Journal of Solution Chemistry

, Volume 9, Issue 6, pp 415–442 | Cite as

The solubility of magnetite and the hydrolysis and oxidation of Fe2+ in water to 300°C

  • Peter R. Tremaine
  • Jacques C. LeBlanc
Article

Abstract

The solubility of carefully characterized magnetite, Fe3O4, in dilute aqueous solutions saturated with H2 has been measured at temperatures from 100 to 300°C in a flow apparatus. Solution compositions included either HCl or NaOH molalities of up to 1 and 40 mmole-kg−1, respectively, and H2 molalities of 0.0779, 0.779, and 8.57 mmole-kg−1. The dependence of the equilibrium solubility on the pH and reduction potential were fitted to a scheme of soluble ferrous and ferric species consisting of Fe2+, FeOH+, Fe(OH)2, Fe(OH) 3 , Fe(OH)3, and Fe(OH) 4 . Solubility products from the fit, corresponding to the reactions
$$\tfrac{1}{3}Fe_3 O_4 + (2 - b)H^ + + \tfrac{1}{3}H_2 \rightleftharpoons Fe(OH)_b^{2 - b} + (4/3 - b)H_2 O$$
and
$$\tfrac{1}{3}Fe_3 O_4 + (3 - b)H^ + \rightleftharpoons Fe(OH)_b^{3 - b} + \tfrac{1}{6}H_2 + (4/3 - b)H_2 O$$
were used to derive thermodynamic constants for each species. The extrapolared value for the Gibbs energy of formation of Fe2+ at 25°C is −88.92±2.0 kJ-mole−1, consistent with standard reduction potentials in the range Eo(Fe2+)=−0.47±0.01 V. The temperature coefficient of the equilibrium Fe molality, (∂m(Fe, sat.)/∂T)m(H2).m(NaOH), changes from negative to positive as the NaOH molality is increased to the point where Fe(OH) 3 and Fe(OH) 4 predominate.

Key words

Magnetite iron oxide water hydrolysis hydrothermal solutions solubility stability diagram corrosion Gibbs energy entropy high temperature ferrous ion 

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Copyright information

© Plenum Publishing Corporation 1980

Authors and Affiliations

  • Peter R. Tremaine
    • 1
  • Jacques C. LeBlanc
    • 1
  1. 1.Research Chemistry Branch, Whiteshell Nuclear Research EstablishmentAtomic Energy of Canada LimitedPinawaCanada

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