Journal of Dental Research, Vol 72, 1519-1525, Copyright © 1993 by International & American Associations for Dental Research Online Journals
Defluoridation of water at high pH with use of brushite, calcium hydroxide, and bone char
M. J. Larsen, E. I. Pearce and S. J. Jensen
Royal Dental College, Aarhus, Denmark.
The aim of this study was to improve the efficiency of the bone-char method
of water defluoridation by pre-treating the water with brushite and calcium
hydroxide. Various amounts of brushite, calcium hydroxide, and bone char
were suspended batchwise in 100 mL of distilled water containing 0.53
mmol/L fluoride for 24 h under gentle agitation. At suitable intervals, pH
and the concentrations of fluoride, calcium, and phosphate in the water
were determined and, when possible, the degrees of saturation with respect
to brushite, hydroxyapatite, and fluorapatite calculated. Bone char used
alone took up fluoride slowly and inefficiently. The addition of brushite
and calcium hydroxide resulted in high concentrations of calcium and
phosphate, making the solutions highly supersaturated with respect to
fluorapatite, and led to a 20-fold increase in fluoride removal from the
water. The combined use of all three salts left low concentrations of
phosphate in solution and optimized the fluoride uptake capacity. Repeated
use of the same bone char for 18 consecutive runs demonstrated that uptake
of fluoride by the bone char was improved by repeated use, provided that
brushite and calcium hydroxide were added. Therefore, addition of the two
salts to the water may prolong the life of the bone char indefinitely,
ensure the removal of fluoride, and thus avoid the problem of determining
when the bone char is exhausted. In conclusion, we show that the bone-char
defluoridation technique can be improved by addition of brushite and
calcium hydroxide to the water. The problem of high terminal pH remains,
however, and further work is required to improve potability.
