THE EFFECTIVENESS OF BONE CHAR IN THE DEFLUORIDATION OF WATER IN RELATION TO ITS CRYSTALLINITY, CARBON CONTENT AND DISSOLUTION PATTERN

The procedure for charring bone has been found to influence the nature of its mineral phase, and also affects the defluoridation capacity of the char. The aim of this study was to examine the efficiency of defl uoridation by char produced from various parts of bones and charred fo r various lengths of time at various temperatures, relating the prepar ation of the char to its X-ray diffraction pattern, its content of pyr ophosphate and its capacity for defluoridation. Bone was charred for 1 and 4 h at 400 degrees C and 30 min, 4 h and 48 h at 550 degrees C. B atches of the chars were suspended in amounts of 0.25 g in 100 mi of d istilled water containing 0.53 mmol/l fluoride for up to 6 days under gentle agitation. At intervals, the pH and concentrations of fluoride, calcium and phosphate in the water were determined and the degree of saturation with respect to the calcium phosphate salts calculated. The charring procedure reduced the organic content of the bone from the 4 4-26% in intact bone to 3.4% in bone charred at 400 degrees C and to a lmost zero when charred at 550 degrees C for 48 h. When charred at 400 degrees C for up to 4 h the X-ray diffraction pattern of the bone sho wed a poorly crystallized apatite similar to that of untreated bone. H eating for 48 h or more at 550 degrees C led to considerably sharper a patite reflections, indicative of a well-crystallized salt. The chars produced at 400 degrees C reduced the fluoride concentration from 10 t o 1-2 parts/10(6) over 6 days, whilst the better crystallized chars re duced the fluoride concentration to only 7-8 parts/10(6), irrespective of whether the char originated from compact or spongy bone. Bone samp les charred for shorter periods at lower temperatures were poorer apat ites, but better fluoride absorbants, an effect unrelated to the carbo n residue or pyrophosphate content.