A sequential extraction procedure according to Tessier et al. is carried out to compare the distribution of six metals (Cd, Cr, Cu, Ni, Pb and Zn) in contaminated clay soils before and after extractive cleaning. Extraction of metals from the ‘soil fractions’ with 0.1 N HC1 or 0.1 M EDTA becomes more difficult in the order: ‘Carbonate’ <‘Fe/Mn-Oxides’ <‘Organic/Sulfidic’ <‘Residual’ Extraction from the ‘residual’ fraction in particular is much harder than from the other three: 50% of the experiments shows a metal extraction efficiency less than 33% from this ‘soil fraction’. Removing the remaining pollution will be difficult without drastic destruction of soil components.
Tuin, B. J. W., & Tels, M. (1990). Distribution of six heavy metals in contaminated clay soils before and after extractive cleaning. Environmental Technology, 11(10), 935-948. https://doi.org/10.1080/09593339009384946