Cerium hydrolysis

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

Hydrolysis is very extensive in Pu(IV) solutions, less so in Pu(Ill) and Pu(VI), and least in Pu(V). The chemical properties of Pu(IV) are somewhat similar to those of Ce(IV) and U(IV) (see Cerium AND cerium compounds). The hydrolysis thermodynamics of Pu(IV) have been assessed in perchlorate solutions (105). The first hydrolysis equiUbrium is... 

The second group includes SAHs obtained by radical grafting of acrylonitrile (AN) on natural polymers, mostly starch, under the action of cerium initiators [43 -46, 50, 51], The proper crosslinked hydrophilic polymer is formed at the stage of alkali hydrolysis of grafted polyacrylonitrile (PAN), the final characteristics depending on many factors, in particular the sort of starch [46], the methods of its preparation [51], the component ratio, etc. The nature of starch is exhibited through... 

The effect on the induced reaction of the acidity cannot be satisfactorily considered with the kinetic data available. It was mentioned that the rate of reaction between hydrogen peroxide and peroxydisulphate is at maximum at about pH 5. In contrast, the value of Fj obtained cerimetrically goes through a flat maximum in the pH range from 1-2. This maximum should be regarded as an apparent one because the hydrolysis of cerium(IV) is considerable at pH s higher... 

Results and Discussion. Of the 12 samples of starch graft copolymer synthesized, half were hydrolyzed to anionic polyelectrolytes. Synthesis data on these 6 samples are given in Table 2. These particular samples were chosen for hydrolysis because the samples can be intercompared to see the effect of synthesis variables on ultimate product properties. Samples 5, 8, and 11 have the same mole ratio of cerium ion to starch backbone, N, in their reaction mixture. Samples 7, 8, and 9 all have the same refctable mass per starch molecule,... 

A Greek team also reported on oxidation of partially saturated heterocycles to fully heteroaromatic rings <1996JHC599> 5-/>-anisyl-4,5-dihydro[l,2,3]triazolo[5,l-/][l,2,4]triazine 91, when treated with cerium ammonium nitrate, underwent an oxidative hydrolysis giving heteroaromatic product 92 in poor yield (20%). 

Silica is known to be volatile in steam (39-40). For instance, the equilibrium concentration of silica in steam at 1 atmosphere from 1200 to 1450 F has been found to range from 0.2 to 0.5 ppm (by weight) showing that the availability of silica in the vapor phase can be substantial under the conditions used in our work. Unfortunately, we cannot predict how much silica will be transferred in our experiments since the rates of either hydrolysis or adsorption on the cerium on alumina additive are unknown. 

Cerium(III) nitrate is used for the separation of cerium from other rare-earth elements. It also is used as a catalyst in hydrolysis of phosphoric acid esters. 

Separation based on valency change.—The easy oxidation of Ce3 to Ce4+ permits its isolation from other rare earths. The separation of cerium is usually performed by selective leaching with acids, or by complete dissolution [129, 130] followed by hydrolysis. The solvent extraction behaviour of Ce(N03)4 has been extensively studied. Among the various extractants, alcohols, ethers, organic and inorganic acids, ketones etc., TBP proved to be most advantageous in large scale operations [131,132]. 

Cerium(IV) ammonium nitrate (CAN) is effective for oxidative hydrolysis of phenyl esters substituted by hydroxyl, methoxyl, and dimethylamino groups in CH3CN-H20 at 0°. 

Bamann et al.119 also found that the hydrolysis of di- and tri-peptides is catalyzed by rare earth ions at pH 8.6. Cerium(IV) and Cem were particularly effective even at a temperature of 37 °C. The same reactions with La111 as a catalyst were much slower and only occurred at an appreciable rate at 70 °C. Many of these reactions merit further study. 

Cerium(III) oxide is quite a strong base compared with boron(IIl) oxide (see Table 9.1), and the acid/base reaction is strongly exothermic. No appreciable hydrolysis occurs for CeCl3, which dissolves in water to give Ce3+(aq). A detailed thermochemical analysis of the factors which lead to the dramatic difference in behaviour between B203 and Ce203 is not straightforward, but the considerations set out in Section 10.2 in the discussion of Table 10.1 are relevant. 

For the thioacetal cleavage in the second step (ia) a classical cerium(IV)-catalysed hydrolysis gives good yields ( > 85 %) with any phosphonium salts we have tested. Subsequent elimination of triphenylphosphine by reaction of the salts 5 with triethylami-ne was always nearly quantitative. 

In the quantitative determination of cerium, use is made of the fact that cerous oxalate is insoluble in neutral and acid solution. Since a quantitative yield is not necessary in this preparation, some of the cerium is sacrificed to insure complete removal of any iron that may be present. In order to have a neutral solution for the hydrolysis of the iron, a slight excess of ceric oxide is used. 

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