Determination of trace amounts of thorium and uranium in coal ash by inductively coupled plasma atomic emission spectrometry after extraction with 2-thenoyltrifluoroacetone and back-extraction with dilute nitric acid

Abstract

A method of sample preparation is described that can be used for the determination of trace amounts of thorium and uranium in coal ash by inductively coupled plasma atomic emission spectrometry. After acid digestion of the samples, the elements are separated independently from the matrix by 2-thenoyltrifluoroacetone (TTA)-benzene extraction procedures. Thorium is extracted with 0.25 M TTA at pH 1.2 in the presence of ascorbic acid. Uranium(VI) is extracted with 0.16 M TTA at pH 3.5 in the presence of EDTA. The amount of EDTA to be added to the sample solutions must be properly controlled because an excess reduces the recovery of uranium. Thorium and uranium are finally measured in the back-extract in 2 M nitric acid. The detection limits were 11 µg l^–1 for Th and 29 µg l^–1 for U and the relative standard deviations ranged from 3.0 to 8.6% for Th and 3.9 to 4.3% for U.