Monazite from complex ores

The separation of basic precipitates of hydrous Th02 from the lanthanides in monazite sands has been outlined in Fig. 30.1 (p. 1230). These precipitates may then be dissolved in nitric acid and the thorium extracted into tributyl phosphate, (Bu"0)3PO, diluted with kerosene. In the case of Canadian production, the uranium ores are leached with sulfuric acid and the anionic sulfato complex of U preferentially absorbed onto an anion exchange resin. The Th is separated from Fe, A1 and other metals in the liquor by solvent extraction. 

A large portion of the REOs are produced from monazite- and bastnaesite-containing ores. In the majority of cases, bastnaesite and monazite ores are relatively complex and contain gangue minerals (calcite, barite, fluorite and apatite) with similar flotation properties as the monazite and bastnaesite. 

There are several large deposits of complex monazite ores, some of which are located in South Africa and Western Australia. Major research and development testwork has been performed on the Mount Weld ore from Western Australia. 

Attempts to separate thorium and uranium from sulfuric acid solution of monazite by solvent extraction with TBP were unsuccessful because distribution coefficients of uranium and thorium from monazite solutions were too low, as these elements are complexed by phosphate ion. Development of extractants with higher distribution coefficients for these metals has made solvent extraction a practical process for recovering uranium and thorium from monazite sulfate solutions and from sulfuric acid solutions of other thorium ores. This section describes processes tested on a pilot-plant scale by Oak Ridge National Laboratory [C5]. 

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