Defluoridation of drinking water by co-precipitation with apatite.
The two-step brushite saturation, apatite precipitation method which has previously been shown to be effective for the partial defluoridation of water containing 10 ppm F has now been tested at lower concentrations. The method also reduced F concentrations in the range 1-5 ppm, but was less efficient at lower F levels. Although co-precipitation as fluorapatite is the intended mechanism here, experiments indicated that F adsorption on the seed material added to the defluoridation effect. When the contribution of co-precipitation was isolated it was found that this mechanism could, on its own, account for a reduction of 2.2-2.6 ppm F in water initially containing 3-5 ppm F. A computer program which determines equilibrium F concentrations when supersaturated solutions are induced to precipitate fluorapatite was used to estimate the maximum possible F removal from water by co-precipitation. Using saturation with brushite as a starting point for precipitation, F reductions similar to those found experimentally were predicted. Computer simulations also suggest that any desired reduction in F concentration may be achieved by adding sufficient Ca and phosphate and/or by raising the initial pH.
Pearce
E I
EI
Dental Research Unit, HRC of NZ, Wellington, New Zealand.
Larsen
M J
MJ
D000327:Adsorption; D001031:Apatites / Q000737:chemistry*; D002118:Calcium / Q000032:analysis / Q000737:chemistry; D002130:Calcium Phosphates / Q000737:chemistry; D002606:Charcoal; D011232:Chemical Precipitation; D003198:Computer Simulation; D017886:Durapatite / Q000737:chemistry; D005457:Fluoridation; D005459:Fluorides / Q000032:analysis* / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D010758:Phosphorus / Q000032:analysis / Q000737:chemistry; D013997:Time Factors; D014881:Water Supply / Q000032:analysis*
D001031:Apatites; D002130:Calcium Phosphates; D002606:Charcoal; D010758:Phosphorus; D017886:Durapatite; C025105:fluorapatite; C494366:calcium phosphate, dibasic, dihydrate; D005459:Fluorides; D002118:Calcium