Extraction and Determination of Thorium from Sulfate and Phosphate Solutions with Tri-n-octylphosphine Oxide W. J. ROSS and J. C. WHITE Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
.A method i s presented for the determination of thorium in samples resulting from the leaching of monazite sands and other raw materials with sulfuric acid, and from subsequent stages in the separation of thorium b y solvent extraction processes. Tri-n-octylphosphine oxide (TOPO) dissolved in cyclohexane i s used to extract thorium b y diluting the sulfate and phosphate concentration with 1M nitric acid and sufficient sodium nitrate. The maximum permissible concentrations o f SUIfate and phosphate are 0.5M and 0.06M, respectively. Thorium i s determined colorimetrically after backextraction with 0.3M sulfuric acid. Cerium(ll1) and the other trivalent rare earths are not extracted. The method i s essentially specific for thorium and requires about one fourth the time required by conventional procedures. Thorium has been determined in the concentration range from 0.01 to 5.8 mg. per ml. with comparable precision.
appIii.:ttion of solvtnt extraction proccsw!: to the refining of thoriumcuntaining w e e . such as monazite sands, h:ts resulted in :i variety of samples for tlI
