Sorption Extraction of Uranium from Fluorine-Containing Media During Reprocessing of Radiochemical Production Wastes

Abstract

Experimental data on the sorption extraction of uranium from fl uorine-containing solutions on different types of modern ion-exchange absorbers and structures in order to improve the technological schemes for reprocessing wastes from radiochemical production are presented. The primary technological relations are studied and the optimal indices in static and dynamic regimes of sorption-desorption extraction of uranium from model systems simulating production fl uorine-containing solutions are determined. A chelate-forming aminophosphonic cation-exchanger Purolite S950 with uranium capacity up to 20% is recommended. It is shown that uranium concentration in the waste ≤0.003 g/liter can be obtained. It is found that uranium desorption by a 15% solution of sodium carbonate is a highly effi cient process with desorption time 10 h and degree of uranium desorption 99.92%.The production of some metals required for nuclear power, for example, uranium, zirconium, hafnium, niobium, and tantalum, is based on methods employing fl uorine-containing solutions. The state of uranium in uranyl fl uoride solutions is determined by the excess concentration of fl uorine ions participating in the formation of complexes. The general expression for the composition of a complex has the form [UO 2 F n ] n-2 . The genetic series of complex uranyl fl uorides is a large class of compounds in which the ratio F/U ranges from 6/1 to 2/1. Depending on the quantitative ratio of the fl uoride and uranyl ions, the cation complex UO 2 F + or the anion complexes UO 2 F 3 -and UO 2 F 4 2-or the neutral compound UO 2 F 2 , which practically does not dissociate in solution, are formed. In conformity to the ionic state, hexavalent uranium in solutions forms complexes with the constants UO 2 F + (3.9 ± 0.3)·10 4 , UO 2 F 2 (8.6 ± 0.8)·10 7 , UO 2 F 3 -(3.1 ± 0.4)·10 10 , UO 2 F 4 2-(7.0 ± 0.5)·10 11 , UO 2 (SO 4 ) 3 4-2500, UO 2 (SO 4 ) 2 2-350, UO 2 (CO 3 ) 3 4-2·10 18 , which will compete in reactions with complexes with much lower equilibrium constants so that the content of uranyl ions accessible for sorption will decrease. The negative effect of the fl uorine is large and can be eliminated by adding a salting-out agent, whose cation forms a stronger complex with the fl uorine atom than the uranyl ion. Aluminum nitrate can serve as such an agent: Al 3+ + F -→ AlF 2+ . The fl uoride complex of aluminum with formation constant 1.35·10 6 is stronger than the uranyl-fl uoride complex UO 2 F + . Aluminum in the molar ratio 1:1 to fl uorine is adequate to completely eliminate the interfering action of fl uorine. The technological schemes for reprocessing solutions from radiochemical production, as a rule, include ammonia processing of uranium-fl uorine-containing solutions followed by ion-exchange purifi cation of the fi ltrate by removal of uranium. At present, high priority is given to improving the technologies for extracting uranium from fl uorine-containing solutions (>7 g/liter of fl uorine) by bringing in modern ion-exchange absorbers.The behavior of...