THE NATURAL RADIOACTIVITY OF THE ROCK PHOSPHATES, PHOSPHATIC PRODUCTS AND THEIR ENVIRONMENTAL IMPLICATIONS

The radioactivity of the Minjingu phosphorite deposit in Arusha-Tanzania was determined by radiochemical and radiometric methods of analysis. The main radioisotopes analysed in the rock phosphate, phosphate concentrate (ground rock phosphate), phosphate fertilizers (superphosphate, and triple superphosphate) and phosphogypsum were U-238, U-235, Th-232 and their progenies. Uranium-238 and its progenies had high activity concentrations of approximately 4000 Bq kg-1 in all materials analysed, whereas phosphogypsum had high Ra-226, in contrast to triple superphosphate fertilizer. Extensive use of ground rock phosphate, and phosphate fertilizers was assessed in relation to their radiological implications to the farmers. The external radiation arising from the use of phosphate fertilizers in agricultural fields was found to be less than 2% of normal background radiation (50 nGy h-1). A model for pathways of the natural radionuclides from the ground rock phosphate, phosphate fertilizers and by-products is proposed in order to assess their long-term impacts on the secondary environment.