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Transplutonium Elements Recovery from Wastes

#3405


Development and Demonstration of the Process for Selective Recovery of Transplutonium Elements from HLW Using Binary Calixarene Extractants

Tech Area / Field

  • CHE-RAD/Photo and Radiation Chemistry/Chemistry
  • ENV-RWT/Radioactive Waste Treatment/Environment

Status
8 Project completed

Registration date
28.11.2005

Completion date
03.06.2011

Senior Project Manager
Genisaretskaya S V

Leading Institute
Khlopin Radium Institute, Russia, St Petersburg

Supporting institutes

  • Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, Russia, Novosibirsk reg., Novosibirsk

Collaborators

  • Atomic Energy Canada Limited, Canada, ON, Chalk River\nUniversité Louis Pasteur, France, Strasbourg\nMemorial University of Newfoundland, Canada, NL, St.John's\nUniversita degli Studi di Parma / Dipartimento di Chimica Organica e Industriale, Italy, Parma\nInstitute of Inorganic Chemistry, Czechia, Prague

Project summary

Management of wastes arising from nuclear power remains one of the most complicated problems in radiochemical industry. The most hazardous components of these wastes are long-lived actinide elements. Their separation from waste bulk and inpidual disposal or transmutation should permit to increase considerably the ecological safety and efficiency of nuclear fuel cycle. A combined approach to reprocessing, i.e. the application of a single extractant for recovery and separation of several radionuclides, is promising. Calixarenes molecule is a convenient platform for designing of extractants with desired properties. Donor centers in substituted calixarenes may best be arranged around metal cation, increasing the extraction effectiveness and selectivity to a great extent.

Our investigation of phosphorylated calixarenes conducted in the framework of projects ISTC 2068 and STCU 09(rus) has made it possible to develop and demonstrate the process for combined recovery of actinide and lanthanide elements, palladium and technetium. Calixarene-alkylphosphinoxides effectively extract radionuclides at concentrations10-20 times lower than conventional trialkylphosphinoxides, which considerably decreases the co-extraction of acid and stable elements (especially iron).

The peculiarities of extraction properties of calixarenes allow to use them not only for group recovery of radionuclides from HLW, but also to solve the urgent problem of rare-earth (REE) and transplutonium (TPE) elements separation. The calixarene-phosphinoxides investigated by us contained only «hard» P=O donor groups. However, it is also possible to introduce some additional «soft» complex-forming centers into calixarenes molecule, to produce binary extractants, extending the area of their application considerably. For example, the «hard» phosphoryl groups positioned at one rim will afford the group recovery of REE - TPE from strongly acidic HLW and the «soft» groups at the opposite rim will provide separation of REE and TPE in low acidic media.

Binary calixarenes containing simultaneously «soft» donor and acidic groups seems to have perspectives. It is known that the effectiveness of extraction and separation of TPE and REE increases in the presence of synergistic additions of strong organic acids like cobalt dicarbollyde (COSAN). Molecule of binary calixarene may simultaneously contain both «soft» donor groups binding TPE cations and acidic groups of COSAN preventing the transfer of nitrate-ion into organic phase and enhancing the selectivity. Such combination may turn to be efficient for solving the problem of TPE - REE separation.

As our studies have shown, all phosphorylated calixarenes efficiently recover technetium and palladium, in addition to TPE and REE, from HLW. This may be a further advantage of calixarenes as extractants. Necessity of recovering technetium-99 is associated with its long half-life and high migration mobility in environmental objects. Reactor palladium is low-radioactive and low-hazardous, but may be used as a matrix for storage of technetium and TPE or their transmutation.

Thus, the project objective is to develop the scientific fundamentals of technology for recovery of TPE and REE from HLW and separation of them by using the extractants of new generation - binary calixarenes - and to demonstrate efficiency of this technology in the course of dynamic tests.

Efforts of academic science (Institute of Inorganic Chemistry, RAS) and technologists (Radium Institute) have been focused on solving these problems. Scientists of IICh (Novosibirsk) have great experience in investigation of extraction equilibria and structures of metal complexes with calixarenes in organic phase. Specialists of KRI (St. Petersburg) participated in development and implementation of new extraction technologies for HLW treatment. Testing on actual HLW can be carried out at experimental setups in Radium Institute hot cells. Specialists of Institute of Organic Chemistry (Kiev) will conduct synthesis of new calixarene extractants.


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