Experimental study on distribution coefficients of REE between Fe-Mn oxyhydroxides and aqueous NaCl solutions

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Distribution coefficients of REE,Y and Sc between Fe-Mn oxyhydroxides and aqueous NaCl solutions are the key to understanding the fractionations of Y and Sc from REE in natural aquatic systems. The variations of the distribution coefficients in the lanthanide series as well as their tetrad effects reflect their relative differences in bondings of REE^<3+> ions between the REE (III) species in the pair of phases. We have established the experimental method to determine the distribution coefficients of REE,Y and Sc between Fe-Mn oxyhydroxides and aqueous NaCl solutions at normal temperature conditions by using ICP-AES techique. Our results indicate that observed fractionations of Y and Sc from REE in natural aquatic systems are due to partitioning them between natural waters adn Fe-Mn oxyhydroixe precipitates in them. The tetrad effect variations of D (REE) strongly suggest that Racah parameters of REE (III) in Fe-Mn oxyhydroixe precipitates are smaller than those of REE^<3+>^+(aq). Our results of D (REE) indicate that the coordination states of Tm, Yb, and Lu ions in Fe-Mn oxyhydroixe precipitates significantly different from those of the other REE.