Rare earth phosphates

Xenotime, like mona2ite, is a rare-earth phosphate. Up to 60% of its rare-earth content is yttria [1314-36-9], Xenotime has a higher... 

Separation and Recovery of Rare-Earth Elements. Because rare-earth oxalates have low solubihty in acidic solutions, oxaUc acid is used for the separation and recovery of rare-earth elements (65). For the decomposition of rare-earth phosphate ores, such as mona ite and xenotime, a wet process using sulfuric acid has been widely employed. There is also a calcination process using alkaLine-earth compounds as a decomposition aid (66). In either process, rare-earth elements are recovered by the precipitation of oxalates, which are then converted to the corresponding oxides. 

Polyhalogenobenzene Hydrolysis. The chlorobenzenes can be transformed into chlorophenols by hydrolysis in a Hquid-phase basic medium. The two most commonly used techniques are treatment in aqueous alkaU medium at a temperature between 200 and 350°C (48), or a milder hydrolysis (200—250°C) treatment with dilute sodium hydroxide in the presence of copper. The hydrolysis may be carried out in the vapor phase (250—400°C) on soHd catalysts based on rare-earth phosphates (49) or copper-beating siUca. 

A series of nickel/(rare earth phosphate) catalysts were investigated by Nagaoka et al. [35] for methane ATR. Among them, Ni/(Gd, Ce or Er phosphate) showed good activity, maintaining a stable CH4 conversion during time on-stream tests... 

Terbium occurs in nature associated with other rare earths. It is found in minerals xenotime, a rare earth phosphate consisting of 1% terbia and in euxenite, a complex oxide containing about 1.3% terbia. It also is found in cerite, monazite, and gadolinite. Also, the element has been detected in stellar matter. Abundance of terbium in the earth s crust is estimated to be 1.2 mg/kg. 

Ytterbium occurs in minerals euxenite, a complex titanium niobotantalate gadolinite, a rare earth iron beryUium sdicate monazite, a thorium-rare earth phosphate and xenotime, also a rare earth-thorium phosphate. Abundance of ytterbium in the earth s crust is estimated to be 3.2 mg/kg. 

Monazite or Xenotime. The rare earth phosphate containing ores are attacked with either concentrated sulfuric acid or sodium hydroxide solution. The processing involves cracking the ore, removing the thorium, and separating the lanthanides. 

Hikichi, Y Murayama, K., Ohsato, H. Nomura, T. 1989. Thermal changes of rare earth phosphate minerals. Journal of the Mineralogical Society of Japan, 19, 117-126. 

Until 1964, monazite, a thorium-rare-earth phosphate, REPO4TI13 (P04)4, was the main source for the rare-earth elements. Australia, India, Brazil. Malaysia, and the United Slates are active sources. India and Brazil supply a mixed rare-earth chloride compound after thorium is removed chemically from monazite. Bastnasite, a rare-earth fluocarbonate mineral REFCO3. is a primary source for light rare earths. From 1965 to about 1985. an open-pit resource at Mountain Pass, California, has furnished about two-thirds of world requirements for rare-earth oxides. In the early... 

The principal resource minerals for thorium are Monazite, a rare earth phosphate, Thorite, ThSi04, and Thorianite or Uranothorianite, (U, Th)02, of which Monazite is the most important. Thorium minerals are mainly concentrated in sedimentary ores derived from the heavy refractory... 

Xenotime, like monazite, is a rare-earth phosphate. Up to 60% of its rare-earth content is yttria [1314-36-9], Y203. Xenotime has a higher proportion of heavy rare earths than does monazite. Xenotime occurs with monazite in beach sand deposits. A second source of xenotime is that of cassiterite (tin ore) deposits. 

Monazite (Ce,La,Y,Th)P04 A rare-earth phosphate. Most concentrates contain 55-65% REO including 2% Y2O3. Marketable REO content 55% (minimum)... 

A bifunctional acid base mechanism (Figure 14.5) was proposed to explain the high selectivity to O-alkylation of rare-earth phosphates. The absence of C-alkylated products by methylation of ga iacol tends to suggest that the guaicolate surface intermediate has a different behaviour on LaP04 and LaP04 doped with cesium hydrogenophosphate. In this latter case, the excellent selectivity to O-alkylation could be due to the softness of the cesium ion (39). 

