Monazite ores

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. 

Lutetium oxide (Lu O ), the oxide found in monazite ore, is a white solid. It is hygroscopic and also absorbs carbon dioxide, making it useful to remove CO in closed atmospheres. 

Plutonium is the only transuranium element which has been found in nature. Until its properties were known it would have been impossible to detect it in the minute amounts in which it occurs, but when its behavior was understood, Seaborg and his co-workers were able to find it in pitchblende, monazite ores, and carnotite in concentrations of about one part in 1014 (63, 73, 76). Peppard and his group found it in somewhat greater amounts in pitchblende from the Belgian Congo (77). Seaborg believes that most of this plutonium arises by fission of the uranium in the ore, though other processes may also be involved (77, 78). 

Hydrometallurgical concentration processes. Because monazite is a relatively chemically inert mineral, only two hydrometallurgical dissolution processes can be efficiently used for recovering thorium and rare earths. Actually, the hydrometallurgical processing of monazite ore concentrate is carried out either by concentrated sulfuric acid or strong alkahne caustic hot digestion. 

Subsequent treatment depends on the intended use of the rare earths. For some applications, particularly the older ones, it is not necessary to achieve a separation of the elements. For example, a mixture of the cerium group metals, called mischmetal, has been used for decades for lighter flints. Thus from a bastnasite or monazite ore base, which contains predominantly the cerium group elements, little further separation work is necessary. However, for basic research into the properties of the elements and their compounds and in applications involving increasingly sophisticated technology the availability of the individual elements in a high purity form is essential. 

In the earth s crust thorium is almost four times more common than uranium, and the radioactive decay of thorium generates a considerable part of the geothermal energy. The primary source of thorium is monazite (Figure M25), a yellow or reddish-brown rare-earth phosphate. Seashore deposits at Travancore in India contain very big quantities of monazite. The mineral formula is (Ce,La,Nd,Th)PO and the thorium content in monazite ores is 5-10%. In 2001 the production of monazite concentrate in the world was 5710 tonnes [52.13], of which India accounted for 5000 toimes or 88%. Other producers were Brazil and Malaysia. 

The measurement scale of the gammalog is the American Petroleum Institute (API) unit. This reference standard allows consistent comparisons between different gamma-ray counting devices. The API standard is a calibration test pit at the University of Houston. The American Petroleum (API) facility is constructed of concrete with an admixture of radium to provide uranium decay series, monazite ore as a source of thorium and mica as a source of potassium. The facility has 4.07% K, 24.2 ppm Th and 13.1 ppm U (Ellis, 1987). The API standard gives 200 API, equal to twice the mean of an average shale. Table 5.8 gives mean API values for some rock-forming minerals. 

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