CASE STUDY ON ENHANCED LANDFILL MINING AT MONT-SAINT-GUIBERT LANDFILL IN BELGIUM: MECHANICAL PROCESSING, PHYSICO-CHEMICAL AND MINERALOGICAL CHARACTERIZATION OF FINE FRACTIONS <4.5 MM

Abstract

Fine fractions obtained by mechanical processing of excavated waste constitute a challenge for (enhanced) landfill mining projects. These fractions are mainly composed of humified organic and weathered inorganic compounds, whereas metals and calorific fractions are depleted. In this study we present data on the chemical composition and grain size distribution of the fine fractions <4.5 mm, as well as on the mineralogical composition of the two finest subfractions (0.18 to 0.5 mm and <0.18 mm). Chemical analyses indicate no trend regarding the enrichment or depletion of heavy metals in the different particle size ranges. Leaching from the finer fractions is somewhat higher than from the coarser fractions (i.e. 1.6 to 4.5 mm and 0.5 to 1.6 mm), although the fraction 0.18 to 0.5 mm shows the lowest overall leaching. Pseudo-total contents of Cu, Zn, Cd, Hg and Pb and leachable contents of Ni exceed Austrian limit values for the production of soil substitutes from wastes. Electron microprobe analyses indicate that Zn and Pb, which exceed limit values for pseudo-total content, are present as Fe-Zn alloy, ZnS and ZnSO4, and metallic Pb and Pb-Ca phosphate, respectively. In summary, dry-mechanical processing, which is a feasible method in the particle size range >4.5 mm, showed a limited effect in the range <4.5 mm. Removal of Pb- and Zn-containing phases is highly challenging due to the diverse mineralogy and fine grain size of few µm. Consequently, it seems unlikely that the Austrian limit values for soil substitutes can be met.