Masaaki Musashi

Column chromatographic boron isotope separation at 5 and 17 MPa with diluted boric acid solution

Boron isotopic fractionation factor (S) between boron taken up in strongly basic anion exchange resin and boron in aqueous solution was determined by breakthrough column chromatography at 5 and 17 MPa at 25 degrees C, using 0.1 mM boric acid solution as feed solution. The S values obtained were 1.018 and 1.012, respectively, which were smaller than the value reported by using the same chromatographic method at the atmospheric pressure at 25 degrees C with the boron concentration of 10mM, but were larger than the values under the same condition with much higher concentration of 100 and 501 mM. Calculations based on the theory of isotope distribution between two phases estimated that 21% (5 MPa) and 47% (17 MPa) of boron taken up in the resin phase was in the three-coordinated B(OH)(3)-form, instead of in the four-coordinated B(OH)(4)-form, at high pressures even with a very diluted boric acid solution. We discussed the present results by introducing (1) hydration and (2) a partial molar volume difference between isotopic molecules. Borate may have been partially dehydrated upon transfer from the solution phase to the resin phase at high pressures, which resulted in smaller S values compared with those at the atmospheric pressure. Instead, it may be possible that the difference in the isotopic partial molar volume difference between B(OH)(3) and B(OH)(4)(-) caused the S value to decrease with increasing pressure.

Chlorine isotope fractionation associated with volcanic activity at the Kusatsu-Bandaiko hot spring in Japan

Stable chlorine isotope compositions (δ37Cl, per-mil: ‰, vs. a standard sample of sea water) of Kusatsu-bandaiko hot water samples, taken regularly in the years between 1974 and 1995 in the Kusatsu-Shirane volcanic region, Japan, were measured mass-spectrometrically. The results show that the δ37Cl values of the waters taken before 1984 were at around−0.12‰, whereas those after 1984 were at around+0.18‰. The δ37Cl values are thus distinct across 1984, which is consistent with the classification by the Cl to S molar ratio (Cl/S): the higher the Cl/S ratio, the larger the δ37Cl value. The δ37Cl value increased as much as 0.30‰ during 5 years between 1980 and 1984. This isotopic enrichment is likely correlated with increasing Cl/S ratios, suggesting that the heavier isotope (37Cl) may have preferentially increased in the original Cl source of the hot spring across 1984 when volcanic activity likely increased at Mt Kusatsu-Shirane.

Chromatographic Study on Boron Isotopic Fractionation at High Pressure

Boron isotopic fractionation factor (S) between boron adsorbed onto kaolin clay and boron in aqueous solution was determined by break-through column chromatography at 25.0 MPa at 5 and 25°C. The S values obtained were 1.0021 at 5°C and 1.0011 at 25°C, and were smaller than those obtained by the batch method performed at the atmospheric pressure at room temperature. Theoretical calculations estimate that more than 90% of boron in the clay phase was taken up as B(OH)3-form at high pressures. Combining the present S values with preliminarily obtained one at 12.0 MPa, it is likely that S value decreases with increasing pressure, which suggests that the difference of the partial isotopic molar volumes between 10B(OH)3 and 11B(OH)3 is larger than that of the volumes between 10B(OH)4 − and 11B(OH)4 −.