Development of the Diamex Process for Treating PHWR High-Level Liquid Waste

The extraction behavior of actinides like U(VI), Pu(IV), and Am(III) as well as of fission products like Tc(VII), Zr(IV), Eu(III), and structural material Fe(III) using nitric acid/simulated pressurized heavy water reactor-high-level waste solution as aqueous phase and N,N'-dimethyl-N,N'dibutyl tetra decyl malonamide (DMDBTDMA) in n-dodecane as solvent was investigated. The present work contributes significantly toward the development of nonphosphorous (environmentally friendly) extractant capable of partitioning long-lived actinides and fission products like 99Tc from relatively short lived fission products like 90Sr and 137Cs as well as inactive components present in high-level waste. The DAm values determined in the temperature range between 15 and 45 deg. C showed a gradual decrease with increase in temperature throughout the acidity range. The effect of N,N di-2-ethylhexyl acetamide (D2EHAA) as phase modifier on the physicochemical properties of DMDBTDMA/n-dodecane solvent was investigated and could be correlated with parameters like the limiting organic concentration value of HNO3, DAm, or phase disengagement time. Overall comparison of diamide extraction (Diamex) and transuranium extraction (Truex) solvents has been made