Monazite deposits

Natural monazite contains not only cations of the light rare-earth elements, but it also incorporates uranium and thorium. Monazite is the principal ore for the commercial extraction of thorium, and it has also been used as a secondary source of uranium. Monazite deposits are located in the United States, Australia, South Africa, Sri Lanka, Brazil, India, Malagasy, and Canada. As shown in Table 1, monazite is capable of incorporating significant amounts of both uranium and thorium (Boatner and Sales 1988, Houk 1943). Because of the chemical durability of monazite, relatively harsh chemical... 

Other additional uranium sources, associated with unconventional deposits or exploited as a by-product of other minerals (e.g. copper and gold), are those found in old mine dumps (gold mines in South Africa), phosphate rocks (Morocco, the U.S.A. and the U.S.S.R.), with a content ranging from 0.001 to 0.07%, in copper deposits, such as the porphyry coppers , in marine black shales with a content ranging from 0.001 to 0.008% (the U.S.A. and Sweden), in coal and lignite deposits with a content normally of 0.001%, exceptionally reaching 1% (the U.S.A.), in monazite deposits with 0.3% (India, Brazil, Australia and Malaysia), in igneous rocks, such as the alkaline intrusives distributed in various parts of the world, and, as has already been mentioned, in sea water. 

Large deposits of monazite (found on the beaches of Travancore, India and in river sands in Brazil), ahanite (in the western United States), and bastnasite (in Southern California) will supply cerium, thorium, and the other rare-earth metals for many years to come. 

Thorium occurs in thorite and in thorianite. Large deposits of thorium minerals have been reported in New England and elsewhere, but these have not yet been exploited. Thorium is now thought to be about three times as abundant as uranium and about as abundant as lead or molybdenum. Thorium is recovered commercially from the mineral monazite, which contains from 3 to 9% Th02 along with rare-earth minerals. 

Whereas certain rocks of igneous origin formed by melting and recrystallization can include minerals enriched in the lanthanides (4), cerium is usually present as a trace element rather than as an essential component. Only a few minerals in which cerium is an essential stmcture-defining component occur in economically significant deposits. Two minerals supply the world s cerium, bastnasite [68909-13-7] LnFCO., and monazite [1306-41 -8] (Ln,Th)PO. ... 

Bastnasite has been identified in various locations on several continents. The largest recognized deposit occurs mixed with monazite and iron ores in a complex mineralization at Baiyunebo in Inner MongoHa, China. The mineral is obtained as a by-product of the iron ore mining. The other commercially viable bastnasite source is the Mountain Pass, California deposit where the average Ln oxide content of the ore is ca 9%. This U.S. deposit is the only resource in the world that is minded solely for its content of cerium and other lanthanides. 

Several countries supply monazite concentrates for the world market. Extensive deposits along the coast of western AustraUa are worked for ilmenite and are the primary source of world monazite. Other regions of AustraUa, along with India and Brazil, also supply the mineral. Because monazite contains thorium [7440-29-1], India and Brazil have embargoed its export for many years. In the United States, commerce in the mineral is regulated by the Nuclear Regulatory Commission. 

Primary Mined particularly for the molybdenum contained in the ores. In some instances, molybdenum could be the only valuable metal recovered from the ore. The Questa deposit in New Mexico is mined exclusively for molybdenum content. In other deposits molybdenum may be the main product recovered together with one or more products. In these deposits the molybdenum content alone would allow for a profitable operation. The ore at the Climax mine in Colorado is of this type. Currently, monazite, pyrite, tin, and tungsten are recovered from the ore none of these by-products exists singly nor together in sufficient quantity so that the ore could be mined profitably merely for the extraction of one or all of these by-products. 

The electrostatic separation method is the exclusive choice in some specific situations, for example in the cases of rutile and ilmenite deposits. These deposits generally contain minerals of similar specific gravities and similar surface properties so that processes such as flotation are unsuitable for concentration. The major application of electrostatic separation is in the processing of beach sands and alluvial deposits containing titanium minerals. Almost all the beach sand plants in the world use electrostatic separation to separate rutile and ilmenite from zircon and monazite. In this context the flowsheet given later (see Figure 2.35 A) may be referred to. Electrostatic separation is also used with regard to a number of other minerals. Some reported commercial separations include those of cassiterite from scheelite, wolframite from quartz, cassiterite from columbite, feldspar from quartz and mica, and diamond from heavy associated minerals. Electrostatic separation is also used in industrial waste recovery. 

