De novo formation of dioxins from milled model fly ash

Mechanochemical treatment reduces the particle size of fly ash and disperses catalytic metals, raising the potential reactivity of fly ash to form and destroy 'dioxins', i.e., polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD + PCDF or PCDD/F). To test this issue, model fly ash (MFA) samples were artificially composed by mixing silica, sodium chloride, and activated carbon, and doping this matrix with five selected catalytic metal chlorides administered as CuCl 2 •2H 2 O, CrCl 3 •6H 2 O, FeCl 3 (anhydrous), ZnCl 2 and anhydrous CaCl 2 . Without additives, these samples were first finely milled for 0 (blank), 1 and 8 h, and the effect on the formation of PCDD/F was investigated during de novo tests. These simulate the conditions prevailing in deposits in the heat-recovery zone of an incinerator, where dioxins are formed and destroyed, and the tests were conducted at the same temperature, reaction time and air flow rate. Metal chlorides produce specific and distinct homologue and isomer patterns. The isomer signatures of 2,3,7,8-PCDD/F, precursor route, and other congeners were recognised and are studied in some detail. Principal component analysis (PCA) was applied to the 2,3,7,8-PCDD/F-congeners, indicating CuCl 2 as major contributor of WHO2005-TEQ values. Surprisingly, for CuCl 2 •2H 2 O the total yield of dioxins reduced drastically with milling. Since this study revealed various unexpected results, as well as experimental limitations, some suggestions for further ongoing work are formulated.

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“…Numerous halogenated compounds, including dioxins and furans successfully are destroyed (Cagnetta et al, 2016, Mubeen et al, 2017.…”

Section: Introductionmentioning

confidence: 99%

PCDD/F Formation in Milled Fly Ash: Metal Chloride Catalysis

Mubeen

Buekens

Cao

et al. 2017

Aerosol Air Qual. Res.

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“…The presence of elements, notably; chlorine, oxygen, and copper is necessary for PCDD/F formation in the De novo synthesis, but contribution of combustion gasses such as CO or CO 2 in the formation of polychlorinated dibenzofuran (PCDF) by this mechanism is remarkably insignificant [1]. Besides the concentration of oxygen, the activity of fly ash also controls the rates of formation of PCDD/F, therefore, since the chlorine in this dioxin synthetic pathway originates from the chloride salt of a transition metal ordinarily found at the surface of fly ash, the contribution of the concentration of chlorine in the combustion gaseous mixture is insignificant [71]. The numerous products generated from the De novo synthesis are in the following order of prominence CBz > CP > PCDFs > PCDDs > dl − PCB [41,83,134].…”

Section: The De Novo Synthesis Of Dioxins and Furansmentioning

confidence: 99%

“…Polychlorinated benzenes are suggested to form by either radical mechanisms or by the combination of chlorine and chlorobenzyl radicals [127]. Eventually, the addition of two chlorobenzyl radicals gives rise to polychlorinated biphenyls, PCBs, which are possible precursors for the formation of PCDFs [71,131]. The De novo mechanism suggests that there are structures similar to the dibenzo-p-dioxins and dibenzofurans in the residual carbon attached to the fly ash [127].…”

Section: The Precursor Synthesis Of Dioxins and Furansmentioning

confidence: 99%

A review of persistent organic pollutants: dioxins, furans, and their associated nitrogenated analogues

et al. 2020

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Dioxins and furans are no doubt the most notorious class of organochlorine toxicants in the environmental system whose adverse effects are detrimental to public health with extreme negative economic impacts. Polychlorinated dibenzop-dioxin and dibenzofurans and dioxin-like compounds such as the polychlorinated biphenyls, carbazoles are in the class of persistent organic pollutants-prioritized under the Stockholm convention as the "dirty dozens", besides being listed as group 1 human carcinogens by the International Agency for Research on Cancer. Because of their recalcitrant nature in the environment, bioaccumulation in lipids of cells of animals and their general toxicities, this family of compounds has received increased scientific interest in pollution and toxicology research. Accumulation of these toxicants in lipids of animals, and human exposure has been traced to animal products such as meat, eggs, milk and fish. Combustion events, industrial and municipal waste incineration practices, open fires and some industrial activities especially those dealing with metallurgy are well-established sources of these environmental contaminants. The critical aspects of dioxins, furans and their analogues; notably their sources their mechanistic formation by precursor initiation, de novo pathways, how they manifest their toxicity by activation of aryl hydrocarbon receptor, detoxification of these chemicals from the environment and the analytical methods used to quantify and detect from environmental sample matrices has been explored in this work. This review also provides an in-depth examination of the toxic characteristic behaviour of dioxins and furans, polycyclic aromatic hydrocarbons as well as the emerging nitrogenated analogues of dioxins such as polychlorinated carbazole, and carbazole itself.

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