Remediation\nof Trace Metals from Aqueous Solution\nUsing a Novel Lignin–Montmorillonite Hydrogel Composite Prepared\nfrom <i>Tectona grandis</i> Sawdust Derived Lignin

Abstract

Water pollution caused by trace metals poses a serious\nrisk to\nhuman health and the environment. An ecofriendly approach was implemented\nto clean up these pollutants, in which an inexpensive and ecofriendly\nhydrogel composite was synthesized using <i>Tectona grandis</i> (teak wood) sawdust. Firstly, lignin was extracted from the sawdust\nby a mild acidolysis process. The extracted lignin was subsequently\ntreated with montmorillonite for the synthesis of the hydrogel. Plausible\nmethods for the process of free radical graft polymerization were\ntheorized. When the hydrogel composite was utilized for the removal\nof Pb(II), Cd(II), Hg(II), and As(III) ions from the water, it exhibited\nhigh adsorption capacity (11.92, 11.58, 11.85, and 11.57 mg g^–1, respectively) for all the trace metals. Kinetics\nand modeling studies revealed that the adsorption kinetics was better\nexplained by a pseudo-second-order kinetic model, and at equilibrium,\nadsorption followed a Langmuir isotherm. It was interesting to note\nthat the synthesized hydrogel possessed excellent reusability and\ndesorption and regeneration properties. Ion exchange and chelation\nproperties of the hydrogel were probably responsible for the adsorption\nmechanism. The regenerated hydrogel showed >50% removal efficiencies\neven after five cycles, showing economic feasibility of its application\nat a large scale.