Smelting is a melting process in which pure alumina is dissolved in a mixture of molten cryolite (Na2AlF6) and fluorspar (CaF2), melting point 950oC. Conducts.

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Presentation transcript:

Smelting is a melting process in which pure alumina is dissolved in a mixture of molten cryolite (Na2AlF6) and fluorspar (CaF2), melting point 950oC. Conducts electric current effectively.

The anode is made of graphite and it is consumed in electrolysis because oxygen is liberated at the anode. Al is deposited at the cathode.

Reaction at the electrodes:

Anode reaction: C(s) + 2O2- → CO2 (g) + 4e-

Cathode reaction: Al3+ + 3e- → Al (l).

Molten Al is tapped from the smelter and kept in a revebatory furnace until it is cast into ingots.

Electro refining of Copper

Slabs of crude copper serve as the anode in the cell and thin sheets of copper as the

cathode. The electrolyte consists of acidic copper sulphate solution cathode. The electrolyte consists of acidic copper sulphate solution. When a suitable

voltage is applied to the electrodes, copper metal is oxidized at the anode and Cu2+ is

reduced to copper at the cathode reduced to copper at the cathode. Metallic impurities that are more active than copper are readily oxidized at the anode but do not plate out at the cathode because their reduction potentials are more negative than that of Cu2+. Less active metals will not be oxidized at the anode; they will be collected below the anode as a sludge that can be processed to recover the valuable metals.

MINING THE PURE METALS

Mining of Gold

Method involves digging a hole and collecting tiny fragments of impure lumps of metals. Gold is recovered from the lump obtained from the mine by flotation method or panning method.

Panning method: the mixture of earth and rock containing gold is swirled with water; because gold is denser it tends to lie at the bottom of the pan while the other solid particles are washed away.

Chemically, gold obtained from the mine can be purified by treating crushed samples of the gold with sodium cyanide solution and oxygen to form the stable AuCN-2 ion, which is soluble in water;

4 Au(s) + 8 CN-(aq) + O2 (g) + H2O (l) → 4 Au(CN)2-(aq) + 4 OH-(aq)

Gold is precipitated from the cyanide complex by reduction with zinc powder.

Zn(s) + 2 Au(CN)2-(aq) → Zn(CN)2-(aq) + 2 Au(s) .

2dsinθ = λ (1)

TECHNIQUES

DIAGRAM