The extraction behavior of americium and europium was studied in TOPO-nitric acid system. The distribution ratios (K
d values) were measured as respective functions of nitric acid, hydrogen ion and nitrate ion concentrations as well as a function of TOPO concentration.
The obtained curve of logK
d vs. nitric acid concentration exhibited a maximum at 0.25 M nitric acid for both americium and europium. The slope of the plot of log K
d vs. log (TOPO) org. was found to be about 2.5 at TOPO concentrations between 0.5 and 5%. It was also found that the value K
d/ (TOPO)
3org. is scarcely affected by hydrogen ion concentration. At 0.1 M nitric acid, the values of K
d/(TOPO)
3org. were shown to be nearly third power dependent on the nitrate ion concentration.
These results lend to support the conclusion that only free TOPO extract americium and/or europium. By using this conclusion, the maximal K
d value and corresponding acidity were estimated. The peak positions of K
d for the extractions of thorium and zirconium were also tried to calculate in this system. These values were satisfactorily consistent with experimental values.
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