Cost-effective approach for fabrication of high-quality expanded vermiculite for Alizarin red S removal from aqueous media

Abstract Vermiculite is widely used for various purposes, such as a hydroponic substrate, soil conditioning, oil cleaning, and trace metal pollution. In this work, natural vermiculite was facilely expanded using H₂O₂ with the assistance of microwave. Expanded vermiculite was characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), nitrogen adsorption isotherm (BET), and energy dissipation. X-rays (EDX). The resultant expanded vermiculite has flake-like structure with the surface area of 73.9 m²/g. Alizarin red S adsorption on expanded vermiculite was studied under variable conditions including pH, initial concentration, adsorbent content, and evolution time. The maximal adsorption capacity of Alizarin red S by expanded vermiculite reached 182.5 mg/g. Among the three adsorption isotherm models, the adsorption of Alizarin red S onto expanded vermiculite obeys both the Freundlich and Temkin models. For adsorption kinetics, the second-order adsorption kinetic model is more suitable than the first-order adsorption kinetic model with R² = 0.8964.