Separation of thorium and uranium from xenotime leach solutions by solvent extraction using primary and tertiary amines

This study addressed the development of a continuous countercurrent extraction-scrubbing-stripping technique using a mixture of primary and tertiary amines as an effective extractant for both thorium (Th) and uranium (U) to simultaneously separate them from the leach solutions of xenotime concentrate from the Yen Phu mine (Vietnam). Systematic studies determined the optimum parameters of the separation, including the optimum concentrations of the mixture of the primary amine (N1923) and tertiary amine (tri-n-octyl amine), the optimum acidity (pH) of the feed liquor (Yen Phu xenotime leachate), the optimum contact time between phases for extraction, scrubbing and stripping processes, and the most suitable stripping reagent mixture. Using the optimum parameters, the optimum stage number and phase volumetric ratio for extraction, scrubbing, and stripping processes were calculated using the calculus method based on the law of matter conservation. The flow rates of both phases for extraction, scrubbing, and stripping were determined from the results of these studies and calculations. To optimize the separation of uranium and thorium from the Yen Phu xenotime leachate, countercurrent simulations of extraction, scrubbing and stripping were done in a series of mixer-settler units. The results indicated that the selective separation of Th and U with almost no loss of rare earths (REs) and a minimal contamination of iron were obtained. The continuous countercurrent extraction-scrubbing-stripping technique shows potential applications in the commercial separation of Th and U from RE leachate after tests using a sequence of mixer-settler units on a pilot scale.