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.
Highlights
Secondary copper recovery is attracting increasing interest because of the growth of copper containing waste including e-waste
The dioxin concentration is normally expressed as toxic equivalency (TEQ) values, where each congener with dioxin-like toxicity has been assigned a toxic equivalency factor (TEF) defined by World Health Organization expert group[3]
The prevalence of PCDFs respect to PCDDs is common in the de novo pathway
Summary
After 4 h milling, which resulted in 76% pollutants destruction, the dioxins concentration increased in the experiment of 6 h compared to 4 h and further decreased at 8 h and longer milling time (Fig. 2a). Here the availability changes over time and, with increased mixing/milling with CaO and SiO2, copper compounds get entrapped into the inorganic matrix due to aggregation/agglomeration of FA particles. They are inactivated over time and cannot explicate their catalytic function. Compound (ng kg−1) 2,3,7,8-TCDD 1,2,3,7,8-PeCDD 1,2,3,4,7,8-HxCDD 1,2,3,6,7,8-HxCDD 1,2,3,7,8,9-HxCDD 1,2,3,4,6,7,8-HpCDD OCDD 2,3,7,8-TCDF 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,7,8,9-HxCDF 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF 3,3′ ,4,4′ -TeCB 3,4,4′ ,5-TeCB 3,3'4,4′ ,5-PeCB 3,3′ ,4,4′ ,5,5′ -HxCB 2,3,3′ ,4,4′ -PeCB 2,3,4,4′ ,5-PeCB 2,3′ ,4,4′ ,5-PeCB 2′ ,3,4,4′ ,5-PeCB 2,3,3′ ,4,4′ ,5-HxCB 2,3,3′ ,4,4′ ,5′ -HxCB 2,3′ ,4,4′ ,5,5′ -HxCB 2,3,3′ ,4,4′ ,5,5′ -HpCB Total Dioxins PeCBz HxCBz
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