•*'>.~>o E. J. Roberts — Cerium by Potassium Permanganate. 



Aim. XXXI. — On the Separation of Cerium by Potassium 

 Permanganate; by Edwin J. Robbets. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ecxviii.l 



One of the most useful methods for the separation of cerium 

 from the rare earth metals which accompany it depends upon 

 its oxidation by potassium permanganate according to the 

 equation : 



3Ce a O s + 2KMn0 4 + H fl O = 6CeO, + 2KOII + 2MnO, . 



This action takes place in a cerous nitrate solution provided 

 some neutralizing agent is present to take up the nitric j*eid 

 set free. Stolba, in 1878,* used zinc oxide for this purpose, 

 and other investigatorsf have since used the method. Dross- 

 bach,^: B6hra,§ Muthmann and Weiss, || Meyei'T and others 

 have used alkali hydroxides or carbonates in place of zinc 

 oxide. More recently, Meyer and Schweitzer** have studied 

 this process, using sodium carbonate. They give the equation : 



8Ce(NO,), + KMn0 4 + 4Na 8 CO, + 8H„0 = 



3Ce(OH) 4 + Mn (OH) 4 + 8NaN0 3 + KNO a + 4C0 2 , 

 and use two different solutions for the precipitation. One, for 

 the complete removal of the cerium, contains one molecule of 

 permanganate to nearly five of sodium carbonate; the other, 

 for the purification of the cerium, contains one molecule of 

 permanganate to less than three of sodium carbonate. It is 

 obvious from the above equation that in the first case large 

 amounts of other earths will be precipitated with the cerium by 

 the excess of alkali, while in the second case the nitric acid 

 will be in excess at the end of the process, leaving consider- 

 able amounts of cerium in solution. The object of the present 

 work was to study the process carefully and to produce, if 

 possible, a sharper separation of the cerium. 



When a little potassium permanganate solution is added to 

 a hot neutral solution containing cerous nitrate, the red color 

 of the permanganate is instantly bleached, and a brown precip- 

 itate appears. If the addition of the permanganate is con- 

 tinned, the color is bleached more and more slowly, the liquid 

 becomes distinctly acid to litmus, and finally the red color 

 becomes permanent. If a little alkali is now added, the color 

 is again bleached, and if the liquid is kept neutral, or very 

 nearly so, the red color will not be permanent until all the 

 cerium is precipitated. The action seems to be as follows : 

 the cerous nitrate is oxidized by the permanganate, probably 

 according to the equation : 



*Jahresber., 1878, 1059. 



f Muthmann and Rolig, Ber. chem. Ges., xxxi, 1718; James, Jour. Am. 

 Chem. Soc, xxx, 982. 



±Ber. chem. Ges., xxix, 2452. §Zeit. angew. Chem., 1903, 1129. 



|| Ann. Chem., cccxxxi, 9. *[f Zeitschr. anorg. Chem., xxxvii, 378. 



**Zeitschr. anorg. Chem., liv, 104-120. 



