TETRAD EFFECT IN LANTHANIDE PARTITIONING BETWEEN CALCIUM-SULFATE CRYSTAL AND ITS SATURATED SOLUTION

The distribution of rare-earth elements (REE's) between anhydrite crystal of calcium sulfate and its saturated solution was investigated at different temperatures. The lanthanide tetrad effect was observed as the apparent distribution coefficients. Furthermore, from the dependence of the apparent distribution coefficients on the growth of the anhydrite crystal, it was found that the process of the REE incorporation into the anhydrite crystal could be divided into two stages, namely, nonselective incorporation followed by thermodynamically controlled differential incorporation. It can be presumed that the factor affecting the extent of the tetrad effect depends effectively on the relative intensity of the two processes of incorporation of REE's into the anhydrite. This result would throw light on understanding of tetrad effects observed in various natural environments.