Europium sulfate

Acid soluble rare earth salt solution after the removal of cerium may be subjected to ion exchange, fractional crystalhzation or solvent extraction processes to separate individual rare earths. Europium is obtained commercially from rare earths mixture by the McCoy process. Solution containing Eu3+ is treated with Zn in the presence of barium and sulfate ions. The triva-lent europium is reduced to divalent state whereby it coprecipitates as europium sulfate, EuS04 with isomorphous barium sulfate, BaS04. Mixed europium(ll) barium sulfate is treated with nitric acid or hydrogen peroxide to oxidize Eu(ll) to Eu(lll) salt which is soluble. This separates Eu3+ from barium. The process is repeated several times to concentrate and upgrade europium content to about 50% of the total rare earth oxides in the mixture. Treatment with concentrated hydrochloric acid precipitates europium(ll) chloride dihydrate, EuCb 2H2O with a yield over 99%. 

It can be seen that the (111) state is highly stable with respect to disproportionation in aqueous solution and is extremely difficult to oxidize or reduce. There is evidence for the existence of the (II) state since tracer amounts of amencium have been reduced by sodium amalgam and precipitated with barium chloride or europium sulfate as earner. The (IV) state is very unstable in solution the potential for americium(III)-ameridum(IV) was determined by thermal measurements involving solid Am02. Amencium can be oxidized to the (V) or (VI) state with strong oxidizing agents, and the potential for the americium(V)-americium(Vl) couple was determined potentiometrically. 

Luminescence measurements of the decomposition products of Eu2(S04)3-8H20 (Brittain 1983) supported these conclusions. Figure 2 shows the spectra obtained for the Do and Dg -> Fj transition regions for europium sulfate before (a) and... 

Selective Reduction. In aqueous solution, europium(III) [22541 -18-0] reduction to europium(II) [16910-54-6] is carried out by treatment with amalgams or zinc, or by continuous electrolytic reduction. Photochemical reduction has also been proposed. When reduced to the divalent state, europium exhibits chemical properties similar to the alkaline-earth elements and can be selectively precipitated as a sulfate, for example. This process is highly selective and allows production of high purity europium fromlow europium content solutions (see Calcium compounds Strontiumand strontium compounds). 

The combination of dicyclopentadienylzirconium dichloride and silver perchlorate activates armed glycosyl sulfoxides in dichloromethane between -20 °C and room temperature, but only very simple acceptors were studied [335]. Other Lewis and Bronsted acids studied include the environmentally benign europium, lanthanum and ytterbium triflates [336], certain polyoxometallates [337], sulfated zirconia [338] and Nafion H [338]. 

As indicated later (see Section VI,8), on addition of the chloride of praseodymium, europium, or other lanthanides to mono- or poly-sac-charide phosphates in D20, the signals of carbon atoms substituted with phosphate groups are recognizable, as they are displaced, relative to the rest of the 13C-n.m.r. spectrum.155 However, this diagnostic method is not applicable to sulfated polysaccharides, as signal displacements were not observed on addition of praseodymium or europium chloride to a solution of a,/3-D-galactose 6-sulfate or its sodium salt.156... 

Am3+ is the most stable oxidation state of the metal. In trivalent state, its properties are simdar to europium. Am3+ reacts with soluble fluoride, hydroxide, phosphate, oxalate, iodate and sulfate of many metals forming precipitates of these anions e.g., Am(OH)3, Am(103)3, etc. 

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. 

On an industrial scale, only the reduction of europium(II) with zinc, followed by its recovery as a divalent sulfate from chloride solution is useful. In practive, it is possible to recover europium from mixtures containing only trace quantities by adding zinc, barium chloride and sulfuric acid the mixed... 

Due to the modifications of the electronic cloud induced by complexation, the quantum yield and the excitation spectrum are also modified. As the direct determination of the absolute quantum yield is very difficult to achieve, one usually finds in the literature quantum yield values determined by comparison to well-known standards, such as quinine sulfate. For example, some values can be found in Georges (1993) or in Klink et al. (2000) for some europium complexes but may be found also in many other papers on lanthanide luminescence. Studies on the correlations between the photophysical properties of a given type of europium complexes and the energy levels can be found in Latva et al. (1997), Klink et al. (2000). A correlation has been found between the excitation properties and the stoichiometry of various Eu(III) complexes (Choppin and Wang, 1997). Note that the changes in the excitation maximum induced by complexation usually amount to a few tenths of nanometers, which requires high resolution for detection. In the case of Eu(III), a correlation has been found between the frequency... 

Europium (II) acetate, formation of, from europium amalgam, 2 68 Europium(III) acetate, 2 66 citrate solution of, 2 67 Europium amalgams, 2 65, 66, 68n. Europium (II) carbonate, 2 69, 71 Europium(II) chloride, 2 69, 71 formation of, from europium amalgam, 2 68 Europium (III) oxalate, 2 66 Europium (III) oxide, 2 66 Europium (II) salts, 2 69 Europium(II) sulfate, 2 69, 70... 

The stabilities of the Eu2+, Yb2+, and Sm2+ ions correlate with the third ionization enthalpies of the atoms and the sublimation enthalpies of the metals. The Eu2+(aq) ion is readily obtained by reducing Eu3+(aq) with Zn or Mg, while preparation of the others requires use of Na/Hg or electrolysis. The aqueous Eu2+ solutions are easily handled, but those of Sm2+ and Yb2+ are rapidly oxidized by air and by water itself. The Ln2+ ions show many resemblences to Ba2+, giving insoluble sulfates, for example, but soluble hydroxides. Europium can be easily separated from other lanthanides by Zn reduction followed by precipitation of the other Ln3+ hydroxides. 

The zinc reduction of Eu + to Eu +, followed by its precipitation as the sulfate, is a traditional step in the separation of europium from other lanthanides. In general, the solubilities of the inorganic compounds of the Ln + ions resemble those of the corresponding compounds of the alkaline earth metals (insoluble sulfate, carbonate, hydroxide, oxalate). Both europium and the Sm + and Yb + ions can also be prepared by other methods (e.g. electrolysis), although these solutions of the latter two metals tend to be short-lived and oxygen-sensitive in particular. Eu + is the only divalent aqua ion with any real stability in solution. Several divalent lanthanides can, however, be stabilized by the use of nonaqueous solvents such as HMPA and THE, in which they have characteristic colors, quite distinct from those for the isoelectronic trivalent ions on account of the decreased term separations. 

Separation of Samarium and Europium. One hundred thirty-five grams of samarium-europium acetate in 450 ml. of solution at 60° was treated with 1.0 g. of sodium in 80 ml. of mercury. One-half milliliter of 30% sulfuric acid was added, and the precipitated europium (II) sulfate... 

The construction of these electrodes is shown in Figure 13.12. The most successful example is the fluoride electrode. The membrane consists of a single crystal of lanthanum fluoride doped with some europium(II) to increase the conductivity of the crystal. Lanthanum fluoride is very insoluble, and this electrode exhibits Nerstian response to fluoride down to 10 M and non-Nerstian response down to 10 M (19 ppb ). This electrode has at least a 1000-fold selectivity for fluoride ion over chloride, bromide, iodide, nitrate, sulfate, monohydrogen phosphate, and bicarbonate anions and a 10-fold selectivity over hydroxide ion. Hydroxide ion appears to be the only serious interference. The pH range is limited by the formation of hydrofluoric acid at the acid end and by hydroxide ion response at the alkaline end a pH range of 4 to 9 is claimed... 

Cu20S04 DICOPPER OXIDE SULFATE 625 EuS EUROPIUM MONOSULFIDE 669... 

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