The influence of ionic strength on yttrium and rare earth element complexation by fluoride ions in NaClO4, NaNO3 and NaCl solutions at 25(circle)C

摘要

Stability constants of the form F beta(1)(M) = [MF2+][M3+](-1) [F-](-1) (where [MF2+] represents the concentration of a yttrium or a rare earth element (YREE) complex, [M3+] is the free YREE ion concentration, and [F-] is the free fluoride ion concentration) were determined by direct potentiometry in NaNO3 and NaCl solutions. The patterns of logio F-10F beta(1)(M) in NaNO3 and NaCl solutions very closely resemble stability constant patterns obtained previously in NaClO4. For a given YREE, stability constants obtained in NaClO4 were similar to, but consistently larger than (F)beta(1)(M) values obtained in NaNO3 which, in turn, were larger than formation constants obtained in NaCl. Stability constants for formation of nitrate and chloride complexes (NO3 beta(1) = [MNO32+][M3+](-1) [NO3-](-1) and (Cl)beta(1)(M) = 3 3 [MCl2+][M3+](-1) [Cl-](-1)) derived from (F)beta(1) (M) data exhibited ionic Strength dependencies generally similar to those of (F)beta(1) However, in contrast to the somewhat complex pattem obtained for F beta(1) (M) across the fifteen member YREE series, no patterns were observed for nitrate and chloride complexation constants: neither NO3 beta(1) (M) nor (Cl)beta(1) (M) showed discernable variations across the suite of YREEs. Nitrate and chloride formation constants at 25 degrees C and zero ionic strength were estimated as log(10NO3)beta degrees(1)(M) = 0.65 +/- 0.06 and log(10CI)beta degrees(1)(M) = 0.71 +/- 0.05. Although these constants are identical within experimental oncertainty, the distinct ionic strength dependencies of (NO3)beta(1)(M) and (Cl)beta(1)(M) produced larger differences in the two stability constants with increasing ionic strength whereby (Cl)beta(1)(M) was uniformly larger than NO3 beta(1) (M).