Studies on the Separation of Alkaline Earth Elements. V. Coprecipitation of Radium in the Induced Precipitate of Lead Sulfate

Abstract A solution of pH 5.50 composed of 0.096 m lead nitrate, 2.07 m ammonium acetate, 1−5×10−4 m barium and 5–50 μC radium per liter, produces an induced precipitate of lead sulfate in proportion to the amount of 0.5 m sulfuric acid added. Under the same conditions, in the absence of barium, a lead sulfate precipitate is obtained in proportion to the amount of sulfuric acid added. But the required amount of sulfuric acid to obtain the same amount of precipitate is larger in this case than that in the case of induction by barium. In both of the above cases, the ratio of the amount of the radium coprecipitated to the original amount of radium in sample solution is almost constant, i. e. 92–97%, irrespective of the amount of lead sulfate precipitate or of sulfuric acid added. This tendency is the same as in the case of coprecipitation of barium with the induced precipitate of lead sulfate as shown in the previous paper. More than 90% of radium is carried down by a precipitate of lead sulfate of 8–20% of lead. Such an extent was not found in the case of the ordinary precipitation of lead sulfate, i. e. in the absence of the masking agent, ammonium acetate for lead ions. In conclusion, the induced precipitation of lead sulfate by barium can be made use of as an efficient method of separation or concentration of radium. For a practical usage of this method, more detailed examination according to each sample should be conducted.