| There is a large area of dredged soil and dredger fill in coastal areas of China,which has the characteristics of high water content,low strength and poor permeability.It is difficult to achieve the expected target by traditional gravity consolidation method.At the same time,the total rate of soil pollution in China was 16.1%,and the rate of arable land occupation exceeded the rate of 19.4%.Situation of soil pollution is serious.As one of the five heavy metals in the soil,because of its low solubility,easy migration,long residence time and features on the human central nervous system damage,lead pollution has been listed as one of the key objects of heavy metal contaminated soil remediation.The electrokinetic remediation method rose at the end of 80s of last century because of its high efficiency,environmental friendly and are widely applied in lead contaminated soil remediation.Then the electric-chelating agent combined remediation technology has achieved fruitful results in improving the repair efficiency.However,due to the biological toxicity and high cost of the artificial chelating agent,it is difficult to further promote the electric-chelating agent combined remediation technology.Based on previous research results,Use natural chelating agent of fulvic acid(FA)-chelating agent which has high solubility and strong adsorption,low cost and good environmental protection and other characteristics of the for electric joint repair,while compare its effect with commonly used artificial chelating agent EDTA,EDDS.By changing the concentration ratio,pH and electric repair time of fulvic acid,the purpose is to explore a more economical and environmental method of electrokinetic removal of lead and soft soil reinforcement comparing with traditional artificial chelating agent remediation.The work done in this paper and the corresponding results are as follows:(1)This paper summarizes the existing methods for the remediation of lead contaminated soil,and classifies the various repair methods from three aspects of physics,chemistry and biology,and analyzes the advantages and disadvantages of various methods.Based on the previous conclusions of a large number ofexperimental research,the advantages and disadvantages of traditional electric chelating repair technology are analyzed.The principle of electro-osmotic drainage reinforcement was analyzed.Combined with previous studies,it was suggested that the chelating agent might have an effect on the electro-osmotic and drainage reinforcement during the electric repair process.Demonstrate many properties of fulvic acid itself and the potential for electric restoration of lead contaminated soil.(2)In this paper,different concentrations of fulvic acid as chelating agents were used to study the internal electric repair of remolded lead contaminated soils.The effects of EDTA and EDDS on lead ion removal and electro-osmotic drainage were compared.The results show that the migration path of lead ions is changed after adding the sting and the agent during the energization process.The addition of 0.5mol/L fulvic acid makes the effect of migration of lead ions in the soil better than that of 0.1 mol/L artificial chelating EDTA and EDDS,but the addition of artificial chelating agent makes the content of dissolved lead higher than that of fulvic acid,and the amount of dissolved lead increased with the concentration of fulvic acid.The addition of EDTA and EDDS increased the total amount of electro-osmotic drainage,but the chemical strength of the treated soil was lower than that of the control group.The high concentration of fulvic acid inhibited the electro-osmotic drainage,but the lower concentration of fulvic acid makes the little impact to electro-osmotic drainage.(3)On the basis of preliminary experimental results,several sets of experiments are proposed which are more likely to approach the optimal treatment concentration,and several sets of tests with longer time are set up to explore more economical and efficient electric repair-reinforcement scheme.The microstructures of the soil treated by different test groups were observed,and the reason for the change of the electro-osmotic properties of the soil was analyzed from the microscopic angle.The results showed that the experiment with 0.3mol/L fulvic acid as the chelating agent had the best effect,and the effect of 1.5mol/L fulvic acid as the chelating agent was the worst,and it was further proved that the effect of excess concentration of fulvic acid is counterproductive.Prolong the repair time can improve the lead removal rate,but the degree of improvement is not obvious,the actual application,should be basedon the actual situation,taking into account the repair goals and time costs,power costs,select a reasonable power time.The observation of the microstructure of the soil shows that the addition of fulvic acid into the soil after the electric repair process makes the voids of the soil smaller and the soil becomes more concocted,which leads to the change of the electro-osmotic properties of the soil and the decrease of the conductivity,Electro-osmotic drainage decreased,and eventually lead to reduced lead removal effect.(4)The appropriate concentration of fulvic acid and EDTA,EDDS were mixed with a certain volume ratio,trying to use the advantages of different chelating agents to improve the combined effect of electric repair and electro-osmotic drainage reinforcement,and from a number of aspects of its repair,reinforcement effect The evaluation.The results showed that the effect of the mixed solution as the chelating agent on the migration of lead ions in the soil was better than that in the control group.The effect of EDDS-FA mixed solution on lead was better than that of EDTA-FA,and the change of EDTA/EDDS concentration in the mixed solution did not change the effect in a great content.The mixed solution as a chelating agent has a certain effect on the displacement of the control group.(5)The potential distribution and current change monitoring of each test group during the testing process show that the voltage in the anode region was higher and the voltage in the cathode region was lower than that in the cathode region.The current change shows a tendency to decrease firstly and then rise. |
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