Takao Oi

Boron isotopic compositions of some boron minerals

Abstract Boron minerals that have different structural formulae but are supposed to have the same geologic origin have been collected and analyzed for the 11 B 10 B isotopic ratio. It has been reconfirmed that minerals of marine origin have higher 11 B 10 B ratios than those of nonmarine origin. It has been found that the sequence of decreasing 11 B 10 B values among the minerals with the same geologic origin is; borax, tincal, kernite (Na borates) > ulexite ( Na Ca borate) > colemanite, iyoite, meyerhofferite (Ca borates). This sequence is explainable on the basis of the difference in crystal structure among the minerals. That is, minerals with higher BO 3 BO 4 ratios, (the ratio of the number of the BO3 triangle units to the number of the BO4 tetrahedron units in the structural formula of a mineral) have higher 11 B 10 B ratios.

Fractionation of Strontium Isotopes in Cation-Exchange Chromatography

Abstract Ion-exchange displacement chromatography of calcium has been carried out successfully for the purpose of observing calcium isotope fractionation effects. Small but definite accumulation of the heavier isotopes has been observed at the front parts of the calcium adsorption bands, which means they are preferentially fractionated into the solution phase. The average values of the single-stage separation factor minus one per unit mass difference between isotopes (∊/Δ M) have been 2.0 × 10−5 for the calcium chloride system, 5.2 × 10−5 for the calcium lactate system, and 2.3 × 10−5 for the calcium acetate system at 25°C. The reduced partition function ratios of the calcium species involved in the present study have been estimated by using separation factor data and available data on calcium hydration under appropriate assumptions. The reduced partition function ratios of the complex species have been found to be larger than that of the simple hydrated calcium ion, which is a cause of the experimental r...

Calculations of reduced partition function ratios of monomeric and dimeric boric acids and borates by the ab initio molecular orbital theory

With the final goal to elucidate boron isotope fractionation observed experimentally, molecular orbital calculations were performed on boric acid and borate monomers and dimers. The geometries of B(OH)3 and B(OH)4 − were first optimized and their vibrational frequencies were calculated at their optimized structures. The estimated 11B-to-10B isotopic reduced partition function ratios (RPFRs) of B(OH)3 and B(OH)4 − and the calculated equilibrium constant of the boron isotope exchange reaction between the two boron species revealed that a more advanced molecular orbital theory with a higher level basis set did not necessarily yield better results. It was concluded that HF/6-31G(d) calculations were most appropriate for the present purpose. The RPFRs of the dimers, H4B2O5, H5B2O6AJA- and H6B2AJA-, estimated from the RPFRs of the monomers by the use of additivity of the logarithm of RPFRs agreed with those calculated using the frequencies of the dimers within a margin of 1%. This error corresponded to the error of 5% on In(RPFR). The equilibrium constant of boron isotope exchange reaction between two boron species among the monomer and dimers at 25°C varied from 1.0207 to 1.0360, indicating the importance of accurate estimation of the RPFRs of polyboric acids and polyborates in real systems.

A Theoretical Study of Isotope Separation by Displacement Chromatography

Abstract A set of equations is derived to describe mathematically the isotope distribution in the separation process of displacement chromatography. Emphasis is placed on nonsteady-state isotope accumulation in the boundary region of a migration band. The results indicate that the isotope profile in the migration band is expressed by where R, ∊, k, R0, L, and x are local isotope fraction, separation coefficient, slope coefficient, original isotope fraction, migration length, and position in the band, respectively. Mathematical treatment is extended to the determination of HETP of experimental systems. The relation between the frontal isotope ratio r L and the migration length is also obtained. The validity of the derived equations is verified by using the reported experimental data on boron isotope separation by ion-exchange chromatography.

Ab initio Molecular Orbital Calculations of Reduced Partition Function Ratios of Polyboric Acids and Polyborate Anions

Abstract Molecular orbital calculations at the HF/6-3 lG(d) level were carried out for polyboric acids and poly-borate anions up to a pentamer to estimate their 11B -to-10B isotopic reduced partition function ratios (RPFRs) and examine the additivity of logarithms of RPFRs. Approximate RPFR-values calculated by the use of the additivity agreed with exact RPFR-values within a margin of 1% error. This error was equivalent to a 5% error on ln(RPFR). The equilibrium constants of mono boron isotope exhange reac-tions between three-coordinate boron and four-coordinate boron ranged from 1.0203 to 1.0360 at 25 °C, indicating the importance of exact evaluation of RPFRs of polymers.

