Crystallization of the (Cd,Ca)CO3 solid solution in double diffusion systems: the partitioning behaviour of Cd~(2+) in calcite at different supersaturation rates

摘要

Considering an ideal solid solution, the partitioning of cadmium in calcite was studied at different levels of supersaturation (5) using counter-diffusion experiments. The effective (non-equilibrium) distribution coefficients of Cd~(2+) in calcite (D_(Cd)), varied between 20 and 100 depending on the initial concentration of reactants and the evolution of supersaturation. A function that relates the D_(Cd) with the supersaturation at nucleation was derived: logD_(Cd) = -0.401og delta + 2.42. The relationship obtained suggests that in natural waters, Cd~(2+) can be incorporated to a greater degree in calcite when the solid solution-aqueous solutions system is near to equilibrium, which can occur in scenarios where the supersaturation rate and hence the supersaturation level are relatively small.