Recycling / disposal of plating sludges

A. Hi, Kim. I can answer question 2 for you. One method which is successful in choosing a cleaner which fits in well with your waste treatment procedures is to take a sample of the cleaner from your supplier and make up a 3% solution. Next, add a copper containing solution such as a used nickel stripper, and waste treat it in your lab. If, upon analysis, you have less than 2 ppm of copper you're in pretty good shape.

Many modern cleaner manufacturers make non-chelating cleaners, and you need to make your supplier aware of your needs from the start -- they may handle all the preliminary lab work for you.

Hope this helps,

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A. Kim, The first thing I would suggest is switching to a non-chelated cleaner. I have experience treating both, and I believe not only will they be easier to deal with as waste, but they will also outperform the chelated cleaners.

You did not specify if your system is running continuous flow or batch treating. My preferred method is continuous flowing rinse waters, with concentrates routed to a separate dump tank for treatment. After neutralization and the addition of polymer, the concentrates should be pumped through the filter press.

Effluent from the filter press should be routed to the waste rinse water tank for second treatment as well as the dilution effect of any possible remaining residuals. As far as treatment, I have tried several methods of treating waste cleaners. My best luck has been with ferric sulphate and industrial grade hydrogen peroxide. Sulfuric acid should be used to drop the pH until all cleaner is reacted. This may not happen until you reach pH 2.5-3.0!

From this point the pH should be raised to about 4.5-5.0 pH. For a 300-gallon tank add approximately 4 gallons of ferric sulphate. Follow this with 10 gallons of hydrogen peroxide. After letting the treated cleaner react with the iron and peroxide for about an hour, gradually add caustic soda to raise the pH to 7.0-7.5. With the addition of the caustic, the mixture will foam up so be sure not to overdo it. This works very well with non-chelated cleaners.

Good Luck,

A. Kim:

We were faced with a similar problem of treating a highly chelated cleaner in our batch treatment facility. Having tested (and rejected) ferric chloride, we had some success with CaCl2 but were not able to reduce the concentration of Ni to our discharge limits (2.4 ppm). Then we finally started working with magnesium hydroxide and this stuff works! Not by itself - in combination with NaOH, but we are treating now a highly chelated cleaner (Enthone Cold Action Cleaner) at, sometimes, a 30% concentration in our wastewater with, at times, 100-200 ppm Ni. The cycle is reported in my reply to question No 565 (using magnesium oxide). Try this stuff - it is good. Knowing how reluctant production people could be to switch cleaners (or, for that matter, change anything in a cycle that works), finding a treatment method that does not require any process changes in plating may be a blessing.

Good luck from PlaterB

Thanks Berl!
Several years ago I read of people who preferred magnesium sulphate to calcium chloride or ferric chloride for handling spent cleaners. So I suspect (but don't claim to know) that the benefit of magnesium hydroxide in your application may have to do with the superiority of magnesium as a chelate breaker, rather than the long reaction time of magnesium hydroxide slurry compared to caustic. If an occasion suggests, you might try the sulphate.

Thanks Phil!
I personally don't believe in continuous treatment of anything anymore. When the settlement agreements between NAMF and EPA were reached 16 years ago and 40CFR required that platers be in 'consistent compliance', I think 'consistent' held an accepted meeting of 'the great majority of the time'. Only if a plater violated the discharge standard again & again was it considered a problem. But under unceasing environmental pressure, 'consistent' has morphed into 'absolutely & utterly flawless' with huge fines for the smallest of infractions.
Although I am big on hiking, camping, fishing, and contribute to the Nature Conservancy and Audubon Society, andam not opposed to environmental laws: I think the EPA is playing Humpty Dumpty to our Alice on this one rather shamefully to satisfy increasing pressure on them but snookering the platers. The technology which EPA proposed -- continuous treatment -- can offer compliance 'the great majority of the time' but it is very far from 'flawless'. I think batch treatment, with the ability to test every batch released, is the only safe approach anymore.

Thanks Mike!
I'm not so sure that non-chelated cleaners are necessary. I have recently become a convert to the proprietary organo-metallic precipitants. They cost a bit, but they produce a smaller quantity of denser, more filterable, sludge while eliminating most of the worry about non-compliance.

Ted Mooney, P.E.
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A. Ted:

The data we obtained developing our cycle seems to indicate that you are right and the main benefit of Mg is its chelate-breaking "power". However, there might be other factors such as the adsorptive properties of magnesium hydroxide sludge that may co-precipitate and, therefore, more fully remove the other heavy metals in the mix.

Help me understand why you are suggesting we try MgSO4 instead of Mg(OH)2. Magnesium hydroxide is so inexpensive, easy to work with and serves the dual purpose of raising the pH, breaking up the chelates and (maybe) co-precipitating the sludge without contributing additional ions (sulphate) in the treated water that I think it is the right substance to use.

Thank you, Berl

"PlaterB" Berl Stein
NiCoForm, Inc.

Rochester, New York

Berl: You've developed a treatment cycle that works fine. You are right about the advantages of magnesium hydroxide, and there is no reason for you to change your process at all.

My point was perhaps more applicable for others: magnesium hydroxide slurry has the one big disadvantage of very long reaction time, and where people are seeking the magnesium for its complex-breaking power, they may be able to eliminate that disadvantage of long treatment time by using a soluble magnesium salt in place of the slurry.

Yes, magnesium hydroxide may also tie up metals by adsorption; I don't know. And, while magnesium sulphate may break the chelate, and quickly -- it probably can't be expected to contribute to filterability the way magnesium hydroxide does.

