How to Strip Plated Silver Off of Copper

A. Hi Jennifer,

We appended your question to a thread where James Totter tells us how to do it. It's pretty aggressive chemistry so you probably want a plating shop to do it for you rather than doing it yourself though.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Dissolve 4 oz/gal sodium nitrate ⇦ this on Amazon [affil link] in concentrated sulfuric acid. Electrostrip with a lead cathode at 3V, 70-120 °F.

A. James Totter's reply should be essentially applicable, Kim; however, remember to develop this process in extremely small batches and with all precautions until you are familiar with it because conventional plating and stripping chemistry proceeds so rapidly on powder (because of it's very tiny mass and huge surface area) that reactions which would be fairly slow on large parts can be virtually explosive on powder.

A. Hi Michael; hi Kathryn.

Silver plating wouldn't be very functional and useful if it easily dissolved away in dishwater or milk & honey; sorry, you need strong chemistry. You can probably find a plating shop who will strip the silver for you; but if you do it yourself, you need chemicals and you will be creating waste products. James has mentioned probably the best electrochemistry. To my knowledge, machines of this type are not available as catalog items, but you could contact the manufacturers of "Brush plating" systems and see what if anything they can offer you. Good luck.

Regards,

A. Hi Bill. Yes, James was describing an electrostrip, with the article you are stripping being the anode.

It is always important for you to describe your own situation and your intentions: if you are doing something different than stripping silver from rejects in order to make the items replateable so you can try again there may be a whole host of different potential solutions which don't require electrical current.

Regards,

 Hi Alfred. James probably didn't "forget" to discuss recovery of the silver; rather, the question he was answering was how to strip the silver in such a fashion as to not harm the underlying copper, so that it can be readily electroplated again. I'm guessing his thoughts, but he probably would not recommend that plating shops try to recover the silver from such an operation in-house because of the potential dangers, and with the cost of recovery probably greatly exceeding the value of the silver.

If you are also from a small plating shop dealing with occasional rejects, that would probably be my answer to you, although electrolytic recovery or ion exchange in the rinse water is probably a possibility if the stripping is part of a regular process rather than a response to an occasional rejected item. We'll see if other readers have thoughts.

Please introduce yourself and your situation if it is different than the original question. Thanks.

Regards,

A. Alfred,

Electroplating, as in a process requiring a power supply, is not involved. The process is essentially the same as immersion plating. Zinc metal powder can be used to precipitate silver, as a metallic powder, from many different solutions. It is basically an exchange process. Silver and zinc switch places. The metallic zinc dissolves and the dissolved silver precipitates as a metal. Theoretically, I'm thinking that 1 g of Zinc will drop about 3.4 g of silver. However, if the solution contains chemicals that will dissolve zinc on their own, additional zinc will dissolve until this chemical is consumed and only then will the silver start dropping. An example of these chemicals, in this case, would be free nitric acid in an acid solution or a lot of hydroxide or free oxidizer in a cyanide solution containing free cyanide.

If you search for "electromotive series" (EM series) on the internet, you will find a chart which has the more active metals, such as magnesium, aluminum and zinc, at the top (usually - sometimes, but not often, the chart is reversed), and the less active metals, such as gold, silver, and copper, at the bottom. The general rule is that a metal in metallic form will drop out in metallic form, any and all dissolved metals that are below it on the chart. This assumes that the more active metal is soluble in that particular solution. There are also other peculiarities that can hinder certain combinations from occurring.

When silver in in a nitrate acid solution, you are much better off using copper than zinc to drop the silver. The main reason is that copper is right next to and above silver on the EM series. Therefore, it is very unlikely that there would be any other metals between copper and silver that would drop along with the silver. With zinc, which is far above copper, there are many other possible metals that might drop along with the silver - lead, cobalt, nickel, iron, e.g. Instead of copper powder, I would use a pure copper bar, the best being clean, scrap bus bar with no solder or plating on it. With copper powder, you are very likely to contaminate the silver with copper, unless you know exactly how much silver is in solution and use exactly the amount of copper needed to drop that exact quantity of silver. Almost impossible to do. With bus bar cut into lengths long enough to stick up out of the solution, so you can easily remove them, you can achieve a purity of 99+% silver, with very thorough rinsing.

A. Hi again, Alfred. Apologies if the site is difficult to navigate, but after 3 postings I still have no idea who you are or where in what process you want to do what it is you want to do, so we're even  🙂

Are you talking about removing the silver values from these exhausted sulfuric acid electrostripping solutions after they have reached their end of life, or are you trying to remove silver from this concentrated sulfuric acid to extend the life of the solution, or what?

Are you working in a large plating shop, or maybe a chemical recovery facility? Sorry, but I'm lost as well. Apparently copper will do what you want done -- so happy to hear it!


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey