Question

In the Parke's process of Ag-extraction, Zn is removed from (Zn-Ag) alloy by using :

• A. Cupellation
• B. Electrolytic refining
• C. Distillation
• D. Fractional crystallization

Answer 1

Answer: (C)

Distillation

Parke's process is used for the desilverization of argentiferous lead (PbS + 0.01 to 1 % Ag) and is based on the distribution principle. Molten zinc and molten lead form a two phase system. Silver is more soluble in molten zinc than the molten lead.

The Zn - Ag alloy is lighter than Pb and freezes fast. The floating solidified Zn - Ag alloy can be easily removed from molten Pb. From Zn - Ag alloy, zinc is separated by distillation. As zinc is volatile at 920${}^{\circ }$C while Ag is not, hence on heating Zn - Ag alloy, zinc goes into vapor phase and Ag remains at the bottom of the vessel.