The potential of ball-milled Serbian natural clay for removal of heavy metal contaminants from wastewaters: Simultaneous sorption of Ni, Cr, Cd and Pb ions

The influence of mechanical milling of natural Serbian clay on removal of heavy metals from an aqueous medium was investigated. The simultaneous sorption of the 4 toxic heavy metals (Ni, Cr, Cd and Pb), which are often present together in numerous polluting spills and in agrochemicals was evaluated. Microstructural and morphological changes in the ball-milled clay were characterized by X-ray diffraction (XRD), particle size distribution (PSD) and scanning electron microscopy (SEM). Induced changes in microstructure were correlated to the cation exchange capacity (CEC), determined by the EPA Method 9081. The CEC value has increased from 77 meq/100 g for the unmilled clay, to 95 meq/100 g for the milled clay. Regarding the untreated clay, the cation competition reveal some differences in their sorption: complete sorption (about 98% of the initial concentration) was achieved for Cr and Pb, while about 19% of the initial concentration of Cd and Ni still persist in the solution. The order of affinity of the metal ions is Pb≈Cr>Cd≈Ni and it has not changed upon milling.