Complexation of Tc(IV) with acetate at varying ionic strengths

Abstract

Abstract In order to accurately model and predict the fate and transport of metals and radionuclides at multiple radio-contaminated sites, there is a need for an understanding on how metals such as technetium interact with their environment. Many contaminated sites are known to contain large amounts of organic ligands that can affect the solubility and mobility of metals. This study focuses on the effect of acetate on the complexation and dissolution of Tc(IV). Studies were performed at pcH 4.5 (±0.3), at which TcOOH+ is the predominant species. The stability constants for the TcOOH-acetate complex were determined at ionic strengths varying from 0.5 to 3.0 M (NaCl), using a solvent extraction method. The stability constants showed the expected increasing trend over the range of ionic strengths, from 2.46±0.03 (I=0.5) to 3.09±0.08 (I=3.0). A stability constant of 2.8±0.16 at zero ionic strength was determined by specific ion interaction theory. Geochemical modeling data suggest that the dissolution of TcO2·1.6H2O is not greatly affected by the presence of acetate, at concentrations equal or less than 20 mM.