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topic 43864 p.2

Electroplating Wastewater Treatment Q&A's, Problems & Solutions



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A discussion started in 1998 but continuing through 2020

2007

Q. Hello everyone. We electroplate Nickel, Zinc (alkaline and acid), copper, and tin. Mostly we plate small parts such as fasteners. We are running barrel line style plating. The stripping operation uses Nitric acid in a cement mixer tumbler to strip the copper off steel fasteners before it is sent to the wastewater treatment.

I'm new to the industry and have come upon a problem that needs some insight from the experienced. After taking charge of a smaller plating shop and wastewater department, I found some things that needed changing. One was reduction of water use in shop. This lead to the reduction of about 6000-8000 gallons of water in a 24 hr period (rinse tanks were putting out 40 gpm). After this change, I am having a tough time getting the copper out of the wastewater. I believe that part of the problem is that we have a stripping/cleaning operation for parts. We strip a lot of copper off parts and this waste goes down into the wastewater treatment. All that extra water just diluted everything before, so the levels were acceptable for the POTW. I think the copper is tied up with some chelating agent ... but need some advice on how to tackle this.

Clay OShell
Head of Plating and Wastewater Treatment - Altoona, Pennsylvania, USA


affil. link
"Operation & Maintenance of Surface Finishing Wastewater Treatment Systems"
by Clarence Roy
from Abe Books
or
info on Amazon

2007

A. Chelate breaking usually involves reducing the pH to about 4.0, maybe lower, and then supplying another ion like aluminum (from aluminum sulphate) or iron (from ferric chloride) or perhaps magnesium from Epsom salt to replace the problem metal, then raising the pH quite high, Clay. Try it in the lab to see how high you can keep the pH when you lower it, how low you can keep it when you raise it, and which co-precipitant works best. People hate the operational mess of lime, but it combines the co-precipitant/chelate breaker with the pH raiser and may be best. Good luck.

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


2007

A. Are you doing acid zinc plating with a bath that contains ammonium ions?

If so, that might be the cause of your problem. At pH 10, there's enough free ammonia to cause complexation problems. If that's your situation, try precipitating at a lower pH, perhaps 9 or so, with a product like DTC or sodium sulfide.

Funny, eh, that the enforcement authorities should not be a little more helpful when you're doing a good thing and conserving water? Once, I got dinged for Zn being about 20% high in a batch of water that I had discharged. This water had been recycled twice and had a TDS of about 15,000 ppm.

Funny, the priorities people have. It's a perverse incentive to leave well enough alone and just leave the water turned up.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


sidebar 2007

thumbs up sign Hello again Dave. The most fascinating course I had in college was "The Philosophy of Language", which observed that the meanings of words morph with time and circumstance; they mean one thing early on, then something vastly different later. Take the word "consistent". Derek Jeter delivers consistent performance for the Yankees, but is anyone foolish enough to believe he bats a thousand?

But somehow "consistent" compliance morphed into meaning "flawless" compliance -- which produced the upside-down logic you describe. If your effluent meets the standards 99 to 99.9% of the time, who could argue that your compliance is not amazingly consistent? Yet you'll be fined for a single error.

Years ago it was anticipated that it would be a simple call to the POTW with "I was 20 percent over on this one batch because . . ."

If anyone doesn't believe that this is just exactly what happened, do you really think the regulation writers of 30 years ago were such ignorant morons that they believed that the simple continuous treatment technology that they proposed and described in their economic justification could deliver flawless performance?

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


2007

I did call, Ted. They did not care at all; in fact, they did not understand why I should be telling them that.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

January 10, 2008

A. As metals enter the treatment process, they are in a stable, dissolved aqueous form and are unable to form solids. The goal of metals treatment by hydroxide precipitation is then to adjust the pH (hydroxide ion concentration) of the water so that the metals will form insoluble precipitates. Once the metals precipitate and form solids, they can then easily be removed, and the water, now with low metal concentrations, can be discharged.
Metal precipitation is primarily dependent upon two factors: the concentration of the metal, and the pH of the water. Heavy metals are usually present in wastewaters in dilute quantities (1 - 100 mg/L) and at neutral or acidic pH values (< 7.0). Both of these factors are disadvantageous with regard to metals removal. However, when one adds caustic to water which contains dissolved metals, the metals react with hydroxide ions to form metal hydroxide solids:

During this process I would keep the pH 8.0 to 8.5 SU.

Chris Willcox
- Dayton, Ohio


February 4, 2008

A. Chris,
You are correct in general with your statements concerning metal hydroxides and pH. If there are chelates present the whole world can change. I would suggest that Clay investigate possible sources of chelates, burnishing compounds, etc.

The whole regulatory issue is could be a never ending discussion. we have an RO unit to produce water that we can recycle. The nature of this beast is it concentrates our discharge. When we get close to the limits we turn off the unit and stop recycling. The real dicotomy here is that we are sending the same total pounds of metal to drain. The POTW would never know the difference either way because we are such a small part of their total treatment.

I understand that there are discussion by those in the compliance field about possibly changing the regs from concentration to total pounds or some combination of the 2. Lets hope clearer heads prevail.

