Crud Formation by Palladium Particles as Insoluble Residues

“Crud” is a problem in the solvent extraction process for nuclear fuel reprocessing. Crud is an emulsion stabilized by dispersed fine solids. Insoluble residues and precipitates play an important role in crud formation. The effect of insoluble residues on crud formation is studied using submicron particles of palladium, which is one of the elements contained in insoluble residues. Experiments are conducted on factors such as palladium concentration, particle size, and acidity. The experimental results indicate that the smallest palladium concentration in the aqueous phase that can stabilize an emulsion is ∼5 g/ℓ and that such an emulsion is of the oil-in-water type. Moreover, the palladium layer on globules is discussed, and a numerical estimation is performed to predict the time when stable emulsions start to form in a mixer-settler.