Behavior of third phase formation in solvent extraction using CMPO(II)

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The TRUEX process has been developed to recover transuranium elements from high level liquid waste. This process uses octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) which is able to extract tri-valent actinides. It is already well known that a third phase appears at the interface when rare earths and other metal ions are extracted from a concentrated solution into TRUEX solvent which consists of CMPO with TBP - dodecane mixture. The basic researches concerning behavior of third phase formation and elimination were done in previous experiments. Succseively, dependency of temperature on organic phase composition, behavior of U extraction, applicability to high level liquid waste and diluent effect were investigated in these experiments. Consequently, these results were made obviously. By composition analysis of solvent which extracted nitric acid, it was found that not only concentration of extracted species, but temperature also influences on the composition of split phase. Extraction of high uranium concentration caused yellow precipitation. Critical concentration for precipitation were constant in each system and not dependent on temperature significantly. This precipitation was considered to affect extraction procedure, so that the condition should be selected carefully. In experiment using simulated waste, it's found that with appropriate condition of TBP concentration and temperature, dilution of concentrated liquid waste would not be necessary. From this work, 1.4 M for TBP concentration and 40 C are promisible and that are typical values for concentrated waste. However, to determine the practical conditon for real waste treatment, further experiments should be done. From comparison of hydrocarbon composed of 12 carbons with n-dodecane as diluent, carbon chain length and banching influence on critical concentration of third phase formation.