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Title: Magnetite solubility and phase stability in alkaline media at elevated temperatures

Abstract

Magnetite, Fe{sub 3}O{sub 4}, is the dominant oxide constituent of the indigenous corrosion layers that form on iron base alloys in high purity, high temperature water. The apparent simultaneous stability of two distinct oxidation states of iron in this metal oxide is responsible for its unique solubility behavior. The present work was undertaken to extend the experimental and theoretical bases for estimating solubilities of an iron corrosion product (Fe{sub 3}O{sub 4}/Fe(OH){sub 2}) over a broader temperature range and in the presence of complexing, pH-controlling reagents. These results indicate that a surface layer of ferrous hydroxide controls magnetite solubility behavior at low temperatures in much the same manner as a surface layer of nickel(II) hydroxide was previously reported to control the low temperature solubility behavior of NiO. The importance of Fe(III) ion complexes implies not only that most previously-derived thermodynamic properties of the Fe(OH){sub 3}{sup {minus}} ion are incorrect, but that magnetite phase stability probably shifts to favor a sodium ferric hydroxyphosphate compound in alkaline sodium phosphate solutions at elevated temperatures. The test methodology involved pumping alkaline solutions of known composition through a bed of Fe{sub 3}O{sub 4} granules and analyzing the emerging solution for Fe. Two pH-controlling reagents were tested:more » sodium phosphate and ammonia. Equilibria for the following reactions were described in thermodynamic terms: (a) Fe(OH){sub 2}/Fe{sub 3}O{sub 4} dissolution and transformation, (b) Fe(II) and Fe(III) ion hydroxocomplex formation (hydrolysis), (c) Fe(II) ion amminocomplex formation, and (d) Fe(II) and Fe(III) ion phosphatocomplex formation. 36 refs.« less

Authors:
; ;
Publication Date:
Research Org.:
Knolls Atomic Power Lab. (KAPL), Niskayuna, NY (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
34346
Report Number(s):
KAPL-4756
ON: DE95009335; TRN: AHC29511%%56
DOE Contract Number:  
AC12-76SN00052
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: May 1994
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 40 CHEMISTRY; MAGNETITE; SOLUBILITY; STABILITY; IRON BASE ALLOYS; CORROSION; SODIUM PHOSPHATES; AQUEOUS SOLUTIONS; IRON HYDROXIDES; PHASE STUDIES; PH VALUE; THERMODYNAMICS; FEEDWATER; WATER CHEMISTRY; AMMONIUM HYDROXIDES; SODIUM HYDROXIDES; SOLVENT PROPERTIES; EXPERIMENTAL DATA

Citation Formats

Ziemniak, S E, Jones, M E, and Combs, K E.S. Magnetite solubility and phase stability in alkaline media at elevated temperatures. United States: N. p., 1994. Web. doi:10.2172/34346.
Ziemniak, S E, Jones, M E, & Combs, K E.S. Magnetite solubility and phase stability in alkaline media at elevated temperatures. United States. https://doi.org/10.2172/34346
Ziemniak, S E, Jones, M E, and Combs, K E.S. 1994. "Magnetite solubility and phase stability in alkaline media at elevated temperatures". United States. https://doi.org/10.2172/34346. https://www.osti.gov/servlets/purl/34346.
@article{osti_34346,
title = {Magnetite solubility and phase stability in alkaline media at elevated temperatures},
author = {Ziemniak, S E and Jones, M E and Combs, K E.S.},
abstractNote = {Magnetite, Fe{sub 3}O{sub 4}, is the dominant oxide constituent of the indigenous corrosion layers that form on iron base alloys in high purity, high temperature water. The apparent simultaneous stability of two distinct oxidation states of iron in this metal oxide is responsible for its unique solubility behavior. The present work was undertaken to extend the experimental and theoretical bases for estimating solubilities of an iron corrosion product (Fe{sub 3}O{sub 4}/Fe(OH){sub 2}) over a broader temperature range and in the presence of complexing, pH-controlling reagents. These results indicate that a surface layer of ferrous hydroxide controls magnetite solubility behavior at low temperatures in much the same manner as a surface layer of nickel(II) hydroxide was previously reported to control the low temperature solubility behavior of NiO. The importance of Fe(III) ion complexes implies not only that most previously-derived thermodynamic properties of the Fe(OH){sub 3}{sup {minus}} ion are incorrect, but that magnetite phase stability probably shifts to favor a sodium ferric hydroxyphosphate compound in alkaline sodium phosphate solutions at elevated temperatures. The test methodology involved pumping alkaline solutions of known composition through a bed of Fe{sub 3}O{sub 4} granules and analyzing the emerging solution for Fe. Two pH-controlling reagents were tested: sodium phosphate and ammonia. Equilibria for the following reactions were described in thermodynamic terms: (a) Fe(OH){sub 2}/Fe{sub 3}O{sub 4} dissolution and transformation, (b) Fe(II) and Fe(III) ion hydroxocomplex formation (hydrolysis), (c) Fe(II) ion amminocomplex formation, and (d) Fe(II) and Fe(III) ion phosphatocomplex formation. 36 refs.},
doi = {10.2172/34346},
url = {https://www.osti.gov/biblio/34346}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun May 01 00:00:00 EDT 1994},
month = {Sun May 01 00:00:00 EDT 1994}
}