The finishing.com Hotline -- Serious Education ... plus the most fun you can have in metal finishing
Stop potassium carbonate buildup in silver cyanide bath or recover silver
April 26, 2009
We are a silver electroforming company.
We have several silver cyanide plating baths.
As we work the level of potassium carbonate increases in the solution which hampers the plating.
How can be stop the increase of potassium carbonate in the silver cyanide plating bath.
I would be obliged if some friend there can advise me.
Currently I am diluting the bath each time - but this is proving costly and time consuming.
Also if I can be advised how can be extract silver from silver cyanide solution as I have plenty of silver cyanide solution which I cannot use due to high potassium carbonate content.
Responses shall be highly appreciated.
With Kind Regards,
plating shop employee - Bhavnagar, Gujarat, India
May 20, 2009
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.Mark Baker
Fellow Plater - Syracuse, NY, USA