The Effect of Gluconate and EDTA on Thorium Solubility Under Simulated Cement Porewater Conditions.

α-Hydroxy carboxylate ligands like gluconate or polyaminocarboxylate ligands such as ethylenediaminetetraacetate (EDTA) are frequently used in decontamination procedures at nuclear power plants. The presence of these organic substances among nuclear wastes could enhance the solubility of actinides by forming soluble complexes. Thermodynamic data on the stability of gluconate and EDTA with actinides are essential to predict their increase in mobility, especially in high pH systems characteristic of cement environments of a nuclear waste repository. In this work, the solubility of thorium oxyhydroxide in the presence of gluconate and EDTA has been studied. The results highlight the key role of these organics in increasing the solubility of thorium at pH = 12. The presence of calcium at concentrations below 10 mol·dm (characteristic of cement porewaters corresponding to cement compositions at the second degradation stage) does not seem to affect significantly the thorium solubility under the studied conditions. [ABSTRACT FROM AUTHOR]