Studies On The Equilibrium Adsorption Of Bs-12 And Tween20 Modified Bentonites To Cd²⁺, CrO₄^2- And Phenol

With industrial development, urban pollution and increasing agricultural intensification of the type and quantity of chemicals, pollutions of groundwater and soil are growing, heavy metal contamination of soil and groundwater which has become one of the limiting factors to restricting China’s environmental sustainability, and receive more and more attention. Therefore, the search for effective ways to control and mitigate heavy metal pollution has become a hot research.Bentonite was modified with different proportions combining amphoteric modifier dodecyl dimethyl betaine（BS-12） and nonionic modifier Tween20 according to cation exchange capacity. The structure of amphoteric and amphoteric-anionic complex modified bentonites were characterized by X-ray diffraction（XRD）, infrared spectroscopy analysis（FTIR）, and determination of specific surface area（BET）, the adsorption regularity of Cd²⁺, CrO₄^2- and phenol on modified bentonites and its affecting factors, i.e. modified ratio, temperature, pH and ionic strength, were studied, and the adsorption mechanisms were discussed also. This master’s thesis aimed to provide a theoretical basis for application of amphoteric-anionic complex modified organic clay in environmental pollution remediation.The results achieved in this paper are as follows:（1） The CEC content of BS modified bentonite increases with the ratio of BS modification, not with Tween20 modification ratio increases, while the specific surface area reducing with the ratio of amphoteric modifier BS-12 and the compounding modifier Tween20 modification increase. Layer spacing d increasing with BS modified proportional increases, the interlayer spacing d of BS modified clay is less than the relevant modification of complex soil, the layers spacing of 50 BS complex modified soil samples increases with modifiers proportional, and 100 BS complex modified soil with little change in the layers spacing between the of modification. XRD and FTIR analysis spectra of modified soil showed that amphoteric surface modifier BS-12 into the main room of bentonite layer by intercalation, and Tween20 major modifications in the bentonite surface.（2） The heavy metal cations Cd²⁺ adsorption equilibrium experiments showed: Langmuir equation for describing soil adsorption of Cd²⁺. BS-12 single-modified bentonite sample increased adsorption capacity of Cd²⁺, BS modified soil samples’ adsorption capacity for Cd²⁺ enhanced with the BS-12 modification proportion increasing. When the complex modification ratio is less than 0.5, Tween20 complex modifications can enhance amphoteric modified soils’ adsorption capacity of Cd²⁺. Presence of phenol adsorption on soil Cd²⁺ inhibited. With increasing temperature and pH increase, complex modifications to increase the amount of soil adsorption of Cd²⁺, ionic strength increases diminished soil adsorption of Cd²⁺. The thermodynamic parameters results show that the, modify soil Cd²⁺ adsorption process is spontaneous entropy increase control; each soil sample to Cd²⁺ adsorption are endothermic process. amphoteric modifier BS-12 and nonionic modifier Tween20 gravity through a combination of electrical and hydrophobic bonds of modified bentonite, bentonite increases the negative charge of the surface layer and the thickness of the hydrophobic layer.（3）Equilibrium adsorption of heavy metal anions CrO₄^2- show that: BS-12 modified bentonite soil increases adsorption capacity to CrO₄^2-, and with an increase in the BS-12 proportion of modified soil the adsorption capacity to CrO₄^2- modest changes, Tween20 + BS-12 complex modifications to improve the soil can be a good effect on CrO₄^2- of bentonite. Freundlich equation CrO₄^2- adsorption characteristics suitable to describe the modified soil. Temperature and ionic strength increase, soil samples increased CrO₄^2- adsorption; pH increased, decreased amount of adsorption. Thermodynamic study showed that the adsorption reaction of CrO₄^2- modified soil is non-spontaneous process of entropy increase control. Mechanism studies suggest that the amphoteric surfactant modified soil increased positive surface charge, the organic surfactant is increased relative CrO₄^2- complexation, nonionic surfactant increases the layer spacing of the three mechanisms modified soil increases modified CrO₄^2- of soil adsorption.（4） Phenol adsorption equilibrium experiments show: BS-modified phenol adsorption capacity of bentonite soil samples increased compared with CK, Tween20 + BS-12 complex modifications can improve soil adsorption of phenol. Henry equation suitable to describe the modified phenol adsorption characteristics in the soil, thermodynamic studies have shown that the modified soil adsorption of phenol was spontaneously controlled by entropy. Temperature, pH increases, ionic strength increase will reduce soil adsorption of phenol, Cd²⁺ coexistence of adsorption of phenol in the modified soil has antagonism. The thermodynamic parameters showed that the adsorption of phenol on each soil sample was assigned the role of physics, is a spontaneous exothermic process. Mechanism of view, adding a certain percentage of non-ionic surfactant-modified bentonite at the same time, increase the adsorption effect modification of the content of soil samples of the organic phase and hydrophobic interactions and complex modifications to improve the soil of phenol.