| Cadmium(Cd),lead(Pb)and arsenic(As)are typical soil heavy metals,the complex heavy metal pollution situation often exists in soil systems,threatening the ecological environment and human health.Biochar(BC)has rich pore structure,large specific surface area and rich oxygen-containing functional groups,these characteristics make biochar adsorption on heavy metals and become a hotspot in soil heavy metal remediation.Iron-based materials hasgradually been paid attention to the passivation of the heavy metals.In this study,we selected paddy soil as research subject and silkworm excrement biochar(BC),ferrous sulphate(FeS04),ferric chloride(FeCl3),reduced iron powder(Fe)and nanometer iron(nano Fe)as the research materials,to carry out a laboratory experiment.This experiments were used to investigate the silkworm biochar and iron-based materials on chemical forms of Cd,Pb and As which were incubated over 7d,14d,28d and 56d.And the remediation mechanism of the passivating agent to heavy metals was discussed from the soil physical and chemical properties,enzyme activity and soil structure changes,in order to find out the feasibility and mechanism of silkworm biochar and iron-based materials passivation to repair heavy metal complex contaminated soil.The main results are as follows:1)All of the treatments could effectively reduce the effectiveness of Cd,Pb and As.In general,the treatment of(BC + FeS04)has the best passivation effect on Cd,Pb and As.Compared to the control experiment,the treatment of(BC +FeS04)mad the content of Cd in organic matter and residual increased by 40.90%,and the content of Cd in exchangeable and bound to carbonates decreased by 28.44%.Compared with the control experiment,the treatment of(BC + FeSO4)mad the content of Pb in organic matter and residual increased by 23.51%.And the the content of As in organic matter and residual increased by 1.89%,the content of As in exchangeable and bound to carbonates decreased by 10.81.2)Different passivation agents could influence the chemical forms of Cd,Pb and As by the changes of the soil properties,such as pH and CEC.All passivation agents promoted the soil pH and CEC.At the end of the culture(56 d),the pH value of the soil increased significantly from 1.65 to 2.01 units,(BC ?Fe)treatment had the maximum value of pH.The CEC increased by 2.01?2.58 cm·kg-1,(BC + Fe)treatment had the maximum value of CEC.3)With the increase in the number of cultivars,the urease activity of different treatments was basically increasing,and reached the highest value at 56 days.The highest value treatment was(BC + Fe),which was 31.27 ?g·g-1.The activity of soil catalase was different under different treatments,at 56d the activities of soil catalase were significantly increased by 86.70%?10.00%,(BC + Fe)and(BC + nano Fe),this two treatments had the highest value,was 0.210 mL·g-1.4)XRD patterns showed that Cd,Pb and As were immobilized on the soil in the form of Cd(OH)N03,Cd(OH)2,Pb5O4,Pb3(C03)2(OH)2,As2O5 and As2O4.(BC + Fe)and(BC + FeS04),the two treatments of Pb5O4 content were higher than other treatments.Comprehensive the above results,(BC + FeSO4)and(BC + FeCl3),these two treatments can significantly improve the soil environment,increase soil pH and CEC,enhance urease activity,and also achieve good passivation for Cd,Pb and As. |
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