Efficient simultaneous biosorption of Pb(II), Cu(II), Cd(II), and oily solutions onto chitosan-coated rubber seed shell activated carbon: Optimization, isotherm, kinetic, and thermodynamic studies

This study assessed the efficacy of chitosan-coated rubber seed shell activated carbon (RSSAC) for the simultaneous removal of Pb(II), Cu(II), Cd(II) ions, and oily solutions from water using Central Composite Design (CCD) under Response Surface Methodology (RSM). Optimal conditions were determined at an initial total adsorbate concentration of 400 ppm, with an adsorbent dosage of 0.06 g, a temperature of 35 degrees C, and an original pH of around 4.5. Under these conditions, simultaneous adsorption resulted in high removal efficiencies of approximately 90 % for oil (360 ppm), 82 % for Pb(II) (328 ppm), 55 % for Cu(II) (220 ppm), and 18 % for Cd(II) (72 ppm). The chitosan-coated RSSAC exhibited maximum adsorption capacities of 610.67 mg/g for Pb(II), 414 mg/ g for Cu(II), 126.67 mg/g for Cd(II), and 622.87 mg/g for oil, showing selectivity in the order of oil > Pb(II) > Cu (II) > Cd(II). Kinetic studies favoured the Pseudo-second-order model (R-2> 0.99), with good fits for oil and Cd (II) using Freundlich and Halsey models (R-2 > 0.997), and Cu(II) and Pb(II) using Freundlich and Temkin models, respectively. Thermodynamic analysis indicated an exothermic nature with decreased efficiency at higher temperatures. Regeneration tests confirmed high reusability over three cycles, particularly for oil, Cu(II), and Cd(II), without significant loss in adsorption efficiency. In conclusion, chitosan-coated RSSAC demonstrates effective selectivity and efficiency for environmental remediation, offering a sustainable and economical solution for the removal of mixed metal ions and oil from contaminated water.