Study On In-situ Passivation Remediation Of Multi-metal Contaminated Soil

With the rapid development of social economy,the acceleration of urbanization process,sewage sludge land utilization and the improper use of chemical fertilizers and pesticides caused by soil heavy metal pollution have became one of the focus environmental problems at home and abroad.Soil heavy metal pollution not only leads to grain reduction,but it also affects human health by the enriched plant–food chain.There are more people and less land in China,and the soil heavy metal pollution is relatively common.Therefore,developing a safe and effient,cheap and easy remediation technology was important to heavy metal contaminated soil.On the basis of relative literatures and review,this experiment selected superphosphate phosphate fertilizer,lime and spotted soil as passivated materials based on the principles of safety,high efficiency,cheapnessand good stability.The passivation effect of heavy metals in soil for 30,60 and 90 was studied through contaminated soil passivation expertiment and pot experiment,and the passivationmechanism was discussed.Screening of a safe,high efficient and cheap passivator,which provides technical support for the remediation of multi-metal contaminated soil.The main results were showed as follows:（1）The passivators selected in this study are:superphosphate phosphate fertilizer（G）,lime（S）,montmorillonite（B）.The passivation rates of Zn,Cd,Pb and As in soil increased with the increment of passivationtime.For Zn,No.17（G:7.68mg/kg;S:30mg/kg;B:50mg/kg）,No.18（G:7.68mg/kg;S:30mg/kg;B:90mg/kg）,No.25（G:17.68mg/kg;S:30mg/kg;B:70mg/kg）,No.24（G:17.68mg/kg;S:10mg/kg;B:90mg/kg）had the best passivation effect,and the passivation rates were 63.9%,62.5%,61.1%and 60.7%.The results showed that No.25,No.18 and No.17 had the best passivation effect on Cd contaminated soil with the passivation rates of 49.7%,52.3%and 56.9%for 90 days,46.4%,48.1%and 59.8%for 60 days,and 46.3%,48.3%and48.8%for 30 days.No.25（17.68 mg/kg;S:30 mg/kg;B:70 mg/kg）,No.9（G:12.68mg/kg;S:30 mg/kg;B:90 mg/kg）,No.10（G:7.68 mg/kg;S:20 mg/kg;B:70 mg/kg）,No.6（G:12.68mg/kg;S:10mg/kg;B:90mg/kg）,No.13（G:7.68mg/kg;s:10mg/kg;B:70mg/kg）,No.16（G:7.68mg/kg;s:30mg/kg;B:70mg/kg）and No.24 passivators had the best passivation effect on Pb contaminated soil,among them No.25,No.9 and No.10 passivators had the best passivation effect on Pb contaminated soil.With the passivation rates of 62.8%、60.2%、60.0%in 60 days,and No.6,No.13（G:7.68mg/kg;s:10mg/kg;B:70mg/kg）,No.16 and No.24 passivators had the best passivation effect on soil Pb in soil,and for No.6、No.13、No.16 and No.24 had 55.6%、55.5%、55.8%and55.9%in 30 days.The results showed that No.17,No.18,No.25 and No.11（G:7.68mg/kg;s:20mg/kg;B:50mg/kg）had the best passivation effect on soil As.The passivation rates of No.18,No.25 and No.11 passivators were 45.1%,47.0%and 43.6%respectively in 60d,and the passivation rate of No.17 passivator for As 90 days was49.4%.（2）No.18 and No.25 had the best passivation effect on multi-metal contaminated soil.The 90 days average passivation rates of Cd,Pb,Zn and As in soil were 57.98%（No.18）and 56.58%（No.25）;The average passivation rates of Cd,Pb and As in soil were 54.03%（No.25）s and 55.4%（No.18）,57.77%（No.18）and 55.53%（No.25）for Zn,Cd and As in 90 days.For Zn,Pb and As in soil,the average passivation rates of No.18and No.25 were 57.37%and 56.47%in 90 days.The average passivation rates of Zn,Cd in soil were 50.95%（No.25）and 62.75%（No.18）in 30 and 90 days,and No.25 had the average passivation efficiency of 56.7%in 60 days.The average passivation rate of Zn and Pb in soil was 62.25%（No.25）;For Zn and As,the average passivation rate in soil was 53.8%（No.18）in 60 days and 54.85%（No.25）in 90 days;The average passivation rate of Cd and Pb in soil was 49.9%（No.25）in 30 days;The 60 days average passivation rate of Cd and As in soil was 46.6%（No.18）and 50.9%（No.25）,and for Pb and As were 46%（No.18）and 54.9%（No.25）.（3）The results of pot experiment showed that when pakchoi and rape were treated with 18 and 25 dominant passivators for 90 days,the reactivation degrees of Cd,Pb,Zn and As in the passivated soil were very low.Compared with the control group,the increase of available Cd,Pb,Zn,As in rhizosphere soil of pakchoi and rape by 9,17,18and 25 passivators were very small.Pakchoi and rape grew well in the soil treated with passivators and the enrichment abilities of Zn,Cd,Pb and As were low with the increase of biomass.（4）Combined with soil passivation experiments and pot experiments,18 and 25had the best passivation effect on complex heavy metals of Zn,Cd,Pb and As.The p H value of two groups of dominant passivator combinations increased after 90 days of treatment,and the forms of heavy metals in the soil were transformed from SE and WSA with low activity to OM and RES with high activity.The transformation degree of Zn,Cd,Pb and As by 25 was more obvious.The increase of OM indicated that the content of soil organic matter was improvedand this could promote the passivation.The heavy metals formed insoluble precipitation（such as sulfide）,and it reduced to the increase of RES content..On the other hand,the soil p H value by No.18 and No.25 treatments increased from 60 to 90 days and tended to be stable.The main mechanism was to keep soil acidity and alkalinity stable and prevent the further activation of heavy metals.The application of superphosphate could not only form precipitation with heavy metals,weaken the active state of Zn,Cd,Pb and As,but also increase the content of RES.It could also beused as fertilizer to ensure the soil fertility.The best passivation effect of superphosphate phosphate fertilizer was fully proved by No.25.For No.18,the composition of bentonite was relatively high.The bentonite had more micropores,huge specific surface area and special crystal structure.There are a lot of exchangeable cations,which was easy to replace H⁺,Al³⁺in soil.On the other hand,it had a good adsorption and fixation effect on Zn,Cd,Pb,As.