Effective extraction performance of a fluorous phosphate for Zr(IV) from HNO3 solution: comparison with a tri-n-butyl phosphate

An efficient separation technology for various radionuclides is important to reduce the amount and toxicity of radioactive waste and to concentrate high radioactivity in small waste volumes. The separation of metal ions such as radionuclides is carried out by a hydrometallurgical process mainly based on a solvent extraction method. Solvent extraction is a separation technique for concentrating and separating a certain target component by using distribution of a solute between two immiscible solutions. The solvent extraction method has been widely adopted to practical process for reprocessing spent nuclear fuel and refining valuable metals. The extraction and separation of Zr(IV) as a fission product from aqueous HNO3 solutions has been investigated extensively because the presence of Zr species in the tri-n-butyl phosphate (TBP)-based reprocessing of spent nuclear fuel is problematic [1]. Zr species are likely to form a liquid–liquid (water, oil) interfacial crud or third phase during Zr extraction procedure by TBP from HNO3 aqueous solution (Figure 1). Formation of third phase is an undesirable process in the reprocessing of spent fuel, as it could potentially cause safety and criticality concerns due to the high metal concentrations. We have recently reported that a Zrloaded organic phase from liquid–liquid extraction with TBP shows hierarchical aggregation behaviors of Zr(NO3)4(TBP)2 coordination complexes, which self-assemble into primary clusters that coalesce further to form superclusters [2]. This supercluster formation portends the formation of third phase and interfacial crud. However, there are still few proposals for development of the extraction system with a new extractant that does not suffer from these problems.