The Transforming And Conversion Characteristics Of Pollutants In The Aquitard Filled With Boundwater

Clay layer in the groundwater system has been seen as impermeable layer for many years. With the discovery of flowing and migrating, it is realized in recent years that it can sometimes be seen as aquitard and is not absolutely impermeable layer. The laws of the migration of chemical elements in the clay layer have been the weak point of the study all the time. Clay usually be used as a block wall or impervious layer to prevent polluting in the groundwater pollution prevent and remediation techniques. It may be permeable and pollutants may also penetrate the clay layer in a certain osmotic pressure. Therefore, the migration strength, action, and kinetics in the clay layer have become important research questions in the study of groundwater pollution control.A large number of domestic and foreign literatures showed that the migration rule of pollutants in the clay is different from that of in the sand, that mainly because there is a lot of bound water in the clay. Therefore, this paper first studied the formation laws of bound water that be existed in the clay, and selected five ions which include NH4+,NO3-,SO42-, Cl-,Cr6+ as text objects, the contents are divided as following sections:First studied the formation features of bound water in the clay when be immersed with pollutants through flask experiments.Second, this paper studied how the concentration of pollutants,consolidation pressure,penetration pressure and solutes impact the permeability coefficient through the infiltration experiments.Finally this paper revealed the retardation effects of several different pollutants in saturated clay when the vertical permeability happened through the penetration test. Through the studies above, a more comprehensive understanding is obtained about the migration mechanism and the concentration variation laws of the pollutants when vertical migration is happened in the saturated clay layer, and provide a theoretical basis for the protection and restoration of groundwater.Flask text showed that in the formation process of bound water in the surface of soil particles, the content of the adsorption bound water was gradually increasing with time was going and close to a fixed value after a period of time and remain the same, that is the adsorption limit; when the solutes were different, the value of content of bound water in the surface of soil particles was as follows:distilled water> water> NO3-> NH4+.The results indicated that some free water was released out because of the presence of the pollutants, leading to decrease of bound water content in the soil particles.The consolidation pressure text showed that the relationship between penetration rate and hydraulic gradient was not linear relationship though.The penetration rate was rapidly increasing at the beginning of the test, after a certain hydraulic gradient, the speed became more faster. When the hydraulic gradient exceeded a certain limited value, the penetration rate became gradually flat and stayed stable finally. It was indicated that the weak boundwater has been transformed form part to all. Boundwater that combined strongly with soil particles no longer transformed when hydraulic gradient exceeded limited value, and seepage wound not be increased any more, leading to seepage velocity approached to a fixed value; The curves of consolidation pressure-penetration rate of the three soil samples were almost consistent, and penetration rate was decreasing with the increase of consolidation pressure. The relationship between permeability and consolidation pressure was polynomial. However, the constant was different according to the clay content; with the increase of the osmotic pressure, the permeability coefficient became larger and larger and in the same magnitude, that is, magnitude of permeability coefficient does not change;the penetration rate of NH4+ and NO3- would increase as the concentration's increase;the penetration test showed that under the same experimental conditions, the water permeability coefficient was slightly greater than that of pollutants, indicating that the retardation of soil samples on the water was smaller than the solutes, that is due to the different action between soil and water put different impact on water and components which existed in the water; The three selected soil samples put an obvious impact on the NH4+, and SO42 was migrating strongly in the three soil samples on the contrary of NH4+,indicating that the migration of different solutes was different when solute was transforming in the clay; penetration test showed that the clay can retarded some the leachate pollution, the effect of no.3 clay on the NH4+ was much better than no.1 and no.2 soil samples, indicating that retardation intensity has positively relationship with soil clay content and dry density, a negatively correlation with porosity.