Waste disposal methods for hydrofluoric acid

Letter 5021

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Would any body know of any specific methods to neutralize and dispose used Hydrofluoric Acid. Please let me know. Thanks you !

Ajit Menon
- Rapid City, SD

Disposal of hydrofluoric can go two ways:

If your receiving stream (meaning surface water OR sewer) has no fluoride limitation, simple neutralization with caustic soda (sodium hydroxide) should be enough. If there are no regulated metals in the stream, that's it. With the current state of discharge regulations it's rare to have no fluoride limit.

If you have regulated metals or a limit on fluoride, lime neutralization/precipitation following by settling or microfiltration is recommended.

Bill Vins microwave & cable assemblies Mesa (what a place-a), Arizona

Yes. It's treated with calcium chloride and lime, for neutralization and fluoride removal. You dose with about 1/2 ounce per gallon of calcium chloride, then add hydrated lime [link is to product info at Amazon] to a pH of about 9. Then, floc out the solids with an anionic polymer.

If you do not need to treat for fluoride, you can neutralize the acid with caustic, instead. You will get much less sludge.

Do a bench scale test first to determine the appropriate dilution factor, if any. If the acid is really strong it may heat up excessively during neutralization, causing the release of HF vapors, and possible damage to equipment. Also, watch the pH probe...during the early stage of neutralization when there is still a lot of free HF,the glass bulb can easily be dissolved. Dave Wichern - The Bronx, New York