Zinc removal from wastewater

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!

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 finishing.com here and it will lead you in the right direction.

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).

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.
Regards,

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.

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.

Regards,

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!

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!!

  Good Morning Daniel

Thanks for your reply. We are going to make some tests in a filter press we rent. I hope the results will be fine.

Best of luck Jessica! Tell us how this worked for you so our colleagues can take this as a possible solution if they have the same problems as you :)

Saludos hermanos colombianos!

A. Hi Rennell. Running the stormwater through a sand filter does not help much because virtually all of the zinc is dissolved rather than suspended. If you google "zinc removal from roof runoff" you will find a lot of info from government agencies as well as vendors of treatment systems. As cynics note, you'll probably be regulated down to whatever analytical limits the regulatory agencies can monitor you to, and analytical equipment constantly improves, so don't waste money on anything that is even remotely marginal.

It's not easy to reliably paint galvanized metal roofs, but if I were you and I were confident that the galvanized roof was the source of the zinc, I'd suggest painting your roof white, with a paint which does not contain zinc or copper. Good luck.

And leave that sand filter in place to catch peeling paint chips because those agency rules will doubtless be causing an awful lot of paint to be applied to, and subsequently peel off of, people's roofs and run down with the storm water. (I'm not against regulation of environmental hazards, but I am opposed to ignoring the law of unintended consequences with an issue so well known and pervasive as paint peeling from galvanizing :-)

Regards,