Some aspects of fundamental chemistry of the Universal Extraction (UNEX) process for the simultaneous separation of major radionuclides (cesium, strontium, actinides, and lanthanides) from radioactive wastes

Scientists at the Idaho National Laboratory (INL) and Khlopin Radium Institute (KRI) collaboratively developed and validated the concept of a Universal Extraction (UNEX) process for simultaneously removing the major radionuclides (Cs, Sr, actinides, and lanthanides) from acidic radioactive waste in a single solvent extraction process. The process chemistry is unique and complicated, since the extractants, chlorinated cobalt dicarbollide (CCD), polyethylene glycol (PEG), and diphenyl-N,N-di-n-butylcarbamoylmethylphosphine oxide (Ph2CMPO), operatesynergistically to extract the major radionuclides.A combination of classical chemistry techniques, infrared (IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy were utilized to identify and explain the structures formed in the organic phase with protons or metal ions. Model systems, CCD-PEG and CCD-bidentate organophosphorus compounds were studied and possible structures of complexes, existing in the organic phase, are proposed and properties of the UNEX extractant are discussed. (author)