Abstract
There is a lot of interest in the behavior of Fe(III) in natural waters because of its importance in the productivity of phytoplankton. The hydrolysis of Fe(III) in natural waters limits the solubility of Fe(III) in aqueous solutions. At the present time, reliable hydrolysis constants for Fe(III) are limited to low temperatures (5-50 °C) in NaCl to 5 m. The hydrolysis constants of Fe(III) and Al(III) are linearly related over a wide range of temperatures (0-50 °C) and ionic strengths (0-5 m NaCl). The near linear correlations allow one to make reasonable estimates for the values of Fe(III) from 0 to 300 °C in dilute solutions and from 0 to 100 °C to 5 m in NaCl solutions. In this paper, the stoichiometric (β i) and thermodynamic (κ i hydrolysis constants for Al(III) in NaCl have been fit to equations of the form logβ i - logK i=a 0I 0.5 + a 1I 0.5/T + a 3I + a 4 I / T + a 5I 2 This equation has been used to estimate the hydrolysis constant for Fe(III) in dilute solutions to 300 °C and in NaCl solutions to 5 m and 100 °C. The cause of the correlation in water is due to the differences in the free energies of ΔG 0(A 13+) - ΔG 0 (Al(OH) j (3-j)) being almost equal to the values of ΔG 0 (Fe 3+) - ΔG 0 (Fe(OH) j (3- j)). An examination of the activity coefficients of Fe 3+ and Al 3+ and the complexes show that the correlation at higher ionic strengths is due to the fact that the activity coefficients ratios are similar γ(Fe 3+) / γ(Fe(OH) j (3-j))≅ γ(Al 3+) / γ(Al(OH) j (3-j)) in NaCl solutions. These linear correlations appear to also hold for other trivalent metals (Cr 3+, As 3+). The results of this study should be useful in examining the speciation of Fe(III) in hydrothermal brines.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1818-1823 |
| Number of pages | 6 |
| Journal | Environmental Science and Technology |
| Volume | 43 |
| Issue number | 6 |
| DOIs | |
| State | Published - Mar 15 2009 |
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ASJC Scopus subject areas
- Chemistry(all)
- Environmental Chemistry
Cite this
The hydrolysis of Al(III) in NaCl solutions-a model for Fe(III). / Millero, Frank J; Woosley, Ryan.
In: Environmental Science and Technology, Vol. 43, No. 6, 15.03.2009, p. 1818-1823.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - The hydrolysis of Al(III) in NaCl solutions-a model for Fe(III)
AU - Millero, Frank J
AU - Woosley, Ryan
PY - 2009/3/15
Y1 - 2009/3/15
N2 - There is a lot of interest in the behavior of Fe(III) in natural waters because of its importance in the productivity of phytoplankton. The hydrolysis of Fe(III) in natural waters limits the solubility of Fe(III) in aqueous solutions. At the present time, reliable hydrolysis constants for Fe(III) are limited to low temperatures (5-50 °C) in NaCl to 5 m. The hydrolysis constants of Fe(III) and Al(III) are linearly related over a wide range of temperatures (0-50 °C) and ionic strengths (0-5 m NaCl). The near linear correlations allow one to make reasonable estimates for the values of Fe(III) from 0 to 300 °C in dilute solutions and from 0 to 100 °C to 5 m in NaCl solutions. In this paper, the stoichiometric (β i) and thermodynamic (κ i hydrolysis constants for Al(III) in NaCl have been fit to equations of the form logβ i - logK i=a 0I 0.5 + a 1I 0.5/T + a 3I + a 4 I / T + a 5I 2 This equation has been used to estimate the hydrolysis constant for Fe(III) in dilute solutions to 300 °C and in NaCl solutions to 5 m and 100 °C. The cause of the correlation in water is due to the differences in the free energies of ΔG 0(A 13+) - ΔG 0 (Al(OH) j (3-j)) being almost equal to the values of ΔG 0 (Fe 3+) - ΔG 0 (Fe(OH) j (3- j)). An examination of the activity coefficients of Fe 3+ and Al 3+ and the complexes show that the correlation at higher ionic strengths is due to the fact that the activity coefficients ratios are similar γ(Fe 3+) / γ(Fe(OH) j (3-j))≅ γ(Al 3+) / γ(Al(OH) j (3-j)) in NaCl solutions. These linear correlations appear to also hold for other trivalent metals (Cr 3+, As 3+). The results of this study should be useful in examining the speciation of Fe(III) in hydrothermal brines.
AB - There is a lot of interest in the behavior of Fe(III) in natural waters because of its importance in the productivity of phytoplankton. The hydrolysis of Fe(III) in natural waters limits the solubility of Fe(III) in aqueous solutions. At the present time, reliable hydrolysis constants for Fe(III) are limited to low temperatures (5-50 °C) in NaCl to 5 m. The hydrolysis constants of Fe(III) and Al(III) are linearly related over a wide range of temperatures (0-50 °C) and ionic strengths (0-5 m NaCl). The near linear correlations allow one to make reasonable estimates for the values of Fe(III) from 0 to 300 °C in dilute solutions and from 0 to 100 °C to 5 m in NaCl solutions. In this paper, the stoichiometric (β i) and thermodynamic (κ i hydrolysis constants for Al(III) in NaCl have been fit to equations of the form logβ i - logK i=a 0I 0.5 + a 1I 0.5/T + a 3I + a 4 I / T + a 5I 2 This equation has been used to estimate the hydrolysis constant for Fe(III) in dilute solutions to 300 °C and in NaCl solutions to 5 m and 100 °C. The cause of the correlation in water is due to the differences in the free energies of ΔG 0(A 13+) - ΔG 0 (Al(OH) j (3-j)) being almost equal to the values of ΔG 0 (Fe 3+) - ΔG 0 (Fe(OH) j (3- j)). An examination of the activity coefficients of Fe 3+ and Al 3+ and the complexes show that the correlation at higher ionic strengths is due to the fact that the activity coefficients ratios are similar γ(Fe 3+) / γ(Fe(OH) j (3-j))≅ γ(Al 3+) / γ(Al(OH) j (3-j)) in NaCl solutions. These linear correlations appear to also hold for other trivalent metals (Cr 3+, As 3+). The results of this study should be useful in examining the speciation of Fe(III) in hydrothermal brines.
UR - http://www.scopus.com/inward/record.url?scp=64549094093&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=64549094093&partnerID=8YFLogxK
U2 - 10.1021/es802504u
DO - 10.1021/es802504u
M3 - Article
C2 - 19368177
AN - SCOPUS:64549094093
VL - 43
SP - 1818
EP - 1823
JO - Environmental Science & Technology
JF - Environmental Science & Technology
SN - 0013-936X
IS - 6
ER -