CHARACTERISTICS OF BONE CHAR RELATED TO EFFICACY OF FLUORIDE REMOVAL FROM HIGHLY-FLUORIDATED WATER

Bone char, prepared from commercially available bone meal by steaming, drying and calcining at 600 degrees C, is one of the systems used to reduce the levels of fluoride (F) in drinking water to less harmful le vels. The purpose of this study was to determine factors which will in crease the efficacy of bone char to remove F from fluoridated water. P olyvinyl chloride pipes were prepared with bone char calcined at diffe rent temperatures (400, 600, 800 degrees C). Bone char regenerated usi ng either an acid or alkaline method was also used to prepare the colu mns. Naturally fluoridated water in Thailand was poured at the top of the column and defluoridated water (effluent) collected at the bottom. The F, calcium and phosphate contents and the pH of the effluent were determined. Bone char materials, before and after the processes of de fluoridation, were characterized using x-ray diffraction and infrared absorption spectroscopy. Results demonstrated: 1) the capacity of the bone char to remove F was inversely related to the crystallinity (refl ecting crystal size) of the bone apatite which in turn was related to the calcination temperature (i.e., the higher the temperature of calci nations, the greater the crystallinity of the bone apatite; the greate r the crystallinity the lower the capacity); 2) the alkaline method of regeneration was more efficient than the acid method in terms of the amount of F removed from the bone char; 3) the crystallinity of the bo ne char increased after defluoridation procedure. It is concluded that the removal of F from the fluoridated water may occur by a dissolutio n-reprecipitation process resulting in the formation of (F,OH)-apatite . This reaction may be a major mechanism operating during the defluori dation of water using bone char. The results suggest that heating at l ow temperature (< 600 degrees C) and regeneration using the alkaline m ethod will maximize the efficacy of bone char in removing F from natur ally fluoridated water.