Purification of Electrolytic Baths

Effect of Electrolytes on the Desorption of Gold in 40% Acetonitrile-Water Solution  

After Tsuchida, N., Ph.D. dissertation, Murdoch Univ., 1984. With permission. 

There are also cyanide baths that are used for the recovery of silver and gold. These baths contain cyanide anions and other salt anions, and several cations that are used for the efficient and more effective recovery of these precious metals and for electroplating purposes. 

The first successful application of activated carbons was made for the purification of nickel plating baths. But it was then extended to the purification of acid copper plating, acid and alkaline tin plating, and to all cyanide baths. However, activated carbon is not suitable for chromium plating baths because activated carbon reduces hexavalent chromium to trivalent chromium. 

The purification of electroplating baths can be carried out using a batch process or a continuous process. In the batch process, the bath solution is treated with activated carbon for 25 to 50 min and then filtered. It is ensured that it is clear and does not contain any activated carbon. The clear filtrate to be used again is the bath. The batch process can also be carried out by filtering the bath solution through a fabric coated with a suitable activated carbon. The frequency of the purification depends upon the operation of the electroplating bath, and the amount of carbon dose depends upon the degree of contamination of the bath, but usually it is 0.5 to 1.3 kg of activated carbon for each 100 liter of the bath solution. 

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