Passivation Effect Of Modified Biochar On Cadmium And Arsenic In Polluted Soil

Heavy metals are common pollutants in farmland soils in China.The pollution of cadmium and arsenic in agricultural land in some provinces in central and southern China is particularly serious,such as Hunan and Jiangxi.Cadmium and arsenic composite contaminated soils are difficult to repair at the same time because of different environmental behavior mechanisms of different elements,which is one of the research difficulties in soil remediation in the future.Oyster shells and shells can be used for immobilized restoration of heavy metal pollution in soil.Iron compounds can effectively alleviate the bioavailability of soil arsenic.The addition of sulfur can reduce the bioavailability of cadmium in soil.Based on the comprehensive analysis literature,shell-modified biochar(SH-BC)and ferrous sulfide-modified biochar(FS-BC)were prepared.The adsorption of Cd and As was analyzed by adsorption experiments and clearly clarify its adsorption mechanism through material characterization.At the same time,the leaching experiment evaluated the effect of the above passivation materials on the leaching effect of Cd and As in soil under short-term and long-term conditions.Finally,rice pot experiment was used to evaluate the effects of different passivation materials on the absorption of Cd and As by plants and their passivation mechanism,which provide the feasibility theory for soil remediation.The main findings of this paper are as follows:1.The SH-BC and FS-BC were prepared by pyrolysis technique.The removal effects of Cd(?)and As(?)on the two materials were investigated.The results showed that the shell and ferrous sulfide particles covered the surface of the biochar;SH-BC and FS-BC have good adsorption effects on Cd(?)and As(?).The rate limiting step for Cd(?)and As(?)in solution is the chemisorption process between the passivating agent and the adsorbate.The Langmuir model provides the best fit of SH-BC and FS-BC for Cd(?)and As(?)adsorption,which occurs mainly in monolayers.2.The effect of passivation on the leaching effect of Cd and As in soil under short-term and long-term conditions was evaluated by leaching experiment.The results showed that:The addition of SH-BC and FS-BC passivator can increase the soil pH and reduce the leaching rate of Cd and As in the soil,thus reducing its migration in soil.3%SH-BC treatment had the best effect on reducing soil available Cd content,and the acid-soluble state was 47.5%lower than that of the control group.The 3%FS-BC treatment had the best fixation effect on soil As.The obligate adsorption state and non-specific adsorption state of As decreased by 34.4%compared with the control.3.The results of rice pot experiment showed that compared with the control group,SH-BC and FS-BC could promote rice growth,effectively reduce the bioavailability of cadmium and arsenic in soil and reduce the accumulation of heavy metals.At the same time,the passivation agent induces the formation of iron spots on the rhizosphere surface of rice,and increases the anchoring effect of rhizosphere iron on Cd and As,thus reducing the migration and absorption of Cd and roots in rhizosphere and non-rhizosphere soil.The accumulation of Cd and As in the shoots(leaves,leaves)of rice was reduced.