Effect of carbonation on leaching behavior, engineering properties and microstructure of cement-stabilized lead-contaminated soils

Cement stabilization/solidification (s/s) is a widely used remediation technology for lead-contaminated sites. However, the physical and chemical transformations caused by carbonation may affect the long-term effectiveness of s/s. This work presents the effect of carbonation on the performance of cement-stabilized lead-contaminated soils. Artificially contaminated soils with different lead contents were stabilized using cement, and a series of semi-dynamic leaching tests, unconfined compressive tests and microstructure tests were performed on carbonated and non-carbonated samples. The experimental results showed that carbonation decreased the effective diffusion coefficient and leached concentration of lead, resulting in 16-36% increase in strength, 13-44% increase in secant modulus and 3.5-6.4% reduction in porosity, and lowering pH values in the pore solution from 11-12 to 8-9. Increasing initial lead content from 0.1 to 2.5% resulted in a marked increase in the effective diffusion coefficient of lead. The variations in lead leaching and strength upon carbonation could be well interpreted by the thermogravimetric analysis, X-ray diffraction analysis and scanning electron microscope results. The main leaching mechanism of lead release in cement-stabilized soils was diffusion, for both carbonated and non-carbonated specimens. Cement was very effective in immobilizing lead, and the cement matrix could be performed much better in retaining lead upon carbonation.