DIAMEX counter-current extraction process for recovery of trivalent actinides from simulated high active concentrate

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 (Am-241, Cm-244, Eu-152, and Cs-134). 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.