Cleaning/leaching a plating tank

A. Usually, the tech data sheet for the process in question will give you a suggested leaching procedure. And usually it is based on using the acid upon which the plating process is based, at a temperature at least as high as the plating process, for 24 hours or so.

A. Wash everything down so there is no visible copper salts on any of the equipment then leach overnight with 10% solution of sulfuric acid with the filter pump going but no filter cartridge.

A. Hi Dennis. By "non-leaching polypro" they mean that nothing will leach out from the polypro itself into the plating bath, like bromine fire-retardants that are used in some polypropylenes. But once you've used a tank for one solution it must be fully cleaned before using it for something else. Sometimes leaching (cleaning a tank by putting into it something very similar to the plating solution) can be a useful part of the cleaning routine.

In this particular case, because I'd be concerned about leftover oils from its earlier use embrittling the cadmium, I'd suggest leaching overnight with a hot caustic and cyanide solution similar to the concentration of the cadmium plating tank.

Regards,

A. Why not send the acid leach juice down to waste treatment and have it do the pH adjustment?

If you do it in the tank, you are liable to get precipitation of metals, and some of the metal hydroxides will glom onto the tank wall.

A. Eric,

If the Koroseal liner is brand new I don't think a leach is necessary. Sometimes with plasticized PVC a little excess plasticizer can come up to the surface and produce an oily film in the solution. However, my experience is that the Koroseal PVC doesn't exhibit this trait. Performing a leach though would not have any detrimental affect on the liner. It is my experience that a slightly caustic leach solution acts faster than an acid one on a monomeric material. The most important part of the leach is the temperature. If you can't apply temperature not much if anything will leach out. Also with regards to temperature you make a note of running at 150 °F. The adhesive system for Koroseal is recommended not to exceed 145 °F. Running above this can cause the liner to pull away from the tank wall. If you have a drop in style Koroseal PVC liner than you can run up to 200 °F without worries.

Comment:
Hello Thomas
There is no universal standard cleaning procedure. Nobody can know the situation with the tank better than you. What is tank's material, what is tank size, what type of solution was used, what temperature was used, for how long it was operational (and how dirty is it?)

Assuming it was some acidic Ni plating bath, I would suggest few steps:
a) clean and rinse the tank few times with water
b) leach it with diluted ~2-3 % Sodium Hydroxide at room temperature for few hours (for example - overnight)
c) rinse with water few times
d) leach with a relevant diluted (!) acid that will be used in a new bath formulation. For example: HCl for Woods Ni strike, Sulfamic acid for Ni Sulfamate bath, etc.

* if tank is equipped with mechanical solution circulation - all cleaning/rinsing solutions have to be circulated through the pipes.

Hello,

Thank you Leon for your reply! Indeed, it was a nickel bath in the tank and I would like to replace it by a new bath of Nickel alloy this time. My idea is not too different from yours : cleaning with NaOH and neutralization with acid. I am going to write a cleaning procedure with the help of your advices.

Thank you again,
Best Regards