Leaching properties of cement-solidified lead-contaminated clay via semi-dynamic leaching tests

The leaching characteristics of cement solidified/stabilized Pb-contaminated kaolin under different pH of leachant are investigated via a series of semi-dynamic leaching tests as well as quantitative evaluation of the effectiveness of solidification/stabilization treatment in remediating Pb-contaminated kaolin. The designed initial pH of leachant is 2, 4, and 7. The results show that the accumulated leached Pb mass at leachant pH of 2 is 47 to 106 times that at leachant pH of 4 and 7. Nevertheless, the difference of the accumulated leached Pb mass between leachant pH of 4 and 7 is marginal. When cement content increases from 12% to 18%, accumulated leached Pb mass decreases by 28% to 68%, indicating that the increasing cement content will enhance the immobilization of Pb. The diffusion coefficient (D_e) of Pb is back-calculated by conducting a theoretical analysis of the relationship between the leaching time and the leached mass ratio. It is found that the values of D_e of Pb at leachant pH of 4 and 7 are very close; and those of Pb at leachant pH of 2 are 3 or 4 orders of magnitude greater than those at the leachant pH of 4 or 7. In addition, an increase of the cement content from 12% to 18% results in a decrease of D_e by 17% to 99%. The present results indicate that the strong acidic leachant (pH<4) and the increase in cement content have significant influence on the leached mass as well as diffusion coefficient of Pb for the cement-stabilized soils.