Assessment of fluoride removal from drinking water by calcium phosphate systems

Static defluoridation of high fluoride (10-12 ppm) water by sixteen different combinations of tricalcium phosphate (TCP), bone char (BC), hydroxyapatite (HAP), and related substances has been investigated. Defluoridation of 100 mL of the water by 300 mg of relatively insoluble phosphates is only 60-70 percent complete. Defluoridation is 30 percent more efficient, however, when a more soluble phosphate is present, which suggests that defluoridation by TCP, BC, and HAP could be similarly improved. The combination of 300 mg BC plus 23 mg monocalcium phosphate (MCP) per 100 mL of high fluoride water appears to be the most efficient, reducing the fluoride concentration from 10.4 mg/L to 0.6 mg/L by coprecipitation over 24 hr at pH 6.5-8.5 (DBO).