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outside China are set to open in Australia: Mount Weld, (22,000 t/y, 11.1% REO
grade eq.), Nolans Project (20,000 t/y, 4.7%), Dubbo (2,580 t/y, 2.7%); Canada:
Strange Lake (12,120 t/y, 3.7%), Nechalacho (9,296 t/y, 4.9), Hoidas Lake (5,000
t/y, 4.6%); South Africa: Zandkopsdrift (20,000 t/y, 3.9%), Steenkampskraal (2,500
t/y, 27.8%); United States: Mountain Pass (42,402 t/y, 9.8%), Bear Lodge (7,000
t/y, 5.2%); Others: Kvanefjeld, Greenland (43,700 t/y, 2.0%), and Norra Karr,
Sweden (5,000 t/y, 2.1%).
Even if the mining projects corresponding to some 191,000 t REO/yr are in
progress, some REE such as Ce are expected to be in surplus but many others
such as Nd, Pr and Y will likely remain in a short term supply deficit
28
.
8.13.4 Extraction and physical beneficiation ofREO
The lanthanide contraction not only explains the occurrence of REE but their di
-
cult beneficiation, chemical processing, separation and refining. According to Gupta
and Krishnamurthy (1992), physical beneficiation takes advantage of the small dif-
ferences in density, magnetisation, surface ionisation potential and/or surface wet-
tability of rare earth minerals and various co-occurring ones such as garnet and
magnetite. Therefore, after a crushing and grinding process the ore is shook on
tables or can undergo magnetic or electrostatic separations and/or bulk flotation
processes, in order to separate heavy minerals which are obtained in chemically
processable concentrations of rare earths. Likewise, bastnaesite is separated from
monazite via a shaking table.
Physical beneficiation is very deposit and mine specific. In the processing of
bastnaesite and monazite at Bayan Obo, 90% of the particles are crushed and ground
to <74 m, before undergoing a magnetic separation. The resulting material is then
concentrated by rougher froth flotation from only '5% to '60% REO. The process
recovers the depressed silicates, iron and niobium oxides from the bottom whilst the
REE minerals and gangue float in the para
n soap made up of the sodium salt
of oxidised mineral oil. A thickening and de-sliming process eliminates the fraction
lower than 5 m and removes the excess of para
n soap from the foam containing
the REO and the gangue which is itself composed of calcite, fluorite and barite. The
latter is subsequently removed with a selective froth floatation using hydroxamic
acid as a chelating agent, at pH 5-6. The trapped substance is then depressed
by Na
2
CO
3
, Na
2
SiF
6
and Na
2
SiO
3
. The resulting slurry is thickened, filtered
and dried. Apart from concentrating rare earth as a co-product, the whole process
recovers magnetite, hematite, fluorite and niobium oxide which form the principal
products. At '85% concentration a single tonne of rare earth mineral may need
anything between 6 and 86 tonnes of raw ore (Gupta and Krishnamurthy, 2005;
Bouorakima, 2011; Gibson and Parkinson, 2011; C-Tempo, 2011).
28
See also http : ==www:slideshare:net=RareEarthsRareMetals=libertas-rareearthreview. Ac-
cessed Nov. 2012.
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