Analysis of low concentration U species within U mill tailings using X-ray microprobe

Abstract

Trace U species (i.e., ppm) found in the combined solid and liquid residues from uranium milling operations, known as tailings, are of scientific interest as tailings management facilities (TMFs) are designed to keep U species and other potentially harmful substances sequestered as solid species to limit exposure to the environment. Use of X-ray microprobe to study U within solid tailings is challenging due to overlapping U Mα1 and K Kα1 X-ray fluorescence (XRF) signals. This problem of overlapping XRF signals is worsened due to the K concentration in the tailings being much higher than that of U. Reported herein is a methodology for using X-ray microprobe and the U Mα1 XRF signal to determine the distribution of U in samples of U mill tailings from the TMF located at McClean Lake, SK. The reported methodology utilizes an excitation energy just above the U M5-edge to avoid excitation of the K K-edge or an excitation energy that is higher than the K K-edge with the resulting XRF spectra being fitted to deconvolute the overlapping U Mα1 and K Kα1 XRF signals. Also discussed is the use of U M5-edge micro X-ray absorption near edge spectroscopy (μ-XANES) to both verify the U X-ray microprobe map collection methodology and to obtain chemical information on the U species present in the tailings.