Effects and Mechanisms of In-situ Cement Solidification/Stabilization on a Pb-, Zn-, and Cd-Contaminated Site at Baiyin, China

Abstract

In order to evaluate the effects and mechanism of in-situ cement solidification/stabilization (S/S) on heavy metal contaminated soils, leaching tests, speciation analysis, and microscopic analysis were conducted after cement treatment of a Pb, Zn, and Cd contaminated site in Baiyin, China. The leaching test results showed that cement could effectively stabilize Cd and Zn, which could reduce 99.5%-100% and 96.6%-98.8% of H2SO4-HNO3 extractable Cd and Zn, respectively. However, the leaching concentration of Pb was 2.6-5.8 times higher than that before 5% cement treatment. After adding 8% cement, H2SO4-HNO3 extractable Cd and Zn were reduced by 99.6%-100% and 94.4%-97.9% respectively. Similarly, the leaching concentration of Pb was 1.9-12.5 times higher than that before 8% cement treatment. The results of sequential extraction test proposed by the European Community Bureau of Reference (BCR) showed that cement could transform acid extractable Cd and Zn to residual form and transform reducible fractions of Pb to oxidizable and residual form, increasing the stability of heavy metals in soil. The microscopic analysis results showed that Pb2+, Zn2+, and Cd2+ could participate in the process of cement hydration and form silicate minerals and hydroxides. In conclusion, cement could be an effective S/S agent to remediate heavy metal contaminated soils, and site characteristics and environmental conditions should also be considered during the construction process.