Extraction of Copper from Copper pyrite
The principle ore of copper is copper pyrite and copper is extracted from this ore. The different steps in extraction of copper are:
Crushing and Concentration:
The ore obtained from mines are broken down into small piece by jaw crusher and then pulverized. The ore being sulphide ore is concentrated by froth floatation process. Pulverized ore is kept in water containing pine oil and the mixture is agitated by passing compressed air. Ore forms froth with pine oil and comes to the surface and is skimmed off while impurities are left in water.
Roasting
The concentrated ore is heated in excess supply of air on the hearth of reberberatory furnace below its melting point. The different changes during roasting are:
a. Moisture and volatile impurities are driven out.
b. Non-metallic impurities like sulphur, phosphorous, arsenic etc. are removed as their oxides.
S + O2 → SO2
P4 + SO2 → 2P2O5
c. Copper pyrite dissociates into individual sulphide
2CuFeS2 + O2 → Cu2S + 2FeS + SO2 major r × n
Small amount of metal sulphides are oxidized to oxides.
2FeS + 3O2 → 2FeO + SO2 minor reaction
2Cu2S + 3O2 → 2CuO + 2SO2
Smelting
The roasted ore, coke and silica (flux) is charged a water jacketed blast furnace when hot air is passed into blast furnace. Fes if oxidized to FeO which combines with S1O2 to form ferrous silicate as slag.
2FeS + 3O2 → 2FeO + 2SO2
FeO + S1O2 → FeS1O3
Flux Ferrous Silicate
As long as Fes is present in the mixture Cu2O can’t be formed as copper has higher affinity for sulphur than oxygen. In molten state FeS & Cu2S are missible and the molten mixture of Cu2S and FeS is called copper malte. The lower end of blast furnace has two openings for slag and copper matte.
Fig: Blast Furnace for extraction of copper
Bassemerisation
The molten matte is mixed with little silica and charged into a Bessemer converter. Lined internally by basic lining of CaO or MgO. Hot air is blown into the mixture which converts remaining FeS. To FeSiO3.
2FeS + 3O2 → 2FeO + 2SO2
FeO + SiO2 → FeSiO3 (slag)
The slag is removed and air is passed. The air oxidized Cu2S partially to Cu2O which then reduces remaining Cu2S to metallic copper. During this process no external reducing agent is used so it is an example of self-reduction.
2CuS + 3O2 → 2Cu2O + 2SO2
2Cu2O + Cu2S → 6Cu + SO2
The reaction is highly exothermic and copper obtained is in molten state. During solidification, SO2 escapes forming blisters on the surface of metal. This variety of copper containing about 2% of impurity is blister copper.
Refining:
Blister copper consists of about 2% of impurities consisting of cliver, Glod, Zinc, Nicket etc. It is mostly purified by electrolytic method. A block of impure copper is anode, a strip of pure copper is cathode while solution of CuSO4 containing dil H2SO4 is e;ectrolyte. On passing current, impure copper dissolves and equivalent amount of pure copper is deposited at cathode. Impurities are collected below anode as anode mud.
CuSO4 (aq) → Cu++ + SO–4
At cathode: Cu++ + 2e → Cu
At anode: Cu → Cu++ + 2e
Physical Properties:
- It is a transition metal having characteristic red color.
- It is highly malleable & ductile and has high electrical and thermal conductivity
- It has high melting point 10830c and bpt 2320c
- It has specific gravity 8.93
Chemical properties
Action of air:
Dry air has no effect but moist air containing CO2gas forms a green layer of basic copper carbonate.
Cu + O2+ CO2 + H2O → CuCO3Cu(OH)2
Moist air basic copper carbonate
On heating in air 9000c, copper forms cupric oxide or black oxide of copper,
4Cu + O2 900 → 2CuO
Cupric oxide
On further heating above 11000c, copper gives cuprous oxide or red oxide of copper.
4Cu + O2 1000 → 2Cu2O
Cuprous oxide
Action of water:
Water has no effect on copper.
Action of Alkalis:
Alkalis has no effect on copper.
Action of Acids:
a) With HNO3
dil HNO3 does not react with copper while moderately conc. HNO3 (1:1) is reduced to Nitric oxide by copper.
3Cu + 8HNO3 → 3Cu (NO3)2 + 2NO + 4H2O
moderately conc.
Conc. HNO3 is reduced to Nitric oxide by copper.
Cu + 4HNO3 → Cu (NO3)2 + 2NO2 + 2H2O
Conc
b) With H2SO4 :
dil. H2SO4 alone does not react but hot dil. H2SO4 in presence of air gives CuSO4
2Cu + 2H2SO4 + O2 → 2CuSO4+2H2O
Hot & dil.
With hot and conc. H2So4, Coppe gives So2 gas.
Cu + 2H2SO4 → CuSO4 +SO2+2H2O
Hot & conc.
c) With HCl:-
Copper reacts with hot and conc HCl in presence of air forming cupric chloride.
2Cu+4HCl+ O2 → 2CuCl2+2H2O
5) Displacement reaction:-
Copper can displace metals lying below it in electrochemical series from their salt solution.
Cu+2AgNo3 → Cu (No3)2+2Ag
3Cu+2Aucl3 → 3Cucl2+2Au
Uses of Copper:-
i) It is in making electrical cables.
ii) It is used in making coins.
iii) It is used in making allays like brass, German Silver.
iv) It is Rold Gold, constantan, bell metal etc.
iv) It is used in making utensits.
v) It is used in making scientifi equipments like calioriemeter boilers .
Extraction of Zinc from Zinc Blende
Concentration:
Zinc blende is concentrated by floath floatation process. The pulverized ore is kept in large tank containing water and pine oil. The mixture is agitated by passing compressed air. Ore forms froth and comes to the surface while impurities are left in water.
