|
Sign In to gain access to subscriptions and/or personal tools.
|
Defluoridation of Water at High pH with Use of Brushite, Calcium Hydroxide, and Bone Char
M.J. Larsen
Royal Dental College, Vennelyst Blud., DK-8000 Aarhus C, Denmark
E.I.F. Pearce
Dental Research Unit, Health Research Council of New Zealand, P.O. Box 27007, Wellington, New Zealand
S.J. Jensen
Royal Dental College, Vennelyst Blud., DK-8000 Aarhus C, 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.
REFERENCES
- Brudevold F., McCann HG, Grøn P. ( 1965). Caries resistance as related to the chemistry of the enamel. In: Wolstenholme GEW, O'Connor M, editors. Caries resistant teeth. London: Churchill, 121-140.
- Chen PS, Toribara TY, Warner H. (1956). Microdetermination of phosphorus. Anal Chem 28:1756-1758.
- Chow LC, Brown WE (1973). Reaction of dicalcium phosphate dihydrate with fluoride. J Dent Res 52:1220-1227. Christoffersen J., Christoffersen MR, Larsen R., Møller IJ (1991). Regeneration by surface-coating of bone char used for defluoridation of water. Wat Res 25:227-229.[CrossRef]
- Duff EJ ( 1971). Orthophosphates. Part II. The transformations brushite to fluorapatite and monetite to fluorapatite in aqueous potassium fluoride solution. J Chem Soc (A):33-38.
- Featherstone Jdb, Glena R., Shariati M., Shields CP (1990). Dependence of in vitro demineralization of apatite and remineralization of dental enamel on fluoride concentration. J Dent Res 69:620-625.[Medline]
[Order article via Infotrieve]
- Gregory TM, Moreno EC, Brown WE (1970). Solubility of CaHPO4.2H2O in the system Ca(OH)2-H3PO4-H2,O at 5, 15, 25, and 37.58C. J Res Nat Bur Stds 74(A):461-475.
- Grøn P., Messer AC (1964). The effect of fluoride and magnesium on the hydrolysis of dicalcium phosphate. J Dent Res 43:866.
- Larsen MJ (1974). In vitro studies of fluoride uptake in enamel. Scand J Dent Res 82:448-454.[Medline]
[Order article via Infotrieve]
- Larsen MJ (1986). An investigation of the theoretical background for the stability of the calcium phosphate salts and their mutual conversion in aqueous solutions. Arch Oral Biol 31:757-761.[CrossRef][Medline]
[Order article via Infotrieve]
- Larsen MJ, Jensen M. (1986). Solubility study of the initial formation of calcium orthophosphates from aqueous solutions at pH 5-10. Arch Oral Biol 31:565-572.[CrossRef][Medline]
[Order article via Infotrieve]
- Larsen MJ, Pearce Eif (1992). Partial defluoridation of drinking water using fluorapatite precipitation. Caries Res 26:22-28.[Medline]
[Order article via Infotrieve]
- LeGeros RZ (1991). Calcium phosphates in oral biology and medicine. Basel: Karger.
- Lin J., Raghavan S., Fuerstenau DW (1981). The adsorption of fluoride ions by hydroxyapatite from aqueous solution. Colloids Surf 3:357-370.[CrossRef]
- McCann HG (1968). The solubility of fluorapatite and its relationship to that of calcium fluoride. Arch Oral Biol 13:987-1001.[CrossRef][Medline]
[Order article via Infotrieve]
- McDowell H., Gregory TM, Brown WE (1977). Solubility of Ca3(PO4)3OH in the system Ca(OH)2-H3PO4-H2O at 5, 15, 25, and 35.58C. J Res Nat Bur Stds 81(A):273-281.
- Merck E. (1992). Reagenzien, Diagnostica, Chemicalien. Darmstadt: Merck.
- Mwaniki D. (1990). Fluoride binding capacity of bone charcoal and its effect on selected micro-organisms. East Afr Med J 67:427-431.[Medline]
[Order article via Infotrieve]
- Mwaniki D. (1992). Fluoride sorption characteristics of different grades of bone charcoal, based on batch tests. J Dent Res 71:1310-1315.[Abstract/Free Full Text]
- Mwaniki D., Nagelkerke N. (1990). Sorption kinetics of fluoride in drinking water by bone charcoal columns. Frontiers Med Biol Eng 2:303-308.
- Phantumvanit P., Guay M. ( 1991). Regeneration of bone char for recycling water defluoridation (abstract). J Dent Res 70:855.
- Phantumvanit P., Songpaisan Y., Møller IJ (1988). A defluoridator for individual households. World Health Forum 9:555-558.[Medline]
[Order article via Infotrieve]
- Willis JB (1961). Determination of calcium and magnesium in urine by atomic absorption spectroscopy. Anal Chem 33:556-559.
- World Health Organization (1971). International standards for drinking-water. Geneva: WHO.
Journal of Dental Research, Vol. 72, No. 11,
1519-1525 (1993)
DOI: 10.1177/00220345930720111001
 CiteULike  Complore  Connotea  Del.icio.us  Digg  Reddit  Technorati  Twitter What's this?
|
|
