Summary for cadmium plating waste products Discussion
Cadmium plating waste products are discussed in the context of aviation plating waste, where Dan Borg described a blackish, water-like liquid and asked what byproducts to expect. The main technical reply, from Ted Mooney, asked whether the process was cyanide cadmium plating, noting that most cadmium plating is cyanide-based. He recommended first chlorinating at pH 10.5 to destroy cyanide, stirring for 30 to 60 minutes, then neutralizing excess chlorine with sodium metabisulfite. After that, he suggested adding a little Ca(OH)2 slurry to raise the pH to about 11 and using flocculant to settle solids. Ted said this approach should reduce cadmium to below 0.5 ppm, and that even lower residuals may be achieved by using a sulfur-based precipitant such as Na2S or DTC before the pH adjustment.
Q. I am currently handling the environmental aspect of waste produced at one of our clients following Cadmium Plating in the aviation industry. I have very limited knowledge on this process and I would appreciate if anyone can shed some light on what to expect as a byproduct of this process. All I know is that they end up with blackish liquid which I have not dared to smell or touch but the viscosity looks very similar to that of water.
Thank you for any support you can provide!
Regards
Dan
Daniel Borg
– Qormi, Malta
February 15, 2012
Is this cyanide cadmium plating? (most is, in my experience.)
I would chlorinate at pH 10.5 to complete cyanide destruction, stir for 30 – 60 minutes, then neutralize excess chlorine with sodium metabisulfite. Then, I’d add a touch of Ca(OH)2 slurry to bring the pH to 11 or so, then add flocculant to settle solids. This ought to bring the Cd down to less than 0.5 ppm.
Lower residuals can be gotten by adding a sulfur based precipitant, like Na2S, or DTC, prior to the pH adjustment.
Dave Wichern
Consultant – The Bronx, New York
February 15, 2012