Impact of Simulated Dry-wet Process on Nickel(Ni)and Lead(Pb)in Stabilization Remediated Soils
Stabilization technology(solidification/stabilization technology)is currently one of the most widely used technologies for the soil remediation of polluted sites.However,heavy metal-contaminated sites are subject to prolonged impacts from complex external environmental factors(such as flooding and drying cycles and leaching)during subsequent utilization after stabilization restoration,which may further lead to alterations in the occurrence state of stabilized heavy metals and their gradual release,posing environmental risks.In this study,typical stabilization remediated soil(SRS)in the Pearl River Delta region was collected,and experiments were designed and conducted to investigate the stability and influencing factors of two heavy metals(Ni and Pb)under simulated flooding and alternating dry-wet conditions.The results revealed that flooding treatments significantly increased the leaching concentrations of heavy metals in SRS.Specifically,the amount of leached Ni after flooding increased 103 times,whereas the effect of flooding on Pb was relatively insignificant.Flooding promotes the transformation of stabilized heavy metals from easily migratable weakly acid-extractable fractions to more stable oxidizable and reducible fractions.After flooding,the weakly acidic-extractable fractions of Ni and Pb decreased by 7.16%and 19.9%,respectively.Flooding affects the stability of heavy metals in SRS by altering the soil pH,Eh,iron-manganese oxides,and DOM.Specifically,the pH and Eh of the soil during flooding decreased,further leading to the reduction of Mn4+and Fe3+in the system and the re-release of heavy metals,coupled with a decrease in the content of amorphous iron oxides.In contrast,dry-wet alternation affects the stability of heavy metals by influencing the dissolution and desorption behavior of hydrolyzed heavy metal compounds.Overall,the effect of dry-wet alternation on the leaching concentration and morphological changes of Ni and Pb in the system were relatively insignificant.Taken together,flooding and dry-wet alternation stresses can alter the stability of heavy metals in the SRS,with the degree of change varying significantly depending on the type of heavy metal and the intensity of external stresses.The leaching concentrations of heavy metals in SRS after simulated stress in this study remained significantly below the relevant standard limits,indicating that the environmental risk of SRS is manageable in the short term.Nevertheless,given the long-term and diverse effects of external environmental factors,effectively extending the supervision chain and conducting regular retrospective evaluations of restored land plots are crucial for achieving the sustainable and safe utilization of contaminated sites.
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