The fluorimetric determination of uranium in nonsaline and saline waters

Abstract

-8 I The procedure determines about 10 percent uranium using 500-ml samples of water. Uranium is concentrated by precipitating uranyl phosphate using aluminum phosphate as a carrier. The aluminum phos! phate is dissolved in 'nitric acid, salted vith aluminum nitrate, and ' i the uranium is extracted with ethyl acetate . A portion of the etj|yl acetate is evaporated in a standard platinum dish and, a fluorescing disc is prepared vith a mixed fluoride flux. Fluorescence measurements are made with a fluorimeter. One precipitation with A1PO* collects more than 95 percent of the uranium. The uranium content of various -7 , -7 ocean waters tested ranged from 2,. 3 x 10 to 3«^ x 10 percent \. ' ' uranium. i INTRdDUCTION ! i In the determination of uranium in waters containing slightly 8 more than 10 percent uranium* it is frequently necessary to con.the uranium prior to its estimation by the fluorescence method using fluoride phosphors. The uranium in waters of low salinity can be concentrated by simple evaporation of the water, but this method is not as useful for saline waters, where the problem is not lil^Ly to concentrate the uranium but to separate it from large amounts of sa'lts that would cause subsequent analytical difficulties. Hernegger and Karlik (193*0 isolated uranium from sea water by precipitating the uranium with ammonium hydroxide using a small amount of ferric iron as a carrier. This carrier has also been used by others (Lahner, 1939; Hoffman, 1939; and Urry, 19^1) for concentrating uranium from xtjcks and from ocean sediments. Other useful collectors for uranium include aluminum hydroxide (Urry, and Orlemann, 19^5) and aluminum phosphate (Tschernichow, 193*0. Aluminum phosphate has certain advantages as a carrier for uranium. Especially important is the ease with which aluminum phosphate can be dissolved with dilute acids even after it is aged or ignited. We have found aluminum phosphate to be an efficient collector even for less than microgram: amounts of uranium. This paper presents a simple fluorimetric method for the determination of uranium in naturally occurring waters. Preliminary concentration of uranium is made by precipitating uranyl phosphate using aluminum phosphate as a carrier. After dissolving the aluminum phosphate in nitric acid and salting the solution with aluminum nitrate, the uranyl nitrate is isolated by extraction with ethyl acetate (Grimaldl and Levine, 19^8). The relative fluores9ence of the disc is measured in a fluorimeter (Fletcher and May, 1950). The procedure is designed to -8 ' determine 10 g of uranium as a lower limit and uses 100to 500-ml samples of water. This work was done on behalf of the Division of Raw Materials of the Atomic Energy Commission,