Separation of cadmium and zinc on an anion exchanger

Theory. Cadmium and zinc form negatively charged chloro-complexes which are absorbed by a strongly basic anion exchange resin, such as Duolite A113. The maximum absorption of cadmium and zinc is obtained in 0.12 M hydrochloric acid containing 100 g of sodium chloride per litre. The zinc is eluted quantitatively by a 2M sodium hydroxide solution containing 20 g of sodium chloride per litre, while the cadmium is retained on the resin. Finally, the cadmium is eluted 

Elements such as Fe(III), Mn, Al, Bi, Ni, Co, Cr, Cu, Ti, the alkaline-earth metals, and the lanthanides are not absorbed on the resin in the HCl-NaCl medium. 

Reagent I. This consists of 0.12 M hydrochloric acid containing 100 g of analytical-grade sodium chloride per litre. 

Reagent II. This consists of 2 M sodium hydroxide containing 20 g of sodium chloride per litre. 

Zinc-ion solution. Dissolve about 7.0 g of analytical grade zinc sulphate heptahydrate in 25 mL of Reagent I. 

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