Study of the extraction of uranium (VI) by bis-(di-n-butyl-phosphate) compounds including a polyheteroatomic chain from nitrate solutions

Compounds 1 to 4 with two di-n-butylphosphate groups linked by a polyheteroatomic chain (BuO)2P(O)OCH2(CH2XCH2)sub(n)CH2OP(O)(OBu)2 (1: n = 0; 2: n = 1, X = 0; 3: n = 2, X = 0; 4: n = 1, X = S) were prepared respectively by action of chlorodi-n-butylphosphate on ethyleneglycol, di and triethyleneglycol, and thiodiethyleneglycol under phase transfer conditions. The extraction of uranium (VI) from aqueous nitrate phase with these compounds, in toluene diluent, was studied. Distribution ratios with compounds 1 to 3 are somewhat greater than those obtained with tri-n-butylphosphate. Extraction studies reveal that polyoxygenated chain of these compounds takes part in U(VI) complexation. The general expression for the complexes is assumed to be UO2(NO3)2Lsub(m) in which L is extractant compound and m the number of molecules coordinated to uranyl cation. Extraction stoichiometry is dependent upon extractant compound and its concentration in organic phase. For the compounds 1 to 3, m = 1.5 when extractant concentration is higher than 0.1 M; m takes the different values 0.5, 1.0 and 1.5 when extractant concentration is lower than 0.1 M. For the compound in which X is sulfur atom, m = 2.0 over all studied concentration range. It was found that in the solvent extraction of uranium (VI) with these compounds, di-n-butylphosphoric acid exhibits a synergistic effect increasing the distribution ratio of U(VI) by a factor of 100. (author)