Monazite sand

It is recovered commercially from monazite sand, which contains about 3%, and from bastnasite, which contains about 0.2%. Wohler obtained the impure element in 1828 by reduction of the anhydrous chloride with potassium. The metal is now produced commercially by reduction of the fluoride with calcium metal. It can also be prepared by other techniques. 

Ytterbium occurs along with other rare earths in a number of rare minerals. It is commercially recovered principally from monazite sand, which contains about 0.03%. Ion-exchange and solvent extraction techniques developed in recent years have greatly simplified the separation of the rare earths from one another. 

Uranium, not as rare as once thought, is now considered to be more plentiful than mercury, antimony, silver, or cadmium, and is about as abundant as molybdenum or arsenic. It occurs in numerous minerals such as pitchblende, uraninite, carnotite, autunite, uranophane, and tobernite. It is also found in phosphate rock, lignite, monazite sands, and can be recovered commercially from these sources. 

Thorium is widely but rather sparsely distributed and its only commercial sources are monazite sands (see p. 1229) and the mineral conglomerates of Ontario. The former are found in India, South Africa, Brazil, Australia and Malaysia, and in exceptional cases may contain up to 20% Th02 but more usually contain less than 10%. In the Canadian ores the thorium is present as uranothorite, a mixed Th,U silicate, which is accompanied by pitchblende. Even though present as only 0.4% Th02, the recovery of Th, as a co-product of the recovery of uranium, is viable. 

The separation of basic precipitates of hydrous Th02 from the lanthanides in monazite sands has been outlined in Fig. 30.1 (p. 1230). These precipitates may then be dissolved in nitric acid and the thorium extracted into tributyl phosphate, (Bu"0)3PO, diluted with kerosene. In the case of Canadian production, the uranium ores are leached with sulfuric acid and the anionic sulfato complex of U preferentially absorbed onto an anion exchange resin. The Th is separated from Fe, A1 and other metals in the liquor by solvent extraction. 

In situ densitometry has been the most preferred method for quantitative analysis of substances. The important applications of densitometry in inorganic PLC include the determination of boron in water and soil samples [38], N03 and FefCNfg in molasses [56], Se in food and biological samples [28,30], rare earths in lanthanum, glass, and monazite sand [22], Mg in aluminum alloys [57], metallic complexes in ground water and electroplating waste water [58], and the bromate ion in bread [59]. TLC in combination with in situ fluorometry has been used for the isolation and determination of zirconium in bauxite and almnimun alloys [34]. The chromatographic system was silica gel as the stationary phase and butanol + methanol + HCl -H water -n HF (30 15 30 10 7) as the mobile phase. 

TLC has very important applications in the isolation and determination of REEs in rocks, ores, and monazite sand. 

The main ore in which lanthanum is found is monazite sands, and it is also found in the mineral bastnasite. Monazite sands contain all of the rare-earth elements as well as some elements that are not rare-earths. Its ores are found in South Africa, Australia, Brazil, and India and in California, Florida, and the Carolinas in the United States... 

Monazite sands contain most of the rare-earths. The sands of the beaches of Florida and parts of Cahfomia contain monazite. Monazite is also found in South Africa, India, and Brazil. Bastnasite is found in southern Cahfomia and New Mexico. 

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. 

Although neodymium is the 28th most abundant element on Earth, it is third in abundance of all the rare-earths. It is found in monazite, bastnasite, and allanite ores, where it is removed by heating with sulfuric acid (H SO ). Its main ore is monazite sand, which is a mixture of Ce, La, Th, Nd, Y, and small amounts of other rare-earths. Some monazite sands are composed of over 50% rare-earths by weight. Like most rare-earths, neodymium can be separated from other rare-earths by the ion-exchange process. 

Samarium is the 39th most abundant element in the Earths crust and the fifth in abundance (6.5 ppm) of all the rare-earths. In 1879 samarium was first identified in the mineral samarskite [(Y, Ce U, Fe) (Nb, Ta, Ti )Ojg]. Today, it is mostly produced by the ion-exchange process from monazite sand. Monazite sand contains almost all the rare-earths, 2.8% of which is samarium. It is also found in the minerals gadolmite, cerite, and samarskite in South Africa, South America, Australia, and the southeastern United States. It can be recovered as a byproduct of the fission process in nuclear reactors. 

