| As the urbanization process in China continues to accelerate,environmental issues are deteriorating.Human production activities,such as sewage irrigation,factory relocation,and pesticide and fertilizer abuse,have led to a dramatic increase in the content of heavy metals in the soil,exacerbating damage to the soil structure and threatening human,animal,and plant health.The solidification/stabilization method is an effective approach to remediate heavy metal contaminated sites and is widely applied.Besides,due to the drawbacks of high energy consumption and pollution of cement,alternatives to cement-based binders have gained popularity in research,and industrial wastes can be utilized in the field of contaminated site remediation.This paper is in accordance with the R&D fund project(ALW2020YF13)of the Institute of Environmentally Friendly Materials and Occupational Health,Anhui University of Science and Technology.The geopolymer is prepared with metakaolin,calcium carbide residue,and desulfurization gypsum for the remediation treatment of copper-cadmium-contaminated soil.Via experiments and data analysis,the macroscopic mechanical properties,p H change,freeze-thaw cycle durability,and chloride environment erosion characteristics of heavy metal contaminated soils solidified by metakaolin-based polymer are researched.Therefore,the microscopic properties of the solidified soils are investigated and the dominant results are as follows:(1)The mechanical properties of solidified contaminated soil demonstrate that the strength of solidified soil decreases as the contaminant content increase and increases when the binder is added and the maintenance age is extended.By fitting analysis,two strength prediction models based on age and binder content are obtained.Compared with uncontaminated soil,the breaking strain of copper-contaminated soil increases,the strength and deformation modulus decrease,and the ability to resist plastic deformation deteriorate.The cadmium soil exhibits slightly increased breaking strain,enhanced deformation modulus,heightened compressibility,and brittle damage characteristics.The p H tests reveal that the p H of solidified soil decreases with increasing contaminant content and curing age and rises with increasing binder content.(2)The freeze-thaw tests indicate that the strength of solidified soil decreases as the freeze-thaw action continues.The rate of strength loss and failure strain both rise and then decrease.The strength,failure strain,and deformation modulus are strongly associated.Microscopic tests suggest that the hydrated gel is the predominant factor in the enhancement of mechanical properties and that the contaminants could be solidified and repaired by a combination of chemical precipitation,adsorption,and ion exchange.The freeze-thaw effect contributed to the decrease in the p H of solidified soil.The p H decrease is minor during the first two freeze-thaw cycles and increases significantly with the continuation of the freeze-thaw effect.(3)The chloride salt erosion tests illustrate that the strength of solidified soil reduces at 28 d of immersion and appears to grow when immersed for 60 d.The change in Na Cl concentration reveals a minor impact on the damage pattern of the specimens.The chloride salt erosion tests indicate that the strength of contaminated soil reduces under the immersion of Na Cl solution.The change in solution concentration reveals a significant impact on the strength but no remarkable impact on the failure mode.The specimens appear to peel,crack or even flake under Na Cl immersion,with inferior appearance integrity.The gel within the solidified matrix dissolved under erosion,disrupting the cementitious structure,and the deterioration is aggravated with increasing Na Cl concentration.The microstructural characteristics of the polymer-solidified heavy metal-contaminated soil in the metakaolin base corresponded to the variation in macroscopic mechanical properties.Figure [61] Table [9] Reference [111]... |
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