Integrated Electrocoagulation–Adsorption with Thermally Activated Bentonite for Simultaneous Pb, Cd, and Ni Removal from Real Laboratory Wastewater

Abstract

Although integrated electrocoagulation–adsorption (EC-Ads) systems have demonstrated considerable potential for heavy metal removal, systematic comparative evaluations using real laboratory wastewater containing multiple metals remain limited. This study investigated the performance of electrocoagulation alone, adsorption alone, and an integrated EC-Ads system employing thermally activated bentonite for the simultaneous removal of Pb, Cd, and Ni from real laboratory wastewater. Electrocoagulation was optimized in terms of pH, current density, and treatment time, whereas adsorption was optimized with respect to adsorbent dosage and contact time. The optimum operating conditions were pH 7, a current density of 0.0133 A.cm⁻², and 60 min for electrocoagulation, followed by 40 g of bentonite per 2 L of wastewater and 60 min for adsorption. Under these conditions, the integrated system achieved total removal efficiencies of 99.06% for Pb, 98.55% for Cd, and 97.34% for Ni, yielding final concentrations of 0.0521, 0.0342, and 0.0452 mg.L⁻¹, respectively. Electrocoagulation functioned as the primary removal stage, while adsorption served as an effective polishing step for residual metals at low concentrations. SEM-EDS, FTIR, and ICP-MS analyses supported complementary removal mechanisms involving surface adsorption, coprecipitation, precipitation, and immobilization in solid phases. Adsorption kinetics were better fitted by the pseudo-second-order model, suggesting that surface interactions played a dominant role in metal uptake. Overall, these findings demonstrate that the EC-Ads system based on thermally activated bentonite is an effective and promising approach for treating real laboratory wastewater containing multiple heavy metals.