Radiochemical characterization of Brazilian phosphogypsum

Abstract

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.