Fractionation of hydrogen isotopes between crystalline hydrates and saturated solution of cobalt dichloride†

Abstract

The hydrogen isotopic fractionation factors between the crystal water (CW) in crystalline hydrates and the saturated aqueous solution of cobalt dichloride, αCW−st.sol, were experimentally determined in the temperature range from 10 to 55 °C under equilibrium condition: αCW−st.sol in cobalt dichloride hexahydrate, CoCl2·6H2O, from 10 to 43°C, and in cobalt dichloride dihydrate, CoCl2·2H2O, at 50 and 55°C. The empirical relationship between lnαC.W.−st.sol and (1/T 2) on the CW of CoCl2·6H2O in the temperature range from 10 to 43°C was obtained as: 103lnαCW−st.sol=−2.46(106/T 2)+17.6. The CW of dihydrate of cobalt dichloride exhibits larger depletion of deuterium than that of hexahydrate. The values of αCW−st.sol in CoCl2·2H2O are similar to that of CuCl2·2H2O and BaCl2·2H2O at 25°C. This fact indicates that the hydrogen fractionation factor between the CW and the saturated aqueous solution of cobalt dichloride strongly depends on the structure of crystalline hydrate rather than the chemical species of cation and/or the crystallized temperature. †Revised version of a paper presented at the International Conference ‘Isotopes 2005 Bath’, 27 June to 1 July 2005, Bath, UK.