Development Of Remediating Agents For Heavy Netal Of Nickel Tin And Lead In Soil

With the promulgation of a series of guidelines,standards,policies and regulations on-site pollution in China,as well as the requirements of sustainable development and green development,it is of great significance to explore the sustainable remediation of heavy metal contaminated sites so as to meet the requirements of both environmental safety and redevelopment.In this study,industrial by-products,agricultural wastes and natural minerals were used to replace part of cement to develop low-cost and lowenergy environment-friendly remediating agents.It was used for the remediation of contaminated sites with high concentration of Ni(5000 mg / kg),Sn(2500 mg / kg)and Pb(5000 mg / kg),and it also fills the blank of remediation of the Sn contaminated sites.The unconfined compressive strength,leaching concentration of heavy metals,freeze-thaw characteristics,and long-term stability were used to evaluate the repair effect of the developed remediating agents,and in order to provide theoretical reference for the site heavy metal remediation project.The main research findings are as follows:(1)Among the four groups of natural mineral-type remediating agents,the PCGGBS-Zeolite CGZ1 group has higher unconfined compressive strength,lower leaching concentration,excellent freeze-thaw characteristics and long-term stability.The unconfined compressive strength was positively correlated with age,and the unconfined compressive strength of each age meets the 0.35 MPa of the EPA's regulations on landfill sites.In the long-term curing process,the leaching concentration of Pb and Ni did not increase significantly,and the leaching concentration of Sn showed a decreasing trend and basically stable from 60 d.After the freeze-thaw cycle,the unconfined compressive strength of the sample increased by a maximum of 16.7%,and the mass loss was 3.03%.The leaching concentrations of Pb and Ni increased between 12.10%-16.64% and 10.08%-12.80%,and the leaching concentration of Sn decreased from 8.15%-83.61%.(2)4A zeolite,rice straw biochar and rice husk biochar were used to optimize the performance of cement-GGBS-zeolite CGZ1 group,it was found that the unconfined compressive strength of the 4A zeolite CG4A1 group and rice straw biochar CGZ1RS1 group samples at all ages were better than that of PC-GGBS-Zeolite CGZ1 group;the leaching concentrations of Ni,Sn and Pb were lower than that of PC-GGBS-Zeolite CGZ1 group,and the leaching concentration of Ni showed a decreasing trend with age.(3)Based on the cement-GGBS-4A zeolite CG4A1 group,1%,3%,5%,and 9% rice straw biochar was added to develop a biochar-type remediating agents,it was found that the unconfined compressive strength of the sample increased with the increase of biochar ratio in the range of 1%-5%.The unconfined compressive strength of the sample was lower than 5%,but still higher than that of the sample without biochar,when the biochar content was 9%.With the increase of the biochar ratio,the leaching concentrations of Pb and Ni were reduced,and the leaching concentration of Sn was also basically reduced,and all of them were lower than that of CG4A1 group.After freeze-thaw cycle,the unconfined compressive strength of the sample was generally increased,the mass loss of the sample was between 1.51% and 2.22%,the leaching concentrations of Pb and Ni were not significantly increased,and the leaching concentration of Sn was significantly reduced.The leaching concentrations of Pb and Ni increased between 1.48%-15.83% and 6.47%-15.02%,and the leaching concentration of Sn decreased between 20.43%-89.48%.