Complex formation between trivalent actinides and pyrocatechol

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A continuous research work was done for the development of powerful chelating agents specific for trivalent and tetravalent actinide ions. In the recent years intensive investigations were carried out using some catecholate chelating ligands connected with the strong complexing power of the catecholate group [1–3]. The catecholate ligand is essential for the metabolism in biological systems especially some substituted catechol derivatives. They can be used as specific sequestering agents for removal of actinides from biological systems [4], which is important for environmental research and nuclear medicine as well. It was found also that some substituted pyrocatechols act as effective extractants for both tracer and macroquantities of transplutonium elements as well as rare earths from strong alkaline solutions [5]. While most of the research was performed studying tetravalent actinides, little is known about the complexation between pyrocatechol and actinides in the trivalent state. Thus, we have chosen to investigate the catecholate reactions with trivalent actinides by means of the solvent extraction method. We found out that hydrolysis and sorption of Am 3+ prevail from pH higher than 6 and because pyrocatecholate ligand is not stable in the alkaline region the experiments have to be performed in argon atmosphere. The complex formation between americium and pyrocatechol is obviously stronger than both sorption and hydrolysis at pH higher than 9. There is also experimental evidence that the ligand itself is extracted by the TBP agent which further complicates the system. The mechanism of complex formation and the stability of the complexes formed will be investigated in detail to serve as a base for comparison with the complexation of some biologically active catechols. This work is supported by the International Atomic Energy Agency and the Swedish Natural Science Council.