Metal finishing Q&As since 1989

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citric acid Destroys Floc

Some of the cleaners my company use in the cleaning and shining of their products contain citric acid. As the wastewater is treated the citric acid destroys the floc and the clarity of the water. Is the anything that be used to precipitate or remove the citric acid before it reaches the clarifier.

Thanks,

Mike Capps
plating/wastewater treatment - Bon Aqua, Tennessee, USA
2004

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First of two simultaneous responses --

Hey Mike,

citric acid in the effluent can tie-up and prevent your metals from dropping out. Dispersing agents in cleaners still do their job in your waste stream. I would recommend batch treating this waste with aluminum sulphate or lime at a low pH (2 or so works in my system). Mix well and let settle before releasing. You should be able to see how it will react with your system. If the treated tank settles out clear, you should be good to go. Probably a good idea to do some jar testing first.

Worked for me most of the time, but we ended up changing to a different cleaner formulation to get away from the hassle.

Good Luck

Trent Kaufman
electroplater - Galva, Illinois
2004

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Second of two simultaneous responses -- 2004

One explanation for your problems is that the citric acid is tying up ions like calcium, magnesium, and/or aluminum that contribute to good coagulation and floc formation. If this is indeed the cause of your problem, an addition of calcium chloride, or some alum based coagulant should fix it. Another possibility is that detergents in the cleaner are the problem. In this case the remedy is the same, but the results will be much poorer.

Can you possibly batch treat this waste separately? That is what I would do.

Dave Wichern
Consultant - The Bronx, New York

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2004

citric acid is a mild chelator, and will tie up metals, so you need to pretreat before going into the flocculating system, or add a chelate breaker. We can recommend companies who supply these, or you can go online to check it out.

There are a number of ways to pretreat if you want to do that.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois