Characterization and Optical Study of ...

Industrial wet phosphoric acid production in Tunisia has led to the accumulation of high amounts of waste phosphogypsum by-products which are stocked mainly in piles. This harmful waste has still caused much anxiety and problems for the living especially in Sfax region (South-East of Tunisia) where it is rejected. In this paper two samples of Tunisian phosphogypsum, differing in their age, were analyzed by different analytical methods in order to compare and study the effect of impurities presence on gypsum’s properties. Infrared spectroscopy allowed the observation of phosphoric acid and fluorosilicates absorption bands as well as the determination of the P/S ratio. X-ray powder diffraction confirmed the presence of impurities of HPO42- (crystallized in ardealite and brushite phases) and SiF62- (crystallized in malladrite phase) in phosphogypsum samples. A shaped-needles phase observed only in old sample micrographs corresponded to the brushite phase. Differential Scanning Calorimetry analysis showed the influence of impurities on the thermal behavior of dehydrated calcium sulfate. Elemental analysis was provided with respect to scanning electron microscopy coupled with energy dispersive X-ray technique, X-ray fluorescence, ultraviolet-visible spectroscopy, flame atomic absorption spectroscopy and selective electrode analysis. Optical properties investigated by photoluminescence measurements allowed not only the identification of the matrix emissions but also the observation of Cd2+, Zn2+ and Mn2+ impurities showing thus their presence in the studied phosphogypsum samples.