Stripping tin plating from copper

? How are you measuring/calculating the normality? If it's based on the specific gravity of the solution, the calculated values are going to rise as tin enters the solution.

A. You might try this: 120 g/l NaOH, make the part anodic at 6 VDC. You can vary the temperature to control the rate, but be aware that if you go too hot the copper might be attacked.

A. Hot Concentrated HCl. I thought tin was very difficult to dissolve, but this works a treat!

A. Tom, My favorite stripper for tin off copper is a 50-50 mixture of Nitric and Muriatic Acids. You have to be extremely careful, and use exhaust ventilation, as it will fume like crazy. Also you have to be really careful with it or it will boil from the top of the container. Be sure to wear an apron ⇦ this on eBay or Amazon [affil links] and face shield ⇦ this on eBay or Amazon [affil links] . It does not leave any noticeable etching and is really fast.

A. Tom, we found that a mixture of 4-6 oz/gal of Ammonium Bifluoride and 10% by volume of Hydrogen Peroxide works well.

A. Try an alkaline strip. Makeup a strip with 6-8 oz/gal strip aid with 10-12 oz/gal caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] . Temperature 120-160 F.

A. Another alkaline approach is to use caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] 100 g/l Sodium chlorite 50 g/l at 90-100 °C Parts will be covered with a brown oxide which can be removed with HCl.

A. Use a hot solution (70 °C) of 2N sodium hydroxide ⇦ this on Amazon [affil links] . This will chemically dissolve the tin. However, if the tin plating has been heated, the tin will migrate into the copper to form an intermetallic. This is much more difficult to remove, but it may be possible if the tin plated copper is anodically polarised in the hot alkali. If not you may need to use an acid stripper.

A. Try 25% sulfuric acid plus 8 oz./gal copper sulphate.

A. Following up on Trevor's advice I think you would need an oxidant added to this caustic solution if you have any thickness.

Suggest sodium chlorite (ite) say 50 g/l.

There will be an oxide film on the surface which can be removed with HCl.

A. Geoff's recommendation of adding chlorite to sodium hydroxide is indeed worthwhile; it will certainly increase the dissolution rate of tin and will probably attack any intermetallic alloy. However, it is a very powerful oxidising agent and I do not know what it will do the substrate. I know that using electrolytic alkaline chlorite for detinning tin cans can result in the formation of ferrite ions from the iron. Using just sodium hydroxide will dissolve all the tin, albeit slowly, but it will not attack the substrate.

A. Hello Sofia,
I would contact the supplier of the TL-106 to make sure this product would fit your needs. If not, there are many suppliers that have tin and tin - lead stripping solutions. I am not at liberty to give you a specific supplier, as it conflicts with this site's editorial standards.

A. Tom,

There are many formulations available (see Metal Finishing Guidebook). To retain the bright copper finish, you will require a stripper which contains an etch inhibitor. You can get information on product availability from any supplier.

Regards,

Hi. The stripping formulation info that Mark refers to is in the 2006 Edition of the Metal Finishing Guidebook, but not in the 2014 Edition -- as new articles come, old articles must go. Sorry, I don't know the most recent edition where it is still available.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
February 2014

A. Hi Chad.
MSA, NaOH used anodically, hot HCl, 50-50 HNO3-HCl, strong NaOH used with or without chlorite added, proprietary strippers, and trying the bifluoride without the peroxide have been suggested. Trying one/some of them is probably the next step, unless you'd prefer to try to treat the peroxide (I think it decomposes fairly quickly especially at warmer temperatures
Good luck!

Luck & Regards,

A. Hi Chad. I see some good technical articles on that:
www.sciencedirect.com/science/article/abs/pii/092134499190006A
www.researchgate.net/publication/248231667_Tin_recovery_from_an_electroplating_sludge
www.techno-preneur.net/technology/new-technologies/metallurgytechnique/tinplating_industry.html

and some patents:
patents.google.com/patent/US6110349A/en
patents.google.com/patent/CN104630826A/en

for recovery of tin from electroplating sludges but they generally seem to assume that the tin was precipitated separate from the other metals, or is at least the major constituent; other materials in your sludge interfere with the recoverability of the tin.

I'm not a chemist, but I don't think trying to smelt an electroplating sludge is either the best way to recover the metal values nor the way to analyze for them. I think dissolving the tin in the sludge to ionic form is key to both.

Another thing to think about is that tin is not generally regulated in your effluent, and that means it may make more sense to remove & recover the bulk of the tin by ion exchange, electrolytic recovery, or evaporation, rather than precipitating it only to have to redissolve it.

While we await help from someone who is knowledgeable in tin analysis, a material balance may help you estimate the tin content of the sludge. Is electroplating of the tin, or stripping of the tin the major source? You might also search the site with the term "tin recovery", where vacuum evaporation and electrolytic recovery are discussed.

Luck & Regards,

A. It would help to know more about the process that generates the tin-bearing waste to see if there is a way to either recover or minimize it at the source.

I have not done this but heard of one company that re-dissolved the tin from the sludge with hot sodium hydroxide, oxidized it to +4 tin to make an alkaline stannate bath. This can be electroplated using SS anodes to recover the tin.