Distribution of uranium related to particle size of phosphogypsum from phosphoric acid production (Huelva, SW Spain)

Abstract

In this work, both uranium and some trace elements distribution along with particle sizes were studied on phosphogypsum, in order to improve the knowledge on the behavior of toxic elements. 238U and 234U concentrations were obtained by alpha spectrometry, whereas Cr, Cu, Zn, Sr, Y, Zr, Cd, Ba, and Pb were determined using X-ray fluorescence. Determination of toxic elements in phosphogypsum was obtained in bulk and in three particle fractions: coarse (> 53 μm), medium (53–20 μm) and fine (< 20 μm). Average values obtained in the different particle fractions for 238U were 100 Bq/kg in bulk, 94 Bq/kg in the coarse fraction, 115 Bq/kg in the medium one and 160 Bq/kg in the fine fraction. 234U concentration average values, in the same order, 105, 96, 121 and 174 Bq/kg, respectively. Elements such as Zn, Sr, Y, Zr, Ba and Pb tend to be concentrated in the fine fraction, whereas the Cd is distributed homogeneously in the three fractions. Results obtained by these techniques have demonstrated that the most toxic elements are not distributed homogeneously into phosphogypsum and that most of these elements are concentrated in the fine fraction (particles < 20 μm), which could be easily mobilized by leaching and/or erosion.