Experimental Study On The Adsorption Characteristics Of Heavy Metals In The Anti-fouling Barrier Of Stone Chip-bentonite Mixture

With the rapid development of industrialization and urbanization in China,the economic level continues to grow,but it also encounters the problem of environmental pollution,which seriously restricts the sustainable development of urbanization.The closure or relocation of chemical plants,metal smelters and printing and dyeing factories has left behind large areas of industrial pollution,resulting in soil and groundwater pollution and posing a serious threat to public health and the surrounding environment.Pollution barriers are widely used in landfill construction and pollution site treatment to prevent the diffusion of pollutants.Therefore,it is very important to study the effect of pollution barrier on the adsorption performance of pollutants.In this paper,the influence of pollutants on the adsorption performance of the mixture of rock-bentonite and rock-bentonite was studied through adsorption test and Zeta potential test,and combined with Comsol Multiphysics numerical simulation.The main research results are as follows:?1?Isothermal adsorption experiments were carried out on bentonite mixture soil at temperatures of 25?,40?and 55?by using Ca Cl₂,Cu Cl₂,Mg Cl₂,Zn Cl₂ and Pb Cl₂ solutions with concentrations of 3 mmol/L,5 mmol/L,10 mmol/L,30 mmol/L,50 mmol/L,80 mmol/L and 100 mmol/L,respectively.The results showed that the adsorption and removal rates of pollutants decreased with the increase of the initial concentration of pollutants at 25?,40?and 55?.When the initial concentration of pollutants was constant,the adsorption removal rate of Ca,Cu,Zn and Pb in the mixed soil increased with the increase of temperature,while the adsorption removal rate of Mg gradually decreased.When the concentration is the same and the temperature is 25?,the influence degree of the mixed soil adsorption pollutant is shown as:Cu>Pb>Zn>Mg>Ca.?2?Ca Cl₂,Cu Cl₂ and Zn Cl₂ solutions with concentrations of 10mmol/L,and 30mmol/L were used to test the mixed soil at 15min,30min,1h,2h,6h and 24h,respectively,to study the influence of adsorption time and concentration on the adsorption performance of the mixed soil.The results showed that the adsorption and removal rates of Ca,Cu and Zn with concentrations of 10 mmol/L and 30 mmol/L increased with the increase of time,and finally reached equilibrium.When the adsorption time is fixed,the adsorption removal rate decreases with the increase of the concentration.It was found that the dynamic adsorption of the mixed soil to the pollutants was most consistent with the quasi-secondary dynamic adsorption model,with R² up to 0.999.The adsorption constants obtained from the quasi-primary dynamic adsorption model indicated that the higher the initial concentrations of Ca,Cu and Zn of the pollutants,the lower the adsorption rate of the mixed soil.The adsorption patterns of Ca,Cu and Zn in the mixed soil are controlled by both intra-particle diffusion and membrane diffusion.?3?Through model fitting,it was found that Mg and Pb adsorption of mixed soil was more consistent with Henry model,Langmuir model had a high degree of fit with Ca adsorption of mixed soil,and Freundlich model had a good correlation with Cu and Zn adsorption.According to the calculation of the d-r model,the adsorption of pollutants adsorbed by mixed soil can be concluded that the adsorption of Cu,Zn and Pb is mainly ion exchange,while the adsorption of Mg is mainly physical adsorption process.The adsorption of Ca by mixed soil at 25?and 40?is mainly physical adsorption,while at 55?,it belongs to ion exchange.?4?The adsorption experiments under different temperature of thermodynamics analysis,found that the mixed soil adsorption of Ca,Cu,zinc,and Pb were positive,indicates that the adsorption reaction is an endothermic process,and irreversible,desorption are less,temperature rise for mixed soil of Ca,Cu,zinc,the adsorption of Pb,mixed soil Cu adsorption,zinc,Pb were negative,and decreases as the temperature increases,show that the adsorption reaction is spontaneous and spontaneous increases with temperature rise,the process of the Mg but show the opposite trend;When the concentration of Ca is low,it is negative,and when the concentration is high,it is positive and gradually decreases to negative value with the increase of temperature.It is further clarified that the increase of temperature is also beneficial to the adsorption of Ca by mixed soil.?5?Through Zeta potential,the influence of concentration and temperature on the adsorption performance of the mixed soil was revealed from the thickness of the double electric layer.The absolute value of Zeta potential decreases with the increase of the initial concentration of the pollutant.The higher the concentration is,the more cations there are on the surface of the soil particles,the smaller the thickness of the double electric layer will be,and the negative electric potential on the surface of the soil particles will be weakened.Concentration is constant,mixed soil and Ca,Cu,zinc,Pb Zeta potential values of suspension system,increase with the rising of temperature,is the increase of reaction temperature,increase the activity of the soil particle surface adsorption potential,and make the mixed soil on the surface of the electric double layer thickness decreases,and lead to negative potential on the surface of the soil particles is abate,on the Zeta potential is expressed as the potential absolute value will be lower,more was due to the adsorption of metal cations.?6?Numerical simulation results show that pollutant concentration,anti-pollution barrier thickness and temperature have great influence on pollutant migration and breakdown time.The higher the initial concentration and temperature,the thinner the antifouling barrier thickness,the higher the concentration at the same depth in the antifouling barrier,and the shorter the time to break through the antifouling barrier.