Copper contamination in cadmium cyanide bath
A discussion started in 2008 but continuing through 2019August 26, 2008
Q. I have inherited a cadmium cyanide bath at work which can only plate at low current density without getting a dark grey to black deposit. The carbonates are high at approximately 9.25 oz/gal but my real concern is I had the bath analyzed for copper contamination and it was 2537 ppm Cu. I took a liter sample and treated it with zinc dust, but the lowest I can drop the copper to is 1700 ppm. We are still looking at ways to lower the copper. The bath parameters now are Cd - 25.1 g/l, Free CN 144 g/l, NaOH 20 g/l. We compared Hull Cells of this bath with another cad bath and the difference in panels is significant. The "clean bath" is bright across the whole panel except minor frosting near high current density end while the copper contaminated panel is dark grey to black starting at approximately 15 ASF.
Before we teat or dilute for carbonates we want to know if there is any way to remove the copper. Currently I sent out plated samples for EDX to see if any copper co-deposits. Currently we are not failing any salt spray tests.
plating shop - Harbor City, California
August 31, 2008
A. You say you inherited the bath at work. Should I presume you mean from another employee? If so, you must first find the cause of the copper contamination i.e. dropped hooks, wire, parts, etc. and eliminate it. Otherwise, your corrective actions will be for naught.
Copper can be removed, to some extent by dummy plating. Because of the electrochemical potential of the metals involved it does not work as well as in other plating baths. Another method (try in a test cell first) is to use a 10% by volume solution of a sulfide type cyanide zinc purifier. This may prove effective with the zinc dust treatment. A third part of the triad of working with your situation would be to have your chemical vendor sell you a non metallic brightener/grain refiner. If you are not using one, I feel you should. Certain ones on the market meet the definition for not being a brightener, i.e., no co-deposited organics.
process supplier - Great Neck, New York
April 28, 2010
Q. I am trying to find the maximum copper content for a cyanide cadmium plating bath. I've seen recommended numbers as low as 10 ppm. In addition, if the copper content gets high (i.e., 2000-3000 ppm) and the operators compensate by increasing the current density, what problems might that lead to? For example, are you now plating a cad-copper alloy? Are you going to see stress, adherence, efficiency problems?Chad Leach
Plating Shop - Dayton, Ohio
April 30, 2010
A. Yes you are co-plating the copper, so all of your properties are impacted. I can't give you a hard limit, but <10 would be good, <50 might be okay, above 80 is too high for sure. 2000 means you need to forget about salvaging your bath. Eliminate the source of your copper contamination and start over with a fresh bath. That's my opinion anyway.
February 12, 2019 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. How do we remove copper contamination in a cadmium bath solution? Only by dummying? Thank youPierre Legault
shop employee - Montreal, Quebec, Canada
A. Hi Pierre. We appended your question to a thread which discusses quite exacting copper contamination levels and what to do about them. If questions remain, please give us good details of your own situation rather than phrasing questions in the abstract -- the thread is moving backwards :-)
Ted Mooney, P.E. RET
Pine Beach, New Jersey
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