Cement-stabilized contaminated soil: Understanding Pb retention with XANES and Raman spectroscopy

Cement-based stabilization is a widespread technique used for the treatment of contaminated soils. Despite its established application, the mechanisms involved in the stabilization of contaminants are not fully understood yet. This work aims to elucidate the fate of a real Pb contaminated soil amended with different binders, by studying Pb local environment prior and after the stabilization process. The study of a complex historically contaminated soil was coupled with the investigation of simplified artificial systems, developed to model Pb local structure in the unknown newly formed hybrid systems of soil and binders. The use of synchrotron-based element-specific X-ray absorption spectroscopy (XAS) permitted to probe the actual transformation of Pb environment in the real contaminated soil after the stabilization process. With the support of the model systems, we can propose as the main mechanism involved in Pb retention in sulfated soil treated with cement, the incorporation and/or adsorption of Pb on calcium silicate hydrates and ettringite.