*4.2. Thermal Treatment*

Thermal modification of sepiolite is the process of calcining natural sepiolite at different temperatures. At the different temperatures, the associated water in hygroscopic, zeolitic, and coordinated and structural octahedral hydroxyls groups will be removed to reduce the water film resistance, increasing the porosity and in doing so, improving the adsorption performance of sepiolite [52–54].

In calcination temperatures around 500 ◦C, the adsorbed water disappears from the sepiolite structure and apertures expand, with magnesium loss from the mineral structure. This increases the metal ion space, which is beneficial for the removal of Cr3+, at the same time. The removal ability of heavy metals from wastewater was improved because of the change of internal cavity structure of the thermally treated sepiolite [55].
