Question

Describe the principle involved in each of the following processes.

(i) Mond process for refining of Nickel.
(ii) Column Chromatography for purification of rare elements.

Answer 1

(i) Mond process converts nickel oxides into pure nickel.

This process involves the fact that carbon monoxide combines with nickel readily and reversibly to give nickel carbonyl.

This process has three steps:

1. Nickel oxide reacts with Syngas at ${200}^o$C to give nickel, together with impurities including iron and cobalt.

$NiO\left(s\right)+H_2\left(g\right)\to Ni\left(s\right)+H_{2}O\left(g\right)$

2. The impure nickel reacts with carbon monoxide at $50–{60}^{o}C$ to form the gas nickel carbonyl, leaving the impurities as solids.

$Ni\left(s\right)+4CO\left(g\right)\to Ni\left(CO{)}_4\right(g)$

3. The mixture of nickel carbonyl and Syngas is heated to $220–{250}^{o}C$, resulting in decomposition back to nickel and carbon monoxide:

$Ni\left(CO{)}_4\right(g)\to Ni(s)+4CO(g)$

(ii) Column chromatography is a method used to purify individual chemical compounds from mixtures of compounds. The methods of separation in chromatography are based on the distribution of the components in a mixture between a fixed (stationary) and a moving (mobile) phase. This is a solid - liquid technique in which the stationary phase is a solid & mobile phase is a liquid. The principle of column chromatography is based on differential adsorption of substance by the adsorbent. The usual adsorbents employed in column chromatography are silica, alumina, calcium carbonate, calcium phosphate, magnesia, starch, etc., selection of solvent is based on the nature of both the solvent and the adsorbent.