Radiochemistry of Bangladeshi Phosphogypsum and Leachate Study

Author(s): Satyajit Ghose , Brian Heaton

Phosphogypsum is a high volume by-product from Phosphate fertilizer factory, named the Triple Superphosphate complex of Bangladesh containing naturally occurring radionuclide. Distribution of 226Ra, 210Pb and 210Po in the fertilizer factory byproduct, phosphogypsum, has been determined using alpha and gamma-spectrometry. Both nuclides (226Ra and 210Po) were found to be concentrated in the finest-grained materials of phosphogypsum. The investigated radionuclide concentration values in PG obtained were comparable with data reported in the phosphogypsum literature, while lower values were found for these radionuclides. Moreover, laboratory radium and polonium leaching experiments of phosphogypsum by deionized water and selective extraction solution have been performed. Radium leaching results showed that fresh phosphogypsum produced the highest concentration of Ra in solution and old phosphogypsum showed a very low transfer to the water. Polonium leaching experiments have shown that only a small amount of polonium is dissolved in filtrated fresh water, this amount is increased when the pH is decreased. It was observed that some extraction solution is more effective at releasing polonium to water from the gypsum matrix. Approximately 32% of 210Po is present on the gypsum surface and not inside the lattice; this position is easily exchangeable with contact of external media (i.e., MgCl2 extraction solution) and 95% of PG was soluble with concentrated cocktail acid solution and a value of 14% 210Po was released with contact of 0.02M sulfuric acid solution. The results obtained in this study can be utilized to verify the environmentally safe use of phosphogypsum as an amendment to agricultural soils.