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citric acid passivation ...waste treatment

2007

what is the way to waste treat the citric acid bath when the bath has been exhausted?

I have been told that the citric acid can "hold" some of the heavy metals and not let them precipitate out during normal waste treatment.

any thoughts?

Chad
tech employee - Rockford, IL

Ed. note: we need your full name, please, Chad.

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First of two simultaneous responses --

There are a number of ways to treat this bath, depending on volume and volume of "other wastewater" treated. You can treat this as a batch, decrease the pH to 2 to weaken the bond between the chealtor and the metal(s), increase pH to the optimum pH range for the target metal, coagulate and floc. This may work, or you may require a precipitant product to aid in cleaving the chelate and metal bond. There are many metal precipitants on the market so choose carefully or talk with your WWT chemical supplier.

You may be able to bleed this into your system, depending on batch size and the flow of your WWT system. Run a bench scale test 1st and see if your current treatment program can handle the chelate stream being introduced. Play around with feed rates and introduce the minimum amount if possible.

Gordon Djani
water treatment - Greenville, South Carolina
2007

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Second of two simultaneous responses --

You could try adding some calcium chloride, elevating the pH with caustic soda [affil links] to about 10, then adding some sodium sulfide, DTC, or Degussa TMT-15 to precipitate the nickel down below about 1 mg/l.

Dave Wichern
Consultant - The Bronx, New York
2007

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Since a citric bath tends to remove only iron and not heavy metals from stainless steel, it by itself is not hazardous waste. You need only neutralize it to bring the pH up to local disposal regulations.

If your plant requires all waste streams to go through a precipitation system, You cannot introduce the citric into that as it will chelate other things and cause problems. Let us know if we can be of any help.

Also, there is usually no need to let the bath get to an "exhausted" state, replenishing the existing bath by adding some fresh acid usually is sufficient. The bath can be kept clean with a pump and filter rig.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2007

We use Stellar Solutions [a finishing.com supporting advertiser] CitriSurf in our passivation and Kleer Kleen for our cleaning bath. Both are approx. 23 gallon tanks and are heated to about 150 degrees Fahrenheit. Can you recommend a durable pump and filter rig that would hold up and do a good job that is not too expensive? Thanks in advance.

John Murley
- Olive Branch, Mississippi, United States
April 1, 2010