ABSTRACT

The D/H fractionation factors between the crystal water of copper chloride dihydrate and a saturated aqueous solution of copper(II) chloride, α_CW-st.sol, and between the saturated aqueous solution and water vapor, α_st.sol-V, were experimentally determined at 25°C in equilibrium. The observed values of α_CW-st.sol and α_st.sol-V, were 0.950 ± 0.002 and 1.052 ± 0.001, respectively. The D/H fractionation factor between the crystal water of copper chloride dehydrate and water vapor in equilibrium, α_CW-V, was calculated to be 0.999 ± 0.002 from the observed values of α_CW-st.sol and α_st.sol-V, and is used to discuss D/H fractionation in crystal water of crystalline hydrates. It is shown that such D/H fractionation is better expressed by α_CW-V than by the conventionally used fractionation factor between crystal water and mother liquor, α_CW-st.sol, because α_CW-V represents the activity ratio, whereas α_CW-st.sol is simply the concentration ratio. Based on the results in this study, we consider that the coordination bond between divalent cupreous ions and oxygen atoms in water molecules and the hydrogen bond between crystal water and chlorine ions contribute substantially to the fractionation of hydrogen isotopes.