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We've been successfully running a small scale alcohol (isopropyl) zadra stripping process for a while now.
We've begun a carbon stripping service for clients and today ran into something we have never seen. During the electrowinning process, a black scale formed on our stainless steel punch plate anodes. The anodes were completely pitch black.
Meanwhile, the cathodes which are stainless screens also loaded with a Cu/Ag/Au mix that was so difficult to take off that in the end, we had to reverse plate them. This is also not normal for us because we usually clean off the screens with a toothbrush and a steel wire brush in a matter of a few minutes.
During the reverse plating, the black element dropped off of the punch plate and loaded onto the screens, which were then technically the anodes.
The elution solution makeup was the same as we always use except that we used ethanol instead of isopropyl alchohol. The vots/amps were also the same as normal.
The only other variable that I can think of was that the leaching agent used by our clients was not cyanide, but rather another leaching product that is on the market with the following make up:
Sodium oxide = 35 - 50%
Nitrogen= 12 -20%
Ammonia = 7-12%
Calcium = 1-5%
Iron = 1-5%
"water insoluble substances": = 3-8%
Does anybody have an idea as to what loaded onto the anodes? Thanks for your comments.