Selective adsorption of Cu, Ni and Zn from steel sludge leachate using polyethyleneimine-functionalized mesoporous hybrid materials in batch and continuous-flow systems.

This study investigates the adsorption properties of amine-functionalized mesoporous organic hybrid materials (μOHMs) for the removal of heavy metals, specifically Cu, Ni and Zn from industrial wastewater streams such as steel sludge. The synthesized microscale (40-60 μm) materials were characterized and evaluated for adsorption performance in synthetic metal solutions and real steel sludge leachate under batch and continuous-flow conditions. Through batch adsorption experiments, equilibrium behavior was characterized using isotherm modeling, with apparent maximum adsorption capacities of 63.5, 43.1, and 36.2 mg/g for Cu, Ni, and Zn, respectively. Kinetic analysis showed that the pseudo-second-order model provided the best empirical description of the adsorption kinetics among the models evaluated. When applied to real steel sludge leachate, μOHMs removed 96.1% of Cu at an adsorbent loading of 1 g/L, while Ni and Zn removal reached 93.2% and 92.5%, respectively, at 6 g/L, with minimal removal of Ca, Mg, and Mn. Under continuous-flow treatment of the steel sludge leachate, Cu and Ni remained below the breakthrough threshold over the 60 min experiment, while Zn exhibited breakthrough at approximately 40 min and Ca, Mg, and Mn showed immediate breakthrough. In single-metal continuous-flow experiments, the experimentally integrated dynamic capacities were 58.0, 41.9, and 45.8 mg/g for Cu, Ni, and Zn, respectively, while the Thomas model provided the best overall representation of the breakthrough behavior. Competitive adsorption experiments in synthetic equimolar multicomponent systems further confirmed preferential Cu adsorption over Ni and Zn. Regeneration studies demonstrated repeated Cu uptake over 50 adsorption-desorption cycles using 0.1 M HNO3, with an average apparent Cu uptake of 33.5 mg/g. Overall, these findings demonstrate the potential of μOHMs for selective metal recovery from complex industrial streams while retaining Ca- and Mg-rich solutions for potential downstream carbon sequestration.