Radiochemical characterization of Brazilian phosphogypsum

This work aims to determine the activity concentrations of the radionuclides in the natural series, including (226)Ra, (210)Pb, (210)Po and the uranium and thorium isotopes, in Brazilian phosphogypsum and the ore rocks from which it is derived. The results show that (226)Ra, (210)Pb, (210)Po and thorium isotopes fractionate preferentially to the phosphogypsum, where percentages (to ore rocks) of 90% for (226)Ra, 80% for (232)Th and (230)Th, 100% for (210)Pb and 78% for (210)Po were found. The distribution of thorium isotopes seems to depend strongly upon chemical processes, since their relative concentrations in phosphogypsum (80%) were higher than expected from the available literature. The uranium isotopes are predominantly incorporated in phosphoric acid as uranyl phosphate, sulphate or fluoride complexes. The concentration ranges found for (226)Ra (22-695 Bq/kg), (210)Pb (47-894 Bq/kg), (210)Po (53-677 Bq/kg) and (232)Th (7-175 Bq/kg) in Brazilian phosphogypsum are wide but are in good agreement with results found in the literature for phosphogypsum from other locations. (C) 2000 Elsevier Science Ltd. All rights reserved.