The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Water Treatment of Phosphoric Acid

I work in Industrial wastewater treatment in a Defense Plant. Our Barrel Plating operation recently started using a phosphoric acid in the plating operation. I have found a cationic polymer that works well for treating the continuous rinses. My problem arises when we attempt to "Batch Treat" the spent bath. We have found that the phosphoric acid wreaks havoc with the floc formation / settling / clarity of our discharge. If anyone out there has dealt with this acid effectively I would appreciate their input. I have used a combination of lime & caustic for pH control.

Thanks!

John Brownlee
Industrial Wastewater Treatment - Red Lion, Pennsylvania, USA
2004

---

2004

I have never seen a problem like that. In my experience, simple neutralization easily precipitates phosphate solutions and they settle well.

Certainly, your observation may be correct and simply outside of my experience, but please also consider these two possibilities: first, that the treated solution is just so laden with solids that you need to allow sufficient sludge accumulation and you may not be doing that; second, that there is some other ingredient in this new treatment than phosphoric acids and phosphates.

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

---

You do not mention what type of metal that you are treating or working with in your facility, so the response needs to be broadly written. Certain metals do form difficult to settle complexes when in the presence of high levels of salts. Brine (loosely defined) will disrupt the formation of particle agglomeration if 1) sufficiently high in strength, and 2) if certain metals are present. For instance, typically a high amount of aluminum, even if normally used as a coagulant, can have difficulty working as such in a high salt background, and acting as such if the salt background is sufficiently high. Other metals that have coagulation "issues" are nickel and zinc.

Phosphates can exacerbate the problem in certain streams, as they lend a rather ionically active, anionic background to a waste stream, that can render a typical anionic polymer reduced in effectiveness.

To counter this effect, you need to add something that is going to take some of the electrons out of the solution, not add to them. A'small dose of ferrous sulfate ⇦ this on eBay or Amazon [affil links] , or a similar reducing coagulant is very low quantities can do this rather quickly and effectively. Stay away from actual "reducing agents" - they don't offer anything but background characteristics.

AS an alternate, maybe you should consider looking into recycling the phosphoric acid instead of treating it. Its not the cheapest solution to work with, and is fairly easily cleaned up and reused. That could save you a lot of money, even in the smallest volumes.

Tom Baker
wastewater treatment specialist - Warminster, Pennsylvania
2004

---

---

January 7, 2013

Q. I need to acquire a few gallons of waste phosphoric acid for an experiment.
It should not have any cadmium, lead or mercury in it.
Otherwise, the ionic metal content is not important.

My question is: What kind of local shop would I be able to visit, where they would produce waste phosphoric acid solutions and be happy to give it away?
Please help with a specific type of shop or industry, because I would have to use a search engine to find the ones nearest me.

If my experiments work, I would want it in larger quantities (55 gallon drums) so a producer who would also be able to supply volume is appreciated even more.

Thanks All,
-Gary

Gary Wilson
- Hudson, New York, USA