Zinc recovery from Waste-to-Energy fly ash – A pilot test study. (December 2020)

• Record Type: Journal Article
• Authors: Karlfeldt Fedje, Karin; Andersson, Sven
• Is Part Of: Waste management. Volume 118(2020)
• Page Start: 90
• Page End: 98
• Publication Date: 2020-12
• Subjects: Waste-to-Energy -- Fly ash -- Leaching -- Zinc recovery -- Precipitation; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2020.07.017
• Languages: English
• ISSNs: 0956-053X

Abstract

Graphical abstract: Highlights: Acidic leaching of MSW fly ash using scrubber liquids was studied in pilot scale. 70% of the Zn in fly ash could be recovered though leaching and precipitation. The leached fly ash was re-incinerated in full-scale tests, thereby destroying the dioxins. Abstract: Zinc recovery from MSWI fly ash using acidic leaching and chemical precipitation was studied at pilot scale. The leached fly ash was re-incinerated in order to destroy toxic dioxins. 75–150 kg/h of fly ash from a Swedish Waste-to-Energy plant was mixed with scrubber liquids from the same flue gas treatment system in a continuously stirred vessel. The resulting slurry was dewatered in a vacuum belt filter. Hydroxide precipitation of the produced leachate, at a pH of around 9, followed by filtration of the formed crystals in a membrane filter press produced a filter cake with up to 80 wt% Zn(OH)2 in dry solids, calculated from Zn(tot). Up to 70% of the zinc content in the fly ash could be recovered. Two 4-hour full scale ash re-incineration tests were performed: leached fly ash was mixed with the waste at a ratio corresponding to a situation where all the fly ash was continuously re-incinerated. The tests showed only an 8% mass increase of produced fly ash, which means that most of it ended up in the bottom ash, although some elements could potentially accumulate in the system if all the fly ash was to be continuously re-incinerated. No negative effects were observed on the bottom ash quality, which suggests that a large portion of the toxic fly ash could be transformed into the bottom ash fraction.