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Zirconium Salts for Radwaste Treatment

#1608


Process Development for the Treatment of Radioactive Waste Using Zirconium Salt of Dibutyl Phosphoric Acid Dissolved in 30% Tributyl Phosphate

Tech Area / Field

  • ENV-RWT/Radioactive Waste Treatment/Environment

Status
8 Project completed

Registration date
30.08.1999

Completion date
05.11.2004

Senior Project Manager
Tocheny L V

Leading Institute
Khlopin Radium Institute, Russia, St Petersburg

Project summary

Extraction is one of the most known methods of radioactive waste treatment and makes it possible to successfully solve the problems of waste solidification and disposal. The main disad-vantages of this method arise, as a rule, from great volumes of secondary aqueous solutions (formed during backwashing of radioactive elements from solvent products) and from the tasks of spent solvent management. Zirconium salt of dibutyl phosphoric acid (ZS HDBP) when used as extractant makes these problems much simpler, and waste treatment cost decreases.

It is known that Zr promotes the extraction capacity of alkyl phosphoric acids. Zirconium salt of dibutyl phosphoric acid (ZS HDBP) is highly promising for removal of residual amounts of U, Pu, Np, as well as for full recoverying Am, Cm, REE, Sr and some other elements from acidic and neutral aqueous solutions. The best diluent of ZS HDBP is 30% TBP solution in hydrocarbons. This solvent can be employed for extraction of the above elements from the waste of different level of activity. Experimental data on application of ZS HDBP with 30% TBP to recovery of radionuclides from high-level waste (HLW) show that this extracting mixture can be used for treatment of liquid waste of other type, first of all for intermediate-level waste (ILW), and also for some low-level waste (LLW).

The main advantage of this solvent consists in the absence of problems caused with its regeneration as ZS HDBP together with extracted radioactive elements can be dissolved in soda, while 30% TBP is recycled.

The simplest way of ILW and LLW treatment consists in extraction of the above elements by the solution of ZS HDBP in 30% TBP, concentrating the elements in the solvent, and their stripping together with ZS HDBP by soda solution followed with joint solidification and further disposal. 30% TBP is recycled, while its decomposition product, HDBP, is removed. A variant of the process without HDBP removal is also possible.

The process using zirconium salts of alkyl phosphoric acids may be disturbed in case of formation of precipitate containing iron in solvent. These difficulties now have been overcome due to obtaining experimental data on conditions under which iron is extracted by ZS HDBP without precipitate formation and can be stripped as separately, as together with other elements.

The proposed research implies to carry out a full cycle of laboratory-scale investigation up ot obtaining solidified radionuclides. The research should include:


— extraction of a-nuclides and other elements that are present in liquid radioactive waste, with solutions of ZS HDBP in 30% TBP, their (the nuclides and elements) concentrating and stripping;
— elaboration fo mathematical model for the element extraction;
— development of a process flowsheet for recovery of a-nuclides and other elements using ZS HDBP dissolved in 30% TBP and verification of the process at centrifugal contactor rig;
— investigation of different solidification methods as applied to backwashes and production of the solidified (vitrified) specimens, containing all the required components.


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