of approxiamtely amperes is passsed through each pot, with a voltage drop of 4.2 to 4.4 volts. This maintains the pot at an operating temperature of nearly 1000 oC as well as causing reduction of the alumina. The molten aluminium collects on the carbon cathode and is syphoned out at a rate of approximately a tonne per day.

OCCURRENCE OF COPPER Copper pyrite or chalcopyrite (CuFeS 2 ). Chalocite (Cu 2 S) or copper glance. Malachite green [CuCO 3.Cu(OH ) 2 Azurite blue [2CuCO 3.Cu(OH) 2 ]. Bornite (3Cu 2 S.Fe 2 S 3 ) or peacock ore. Melaconite (CuO) etc. STEPS INVOLVED IN EXTRACTION CONCENTRATION ROASTING SMELTING BESSEMERIZATION REFINING

The finely crushed ore is concentrated by Froth-Floatation process. The finely crushed ore is suspended in water containing a little amount of pine oil. A blast of air is passed through the suspension. The particles get wetted by the oil and float as a froth which is skimmed.The gangue sinks to the bottom. CONCENTRATION OF ORE

FROTH FLOATATION PROCESS

ROASTING The following reaction takes place. 2CuFeS 2 + O 2  Cu 2 S + 2FeS + SO 2 S + O 2  SO 2 4As + 3O 2  2As 2 O 3 4Sb + 3O 2  2Sb 2 O 3 Cuprous sulphide and ferrous sulphide are further oxidized into their oxides. 2Cu 2 S + 3O 2  2Cu 2 O + 2SO 2 2FeS + 3O 2  2FeO + 2SO 2

SMELTING PROCESS (REDUCTION BY CARBON) SMELTING IS CARRIED OUT IN BLAST FURNACE 1 HOT AIR BLAST 2 MELTING ZONE 3, 4 REDUCTION ZONE 5 PREHEATING ZONE 6 ORE,SILICA,COKE 7 EXHAUST GASES 8COLUMN OF ORE,SILICA,COKE 9 REMOVAL OF SLAG 10 MOLTEN MATTER 11COLLECTION OF WASTE GASES

PROCESS OF SMELTING The roasted ore is mixed with coke and silica (sand) SiO 2 and is introduced in to a blast furnace. The hot air is blasted and FeO is converted in to ferrous silicate FeSiO 3

SMELTING The roasted ore is mixed with coke and silica (sand) SiO 2 and is introduced in to a blast furnace. The hot air is blasted and FeO is converted in to ferrous silicate (FeSiO 3 ). FeO + SiO 2  FeSiO 3 Cu 2 O + FeS  Cu 2 S + FeO FeSiO 3 (slag) floats over the molten matte of copper

BESSEMERIZATION Copper metal is extracted from molten matte through bessemerization. The matte is introduced in to Bessemer converter which uphold by tuyers. The air is blown through the molten matte. Blast of air converts Cu 2 S partly into Cu 2 O which reacts with remaining Cu 2 S to give molten copper.

BESSEMERIZATION 2Cu 2 S + 3O 2  2Cu 2 O + 2SO 2 2Cu 2 O + Cu 2 S  6Cu + SO 2

REFINING OF COPPER Blistercopper is refined by electrolysis. Blocks of blister copper are used as anodes and thin sheets of pure copper act as cathodes. The cathode plates are coated with graphite in order to remove depositing copper. The electrolyte is copper sulphate (CuSO 4 ) mixed with a little amount of H 2 SO 4 to increase the electrical conductivity. Optimum potential difference is 1.3 volt for this electrolytic process

Continue… During electrolysis, pure copper is deposited on the cathode plates and impurities which are soluble and fall to the bottom of the cell as anode mud or sludge.

REFINING OF COPPER Cu  Cu e- (at the anode) Cu +2 +2e-  Cu (at the cathode) This electrically refined copper is 100% pure