Determination of uranium by a spot developed on filterpaper

Abstract

On a filterpaper, potassium ferrocyanide reacts with uranium and develops a brown color. An attempt has been made to determine the uranium content of ores of domestic mines by measuring the light absorbancies of the homogeneous spots made in about the same size on the filterpapers. The method proposed here can be applied to samples containing not much copper or nickel. The procedure is as follows: the sample is treated with aqua regia for 3 hours, the residue is filtered off, and the uranium is precipitated by ammonium hydroxide with other elements including iron. The precipitate is then dissolved in a few ml of conc. nitric acid, and the solution is evaporated to dryness on a water-bath. To this residue, 0.15 ml of conc. nitric acid and 5 ml of aluminum nitrate solution {100 g Al (NO₃)₃·10 H₂O in 100 ml H₂O} are added, and the residue is dissolved on the water-bath. The solution is transferred to a 10 ml stoppered measuring cylinder, and the volume of the solution is adjusted to 5 ml with rinsing water. The previous vessel is once more rinsed with 1ml of aluminum nitrate solution, the rinsing solution is poured into the measuring cylinder, and the volume of the solution is adjusted to 6 ml. Two ml of ethyl acetate are added, the uranium is extracted in the ethyl acetate layer, and 1 ml of ethyl acetate containing uranium is washed with 1 ml of aluminum nitrate. Five hundredth ml of this ethyl acetate solution is dropped on the filterpaper. The dried filterpaper is dipped in 2% potassium ferrocyanide solution for 20 sec, and then washed in running water for 10 sec. 2 filterpaper is dried in a dark place. The light absorbancy of the spot thus prepared on the filterpaper is measured by a densitometer. A working curve must be prepared for every determination. Maximum error is within 10 %.