Samples Containing Thorium or Uranium

Minerals

Thorium-bearing minerals are widespread, but generally in small amounts. Monazite is the principal source of Th. Uranium is estimated to be present in the earth's crust at about 4 ppm and occurs combined with silicates, phosphates, and zirconates.

The use of lithium tetraborate (Li₂B₄O₇) has proven to be a very useful way of opening out minerals associated with the rare earths, including Th and U. A procedure reported by Knaack, C., Cornelius, S.B. and Hooper, P.R., GeoAnalytical Lab, Washington State university, December, 1994 involves fusion of the sample (2 grams) with an equal amount of the lithium tetraborate flux in a carbon crucible at 1000 °C in a muffle furnace for 30 minutes. The fuseate is then treated with HF, nitric, and then perchloric acids with a repetition of the perchloric acid treatment to dissolve fluorides. The Final solution is made to 60 mL and contains nitric acid, hydrogen peroxide, and HF, where In, Re, and Ru are added as internal standards for an ICP-MS measurement. This method is reported to be applicable for the lanthanides (La thru Lu) together with Ba, Rb, Y, Nb, Cs, Hf, Ta, Pb, Th, U, Sr, and Zr.

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