Of all the 17 rare-earths in the lanthanide series, terbium is number 14 in abundance. Terbium can be separated from the minerals xenotime (YPO ) and euxenite, a mixmre of the following (Y, Ca, Er, La, Ce, Y, Th)(Nb, Ta, Ti O ). It is obtained in commercial amount from monazite sand by the ion-exchange process. Monazite may contain as much as 50% rare-earth elements, and about 0.03% of this is terbium. 

Holmium is the 12th most abundant of the rare-earths found in the Earths crust. Although it is the 50th most abundant element on Earth, it is one of the least abundant lanthanide metals. It is found in gadolinite and the monazite sands of South Africa and Austraha and in the beach sands of Florida and the Carolinas in the United States. Monazite sand contains about a 50% mixture of the rare-earths, but only 0.05% by weight is holmium. Today, small quantities of holmium are produced by the ion-exchange process. 

Lutetium is the 60th most abundant element on Earth, and it ranks 15th in the abundance of the rare-earths. It is one of the rarest of the lanthanide series. It is found in monazite sand (India, Australia, Brazil, South Africa, and Florida), which contains small amounts of all the rare-earths. Lutetium is found in the concentration of about 0.0001% in monazite. It is difficult to separate it from other rare-earths by the ion-exchange process. In the pure metallic form, lutetium is difficult to prepare, which makes is very expensive. 

Thorium is the 37th most abundant element found on Earth, and it makes up about 0.0007% of the Earths crust. It is mostly found in the ores of thorite, thorianite (the oxide of thorium), and monazite sand. It is about as abundant as lead in the Earths crust. As a potential fuel for nuclear reactors, thorium has more energy potential than the entire Earths supply of uranium, coal, and gas combined. 

Costa-Ribeiro C, Barcinski MA, Figueiredo N, et al. 1975. Radiobiological aspects and radiation levels associated with the milling of monazite sand. Health Phys 28 225-231. 

Gadolinium is produced from both its ores, monazite and bastnasite. After the initial steps of crushing and beneficiation, rare earths in the form of oxides are attacked by sulfuric or hydrochloric acid. Insoluble rare earth oxides are converted into soluble sulfates or chlorides. When produced from monazite sand, the mixture of sand and sulfuric acid is initially heated at 150°C in cast iron vessels. Exothermic reaction sustains the temperature at about 200 to 250°C. The reaction mixture is cooled and treated with cold water to dissolve rare earth sulfates. The solution is then treated with sodium pyrophosphate to precipitate thorium. Cerium is removed next. Treatment with caustic soda solution fohowed by air drying converts the metal to cerium(lV) hydroxide. Treatment with hydrochloric or nitric acid sol-... 

The monazite sand is heated with sulfuric acid at about 120 to 170°C. An exothermic reaction ensues raising the temperature to above 200°C. Samarium and other rare earths are converted to their water-soluble sulfates. The residue is extracted with water and the solution is treated with sodium pyrophosphate to precipitate thorium. After removing thorium, the solution is treated with sodium sulfate to precipitate rare earths as their double sulfates, that is, rare earth sulfates-sodium sulfate. The double sulfates are heated with sodium hydroxide to convert them into rare earth hydroxides. The hydroxides are treated with hydrochloric or nitric acid to solubihze all rare earths except cerium. The insoluble cerium(IV) hydroxide is filtered. Lanthanum and other rare earths are then separated by fractional crystallization after converting them to double salts with ammonium or magnesium nitrate. The samarium—europium fraction is converted to acetates and reduced with sodium amalgam to low valence states. The reduced metals are extracted with dilute acid. As mentioned above, this fractional crystallization process is very tedious, time-consuming, and currently rare earths are separated by relatively easier methods based on ion exchange and solvent extraction. 

There are several processes for commercial thorium production from monazite sand. They are mostly modifications of the acid or caustic digestion process. Such processes involve converting monazite to salts of different anions by combination of various chemical treatments, recovery of the thorium salt by solvent extraction, fractional crystallization, or precipitation methods. Finally, metalhc thorium is prepared by chemical reduction or electrolysis. Two such industrial processes are outlined briefly below. 