Ted Mooney, P.E.
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A. Bob, I'd need more information to help you on this one. How large do plan on making this operation? How many parts do plan to process in what time period? What size tanks? What solution?

You will either be paying for the spent solution to be hauled away, or have to purchase the equipment to change the wasted solution into sludge and treated wastewater.

Then you'll probably want a sludge press to reduce the amount of sludge hauled away, and reduce costs. Reducing the H2O content also lowers the weight of the sludge. Seeing your question, I think I can assume that you are currently not producing hazardous waste. Using the sludge press will help you stay under generating more than 220 lb. per month, which means you'll be a CEQG (conditionally exempt quantity generator) according to CFR title 40.

Then you'll either have to treat the wastewater a second time for reuse in your processing line (perhaps with an IX system), or pay to have it hauled away also.

Lastly, the cost difference between having the sludge hauled to a landfill (and you being responsible for it till the end of time) and having it incinerated is astronomical!

Hope this helped you out some, feel free to ask for more info if you want!

A. Hi Becky.

When you say 'burn' perhaps you mean 'dry', but it is probably important not to expose chrome to oxidizing conditions like burning to avoid oxidizing it back to toxic and carcinogenic hexavalent chrome.

Usually a large mass of sludge results when neutralizing plating solutions, and filter presses accommodate large amounts of sludge and are easily emptied. Other styles of filters are effective for 'polishing' of liquids, but aren't well suited for mass quantities of sludge. Luck & Regards,


Ted Mooney, P.E.
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A. There are certified haulers/treatment facilities that can take this 15 gallons off your hands. That will be less expensive than running it through your system, and then having to have 15,000 gallons hauled and treated :-)

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Chrome is not particularly difficult to treat, but it is different. In theory you reduce the hexavalent chrome to trivalent with a reducing agent like sodium metabisulphite, monitoring the process with an ORP meter and by eye (the solution will be blue-green rather than amber when the hex-chrome is gone). Then you precipitate it by raising the pH. But chrome is toxic and a powerful oxidizing agent, bisulphite is a strong reducing agent that gasses toxic sulfur dioxide when at low pH, and the chrome precipitate is slimy and difficult to filter. All in all, a somewhat difficult thing to experiment with, with a lot of potential for messing up your system.

Ted Mooney, P.E.
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finishing.com - Pine Beach, New Jersey

A. I agree. Any hexavalent chrome solution of greater concentration than a dragout rinse is not practically treated at any but the largest facilities, although shops that produce a lot of chrome-bearing rinse water routinely treat it easily. If the chromic acid you have is still in it's container and commercially useful, consider finding a chemical trading post whereby companies make chemicals they no longer want available to others that can use them. Everybody's happy! Some states have them.

A. I have been treating chrome now for 10 years, i.e., chromic acid, Alodines, and deox baths. I have made my own solution for treating chrome. It is composed of approx. 5 different chemicals and is based on the ORP concept, however the sludge will pass a TCLP.

Thanks, Michael. I agree that it's doable, and not just by "the largest facilities". I've treated fairly large batches of chrome, too. I don't know whether the chrome batches alone would pass the TCLP test, but combined with the other shop waste they did.

But I feel that for Jon's one-time problem it is more practical to send 15 gallons off site than to thrust the complications of chrome treatment onto his waste treatment system which wasn't designed for it. Thanks again.

Regards,

Ted Mooney, P.E.
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A. Hi Joyce. Is this a sludge from the wastewater treatment of a general plating shop, which contains among other things some chrome . . . or is it the bottom sludge from a self-regulating chrome plating bath? If you can describe in more detail the concentration of chromic oxide, the contaminant levels, and the volumes you are contemplating, someone may be able to assist you with some direction. In response to the general question of whether wastewater treatment sludges from plating shops are economically recyclable however, the current short answer is usually no. Good luck.

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

A. The answer is yes.You can do it in Gauteng

 Hi, Piet, and thanks.

But Joyce's question was how she can do it ("...like to know the technology..."), rather than where she can find someone to do it for her (I think).

Can you introduce the general technology for how she can do it?

Regards,

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

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A. Yes. These wastes could also be treated by the biohydrometallurgy, and further recovering the valuable metals from them ⇨

A. Haz waste exemptions by recycling: 40CFR261.6(c)(2) for wastes recycled on site, without storage. Metal containing waste is generally going to be subject to the same regulation as waste which is disposed. There are some exceptions, for example storage time, but until and unless your recycler can show you clearly where in the regulations there are exemptions, you should continue to treat waste treatment sludge as hazardous waste. Is is unlikely that there is enough nickel or chromium in waste pickle solution to make reclaimation economically viable.

A. Hi, Hafiz.

Berl offered a link to his procedure. But as a general answer rather than a specific procedure, you reduce the pH to the point where the magnesium can become highly soluble, say pH 5 or less. Then you add a good bit of magnesium salt or hydroxide, certainly more than a stoichiometric amount for the metals you are trying to drive out. Then you raise the pH up to about 10 or 11.

Do this in beakers in the laboratory, measuring things, before carefully scale it up to your full batch size after you have achieved satisfactory lab results. Good luck.

Regards,

Ted Mooney, P.E.
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finishing.com - Pine Beach, New Jersey

A The most obvious place to ask this question is AtoTech where you originally bought the chemicals.

That said, the answer may well be: "We have no better idea than to properly dispose it through a permitted treatment and disposal company."

And that will not be cheap.

It should be motivation to take better care of your chrome bath in the future. There are certainly chrome baths being operated which are now decades old.