Effective removal of heavy metal ions (Pb, Cu, and Cd) from contaminated water by limestone mine wastes

Limestone mining waste and its derived CaO were checked as an adsorbents of pb^{+ 2}, Cu^{+ 2}, and Cd^{+ 2} ions from water solution. The characterization of Limestone and CaO was studied by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and Scanning Electron Microscope (SEM). The optimum conditions of sorbent dosage, pH, initial concentration, and contact time factors were investigated for pristine limestone and CaO absorbents. The results indicate that the optimum initial concentrations of (C_i) were 1200, 500, and 300 ppm for Pb, Cu, and Cd, respectively, using CaO adsorbent, while using the pristine limestone adsorbent, the corresponding optimum initial concentrations were 700, 110, and 50 ppm. In the ternary system sorption, the results indicated that the selectivity sequence of the studied metals by CaCO₃ can be expressed as Pb^{+ 2} > Cd^{+ 2} > Cu^{+ 2}, while CaO exhibits a higher selectivity for Pb^{+ 2} compared to Cu^{+ 2} and Cd^{+ 2}. Hence, various adsorption isotherm and kinetic models were examined to explore different patterns and behaviors of adsorption. So, the results indicate that CaO has great potential for eliminating cationic heavy metal species from industrial water solutions.