Chelator-enhanced Zea Mays Remediation Risk Of Chelated Heavy Metal Migrating With Runoff In Contaminated Soil

In this paper,the typical non-biodegradable chelating agent EDTA and biodegradable chelating agent GLDA are selected as the research objects,and strengthened the extraction of corn to restore Pb and Cd contaminated soil at the seedling stage and jointing stage,and studied the effect of chelating agent type,concentration and activation time on the extraction and remediation effect of corn;This paper explores the output characteristics of chelated heavy metals in underground runoff and surface runoff through simulated rainfall experiments;Further,by studying the soil adsorption of EDTA and GLDA chelated heavy metals and the infiltration of the undisturbed soil,the adsorption(or hysteresis)and dispersion parameters of the soil in the lower vadose zones are determined.Based on the Convection-Dispersion Equation(CDE),the experiment uses the Hydrus-1D moisture and solute transport simulation software developed by the American Salt Soil Laboratory to build a mathematical model of the migration of chelated heavy metals in the lower vadose zones and evaluate the impact of groundwater quality.The results are as follows:(1)Experimental studies on chelation-enhanced corn extraction and remediation indicate:First,1.5mmol/kg low-concentration EDTA and GLDA can promote the growth of corn at the seedling stage and jointing stage;Secondly,the best time for chelation strengthening is on the 7th day;Third,as the concentration of the chelating agent increases,the extraction amount of heavy metals in corn increases;Fourth,the experimental results show that 6.0mmol/kg EDTA enhanced extraction of corn at the jointing stage is the most advantageous,and6.0mmol/kg GLDA enhanced extraction of corn at the jointing stage is the most advantageous.(2)Under the condition of chelation enhanced corn extraction and remediation,the leaching characteristics of heavy metals along with surface runoff and water quality evaluation studies show that:First,for Cd,the difference in total amount of heavy metals from ground runoff output under the conditions of the two chelating agents is small.For Pb,GLDA is significantly higher than EDTA.Secondly,under the condition of EDTA chelation enhanced corn seedlings,the average output concentration of Cd is 2.9-4.3 times higher than that of surface water environmental quality standards,and Pb is 22.0-46.1 times higher than the standard.For jointing stage corn,the average output concentration of Cd is 2.5-3.7 times higher than that of surface water environmental quality standards and 19.7-49.0 times that of Pb;Under GLDA chelation-enhanced corn at the seedling stage,the average output concentration of Cd is 3.4-5.2 times higher than that of Class V water quality standards and56.5-106.3 times higher than Pb.For the corn at the jointing stage,the average output concentration of Cd is 3.3-3.9 times higher than that of the surface water environmental quality standard,and Pb is 45.3-69.5 times higher than the standard.(3)Under the condition of chelation enhanced corn extraction and remediation,the leaching characteristics of heavy metals along with underground runoff and water quality evaluation studies show that:First,the total leaching of Cd and Pb underground runoff increases with the concentration of chelating agent,and the output of 7-day activation is higher than that of 3days in the same concentration of chelating agent.In addition,for Cd and Pb,the total output of heavy metal runoff with EDTA is significantly higher than that of GLDA.Secondly,under EDTA chelation enhanced corn seedling stage,the average leaching concentration of Cd is29.3-41.1 times higher than that of groundwater environmental quality standards,and Pb exceeded 3.1×10~4-5.3×10~4 times.For jointing stage corn,the average leaching concentration of Cd is 42.9-80.8 times higher than that of groundwater environmental quality standards,and the standard of leaching Pb is 4.5×10~4-12.6×10~4 times;Under GLDA chelation-enhanced corn at the seedling stage,the average leaching concentration of Cd is6.4-11.3 times higher than that of groundwater environmental quality standards,and Pb exceeded 0.2×10~4-0.6×10~4 times.For the corn at the jointing stage,the average leaching concentration of Cd is 12.4-24.0 times that of Class V water quality in the groundwater environmental quality standards,and that of Pb is 1.6×10~4-2.7×10~4 times.(4)This article selects the jointing period with the best extraction effect and greater pollution of underground runoff as an example.The groundwater quality standard(GB/T14848-2017)is used as the evaluation standard,and combined with the prediction results of the migration of chelated heavy metals with runoff to evaluated the risk of groundwater pollution.The result shows:6.0mmol/kg GLDA enhanced remediation does not exist the risk of chelated heavy metals infiltrating the groundwater;The 6.0 mmol/kg EDTA chelation-enhanced situation poses a risk of groundwater contamination.When the groundwater level is 3m,the chelated Cd and Pb pollution time of the compound contaminated soil appears on the 11th to 35th days,and the peak concentrations of heavy metals Cd and Pb exceed 3.82 and 103.80 times of the standard respectively;When the groundwater level is 5m,the chelated Cd and Pb of the compound contaminated soil appear on the 20th-55th day,and the peak concentrations of Cd and Pb exceed 2.98 and 80.82 times respectively.