Yong-Hong Zhang

Zinc Isotope Effects Observed by Liquid Chromatography with Benzo-15-Crown-5 Resin

The chromatographic fractionation in Zn isotopes was performed on the synthesized benzo-15-crown-5 resin at 313 and 343 K. The lighter isotopes were found enriched in the resin phase. The isotope fractionation coefficients (ε) were 3.4 and 2.9×10−4, 4.7 and 4.7×10−4, and 6.7 and 5.7×10−4 for the 66Zn/64Zn, 67Zn/64Zn and 68Zn/64Zn isotopic pairs at 313 and 343 K, respectively. They reflected mass-dependence among the Zn isotopes at each operated temperature but did not show 1/T2 -temperature proportionality. The temperature effects of the composition of Zn species both in the solution phase and in the resin phase may account in part for the latter observation. The magnitudes of εs in this study were comparable to the ones obtained by ion exchange chromatography, but much smaller than those observed in the solvent extraction systems with a crown ether in the organic phase.

Strontium Isotope Effects Observed in Liquid Chromatography with Crown Ether Resins

Liquid chromatography using highly porous silica beads in which the pores were embedded with a benzo-15-crown-5 ether resin or using dicyclohexano-18-crown-6 ether resin as column packing material was employed to study strontium isotope fractionation. While no appreciable isotope effects of strontium were observed for the dicyclohexano-18-crown-6 ether resin, the enrichment of heavier isotopes of strontium was observed in the frontal parts of the strontium chromatograms for the benzo-15-crown-5 ether resin with the isotope effects on the order of 10−4. The observed strontium isotope effects were massdependent, indicating that they mostly come from isotope effects based on molecular vibration. Molecular orbital calculations supported the present experimental results in a qualitative fashion.

Ion exchange properties and selectivity of lithium isotopes on ion exchangers in the hydrogen form prepared from LiTixZr2−x(PO4)3 (0 ≤x≤ 2)

LiTixZr2−x(PO4)3 (0 ≤ x ≤ 2) (LiTZP(x)) were synthesized by heating stoichiometric mixtures of lithium carbonate, zirconyl nitrate, titanium oxide and phosphoric acid at 950 °C for 10 hours. Ion exchangers in the hydrogen form (HTZP(x)) were prepared by the acid treatment of LiTZP(x) and their cation exchange properties were investigated with group 1 and group 2 metal ions. While the topotactic ion exchange from LiTZP(x) to HTZP(x) occurred for 0 ≤ x ≤ 1.5, the main phase of HTZP(2.0) was semicrystalline layered Ti2O3(H2PO4)2·2H2O. All the ion exchangers obtained were not very stable and partially decomposed under basic conditions. HTZP(x) (0 ≤ x ≤ 1.5) showed high selectivity towards the lithium ion from among group 1 metal ions, whereas HTZP(2.0) showed no specific affinity towards any group 1 metal ions. The H+/Li+ ion exchange equilibrium in acidic conditions at 25 °C was attained within 7 days for HTZP(0.0), in 1 day for HTZP(0.5), HTZP(1.0) and HTZP(1.3) and within 1 min for HTZP(2.0). The H+/Li+ ion exchange rate thus increased with increasing x. The exceptionally high ion exchange rate on HTZP(2.0) could be ascribed to the layered structure of the main phase of HTZP(2.0). All the ion exchangers synthesized preferentially took up the lighter isotope of lithium (6Li) over the heavier counterpart (7Li). The maximum value of the lithium isotopic separation factor (S) was 1.044 obtained at x = 1.0 to 1.3. This indicated that the size and the nature of ion exchange sites was a determining factor of S, which depended on the differences in the ionic radius and electronegativity of titanium(IV) and zirconium(IV).

Zinc isotope accumulation in liquid chromatography with crown ether resin

Liquid chromatographic separation of zinc isotopes was attempted in the breakthrough manner using benzo-15-crown-5 resin as column packing material at 313 K, and a 20 m long development was successfully achieved. The value of the single-stage separation factor was 1.00035 for the 66Zn/64Zn isotopic pair, 1.00047 for 67Zn/64Zn pair, and 1.00060 for the 68Zn/64Zn pair, which were equivalent to those obtained by a 5 m long chromatographic experiment under the same conditions. Contrary to this, the HETP value was 0.19 cm at the 20m development while it had been 0.09 cm at the 5 m development. Connecting separation columns with polytetrafluoroethylene tubes not packed with the resin may be responsible for this migration distance dependence of the HETP.

Cerium isotope effects in Ce(III) malate and lactate complex formation studied by long-distance displacement chromatography †

Isotope effects of cerium were observed in malate and lactate complex formations during the long-distance displacement chromatographic processes at 313 K. Heavier isotopes were found fractionated in the frontal edges of the Ce adsorption bands in both the systems, registering a preference of the heavier isotopes for the Ce(III) complexes in the solution phase over the simply hydrated Ce(III) ions in the resin phase. The fractionation coefficients ϵ for the 136Ce/140Ce, 138Ce/140Ce and 142Ce/140Ce isotopic pairs were 7.1 × 10−6, 5.2 × 10−6 and −2.1 × 10−6 for the malate system, and 4.8 × 10−6, 4.5 × 10−6 and−2.6×10−6 for the lactate system, respectively. They all show the mass-dependent law if the deviation of ϵ for the 138Ce/140Ce pair was considered merely due to the isobaric interference in Ce isotopic ratio measurements, suggesting the molecular vibration, rather than the nuclear field shift, mainly contributes to the Ce isotope effects in the complex formation systems. The absolute values of ϵ between the two systems are comparable, suggesting no instinct difference in structural properties between Ce malate and lactate complexes involved. Revised version of a paper presented at the International Conference ‘Isotope 2005 Bath’, 27 June to 1 July 2005, Bath, UK.

Synthesis of Zirconium Phosphate, HZr2(PO4)3, in Pores of Silica Beads and Some Ion Exchange Separation Properties of the Composite Obtained

Abstract Zirconium phosphate, HZr2(PO4)3 (HZP), was synthesized in inner pores of highly porous silica beads, and the ion exchange properties of HZP-loaded silica beads (HZP-SiO2) thus obtained were examined. The ion exchange properties of HZP-SiO2 were basically equivalent to those of HZP in the form of powders. Chromatographic lithium isotope separation was attempted using HZP-SiO2 as column packing material. The heavier isotope was effectively accumulated in the frontal part of the lithium chromatogram. However, the tailing phenomenon was observed at the rear boundary of the chromatogram, and no effective accumulation of the isotope separation effect was observed in the tail.

Some Ion Exchange Properties of Porous Silica Beads Loaded with Semicrystalline Titanium Phosphate

Abstract Semicrystalline titanium phosphate, Ti2O3(H2PO4)2·2H2O (TiOP), has been synthesized mainly in the interior pores of porous silica beads, and some ion exchange properties of TiOP‐loaded silica beads thus obtained (TiOP‐SiO2) and their thermally treated product at 500°C (TiOP‐SiO2(500)) were investigated. The degree of TiOP‐loading was 16.5% on an average. As a whole, TiOP‐SiO2 and TiOP‐SiO2(500) retained the ion exchange properties including very high ion exchange rates that TiOP and its thermally treated product at 500°C obtained in the form of powders possessed.