Stabilization Effect Of Nano-zirconia Loaded Biochar On Arsenic Contaminated Soil

Nowadays,soil arsenic pollution is a serious issue in China,and the high toxicity of arsenic seriously affects the quality and safety of agricultural products and human health.Biochar,as a low-cost and easily-operated solidifying/passivating agent with low secondary pollution,has been widely used in the treatment of soil heavy metal pollution.Nano-zirconia are also has a wide application prospect in remediation of heavy metal contaminated soil due to its huge specific surface area and high selective adsorption.Pine biochar（BC）was used as carrier in this study,and Nano-zirconia loaded biochar（N-ZrO₂-BC）was synthesized to investigate its adsorption and fixation characteristics on As（V）in soil.Firstly,the materials were characterized by SEM,FT-IR and XPS to analyze the differences of surface structure and functional groups before and after biochar modification.The kinetics of arsenic removal and adsorption isotherm of N-ZrO₂-BC in solution were studied by adsorption experiment;Then,the soil culture experiment was carried out to evaluate the solidification effect of arsenic on soil,and the speciation of arsenic in soil was analyzed.Finally,the effect of N-ZrO₂-BC on the migration behavior of arsenic was investigated by simulated leaching experiment.The results of this study will provide a theoretical basis for in-situ remediation of arsenic contaminated soil and safe use of farmland.The main results are as follows.1.SEM,FT-IR and XPS results showed that precipitation and surface complexation were the main adsorption mechanism of As（V）on the surface of N-ZrO₂-BC.SEM results showed that the modified biochar basically maintained the carbon skeleton structure of pine biochar,and the surface of the modified biochar was evenly distributed with fine particles.FT-IR results showed that hydroxyl and zirconia played an important role in the adsorption and removal of As（V）,the modification of loaded nano-zirconia could significantly increase the adsorption of As（V）.XPS results showed that Zr existed in the form of Zr-O chemical bonds on the surface of N-ZrO₂-BC after modification,and played an important role in the adsorption of As（V）by N-ZrO₂-BC.2.The adsorption experiment showed that the second-order kinetic equation had a good fitting effect on the adsorption curve of As（V）on N-ZrO₂-BC surface,which indicated that chemical adsorption was the main factor controling the reaction rate.The Freundlich isotherm adsorption equation can describe the adsorption behavior of N-ZrO₂-BC on As（V）,which indicated that the adsorption process of As（V）tended to be the combination of monolayer and multilayer.The saturated adsorption capacities of BC and N-ZrO₂-BC for As（V）were 1.757and 7.867 mg·g^-1·h^-1,respectively.The As（V）adsorption capacity of N-ZrO₂-BC was significantly higher than that of BC.3.Soil culture experiments showed that the stabilization efficiency of arsenic in soil with2%N-ZrO₂-BC reached 99.30%after treatment of 60 days,and the extractable arsenic content was reduced to 3.07μg·L^-1,which lower than 0.01 mg·L^-1.Comparing with the control,the results of the combined arsenic content in soil showed that the acid extractable arsenic content in the soil was significantly reduced and the residual arsenic content was significantly increased after the application of N-ZrO₂-BC.However,the soil acid extractable arsenic content was all increased under the treatment of BC increased,and the residual arsenic content was not changed significantly.It can be seen that the addition of N-ZrO₂-BC can promote the conversion of active arsenic into stable arsenic.Comparing with the control,the content of acid extractable arsenic in soil decreased by 90.57%,and the content of residual arsenic increased by 51.46%,indicating that the addition of 2%N-ZrO₂-BC could effectively promote the transformation of active arsenic to stable arsenic in soil.The addition of 2%N-ZrO₂-BC showed a good passivation effect on soil arsenic,and it was a more reasonable and effective addition for arsenic-contaminated soil.4.Comparing with the control,the simulated leaching experiment showed that the application of N-ZrO₂-BC in soil effectively reduced the concentration of arsenic in the leaching solution.The arsenic concentration was lower than 0.01mg·L^-1,which reached the level of groundwater standard.After the leaching,the release rate of soil arsenic could be as low as0.02%,which was 95.30%lower than the control,and the total cumulative release was 53.03%.The arsenic content in the soil column（10～40 cm）was significantly lower than the control.N-ZrO₂-BC treatment showed a good solidification effect on arsenic to reduce the risk of soil and groundwater pollution.