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Ammonium bifluoride wastewater

We are installing a chemical deburring process that will use 4 compounds including ammonium bifluoride and oxalic acid. What are my options for discharging the bath (approximately 500 gallons)? We currently do not have a pretreatment system at the location.

Ken Brown
EHS Coordinator - Ft. Mill, South Carolina, US
2004

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2004

You will want to find out from your local POTW what their limit is on fluoride. As you may recognize, this is often a regulated substance in the effluent, but is not a metal that you can efficiently precipitate out. Calcium fluoride can be formed but may not reliably meet your limits.

Ammonia is also a problem in high concentration because it will complex the metals. There are times when a project like this needs to start with a treatability study, and this may be the case here. I have the general feeling that ion exchange technology will prove to applicable to this situation, rather than simply an end-of-pipe chemical precipitation system.

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

Ted is absolutely right on about the fluoride and discharge. Some POTW's and other discharge regulators frown on even low levels of the ion in waste water. The ammonia will also likely be an issue to be dealt with as well.

The oxalic acid, however, should also be of some concern, as it will typically form complexed metal solids and compounds that are notoriously difficult to treat, and in some areas, are considered downright hazardous.

Treatability would be the key. I'm not in favor of the ion exchange approach, however, as this is a concentrate and return technology - meaning that you might collect it (if its dilute enough) but you still have to treat it - along with everything else in the water too. There are some chemical treatment techniques that are very effective in dealing with one or more of these ions.

Tom Baker
wastewater treatment specialist - Warminster, Pennsylvania
2004