The mineral
bastnäsite is one of a family of three
carbonateIn chemistry, a carbonate is a salt or ester of carbonic acid, characterized by the presence of the carbonate ion, or a carbonate functional group O=C2....
-
fluorideFluoride is the anion F
−, the reduced form of fluorine. Both organic and inorganic compounds containing the element fluorine are sometimes called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are distinct relative to other...
minerals. There is bastnäsite-(
CeCerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is...
) with a formula of (Ce, La)CO
3F. There is bastnäsite-(
LaLanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is a lanthanoid. It is found in some rare-earth minerals, usually in combination with cerium and other rare earth elements...
) with a formula of (La, Ce)CO
3F. There is also bastnäsite-(
YYttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanoids and has historically been classified as a rare earth element. Yttrium is almost always found combined with the lanthanoids in rare earth minerals and is...
) with a formula of (Y, Ce)CO
3F. Most bastnäsite is bastnäsite-(Ce), and
ceriumCerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is...
is by far the most common of the rare earths in this class of minerals. Bastnäsite and the phosphate mineral
monaziteMonazite is a reddish-brown phosphate mineral containing rare earth metals and is an important source of thorium, lanthanum, and cerium. It occurs usually in small isolated crystals...
are the two largest sources of cerium and other
rare earth elementAs defined by IUPAC, rare earth elements or rare earth metals are a collection of seventeen chemical elements in the periodic table, namely scandium, yttrium, and the fifteen lanthanoids...
s.
Bastnäsite was first described in 1841 from and named for the
BastnäsBastnäs is an ore field near Riddarhyttan, Västmanland, Sweden. The mines in Bastnäs were earliest mentioned in 1692. Iron, Copper and Rare earth elements was extracted from the mines and 4,500 tons of cerium was produced between 1875 and 1888....
mine near
RiddarhyttanRiddarhyttan is a locality in Skinnskatteberg Municipality, Västmanland County, Sweden with 500 inhabitants in 2005. It has an old iron mining tradition, which can be followed back to the last centuries before Christ, the last mine was closed down in 1979....
, Västermanland,
SwedenSweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe...
.
Bastnäsite also occurs as very high quality specimens at the Zagi Mountains, Pakistan.
Bastnäsite occurs in alkali
graniteGranite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as porphyry. Granites can be pink to dark gray or even black, depending on their...
and
syeniteSyenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts ....
and in associated
pegmatiteA pegmatite is a very coarse-grained, intrusive igneous rock comprised of interlocking grains usually larger than 2.5 cm in diameter; such rocks are referred to as pegmatitic....
s. It also occurs in
carbonatiteCarbonatites are intrusive or extrusive igneous rocks defined by mineralogic composition consisting of greater than 50 percent carbonate minerals. Carbonatites may be confused with marble, and may require geochemical verification....
s and in associated fenites and other
metasomatitesMetasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...
.
Mining history
In 1949, the huge carbonatite-hosted bastnäsite deposit was discovered at
Mountain PassMountain Pass is an unincorporated community in San Bernardino County, California, United States. It is situated on Interstate 15 in the southeast mountainous desert region of the state approximately from the Nevada border at an altitude of...
,
San Bernardino County, CaliforniaSan Bernardino County is a county in the U.S. state of California. As of the 2000 census, the population was 1,709,434. As of 2007, the population was estimated by the California Department of Finance to have grown to 2,028,013...
. This discovery alerted geologists as the existence of a whole new class of rare earth deposit: the rare earth containing carbonatite. Other examples were soon recognized, particularly in Africa and China. The exploitation of this deposit began in the mid-1960s after it had been purchased by Molycorp (Molybdenum Corporation of America). The lanthanide composition of the ore included 0.1% europium oxide, which was sorely needed by the burgeoning color television industry, to provide the red phosphor, so as to maximize picture brightness. The composition of the lanthanides was about 49% cerium, 33% lanthanum, 12% neodymium, and 5% praseodymium, with some samarium and gadolinium, or distinctly more lanthanum and less neodymium and heavies as compared to commercial monazite. However, the europium content was at least double that of a typical monazite. Mountain Pass bastnäsite was the world's major source of lanthanides from the 1960s to the 1980s. Thereafter, China became increasingly important to world rare earth supply. Chinese deposits of bastnäsite include several in Sichuan Province, and the massive deposit at
Bayan OboBayan Obo is a mining town in the autonomous region Inner Mongolia, northern China.The mines north of the town are the largest deposits of rare earth metals yet found....
,
Inner MongoliaInner Mongolia is a Mongol autonomous region of the People's Republic of China, located in the country's north....
, which had been discovered early in the 20th century, but not exploited until much later. Bayan Obo is currently (2008) providing the lion's share of the world's lanthanides. Bayan Obo bastnäsite occurs in association with monazite (plus enough magnetite to sustain one of the largest steel mills in China), and unlike carbonatite bastnäsites, is relatively closer to monazite lanthanide compositions, with the exception of its generous 0.2% content of europium.
Ore technology
At Mountain Pass, bastnäsite ore was finely ground, and subjected to flotation to separate the bulk of the bastnäsite from the accompanying barite, calcite and dolomite. Marketable products include each of the major intermediates of the ore dressing process: flotation concentrate, acid-washed flotation concentrate, calcined acid washed bastnäsite, and finally a cerium concentrate, which was the insoluble residue left after the calcined bastnäsite had been leached with hydrochloric acid. The lanthanides that dissolved as a result of the acid treatment were subjected to solvent extraction, to capture the europium, and purify the other individual components of the ore. A further product included a lanthanide mix, depleted of much of the cerium, and essentially all of samarium and heavier lanthanides. The calcination of bastnäsite had driven off the carbon dioxide content, leaving an oxide-fluoride, in which the cerium content had become oxidized to the less basic quadrivalent state. However, the high temperature of the calcination gave less-reactive oxide, and the use of hydrochloric acid, which can cause reduction of quadrivalent cerium, led to an incomplete separation of cerium and the trivalent lanthanides. By contrast, in China, processing of bastnäsite, after concentration, starts with heating with sulfuric acid.