Due to structural factors, the inner surface area of natural bentonite is relatively large, and the inner surface brings huge inner surface energy, which makes it have better adsorption capacity. Although bentonite has good adsorption performance, under unmodified conditions, when natural bentonite is in water, the interlayer ions will undergo hydrolysis reaction, reducing its adsorption capacity, which limits the application of bentonite in pollution treatment. Therefore, there are It is necessary to modify the bentonite.
1. Bentonite modification technology
(1) High temperature modification
The water film on the surface of natural bentonite can hinder the adsorption of pollutants. The water will evaporate and take away some impurities, so that the spatial structure of bentonite is expanded, and the internal pores are opened to create space for the adsorption of pollutants. However, when the calcination temperature is too high, the high temperature will damage the structure of bentonite, reduce its porosity, and reduce its adsorption performance.
(2) Ultrasonic modification
Short-time ultrasonication will loosen the structure of bentonite, increase the interlayer distance, and make it easier for harmful heavy metal ions to enter; long-term ultrasonication will make the Si- The change of O-Si bond increases the contact chance of metal ions and aluminum oxygen sites on the surface of bentonite, which enhances the specific adsorption of bentonite to metal ions.
(3) Metal modification and magnetic modification
Common metal modifiers are Fe and La, among which lanthanum modified bentonite (LMB) is an adsorbent widely used in phosphorus treatment. With the development of technology, metal ions no longer function simply as metal modifiers, but are embedded in bentonite as magnetic agents.
(4) Acid modification
Bentonite interlayer ions are originally Na+, Ca2+, Mg2+, Al3+, etc. Acid modification is to soak bentonite with acid to precipitate interlayer cations and dredge the channels between bentonites , making it easier for the adsorbate to diffuse inside. At the same time, H+ enters the interlayer of bentonite, replaces the original ions, weakens the interlayer force of bentonite, and increases the cation exchange capacity (CEC) and adsorption capacity.
(5) Organic modification
Because of the existence of interlayer ions, natural bentonite is hydrophilic, which is not conducive to the adsorption of organic pollutants. Organic modification is to use functional groups in organic matter or organic matter to replace the cations of the bentonite layer, which not only makes the modified bentonite become lipophilic and hydrophobic, but also increases the interlayer distance, strengthens the dirt holding capacity, and ion exchange. ability. According to the principle of similar compatibility, its surface adsorption capacity for organic pollutants is improved.
(6) Inorganic modification
Inorganic modification refers to the use of the interlayer positive ion exchange characteristics of bentonite, and according to the hydrolysis reaction of inorganic materials, the metal ions in it enter the interlayer of bentonite To replace the interchangeable positive ions, so as to prepare inorganic modified bentonite. After bentonite is inorganically modified, the interlayer spacing is significantly enlarged, the specific surface is increased, and the adsorption effect is significantly improved.
(7) Inorganic-organic composite modification
Inorganic-organic composite modification refers to the use of bentonite’s large layer gaps and the characteristics of positive ion exchange, first using inorganic high polymers to make the interlayer domain Unfold and then use an activator to change the surface properties of the bentonite.
2. Application of modified bentonite in environmental governance
(1) Heavy metal pollutants
Bentonite was modified with different concentrations of hydrochloric acid, nitric acid, phosphoric acid and sulfuric acid to study the effect of modified bentonite on Cd-Zn-Pb-Cu quaternary complex the adsorption effect. It was found that with the increase of acid concentration, the adsorption capacity of Pb ion and Cu ion decreased in different degrees. The adsorption of heavy metal pollutants was studied by polyanionic cellulose and xanthan gum modified bentonite, and it was found that its adsorption effect on Pb ionsThe fruit is better.
(2) Organic pollutants
Na-based bentonite was used to adsorb carcelaldehyde, and the adsorption results were obtained through different adsorbate concentrations and different solid-liquid ratios. The maximum unit adsorption capacity was 110mg/g. Using thermally modified bentonite (CVL) to study the adsorption performance of ciprofloxacin, it is found that the maximum unit adsorption capacity can reach 114.4mg/g at 25°C. Alkali modification, salt modification, and surfactant modification were carried out on bentonite respectively, and the removal rates of methylene blue for three different modified bentonites were found to be 73.25%, 81.62%, and 85.06%, respectively. Cationic starch-bentonite system was used for adsorption treatment, and it was found that cationic starch-bentonite system had an obvious treatment effect on simple pollutants.
(3) Inorganic pollutants
The study found that the adsorption and flocculation performance was the best when the mixed water samples were treated with fiber cotton first, and then treated with chitosan-modified bentonite. In agricultural production, nitrogen and phosphorus are important fertilizer raw materials and play an important role in food production. However, the loss of nitrogen and phosphorus in the soil in recent years has polluted water resources. The natural soil has a low retention rate of the two, but the retention rate of bentonite (LMB) modified by lanthanum can reach 93.9%. Therefore, lanthanum-modified bentonite can not only ensure the retention of nitrogen and phosphorus in the soil, but also control the pollution of agricultural production, and has a good application prospect.
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