ABSTRACT

The behavior of fluoride during the precipitation of calcium carbonate from calcium bicarbonate solution was studied experimentally. Magnesium ions in parent solutions cause the coprecipitation of fluoride with calcium carbonate. The amount of fluoride coprecipitated with calcite increases with increasing concentration of magnesium ions in parent solutions, whereas the amount of fluoride coprecipitated with aragonite decreases. It may suggest that the mechanism of the coprecipitation of fluoride with calcite is different from that with aragonite. The amount of fluoride coprecipitated with aragonite is larger than that with calcite. The experimental result agrees with the observed fact that the fluoride contents of skeletal aragonite of marine organisms and of natural aragonite formed inorganically in sea water are higher than those of skeletal calcites. Fluoride in parent solutions greatly favors calcite formation.