Experimental determination of the complexation of strontium and cesium with acetate in high-temperature aqueous solutions

Radionuclides are present in contaminated surfacial waters, but their behav ior in the presence of natural organic acids is poorly known. Dissociation constants for the strontium acetate (SrCH3COO+) and cesium acetate (CsCH3CO O0) ion pair were determined by potentiometry at temperatures from 25 to 17 5 degreesC at the saturation pressure of water. Logarithms of measured diss ociation constants (log K) decrease with increasing temperature, showing th at Sr and Cs complexing increases as temperature rises. Log K for SrCH3COO decreases from -1.38 at 25 degreesC to -2.10 at 175 degreesC, whereas log K for CsCH3COO0 decreases from 0.00 at 25 degreesC to -0.85 at 175 degreesC . Species distribution calculations performed by means of the experimentall y determined dissociation constants in this study suggest that acetate comp lexes do not dominate either aqueous St or Cs speciation in most natural fl uids; Cs acetate complexes likely never account for more than a few percent of the total Cs in solution. Although Sr-acetate complexing is more import ant, it may only dominate in extreme conditions. Copyright (C) 2001 Elsevie r Science Ltd.