Experimental study on the fractionation of yttrium from holmium during the coprecipitation with calcium carbonates in seawater solutions

摘要

The partitioning of Y and Ho between CaCO_3(calcite and aragonite respectively) seawater was experimentallyinvestigated at 25°C and 1 atm. Both Y and Ho were observed to be strongly partitioned into the overgrowths of calcite oraragonite. Their partition coefficients, DY and DHo, were determined to be –520-1400 and –700-1900 in calcite, –1200--2400 and –2400-4300 in aragonite, respectively. Y fractionates from Ho during the coprecipitation with either calcite oraragonite. Within our experimental conditions, the fractionation factor, k = DY/DHo, was determined to be –0.62-0.77 incalcite and –0.50-0.57 in aragonite, respectively. The aqueous complexation of Y and Ho, which is a function of solutionchemistry, probably plays an important role in both the partitioning and the fractionation. Further analyses suggest thatthe difference in covalency between Y and Ho associated with changes in their coordination environments is the determi-nant factor to the Y–Ho fractionation in the H_2CO_3–CaCO_3system.