Solubility of siderite (FeCO3) in NaCl solutions

Carlos A.R. Silva, Xuewu Liu, F. J. Millero

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47 Scopus citations


The solubility of siderite (FeCO3) at 25°C under constant CO2 partial pressure [p(CO2)] was determined in NaCl solutions as a function of ionic strength. The dissolution of FeCO 3(s) for the reaction FeCO3(s) + 2H+ = Fe 2+ + CO2(g) + H2O Ko* = [Fe2+] pCO2/[H+]2 has been determined as a function of pH = - log[H+]. From these values we have determined the equilibrium constant for the stoichiometric solubility to FeCO3(s) in NaCl Ksp* = [Fe2+] [CO 32-] These values have been fitted to the equation log[Ksp*] = -10.9 + 2.518 I0.5 - 0.657 I with a standard error of s = 0.15. The extrapolated value of log(Ksp o) - 10.9 in water is in good agreement with data in the literature (-10.8 to - 11.2) determined in solutions of different composition and ionic strength. The measured values of the activity coefficient, γ T(Fe2+) γT(CO32-), have been used to estimate the stability constant for the formation of the FeCO3 ion pair, K*(FeCO3). The values of K*(FeCO3) have been fitted to the equation (s = 0.09) log[K*(FeCO3)] = 6.3 - 2.3135 I0.5 + 0.7091 I. The value of log[Ko(FeCO3)] in water found in this study (6.3 ± 0.2) is slightly higher than the value found from extrapolations in 1. 0 m NaClO4 solutions (5.9 ± 0.2). These differences are related to the model used to determine the activity coefficients of the Fe(II) and carbonate species in the two solutions.

Original languageEnglish (US)
Pages (from-to)97-108
Number of pages12
JournalJournal of Solution Chemistry
Issue number2
StatePublished - Dec 1 2002


  • Activity coefficients
  • Pitzer equations
  • Siderite
  • Sodium chloride
  • Solubility

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Physical and Theoretical Chemistry


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