Question

Which of the following is correct ?

• A. All of these
• B. Zone refining method is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal
• C. Liquation process is used for metals like Sn
• D. Distillation process is used for refining of metals having very low boiling points like Zn and Hg

Answer 1

The correct option is A All of these

(a) The principle of zone refining is that the impurities in an ingot or ore of metal are more soluble in the melt state when compared to the corresponding solid state of the impurities.
In the zone refining process, the impurities are concentrated at one end of the block of metal so that the rest of the block is purified. It can be noted that the segregation coefficient (which is defined as the ratio of impurity in the solid state to the impurity in the liquid or melt state) is generally less than 1. This implies that when the conditions are set at the solid-liquid boundary, the atoms of the impurity tend to diffuse into the liquid region.

(b) Distillation is a process that can be used to separate a pure liquid from a mixture of liquids. It works when the liquids have different boiling points. For example, this method is very useful for purification of low boiling metals like zinc and mercury containing high boiling metals as impurities. The extracted metal in the molten state is distilled to obtain the pure metal as distillate.

(c) In the process of liquation, a low melting metal like Sn can be seperated from high melting impurities.