Abstract
ABSTRACTMechanochemical 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 CuCl2•2H2O, CrCl3•6H2O, FeCl3 (anhydrous), ZnCl2 and anhydrous CaCl2. 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 CuCl2 as major contributor of WHO2005-TEQ values. Surprisingly, for CuCl2•2H2O 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.
Highlights
Polychlorinated dibenzo-p-dioxins and dibenzo-furans, are highly toxic pollutants and released into the atmosphere from different industrial processes, including municipal solid waste incineration (MSWI) (Cheruiyot et al, 2016)
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 CuCl22H2O, CrCl36H2O, FeCl3, ZnCl2 and anhydrous CaCl2
PCDD/F are ubiquitous in the air due to their stability, persistence, bio-accumulative and lipophilic nature, dioxins are dispersed globally through long range transport mechanism (Wu et al, 2009) and mostly high chlorinated PCDD/F remain in atmosphere, as these are captured by particles (Lee et al, 2016)
Summary
Polychlorinated dibenzo-p-dioxins and dibenzo-furans (dioxins, PCDD/F), are highly toxic pollutants and released into the atmosphere from different industrial processes, including municipal solid waste incineration (MSWI) (Cheruiyot et al, 2016). To avoid environmental pollution and health impacts, feasible and cost- effective pollution control technologies have been adopted vigorously in past few decades. One such example is injection of activated carbon in most MSWIs on a wider scale to adsorb gaseous dioxins (Everaert et al, 2003; Hajizadeh et al, 2011; Kawashima et al, 2011). For. MSWI fly ash is burdened by heavy metals and dioxins; its PCDD/F-load varies with waste composition, combustion conditions, and pollution control techniques used (Weber et al, 2001; Kao et al, 2006; Vehlow, 2015). De novo synthesis assumes chlorination and subsequent oxidation of carbonaceous structures (Stieglitz and Vogg, 1987; Addink and Olie, 1995; Olie et al, 1998)
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