Procedures for isolation and determination of thorium

The cation-exchange behaviour of micro and trace quantities of thorium on Dowex 50-X8 in the presence of carbonate and phosphate has been studied. Carbonate causes loss of thorium to the column effluent at pH 10.In the presence of phosphate, thorium is incompletely sorbed in the pH range 2-4.5, the loss being maximum at pH 3.8. Outside this range, thorium is quantitatively sorbed and recovered. A method that does not employ ion-exchange has been developed for the microdetermination of thorium in phosphate solution. The phosphate is precipitated as bismuth phosphate and thorium is leached from the precipitate with ammonium carbonate solution and determined with Arsenazo III. Uranium, molybdenum and vanadium are removed with Alamine 336. The results obtained for a standard ore are in excellent agreement with the certified value.