Interaction of zirconium with pertechnetic acid in the course of extraction from nitric acid solutions with tributyl phosphate in diluent in the presence of uranyl nitrate at various temperatures and its mathematical description

Abstract

Database on the extraction of zirconium and technetium, present separately and simultaneously, into 30% TBP is presented. With increasing temperature, the distribution ratio of Zr without Tc increases, and that of Tc without Zr decreases; however, because of the coextraction, the temperature dependence of the distribution ratios of these elements, present simultaneously, is leveled off. In the presence of uranyl nitrate, the effect of Tc on the extraction of Zr is preserved, whereas the effect of Zr on the extraction of Tc decreases to fully disappear in the case of the solvent saturation with uranyl nitrate. The interactions in the system are described within the framework of a new approach to modeling using five additional chemical equations. Their apparent equilibrium constants and coefficients of the temperature dependence are determined. The temperature coefficients are determined for the constants of six previously introduced equations of the extraction of zirconium and technetium, including the extraction in the presence of uranyl nitrate.

Distribution Coefficient Model for Zirconium and Technetium Extraction from Nitric Acid Solution

“…Experimental results show that the zirconium distribution coefficient reduces as zirconium concentration increases. ,, This happens to an extent that cannot be explained by saturation of the solvent. The distribution coefficient decreases because zirconium can form inextractable polymers as the zirconium concentration increases .…”

“…The methods of Tachimori and Shibahara and Gonda neglect TBP coordinated with zirconium. The models of Puzikov et al ,,, and of Natarajan et al do not define clearly the method to calculate free TBP.…”

“…Zirconium isotopes, such as the high-energy γ-radiation emitter 95 Zr and the long-lived pure β-particle-emitter 93 Zr, are generated by nuclear fission of U and Pu . As zirconium can significantly affect the extraction of technetium in spent nuclear fuel reprocessing processes, ,− its distribution in separation processes can significantly affect the routing of technetium. Therefore, it is important to predict the zirconium distribution in the Advanced PUREX process in the presence of uranium and technetium.…”

“…Although several methods ,,− have been published for calculating the distribution coefficient of technetium ( D Tc ), where some method also proposed to calculate D Tc in the presence of both uranium and zirconium, ,,− it is not easy to predict the distribution of zirconium per se between the nitrate aqueous solution and the TBP–diluent organic extractant. Without a reliable distribution coefficient model for Zr ( D Zr ), it is hard to predict D Tc in the presence of zirconium.…”

“…Later, the model of Rozen and Zel'venskii was used to simulate the flowsheet of Shibahara and Gonda in the absence of technetium. The use of the models of Kolarik and Dressler and of Puzikov and co-workers , is reported for the simulation of flowsheets related to technetium separation. ,,,,,, Bascone et al also used the model of Natarajan et al in their flowsheet simulations for technetium separation.…”