Remediation of Trace Metals from Aqueous Solution Using a Novel Lignin–Montmorillonite Hydrogel Composite Prepared from Tectona grandis Sawdust Derived Lignin

Abstract

Water pollution caused by trace metals poses a serious risk to human health and the environment. An ecofriendly approach was implemented to clean up these pollutants, in which an inexpensive and ecofriendly hydrogel composite was synthesized using Tectona grandis (teak wood) sawdust. Firstly, lignin was extracted from the sawdust by a mild acidolysis process. The extracted lignin was subsequently treated with montmorillonite for the synthesis of the hydrogel. Plausible methods for the process of free radical graft polymerization were theorized. When the hydrogel composite was utilized for the removal of Pb(II), Cd(II), Hg(II), and As(III) ions from the water, it exhibited high adsorption capacity (11.92, 11.58, 11.85, and 11.57 mg g–1, respectively) for all the trace metals. Kinetics and modeling studies revealed that the adsorption kinetics was better explained by a pseudo-second-order kinetic model, and at equilibrium, adsorption followed a Langmuir isotherm. It was interesting to note that the synthesized hydrogel possessed excellent reusability and desorption and regeneration properties. Ion exchange and chelation properties of the hydrogel were probably responsible for the adsorption mechanism. The regenerated hydrogel showed >50% removal efficiencies even after five cycles, showing economic feasibility of its application at a large scale.