1965 Volume 14 Issue 3 Pages 199-205
According to the standard method, the co-precipitation with ferric hydroxide with ammonia water (pK 4.72) was utilized for the separation of 140La from a mixture of 140Ba-140La. Almost all 140Ba in the case without carriers and about 7 % of 140Ba in the case with carriers were co-precipitated with ferric hydroxide. Therefore, the high purity of 140La could not be obtained by this method.
To separate pure 140La from a 140Ba-140La mixture, several organic bases such as pyridine (pK 8.77), α-picoline (pK 7.52), benzylamine (pK 4.63), n-butylamine (pK 3.39) and ethylenediamine (pK 4.07) were also used as precipitants. By using these organic bases, it was possible to maintain a pH value of a test solution within a narrow range easily.
When pyridine was used instead of ammonia water, only 0.04-0.2% of 140Ba was co-precipitated without carriers. And, by α-picoline only 0.1-0.8% of 140Ba was co-precipitated.
When benzylamine wsa used as a precipitant, the purity of 140La was nearly equal to the case of ammonia water.
The contamination of 140Ba is inversely related to the degree of the pK value of the precipitants, that is the quantity of 140Ba co-precipitated with ferric hydroxide increases in the concentration of OH- ion in the solution.
Although a similar result was obtained in the case of 90Sr-90Y, the purity of 140La is lower than that of 90Y. This may be because Ba2+ has a greater affinity for Fe (OH) 3 than Sr2+.