Cerium separation from

Although rare-earth ions are mosdy trivalent, lanthanides can exist in the divalent or tetravalent state when the electronic configuration is close to the stable empty, half-fUed, or completely fiUed sheUs. Thus samarium, europium, thuUum, and ytterbium can exist as divalent cations in certain environments. On the other hand, tetravalent cerium, praseodymium, and terbium are found, even as oxides where trivalent and tetravalent states often coexist. The stabili2ation of the different valence states for particular rare earths is sometimes used for separation from the other trivalent lanthanides. The chemicals properties of the di- and tetravalent ions are significantly different. 

Lanthanum - the atomic number is 57 and the chemical symbol is La. The name derives from the Greek lanthanein for to be hidden or to escape notice because it hid in cerium ore and was difficult to separate from that rare earth mineral. It was discovered by the Swedish surgeon and chemist Carl-Gustav Mosander in 1839. In 1842, Mosander separated his lanthanium sample into two oxides for one of these he retained the name lanthanum and for the other he gave the name didymium (or twin). 

Cerium is separated from other rare-earth elements by an ion-exchange process in which it reacts with fluoride. This compound is then reduced with calcium metal (3Ca +2CeF — 2Ce + 3CaFj). Cerium can also be produced by the electrolysis of molten cerium salts. The metal ion collects at the cathode, and the chlorine or fluorine gases of the salt compound at the anode. 

Two sets of experiments were made to show the effect of steaming temperature on stability. In the first set, steaming was done non-interactively. Cerium/alumina additive was steamed (100% steam, 1 atm) for 5 hours in a fixed bed from 1200 to 1450 F. SO2 removal ability was then measured on these steamed samples diluted with cracking catalyst. The data in Figure 14 show that, for steamings done separate from cracking catalyst, losses of SO2 removal ability are small but become more pronounced above 1350 F. 

Ceric ammonium nitrate is prepared by electrolytic oxidation of cerous nitrate in nitric acid to ceric nitrate, followed by the addition of ammonium nitrate solution. It is separated from the solution by crystaUization. It may be prepared alternatively by dissolving cerium(II) oxide, Ce0 H20 in concentrated nitric acid followed by treatment with ammonium nitrate. 

Cerium is obtained from its ores by chemical processing and separation. The process involves separation of cerium from other rare-eartb metals present in the ore. Tbe ore is crushed, ground, and treated with acid. Tbe extract solution is buffered to pH 3 and tbe element is precipitated selectively as Ce4+ salt. Cerium also may be separated from other metals by an ion-exchange process. 

After separation from other rare earths, ytterbium is usually obtained as its oxide, Yb203. If separated as oxalate, oxalate is converted into oxide by high temperature. Ytterbium oxide is reduced to metallic ytterbium by heating with lanthanum metal in high vacuum. The metal is purified by sublimation and collected over a condenser plate. Aluminum, zirconium, and cerium also are effective reducing agents and may be used instead of lanthanum. 

Double sulphate precipitation is one of the most common methods used in industry for the separation of cerium group from yttrium group rare earths. Various other precipitants such as chromates, double chromates, ferrocyanides, phosphates etc. have been tried. 

A mixture of well-known extractants, di-(2-ethylhexyl)phosphoric acid (HDEHP) and CMPO, in n-paraffin was used for the study of combined extraction of different actinides (americium, plutonium, and uranium) and lanthanides (cerium and europium) and their separation from fission products (cesium, strontium, ruthenium, and zirconium).54 Combined extraction of MAs and lanthanides was studied together with group separation of MAs from lanthanides by selective stripping with a solution of diethylenetriaminepentaacetic acid (DTPA), formic acid, and hydrazine hydrate. This solution strips only MAs, leaving lanthanides in the organic phase. Subsequently, the lanthanides are stripped using a mixture of DTPA and sodium carbonate. 

Monomeric Cp3Ce(OtBu) could be separated from the reaction mixture by crystallization (Fig. 32, Table 14). The four ligands define a tetrahedron around the cerium atom with an almost linear Ce-O-C angle (176.3(6)°). 

Heterogeneous catalysts, either as metals or as metal oxides, are easier to separate from the effluent stream and when coated onto porous carriers are more active than homogeneous catalysts in promoting oxidation. Some examples of heterogeneous catalyzed systems operating at subcritical temperatures (WAO conditions) include the following ruthenium supported on cerium (IV) oxide, the most active metal catalyst among precious metals... 

Separation. Cerium and thorium salts are precipitated in Group IIIA. They may be separated from the other metals of the group by dissolving the precipitate in dilute HC1 and adding oxalic acid solution, when the oxalates of both metals are precipitated. The thorium and cerium may be separated (a) by dissolving the thorium oxalate in a mixture of ammonium acetate solution and... 

In general, lanthanides can be separated from mixtures with other elements by precipitation as oxalates or fluorides. Cerium and europium can conveniently be removed from the others, the former by oxidation to CeIV and precipitation as the iodate, and the latter by reduction to Eu2+, which can be precipitated as EuS04. 

Cerium is separated from the other rare earths based on differences in adsorption and selective elution. In a typical process, thorium free rare-earth solutions are run... 

It maj- also be separated from solutions of uranium salts bj the addition of a little cerium salt and precipitation with aqueous hydrofluoric acid, or with oxalic acid or bj adding a small quantity of thorium nitrate and precipitating with t-nitrobenzoic acid. It may also be absorbed bj- charcoal,iDasic ferric acetate, and by various oxides, sulphides, sulphates, and gelatinous silica. In the case of charcoal the uranium X is completely removed from a solution of a... 

The principal source of thorium is monazite (p. 425), a phosphate of cerium and lanthanum with up to 15% of thoria. It is dissolved in concentrated sulphuric acid and the thorium phosphate precipitated with magnesium oxide. The washed phosphate heated with sodium carbonate gives crude thoria, ThOg, which is converted to the soluble oxalate and separated from the insoluble oxalates of cerium and lanthanum. After ignition to oxide the nitrate is made, purified by recrystallisation, and again calcined to thoria. 

The classical chemical methods to separate lanthanoids were based upon the redox behavior of Ce, Sm, Eu, and Yb , Other classical methods (fractional crystallization) are essentially physical processes. Cerium is oxidized to the 4-I- state and separated from the 3+ rare earths by solvent extraction, iodate precipitation, or selective hydrolysis or precipitation of basic Ce(IV) compounds in weakly acidic solution. Europium is reduced and maintained in H2O as Eu " by Zn amalgam and precipitated as EUSO4. Sm and Yb are extracted from H2O by reduction into dilute Na or Li amalgam. 

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