Silver cyanide plating bath: stop or remove carbonate buildup or recover silver

A. Everything that I have read is NO, because of the much greater solubility of the potassium salt. No idea on any other methods that are commercially available.

A. Thread no. 473 offers some ideas, Andrew. Regards,

A. Hi Andrew,

you can remove Carbonates from Silver Potassium Cyanide bath by the use of Barium Cyanide; the carbonates are precipitated as Barium carbonate. You would need to do the precise calculations based on the chemical reactions yourself, However , of late in the USA & Australia Barium Cyanide has become very scarce and you may wish to try the other method, that is the addition of Calcium Hydroxide

However here to there are problems, lime is readily available but what you can buy is of very poor quality, (it is full of impurities); you would need to talk to a lime manufacturer about which type of lime is the purest in terms of metals & organic materials , once again you would need to do the math to find out exactly how much to add.

Regards,

A. Calcium Nitrate also can precipitate carbonates.

In my establishment, we intentionally allow the level of Silver to drop. Take out a calculated volume of bath, dump out carbonates by treating with calcium Nitrate and then precipitate single Silver Cyanide from that bath using Silver Nitrate. Wash the precipitate and then add it back to the electrolyte along with required free cyanide. In effect the carbonate in the bath taken out for reaction is dumped off. If this is carried out as a routine, It is possible to control level of carbonates.

A. The rise of carbonates is a natural thing in cyanide silver plating. There is no way to stop the rise, only slightly minimizing it. The use of fine silver anodes helps over the use of S/S, silver anodes should be bagged. There is a process where you treat the bath with calcium nitrate. This will reduce the carbonate level effectively. A good precious metal supplier will have the process for you. It has been so long since I've done the process I'm not sure of the exact amounts needed to reduce the carbonates per US gallon. Don't quote me, but I think that in order to reduce one ounce of carbonate per gallon you need two ounces per gallon of calcium nitrate added to the bath. You don't want to remove all the potassium carbonate however. Take the level down to the concentration you would have in a new bath. A mechanical mixer is needed for a period of time, then shut off. The carbonates settle at the bottom of the tank overnight. The silver plating solution is then filtered off until the carbonate "sludge" is removed from the bottom of the treatment tank. You will lose a little bit of the bath because it will be absorbed in the unwanted carbonate sludge. Again, double check this with your supplier. Good Luck to you.