Characterization of phosphogypsum wastes associated with phosphoric acid and fertilizers production

摘要

The present work is directed to characterize the phosphogypsum (PC) wastes associated with phosphoric acid produced by the wet process in industrial facility for the production of fertilizers and chemicals in Egypt. The PG waste samples were characterized in terms of spectroscopic analysis (X-ray diffraction, X-ray fluorescence, IR spectra) and radiometric analysis (γ- and α-measurements). The y-ray measurements showed that the average activity concentrations are 140 ± 12.6, 459 ± 36.7, 323 ± 28.4, 8.3 ± 0.76 and 64.3 ± 4.1 Bq/kg for U-238, Ra-226, Pb-210, Th-232 and K-40, respectively. The α-particle measurements of uranium isotopes showed that the average activity concentrations of U-238, U-235 and U-234 were 153 ± 9.8, 7 ± 0.38,152 ± 10.4 Bq/kg, respectively. The average radiochemical recovery (%) of the destructive a-particle measurements is ～70% with a resolution (FWHM) of ～30 keV. Activity ratios of U-238/Ra-226 and U-238/Pb-210 were less than unity (i.e., <1) and equal to 0.31 ±0.02 and 0.47 ±0.16, respectively. The isotopic ratios of U-238/U-235 and U-238/U-234 (in PC and PR samples) were close to the normal values of ～ 21.7 and ～ 1, respectively and are not affected by the wet processing of phosphate rock (PR). The obtained results of PG waste samples were compared with phosphate rock (PR) samples. The radiation hazard indices are namely, radium activity index (Ra-Eq > 370 Bq/kg), total absorbed gamma dose rate (D_(γr) > 5 nGy/h) and radon emanation fraction (Rn-EF > 20%). Uncertainty of the sample counting was 95% confidence level of α. The results indicated the necessity to find suitable routes to decrease and/or redistribute the radionuclide of environmental interest (i.e., Ra-226) in PG wastes, consequently to reduce its radiation impacts in the surrounding environment.