The Interaction Between Kaolinite Colloid And Eu(?)/Am(?)

Environmental colloids widely exist in underground aquifers.Because of their large specific surface area and surface charges,stable colloids can load radionuclides in the transport process,which significantly affects the transport and fate of radionuclides in groundwater environment,thus posing a potential threat to the groundwater environment.Although it has been realized the importance of environmental colloids to the environmental behavior of radionuclides,the binding characteristics and coupling transport laws of radionuclides and environmental colloids are still unclear.In the real environment,there will be multi-component composite colloids.The properties of composite colloids are not the simple superposition of the properties of single component colloids.There may be synergistic effects and antagonistic effects among the components.The control effect of environmental colloids on radionuclide environmental behavior are closely related to the stability and adsorption law of colloids under different conditions.It is of great significance to deeply understand the aggregation stability and adsorption of colloids under different environmental conditions for evaluating the transport capacity and environmental risk of colloids and their pollutants.In this work,the kaolinite colloid(KC),which represents one of the typical environmental mineral colloids was studied in detail.To understand the interaction between Eu(?)/Am(?)and KC,and reveal the regulation and mechanism of Eu(?)/Am(?)transport controlled by kaolinite colloid,the colloid stability,the adsorption of Eu(?)/Am(?),and KC-Eu(?)/Am(?)co-transport behavior were explored.The result of this work can provide a basis for further elucidating the environmental behavior of kaolinite colloid and symbiotic pollutants.This thesis can be divided into six chapters.Chapter 1: Introduction.The research progress of the interaction between environmental colloids and radionuclides were reviewed,and the significance,contents,purpose and innovation of this work were also summarized.Chapter 2: Study on the stability and aggregation kinetics of kaolinite colloid.The effects of various environmental factors on the stability of kaolinite colloid were studied in this chapter.Chapter 3: The adsorption of Eu(?)/Am(?)on kaolinite.The influence of different physico-chemical conditionss on the adsorption behavior and its mechanism were discussed.Chapter 4: Co-transport behavior of kaolinite colloid and humic acid(HA)with Eu(?)in saturated quartz sand column.On the basis of the results of the individual transport behaviors of kaolinite colloid,humic acid and Eu(?),we mainly studied the effects of kaolinite colloid and humic acid on Eu(?)transport behaviors.Chapter 5: Effects of kaolinite colloid and humic acid on Am(?)transport behaviors in saturated quartz sand column.The effects of various physical and chemical conditions on the individual and co-transport behaviors for kaolinite colloid,humic acid and Am(?)were discussed in detail,the law of co-transport was obtained.Chapter 6: Summary and prospect.We not only summarized the research results and shortcomings of this work,but also put forward the future research contents and direction of this work.The main conclusion for this work include:(1)The stability of kaolinite colloid concerning colloidal aggregation was investigated as a function of temperature,kaolinite colloid concentration,acidity,electrolytes as well as HA concentration by dynamic light scattering(DLS)technique,the aggregation mechanism was discussed with the aid of Derjguin Landau Verwey Overbeek(DLVO)model.The results showed that the kaolinite colloid was favorable for dispersion under the high pH and low salinity conditions,the colloidal aggregation rate and the average hydrodynamic diameter increased significantly as ionic strength increased or pH decreased.Cations with higher valence showed more significant contribution in inducing colloid aggregation,which was generally in accordance with the Schulze-Hardy rule.HA was capable to greatly increase the colloidal stability by altering the surface electrostatic potential and steric effect.DLVO model suggested that the electrostatic force between colloid particles controlled the aggregation and destabilizing trend of colloid,the critical coagulation concentration(CCC)calculated from DLVO theory was in consistent with kinetic aggregation experiments.(2)The adsorption behaviors of Eu(?)/Am(?)on kaolinite colloid were studied by static batch experiments,the effects of ionic strength,pH,kaolinite colloid concentration,contact time,Eu(?)concentration and temperature on the adsorption behaviors of Eu(?)/Am(?)were investigated.The adsorption mechanism was preliminarily understood and the corresponding thermodynamic parameters were obtained.It could be found that the adsorption of Eu(?)on kaolinite colloid was a fast equilibrium progress,and the adsorption behaviors were strong chemical adsorption.The pH and ionic strength had great influence for the adsorption of Eu(?).Under the condition of low pH,the adsorption mechanism belonged to ion exchange and outer coordination.It was mainly inner coordination or surface precipitation when the pH was high.The Langmuir isothermal model could better describe the adsorption process of kaolinite colloid for Eu(?),which also meant that the adsorption behaviors of Eu(?)onto kaolinite colloid were endothermic reaction,the high temperature was conducive to its adsorption behavior and the adsorption process belong to monolayer adsorption.Consistent with the results of the adsorption behaviors of Eu(?),both pH and ionic strength had significant influence on the adsorption behaviors of Am(?),and the adsorption process was also a fast equilibrium process.(3)Europium(?)is often studied as a chemical analogue of trivalent lanthanides and actinides.In this work,the influence of kaolinite colloid on the transport of Eu(?)was studied by column penetration experiment.The effects of kaolinite colloid concentration,pH,ionic strength,background ion and HA concentration on the individual transport and co-transport of Eu(?)and kaolinite colloid were discussed in detail.The mechanisms controlling co-transport processes were also confirmed by assessing the evolutions of effluents particle size and zeta potential in the column.It was found that the co-transport of KC-Eu(?)could be obviously facilitated under high concentration colloid and pH conditions,and inhibited at high ionic strength,which were related to the stability,adsorption capacity to Eu(?)and mobility of kaolinite colloid under different conditions.The kaolinite colloid was stable and had strong adsorption capacity for Eu(?)under the conditions of low ionic strength or high pH,which promoted the transport of Eu(?)in saturated quartz sand column.However,with the ionic strength increasing or pH decreasing,the stability,adsorption capacity for Eu(?)and transport of colloid were reduced,which hindered the transport of Eu(?)in saturated quartz sand column.HA could obviously promote the transport of KC-Eu(?),which attributed to the synergistic effect between kaolinite colloid and HA.Knowledge generated from this study indicated that combined effects of kaolinite colloid and HA on radionuclides transport were dominated by the amount of HA.It can be expected that kaolinite colloid can significantly promote the transport of radionuclides in groundwater with rich humic acid content.(4)The influence of kaolinite colloid on Am(?)transport behaviors were studied through column experiments.The effects of flow rate,colloid concentration,pH,ionic strength and humic acid on kaolinite colloid and Am(?)individual transport and co-transport behaviors were studied,respectively.It could be found that high flow rates facilitated the co-transport of KC-Am(?),while co-transport behaviors were inhibited under the low flow rate.Increasing the kaolinite colloid concentration and pH value could effectively promote the co-transport of KC-Am(?),but the co-transport behaviors of KC-Am(?)would be significantly inhibited with increasing the ionic strength,which was closely related to the stability of kaolinite colloid and the adsorption capacity to Am(?)of kaolinite colloid and sand column.HA could significantly promote the co-transport of KC-Am(?).HA can not only improve the stability of kaolinite colloid,but also promote the adsorption of Am(?),there was a synergistic effect between kaolinite colloid and humic acid.