Masahisa Kakiuchi

The hydrogen isotopic fractionation factors between the crystal water (CW) in crystalline hydrates and the saturated aqueous solution of cobalt dichloride, alpha CW-st.sol , were experimentally determined in the temperature range from 10 to 55 degrees C under equilibrium condition: alpha(CW-st.sol) in cobalt dichloride hexahydrate, CoCl2 center dot 6H(2)O, from 10 to 43 degrees C, and in cobalt dichloride dihydrate, CoCl2 center dot 2H(2)O, at 50 and 55 degrees C. The empirical relationship between ln alpha C.W.-st.sol and (1/ T-2) on the CW of CoCl2 center dot 6H(2)O in the temperature range from 10 to 43 degrees C was obtained as: 10(3) ln alpha(CW-st.sol) =-2.46(10 6 /T-2 )+17.6. The CW of dihydrate of cobalt dichloride exhibits larger depletion of deuterium than that of hexahydrate. The values of alpha(CW-st.sol) in CoCl2 center dot 2H(2)O are similar to that of CuCl2 center dot 2H(2)O and BaCl2 center dot 2H(2)O at 25 degrees 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.