The Behavior of Actinides in Two-Phase Aqueous Systems Based on Polyethylene Glycol

Abstract

As one of the most effective analytical and technological separation techniques, liquid/liquid extraction is based on distribution of compounds between an aqueous solution and an organic solvent immiscible towards the former. The effectiveness of the process markedly depends on the energy difference between solvation and hydration of extracted compounds in the two phases. Water-soluble organic and inorganic agents of high hydration energy usually form poorly extracted complexes in traditional extraction systems. Meanwhile, a number of water-soluble organic reagents exhibit significant complexing ability and selectivity with respect to metal ions including lanthanides and actinides. Such reagents could substantially extend the sphere of applications of liquid-liquid extraction to separation and concentration of elements. Among reagents of this type are various derivatives of aminoacetic acids (so called complexones), a number of organic photometric reagents such as Arsenazo III and other complexones. Most water-soluble reagents do not usually form extractable complexes in conventional extraction systems due to the high hydration energy of the species to be extracted. These reagents can be used in heterogeneous aqueous systems with considerable amounts of water in both phases where the effect of hydration on transfer of the extracted complex from one phase to another is not significant. Such extraction systems use water-soluble polymers whose salting out from an aqueous electrolyte solution results in formation of a second liquid phase.1 One of these is poly(ethylene glycol) (PEG), a cheap, easily available, and non-toxic polymer producing two-phase aqueous systems with various salts.1,2 These systems are of interest to us from a practical point of view, since they contain no organic solvents which are usually volatile, explosive, and toxic.