DIAMEX Counter‐Current Extraction Process for Recovery of Trivalent Actinides from Simulated High Active Concentrate

Abstract

The partitioning of trivalent actinides was demonstrated with a new version of the French DIAMEX (DIAMide EXtraction) process. A continuous counter‐current experiment using a 16‐stage centrifugal extractor battery was tested using 1 mol/L N,N′-dimethyl‐N,N′-dioctyl‐hexylethoxy‐malonamide (DMDOHEMA) in TPH as the extractant. A high active concentrate (HAC), obtained after concentration and denitration of a high active raffinate (HAR) with a concentration factor of 10, was used as a feed. Based on results from cold and hot batch extraction experiments and computer code calculations, a flowsheet was developed and a full test was carried out using a simulated HAC solution spiked with radionuclides (²⁴¹Am, ²⁴⁴Cm, ¹⁵²Eu, and ¹³⁴Cs). In the DIAMEX process, five extraction stages were sufficient to obtain Am and Cm (feed/raffinate) greater than 5000 and for the coextracted lanthanides decontamination factors between 1100 and 4500. Co‐extraction of zirconium, molybdenum, and palladium was prevented by using oxalic acid and HEDTA. The back extraction comprising 4 stages was also efficient and the recoveries of actinides were greater than 99.8%, which can be further improved by a minor process flowsheet optimisation. The experimental steady‐state concentration profiles of important solutes were determined and compared with model calculations and good agreement was generally obtained.