Speciation of heavy metals in extracted soil solutions by a cation exchange batch equilibrium method

Abstract

A new method for the speciation of heavy metals in extracted soil solutions has been developed. The method is based on the forced shift of equilibrium with increasing amounts of cation exchange resin (batch mode), and enables the determination of operationally defined fractions of ‘cationic labile metal species’ in solution. In order to compare different soil solutions, the required amounts of cation exchange resin is refered to the calcium (Ca) concentration of each sample solution. By using a reference solution without complexing agents, this method allows the simultaneous determination of an approximative concentration of free (hydrated) metal ion (Me2+) as well. The method is applied to different extracted soil solutions of polluted Swiss topsoils [using water or 0.01M sodium nitrate (NaNO3) as extracting media].