Effect of carbonation on leaching properties of cement stabilized/solidified lead contaminated soil

This study explores the effect of carbonation on leaching properties of cement stabilized/solidified lead contaminated soil using the semi-dynamic leaching tests. Artificially contaminated soils with three different lead contents are solidified with different amounts of cement. The solidified samples are curing under the standard conditions for 28 days, and part samples are selected to conduct accelerated carbonation tests, while the residual samples continued to cure. The environmental safety of cement stabilized/solidified lead contaminated soils are assessed; and the leaching mechanism of lead is discussed using the diffusion coefficient of lead and leaching index of solidified/stabilized lead contaminated soils. The results indicate that the rate of lead leaching decreases with increasing the leaching time. The results also show that a linear function adapts approximately the cumulative amount of lead leaching with square root of leaching time. The cumulative amount of lead leaching of the carbonated samples are 0.68 to 0.91 times that of the standard curing samples, indicating that lead is solidified/stabilized with carbonation. The diffusion coefficient of lead of solidified/stabilized soils ranges between 2.12x10(-12) cm(2)/s and 1.39x10(-9) cm(2)/s, and the leaching index changes from 8.86 to 11.7. The carbonation curing results in a decease in diffusion coefficient of lead and a slight increase in leaching index. The leaching mechanism of lead from the solidified/stabilized soils with low lead concentration is controlled by surface wash-off. However, the leaching mechanism of lead from the solidified/stabilized soils with high lead concentration is a combined result of surface wash-off and diffusion, and the diffusion controls the process.