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

Abstract

Radionuclides are present in contaminated surfacial waters, but their behavior in the presence of natural organic acids is poorly known. Dissociation constants for the strontium acetate (SrCH3COO+) and cesium acetate (CsCH3COO0) ion pair were determined by potentiometry at temperatures from 25 to 175°C at the saturation pressure of water. Logarithms of measured dissociation constants (log K) decrease with increasing temperature, showing that Sr and Cs complexing increases as temperature rises. Log K for SrCH3COO+ decreases from −1.38 at 25°C to −2.10 at 175°C, whereas log K for CsCH3COO0 decreases from 0.00 at 25°C to −0.85 at 175°C. Species distribution calculations performed by means of the experimentally determined dissociation constants in this study suggest that acetate complexes do not dominate either aqueous Sr or Cs speciation in most natural fluids; Cs acetate complexes likely never account for more than a few percent of the total Cs in solution. Although Sr-acetate complexing is more important, it may only dominate in extreme conditions.