Euxenite is a titanotantalum/niobium-containing mineral and has a complex formula (Table 24.1) with variable chemical composition. It is usually found in sand deposits together with monazite, xenotime, zircon, beryl, columbite and other minerals. 

A large portion of monazite production comes from mineral sand deposits. In the beneficiation of monazite from mineral sand deposits that contain garnet, ilmenite, shell and silicates, the physical concentration and combination of physical preconcentration-flotation is used. Several reagent schemes using flotation were developed throughout various studies [8-10] and some have been confirmed in continuous pilot plants. 

India has very large deposits of monazite on the coastal shores of Kerala and Chennai. A typical mineral composition of this type of deposit is 60% ilmenite, 1.2% rutile, 5% zircon, 6.4% garnet, 4% silinanite, 16% quartz, 2.5-5% monazite and 1-7% shell. Research work involved different anionic collectors and pH during monazite flotation, along with the level of sodium silicate used as depressant. 

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. 

The most abundant titanium sand deposits are black sands in streams and on beaches of volcanic regions. The principal black minerals are magnetite, titanoferous magnetite and black silicates, chiefly angite and homblend. It is quite difficult to produce an ilmenite suitable for pigment product from black sand, but other sand deposits that contain rutile, ilmenite and often monazite are found in Australia, USA, India and Africa. These deposits are either alluvial or marine in origin. 

Praseodymium is mainly found in monazite sands and bastnasite ores. The monazite sands contain all of the rare-earths and are found in river sand in India and Brazil as well as in Florida beach sand. A large deposit of bastnasite exists in California. 

Europium is the 13th most abundant of all the rare-earths and the 55th most abundant element on Earth. More europium exists on Earth than all the gold and silver deposits. Like many other rare-earths, europium is found in deposits of monazite, bastnasite, cerite, and allanite ores located in the river sands of India and Brazil and in the beach sand of Florida. It has proven difficult to separate europium from other rare-earths. Today, the ion-exchange... 

Contents of REE in massive sulfides from the BMC are strongly controlled by the abundance of and REE concentrations in phosphate minerals, specifically apatite, xenotime and monazite. Strong positive Eu anomalies in apatite, account for the anomalous Eu signatures of exhalative sulfides whereas REE in monazite masses are largely reflective of detrital sources and may mask hydrothermal signatures. Limited release of mobile trace elements (LREE and Eu) during green-schist facies metamorphism has partly modified REE profiles for VMS deposits of the BMC. 

FIecht, L. Cuney, M. 2000. Flydrothermal alteration of monazite in the Precambrian crystalline basement of the Athabasca Basin (Saskatchewan, Canada) Implications for the formation of unconformity-related uranium deposits. Mineralium Deposita, 35, 791-795. 

Large thorium deposits have heen found in many parts of the world. It occurs in minerals thorite, ThSi04, and thorianite, Th02"U02. Thorium also is found in mineral monazite which contains between 3 to 9% Th02. Th02 is the principal source of commercial thorium. Abundance of thorium in earth s crust is estimated at about 9.6 mg/kg. Thorium and uranium are believed to have contributed much of the internal heat of the earth due to their radioactive emanations since earth s formation. 

Zirconium is found in small amounts widely spread throughout nature, occurring in many alluvial deposits of lake and stream beds and ocean beaches. The most important mineral is zircon, or zircon orthosilicate, ZrSi04. Other zirconium minerals are eudialite, (Na, Ca, FeleZrSieOislOH, Cl), and baddeleyite, Zr02. It also occurs in monazite sand. The abundance of zirconium in the earth s crust is estimated as 165 mg/kg. 

Phosphates. The two major phosphate bearing ores are monazite and xenotime, the former being a source of light lanthanides and the latter a source of the heavy rare earths, see Table IV. Deposits in the form of heavy mineral sands are the major source of monazite. They are usually exploited as a byproduct of rutile, ilmenite, and zircon mining operations. 

A similar type of deposit of monazite and xenotime is in the placer tin deposits especially in Southeast Asia. 

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