Ultrasonication-assisted synthesis of lignin/clay nanocomposites for highly efficient cadmium removal: Characterization, adsorption and thermodynamic insights

Wastewater pollution has become a critical global environmental issue. This study focuses on synthesizing of new biosorbents by incorporating extracted lignin into two types of clays: fibrous sepiolite (SP) and phyllosilicate bentonite (BT). The goal was to develop cost-effective adsorbents capable of removing toxic metals, particularly cadmium. The physicochemical properties of the resulting materials were analyzed using various techniques, confirming the effective incorporation of lignin into the clay substrates, resulting in two distinct materials called (SL) and (BL). The effectiveness of the modified clays was thoroughly evaluated by examining adsorption performance, kinetics, thermodynamics, and mechanisms governing Cd (II) adsorption. Equilibrium isotherms and kinetic models demonstrated that Cd (II) adsorption on SP and BT followed the Langmuir and Freundlich isotherms, respectively, displaying pseudo-second-order kinetic behavior for both materials. On the other hand, SL and BL modified clays showed a better fit with Langmuir and Freundlich isotherms, respectively, as well as Elovich and Avrami fractional order kinetics, resulting in high correlation coefficients. The maximum Cd (II) adsorption capacities for SL and BL were determined at 118.44 and 157.32 mg/g, respectively, confirming the high efficiency of the modification. Thermodynamic analysis suggested that the Cd (II) adsorption process is both endothermic and spontaneous.