The OECD/NEA TDB review of selected organic ligands

Abstract

Within the scope of the OECD Nuclear Energy Agency (NEA) Thermochemical Data Base Project (TDB) a comprehensive review of selected organic ligands has been carried out by the authors. The selected ligands are oxalate, citrate, ethylenediaminetetraacetate (edta) and α-isosaccharinate (isa), and the elements considered in the review are U, Np, Pu, Am, Tc, Ni, Se and Zr, as well as the necessary basic data concerning protonation of the ligands and interactions with the major competing elements Na, K, Mg and Ca. This review on organic ligands showed that the pragmatic ionic strength correction procedure, the Specific ion Interaction Theory (SIT), chosen as the default method for all NEA TDB reviews, can be applied successfully also to organic ligands. The SIT interaction parameters derived from ligand protonation data for different media, e.g. NaCl and KCl, pass the consistency test when applied to other systems evaluated in the organics review, e.g. solubility data. Hence, the thermodynamic constants selected in this NEA TDB organics review can be used with some confidence in real world applications, provided that SIT is used in the speciation calculations.

Complexation of Uranium(VI) with Thiodiacetic Acid in Solution at 10–85 °C

“…[17] To allow the comparison at different temperatures, the constants in molarity were converted into the constants in molality according to Equation (2). [18] log 10 K m = log 10 K M + Σ r ν r log 10 ϑ…”

Complexation of Tc(IV) with EDTA at varying ionic strength of NaCl

“…In this work, the concentration of free ligand, [EDTA 4− ], was calculated using previously published pKa values [25,26] presented with Table 1. Tc(IV) hydrolysis stability constants were also published [5,27] and shown with Table 2; we define the following terminology for the hydrolysis:…”

“…For these reasons, Tc(VII) concentration in the vadose zone and groundwater is not limited by adsorption or solubility processes, but displays a high mobility in oxic environments. Under reducing conditions, Tc can be found as Tc(IV), which form sparingly soluble species [5] able to sorb onto mineral surfaces [6]. As a result, Tc(IV) is thought to be relatively immobile, in reducing subsurface environments [7].…”

Radioactive contaminants in the subsurface: the influence of complexing ligands on trace metal speciation

“…Nowadays, such work is mainly triggered by radioactive waste management needs. (HUMMEL et al 2005b).…”

“…This is a strong indication of the internal consistency of the speciation model derived in the NEA TDB review. (HUMMEL et al 2005b). …”