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. 2016 Mar 15:6:22925.
doi: 10.1038/srep22925.

Dioxins reformation and destruction in secondary copper smelting fly ash under ball milling

Giovanni Cagnetta  1 , Mohammed Mansour Hassan  1 , Jun Huang  1 , Gang Yu  1 , Roland Weber  1   2
Affiliations

Dioxins reformation and destruction in secondary copper smelting fly ash under ball milling

Giovanni Cagnetta et al. Sci Rep. .

Abstract

Secondary copper recovery is attracting increasing interest because of the growth of copper containing waste including e-waste. The pyrometallurgical treatment in smelters is widely utilized, but it is known to produce waste fluxes containing a number of toxic pollutants due to the large amount of copper involved, which catalyses the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans ("dioxins"). Dioxins are generated in secondary copper smelters on fly ash as their major source, resulting in highly contaminated residues. In order to assess the toxicity of this waste, an analysis of dioxin-like compounds was carried out. High levels were detected (79,090 ng TEQ kg(-1)) in the ash, above the Basel Convention low POPs content (15,000 ng TEQ kg(-1)) highlighting the hazardousness of this waste. Experimental tests of high energy ball milling with calcium oxide and silica were executed to assess its effectiveness to detoxify such fly ash. Mechanochemical treatment obtained 76% dioxins reduction in 4 h, but longer milling time induced a partial de novo formation of dioxins catalysed by copper. Nevertheless, after 12 h treatment the dioxin content was substantially decreased (85% reduction) and the copper, thanks to the phenomena of incorporation and amorphization that occur during milling, was almost inactivated.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1
Figure 1. Dioxins destruction percentages after 4 h ball milling with different co-milling reagent mixtures.
Figure 2
Figure 2
MC destruction of dioxins (a) and chlorobenzenes (b) with CaO:SiO2 = 4:1 as co-milling reagent.
Figure 3
Figure 3
Numerical solution for differential equations system (6), showing trends of: total dioxins with experimental points, their components (i.e. Dioxins(1) and Dioxins(2)), and their degradation products P (a); reagents (i.e. CaO and its activated form CaO*), and catalyst (i.e. copper compounds Cu) (b).
Figure 4
Figure 4. Hypothesized MC destruction pathways of PCDD/Fs and dl-PCBs, their reformation, and catalyst deactivation.
See this image and copyright information in PMC

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