Effect Of Thermal Modified Attapulgite On The Passivation Of Heavy Metal In Contaminated Soil

Attapulgite is a kind of cheap and easily available inorganic mineral material.Because of the adsorption,ion exchange,it has been applied to the in situ remediation of heavy metal in contaminated soil.In addition to containing crystal structure,natural attapulgite also contains many crystalline water and acid soluble substances.In order to increase the adsorption performance of attapulgite,heat treatment or acid treatment of attapulgite is usually used to get through the inner channel of attapulgite,exposing more inner surface and active group.The passivation agent was made of attapulgite which was from Gansu Jingyuan and which was by the process of air drying,crushing,high temperature modification and cooling.The effect of different modification temperature and modification time on the passivation of heavy metals by attapulgite was studied by means of passivation of heavy metal in artificial contaminated soil.The attapulgite obtained by selecting the best heat modification condition was used as passivation agent to immolizate the heavy metal in contaminated soil near the DongDa Gou.The experiment studied the pH,the water soluble state,DTPA extraction state of the C u,Zn,N i.The distribution of the Cu,Zn,N i were studied.The effect of heat modified attapulgite on the passivation of heavy metal in contaminated soil was analysed.The experimental results showed that:(1)Lower temperature(less than 350?),shorter time(less than 0.5 h)had little significant effect on the passivation capacity of attapulgite.The passivation capacity of attapulgite was improved significantly when the modification temperature was 350? and 400?.When the temperature was higher than 400 ?,the capacity of the attapulgite for heavy metal was reduced.At higher temperature,the longer the modification time was,the smaller the capacity of heavy metal passivation was and even was lower than the unmodified attapulgite.The content of C u,Zn,Cr and N i in maize plants could be significantly reduced by adding the passivation agent,and which was decreased gradually with the increase of passivation capacity.(2)The pH of attapulgite was alkaline.After 30 days passivation treatment,The pH of contaminated soil was increased.And with the increase of attapulgite addition,soil pH also showed an increasing trend.For Cu,Zn and N i in contaminated soil,the increase of soil p H was more conducive to passivation.(3)The content of water soluble and DTPA extracted of heavy metals could be significantly reduced by the addition of passivation agents.At lower addition,the water soluble state of C u,Zn and N i in soil was decreased to the minimum,and the change was no longer obvious with the increase of passivation agent.The DTPA extraction state of C u and Zn gradually was decreased with the increase of passivating agent.When the amount of passivating agent was 64 g/kg,the DTPA extraction state of N i was minimized.(4)When the content of passivation agent was more than 32g/kg,with the increase of the amount of the passivation agent,the acid soluble state,the reduced state and the oxidation state of C u were transformed into the residual state,while the acid soluble state and the reduced state of Zn were transformed into the residua l state.N i in the soil was mainly in the form of acid soluble and residual state,when the content of passivation agent was more than 16g/kg,with the increase of the amount of the passivation agent,the acid soluble state of N i were transformed into the residual state.(5)The content of C u-DTPA,Zn-DTPA and N i-DTPA extraction state had the significant correlation with the chemical forms.But the the correlation between the water solub le and the chemical forms did not significant.The acid soluble states of C u and Zn had a negative correlation with residual state,and had a significant positive correlation with the reduction and oxidation states.There was a significant negative correlation between the soluble acid of Ni and residual state in soil.(6)Mobility of heavy metals in soil was significantly reduced by the addition of passivation agent.The Mobility of C u was significantly decreased when the content of passivation agent was more than 32g/kg,and which was gradually reduced with the increase of the amount of passivation agent.So was for Zn.The Mobility of Zn was the lowest when the amount of passivation agent was increased to 256g/kg,when the passivation agent AT37,AT38 and AT39 were applid,the migration and transformation ability of Zn was changed from strong vitality to low activity.The Mobility of N i was the lowest when the amount of passivation agent was increased to 64g/kg,and which was not obvious with the increase of the amount of the passivation agent.