Mechanical properties and microstructural behavior of reactive MgO carbonated Pb-contaminated red clay

Abstract

The presence of heavy metals in soil negatively impacts its mechanical properties. Reactive MgO carbonation presents a promising approach to enhance the solidification of Pb-contaminated sandy soils. However, the mechanical properties and structural behavior of contaminated soils during carbonation can vary significantly due to differences in soil composition. This study examines the potential application and underlying mechanisms of reactive MgO carbonation in improving the mechanical properties of Pb-contaminated red clay. The findings demonstrate that Pb-contaminated red clay transitions from a plastic to a brittle state following reactive MgO carbonation. After 1 h of treatment, the strength of the red clay exceeded 3 MPa, even at high Pb2⁺ concentrations. The deformation modulus to unconfined compressive strength (UCS) ratio was calculated to be 37.761, with the failure strain primarily ranging from 1.5% to 4.0%. A strength prediction model for the reactive MgO-stabilized Pb-contaminated red clay was proposed, which showed good predictive accuracy. Furthermore, reactive MgO carbonation significantly reduced the Pb leaching concentration in the high-level Pb-contaminated soil to below 0.1 mg/L. Microscopic analysis revealed that an optimal amount of hydrated magnesium carbonates (HMCs) formed a stable and compact structure with the soil particles. However, long-term carbonation causes red clay particles to become sandy, and excessive HMCs can harm the soil structure. Therefore, to maximize the strength improvement while avoiding structural damage, the carbonation time should be controlled to 1 h.

Keywords

• Reactive MgO
• CO2 carbonation
• Pb-contaminated red clay
• Mechanical properties
• Soil structure