Improving the Robustness of Trivalent Actinides/Lanthanides Separation by Bis(2,4,4-trimethylpentyl)dithiophosphinic Acid: Batch Extraction and Process Demonstration

Abstract

ABSTRACT Separation studies during the past decades have demonstrated that ligands with “soft” donor atoms (e.g., N and S, relative to O) show greater affinity to An(III) over Ln(III) in solvent extraction. Among these ligands for An(III)/Ln(III) separation, bis(2,4,4-trimethylpentyl) dithiophosphinic acid (HBTMPDTP), the active component of the commercially available Cyanex 301 product, has been found to exhibit exceptionally high selectivity for An(III) over Ln(III). However, effective Ln(III)/An(III) separation in this system can only be achieved under relatively high and narrow pH conditions, thus requiring accurate control of the acidity during the extraction. To cope with this problem, in this work we deliberately select formic acid as a buffer reagent to control and stabilize the pH for An(III)/Ln(III) separation by HBTMPDTP. Both batch extraction and process demonstration experiments were conducted to verify the applicability of the proposed extraction system. In particular, the process testing on 14-stage centrifugal contactors with simulated waste confirms that the pH can be well stabilized, and meanwhile high An(III)/Ln(III) separation factors are maintained. Decontamination factors of Am(III) from Ln(III) as high as 50,000 were achieved. This work has successfully demonstrated the efficiency of An(III)/Ln(III) separation and the robustness of operation in the modified system.