Method for extracting palladium from high-level liquid waste

Abstract

The invention provides a method for extracting palladium from high-level liquid waste, which belongs to the technical field of radioactive waste after treatment. The high-level liquid waste adopts nitric acid system, and the method comprises the following concrete steps of: a, adequately mixing the high-level liquid waste with extract phase; b, separating extract phase containing palladium from the mixture after extraction equilibrium; c, washing the separated extract phase containing palladium; d, repeating steps b and c 1 to 5 times; e, adding stripping agent to the washed extract phase containing palladium to perform back extraction; and the method is characterized in that triisobutyl phosphine sulfide (TiBPS) is adopted as extracting agent, and thinning agent is added for preparing the extract phase. The method has the following advantages: a, the extracting ratio of palladium in the nitric acid system is high by using TiBPS as extracting agent; b, the concentration range of adaptable nitric acid is wide, Purex process can be directly linked, mixtion is not required in the extraction process, and waste minimization and processing equipment simplification can be realized; c, the selectivity is good; and d, back extraction is easy.

Description

technical field [0001] The invention belongs to the technical field of radioactive waste reprocessing, and in particular relates to a method for extracting palladium from high-level radioactive waste liquid. Background technique [0002] The nuclear fuel in the reactor produces rich metal palladium during the fission process, and its content varies with the type of reactor and the burnup. For example, a pressurized water reactor with a burnup of 33000MWd / t produces about 1.33Kg Pd / tU; A fast breeder reactor with a burnup consumption of 80GWd / t produces about 4.34Kg Pd / tU. After the spent fuel is reprocessed, most of the metal palladium enters the high-level waste liquid. In the vitrification process of high-level waste liquid, the fission product palladium may form interface dirt with some degradation products of tributyl phosphate (TBP), and due to the high melting point of palladium, it will form an independent phase during the vitrification process and deposit on the Th...

AI Technical Summary

Problems solved by technology

Most of the reported extraction agents for extracting palladium from high-level radioactive waste have some shortcomings.

Such as tributyl phosphate (TBP) in 0.6-0.7mol / L HNO 3 The distribution ratio of palladium in the extraction of medium is the best, and the maximum extraction distribution ratio is about 1.3; the optimum concentration of nitric acid for the extraction of palladium by trialkylphosphorus oxide (TOPO) is less than 1mol / L, and the maximum extraction distribution ratio of Pd(II) is slightly higher than that of TBP Large; 0.05mol / L dioctyl sulfoxide-Solvesso100 solution system in 3.0mol / L HNO 3 The maximum distribution ratio of extracting Pd(II) in the medium is less than 10; the extraction of Pd(II) nitrate with dialkyl sulfide is very effective, and the distribution ratio of extracting palladium in 1-6mol / L nitric acid solution can reach several hundred, but At the same time, Mo, Zr and other elements are co-extracted, and the extraction time is long, and the distribution equilibrium can only be slowly reached after 8-10 hours; bis(2,4,4-trimethylpentyl)dithiophosphonic acid (Cyanex 301) can Effectively extract Pd(II) from high-level waste liquid, but this extractant has poor stability and is easily oxidized; the distribution ratio of amine extractant to extract palladium in more than 1mol / L nitric acid solution is low, and the selectivity is poor α-benzoin oxime-Solvesso100 is in the scope of 0.1-4mol / L in nitric acid concentration, and the extraction rate to Pd is more than 99.5%, and the decontamination to nuclides such as Ru, U, Pu is all very good, but this method The decontamination of Mo is poor, and the stripping is difficult