Zinc Isotope Variability in Three Coal-Fired Power Plants: A Predictive Model for Determining Isotopic Fractionation during Combustion

Abstract

20The aim of this paper is to assess the Zn isotopic variabilty in feed materials and in 21 combustion by-products collected from three different coal-fired power plants and to 22 develop a generalized model that accounts for the Zn isotopic fractionation occuring 23 during coal combustion processes. Partitioning of Zn between combustion residues and 24 the isotopic composition of feed materials and by-products were determined to 25 furthermore calculate the isotopic signature of gaseous stack emissions using mass 26 balances. We show that the  66 Zn signature of the fly ash samples produced from coal 27 combustion plants can be explained by a Rayleigh fractionation model and propose that 28 the enrichment of heavy isotopes in fly ash is due to condensation in an open system. 29Rayleigh isotope fractionation models using α coal-fly ash of 1.0003 and 1.0007 account for 30 the observed isotope signatures in fly ash. The isotopic signatures of Zn in the coals 31 (δ 66 Zn IRMM ranging between +0.73 and +1.18‰) fall within the previously determined 32 isotope range for peat (+0.6 -+2.0‰). The Zn isotopes in the by-products (bottom ash 33 and fly ash) are highly fractionated relatively to the Zn ratios found in coals, reaching 34 δ 66 Zn IRMM values up to +1.66‰ in the fly ash due to the preferential condensation of the 35 heavy isotopes in the electrostatic precipitators. The bottom ash collected in these power 36 plants, however, display lower δ 66 Zn IRMM (ranging between +0.26‰ and +0.64‰). The 37 observed direction and magnitude of isotope fractionation in this study suggest that Zn 38 fractionation patterns follow the same pattern in coal-fired power plants but the isotope 39 signatures of the by-products depend on those of the fuels. Our model to predict the 40 δ 66 Zn of the flue gas suggests that the isotopic composition of the flue gas becomes 41 more enriched in the lighter isotopes when more Zn is retained in the fly ash and the 42 fraction of Zn remaining in the bottom ash decreases. Since the percentages of Zn in the 43 gas stack of the coal-fired power plants studied here are lower than 10% of the total Zn 44 3 that is evaporated, we predict that 66 δZn IRMM of the flue gas emitted through the stack 45 will be isotopically light and below -0.5‰. The relation between Zn isotopic 46 fractionation and the evaporation/condensation processes clearly demonstrates the 47 potential of Zn isotopes for tracing environmental pollution. Based on our Zn isotope 48 analysis in combination with previous published data for antropogenic materials, we 49 suggest that Zn isotopes are a powerful tool to discriminate the sources of Zn in the 50 atmosphere. 51 52

New Insights from Zinc and Copper Isotopic Compositions into the Sources of Atmospheric Particulate Matter from Two Major European Cities

“…The influence of emissions from metallurgy for Zn is supported by (i) the lack 332 of correlation between  66 Zn IRMM and the EF Sb (Figure 2b), and between the EF Zn , EF Sb and 333 EF Fe ( Figure 3); (ii) the high variability in the  66 Zn IRMM at the low and high traffic sites, and 334 the similarity in the EF Cd and EF Zn in both sites ( Figure 1a and Table 1); and (iii) the known 335 light isotope signature of Zn in PM emitted from metallurgical and coal combustion 336 processes. [15][16][17] Significant contribution from brake wear to Cu enrichment in PM 10 is 337 supported by (i) the correlation between the EF Cu , EF Fe and EF Sb , which are typical tracers of 338 brake wear (Figure 3), and (ii) the Cu/Sb ratios in the PM 10 (Table 1) which are close to the 339 Cu/Sb ratios previously reported for brake wear particles. 47,54 340 In London, we propose that Zn and Cu in PM 2.5-80 are dominated by non-exhaust 341 emissions from road vehicles.…”

“…13,16,17 The Cu/Sb ratios of PM 2.5-80 (Cu/Sb = 19±7) are 348 significantly higher than those typically found in brakes (Cu/Sb = 4.6±2.3) 47,54 and those of 349 With respect to Zn, we constrain the isotope signature of natural sources (wind-blown 365 mineral dust and soil) using values determined for igneous rocks. 11 The anthropogenic 366 signatures include (i) ore concentrates and sphalerite [12][13][14] representing non-exhaust traffic 367 sources (i.e., tire wear, galvanised steel), and (ii) PM collected around smelters and from 368 coal-fired power plants representing PM from high temperature processes.…”

Very low isotope ratio of iron in fine aerosols related to its contribution to the surface ocean

“…On the basis of the results of chemical analysis and Fe speciation presented here, we consider that isotope fractionation must have occurred during evaporation of Fe species at high temperature. Some studies on kinetic isotope fractionation of Zn during evaporation have been conducted [ Mattielli et al ., ; Black et al ., ; Ochoa Gonzalez and Weiss , ]. In particular, Mattielli et al .…”

Tracing of anthropogenic zinc sources in coastal environments using stable isotope composition

“…Previous work suggested that zinc isotopes fractionate during major anthropogenic process such as smelting (Shiel et al, 2010, Weiss et al, 2007, combustion (Matielli et al, 2007, Ochoa andWeiss, 2015) and electroplating (Kavner et al, 2008), generating anthropogenic fingerprints isotopically distinct from natural isotopic compositions (Guegien, 2008;Yin et al, 2016,). High-temperature processes involved during roasting and smelting of ores tend to fractionate zinc isotopes in the gas phase, with an enrichment of the lightest isotopes in air emissions and heavier isotopes in slags and effluents Borok et al, 2010;Ochoa Gonzalez and Weiss, 2015;Ocho Gonzalez et al, 2016;Yin et al, 2016).…”

“…High-temperature processes involved during roasting and smelting of ores tend to fractionate zinc isotopes in the gas phase, with an enrichment of the lightest isotopes in air emissions and heavier isotopes in slags and effluents Borok et al, 2010;Ochoa Gonzalez and Weiss, 2015;Ocho Gonzalez et al, 2016;Yin et al, 2016). In contrast to these anthropogenic high temperature processes, geological high temperature processes including magmatic differentiation seems not produce significant isotopic fractionation resulting in a homogeneous zinc isotopic composition of the bulk Earth (Chen et al, 2013).…”