 Occurrence and Extraction
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| Thorium is found in small amounts in most rocks and soils, where it is about three times more abundant than uranium, and is about as common as lead. Soil commonly contains an average of around 12 parts per million (ppm) of thorium. Thorium occurs in several minerals, the
most common being the rare earth-thorium-phosphate mineral, monazite, which contains up to about 12% thorium oxide. There
are substantial deposits in several countries. 232Th decays very slowly (its half-life is about three times the age of the earth) but other thorium isotopes occur in the thorium and uranium decay chains. Most of these are short-lived and hence much more radioactive than 232Th, though on a mass basis they are negligible. India is believed to have 25% of the world's Thorium reserves.
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| Thorium has been extracted chiefly from monazite through a multi-stage process. In the first stage, the monazite sand is dissolved
in an inorganic acid such as sulfuric acid (H2SO4). In the second, the Thorium is extracted into an organic phase containing an amine. Next it is separated or "stripped" using
an anion such as nitrate, chloride, hydroxide, or carbonate, returning the thorium to an aqueous phase. Finally, the thorium
is precipitated and collected
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