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The adsorption process is one of the most cost-effective methods for eliminating various types of pollutants from water. Clay minerals can be converted into biosorbents for environmental remediation. This literature review summarizes the different types of natural clays, their crystal structures, classifications, physical and chemical properties, and industrial applications. Also the main results of recent studies on the process and mechanism of adsorption on natural clay materials to eliminate heavy metals and highly emerging toxic dyes. The Langmuir and Freundlich models are the most commonly used isotherms in most previous studies. In addition, the adsorption kinetics of the majority of dyes and heavy metals using natural clays are based on the pseudo-second-order model. High adsorption capacities of 909.09 mg g−1 for synthetic dyes and 179 mg g−1 for heavy metals were observed. This review article suggests that clays can be modified by various methods to improve their adsorption efficiencies by increasing their specific surface areas. The clays' low cost and ability to regenerate show that these materials are environmentally friendly and beneficial for industrial ecology.

This paper reports the feasibility of using dried plants to remove As(V) from aqueous solution under different experimental conditions. For this purpose, micro-particles of both Calami rhizoma and Withania frutescens plants, have been separately used without pre-treatment as natural adsorbents. Effect of various process parameters, namely adsorbent dose, contact time, initial As(V) concentration, temperature, and pH has been studied. The experimental data were analyzed using Freundlich, Langmuir, and Temkin isotherm models to determine the mechanistic parameters related to the adsorption process. It was found that the Langmuir and Freundlich models fitted well. Thermodynamic parameters, viz, free energy change (ΔG0), enthalpy change (ΔH0), and entropy change (ΔS0), were also determined. The negative values of free energy change indicated the spontaneous nature of the adsorption and the positive values of enthalpy change suggested the endothermic nature of the adsorption process. The presence of some competing ions like Cl−, NO3-, Mg2+, Cd2+, Cu2+, and Zn2+ did not affect the arsenate uptake or removal, whereas HPO42- strongly interfered negatively.