On Sunday,

Photo: Thomas Goethe, St. Petersburg Times

[“Empire Organic Greenhouses” was composting grass clippings with drywall to produce a product that is sold nationally through K-Mart.]

“For example, U.S. Pat. No. 4,734,200 discloses a process for treating acidic process waste water containing SiF.sub.6.sup.-2 and phosphorus-type contaminants, in which the waste water is treated with a strong base ion...

Similarly, U.S. Pat. No. 4,965,061 discloses a process for producing hydrofluoric acid from waste
water containing SiF.sub.6.sup.-2, in which the SiF.sub.6.sup.-2 is reacted with (NH.sub.4).sub.2
SO.sub.4 at a high pH to form (NH.sub.4).sub.2 SiF.sub.6, from which ammonia, Si(OH).sub.4
and HF are eventually produced.
exchange resin to remove SiF.sub.6.sup.-2.

==

United States Patent
                                                                   6,355,221
 Rappas
                                                             March 12, 2002

Process for removing soluble fluoride from a waste solution containing the same

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