Contaminant patterns in soils from landfill mining.

Landfill mining is used to close the material loops by recovering recyclables from landfills. Previous research has focused on material composition reporting that, worldwide, landfills mainly consist of soil-like materials ("soils") and combustibles. Although soils have been investigated in a few studies, the results are limited to the presentation of substance concentrations without further analysing the substance patterns (e.g. correlation between substances). This research identifies similarities in substance concentrations within and between landfills, analysing approximately 300 soil samples from eight excavated landfills. Statistical tests enabled the determination of substance variations and correlations. Substance concentration correlations were found between several heavy metals (in particular zinc), sulphate and electrical conductivity, as well as ammonium nitrogen and biodegradability. With regard to contamination prediction, sulphate, pH and total organic carbon proved to be the most efficient indicator elements. Legal limit values have proven to be efficient to manage substance flows in terms of chloride, sulphate, cadmium, lead and zinc, but were ineffective with respect to biodegradability, PCB, benzo[a]pyrene and cyanides.