Bench-scale mixer-settler study of the extraction and stripping of uranium from solution

Abstract

A bench-scale mixer-settler has been developed for studying the extraction and stripping of uranium from solution. Mixer and settler behaviour were investigated. In determining mixer characteristics Sauter mean diameters and droplet distributions were measured using photographs of the dispersions. Overall extraction efficiencies were also measured. Settler behaviour was determined by measurement of dispersion band heights. The results showed that this apparatus did behave in a manner consistent with the data reported for larger-scale equipment. Extraction and stripping efficiencies were found to be high and varied with change in Sauter mean diameter. It was determined that extraction efficiencies could be predicted (1) based on solution of the diffusion equation for uptake by a sphere from a solutin of limited volume, and (2) based on a mass transfer model requiring evaluation of the individual aqueous and organic phase mass transfer coefficients. Using an equation first proposed by Ryon and Lowrie, settler behaviour was characterized by means of a normalized band height corresponding to a specific throughput of 0.144 cm s −1. Normalized band heights were observed to depend on solution composition and stirrer speed. Crud formation was also studied but solid characteristics were such that dispersion band heights were reduced, i.e. coalescence in the settler was enhanced.