Effects Of High Concentration CO₂ Invasion On Physicochemical Properties Of Clay Layer Of Groundwate

With the increasing shortage of groundwater and serious environmental pollution,it is critical for human to determine the causes of groundwater pollution.As is known to all,the process of urbanization,industrialization,agriculture and mining industry can have a negative effect on the groundwater quality.However,in addition to these,there still exist some reasons we have overlooked,and this paper mainly talks about the missing factors.Recently,CO₂geological storage is considered to be one of the most important and effective means for reducing the concentration of CO₂ in the atmosphere.But there is leakage risk of CO₂ due to different kinds of influences.High concentration of CO₂ leakage spreading to groundwater claypan can change the physicochemical characteristics of claypan.Lab simulation tests and software simulation were used to explore the effect of high concentration CO₂ invasion on groundwater claypan.The main research content and conclusion of this study are as follows:?1?For lab simulation tests,clay columns were used to simulate the claypan and CO₂was injected into these columns to simulate the process of invasion.During this six-month experiment,the change of clay temperature,moisture content and negative pressure were monitored in real time.At the end of this experiment,the clay sample was taken out from the clay column for property detection including pH,thermal parameter,soluble salt,bulk density,specific gravity,capillary porosity,and also for the XRF,XRD,SEM test;?2?Through the analysis of test data,the change of clay property can be found out easily.High concentrations of CO₂ invasion had not change the clay temperature obviously.Moisture content of clay decreased after the process of invasion,while the negative pressure increased.The pH value of clay sample after invading was higher than the original clay.And the relationship between thermal diffusivity and height showed to be negative,while there was a positive correlation between height and thermal diffusivity,or specific heat.Moreover,we also found a positive correlation between moisture content and thermal diffusivity,specific heat.Bulk density of the test clay sample was lower than the original clay,while the specific gravity showed the opposite trend.The capillary porosity and total porosity of the test clay sample changed obviously with the value increasing from 25.65%,44.00%to 34.27%,51.27%,respectively.The chemical composition of the clay in the column had undergone some changes.The contents of Fe,Mn,and Al in the clay had increased substantially,while the contents of Ca,P,and Na had decreased;the mineral phases had also changed,there were lamellar and rod-like mineral deposits on the surface of the clay particles;?3?The software called TOUGHREACT was used to simulated the process of CO₂invasion.The modeling can show us in one visual sweep how high concentration CO₂invasion affects the properties of claypan,including pH,main mineral,secondary mineral,liquid component,permeability and porosity;?4?It can be found from the simulation data that high concentration CO₂ invasion will lead to a significant drop of pH,and with the increase of invasion time,the pH value decreases more obviously.Sodium montmorillonite and kaolinite in the clay layer will develop a precipitation reaction.Calcium montmorillonite,chlorite,and illite may dissolve.There will be a certain increase in calcium,sodium,and bicarbonate ions.Permeability will increase slightly after 10-year,50-year,100-year,and 1000-year invasion.For 1000-years invasion,the permeability may increase from 8.816×10^-1616 to 8.822×10^-16,and the porosity will increase from 0.44 to 0.4401,which is also slightly.According to the analysis of the results under the experimental conditions,the physical and chemical properties of the clay layer will not change much.Since the test conditions have not reached the ideal state,the results are also of some reference.Therefore,high concentrations of CO₂ invasion will not substantially change the permeability of the clay layer,but it may have a slight effect on the acidity and alkalinity of groundwater.In general,the leakage of high-concentration CO₂ to the claypan has little impact on groundwater.