**2.1. Type 1:1**

This group of mineral is also called kaolin minerals, which is the basic mineral for kaolinite, dickite and hallocite [14]. They consist of single tetrahedral sheet of SiO4 and an octahedral sheet with Al3+ as octahedral cation. Both sheets combine to form a common a unit in such that the tip of silica tetrahedral points toward the octahedral sheet [3]. The layer of the tetrahedral sheet is invented over the octahedral sheet with oxygen atoms and hydroxyls ions present to balance the charges being shared by the silica in the tetrahedral sheet and the aluminum in

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**Figure 1.** Schematic diagrams of octahedron and tetrahedron sheets. Top: (A) an alumina octahedron in which the central aluminum ion is coordinated to six hydroxyls; (B) an alumina octahedral sheet formed by linking octahedra through edge-sharing. Bottom: (A) a silica tetrahedron in which the central silicon ion is coordinated to four oxygens; (B) a tetrahedral sheet formed by linking silica tetrahedra through corner-sharing [11].

**Figure 2.** Typical structure of Kaoline mineral [15].

the octahedral sheet. With the layer charges close to zero, the kaolin mineral has essentially no interlayers and does not show interlayer expansion in the water because the contiguous layers within particles are strongly held together by Al-OH and O-Si-OH bonding supplemented by dipole–dipole and van der Waal interaction. **Figure 2** represents the typical structure of kaoline mineral [15].
