Hg2+ reduction and re-emission from simulated wet flue gas desulfurization liquors

“…7,13 In an excess of sulphite ions, the formation of stable complexes such as Hg(SO 3 ) 2 2-or Hg(OH) 2 could have prevented Hg 0 re-emission during the first 120 minutes through Eq. 2 and 5.…”

Section: K 40ºcmentioning

confidence: 99%

“…10 Under conditions where Hg(SO 3 ) 2 2-predominated, the rate of reduction of the mercuric ion to Hg 0 via coordinated sulphite showed an inverse dependence with the concentration of uncoordinated sulphite, whereas it was unaffected by the amount of sulphite liberated by dissociation. In addition to the influence of sulphur species, the kinetics of mercury reduction reactions in the scrubber are affected 13,15,16 In this paper the stability of Hg 2+ in the absorbing solutions with sulphite ions and different anions was evaluated by analyzing the re-emission of mercury, pH and redox potential simultaneously. The objective of this work was to assess the role of sulphate, nitrate, chloride, fluoride and carbonate anions on the re-emission of mercury.…”

Section: Introductionmentioning

confidence: 99%

Effect of anion concentrations on Hg2+ reduction from simulated desulphurization aqueous solutions

Ochoa-González

Dı́az-Somoano

Martı́nez-Tarazona

2013

Chemical Engineering Journal

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The influence of different anions on the stability of mercury in absorbing solutions containing sulphite ions was investigated. The re-emission of gaseous mercury in the presence of fluoride, chloride, bromide, nitrate, carbonate and sulphate ions from the scrubbing solution was determined. Fluoride, chloride and bromide ions contribute to mercury stabilization, bromide being the most efficient anion for retaining mercury in sulphite aqueous solutions. High carbonate concentrations prevent the reduction of mercury by sulphite ions due to the stabilization of the complexes formed between oxidised mercury, hydroxide and sulphite ions or through the formation of mercury carbonate species. However, nitrate and sulphate ions do not influence the equilibrium between mercury and sulphite ions and, as a consequence, the re-emission of mercury is not modified. The results of this study suggest that the pH is one of the most important parameters for achieving an efficient control of mercury pollution in desulphurization systems. The re-emission of mercury was observed to increase when the pH value of the slurries was higher than 6 due to the stabilization of the mercury in the form of . Since the pH depends on the concentration of SO 2 in the flue gas and the type of limestone, the alkalinity that comes from the sorbent used in the scrubber may play an important role in mercury capture in such systems.

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“…Insoluble Hg 0 passes through WFGD without being captured. Chemical reduction of the dissolved Hg 2+ reduces total mercury removal efficiency in WFGD due to re-volatilization of Hg 0 (Wo et al, 2009;Ochoa-González et al, 2013). Flue gas and slurry composition, operating temperature, limestone injection rate, and slurry pH are the key factors affecting the re-volatilization of Hg 0 (Acuña-Caro et al, 2009;Ochoa-González et al, 2012;Schuetze et al, 2012).…”

Section: Mercury Transformation During Wet Flue Gas Desulfurization (mentioning

confidence: 99%

Mercury transformation and speciation in flue gases from anthropogenic emission sources: a critical review

et al. 2016

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Abstract. Mercury transformation mechanisms and speciation profiles are reviewed for mercury formed in and released from flue gases of coal-fired boilers, non-ferrous metal smelters, cement plants, iron and steel plants, waste incinerators, biomass burning and so on. Mercury in coal, ores, and other raw materials is released to flue gases in the form of Hg 0 during combustion or smelting in boilers, kilns or furnaces. Decreasing temperature from over 800 • C to below 300 • C in flue gases leaving boilers, kilns or furnaces promotes homogeneous and heterogeneous oxidation of Hg 0 to gaseous divalent mercury (Hg 2+ ), with a portion of Hg 2+ adsorbed onto fly ash to form particulate-bound mercury (Hg p ). Halogen is the primary oxidizer for Hg 0 in flue gases, and active components (e.g., TiO 2 , Fe 2 O 3 , etc.) on fly ash promote heterogeneous oxidation and adsorption processes. In addition to mercury removal, mercury transformation also occurs when passing through air pollution control devices (APCDs), affecting the mercury speciation in flue gases. In coal-fired power plants, selective catalytic reduction (SCR) system promotes mercury oxidation by 34-85 %, electrostatic precipitator (ESP) and fabric filter (FF) remove over 99 % of Hg p , and wet flue gas desulfurization system (WFGD) captures 60-95 % of Hg 2+ . In non-ferrous metal smelters, most Hg 0 is converted to Hg 2+ and removed in acid plants (APs). For cement clinker production, mercury cycling and operational conditions promote heterogeneous mercury oxidation and adsorption. The mercury speciation profiles in flue gases emitted to the atmosphere are determined by transformation mechanisms and mercury removal efficiencies by various APCDs. For all the sectors reviewed in this study, Hg p accounts for less than 5 % in flue gases. In China, mercury emission has a higher Hg 0 fraction (66-82 % of total mercury) in flue gases from coal combustion, in contrast to a greater Hg 2+ fraction (29-90 %) from non-ferrous metal smelting, cement and iron and/or steel production. The higher Hg 2+ fractions shown here than previous estimates may imply stronger local environmental impacts than previously thought, caused by mercury emissions in East Asia. Future research should focus on determining mercury speciation in flue gases from iron and steel plants, waste incineration and biomass burning, and on elucidating the mechanisms of mercury oxidation and adsorption in flue gases.

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Hg2+ reduction and re-emission from simulated wet flue gas desulfurization liquors

Cited by 101 publications

References 15 publications

Simultaneous removal of SO2, NO and Hg0 by wet scrubbing using urea + KMnO4 solution

Simultaneous removal of SO2, NO and Hg0 by wet scrubbing using urea + KMnO4 solution

Effect of anion concentrations on Hg2+ reduction from simulated desulphurization aqueous solutions

Mercury transformation and speciation in flue gases from anthropogenic emission sources: a critical review

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