Roasting:
The concentrated are is heated in excess supply of air above 9000c on the hearth of reberveratory furnace. During roasting. Zinc sulphide is converted to Zinc Oxide.
2ZnS + 3O2 → 2ZnO + 2SO2
Small amount of ZnS may be oxidized to ZnSO4 but above 9000c , ZnSO4 decompose forming Zinc Oxide (ZnO)
ZnS + 2O2 → ZnSO4
ZnSO4 above 900 → 2ZnO + 2SO2 + O2
Reduction (Smelting):-
ZnO obtained during roasting is mixed with coke and heated strongly where ZnO is reduced to Zn by carbon.
ZnO + C → Zn + CO
The reduction is done in vertical refort. In this process roasted are mixed with coke in the ration of 2:1 and small briquets are made. These briquets are fed into vertical report furnance, from the charging door. The report is heated externally by burning produce gas (w+N2) to about 14000c. The vapour of zn is camed to condenser where it condenses to give molten zinc called spelter zinc.
Purification:-
Zinc spelter contains pb, fb, cd, as, etc. as impurities. Impure zinc can be purified by following methods.
a. By fractional distillation:-
The bpt of Pb, Fb are higher than that of zinc while that of cadmium, arsenic are lower than that of zinc. When distillation is carried out around 1000°c, zinc, Cd, As, etc. distill off leaving Pb and Fe the distillate is then heated to 800°c where cd and as distill off leaving pure zinc. This sample of Zn is about 99% pure.
b. By electrolysis:-
Zinc of higher purity can be obtained by electrolysis. Pure zinc rod is used as cathode while a block of impure zinc is used as anode. A mixture of ZnSO4 and dill H2SO4 is used as electrolyte. On passing current impure zinc dissolves and equivalent amount of pure zinc is deposited at cathode.
Physical Properties
i. It is a blueish white lusticous metal.
ii. zinc is brittle at ordinary temperature but it becomes malleable from 100-150. c then again it become brittle.
iii. It melts at 420. c and boils at 900. c and has sp. Gravity 7.13.
Chemical Properties
1. Action of air:-
Dry air has effect on zinc but in moist air, zinc forms a protective layer of basic zinc carbonate.
Zn + O2 + H2O + CO2 → ZnCO3.Zn (OH)2
When heated in air, zinc burns greenish blue flame forming clouds of light, white power of zinc oxide which is commonly known as ‘philosopher’s wool. Beside this name, other common names are ‘Zinc white and china white.
2Zn + O2 → 2ZnO
2. Action of water:-
Pure zinc does not react with water but impure zinc displaces hydrogen gas. Zn-inc reacts with hno3 in four different concentrations giving different reduced product.
Zn + H2O → ZnO + H2
3. Action with acids:
Dilute H2SO4 and dil. HCl gives H2 gas with zinc
Zn + dil. H2SO4 → ZnCl2 + H2
Zn + dil. HCl → ZnSO4 + H2
With hot and conc. H2SO4 zinc gives SO2 gas
Zn + 2H2SO4 → ZnSO4 + SO2 + 2H2O
Zinc reacts with HNO3 in four different conditions giving different product:
i. with very dil. HNO3
With very dil. HNO3, Zn gives ammonium nitrate
4Zn + 10HNO3 → 4Zn(NO3)2 + NH4NO2 +3H2O
ii. with dil. HNO3
Zinc reduces dil. HNO3 to nitrous oxide (N2O)
4Zn + 10HNO3 → 4Zn(NO3)2 + N2O +5H2O
iii. With modrately conc. HNO3
Zinc reduces moderately conc. HNO3 to NO (nitric oxide)
3Zn + 8HNO3 → 3Zn(NO3)2 + 2NO2 +4H2O
iv. With conc. HNO3
Zinc reduces conc. HNO3 to NO2 (nitrogen dioxide)
Zn + 4HNO3 → Zn(NO3)2 +2 NO2 +2H2O
4. Reaction with Alkalies:-
Zinc readily dissolve in hot and conc. solution of caustic bases like NaOH , KOH, etc giving hydrogen gas.
Zn + NaOH → Na2ZnO2 + H2
Zn + KOH → K2ZnO2 + H2
5. Displacement Reaction:-
Zinc can displace less electropositive metals from their salt solution
Zn + CuSO4 → ZnSO4 + Cu
Zn + 2Na[Au(CN)2] → NA2[Zn(CN)4] + 2Au
Uses of zinc:
- It is used for galvanization of iron.
- It is used in making alloys like Brass. German metal, German silver, etc
Galvanization
The process of applying a coat of zinc on base metal like iron is galvanization Iron is galvanized to protect iron from resting the galvanization is done in following steps.
i. cleaning and picking:
Before applying zinc coat on iron, the surface of iron should be clean. The cleaning is done first by sand blast and then washed by dipping in diluted acid. The process of cleaning iron by using dil. acid is called picking.
ii. Applying of zinc coat:
The coat of zinc can be applied on iron surface by 3 methods.
a. By electroplating:-
Zinc can be electroplated on iron by keeping iron article as cathode, zinc as anode and znso4 solution as electrolyte. On passing current a layer of zinc is coated on iron article.
b. By metallizing :-
Zinc can be directly applied by dipping iron article in molten zinc this process is generally used for galvanization of iron sheets. Iron sheets are dipped in molten zinc bath & then passed through huge rollers that distributer zinc coat equally.
c. By sherardizing:-
The process is used for galvanization of small iron articles like nail, screws etc. In this process iron article are mixed with zinc dust and then heated in enclosed vessel for few hours when coat of zinc is applied on iron.
· It is used in making amalgam.
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