The principal steps in producing refined thorium compounds from thorium-bearing ores are concentration of thorium minerals, extraction of thorium from concentrates, purification or refining of thorium, and conversion to metal or the thorium compound finally wanted. This section describes the concentration of monazite, the principal source of thorium in the past; the extraction of thorium from monazite; and the recovery of thorium from leach liquors by solvent extraction. Purification of thorium is described in Sec. 9 and conversion in Sec. 10.

1.12Concentration of Monazite

Monazite is usually a minor constituent of deposits of other minerals, all of which must be separated and processed for a profitable venture. As an example, the mineral constituents of beach sands in Travancore, India, which are dredged for their zirconium, titanium, thorium, and rare-earth content, are as follows:

Monazite, (RE, Th, U)P04,0.5 to 1.0% Rutile, Ti02,3 to 6%

Dmenite, FeTi03, 65 to 80% Zircon, ZrSi04,4 to 6%

Garnet, (Fe, Mg, Ca)3 Al2Si04,1 to 5% Sillimanite, Al2SiOs, 2 to 5%

Beach sands are usually first treated by crude specific gravity methods to separate the denser minerals from silica and produce concentrate that, at Travancore, has approximately the above composition. Then the heavier minerals are separated in a series of strong electromagnets of progressively increasing intensity. The low-intensity magnet removes the most magnetic constituent, magnetite. The first pole of the high-intensity magnet separates ilmenite; the second pole, garnet; the third pole, coarse grains of monazite; and the strongest pole, fine grains of monazite. The rare earth elements in monazite make it paramagnetic. The nonmagnetic residue is treated by flotation and other means to recover rutile, zircon, and some gold. A further specific gravity treatment of the monazite fraction produces a monazite concentrate 98% percent pure.