Zhu, et al., (2015) reported that rare earths play critical roles in the applications of advanced materials. Recently, the recovery of rare earths from a variety of resources has gained much interest. Radioactive elements of uranium and thorium are usually associated with rare-earth deposits. The separation of uranium and thorium from rare earths is often a big concern in rare-earth industry in order to reasonably manage the radioactive nuclides. This paper reviews the technologies used for separating uranium and thorium from rare earths in rare earth production, particularly in China. Some potentially applicable methods, such as precipitation and solvent extraction for the separation of uranium and thorium from rare earths in different media were also reviewed.
Bastnasite [and allanite] and monazite are the main resources of light rare earths including lanthanum, cerium, praseodymium and neodymium which generally account for more than 90% of the total rare earths (TRE). Particularly in bastnasite, the four light rare earths account for more than 98% of TRE. The main rare earth element
The main rare earth element in xenotime is yttrium which accounts for about 60% of TRE. Other rare earths in xenotime with relatively high content are gadolinium, dysprosium, holmium, erbium and ytterbium. Due to their similar chemical structures to rare earths, uranium and thorium are often present in rare earth minerals via lattice substitution, resulting in radiation issues in rare earth processing. Jordens et al. (2013) reviewed the content of uranium and thorium in the above rare earth minerals (Table 1). Up to 5% of uranium is usually found in xenotime and rarely in monazite although occasionally found very high to 16%. Large amounts of thorium are commonly found in monazite which even can be up to 20%.
Bastnasite usually hosts small amount of uranium and often certain amount of thorium. There is another kind of rare earth resources, ion desorption clays mainly found in China. These resources contain very small amounts of uranium and thorium to be about 20–30 ppm ThO2 and U3O= based on total REO (rare earth oxide).These rare earth resources are found in southern China and they are rich in yttrium and other heavy rare earths. They also are the main sources for heavy rare earth production in the world. No measures are taken for the control of the radiation of uranium and thorium due to their low concentrations in those deposits.
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