Metallurgical operations-Step 4 - Refining of metals

Question 1

Principle of Distillation

Answer 1

Useful for low boiling metals like zinc and mercury. The

impure metal is evaporated to obtain the pure metal as distillate. Mercury, Zinc

Question 2

Principle ofLiquation

Answer 2

A low melting metal like tin can be made to flow on

a sloping surface. In this way it is separated from higher melting impurities. eg tin and lead

Question 3

Principle of Electrolytic refining

Answer 3

In this method, the impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal.
The more basic metal remains in the solution and the less basic. The net result of electrolysis is the transfer of metal in pure form from the anode to the cathode:
ones go to the anode mud. eg copper and zinc

Question 4

Principle of Zone refining

Answer 4

This method is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal. e.g., germanium, silicon, boron,
gallium and indium.

Question 5

Principle of Vapour phase refining

Answer 5

In this method, the metal is converted into its volatile compound and collected elsewhere. It is then decomposed to give pure metal.

Question 6

Principle of Chromatography

Answer 6

This method is based on the principle that different components of a mixture are differently adsorbed on an adsorbent. eg Lanthanoids

Question 7

Role of CO in Mond’s process

Answer 7

Suitable reagent to form volatile compound with Nickel

Question 8

Role of iodine in van Arkel’s process

Answer 8

Suitable reagent to form volatile compound with Zirconium or titanium

Question 9

Equations of Mond’s process

Answer 9

Ni + 4CO -> [Ni(CO)4] ; temp = 330 – 350 K

Ni(CO)4 -> Ni + 4CO ; temp = 450 – 470 K

Question 10

Equations of van Arkel’s process

Answer 10

Zr + 2I2 → ZrI4

ZrI4 → Zr + 2I2; temp= 1800 K

Question 11

Two requirements of vapour phase refining

Answer 11

(i) the metal should form a volatile compound with an available reagent,
(ii) the volatile compound should be easily decomposable, so that the recovery is easy.

Question 12

What criterion is followed for the selection of the stationary phase and mobile phase in chromatography?

Answer 12

The mobile phase may be a gas, a liquid or a
supercritical fluid. The stationary phase is immobile and immiscible. The mobile phase and the stationary phase are chosen such that components of the sample have different solubilities in the two phases.