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EVALUATION OF EMISSIONS AND CONTROL TECHNIQUES FOR REDUCING FLUORIDE EMISSIONS FROM GYPSUM PONDS IN THE PHOSPHORIC ACID INDUSTRY
Citation:
Linero, A. AND R. Baker. EVALUATION OF EMISSIONS AND CONTROL TECHNIQUES FOR REDUCING FLUORIDE EMISSIONS FROM GYPSUM PONDS IN THE PHOSPHORIC ACID INDUSTRY. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/2-78/124.
Description:
The report gives results of a study of gaseous emissions from gypsum disposal and cooling water ponds to determine their potential as sources of airborne fluorides from the manufacture of phosphoric acid. A model of the chemistry within the pond environment was developed. Previous emission rate studies were evaluated with respect to assumptions, methodologies, and conclusions: none provided a sufficient basis for determining a fluoride emission factor. The ponds, found in major phosphate production areas (e.g., Florida, North Carolina, and the Western U.S.), usually cover several hundred acres. Process water enters a pond at over 100 F, and leaves at lower temperatures after evaporative cooling. Ambient concentrations near a typical pond were calculated by predictive modeling methods, assuming emission rates of 0.1, 1, and 10 lb per acre per day. At the higher rates, control of fluoride emissions appears necessary. An analysis of possible control methods indicated that liming is too expensive an alternative. The most promising method appears to be the Swift process for fluorosilicic acid recovery, coupled with segregation of the cooling and gypsum pond waters. The hemi/dihydrate process also appears to be promising.