Addition/Correction pubs.acs.org/est
Correction to X‑ray Absorption Spectroscopic Quantification and Speciation Modeling of Sulfate Adsorption on Ferrihydrite Surfaces Chunhao Gu, Zimeng Wang, James D. Kubicki, Xiaoming Wang, and Mengqiang Zhu* Environ. Sci. Technol. 2016, 50, 8067−8076; DOI:10.1021/acs.est.6b00753. We also note that the incorrect FeO − --Na + and FeOH2+--NO3− constants of the sulfate-ferrihydrite model was applied in the demonstration of the MINFIT program2 as the third example. The success of the demonstration does not rely on the correction of the equilibrium constants. However, if readers of that paper3 or MINFIT users want to use or reproduce the sulfate-ferrihydrite model, they are advised to refer to this correction. We apologize for this error and hope that this correction provides a prompt clarification.
W
e regret that a reference error occurred in the selection of the logK0 values of FeO−--Na+ and FeOH2+-− NO3 . We realized that in Fukushi et al.1 for the two outersphere surface complexes, the site-occupancy-based equilibrium constants were actually written using FeO− and FeOH2+, respectively. The molarity-based equilibrium constants were written using FeOH as in most conventional fashion. We referred to wrong constants and consequently the determined equilibrium constants for sulfate inner- and outer-sphere surface complexation were incorrect. We corrected the equilibrium constants for FeO−--Na+ and FeOH2+--NO3− and performed new model calibration (Table 1). The new equilibrium constant LogK0 for (FeO)2SO2
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Table 1. Equilibrium Reactions for the Surface Complexation Model for Sulfate Adsorption on Ferrihydrite (Replaces Table 2 in Gu et al.4)a equilibrium reactions Ferrihydrite (de)protonation and electrolyte adsorption FeOH + H+ ⇌ FeOH2+ FeOH ⇌ FeO− + H+ * FeOH + Na+ ⇌ FeO−--Na+ + H+ * FeOH + H+ + NO3− ⇌ FeOH2+--NO3− Sulfate inner- and outer-sphere surface complexation * 2FeOH + 2H+ + SO42− ⇌ (FeO)2SO2 + 2H2O * FeOH + 2H+ + SO42− ⇌ FeOH2+--HSO4− Aqueous reactions SO42− + H+ ⇌ HSO4− SO42− + Na+ ⇌ NaSO4− H2O ⇌ H+ + OH−
logKθ
ψ0
ψβ
+1 −1 −1 +1
0 0 +1 −1
3.7 −12.1 −7.8 8.2
5.06 −10.74 −6.44 9.56
0
0
15.6
20.70
+1
−1
16.4
17.76
NA NA NA
NA NA NA
1.98 0.88 −13.997
NA NA NA
logK0
REFERENCES
(1) Fukushi, K.; Aoyama, K.; Yang, C.; Kitadai, N.; Nakashima, S. Surface complexation modeling for sulfate adsorption on ferrihydrite consistent with in situ infrared spectroscopic observations. Appl. Geochem. 2013, 36, 92−103. (2) Wang, Z. MINFIT: Simply Use MINEQL+ to Fit Data. http:// minfit.strikingly.com. (3) Xie, X.; Giammar, D. E.; Wang, Z. MINFIT: A spreadsheet-based tool for parameter estimation in an equilibrium speciation software program. Environ. Sci. Technol. 2016, 50 (20), 11112−11120. (4) Gu, C.; Wang, Z.; Kubicki, J. D.; Wang, X.; Zhu, M. X-ray absorption spectroscopic quantification and speciation modeling of sulfate adsorption on ferrihydrite surfaces. Environ. Sci. Technol. 2016, 50 (15), 8067−8076.
a
* denotes the equilibrium reactions that need correction. All other footnotes in the previous table are still applicable.
becomes 15.6 (previously 16.0) and that for FeOH2+--HSO4− becomes 16.4 (previously 19.6). It is reasonable that the correction of FeO−--Na+ and FeOH2+--NO3− equilibrium constants had larger impacts on the equilibrium constant of the outer-sphere FeOH2+--HSO4−. Simulation of the adsorption envelopes and respective fractions of inner- and outer-sphere surface complexes gave similar fits to experimental data compared with the previous model (Figure 2). The new model could also simulate the lack of impact of ionic strength on inner-sphere surface complexes and its suppression on outer-sphere surface complexes. The correction of equilibrium constants does not alter the conclusion of the paper or affect the applicability and robustness of the model. © XXXX American Chemical Society
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DOI: 10.1021/acs.est.7b02036 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
Addition/Correction
Figure 2. Comparison of sulfate adsorption envelopes and surface-complexation modeling results for sulfate adsorption on ferrihydrite at ionic strengths of 0.02, 0.1, or 0.5 M (replaces Figure 4 in Gu et al.4).
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DOI: 10.1021/acs.est.7b02036 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
