Cerium hydrogen sulfate

An analytical application of cerimetry that is stiU in use is the determination of hydrogen peroxide by titration with a 0.1 M cerium(IV) sulfate solution to the pale blue end point of a ferroin indicator (Hurdis and Romeyn, 1954). The reaction is ... 

The fast reaction between cerium(IV) sulfate and hydrogen peroxide is useful to determine the concentration of hydrogen peroxide in solution by cerimetric titrations (see section 3). However, the decomposition of hydrogen peroxide by cerium(IV) in perchloric acid solution is slow at pH values above 0.7 (Baer and Stein, 1953 Ardon and Stein, 1956), at which colloid polymeric cerium(IV) complexes are formed. These are able to interact with hydrogen peroxide to afford colored complexes that are only slowly decomposed. At very low pH values, the polymeric complexes are not formed and decomposition of hydrogen peroxide is fast. 

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%. 

The solution and precipitate were separated by filtration. Qualitative analysis of the precipitate showed that it contained cerium(III) and sulfate ion. [No precipitate appeared when m-bisoxalatodiaquochromate(111) ion and cerium(IV) were allowed to react at this acidity under conditions where the sulfate and/or cerium concentrations were somewhat lower.] The filtrate, including washings, was diluted to a measured volume, and two measured aliquots of this solution were withdrawn for study. The first aliquot was passed onto a cation exchange column in the hydrogen form. Elution with 1M sulfuric acid left a small dark violet band of hexaaquochromium(III) ion at the top of the column, while the rest of the chromium passed through the column. [In separate experiments it was confirmed that the Cr(OH2)fe+3 ion is retained as a dark violet band at the top of the resin when the resin is eluted with 1M sulfuric acid. This is in agreement with the observations of King and Dismukes (23).] Analysis of the effluent solution showed that 4 to 5% of the chromium had been retained by the column. 

For the cerium(IV)-m-Cr(OH2)2(0204)2 reaction the role of cerium(III) has been described here, and the role of hydrogen ion and sulfate ion will be described elsewhere... 

Not until similar information is obtained on the effect of cerium(III), hydrogen ion, and sulfate ion on the oxidations of Cr(C2C>4)3 3 and Cr(OH2)4C204+, will it be appropriate to discuss the relative reactivities of the three oxalato complexes toward cerium(IV). 

During reducing conditions, cerium sulfate decomposes around 550-750 K (1) to SO2, which then easily reacts with adsorbed hydrogen atoms on the well dispersed PM particles to fonn H2S, according to ... 

Cerium sulfate, Ce3(804)3 5HsO, is prepared by heating 3 g. of the chloride with 5 ml. of cone. H 3SO 4 until all the hydrogen chloride has been removed. Then 20 ml. of water is added and the product is allowed to crystallize in a desiccator. 

The oxides, (R.E.)203, are readily soluble in acids unless they have been ignited at high temperatures, in which case they dissolve more slowly. However, cerium(IAr) oxide dissolves in acids exceedingly slowly. It may be converted to the anhydrous sulfate by heating with concentrated sulfuric acid or may be reduced to cerium (III), and thus rendered soluble, by means of hydrogen peroxide or alkali metal iodide in acidic solution. 

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