Inventory of MSWI Fly Ash in Switzerland: Heavy Metal Recovery Potential and Their Properties for Acid Leaching

Abstract

From the year 2021 on, heavy metals from Swiss municipal solid waste incineration (MSWI) fly ash (FA) must be recovered before landfilling. This is predominantly performed by acid leaching. As a basis for the development of defined recovery rates and for the implementation of the recovery process, the authorities and plant operators need information on the geochemical properties of FA. This study provides extended chemical and mineralogical characterization of all FA produced in 29 MSWI plants in Switzerland. Acid neutralizing capacity (ANC) and metallic aluminum (Al0) were additionally analyzed to estimate the effort for acid leaching. Results show that all FA samples are composed of similar constituents, but their content varies due to differences in waste input and incineration conditions. Based on their geochemical properties, the ashes could be divided into four types describing the leachability: very good (6 FA), good (10 FA), moderate (5 FA), and poor leaching potential (8 FA). Due to the large differences it is suggested that the required recovery rates are adjusted to the leaching potential. The quantity of heavy metals recoverable by acid leaching was estimated to be 2420 t/y Zn, 530 t/y Pb, 66 t/y Cu and 22 t/y Cd.

Optimization of Metal Recovery from MSWI Fly Ash by Acid Leaching: Findings from Laboratory- and Industrial-Scale Experiments

“…Table 1 summarizes the mean value of the FA composition over the entire project duration and indicates the standard deviation for each element concentration. Compared to the average heavy metal concentrations of Swiss fly ash [2], the FA treated at MSWI plant Linth shows elevated Zn (52,593 mg/kg), Pb (9378 mg/kg), Cu (2671 mg/kg) and Cd (332 mg/kg) concentrations.…”

“…The time-resolved monitoring of the process conditions in reactor 3 have shown that in a continuous process, the L/S-ratio significantly influences process stability (Figure 3). This is by enhancing or diminishing the effects of naturally occurring fluctuations in both FA and acid scrub water compositions [2]. The FA as well as the scrub water composition depend strongly on the waste input as well as the type and condition of the flue gas cleaning system or dust removal system.…”

“…Due to the incineration of heavy metal bearing objects (e.g., electronics or batteries) contained in the waste, the FA is highly enriched in heavy metals. Swiss FA contain up to 6.6 wt.% Zn, 1.9 wt.% Pb, 0.6 wt.% Cu, and 0.05 wt.% Cd [2], and such elevated heavy metal concentrations have been observed in ashes from other countries [3]. Thus, FA comprises a large potential for recyclable metals where mainly the elements Zn, Pb, Cu, and Cd are of interest.…”

Status of Coal-Based Thermal Power Plants, Coal Fly Ash Production, Utilization in India and Their Emerging Applications

“…In addition, SiNPs were also synthesized by chemical method. The purity of the synthesized silica nanoparticles [90] was 88%-96% [91]. The synthesized iron oxide nanoparticles were mainly magnetite, maghemite, and hematite by chemical approaches whose purity was 85%-92% [92].…”

Special Issue on “Advanced Technology of Waste Treatment”

“…Therefore, Ekanthalu et al [15] applied hydrothermal carbonization (HTC) to produce energy-rich hydrochar products and to enable phosphorous recovery. Based on an inventory of MSW incineration fly ash in Switzerland by Zucha et al [16], Weibel et al [17] studied metal recovery from these materials by acid leaching, whereas Wolffers et al [18] investigated co-leaching of MSW incineration fly ash and waste wood fly ash. These leaching processes yield aqueous solutions which are used by Hettenkofer et al [19] for copper recovery using polymer-assisted ultrafiltration.…”