Characterization of semicrystalline titanium(IV) phosphates and their selectivity of cations and lithium isotopes

A semicrystalline layered titanium phosphate (scTiOP), which showed the chemical properties of a cation exchanger, was synthesized from a mixed solution of titanyl sulfate and ammonium dihydrogenphosphate solutions under mild conditions. Based on the results of 31P MAS NMR measurements, infrared measurements, thermogravimetry–differential thermal analysis, ICP atomic emission spectroscopic analysis and powder X-ray diffraction analysis, the ion exchanger was identified as Ti2O3(H2PO4)2·2H2O. Ion exchangers with varying degrees of condensation of the dihydrogenphosphate groups, and consequently having three-dimensional cross-linked structures with minutely controlled ion exchange sites, were obtained by the thermal treatment of scTiOP at different temperatures. The ion exchangers obtained by thermal treatment at temperatures from 200 to 600 °C showed a high affinity toward sodium ion among the alkali metal ions, whereas scTiOP and the ion exchanger treated at 100 °C showed no specific selectivity of any alkali metal ion. The single-stage separation factor, S, for the lithium isotopes was a slow increasing function of the temperature of the thermal treatment up to 600 °C, and the maximum S value at 25 °C was 1.028. The occurrence of a high affinity to sodium ion, the increase in S value and the development of a three dimensional –O–P–O– network seemed mutually correlated.

Determination of rare earth elements in hot spring and crater lake waters by epithermal neutron activation analysis

Determination of the rare earth elements (REEs) in acidic hot spring and crater lake waters by neutron activation analysis (NAA), in which activation was performed mostly by epithermal neutrons (epithermal NAA) was investigated. Nine REEs, La, Ce, Sm, Eu, Tb, Ho, Tm, Yb and Lu, out of fourteen naturally existing REEs were determined at ppb levels with satisfactory precision. The epithermal NAA was found to be more effective in the determination of Sm, Tb, Ho and Yb than normal NAA, in which activation was performed mainly by thermal neutrons. Combined use of the epithermal and normal NAAs enabled the determination of eleven REEs, La, Ce, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb and Lu.

Experimental Studies on the Mobility of Lanthanides Accompanying Alteration of Andesite by Acidic Hot Spring Water

Abstract The mobility of lanthanides (Lns) accompanying interactions of powdered andesitic rocks with acidic hot spring water and acidic hot spring water vapor/steam was studied in the experiments set up in the field. At the early stage of rock alteration, light Lns were slightly easier to be leached out by acidic hot spring waters from andesitic rocks than heavy Lns. This result qualitatively agreed with the result obtained in the previous experiments carried out in the laboratory. It was also found that the Ln abundance patterns (Ln patterns) obtained by normalization with Ln contents of the original rock showed slightly positive Eu anomalies at the early stage of rock alteration and turned to show negative Eu anomalies and the extent of negative anomaly monotonously increased as rock alteration proceeded. This trend in the direction of Eu anomaly was correlated to the degrees of decompositions of major rock-forming minerals and interstitial materials in the rock. At the earliest stage of rock alteration in acidic environments, the interstitial materials with relatively low Eu contents were decomposed, which resulted in the positive Eu anomaly. In the following stage, feldspar that had a relatively high Eu content was decomposed, which led to the negative Eu anomaly.

Synthesis and characterization of polypyridineruthenium(II) complexes containing a linear ambidentate ligand, NCO− or NCS−, and reaction of isocyanato complexes under acidic conditions

Abstract Isocyanato and isothiocyanatopolypyridineruthenium complexes, [Ru(NCX)Y(bpy)(py)2]n+ (bpy=2,2′-bipyridine, py=pyridine; X=O, Y=NO2 for n=0, and Y=py for n=1; X=S, Y=NO2 for n=0, Y=NO for n=2, and Y=py for n=1), were synthesized by the reaction of polypyridineruthenium complexes with potassium cyanate or sodium thiocyanate salt. Isocyanatoruthenium(II) complexes, [Ru(NCO)(NO2)(bpy)(py)2] and [Ru(NCO)(bpy)(py)3]+, react under acidic conditions to form the corresponding ammineruthenium complexes, [Ru(NO)(NH3)(bpy)(py)2]3+. The molecular structures of [Ru(NCO)(bpy)(py)3]ClO4, [Ru(NCS)(NO)(bpy)(py)2](PF6)2 and [Ru(NO)(NH3)(bpy)(py)2](PF6)3 were determined by X-ray crystallography.

Determination of rare earth elements in hot spring water and crater lake water samples by neutron activation analysis incorporating coprecipitation process using aluminium as a collector

Hot spring water and crater lake water samples were analyzed for their rare earth elements: (REEs) by neutron activation method, which, in the irradiation, sample preparation, incorporated a coprecipitation process in which aluminium was used as a collector. Ten REEs, La, Ce, Sm, Eu, Gd, Tb, Dy, Tm, Yb and Lu, were consequently detected and determined at the ppb level with satisfactory precision. It was shown that the aluminium coprecipitation is effective in enhancing concentrations of the REEs and reducing the amounts of interfering nuclides before neutron irradiation.