Kurt Sammons
- Inman, South Carolina



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



February 25, 2010

Q. I am making tests for removal of Nickel (doesn't react with hydroxide and sulfide) using product Bulab (Buckman) that is the base of DTC.
However when we reduced the pH to < 2 it forms a brown precipitate that if it is separated presents better efficiency. Which is the best pH for use of DTC?
Which is dosage of DTC so that the final wastewater treated is not toxic?

Tatiana Bigardi
- Jundiai, São Paulo, Brazil



July 18, 2018

Q. I have some questions, currently the chemicals that I have used in WWTP are coagulant, polymer neutralide, and decomplex 200, so what is the way to reduce the nickel value?

wan muhammad
tnp - Pahang, Malaysia


affil. link
"Plating Waste Treatment"
by Kenneth F. Cherry
from Abe Books
or
info on Amazon

July 2018

A. Hi Wan. The first step is jar testing while adhering to the basics. If you can't get proper levels in jar tests with the basic approaches, then you would need to either see how to modify the process which is generating the nickel problem or start applying more complex reductants like TMT-15 or sulphides or DTC.

What is the source of the nickel, what other processes mix with it before WWTP, and what pH do you precipitate at? What is the allowable nickel ppm in the discharge, and what is your current dissolved and filterable nickel in ppm? Thanks.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading


July 19, 2018

A. Hello Mr. Muhammad,
Check the source chemical for addition of a chelating agent, which will make your treatment method more difficult. For example, the ubiquitous Reliant Nickel acetate seal has a chelator added. To perform a 'destruct' rendering it possible to separate as solids and clean dischargeable wastewater, it must be brought to pH greater than 11 to break the chelation effect. We don't have to use any polymers etc to do this, just solid sodium hydroxide added while mixing (watch your temperature!). If a smut reducing additive has been put in the bath, which contains even more chelator, an additional first step may be necessary, which is to first drop the pH to about 3.5 using Ferric Chloride (about 1 kilo per 1000L) and then Nitric acid to further reduce the pH. Then proceed bringing the pH way back up again. Not knowing what exactly you are starting with, this is just a simple example of one way to deal with a heavily chelated plating chemical.
As Ted says, you'll want to jar test before trying to full-scale the treatment process. Good luck!

rachel_mackintosh
Rachel Mackintosh
Plating Solutions Control Specialist / Industrial Waste Water Treatment - Brattleboro, Vermont


July 22, 2018

A. Hi All

Excellent advice on the treatment of waste water but I would suggest that there is another approach.

If expensive chemicals do not enter the waste stream they do not have to be removed by even more expensive treatment.

Assuming we are discussing plating wastes, I would look first at the plant and its operation. Much can be achieved by …

Jigging with minimal solution traps (not so easy on a barrel line).
Counter-flow rinses
Adequate draining time over the tank (without drying out); Operators rarely understand the importance of this.
Fine demin spray rinse over the tank; With a little practice you can balance evaporation/dragout losses, you save chemicals ($s) and never have to top up again!
Recirculated rinses with deioniser.

It is possible in some cases to completely eliminate the need for any effluent treatment.

geoff smith
Geoff Smith
Hampshire, England



September 30, 2020 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Good night everybody!

I really need your help.

Actually I am treating a wastewater which contains nickel, cooper and cyanide. First, in order to removal cyanide, we use hydrogen peroxide at pH 10.5 for one hour. Then, we treat those heavy metals by using NaOH and ferric chloride carrying the process until about pH 8.0 - 8.5. We have measured total cyanide after this process with results less than 0,1 ppm, but nickel and copper are still there. No matter how we adjust the pH value to precipitate, they persist. We also have a very high COD about 1400 ppm. I really appreciate some advices here. Thanks a lot!

Carolina Carvajal
- Bogota Colombia


September 2020

A. Hi Carolina. We added your inquiry to a long thread on the subject, which should offer food for thought. You might also look at thread 40394, "Cyanide plating waste water treatment", for additional insights. But just for four quick thoughts:

1. You must figure out where the 1400 ppm of COD is coming from, not only to control it, but because it might be interfering with the nickel removal.
2. Filter a sample of the wastewater before testing so you are sure whether the excess nickel is in dissolved or precipitated form so you know whether the chemistry or the solids-liquid separation step must be improved.
3. Just a reminder that you do jar testing to figure out what will work, you don't make adjustments to your treatment regiment based on untested theory.
4. Ferric chloride is a chelate breaker/co-precipitant and there may be better ones; but what the word 'co-precipitant' implies is that you add it before things are precipitated, not after. The idea is that there is a limit to the total metal that can stay dissolved at a given pH and if you add iron or another metal it reduces how much nickel can stay dissolved. If you're sure that cyanide is absent, lower the pH in your beaker to 3.5 with acid, then add the co-precipitant, then raise the pH and see if there is improvement.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading


October 2, 2020

A. You may have chelators or ammonia that are interfering with metals precipitation. I'd recommend that you jar test with a stronger chelate breaker.

Lyle Kirman
- Cleveland Heights, Ohio


October 3, 2020

Q. Thank you both for your answers.
We tried to coagulate the water after the oxidation process and just before the addition of FeCl3 seeing a little improvement related to COD removal. I guess we should try using another breaker culture as you suggested, Do you have any recommendation of the product we could possibly use?
Thanks a lot!

Carolina Carvajal [returning]
- Bogota Colombia

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