In one acid digestion process, monazite sand is heated with 93% sulfuric acid at 210°C. The solution is diluted with water and filtered. Filtrate containing thorium and rare earths is treated with ammonia and pH is adjusted to 1.0. Thorium is precipitated as sulfate and phosphate along with a small fraction of rare earths. The precipitate is washed and dissolved in nitric acid. The solution is treated with sodium oxalate. Thorium and rare earths are precipitated from this nitric acid solution as oxalates. The oxalates are filtered, washed, and calcined to form oxides. The oxides are redissolved in nitric acid and the acid solution is extracted with aqueous tributyl phosphate. Thorium and cerium (IV) separate into the organic phase from which cerium (IV) is reduced to metalhc cerium and removed by filtration. Thorium then is recovered from solution. 

Thorium dioxide is obtained as an intermediate in the production of thorium metal from monazite sand (See Thorium). 

Thorium nitrate is obtained as an intermediate in making thorium metal from monazite sand. Also, the salt is prepared by heating thorium metal or its oxide or hydroxide with nitric acid, followed by evaporation of the solution and crystaUization. 

Uranium occurs in nature in many rocks, minerals and sediments. The principal uranium minerals are pitchblende, carnotite, uranitite, tobernite, uranophane, autunite, and davidite. Uranium also is found in very small quantities in monazite sand, phosphate rock, and lignite. Although uranium is present in very smaU quantites, these sources also are used for commercial recovery of the metal. 

The element was discovered in 1794 by the Swedish chemist Gadolin. He named it after the small town Ytterby in Sweden where the mineral containing yttria was found. Mosander in 1843 determined that the yttria consisted of three oxides yttria, erbia, and terbia. Yttrium occurs in all rare earths. It is recovered commercially from monazite sand, which contains about 3% yttrium. It also is found in bastnasite in smaller amounts of about 0.2%. Abundance of yttrium in earth s crust is estimated to be 33 mg/kg. The metal has been detected in moon rocks. 

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. 

Because of its lower cost, mesothorium 1 is frequently substituted for radium in therapy and in the manufacture of luminous watch-dials. The commercial process for extracting it from the by-products of monazite sand was long kept secret, but after Soddy and W. Marckwald independently discovered that it is chemically identical with radium, the process for extracting the latter element from pitchblende was adapted so that it could be used for recovering mesothorium 1 (84,94). 

When Edgar Fahs Smith was investigating monazite sand under the direction of F. A. Genth (1820—1893), the latter always appropriated the zirconium sulfate that was extracted, and would say as he carried it away, Zirconium is not simple there is another element concealed in it, and when I have leisure I shall endeavor to isolate it (18). It was in zirconium ores that large quantities of element 72 were first revealed (19,20,21). 

Acid breakdown of monazite. — Most monazite sands do not require grinding when they are treated with H2SO4. Their calcium content is often very low and is quite suitable for acid attack. There are many variations of this process and the trade secrecy of the commercial processes prevents an elaborate description of the methods. Fig. 4 presents a schematic picture of acid breakdown and the recovery of thorium and the rare earths. 

Sulphuric acid vs. caustic soda breakdown. —Although a greater variety of monazite sands can be processed by sulphuric acid treatment than by the... 

The crude monazite sands are first concentrated by the general mechanical and physical treatments of mineral dressing. Brazilian monazite sands are processed mainly by the electromagnetic separation technique. The Indian monazite industry is essentially based on the recovery of rutile and ilmenite. Ilmenite has a magnetic susceptibility very close to that of monazite and thus direct electromagnetic separation cannot be applied to the Indian Travancore monazite sands. 

Thorium occurs in monazite sand in Brazil, India, North and South Carolina this ore contains 3-9% thorium oxide, and is the chief source thorium is also found in thorite containing about 60% oxide and in thorianite. about 80% oxide. When heated with concentrated H2SO4 the minerals form thonum sulfate, from which, by a senes of reactions, thonum nitrate, the chief commercial compound, is obtained. 

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