Is there an alternate method instead of freezing to remove carbonates from a cyanide copper plating bath? B. J.
This must be a “hot topic” since I have received three e-mails on this subject in the last two months! I assume you are talking about a sodium-based bath. Freezing out works well in sodium-based baths but not potassium-based baths. Yes, there is another way to remove carbonates from a copper cyanide plating bath. The process uses barium cyanide to replenish the cyanide instead of sodium cyanide.
A pound of barium cyanide will remove approximately 0.5 lb of sodium carbonate and generate approximately 0.5 lb of sodium cyanide. The barium carbonate that forms is insoluble and must be removed by filtration. The filtration is critical since even small amounts of the precipitate will give you a rough plate.
Barium cyanide is not the easiest material to find. Talk to your chemical vendor about purchasing this material. You can also find chemical vendors that may sell the material by using the vendor database on www.pfonline.com. If they cannot help you then try a search using Google.
There is a brief discussion on this topic on www.finishing.com, Letter 473. Some other alternatives are discussed in this letter.