Metals in RDF and other high calorific value fractions from mechanical treatment of MSW: analysis and sampling errors

Abstract

RDF and other high calorific value fractions derived from MSW by mechanical treatment processes contain goods such as cans, cables, zippers or batteries which are highly concentrated in metals. The objective of this study was to investigate the importance of these metal carriers (i) for total metal loads and (ii) for sampling errors. Six different products derived from MSW were analysed for carrier bound and total loads of Al, Cd, Cr, Cu, Fe, Ni, Pb and Zn. Sophisticated sample preparation procedures were applied in order to quantify the separate analyte loads from metallic carriers. Typical values for total metal contents and shares of carrier bound loads were found as follows: Al, 20 g kg⁻¹ (30%); Cr, 0.4 g kg⁻¹ (50%); Cu, 5 g kg⁻¹ (80%); Fe, 40 g kg⁻¹ (80%); Ni, 0.15 g kg⁻¹ (70%); Pb, 0.4 g kg⁻¹ (40%); and Zn, 2 g kg⁻¹ (30%). NiCd-batteries were found in three materials representing 30–70 % of total Cd contents (total 6–20 mg kg⁻¹). Sampling errors related to the distribution of analyte carriers were in most cases found in the range of 50–150 % relative standard deviation in spite of the large sample masses of 200–800 kg. The results demonstrate: (1) metal carriers are responsible for significant analyte loads; if they are not adequately considered, total metal contents may be severely underestimated; (2) sampling errors are dominated by the distribution of carriers; (3) correct analysis of total metal contents including loads from metallic components requires expensive sample preparation.