Fractionation of hydrogen isotopes in crystal water of copper chloride dihydrate-saturated solution-water vapor system

Abstract

The D/H fractionation factors between the crystal water of copper chloride dihydrate and a saturated aqueous solution of copper (II) chloride, αCW-st.sol, and between the saturated aqueous solution and water vapor, αst.sol-v, were experimentally determined at 25°C in equilibrium. The observed values of αCW-st.sol and αst.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 dihydrate and water vapor in equilibrium, αCW-v, was calculated to be 0.999 ± 0.002 from the observed values of αCW-st.sol and αst.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 αCW-v than by the conventionally used fractionation factor between crystal water and mother liquor, αCW-st.sol. because αCW-V represents the activity ratio, whereas αCW-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.