*4.3. Magnetic Modification*

After treatment of heavy metal contaminated wastewater by sepiolite, it is difficult to achieve good separation of mineral/water mixtures, which leads to the difficulty of secondary reuse of sepiolite. The magnetization of sepiolite provides an effective way to facilitate separation and allows further treatment and/or reuse. In addition to using iron-based systems, the Fe3+ present in the modified sepiolite has oxidative properties, and the dissolution of Fe3+ adds acidity, which is beneficial to the removal of heavy metal ions [46,56–58]. In the process of adsorption, the phase structure of magnetic sepiolite did not show any obvious change. The adsorption mechanism is an ion exchange process between heavy metal ions and zeolite in the magnetised sepiolite crystal and coupled adsorption occurs between the heavy metal ions and the hydroxyl groups (Fe–OH and Si–OH) on the surface of magnetised sepiolite [59].
