Experimental estimation of the bisulfite isomer quotient as a function of temperature: Implications for sulfur isotope fractionations in aqueous sulfite solutions

Journal Article · Mon Oct 16 00:00:00 EDT 2017 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/j.gca.2017.10.005· OSTI ID:1480783

Eldridge, Daniel L. ^[1]; Mysen, Bjorn O. ^[1]; Cody, George D. ^[1]

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1. Carnegie Inst. of Washington, Washington, D.C. (United States)

Bisulfite (HSO₃^-) and sulfite (SO₃^2-) compounds play key roles in numerous geochemical and biochemical processes extending from the atmosphere to the subseafloor biosphere. Despite decades of spectroscopic investigations, the molecular composition of HSO₃^- in solution remains uncertain and, thus, the role of bisulfite in (bio)chemical and isotope fractionation processes is unclear. We report new experimental estimates for the bisulfite isomer quotient (Qi= [(HO)SO₂^-]/[(HS)O3-]; [] = concentration) as a function of temperature from the interpretation of Raman spectra collected from aqueous NaHSO₃ solutions contained in fused silica capsules. In pure NaHSO₃ solutions (1Na⁺:1HSO₃^-, stoichiometric) over [NaHSO₃] = 0.2–0.4 m (moles/kg H₂O), the following relationship is obtained: ln(Q_i)=[formula omitted]-1.9642(±0.1081),where T = 278–358 K (5–85 °C) (based on 50 determinations; additional significant figures are provided to avoid rounding errors). This relationship suggests that the minor isomer, (HS)O₃^-, may comprise 23–38% (±3%) of the mole fraction of HSO₃^- over 5–85 °C, respectively, which is higher in relative abundance than has generally been understood previously. We additionally provide estimates for Q_i in NaHSO₃ solutions containing a total ionic strength of µ = 1.0 m (0.2 m NaHSO₃+ 0.8 m NaCl) and different pH (3.3–4.5), but do not appear to resolve any significant differences in Q_i as a function of these additional variables. These new values of Q_i are employed to re-assess the bulk sulfur isotope fractionations among bisulfite and other S(IV) compounds as a function of temperature, which appear to be highly dependent on the amount of (HS)O₃^- present. Our new constraints on the bisulfite isomer quotient may allow for a detailed assessment of the molecular composition and isotope mass balance of S(IV) solutions containing HSO₃^-, and may be useful in the further investigation of the mechanisms and isotope fractionations associated with a number of processes that involve bisulfite compounds. Furthermore, these may include the intracellular enzymatic transformations of sulfite and bisulfite compounds that occur as part of dissimilatory sulfate reduction, which is a major and geologically important form of anaerobic respiration.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1480783
• Journal Information: Geochimica et Cosmochimica Acta, Vol. 220, Issue C; ISSN 0016-7037
• Publisher: The Geochemical Society; The Meteoritical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Sulfite
Bisulfite
Raman spectroscopy
Isotope effects
Dissimilatory sulfate reduction