Partitioning of heavy metals in a soil contaminated by slag: A redistribution study

In order to interpret reasonably the partitioning of heavy metals in a cont aminated soil as observed from applying a sequential extraction procedure, information on possible redistribution processes of the metals during the v arious extraction steps is essential. For this purpose, sequential extracti on (extended Tessier procedure) was used to study the chemical partitioning of Ag, Cu, Ni, Pb, and Zn in a soil contaminated either by a slag from coa l firing or by a slag from pyrite roasting. Through additional application of sequential extraction to the pure slags as well as to the uncontaminated soil, it was shown that during the various extraction steps applied to the soil/slag mixtures, substantial redistribution processes of the metals bet ween the slag- and soil particles can occur. In many cases, metals ions rel eased during the extraction dth acid hydroxylamine or acid hydrogen peroxid e are partially readsorbed by solid constituents of the mixture and will th erefore be found in the subsequent fractions extracted. As a result, one ha s to realize that (i) it will be difficult to predict the chemical partitio ning of these metals in contaminated soils by investigating pure slags only , and (ii) information on the partitioning of a metal in a slag contaminate d soil will not necessarily give any relevant information on the form of th is metal in the slag or in the slag/soil mixture, because the redistributio n processes during sequential extraction will not be the same as those occu rring in the soil solution under natural conditions.