Removal of Pb2+ from synthetic solutions and industrial wastewater using a magnetic hydrochar composite of spent tea leaves modified with MOF-199.

In this study, a sustainable magnetic composite adsorbent (STL-HC/MF/MOF-199) was developed from hydrochar derived from spent tea leaves and modified with manganese ferrite nanoparticles and MOF-199 for efficient Pb2+ removal from aqueous solutions and real industrial wastewater. Process parameters affecting adsorption performance were optimized using response surface methodology, resulting in a highly reliable statistical model with excellent predictive accuracy. The incorporation of magnetic nanoparticles and MOF-199 significantly enhanced adsorption kinetics and capacity compared to the pristine hydrochar. Pb2+ uptake by STL-HC/MF/MOF-199 was well described by the pseudo-second-order kinetic model, while equilibrium data showed the best agreement with the Langmuir isotherm model. The maximum adsorption capacity of the composite (52.65 mg/g) was substantially higher than that of the unmodified materials. Thermodynamic analysis confirmed that the adsorption process was spontaneous and endothermic over the investigated temperature range. Importantly, STL-HC/MF/MOF-199 demonstrated high Pb2+ removal efficiency in real industrial wastewater from metal plating and battery recycling facilities, reducing Pb2+ concentrations to below 0.1 mg/L under the investigated adsorption conditions, even in the presence of competing ions. The composite also exhibited favorable reusability over multiple adsorption-desorption cycles. Overall, this work highlights the potential of a waste-derived magnetic MOF composite as an efficient, robust, and sustainable adsorbent for Pb2+ removal from complex wastewater systems.