The oxidation of sulfur(iv) by reaction with iron(iii): a critical review and data analysis

Abstract

The dependences on ionic strength of the hydrolysis constants of Fe and of the first dissociation constant of sulfurous acid are briefly reviewed. The data are needed to derive from apparent stability constants reported in the literature the stability constants for the three iron-sulfito complexes defined by the equilibria (c1) FeOH + HSO = FeSO + HO, (c2) FeSO + HSO = Fe(SO) + H, (c3a) Fe(SO) + HSO = Fe(SO)H, where K = 1982 ± 518 dm mol, K = 0.72 ± 0.08, K = 189 ± 9 dm mol (ionic strength μ = 0.1 mol dm). The rapid formation of these complexes is followed by a slower decomposition leading to the formation of SO radicals; the associated rate coefficients are k = 0.19 s, k ≈ 0.04 s, and k ≈ 0.08 s, respectively. The subsequent reaction leads to dithionate and sulfate as products. Overall rates and product yields from a variety of studies of the slow reaction are found to be consistent with a mechanism, in which the production of dithionate occurs mainly by the reaction of SO with FeSO and that of sulfate by the reaction of SO with FeOH and/or Fe. The role of copper as a catalyst is also analyzed. Rate coefficients for individual reactions are estimated from the data at low pH (μ = 1.0 mol dm) under conditions where the 1 : 1-complex is prevalent. They are extrapolated to lower ionic strengths for an analysis of the data obtained at higher pH to explore conditions when reactions of the higher complexes become important. The overall rate and the product yields of the reaction depend critically on the pH, the initial ratio of S(iv) to Fe(iii) and the ionic strength of the solution.

Relative humidity and O<sub>3</sub> concentration as two prerequisites for sulfate formation

“…The kinetics and mechanisms of the formation of sulfate, a major component of SNA, are complex and remain unclear (Ervens, 2015;Harris et al, 2013;Warneck, 2018). For example, two key questions concerning sulfate forma-tion are (1) exactly how various parameters (oxidants, catalysts, meteorological conditions, etc.)…”

“…According to laboratory-based Raman spectroscopy studies, sulfate can be produced via the aqueous oxidation of SO 2 by NO 2 + O 2 , with an SO 2 reactive uptake coefficient of 10 −5 , which represents an atmospherically relevant value (Yu et al, 2018), whereas others have suggested that this route is of minor importance in the atmosphere (Li et al, 2018;Zhao et al, 2018). In addition, Xie et al (2015) proposed that NO 2 could enhance the formation of sulfate in certain cases, for example, in biomass burning plumes or dust storms (He et al, 2014). Evaluation of the contribution of TMIs + O 2 reactions appears to be more complex since it depends on aerosol acidity, solubility, oxidation state, and the synergistic effects of different TMIs (Deguillaume et al, 2005;Warneck, 2018).…”

“…In addition, Xie et al (2015) proposed that NO 2 could enhance the formation of sulfate in certain cases, for example, in biomass burning plumes or dust storms (He et al, 2014). Evaluation of the contribution of TMIs + O 2 reactions appears to be more complex since it depends on aerosol acidity, solubility, oxidation state, and the synergistic effects of different TMIs (Deguillaume et al, 2005;Warneck, 2018).…”

Acid strength dependent behaviour of Gd(III) ions in aqueous medium and its effect on Gd(III) separation from aqueous phase

“…The magnitude of electrolyte effect not only depends on the concentration of the electrolytes but is also highly dependent on the charges of the participants in any ionic equilibrium. So the effect of added electrolyte on any ionic equilibrium strongly depends on a property of the solution called ionic strength which takes into account of both charge and concentration of the existing ionic species in solution [9][10][11]. Also, it is a well-established fact that relationship between solution ionic strength and solubility of electrolyte is the key factor that dominates various processes in biochemical reactions, industrial and environmental chemistry.…”

RH and O<sub>3</sub> concentration as two prerequisites for sulfate formation

“…the formation of sulfate in certain cases, for example, in biomass burning plumes or dust storms (He et al, 2014). Evaluation of the contribution of TMI + O2 reactions appears to be more complex since it depends on aerosol acidity, solubility, oxidation state, and the synergistic effects of different TMIs (Deguillaume et al, 2005;Warneck, 2018).…”