Study On Adsorption Mechanism Of Pesticide Wastewater Treated By Montmorillonite

Pesticide is an important and indispensable special means of agricultural production in modern agriculture.Herbicide,as a class of pesticides,is not widely used in the control of weeds in farmland and killing weeds and irrigation in non-agricultural farmland.Unregulated use and handling results in herbicide residues in the environment,with most of the compounds stored in aquatic environments.The treatment of herbicide wastewater pollution has always been a hot topic.Atrazine(ATZ)and dimethyl tetrachloride(MCP)are two herbicides widely used today.Montmorillonite(Mt)has the characteristics of large specific surface area and excellent physical and chemical properties.It can form stuck chamber structure under certain conditions,and has a wide range of applications in the field of environmental mineral materials.However,it still has some shortcomings such as poor porosity,easy accumulation of laminates and difficult exposure of adsorption sites,which limit its adsorption capacity.In this paper,two commonly used pesticides,ATZ and MCP,were used as adsorbents,Mt,which formed more cell structure by stripping treatment,was loaded with hydrotalcite(LDHs)to prepare LDH@Mt composite material,and the prepared LDH@Mt composite material was modified by plasma technology to explore the adsorption properties of ATZ and MCP.The adsorption mechanism was investigated by the energy distribution theory of site.The main research results are as follows:(1)In view of the problems of poor dispersion of Mt particles,easy agglomeration and easy accumulation of laminates,Mt samples were stripped at high speed at different times.After 30min of stripping,Mt samples were dispersed,and the end-plane of laminates supported each other and combined to form a stuck cell structure,with higher specific surface area and significantly increased pore structure.The adsorption of ATZ and MCP in wastewater by stripping samples(Mt S)was studied.The adsorption kinetics fit better with the quasi-second-order kinetics and internal diffusion model.Since the Langmuir isotherm is used to describe locally homogeneous surfaces,while Mt is a complex heterogeneous adsorbent,the Generalized Langmuir isotherm is in better agreement with the Generalized Langmuir isotherm used for heterogeneous adsorbent.Theoretical analysis of site energy distribution showed that the average potential energy of the sample after stripping increased,and the high energy sites were occupied by ATZ and MCP molecules at low concentration in the adsorption process.With the progress of adsorption reaction,the adsorption amount increased,and then the low energy sites were occupied.After stripping,the lamellar end-plane of the sample supported each other to form a stuck cell structure,exposing more adsorption sites to be activated for the adsorption of ATZ and MCP.In addition,Mt S-30 showed strong adsorption adaptability to ATZ and MCP at different pH values,and the adsorption capacity remained good after 5 cycles.(2)To solve the problem of Mt lamellar collapse after stripping,MT-loaded LDHs composite material(LDH@Mt)was prepared by in-situ growth method.The two supported each other and combined to form a more stable frame structure with good specific surface area and pore structure.The adsorption kinetics data conform to the quasi-second-order kinetics and internal diffusion model.Compared with the Langmuir model,the adsorption isotherm can better fit the Generalized Langmuir model.The site energy distribution theory proved that the site energy E~*and the average site energy of LDH@Mt were higher than that of single LDHs and Mt,indicating that more adsorption sites were exposed after the combination of the two supported each other,overcoming the problem of easy collapse of the lamellar structure formed by Mt after stripping,and improving the adsorption capacity of ATZ and MCP.In addition,the adsorption of ATZ and MCP by LDH@Mt at different p H values has little effect.The cyclic experiments show that LDH@Mt has good reusability.The adsorption capacities of LDH@Mt,LDH@Bt,LDH@IMt and LDH@Chl for ATZ and MCP were compared.LDH@Mt has a better three-dimensional structure than the other three composites,and the adsorption experiment results show that LDH@Mt has the largest adsorption capacity of ATZ and MCP.(3)plasma technology is used to modify LDH@Mt.The results show that there is no obvious change in the morphology of samples after plasma treatment.The defects change the surface functional groups of Mt laminars and increase the number of oxygen-containing functional groups.Further stabilize the card room structure.The experimental results of adsorption kinetics fit the quasi-second-order kinetics and internal diffusion model.The Generalized Langmuir model is better obtained by adsorption isotherm.The energy distribution theory of site confirms that the energy of E~*and the average site of plasma/LDH@Mt samples increase,which indicates that after plasma treatment,the oxygen-containing functional groups on the surface of Mt laminae are increased,thus generating more adsorption sites and improving the adsorption capacity of ATZ and MCP.In addition,pH changes have no significant effect on the adsorption capacity of plasma/LDH@Mt ATZ and MCP,and the adsorption capacity is still good after 5 cycles.In conclusion,plasma modification LDH@Mt provides an effective strategy for the treatment of pesticide pollutants in wastewater.