DETERMINATION OF THORIUM AND URANIUM IN MINERAL SANDS BY ION CHROMATOGRAPHY

Thorium and uranium can be determined by ion chromatography using a C,, reversed-phase column and a complexing eluent of hydroxyisobutyric acid followed by post-column derivatization with Arsenate III and detection at 658 nm. A number of sample dissolution and clean-up procedures were evaluated in order to permit the application of the chromatographic method to the analysis of mineral sands. Dissolution procedures investigated included a variety of acid digestions and alkali fusion with peroxide, berate, carbonate, hydroxide and pyrosulphate fluxes. Sample clean-up protocols were then studied in order to overcome matrix interference effects. The optimal sample preparation procedure involved a tetraborate fusion/nitric acid leach followed by either cation-exchange pretreatment, or simply dilution in concentrated hydroxyisobutyric acid, depending upon the sample type. The results obtained using the chromatographic method showed good agreement with X-ray fluorescence and inductively coupled plasma mass spectrometry for ilmenite, synthetic rutile, zircon and rutile mineral sands with detection limits (in the original mineral sand) in the order of 1.0 mu g/ml for the two analytes.