Evaluating the adsorptive capacity of three Tunisian clays deposits for several potentially toxic metals in phosphogypsum waste

The occurrence and the treatment of potentially toxic metals in wastes are investigated by many studies, especially in territories exploited by industrial activities. Improper phosphogypsum waste storage is of serious environmental concern. The present work aimed to evaluate the potential of natural clay minerals from the Gabes area, southern Tunisia for sorption of several toxic metals (Zn, Cd, Cr, and As) that may leach from waste phosphogypsum. Clay materials are known by their versatility as adsorbents due to their low cost, great surface area, interchange capacity, and abundance in nature. The three clay samples collected in various locations in the Gabes district-Southern Tunisia were characterized by different techniques including X-ray fluorescence (XRF) and X-ray diffraction (XRD). The natural clays are mainly composed of alumina, iron, silica, calcium, and magnesium oxides. Chemical analysis of phosphogypsum waste indicated a high concentration of potentially toxic metals, particularly Cd, Cr, Zn, and As. Contents of the radioactive elements U and Thin contrast, were low not of environmental concern. Adsorption data showed that the studied three natural clay samples removed substantial amounts of metals (Zn, Cd, Cr, and As) from phosphogypsum waste. The removal efficiency followed pseudo-second-order kinetic model. These results suggest that the natural clays from Gabes area, Tunisia, turned out to be an effective natural adsorbent for capturing metals from phosphogypsum waste and can be effectively used for the treatment of contaminated wastewaters in the environment.