In addition to the orthophosphates, there are also a small number of reports on nanomaterials of other rare earth phosphate salts (Tang et al., 2005c). In this section, we will discuss the chemical synthesis of rare earth orthophosphates in aqueous solutions, nonaqueous solutions, and dry methods, together with the brief discussion of the luminescent properties, as well as the applications in biosensing. 

In addition to the orthophosphates, other rare earth phosphates could also be obtained through hydrothermal routes. Tang et al. reported the synthesis of so-called CeP (with a composition of Ce(FIP04)2" H2O) nanotubes (Tang et al., 2005c). Concentrated phosphoric acid solution of 6 M was heated to a temperature ranging from 50 to 110 °C to form a condensed lirrear polyphosphate (P 03 +i) +2 Then, the (NH4)2Ce(N03)e solution is... 

Nonaqueous solution methods The syntheses of rare earth phosphate NCs in nonaqueous solutions mainly include the solvothermal method, polyol method, the synthesis in ionic liquids, and the synthesis in high-boiling coordinating solvents like TOPO or OA. 

Properties and applications of rare earth phosphate nanomaterials... 

Luminescence Buissette et al. (2006a) presented a feature article on the aqueous colloidal synthesis and luminescence of rare earth phosphates and vanadates, which could be a good reference for the works in this field. 

The traditional radioimmunoassay technique could be utilized with rare earth phosphate NPs. Lin et al. reported the LuP04-apoferritin coreshell NPs synthesized in apoferritin templates. The NPs were further modified with biotin and exhibited affinity for streptavidin-modifed magnetic beads or streptavidin-modifed fluorescein isothiocyanate. Radioactive Lu was used to label the NPs (Wu et al., 2008a). 

Catalytic properties Phosphorus is known to have deactivation effects for some automotive catalysts and the formation of CeP04 has been identified in phosphorus contaminated catalysts (Uy et al., 2003). Nanocrystalline LaP04 would act as Lewis acid in a catalytic process, which could be determined by a temperature-programmed ammonia adsorption/desorption process (Onoda et al., 2002 Rajesh et al., 2004, 2007). In addition, the rare earth phosphate NCs could act as supports for example, Pd, Pt, or Rh supported on RPO4 show excellent catalytic reduction of NO into N2 and O2 (Tamai et al., 2000), and gold supported on RPO4 shows catalytic activity and stability for CO oxidation. 

The solubility of rare earth phosphates is fairly low in neutral or acidic aqueous solutions, for example, the sp values for LaP04 and CeP04 are 4.0 x 10 and 1.6 x 10 , respectively. Therefore, rare earth phosphates can be obtained by the reaction of soluble rare earth salts with alkali metal phosphates. Usually, the product has the following formula REPO4 H20... 

Scandium, yttrium, and lanthanum, in group Ilia of the periodic table, usually occur in nature with the fourteen rare-earth elements, cerium (atomic number 58) to lutetium (atomic number 71). All of these elements except promethium (which is n ade artificially) occur in nature in very small quantities, the principal source being the mineial monazite, a mixture of rare-earth phosphates containing also some thoriurn phosphate. 

Monazite, a rare-earth phosphate, is one of the most abundant rare-earth minerals. It occurs as an accessory mineral in granitic and metamorphic rocks, pegmatites, vein deposits, as a dendrital mineral in placer deposits and as a... 

The minerals in a coal clearly reflect its geochemical environment of deposition and diagenesis rather than the composition of the source rocks. Ferromagnesian minerals such as pyroxenes, amphiboles, and ohvines are very rare in coal feldspars are also uncommon. These minerals are unstable in low-pH peat-swamp environments and are apparently destroyed in the early stages of coalihcation. In contrast, more resistant accessory minerals such as rutile, zircon, and rare-earth phosphates are relatively common in coal. 

Rare earths Phosphates, some organic association... 

An X-ray diffraction and P MAS NMR study of rare-earth phosphate glasses of composition (R203)(x)P205)(l — x) where x = 0.175-0.263 and R = La-Er (except for Pm), is presented. The structures of these materials were investigated as a function of (a) rare-earth atomic number and (b) glass composition. The results show an increase in rare-earth coordination number from six to seven as the rare-earth ion increases in size. ... 

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