Passivation Effect Of Alkali-modified Attapulgite On Heavy Metals In Soil

With the deterioration of soil environment,the management and remediation of soil heavy metal pollution has become a hot issue in the research field.Large areas of soil contaminated by heavy metals and other toxic elements,and make some of the toxic elements in agricultural products exceeded the standard,which threaten human health.The modification of attapulgite can improve the passivation effect on soil polluted by heavy metals to a certain extent,which lays a theoretical foundation for the development and utilization of attapulgite and the treatment of heavy metals in soil.This study is mainly aimed at the effect of attapulgite modified by quicklime.In this study,the mass ratios of attapulgite and quicklime were 1:1,2:1,3:1,4:1,5:1,6:1,7:1.The mixtures were stirred with water for 12,24,36,48,72,96 and 108 h.And 49 kinds of alkali modified attapulgite passivation agents were obtained.The alkali modified attapulgite passivation materials were added to the artificial soil.And the concentrations of Cd,Ni,Cu,Cr,Zn were 2 mg/kg,400 mg/kg,800 mg/kg,800 mg/kg,800 mg/kg in artificial soil respectively.Taking maize as a test plant,the maize was planted in the greenhouse by direct seeding method.And the passivation agent added heavy metal contaminated soil sample was 32 g/kg.The concentration of heavy metals in maize plants was determined.Then acid extractable heavy metal concentrations were determined after 30 days.In addition,five kinds of optimal passivation agents were selected by the acid extractable heavy metal content and concentration of heavy metals in Maize.The five kinds of optimal passivation agents were applied to the polluted soil at mass ratios of 0,10,20,40,60 and 80g/kg respectively.Then the soil's pH,EC,DTPA extractable concentrations and BCR continuous extraction were determined after 30 days.The results show that:After adding 49 kinds of alkali modified attapulgite,the change of heavy metal content in maize plants and alkali modified attapulgite are consistent.With the addition of passivation agents,the contents of heavy metals in maize plants are less than other passivations.The best alkali modified attapulgite passivation of heavy metals Cu,Cr,Zn,Ni and Cd contaminated soil conditions were D1,D2,D3,D4,D5.Modified time of D1,D2,D3,D4,D5 were 48 h,72h,48 h,72h and 72 h.And the mass ratios of attapulgite and quicklime of D1,D2,D3,D4,D5 were 2:1,2:1,3:1,3:1,4:1.After adding passive materials,the concentrations of heavy metals Cd,Ni,Cr,Zn and Cu in maize plants are the lowest,and the quality ratio of attapulgite and lime significantly affect the concentration of heavy metals in maize plants.The pH and EC value increase with the increase of the addition of passivation agents.With the increase of the addition of passivation agents,DTPA extractable concentrations of Cu,Cr,Zn,Ni and Cd decrease.The corresponding maximum removal rate of DTPA extractable concentrations of Cu,Cr,Zn,Ni and Cd are 46.34%,28.94%,39.10%,29.04% and 22.65%.With the addition of passivation agents,there are significant difference between water-soluble and DTPA extractable concentrations of heavy metals.With the addition of passivation agents,the acid extractable,reducible form and oxidizable form concentrations of Cu gradually transform into residual from;the acid extractable concentrations of Cr and Zn transform into residual from;the acid extractable concentrations of Ni and Cd transform into reducible form and oxidizable form residual from.