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Q&As since 1989


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Fluoride waste treatment

We are looking to install a bath that uses potassium fluoride [affil links] or Ammonium Bifluoride. However, we need to know what are the steps to waste treat fluorides. Thanks.

Vero Dewis
 

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The addition of calcium will precipitate the fluoride out as CaF, very insoluble material.

George Shahin
Atotech - Rock Hill, South Carolina
 

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Precipitation with lime or calcium chloride and caustic are the most common. However, the residual fluoride concentration is usually 15-30 mg/l and this may be higher than you discharge limit.

Another drawback to this treatment method occurs when it is used to treat large volumes with very dilute fluoride concentrations. It takes a relatively large excess of calcium ions (several hundred ppm) to drive the fluoride concentration down below 20 mg/l. This can lead to very high chemical consumption. So, if you have a very dilute fluoride wastestream, and/or a very low discharge limit, you may want to investigate either enhanced chemical treatment, or use of IX or a membrane to concentrate the fluorides before treatment, or an IX polish after calcium treatment.

Lyle Kirman
consultant - Cleveland Heights, Ohio
 

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Dear friend ,

In INDIA , M/s ATIRA , have claimed to develop a wonderful technology involving electro-coagulation with non-consummable electrode . Requires very low electricity . I have tried Electrocoagulation with consumable Aluminum anodes , but cost you know is not comparable with technique involving no electrode consumption.

Regards,

SHAILESH KUMAR JHA