Fourth, the application of organic bentonite in wastewater treatment, mechanism, law and influencing factors
Organic bentonite and its preparation method
Although bentonite has better adsorption properties, its performance is poor due to the strong hydrophilicity of the siloxane structure and the hydrolysis of interlayer cations, so that the unmodified bentonite (original soil) Application of Bentonite in Wastewater Treatment. As early as Jo rdan  first prepared organic bentonite; afterwards, some people at home and abroad with quaternary ammonium salt cationic surfactant modified bentonite, organic bentonite, greatly improve the performance of bentonite to remove organic matter in water, and achieved good results , And the organic bentonite treatment of organic matter in water performance, mechanism and influencing factors made a systematic and in-depth study.
Organic bentonite is the largest family of organoclays in the family. It is composed of organic molecules, ions, polymers with covalent bonds, ionic bonds, hydrogen bonds, dipoles and van der Waals forces and montmorillonite combination of montmorillonite organic compounds. Montmorillonite has salt ion exchange, acid, alcohol acylation, addition and other reactivity; different types of reactions to form different bond-type organic compounds. Montmorillonite and halosilanes, hydroxysilanes, alkyl halides, acid chlorides, alkylene oxides and other reactions to form a covalent bond-based organic complexes; montmorillonite and neutral molecules such as alcohols and other reactions, the formation of hydrogen bonds , Dipolar-based organic compounds. Organic bentonites used in wastewater treatment are made from bentonites modified with quaternary ammonium cationic surfactants.
There are two types of organobentonites currently used in water treatment: one is organic bentonite (including mono-cationic organobentonites and double-cationic organobentonites) that are surface-modified with a single quaternary ammonium cation; the other is made of two different Quaternary ammonium salt of carbon chain cationic surfactant modified double quaternary ammonium cationic organic bentonite. Many authors have studied the preparation of organobentonites [46-50].
Common methods for the preparation of organic bentonite have both explicit and dry method . The organic bentonite is prepared by the wet method, the bentonite is made into a slurry by using water as the dispersion medium, the organic bentonite is prepared by exchanging exchange reaction with the ammonium salt cations, and the organic bentonite is washed with water and dried with organic bentonite under mild conditions. Dry preparation of organic bentonite is roughly as follows: Bentonite and the amount of quaternary ammonium cationic surfactant (accounting for 15% to 55% by weight of bentonite) were thoroughly mixed, at a dry and higher than the quaternary ammonium salt cationic surfactant melting point The reaction at a temperature of 5 to 30 minutes, the reaction is completed, the ground, sieved to obtain organic bentonite. Organic bentonites used in water treatment are commonly prepared by wet processes. Common organic bentonites are produced by cation exchange using a single, long-chain quaternary ammonium salt cationic surfactant. As the quaternary ammonium salt cations enter the interlayer of bentonite, the interlayer spacing of organic bentonite increases to some extent compared with the original one, and the change value is related to the type and concentration of cationic surfactant used in the modification [51-53]. However, when the amount of cationic surfactant used in the modification exceeds the cation exchange capacity (CEC) of the original soil, the interlayer spacing of the organobentonites no longer increases with the increase of the surfactant concentration . Studies by Zhang et al.  showed that more than 99% of the quaternary ammonium cations were exchanged for adsorption when the amount of quaternary ammonium salt added was less than 70% of that of montmorillonite CEC. There were two adsorption modes: one was exchange reaction ; Second is quaternary ammonium salt adsorption at the non-exchange points. The organic bentonite modified by cationic surfactants can improve the hydrophobicity due to the increase of organic carbon content. Therefore, the ability to remove organic compounds in water is greatly enhanced.