Effect of extractant structure on third phase formation in the extraction of uranium and nitric acid by N,N-dialkyl amides

The influence of the molecular structure of amides on the third phase forma tion in the extraction of uranium and nitric acid was investigated. Nine am ides namely, dibutyl hexanamide (DBHA), diisobutyl hexanamide (DiBHA), dibu tyl octanamide (DBOA), di hexyl hexanamide (DHHA), dibutyl dodecanamide (DB DA), diisooctyl butanamide (DiOBA), di n-octyl isobutanamide (DOiBA), di n- octyl butanamide (DOBA), and di n-octyl hexanamide (DOHA) were synthesized and used. The limiting organic concentration (LOC) of uranium (VI) for thir d phase formation was studied as a function of nitric acid concentration us ing 0.5 M solutions of these amides in dodecane. The LOC for extraction fro m neutral medium (with near zero free acidity) was also measured at four di fferent temperatures. The LOC values were found to increase in general with an increase in the total number of carbon atoms in the amide from 14 to 22 . The LOC values of DBHA (C. No. 14), DiBHA (C. No. 14), DBOA (C. No. 16) w ere lower compared to that of DHHA (C. No. 18), DBDA (C. No. 20), DOHA (C. No. 22), which have relatively longer carbon chain length. Further it was o bserved that introduction of branching at the nitrogen side increases the L OC value as compared to the straight chain analogue, as in the case of DiOB A and DiBHA. In the latter case, however, this effect is not very pronounce d perhaps due to the smaller carbon chain length. Introduction of branching at the position alpha to the carbonyl group was found to sharply decrease the LOC value due to steric hindrance as can be seen in the case of DOBA an d DOiBA. Further, by varying the carbon chain length on both acyl and nitro gen sides, keeping the total carbon number invariant, it was found that the LOC increases considerably on increasing the chain length on the acyl side . On the contrary, the LOC for nitric acid extraction was not influenced si gnificantly by the structure of the amide. Nevertheless, the distribution r atio at the point of dissolution of the third phase was found to decrease w ith introduction of branching on either end of the amide and more so, if br anching was introduced on the acyl end of the amide.