**3. Natural Sepiolite**

The mineral sepiolite was discovered by German scholar Woemer in 1789, and the original name of sepiolite *Meerschaum* means "foam of the sea" in German. In 1847, it was officially renamed sepiolite. It is a clay mineral with light color and low density, and has the chemical formula Mg8(OH2)4[Si6O15]2(OH)4·8H2O [39]. In 1947, sepiolite was first discovered in Jiangxi, China by Chinese geologists Zhang Renjun. By genetic classification, we can divide the sepiolite into two types: sedimentary and hydrothermal sepiolite. The world has proven reserves of around 80 million tons, the main production of raw sepiolite is from deposits in Spain, followed by China, the United States, and Turkey [40]. China has about 30% of the world's sepiolite reserves. Among Chinese sepiolite reserves, 70% of sepiolite comes from Hunan Province. The city of Xiangtan, in Hunan province, hosts more than 20 million tonnes of sepiolite reserves.

Sepiolite is a clay mineral with a hydrous magnesium silicate, it is a member of the orthorhombic crystal system. It presents a structure of needle-like particles and has talc-like layers that consist of two layers of tetrahedral silica and a central octahedral magnesium layer [41]. As a result of its particular crystal structure, sepiolite has grea<sup>t</sup> sorptive, rheological, and catalytic properties, and it is also widely used in a variety of industrial and commercial applications.

The structure of sepiolite is a fibrous needle form, with a hollow channel in the direction of the fiber, which gives special rheological properties. The flow properties of sepiolite means that it is used in drilling muds as a thickener and suspension agen<sup>t</sup> [42,43]. The acidity and alkalinity of sepiolite itself makes its catalytic activity more versatile and widespread. As a negative charge carrier, sepiolite can be utilized to remove pollutant cations [44]. It has a large specific surface area, which can reach 800–900 m2/g, and with its porous properties, provides its good access to adsorption sites. This performance can play a part in applications for bleaching, cleaning agent, and other sorption functions. We focus here on those applications relevant to metal adsorption in the context of local environmental contamination.
