Mechanical properties and stability of zinc-contaminated red clay cured by MICP synergistically activated MgO

Abstract

Microbially induced carbonate precipitation (MICP) technology offers an innovative approach for the solidification and stabilization of heavy metal-contaminated soils; However, the mechanical strength and long-term stability of this remediation method have not been thoroughly investigated. This study introduces an innovative curing and stabilization technique using MICP-activated MgO to address the geotechnical challenges posed by zinc ion-contaminated soils. To investigate the effect of zinc ions on soil and the optimal efficacy of MICP-activated MgO in curing zinc contamination, experiments were conducted on zinc-contaminated soils with varying zinc ion concentrations (0.05%, 0.1%, 0.5%, 1.0%), dry densities (1.35, 1.4, 1.45, 1.5 g/cm³), and activated MgO admixtures (1%, 2%, 5%, 10%). The effectiveness of MICP-activated MgO was evaluated through macroscopic analysis and stability tests, including unconfined compressive strength tests, direct shear tests, and the Toxicity Characteristic Leaching Procedure (TCLP). The results indicated that zinc ions disrupted soil particle cementation, enlarged inter-particle pores, and significantly reduced both unconfined compressive strength and shear strength. The optimal dosage of MICP-activated MgO for curing zinc-contaminated soil was determined to be 10%, resulting in an unconfined compressive strength of 1.196 MPa and a Zn²⁺ leaching concentration of 0.1414 mg/L. The combined actions of MICP-activated MgO facilitated the formation of alkaline magnesium carbonate, calcium carbonate, and magnesium hydroxide. These compounds filled the inter-particle pores of zinc-contaminated soil, encapsulating and co-precipitating zinc ions, thereby enhancing the soil's strength and stability. These findings establish a theoretical foundation for the engineering application of MICP-activated MgO in the remediation of zinc-contaminated soils.

Keywords

Microbially induced carbonate precipitation (MICP) / Strength / Curing / Toxicity characteristic leaching procedure

Funding

Project “Research on remediation of typical heavy metal contaminated soil in Henan Province based on EICP technology”. (25200810005) supported by Henan Science and Technology R&D Program Joint Fund. Project “Ion migration and solidification repair mechanism of heavy metal contaminated soil in karst area” (No.KDL＆Guangxi202303) supported by Guangxi Key Science and Technology Innovation Base on Karst Dynamics. Project Evolution law and mechanism of macro and micro characteristics of activated magnesium oxide microbial synergistic solidification of heavy metal contaminated soil” (No. 42262030) supported by the National Natural Science Foundation of China. Project “Research on mechanical properties of fiber-microbe synergistic curing of calcareous sand”. (Guikeyan 2023-XT-02) supported by the open subject of Guangxi Key Laboratory of Geotechnical Mechanics and Engineering.

CRediT authorship contribution statement

Yu Song: Investigation, Funding acquisition. Wei Liu: Writing - review & editing. Qiaqi Li: Funding acquisition, Conceptualization. Yuling Chen: Visualization. Jichun Cheng: Project administration. Jianwei Zhang: Software. Junjie Zheng: Software, Methodology.

Data availability

Not applicable.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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