Application of magnetic adsorbents for removal of heavy metals from wastewater: a review study

Currently, heavy metals exist in most of the industrial wastewaters and water supplies are among the most severe environmental contaminants. As such, removal of these metals from water and wastewater is an essential process for protecting public health and the environment. Thanks to its biocompatibility, flexibility, low cost, and satisfactory results, the adsorption method has been widely used for such a purpose, making it necessary to develop inexpensive adsorbents in removing these metal contaminants. In recent years, the use of magnetic adsorbents has gained attention because of their magnetic property, which facilitates the separation and removal of the adsorbent using an external magnetic field. Numerous research works have been conducted in this field, showing that magnetic composites, especially the nano-sized ones, exhibit superiority over other adsorbents. Given their high adsorption yields, these have been used as efficient and cost-effective adsorbents for removing heavy metal contaminants. In this research, application of magnetic adsorbents for removing heavy metal contaminants, risks and sources of the heavy metal contaminations, methods for synthesis of magnetic adsorbents, and magnetic, physical and chemical properties of the magnetic adsorbents were investigated based on existing stack of relevant studies. Moreover, equilibrium, kinetic, and thermodynamic behaviors of the adsorption process of heavy metal ions were studied using the Langmuir and Freundlich isothermal models, pseudo first-order and pseudo-second-order kinetic models, and a suit of thermodynamic parameters including changes in enthalpy (ΔH°), entropy (ΔS°), and free Gibbs energy (ΔG°).