The Study Of Agricultural Production Of Heavy Metal Contaminated Soil After Chemical Washing And Treatment Of Spent Solution After Soil Washing

Soil washing can quickly remove heavy metals from contaminated soil,but the destruction of soil properties and structure caused by the washing process has attracted much attention.In this paper,EDTA compounded with GLDA and citric acid as the mixed chelators were used to wash multi-metal contaminated soil.The changes in fractions of heavy metals in soil,soil physicochemical properties,soil biological properties and agricultural production of soil after washing were studied for the sake of remediation and safe agricultural production of multi-metal contaminated farmland soils.In addition,the treatment of spent solution after soil washing by adsorption and microbial methods was discussed in this study,which provides scientific basis for solving the problems of spent solution discharge and reducing the economic and environmental costs of soil washing remediation.The main results of this study are as follows:?1?Batch experiments showed that soil washing can decrease the total concentration of heavy metals in soils,but residual leaching agent can cause transformation of metal fraction in soils and result in increasing the content of available metals in soils,especially in alkaline contaminated soils.It was found that the changes of soil physicochemical properties,soil enzyme activity and soil fertility after washing could affect the germination and growth of Chinese cabbage.Compared with Fe Cl₃and EDTA,the mixed reagent MC had less effect on soil physicochemical properties and soil enzyme activities,and had the least effect on the growth of Chinese cabbage.Therefore,MC was a moderate leaching agent for removing heavy metals from multi-metal contaminated soil.?2?The results of pot experiments showed that the removal rates of Cd,Pb,Cu and Zn in alkaline contaminated soil by EDTA and MC were 47.26%,62.84%,31.67%,27.66%,and 41.07%,47.06%,14.74%,26.50%,respectively.For acid contaminated soil,the removal rates of Cd,Pb,Cu and Zn by EDTA were 45.4%,97.2%,35.7%and 7.56%,respectively.And the removal rates of Cd,Pb,Cu and Zn by mixed reagent MC were 89.9%,30.4%,23.6%and 2.90%,respectively.Obviously,the removal efficiency of Cd,Cu and Zn from soils as much as those of the only EDTA washing,moreover,the application dose of EDTA decreased by 80%.?3?The results of pot experiment showed that the effects of leaching treatment on the biomass of the leaf and shoot of Chinese cabbage were not significant.The contents of Cd,Cu and Zn in the leaf of Chinese cabbage planted in alkaline soil after MC leaching were not significantly different from those of the control,which were 1.78 mg·kg^-1,5.35 mg·kg^-1and 18.93 mg·kg^-1,respectively.However,compared with the control,the content of Pb in the shoot of cabbage treated with MC washing increased by 37.8%.For acid soils,the contents of Pb and Cu in the shoot of cabbage treated with MC washing increased by 2.3 and 1.5 times.The metal content in cabbage leaf exceeded the limit of Food Standards of China for all treated soils.The results of planting two batch maize showed that the effect of washing on maize biomass was not significant.For alkaline soils,Cd,Cu and Zn contents in maize shoot of the first batch decreased by 52.3%,8.0%and 40.8%compared with control treatments,and the similar results were obtained for acid soils.In the second batch,compared with the control treatment,the metal contents of maize leaf increased after washing,especially alkaline soil,which indicated that the effect of amendments on the fractions of residual metal after washing had a certain aging effect.?4?The results of treatment of spent solution after soil washing showed that although biochar and mineral adsorbent can adsorb Cu?II?,it is difficult to adsorb Cu-EDTA complex.The results of treatment of spent solution after soil washing with DTC supported on active carbon showed that the adsorption for Cu increased but the adsorption for Cd,Pb and Zn decreased significantly.The adsorption of Cu?II?increased significantly after DTC supported on active carbon with ultrasound,water-bath at 60?,ultrasound and water-bath at 60?.?5?The results of SRB treatment of spent solution after soil washing showed that the maximum removal of heavy metals were obtained in 3 days reaction time and 1:1?v/v?of SRB and spent solution.Under this condition,the removal rates of Cd,Pb and Cu from EDTA spent solution by SRB were 25.8%,10.9%and 98.9%,respectively,and the removal rates of Cd,Pb and Cu from MC spent solution were 77.5%,44.1%and 94.1%,respectively.?6?Microorganisms isolated from MC spent solution can also remove heavy metals from spent solution,and the removal efficiency of heavy metals can be improved by domesticating them.