Thermal treatment of municipal solid waste incineration fly ash in a rotary kiln
Source: BAM, Division Thermochemical Residues Treatment and Resource Recovery
Thermal co-treatment with combustible waste is an environmentally friendly and cost-efficient option to dispose of municipal solid waste incineration (MSWI) fly ash. The aim of this study was to assess pelletisation as a pretreatment for MSWI fly ash. Thus, MSWI fly ash was characterised after sampling, pelletisation and thermal treatment and the transfer of relevant components to secondary fly ash and flue gas was investigated. MSWI fly ash pellets with a water content of about 0.15 kg/kg and a diameter of about 8 mm were produced and treated in a pilot-scale rotary kiln at temperatures between 450 °C and 1050 °C.
The amounts of selected elements in the MSWI fly ash before and after thermal treatment and in the generated secondary fly ash were analysed in order to understand the fate of each element. Additionally, leachable contents of selected elements and the total contents of persistent organic pollutants were determined in the thermally treated MSWI fly ash. The low total content of mercury (0.7 mg/kg) and the low leachate content of lead (<0.36 mg/kg), already at the lowest treatment temperature of 450 °C classified thermally treated MSWI fly ash pellets as nonhazardous waste. However, at least 650 °C were necessary to significantly reduce the toxic equivalency of dioxins and dioxin-like polychlorinated biphenyls. The removal of toxic heavy metals like cadmium and lead is significantly improved between 850 and 1050 °C. This treatment led to the enrichment of e.g. copper (up to 11,000 mg/kg), lead (up to 91,000 mg/kg) and zinc (up to 21,000 mg/kg) and turned secondary fly ash into a potential raw material for metal recovery (e.g. via acidic leaching). Because of the high contents of total dissolved solids observed in the leachate of thermally treated MSWI fly ash pellets, a wet extraction procedure is recommended to enable their safe disposal at non-hazardous waste landfills.
Combined disc pelletisation and thermal treatment of MSWI fly ash
F. Huber, Hannes Herzel, Christian Adam, O. Mallow, D. Blasenbauer, J. Fellner
Waste Management, Volume 73, March 2018, Pages 381-391
BAM Department Materials and the Environment, Division Thermochemical Residues Treatment and Resource Recovery