Method And Application Of Using Short Column To Determine The Adsorption Isotherm Of A Clayey Soil

With the rapid development of China's economy and industry,soil and groundwater have been contaminated,producing a large number of contaminated sites.As one of underground pollution prevention and control measures,service performance of barrier has become the focus of attention.To clayey soil barrier,adsorption property is the basis of the service performance evaluation.The adsorption parameters determined by Batch experiment and column experiment is difficult to fully reflect the nonlinear adsorption behavior of clayey soils under complex conditions.Therefore,the research of clayey soil barrier adsorption characteristics and its influence on the breakthrough time has important theoretical significance and engineering application value.In this paper,based on the former researches,the mechanism and analysis methods of pollutant migration were summarized.Kaolin soil as the research object,heavy metals Pb2+ ions as the target of pollutant,put forward a experimental method that using short column to determine the sorption isotherm of clayey soil,through error analysis and conservation of mass analysis to assess the reliability of short column test.Studied the effect of pollution sources concentration,waterhead and solid/soil on sorption isotherm and distribution coefficient Kd.According to different pollution sources concentration,put forward a method of obtaining adsorption parameters in a certain range and use Geo-studio software to analysis the effect of adsorption curve and adsorption parameters?pollution sources concentration?waterhead and breakthrough standard on breakthrough time of compacted clayey soil.On the basis of the practical experience of site investigation in home and abroad and the relevant technical literatures,drilling and sampling techniques have been studied.Field and laboratory studies are carried out to analysis leachate migration in the loess liner.Put forward suggestions for the improvement of evaluation method about barrier service performance.Some main conclusions are as follows:(1)Short column experimental method is that providing waterhead and different concentrations of pollutants solution by markov bottle on a group of 2cm soil column,determine the breakthrough curve of the target of pollutant,cut soil sample into slices after breakthrough curve is stable,determine the distribution coefficient Kd and obtain the sorption isotherm directly.The maximum relative standard deviation of conservation of mass analysis with digestion test is 8.96%,show that short column experimental method is reliable.(2)The sorption isotherm and distribution coefficient Kd determined by short column experiment present nonlinear,Kd values decrease with the increase of concentration,Langmuir adsorption model can be used on the fitting.The adsorption quantity and Kd determined by short column experiment is less than the adsorption quantity and Kd determined by Batch experiment.The effect of waterhead on the sorption isotherm and sorption parameters is not obvious.(3)Using the isothermal adsorption curve determined by short soil column experiment to predict the breakthrough curves,its results agree well with the measured breakthrough curves while concentration is more than 400 mg/1,but while concentration is less than 200 mg/1,the results is obvious different between them,and the more lower of the concentration,the more obvious of the differences,therefore,assuming that adsorption is linear,adsorption parameters can be obtained by the inverse analysis of breakthrough curves.(4)The breakthrough time of 2m thick compacted clay liner based on adsorption parameters of short column experiment is less than Batch test,show that Batch test has been overestimating the extent of soil adsorption,the adsorption parameters of short column experiment should be used to analysis the breakthrough time;While the pollution concentration is 50 mg/1?400 mg/1?1000 mg/1,the breakthrough time of compacted clay liner respectively 600 years?150 years and 92 years,show that with the increase of concentration the breakthrough time reduces significantly.In engineering applications,high permeability and strong adsorption ability material were added in the surface of compacted clay liner and reduce the pollution sources concentration can extend the breakthrough time.With the increase of waterhead,breakthrough time of compacted clay liners decrese.While the breakthrough standards are different,breakthrough time is different also.(5)Drilling sampling quality depends on the soil sample test items and the types of pollutants;This paper combed the drilling sampling methods used for different types of contaminated sites(see table 6.3).(6)the adsorption retardation effect of the compacted and natural loess to COD is significant.The effect of dispersity and retardation factor can not be neglected under this landfill with a high leachate head.The migration depth of Cl ion and COD is 15 m and 5m after 50 years.