Formation and potential mechanisms of polychlorinated dibenzo-p-dioxins and dibenzofurans on fly ash from a secondary copper smelting process

Abstract

Secondary copper smelting (SeCu) is widely considered to be an important source of polychlorinated dibenzop-dioxins and dibenzofurans (PCDDs and PCDFs; PCDD/Fs). Laboratory experiments were performed using SeCu fly ash as a matrix for thermochemical reactions to investigate the effects of fly ash on the formation of PCDD/Fs and the potential mechanisms. Thermochemical reactions on SeCu fly ash over a temperature range of 250-450°C and reaction times of 10-120 min caused the PCDD/F concentrations in the fly ash to increase significantly. The PCDD/F concentrations formed in the thermal reactions were about 99-139 times higher than the PCDD/F concentrations in the original fly ash, clearly indicating that fly ash promoted the formation of PCDD/Fs. The PCDFs dominated the PCDDs, and the PCDF/PCDD concentration ratio was about 30-40. Octachlorodibenzofuran ( O C D F ) , o c t a c h l o r o d i b e n z o -p -d i o x i n , a n d t h e heptachlorodibenzofurans were the most dominant homologs that were formed. A comparison of the PCDD/F patterns produced in the thermochemical reactions and the patterns in the original fly ash suggested that the chlorination of less chlorinated PCDFs might be an important pathway in the formation of higher chlorinated furans. The results of this study indicated that SeCu fly ash has a high PCDD/F formation potential. It is crucial to have the fly ash filter at low temperature and that fly ash in the cooling system should be minimized.

Thermochemical Formation of Polybrominated Dibenzo-p-Dioxins and Dibenzofurans Mediated by Secondary Copper Smelter Fly Ash, and Implications for Emission Reduction

“…21,22 The fly ash had a bromine content of 0.3%, determined using a scanning electron microscope with energy dispersive X-ray analysis. 22 The porosity and specific surface area of the fly ash were determined using a Brunauer− Emmett−Teller analytical system. 22 The specific surface area of the SCu fly ash was 3.5 m 2 g −1 (Supporting Information (SI) Table S3).…”

Concentrations and patterns of polychlorinated biphenyls at different process stages of cement kilns co-processing waste incinerator fly ash

“…We previously found very similar results for PCDD/Fs and PCNs (Liu et al, , 2016. Solid residues, such as fly ash, deposited in industrial thermal facilities can catalyze the formation of unintentionally produced POPs to a maximum extent of two orders of magnitudes (Jiang et al, 2015a,b;Wang et al, 2015). Therefore, long-term accumulation of solid particles in the cement kiln 1 system, especially at the cyclone preheater outlet, suspension preheater boiler, humidifier tower, and back-end bag filter, might be an important contributor to the higher concentrations of PCBs at these sites in cement kiln 1 than in kiln 2.…”

Formation of Polychlorinated Biphenyls on Secondary Copper Production Fly Ash: Mechanistic Aspects and Correlation to Other Persistent Organic Pollutants

“…The formation of PCBs and other chlorinated organic chemicals is likely favoured by the presence of carbon, chlorine, and transition metals such as Cu on the surface of fly ash 26 27 28 29 . High concentrations of carbon, chlorine, oxygen, and transition metals especially for Cu on the prepared fly ash surface have been determined in the published work 30 31 . The surface properties of the fly ash used in this study were determined in the published work 30 31 and the fly ash was found to have a high surface area that would allow relatively large quantities of POPs to be adsorbed.…”

“…High concentrations of carbon, chlorine, oxygen, and transition metals especially for Cu on the prepared fly ash surface have been determined in the published work 30 31 . The surface properties of the fly ash used in this study were determined in the published work 30 31 and the fly ash was found to have a high surface area that would allow relatively large quantities of POPs to be adsorbed. The cooling zone of an incinerator or a smelter comes before the filter bag or other air pollution control devices, and is the main formation zone of dioxins and dioxin-like compounds because the temperature is favourable for formation of these compounds.…”

“…In addition to PCBs, unintentionally produced POPs include PCDDs, PCDFs and PCNs, which have similar structures and physicochemical properties to PCBs. We have investigated the production of PCDDs, PCDFs, and PCNs using simulations that are described in previous studies 30 31 . Correlation analyses were performed between the total concentrations and contributions of the different homologue groups of these POPs, and used to attempt to identify mechanisms of formation for PCBs and other POPs.…”