Third, the application of modified bentonite in wastewater treatment
Although bentonite has better adsorption performance, but directly used in wastewater treatment, often can not achieve good treatment effect. Bentonite generally used for wastewater treatment is modified once or twice, or the bentonite is melted and burned into granular large-area material to further enhance its adsorption capacity and removal effect. Bentonite modified two common methods: First, activation of live; the second is to add inorganic or organic compounds or at the same time by adding inorganic and organic compounds made of composite bentonite to meet the needs of different uses, and improve its ability to deal with wastewater.
There are many methods to activate bentonite, such as acidification method, oxidation method, reduction method, melting method and hydrogenation method, among which the acidification method (treated with sulfuric acid or hydrochloric acid) is relatively simple and easy. The reason why bentonite can be activated is determined by the structural characteristics of the montmorillonite. When acid is used to activate bentonite, the acid undergoes a physicochemical reaction with aluminosilicate. First, K +, Na + , Ca2 +, Mg2 + and other cations into soluble salts of the acid to dissolve, thereby weakening the original interlayer force, the lamellar lattice delamination, the spacing of the crystal layer is enlarged, the channel is dredged, the active surface increases, and the adsorption of bentonite The ability is also significantly improved. At the same time, under the action of acid, H + in the acid will gradually replace Ca2 + and Mg2 + which are located on the lattice surface, and part of replaced H + will be replaced by Al3 + in the solution to produce aluminum with much stronger adsorption capacity than H + Ion or salt basic aluminum ions, so that the activity of bentonite adsorption more enhanced. Therefore, the acidification process can achieve a better activation purposes, prepared with strong adsorption capacity and decolorization ability of scientific research bentonite (activated clay). Ke Jiajun 32 expounded the relationship between the activity and the structural characteristics of activated bentonite. Wang Yanqin et al  had made on the preparation of cationic bentonite and nature of the study.
The authors have comparatively studied the performance of bentonite and acidic bentonite adsorbing heavy gold ions , and discussed the suitable conditions for removing bentonite from lead, cadmium, nickel, copper, chromium and zinc in acidic water by using acidic bentonite. Bentonite (original soil) to remove heavy metals in wastewater better, and easy to separate; acidic bentonite treatment of heavy metal ions in electroplating wastewater, the effect is very good. Zhang et al.  used the modified bentonite coagulant Scpb to treat the dyeing wastewater with acid bentonite, PAC and SCM C, and the COD removal rate reached over 60% , To turbidity more than 70%, decolorization rate higher than 60%.
Isaacso n et al  with humus, Na, H, Ca, Cu, Al and Fe modified montmorillonite gas and water phase to remove the phenolic compounds, montmorillonite modified with different metal salts adsorption phenol The order of the compounds is as follows: Fe-> Al-> Cu-> Ca-montmorillonite. The results of Chen et al.  showed that the natural montmorillonite was modified by sodium modification and inorganic polymer, which greatly enhanced the adsorption capacity of natural montmorillonite to organic pollutants. Modified montmorillonite When the amount is 0.1%, the red dyeing wastewater is treated, the COD removal rate is 85% and the decolorization rate is over 88%; the blue wastewater is treated, the COD removal rate is 94% and the decolorization rate is 98%. Ye Zhou  MMH-bentonite containing Al (OH) 3 and Mg (OH) 2 modified with AICl3 and MgCl2 under alkaline conditions; MM H- The COD removal rate has significantly improved. Srinivasan et al  modified bentonite with Al (O H) 3 to study the adsorption and desorption behaviors of octachlorodioxacin modified bentonite.
In addition to activation of bentonite, adding inorganic or organic modified, but also by adding inorganic, organic inorganic-organic composite bentonite, to further improve the adsorption properties of bentonite. Estes et al.  modified sodium montmorillonite with sodium citrate-sodium bicarbonate-sodium dithionate. The results showed that the ability of montmorillonite to adsorb low-molecular-weight halohydrocarbons in water was much higher than that of native montmorillonite. Low concentration of NaCl (> 0. 1m ol / L), montmorillonite adsorption capacity decreased. Sun Jiasou et al.  made bentonite, aluminum sulfate and cetyltrimethylammonium bromide (C TM AB) as bentonite composite adsorbents and used them to treat gas-washing wastewater. When the amount of composite adsorbent was 20g / L , P H3. 8, the CO D value of the gas scrubbing wastewater can be reduced from 13850mg / L to 2286mg / L, the removal rate is 83.5%; the phenol is reduced from 1570mg / L to 630mg / L, the removal rate is 59.9% 6%. Oil substances decreased from 1500mg / L to trace; SS from 2018mg / L to 30mg / L, the removal rate of 98.6%. 5%, 99. 7%, 100%, 100%, 99. 8%. By the bentonite composite adsorbent treated wastewater, and then activated carbon adsorption, COD, phenol, oil, . Srinivasan et al. [42-43] also studied the structure and properties of inorganic-organic composite bentonites in more detail and used them to remove priority organic pollutants such as benzo (a) pyrene and polychlorophenol in industrial wastewater. Shen Xueyou et al.  obtained ZnO-bentonite and CuO-bentonite by modifying bentonite with Zn (NO3) 2 and Cu (NO3) 2, respectively. The effects of ZnO-bentonite, CuO- bentonite and activated bentonite on the aniline photochemistry The results showed that the modified bentonite can effectively catalyze the photolysis of aniline. Thus, the modified bentonite has a good application prospect both in the adsorption of wastewater and in the catalytic photolysis of organic pollutants in water.