The Study On Adsorption And Desorption Of Cr(?)in Soil

Soil pollution is concealed and latent and is not easy to control after pollution,but also affect the biological cycle and water cycle process,so the attention and protection on the soil environment is particularly important.This study was established to estimate the adsorption and desorption behavior of hexavalent chromium in soil.Adsorption and desorption studies are useful for obtaining the chemical species mobility and their necessary information in the distribution of soil,water and air.This information can be used in predicting and estimating the availability of chemical degradation,transformation and uptake of organisms,soil transmittance,volatilization in soils and soil erosion rates,as well as for comparison and modeling.The adsorption and desorption characteristics of Cr(?)on the soil were studied by the batch adsorption experiment and the mixed displacement experiment.The data of the batch adsorption experiment can be fitted with the Henry model and the Freundlich model,which show that the adsorption characteristics of Cr(?)can be described by these two isothermal adsorption models.The adsorption and desorption of Cr(?)on the soil were studied by changing the initial concentration and the p H value of the influent.The experimental results showed that the adsorption capacity of Cr(?)could decrease with the initial concentration and the p H value decreases.Two groups of experimental were interrupted 61 hours before the de-sorption experiment,and the solute concentration decreased significantly after resuming water supply,indicating that the adsorption of Cr(?)on the soil was affected by the non-equilibrium action.The results of desorption experiments show that the Cr(?)leaching process in the soil under the strong acidic solution is relatively slow,the other experimental groups show that Cr(?)is easy to leach,the adsorption mechanism of Cr(?)is mainly weakly adsorbed.During the experiment,the p H value of the effluent was in the range of 7-8,which tends to the original p H value of the soil,indicating that the soil has a good cushioning effect on the acid solution.Numerical simulation is a commonly used method to study the solute transport in soil.In this paper,CXTFTI software developed by United States Department of Agriculture was used to fit the breakthrough curve of solute.Firstly,the equilibrium model and the physical non-equilibrium model(TRM)were used to fit the trace ion breakthrough curve to determine the dispersion coefficient and flow rate.Then the chemical non-equilibrium model(TSM)was used to fit the breakthrough curve of Cr(?)to obtained the solute transport parameters.The fitting results are well,the correlation coefficient is more than 0.98.The retardation factor(R)value is about 10,indicating that the adsorption capacity of Cr(?)is weak.The ? value is about 0.6 indicates that about 60% of the adsorption sites is instantaneous,and 40% is limited by the rate,and its regularity satisfies with the first order kinetic equation.