Demonstration of trivalent actinide partitioning from simulated high-level liquid waste using modifier-free unsymmetrical diglycolamide in n-dodecane

Abstract

Partitioning of trivalent americium from fast-reactor (FR) simulated high-level liquid waste (SHLLW) has been demonstrated, for the first time, using a modifier-free organic phase containing an unsymmetrical diglycolamide, N,N,-didodecyl-N′,N′-dioctyl-3-oxapentane-1,5-diamide (D³DODGA), in n-dodecane (n-DD). The extraction behavior of various metal ions present in the FR-SHLLW that contained about 3.2 g/L of trivalent metal ions (Am(III) and Ln(III)) was studied using a solution of 0.1 M D³DODGA/n-DD, by batch equilibration mode. The extraction of Am(III) was accompanied by the co-extraction of all lanthanides and unwanted metal ions such as Zr(IV), Y(III), and Pd(II) from FR-SHLLW. The co-extraction of unwanted metal ions was minimized by adding a suitable aqueous soluble complexing agents to FR-SHLLW, prior to extraction. As a result, trans-1,2-diaminocyclohexane-N,N,N′N′-tetraacetic acid (CyDTA) was identified as an appropriate reagent for preventing the extraction of zirconium and palladium, that posed problems during recovery of trivalent metal ions from the loaded organic phase. The stripping of behavior of Am(III) and Ln(III) from the loaded organic phase was studied using dilute nitric acid in batch equilibration mode. Based on those results, a counter-current mixer-settler run was performed in a 20-stage mixer-settler. About 99.9% of Am(III), Ln(III) and Y(III) from FR-SHLLW in 0.1 M D³DODGA/n-DD was achieved in 20 contacts and the recovery of Am(III) and other trivalents from the loaded organic phase was achieved in 5 contacts using 0.01 M nitric acid. The study demonstrated the possibility of using the modifier-free reagent, D³DODGA, for the separation of trivalent actinides from FR-SHLLW.