ABSTRACT

The rare earth element (REE) partition coefficients between calcite and aqueous solution were obtained experimentally under the conditions of pH, ionic strength and REE concentration level in the parent solution which were relatively close to those in seawater environment. Two different concentration levels of the REE dopant solutions were used in the experiments. The obtained partition coefficients for Sm, which have relatively high values, range from 20.8 to 116, and those for Lu, which show relatively low values, range from 10.9 to 79.1. The mutual fractionations among REEs are relatively small. On the partition coefficient versus ionic radius diagram, the patterns show weak convex upward shape having a vague maximum in the light REE, but these curves are not likely to be parabolic as expected from the trace element partitioning studies for the phenocryst-magma pairs. Therefore, it was considered that the REE partitioning between calcite and aqueous solution is not mainly controlled by the crystal structure-ionic radius effect. As for the factors on the REE partitioning experiments, crystal growth rate, REE concentration level and dominant REE species in the solutions were examined, but any clear relationships were not found, although the REE concentration level might be operative. Because the experimental condition in the present study are relatively close to the natural ones, the REE partition coefficients obtained in the present study would be useful for examining the REEs abundances in natural CaCO₃ materials.