Experimental Study On Solidification And Long-term Stability Of Heavy Metal Contaminated Soil In Electroplating Site

Remediation of heavy metal contaminated sites is one of the important environmental concerns in the process of industrialization and urbanization in China,especially in coastal areas.Due to the discharge of electroplating wastewater from electroplating plants,a large number of electroplated contaminated sites have emerged.The solidification and stabilization method is one of the more mature repair technologies for repairing heavy metal contaminated soil,and the choice of curing agent and the long-term stability of heavy metal contaminated solidified soil have also become the main content of many scholars.To this end,this article combined with the heavy metal contaminated soil of the electroplating contaminated site in Ningbo area,selected M-LOCKER curing agent and self-made curing agent(CB curing agent)to carry out the curing test of contaminated soil,and discussed the M-LOCKER cured soil and CB curing agent Environmental safety,strength characteristics,long-term stability and microscopic mechanism of solidified soil.The main contents are as follows:(1)Through the TCLP(toxic leaching test),the effect of the amount of curing agent,the concentration of heavy metal chromium and the curing age on the curing rate of solidified soil was verified.The results show that:(1)A certain amount of MLOCKER curing agent has a certain limit of curing ability.(2)As the amount of curing agent increases,the curing rate of chromium-contaminated cured soil increases significantly.(3)As the age increases,the solidification rate of the MLOCKER solidified soil decreases,while the solidification rate of the self-provision curing agent solidified soil increases with the increase of the age.(4)The maximum curing rate of M-LOCKER cured soil is 96.2%,and the maximum curing rate of CB curing agent cured soil is 94.3%.(5)When using M-LOCKER and CB curing agent to cure natural soil,the curing rate can reach more than 90%.(2)Through the unconfined compressive strength test,the influence law of curing age,curing agent content and heavy metal chromium concentration on the unconfined compressive strength of cured soil was revealed.The results show that:(1)The unconfined compressive strength of M-LOCKER solidified soil and CB solidified solidified soil both increase with the increase of curing age.(2)The unconfined compressive strength of chromium contaminated solidified soil decreases with the increase of heavy metal chromium concentration.(3)The unconfined compressive strength of the M-LOCKER solidified soil decreases with the increase of the amount of the curing agent,so it is necessary to add the M-LOCKER curing agent appropriately rather than choose to add excessively.The unconfined compressive strength of the CB curing agent cured soil increases with the increase of the curing agent content.(4)The strength of CB curing agent cured soil is higher than that of M-LOCKER cured soil.The maximum unconfined compressive strength of M-LOCKER cured soil 28 d is 1.756 MPa,and the maximum value of CB curing agent cured soil 28 d unconfined compressive strength is 4.450 MPa,Both meet the standard strength requirements.(5)When M-LOCKER and CB curing agents cure natural contaminated soil,the maximum 28 d unconfined compressive strength of the cured soil is 1.806 MPa and 4.321 MPa,respectively,which also meet the strength requirements.(3)Through the dynamic load test and SEM(scanning electron microscope test)of TAJ-20 dynamic triaxial apparatus,the long-term stability and microscopic mechanism of chromium-contaminated solidified soil were studied.The results show that:(1)After curing for 90 days,after a long-term dynamic load test,the curing rate and unconfined compressive strength of M-LOCKER solidified soil and CB solidified solidified soil both decreased,but the trend is roughly Same before load.(2)After the dynamic load is applied,the average curing rate of the M-LOCKER solidified soil is 74.1%,which is 1.62% lower than before the dynamic load is applied;the maximum unconfined compressive strength of the M-LOCKER solidified soil is 1.899 MPa,which is a decrease 6.4%.The average curing rate of the CB curing agent cured soil is 83.43%,which is a decrease of 1.44%;the maximum value of its unconfined compressive strength is 4.184 MPa,which is a decrease of1.4%.(3)Under the low dynamic stress,the cumulative plastic strain of the chromiumcontaminated solidified soil accumulates faster at the initial stage of vibration,but tends to be gentle as the number of vibrations increases.(4)The cumulative plastic strain of the solidified soil decreases with the increase of heavy metal chromium concentration,the cumulative plastic strain of the M-LOCKER solidified soil increases with the increase of the curing agent content,and the CB curing agent cured soil with the curing agent content The increase decreases first and then increases.(5)After adding curing agent and with the increase of curing age,the particles of chromium-contaminated solidified soil will become closer,but after a long-term dynamic load,the relationship between the particles decreases and the particles become loose,thus Will lead to a reduction in the solidification rate of solidified soil and unconfined compressive strength.