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Cobalt ions more difficult to remove from wastewater than nickel?

Q. During a meeting with plating "experts" someone mentioned that it was better to stay away from nickel-cobalt electroforming since the waste treatment of effluents containing cobalt was far more complicated than those containing just nickel. It didn't make sense to me, since it is well known that nickel and cobalt are similar in many ways and that conventional nickel anodes always contain a certain amount of cobalt. Can anyone comment?

Guillermo Marrufo
Monterrey, NL, Mexico
February 15, 2012

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February 16, 2012

I assume you will remove nickel and cobalt as either hydroxides or sulfides. The sulfides and hydroxides of both are so very low, and similar, that I cannot see any reason cobalt would be more difficult than nickel.

Most local wastewater discharge limits for nickel are in the 1 - 2 ppm range, and most do not limit cobalt at all, although some include cobalt+nickel to be reported as nickel.

Since cobalt is 4X the price of nickel, I'm curious why you would want to use it to replace or alloy with nickel. Their physical properties and corrosion resistance are similar, and they are equally easy to plate or electroform.

The only instance of Ni-Co alloy plating I have ever seen was plating of timing mechanisms I did back in the 60s, and where the alloy produced some special magnetic properties.

Jeffrey Holmes, CEF
Spartanburg, South Carolina