Disposing of nickel acetate and copper acetate solution

A. Hi Jose. Two different factors affect what you can/must do with waste products. The first factor, as you already understand, is what the waste product is. But the second factor is the origin of the waste product (what kind of operation generated it or it was used in). Perfectly innocuous wastes, let alone wastes containing heavy metals, may be "categorically" regulated. For example, a plating shop cannot discharge any of their waste without a permit, even hypothetical final rinsewater which could so dilute as to be drinkable :-)

If you work for a school, it is perhaps possible that the city officials are right; if you are a shop with an electroplating operation, they are wrong, and their ignorance may not be an excuse for you, especially if you don't have it in writing. Legally, the best course of action is to call a licensed waste hauler, and have the waste manifested and properly disposed of.

There used to be a lot of "industrial waste exchanges" in large metro areas like yours, which would take your waste product and connect it with potential users. You can look to see if there is one, but I think the EPA's ruling that "the generator is responsible for the waste forever" torpedoed that effort towards sustainability. I look into the subject periodically but only find broken links and white papers from the 80s & earlier -- so I'd be happy to be updated if any industrial waste exchanges are still alive within the US.

Regards,

A. Nickel acetate is used in sealing dyed anodized coatings. You might contact an aluminium finisher.

copper acetate [affil links] is used in some solutions for the antiquing of brass and bronze. Some artist or sculptor might want it.

A. Hi Jake. I am having a bit of difficulty following your line of thought, but I think you are suggesting that you would like to remove the nickel from your spent nickel acetate solution via autocatalytic plate-out as you employ on your ENP solution? And that, in order to do that, you want to remove the acetate first? Unfortunately, I don't quite know what 'remove the acetate' would physically mean in such a scenario.

The nickel acetate concentration is probably somewhere in the 6 g/l order of magnitude, so the nickel content is in the 1.5 g/l range. Although this is far too high for discharge, it's still very low for efficient plating out, so the prevailing treatment method is 'chemical destruct' (basically, neutralize the acid to cause the nickel to precipitate as a hydroxide). Once you do that neutralization, the nickel is no longer in solution, so it can't be plated out autocatalytically or with electricity. If you'd like to try some lab experiments you could put an anode and cathode rod in a beaker [beakers on eBay or Amazon [affil links] with a low voltage and see what you learn, but I doubt that you will be able to plate out the nickel in any practical way. Good luck though!

Regards,

A. Hi again Jake. Glad to hear that I misread your intention. Getting the nickel out of a nickel acetate seal by autocatalytic removal of nickel sounded a bit crazy :-)

But the following posting from Rachel Mackintosh crossed in the mail and answers your question. Good luck.

Regards,

A. NA seal is awesome and the results are totally worth the hassle of getting rid of it.

Getting rid of it is pretty easy.

Let the bath cool enough to transfer without damaging tanks or pumps. Move to a destruct tank.

Turn on the mixer.

Using a handheld pH meter, slowly add solid sodium hydroxide to pH 10.5-11. Yes, nickel drops out lower than that, but the seals are heavily chelated and you have to break chelation to allow the insoluble hydroxides to form freely. (side note: do not be tempted to mess around with the 'no surface smut!!! yayyy!!!' additives sold for these tanks. It's more chelator and will make destruct a BEAR. Just keep your seal bath filters running and change the bath frequently.) Let it mix for a minute or two and then turn off the mixer and leave it alone for a few days to settle. Sample the supernatant and have it tested for Nickel and any other heavy metals you might introduce into the seal from whatever dyes you use (Chromium and Copper are common). Clean lab results? Send the supernatant to be pH adjusted and run through your normal waste system with the rest of the rinse waters. Send the sludge to the filter press. It can be sent for nickel reclamation but no one wants nasty filter cakes unless you've got a truckload! Bad results? Possibly a chelator issue and I've only ever been able to break a stubborn one by dropping it to pH 3.5 using nitric acid and ferric chloride ⇦this on eBay or Amazon [affil links] in tandem, mixing heartily, and THEN performing the hydroxide destruct as before.

So do your jar testing first, preferably on every spent bath batch, until you are 100% confident that your spent bath is consistent and your method is repeatable.

Cheers!

That's brilliant.

Thank you for everyone's help.

Regards Jake

A. Chelating Ion Exchange is another way to remove the metals from spent sealing solutions, however the solution needs to be cooled to < 120 °F. I don't understand why you are concerned with acetate in the discharged water. Acetate is eminently biodegradable, and not regulated as far as I know.

A. Adding to Rachel's comments, we added a small amount of aluminum sulphate and a flocculent, followed by the flash stir. The stuff drops out like a rock. Be careful with adding too much aluminum sulphate as it will interfere with (Hach) testing before you decant.