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Measurements of chemical and radionuclide concentrations in the phosphate deposits around Gafsa in Tunisia

Mounira Khelifi, Ridha Ben Salah, Mansour Ouselati4, Hasan Baltas, Jochen Gschnaller, Habib Hamed, Zied Said, Khaled Alzimami, Saad Saguem and Darwish Al-Azmi

Environmental radiation measurements are useful to identify areas of potential natural radiation hazard and assess the human population dose due to terrestrial radiation, particularly in areas of mining activities where enhanced radiation levels are expected to be present. Measurements have been carried out of the concentrations of primordial radionuclides in samples of phosphate layers collected from Gafsa City and its surrounding region in central of Tunisia, Moularaes and Kef Schfayer. The chemical composition in the phosphate samples was also analysed by Xray diffraction technique (XRD). Measurements of radon concentration levels, indoors and outdoors, were performed in some workplaces situated within the phosphate deposit area using solid state nuclear track detectors. The results show that concentration ranges (minimum to maximum, in Bq .kg-1) of the naturally occurring radionuclides, comprising 40K, 226Ra, 238U and 232Th from Moularaes are 21.6-149.4, 360.9-580.2, 20.3-85.8 and 12.5-70.6 respectively. The corresponding concentrations ranges (Bq.kg-1) from Kef Schfayer are 15.2-28.8, 285.7- 447.9, 6.9-24.9 and 26.9-76.4, respectively. The calculated absorbed doses are higher than the global population weighted average. The chemical analysis shows that the phosphate layers are composed of CaO, P2O5, SiO2, Al2O3, SO3 and Fe2O3, The concentrations and chemical distributions of heavy metals (Cd, Cr, Zn, Ni, Cu, Cd and U) in Moularaes and Kef schfayer phosphate ores were investigated. The margin of concentrations in ppm of Cd, Cr, Zn, Ni, Cu, Cd, U in Moularayes are 116-209, 74-241, 47-60, 0.66-10.23, 18-54, 112-206.3 respectively, the variation of this heavy metal in ppm in Kef Schfayer are 102-237, 106-176, 33-56, 4.21-13.96, 29-64, 132-168.4, respectively. The radon concentration levels as measured in some workplaces in kef Eddour lounder within the area were found to be within the range of of 5 to 130 Bq.m-3 and an average value of 23.8 Bq .m-3, which are below the ICRP action levels. The results may be useful in the assessment of the exposures and the radiation doses due to naturally radioactive element contents in the phosphate samples.