| In the southwest of China,where there are abundant hydropower resources,electrolytic aluminum enterprises have entered various states in Yunnan one after another.Since 2016,electrolytic aluminum waste residue has been included in the National Hazardous waste list by the Ministry of Environmental Protection,many electrolytic aluminum enterprises are faced with the problems of site selection and environmental impact assessment of hazardous waste slag storage,and the landfill sites of these electrolytic aluminum enterprises cause great pollution risk to the groundwater in the area where the project is located.In this paper,experimental and computational methods are used to study the migration of fluoride in the variable saturation zone.The following conclusions were drawn from the study:(1)The results of static adsorption using the initial step concentration showed that the adsorption capacity of red clay on fluoride in the early stage of adsorption was stronger,and the amount of adsorption gradually decreased in the same time in the middle and late stage.after 50 hours,the adsorption rate decreased and the adsorption was not obvious.(2)Through the determination and calculation of fluorine content in solution and red clay during static adsorption test,the linear isothermal equation,Langmuir equation and Freundlich equation are fitted.From the fitting results,the static adsorption of fluoride by red clay does not accord with Langmuir equation and Freundlich equation,but more with isothermal linear adsorption equation,The fitting results are R2 greater than 0.98.(3)The results showed that the adsorption capacity of each layer of soil in the column was relatively large,which was consistent with the isothermal adsorption results,which indicated that the red clay had a good removal effect on fluoride pollutants,indicating that the influence of soil adsorption capacity must be taken into account in evaluating the transport of fluoride pollutants in red clay.(4)In the process of vertical migration of the saturated red clay column,the concentration of fluoride pollutants before and after passing through the saturated capillary zone will vary according to the conditions of the capillary zone.Fluoride penetrates first without capillary water,second with suspended capillary water,and finally with supported capillary water;fluoride adsorbs most with supported capillary water,second with suspended capillary water,and finally with no capillary water;fluoride absorbs least before and after passing through saturated capillary water When changes occur,a portion of the residue will remain in the saturated capillary zone,and the total residue will be shown as,in the presence of supporting saturated capillary zone > in the presence of suspended saturated capillary zone > without capillary water conditions.This is due to the difference of capillary force,which leads to the different time of fluoride migration in red clay,which leads to the difference of adsorption amount,and the largest amount of soil adsorption in the supporting capillary zone with the longest migration time;(5)By using the method of changing soil initial moisture content and soil residual moisture content in Hydrus-1D software to distinguish the supporting capillary water belt,hanging capillary water belt and capillary water belt,it can better represent the actual process.(6)The block coefficient of fluoride in saturated red clay obtained from the measured adsorption isotherm is 2.41,which indicates that the flow rate of groundwater is 2.41 times that of fluoride migration in groundwater.This indicates that the adsorption of fluoride in saturated red clay is obvious,indicating that the effect of solid phase adsorption must be considered in the process of evaluating fluoride pollution in the future. |
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