Glass recovery and production of manufactured aggregate from MSWI bottom ashes from fluidized bed and grate incineration by means of enhanced treatment.

Enhanced treatment of incineration bottom ashes (IBA) from municipal solid waste incineration can contribute to a circular economy since not only metals can be recovered but also glass for recycling. Moreover, the remaining mineral fraction can be utilized in concrete as manufactured aggregate. To evaluate the effects of an enhanced treatment, three IBAs from fluidized bed combustion (FB-IBAs) and three grate incineration bottom ashes (G-IBAs) were standardly treated in a jig and further processed on a pilot scale, including improved metal recovery and sensor-based glass separation. The removed glass fractions were weighed and their composition was assessed by means of manual sorting. The manufactured aggregate was also sorted manually and its total and leachate contents were determined before and after aging. Results showed general differences between FB-IBAs and G-IBAs. For G-IBAs, higher contents of heavy metals and residual metal pieces were determined, while the share of glass removed was low compared to FB-IBA. The treated mineral fractions from G-IBA contained more mineral agglomerates, whereas FB-IBAs contained more glass. However, the glass-fractions removed from FB-IBAs need further treatment to be accepted in glass recycling. Austrian limit values for utilization in concrete were met by all manufactured aggregates produced from FB-IBA, but only by one from G-IBA. Overall, the enhanced treatment in the study performed well compared to the literature. Nevertheless, further investigations are necessary to improve the recyclability of the recovered glass fractions and to determine the technical suitability of manufactured aggregates produced from IBAs.

The environmental performance of enhanced metal recovery from dry municipal solid waste incineration bottom ash.

This study assesses the environmental performance of the municipal solid waste (MSW) incineration bottom ash (IBA) treatment plant in Hinwil, Switzerland, a large-scale industrial plant, which also serves as a full-scale laboratory for new technologies and aims at an optimal recovery of metals in terms of quantity and quality. Based on new mass-flow data, we perform a life cycle assessment that includes the recovery of iron, stainless steel, aluminium, copper, lead, silver and gold. Fraction-specific modelling allows for investigating the effect of the metal fraction quality on the subsequent secondary metal production as well as examining further metal recycling potentials in the residual IBA. In addition, the implications on the landfill emissions of IBA residues to water were quantified. The impact assessment considered climate change, eco- and human toxicity and abiotic resource depletion as indicators. Results indicate large environmental savings for every impact category, due to primary metal substitution and reduction of long-term emissions from landfills. Metal product substitution contributes between 75% and >99% to these savings in a base scenario (1'000-year time horizon), depending on the impact category. Reductions in landfill emissions become important only when a much longer time horizon was adopted. The metal-based analysis further illustrates that recovering heavy non-ferrous metals - especially copper and gold - leads to large environmental benefits. Compared to the total net savings of energy recovery (215 kg CO2-eq per tonne of treated waste, average Swiss plant), enhanced metal recovery may save up to 140 kg CO2-eq per tonne of treated waste.

Precious metals and rare earth elements in municipal solid waste--sources and fate in a Swiss incineration plant.

In Switzerland many kinds of waste, e.g. paper, metals, electrical and electronic equipment are separately collected and recycled to a large extent. The residual amount of municipal solid waste (MSW) has to be thermally treated before final disposal. Efforts to recover valuable metals from incineration residues have recently increased. However, the resource potential of critical elements in the waste input (sources) and their partitioning into recyclable fractions and residues (fate) is unknown. Therefore, a substance flow analysis (SFA) for 31 elements including precious metals (Au, Ag), platinum metal group elements (Pt, Rh) and rare earth elements (La, Ce, etc.) has been conducted in a solid waste incinerator (SWI) with a state-of-the-art bottom ash treatment according to the Thermo-Re® concept. The SFA allowed the determination of the element partitioning in the SWI, as well as the elemental composition of the MSW by indirect analysis. The results show that the waste-input contains substantial quantities of precious metals, such as 0.4 ± 0.2mg/kg Au and 5.3 ± 0.7 mg/kg Ag. Many of the valuable substances, such as Au and Ag are enriched in specific outputs (e.g. non-ferrous metal fractions) and are therefore recoverable. As the precious metal content in MSW is expected to rise due to its increasing application in complex consumer products, the results of this study are essential for the improvement of resource recovery in the Thermo-Re® process.

Analysis of total copper, cadmium and lead in refuse-derived fuels (RDF): study on analytical errors using synthetic samples.

Components with extraordinarily high analyte contents, for example copper metal from wires or plastics stabilized with heavy metal compounds, are presumed to be a crucial source of errors in refuse-derived fuel (RDF) analysis. In order to study the error generation of those 'analyte carrier components', synthetic samples spiked with defined amounts of carrier materials were mixed, milled in a high speed rotor mill to particle sizes <1 mm, <0.5 mm and <0.2 mm, respectively, and analyzed repeatedly. Copper (Cu) metal and brass were used as Cu carriers, three kinds of polyvinylchloride (PVC) materials as lead (Pb) and cadmium (Cd) carriers, and paper and polyethylene as bulk components. In most cases, samples <0.2 mm delivered good recovery rates (rec), and low or moderate relative standard deviations (rsd), i.e. metallic Cu 87-91% rec, 14-35% rsd, Cd from flexible PVC yellow 90-92% rec, 8-10% rsd and Pb from rigid PVC 92-96% rec, 3-4% rsd. Cu from brass was overestimated (138-150% rec, 13-42% rsd), Cd from flexible PVC grey underestimated (72-75% rec, 4-7% rsd) in <0.2 mm samples. Samples <0.5 mm and <1 mm spiked with Cu or brass produced errors of up to 220% rsd (<0.5 mm) and 370% rsd (<1 mm). In the case of Pb from rigid PVC, poor recoveries (54-75%) were observed in spite of moderate variations (rsd 11-29%). In conclusion, time-consuming milling to <0.2 mm can reduce variation to acceptable levels, even given the presence of analyte carrier materials. Yet, the sources of systematic errors observed (likely segregation effects) remain uncertain.

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

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.