Phosphoric acid-modified bentonite-chitosan composite beads: a novel and cost-effective adsorbent for multi-metal wastewater treatment.

This study introduces a novel, cost-effective adsorbent made from phosphoric acid-modified bentonite-chitosan composite beads, designed to remove Cu2⁺, Ni2⁺, and Zn2⁺ from aqueous solutions. Characterization of the composite revealed a mesoporous structure and the presence of functional groups that enhance its adsorption properties. Using response surface methodology, the adsorption capacities were determined as 362.24 mg/g for Cu2⁺, 279.51 mg/g for Ni2⁺, and 210.54 mg/g for Zn2⁺ under optimal conditions. A pH study further improved the adsorption capacities to 381.29 mg/g for Cu2⁺, 305.98 mg/g for Ni2⁺, and 225.04 mg/g for Zn2⁺. The adsorption process followed pseudo-second-order kinetics and was best described by the Langmuir isotherm model, suggesting that the adsorption occurred on a single layer of the adsorbent surface via chemical bonds. In competitive adsorption scenarios, Cu2⁺ was removed more efficiently than Zn2⁺ and Ni2⁺. The removal efficiencies achieved were 88.59% for Cu2⁺, 72.30% for Ni2⁺, and 62.07% for Zn2⁺ using 1 g/l adsorbent within 30 min for treating industrial effluent. Thermodynamic analysis confirmed that the adsorption process was spontaneous and endothermic. The adsorbent maintained good performance over 10 regeneration cycles, demonstrating its reusability. The primary adsorption mechanisms include electrostatic attraction, surface complexation, and ion exchange. The developed adsorbent proved to be an efficient, sustainable, and environmentally friendly solution for removing heavy metals from wastewater. This cost-effective material can be readily implemented in industrial wastewater treatment plants to tackle heavy metal contamination.