Solubility of Fe₂(OH)₃Cl (pure-iron end-member of hibbingite) in NaCl and Na₂SO₄ brines

Pure-iron end-member hibbingite, Fe₂(OH)₃Cl(s), may be important to geological repositories in salt formations, as it may be a dominant corrosion product of steel waste canisters in an anoxic environment in Na–Cl- and Na–Mg–Cl-dominated brines. In this study, the solubility of Fe₂(OH)₃Cl(s), the pur...

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Bibliographic Details
Published in:Chemical geology 2011-01, Vol.280 (1-2), p.26-32
Main Authors: Nemer, Martin B, Xiong, Yongliang, Ismail, Ahmed E, Jang, Je-Hun
Format: Article
Language:English
Subjects:
Brines
confidence interval
Confidence intervals
corrosion
Data points
Formations
geochemistry
hydrogen
iron
magnesium
Mathematical models
radioactive waste
Repositories
sodium chloride
sodium sulfate
Solubility
Statistics
steel
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Summary:Pure-iron end-member hibbingite, Fe₂(OH)₃Cl(s), may be important to geological repositories in salt formations, as it may be a dominant corrosion product of steel waste canisters in an anoxic environment in Na–Cl- and Na–Mg–Cl-dominated brines. In this study, the solubility of Fe₂(OH)₃Cl(s), the pure-iron end-member of hibbingite (Feᴵᴵ, Mg)₂(OH)₃Cl(s), and Fe(OH)₂(s) in 0.04m to 6m NaCl brines has been determined. For the reactionthe solubility constant of Fe₂(OH)₃Cl(s) at infinite dilution and 25°C has been found to be log₁₀K=17.12±0.15 (95% confidence interval using F statistics for 36 data points and 3 parameters). For the reactionthe solubility constant of Fe(OH)₂ at infinite dilution and 25°C has been found to be log₁₀K=12.95±0.13 (95 % confidence interval using F statistics for 36 data points and 3 parameters). For the combined set of solubility data for Fe₂(OH)₃Cl(s) and Fe(OH)₂(s), the Na⁺–Fe²⁺ pair Pitzer interaction parameter θNₐ₊ / Fₑ₂₊ has been found to be 0.08±0.03 (95% confidence interval using F statistics for 36 data points and 3 parameters). In nearly saturated NaCl brine we observed evidence for the conversion of Fe(OH)₂(s) to Fe₂(OH)₃Cl(s). Additionally, when Fe₂(OH)₃Cl(s) was added to sodium sulfate brines, the formation of green rust(II) sulfate was observed, along with the generation of hydrogen gas. The results presented here provide insight into understanding and modeling the geochemistry and performance assessment of nuclear waste repositories in salt formations.
ISSN:0009-2541
1872-6836
DOI:10.1016/j.chemgeo.2010.10.003