| Budget Amount *help |
¥6,700,000 (Direct Cost: ¥6,700,000)
Fiscal Year 1986: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1985: ¥5,800,000 (Direct Cost: ¥5,800,000)
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| Research Abstract |
An ion chromatographic method for determining traces of F in insoluble carbonate minerals, such as calcite, protodolomite and dolomite, has been developped. About 100 mg of finely powdered sample were taken in a small beaker together with 5 mL of H-type ion-exchange resin and some water. After stirring of the mixture for several hours, the aqueous phase was analyzed by ion chromatography. This method allows to determine F in carbonate minerals at the low ppm level.
The partition of <F^-> between calcite and solution was studied by applying this analytical method to calcite precipitated from aqueous solution containing <F^-> . The partition equilibrium of <F^-> was attained by continuous stirring of the solution with calcite for 300 h. As in the case of aragonite, it was confirmed that the value [F]/ <(alpha)_F> <(alpha)(^(0.5)_(Ca))> is constant, where [F] is F concentration in calcite (in mol/g), <(alpha)_F> and <(alpha)_(Ca)> are <F^-> and <Ca^(2+)> activities in aqueous phase, respectively. This relationship revealed that a <CO(_3^(2-))> ion in calcite can be replaced by <2F^-> ions. The value was estimated to be 16 at 15゜C. The corresponding value for aragonite was 89, so that F content is 5 times higher in aragonite than in calcite, provided that both minerals are in equilibrium with the same solution.
The F content of calcitic deposits from spring waters was explained by this uptake mechanism. It is advisable to use [F] <(alpha)(^(0.5)_(CO_3))> / <(alpha)_F> instead of the above value, because such spring waters are supersaturated with calcite.
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