The use of model compounds to elucidate metal forms in sewage sludge

Model phases of metal precipitates and organically bound metal were used to corroborate the nature of metal species found in sewage sludge by a sequential chemical extraction scheme. Model phase extractions supported the identification of the major species of Cd and Ni as carbonate (EDTA-extractable), Zn as organically-bound (Na(4)P(2)O(7)-extractable) and Pb as organically-bound or carbonate, although considerable overlap of fractions was apparent. Identification of the major species of Cu as sulphide (HNO(3)-extractable) could not be confirmed. The selectivity and efficiency of certain reagents was found to differ when used in sequence with other reagents, as opposed to being applied individually to model metal phases. Sample preparation was found to influence metal fractionation profiles in a model organic phase.