Reducing chloride concentration in acid copper bath

A. No prizes for brevity, cousin Sanjiv, especially on a page that already offers you 14 years of detailed Q&A's on that exact subject. Can you afford precipitation with silver salts as suggested or are the levels too high? Thanks.

Luck & Regards,

A. Although some people think it's overkill, many experienced plating people feel that all water used in plating shops should be deionized. But when you are dealing with a situation where you virtually know that the incoming water quality is screwing up the plating, it MUST be de-ionized. To try to redesign the plating chemistry to allow for the fact that incoming water is wrecking it is the wrong tack, John. Get a small deionizer.

A. My experience is more in plating than in water treatment, but I would leave the RO unit in place, but put a deionizer after it for the feed water to the copper plating tank. That should mean little load on the deionizer.

However, look for other sources of chloride as well, such as hydrochloric acid activation before plating. If that is used, it may be best to close loop the last rinse before plating through a deionizer to keep that chloride from reaching the plating tank.

A. Dear John
It is difficult to believe, that you have so much chlorides in city water that you can't remove them using RO. I recommend revising the equipment. Possibly chlorides are dragged from activation - check it. Instead of diluting of the bath you can precipitate chlorides using calculated amount of silver sulphate. After precipitation the bath must be filtered very carefully.
Greetings,

A. I also find it hard to believe your problem is coming from your water. As there is little evaporation in an acid copper you will only be adding from drag in and if you dilute then the water you top up with needs to be chloride free.

I believe the principal of using Zn dust is that reduction of Cu+2 to Cu+1 allows the Cl- to be precipitated as Cuprous chloride which is relatively insoluble and will drop the chloride to an acceptable level. You must do this in a storage tank to be effective or the Cl will redissolve.
Alternatively use a silver salt such as sulphate or oxide to precipitate as AgCl but due to the cost of silver calculate accurately the amount required to reduce to an acceptable level.

A. Hello,

I agree absolutely to the further responses. If you have an Osmosis, please check also the maintenance of your membranes and the conductivity of the DI-Water directly after. Also consider drag in.

To eliminate chloride there are different ways, like others have mentioned, most success you will have with Ag2CO3, Ag2SO4 or Ag2O. If you really have lots of problems and you always have to dilute the solution, then might it would be helpful, installing a small electroplating cell behind your tank with an own pump and filtration circuit, use 1 or 2 stripes of silver anodes, as cathode you can use copper plates. Connect with a lab rectifier and let it run like this during your production and observe.

Just an input.

Regards,

A. sodium thiosulphate ⇦this on eBay or Amazon [affil links] will adjust the chlorine in your solution.

"The Canning Handbook of Surface Finishing Technology"

on AbeBooks

or eBay or

Amazon

(affil links)

A. Hi James. The Canning Handbook says: "in the case of serious contamination it is usually necessary to empty the vat, clean the anodes, and make up new solution" :-(
... but I'm not sure that 120 ppm is 'serious contamination' if the target is 50 ppm.

Luck & Regards,

A. C'mon please cousin Abhishek. It isn't constructive to blow off all suggestions from 5 previous responders without comment and start over :-)

Tell us about your water analysis (after the water treatment system if you use one); tell us whether you use HCl as your acid activator and, if so, whether you have a closed loop DI on its rinse to keep the chloride out of the copper tank. If neither of these is the source, where do you think the chloride is coming from?

You are probably right that chloride contamination is the cause of your dull plating -- what is the chloride concentration?

Have you tried precipitating the chloride with silver sulphate as Janusz suggested? or the zinc dust in a separate tank as Geoff suggested? or with an electrolytic cell as Dominik proposed? or with sodium thiosulphate as suggested by Jeff? Thanks.

Luck & Regards,

A. Hi again. Geoff told us above what he knows about the use of zinc dust in acid copper, including the need to do it in another tank because otherwise the chloride will redissolve. Chris Owen tells us in thread 11800 what he knows about it, including that if you don't do it in another tank and filter it, the precipitate would cause roughness until it redissolves.

You've got actual experience using it -- terrific! Keep the discussion going and maintain interest in it, by please telling us what you have learned from doing so :-)    Thanks!

Luck & Regards,