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letter 39370

Zinc removal from wastewater

A discussion started in 2006 & continuing through 2017 -- add your Q to bring it back to the Hot Topics page.


Q. We have a bathing tub of size 900' by 8' and 10' deep. It contains 1.6 mgallon of water with approximately 6 ppm zinc. Now we want to pump all water at 300 gpm and throw in the ocean, but before that we have to remove zinc. Is there any device or technique that can be used?

K. [last name deleted for privacy by Editor at request]
university - Pennsylvania


A. Hi, K. This is a very substantial volume! You want to treat and discharge as much zinc-bearing waste in a week as 10 or more large industrial zinc plating plants would discharge. And each of the ten would have at least one certified waste water treatment system operator plus a safety and environment manager.

So this is not something that can be done casually with internet forum advice, but must be carefully orchestrated and monitored. I think you should contract with an experienced treatment company to do on-site treatment, perhaps by passing the water through ion-exchange columns and hauling them off site for regeneration, but certainly not discharging at a rate of 300 GPM. Further, I didn't know that ocean dumping was even legal. Good luck!

Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


A. Without knowing the exact makeup of the "lake" you are wanting to treat is is difficult to offer a solution.

1. Are there any complexing agents in the water?
2. 6 ppm is not that bad. Actually more is better from the treatment side of things.

I would check with the supporting vendors on this site, contract a "portable batch treatment system".

Finding a treatment system that is capable of treating 1.6 mgallon in a week is probably not going to happen. That would require a system capable of effectively treating at 158 GPM running 24 hours a day. Plan on the process taking about two to three weeks, and look for a system that is used for precipitation OR you could contract out membrane filtration, Reverse osmosis or even Ion exchange.

There are lots of companies that offer these services, just look around here and it will lead you in the right direction.

Ryan Cook
Toccoa, Georgia


A. I agree with Ted. This is a large volume of water, and thought must be put into this as there will be cost issues to consider. Ion exchange columns will work but this may be overkill in this situation. You can flow the water through a filter type media to lower the zinc or you may just need to adjust the pH and drop out through hydroxide precipitation. Contact or consult with people in the heavy metals field (Wastewater Treatment industry).

Gordon Djani
- Greenville, South Carolina


A. Sir:
I once had this problem for a client, but do not know if he followed through or not. In Zinc Abstracts I found that passing the water through ground-up automobile tires the zinc ion was absorbed in the carbon in the automobile tires. The generated ground up automobile tires was then used on an agricultural field for available zinc ion. The crop was either corn or sugar beets. The water passing through the ground-up automobile tires had only a few tenths of a ppm still dissolved.

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota

November 5, 2009

A. Fairly high levels of Zn, but you might want to check with companies like Tigg Corporation or Great Lakes Carbon. They both have mobile units for ion exchange up to 500 - 600 gpm. Forms of activated alumina have fairly high adsorption capacities for Zn (up to around 60 - 70 mg/g) and they are familiar with the process.

Activated alumina is being used for Zn removal from ballast water, and storm water run off at a couple of galvanizing yards.

William Reid
- Naperville, Illinois, USA

February 11, 2013

Q. We run a batch treatment waste stream and we have found a high level of zinc in the first stage cleaning rinse tanks. We have tried pH adjust and numerous chemicals to drop the zinc of the this waste stream with no luck, however, we are only having this problem in the chelated rinses after our cleaners. In the rinses after our zinc plating and chromating tanks we are able to drop the zinc out fairly easily.

Any insight anyone has would be greatly appreciated.

Mike Seidl
Waste Treatment Operator - Hudson, New Hampshire, USA

February 13, 2013

A. Hi Mike. How is substantial zinc getting into the rinses after the cleaners? If you are replating rejects by simply running them through your line again, stripping the zinc in the electrocleaner, you may have to change something -- like stripping the zinc in acid before re-running them so these chelated cleaners don't get so loaded with zinc.

As for treatment of chelated cleaners, the usual process is to lower the pH to the acid range, say pH 3.0, add a good bit of magnesium sulphate or calcium chloride to try to tie up the chelating agents, then raise the pH to the proper range for precipitation of the zinc (maybe 10.0).

Hopefully Dave Wichern will stop in and offer a more precise suggestion.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

simultaneous February 14, 2013

A. Why, thanks Ted!

Anyway, your suggestion is pretty good. The only things I'll add are; I'd try ferrous sulfate addition at low pH, then bring it up to about 9.2 - 9.5. In my experience, 10 is a little high for Zn. However, what you suggested might work better. Experiment will tell.

A good way to go about this is to do a series of jar test experiments where the pH is varied from, say, 8.8 to 10.5 in 0.3 pH unit increments and see what works best. If the lowest residual is still higher than you want to see it, try adding various coagulants/co-precipitants at the optimal pH and see if that helps. If it does not, you will need to add some precipitant like sodium sulfide (my choice) or DTC.

Good luck!

dave wichern
Dave Wichern
Consultant - The Bronx, New York

February 14, 2013

A. One possibility is to use a chelate breaker. Another possible solution is to use only softened water for the cleaner and switch to a non-chelated cleaner formulation. There are cleaners that will do a fine job and still be treatable by hydroxide precipitation.

Lyle Kirman
consultant - Cleveland, Ohio

Removal of Zinc from 140000 ppm to 3 ppm in wastewater

August 18, 2017

Q. Good afternoon

We are dealing with some problems in our current system for treating wastewater. Due to the high Zinc concentration, we are producing a huge volume of sludge at the end of the process. The treatment we use increases the pH until 6 with magnesium oxide and then, we add an organic flocculant in order to remove some iron present in the effluent. After this stage, we increase the pH until 10 with sodium hydroxide adding another organic compound to improve settling velocity of the sludge. However, the volume of sludge we produce is very huge in comparison of the amount of clean water (about three times more in the clarifier). We are looking for some options to decrease its volume and enhance the performance of the treatment plant.

Thank you for your replies.

Kind regards,

Jessica Moná
engineer - Medellín, Colombia

August 22, 2017

A. Hi Jessica,

Do you have 14% in weight of zinc metal in solution? It is nearly 24% in weight of the hydroxide, and in volume it is nearly all of your wastewater, it will be very difficult to remove by precipitation...

Where is the wastewater from? Is it a one-time treatment or you produce this kind of waste all the time?

Regards and best of lucks!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

August 27, 2017

Q. Hi Daniel

Thanks for your reply

We are producing this kind of wastewater once per week in amounts 7 m3 average. We know the zinc concentration is huge (140 g per liter) but our process requires an ungalvanized stage. Do you believe a filter press could solve my problem? Or What methodology at low cost, Can we use to treat the wastewater?

I'm anxious to read your answer.

Thank you so much

Best Regards!

Jessica Moná [returning]
engineer - Medellín, Colombia

August 29, 2017

A. There are many filter options that could help, I think you should treat this in batch and pass it through a filter press when you get an even and good floc size.

If your biggest issue is Zinc, you should stop at pH 9, if you get over 10 you are redissolving some zinc, it is amphoteric and you may not get it out the water completely.

If you did things right, your filter press should give you almost clean water (pH ~ 9). You should see if further treatment is necessary, it varies from place to place, but if you don't have much organic it should be fine.

I use filter presses here in plant and they are very reliable, but there are some other type of filters. Best of lucks finding the best choice for you!

Best regards!!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

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