UC Irvine

Solvent extraction is one of the most used techniques for Used Nuclear Fuel (UNF) reprocessing and Rare Earth Elements (REE) separation. Therefore, understanding the extraction kinetics is a key aspect for enabling further advancements in design and operation of future units for sustainable nuclear energy generation. For this project, a constant interfacial area stirred cell, a so called Nitsch Cell, was built, tested and optimized for studies on solvent extraction kinetics. In addition, the cell was utilized for the investigation of the extraction of trivalent dysprosium (III) into the extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (or also known as HEHEHP) dissolved in Isopar L. The extraction mechanism was defined, as well as the rate controlling step and the forward reaction rate expression. The experimental results indicated that the extraction rate was not independent of the interfacial area. Furthermore, the extraction rate showed a linear increase with the stirring speed from 150 rpm to 400 rpm, indicating that the kinetic regime was diffusion-limited in that range. Decreasing the extractant concentration 4 times resulted in a shift of the observed kinetic constants to approximately 10 times lower, but the extraction regime did not change as the chemical reaction rate remained fast compared with the diffusion rate. The initial dysprosium fluxes and their dependency on the stirring speed were also analyzed and the individual mass transfer coefficients of each hydrodynamic condition were provided from this study.