Hydrophobic agglomeration behaviors of clay minerals as affected by siloxane structure

Abstract

Due to the very hydrophobic characteristic, silica tetrahedron (siloxane) structure on clay minerals surfaces was believed to affect many surface property of clay minerals, such as surface wettability, dispersion and agglomeration property. In this work, kaolinite and talc, with different number of siloxane surfaces, were chosen for studying how the siloxane structure affected hydrophobic agglomeration behaviors in aqueous solution. In-situ turbidity measurement of flocs suspension in the settlement progress had been applied to characterize the agglomeration behaviors of clay minerals. Through molecular dynamics simulation (MDs) results, it was found that the hydroxyl surface of kaolinite was very hydrophilic, while the siloxane surface of kaolinite (on the Si-tetrahedral side) and talc (both basal surfaces) showed a strong hydrophobicity due to the highly symmetrical siloxane structure. As a result, the talc and kaolinite showed vast differences on hydrophobic agglomeration behaviors. Because of the much more exposed siloxane structures on talc surface, the hydrophobic agglomeration degrees are far stronger than that of kaolinite due to the both hydrophobic basal surfaces. Besides, the sizes of talc flocs are also far larger than that of kaolinite due to the formation of layer by layer floc structure. Therefore, the siloxane structure on clay minerals surface has a significant influence on the agglomeration behaviors, including the agglomeration degree and the size of resulted flocs. It is the first time that the hydrophobic agglomeration behaviors were correlated to the siloxane structure on clay mineral surfaces, which has profound guiding significance on the study of dispersion stability of colloidal clay minerals.