Lanthanide mineral bastnaesite

Eight common lanthanide or lanthanide-bearing minerals that account for most concentrated supplies of lanthanides in nature are discussed briefly below. Another mineral (bastnaesite) that is of present commercial importance is discussed also. 

The bastnaesite-synchisite series of lanthanide minerals can be considered in terms of stoichiometric ratios of RCO3F to CaCOj in proportions 1 0, 1 1, 2 1, and 3 2. The minerals of this series are much more rare than allanite or apatite but are fairly common in alkalic rock suites and in some metamorphic terrains. This mineral occurs in commercially important amounts in carbonatite associated with other alkalic rocks at Mountain Pass, California. The mineral is usually light-lanthanide rich, although rare heavy-lanthanide rich examples are known (fig. 21.28). 

Scandium is very widely but thinly distributed and its only rich mineral is the rare thortveitite, Sc2Si20v (p. 348), found in Norway, but since scandium has only small-scale commercial use, and can be obtained as a byproduct in the extraction of other materials, this is not a critical problem. Yttrium and lanthanum are invariably associated with lanthanide elements, the former (Y) with the heavier or Yttrium group lanthanides in minerals such as xenotime, M "P04 and gadolinite, M M SijOio (M = Fe, Be), and the latter (La) with the lighter or cerium group lanthanides in minerals such as monazite, M P04 and bastnaesite, M C03F. This association of similar metals is a reflection of their ionic radii. While La is similar in size to the early lanthanides which immediately follow it in the periodic table, Y , because of the steady fall in ionic radius along the lanthanide series (p. 1234), is more akin to the later lanthanides. 

There are over 100 minerals known to contain lanthanides but the only two of commercial importance are monazite, a mixed La, Th, Ln phosphate, and bastnaesite, an La, Ln fluorocarbonate (M C03F). Monazite is widely but sparsely distributed in many rocks but, because of its high density and inertness, it is concentrated by weathering into sands on beaches and river beds, often in the presence of other... 

Cations of the lanthanide elements also produce colours in some minerals through intra-electronic transitions within 4/orbitals (Adams, 1965 Bernstein, 1982). Absorption bands are usually sharp and weak, leading to pastel shades. Examples of such coloured minerals are monazite, bastnaesite, rhabdophane, xenotime, gadolinite, and certain apatites, calcites, scheelites and fluorites. As noted earlier, some rare earth-bearing minerals, notably fluorite and monazite, also display the alexandrite effect (Berstein, 1982 Schmetzer et al., 1980). 

The lanthanides can be found in the earth s crust at a wide range of concentrations. For example, thulium is present at only 0.5 ppm, whereas lanthanum and cerium are present at 30 and 60 ppm, respectively. The mineralized forms of the lanthanides that are of greatest commercial and mining interest are mon-azite, bastnaesite, and cerite. The most common commercial forms of the lanthanides are the oxides and carbonates, which have low solubility and mobility. In contrast, the lanthanide chlorides, nitrates, and acetates, because of their high solubility, are more likely to leach into groundwater and surface water. 

Placer deposits of potential future value as lanthanide ores invariably have the lanthanides present in common lanthanide or lanthanide-concentrating minerals (e.g., apatite, allanite, monazite, xenotime, zircon). Most pegmatites of potential value as ore have the lanthanides as common lanthanide-bearing minerals too (those previously mentioned plus fluorite). Alkalic rock complexes may produce commercially useful concentrations of common lanthanide-bearing minerals (e.g., apatite, perovskite) or rare ones (e.g., bastnaesite). 

The minerals from which most lanthanide production currently comes are bastnaesite, monazite, and xenotime. Bastnaesite is the major source for the light lanthanides (La-Gd) and xenotime-monazite mixtures for the heavy lanthanides, with the light lanthanides as coproducts. 

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