Experimental Study On Adsorption Characteristics Of Fluoride On Unsaturated Red Clay And Limestone

The surface of the tailings pond and hazardous waste landfill site in karst area are often covered by red clay layers with different thicknesses,while the underlying areas are carbonate karst areas,and red clay and some carbonate layers are often unsaturated zones.It is of great significance to study the adsorption characteristics of fluorine on unsaturated red clay and carbonate rocks,which provides theoretical basis for preve-ntion and remediation of soil and groundwater pollution in karst areas.Based on the on-site investigation of red clay in southwest Yunnan and the analysis of hydrogeological conditions in the study area,the red clay and limestone in this area are taken as test samples,and on this basis,indoor physical tests are carried out,and the following conclusions are obtained:(1)Static adsorption tests show that,regardless of the initial concentration,with the adsorption process going on,the PH value gradually increases with time,the adsorption amount increases,and the adsorption behavior of red clay for fluoride accords with Freundlich temperature adsorption equation.(2)The adsorption coefficient of fluoride in red clay is different under different concentrations.The higher the initial concentration,the greater the soil adsorption coefficient,that is,the better the soil adsorption trend.(3)Dynamic tests show that the adsorption coefficient of red clay increases with the increase of initial concentration of sodium fluoride solution under unsaturated conditions.Compared with the conclusion of static adsorption test,the adsorption coefficient of red clay obtained from dynamic adsorption test is lower than that of red clay.(4)The dynamic adsorption test of limestone shows that the adsorption ratio of limestone with different particle sizes increases with the increase of initial concentration.At the same concentration,the smaller the particle size,the larger the adsorption ratio.Therefore,the adsorption coefficient of limestone with small particle size is larger than that with large particle size.(5)the correlation coefficient of Thomas model is higher than that ofAdams-Bohart model.both models can explain the dynamic adsorption mechanism of limestone for fluorine,but limestone has better adsorption effect for low concentration fluorine.