Solubility of Rhodochrosite (MnCO3) in NaCl Solutions

Yanxin Luo, Frank J. Millero

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10 Scopus citations


The solubility of rhodochrosite (MnCO3) at 25°C under constant carbon dioxide partial pressure p(CO2) was determined in NaCl solutions as a function of ionic strength I. The dissolution of MnCO 3(s) for the reaction MnCO3(s) + 2H+ = Mn 2+ + CO2(g) + H2O Kso* = [Mn2+]p(CO2)/[H+]2 has been determined as a function of pH. From these values, we have determined the equilibrium constant for the stoichiometric solubility of MnCO3(s) in NaCl solutions Ksp* = [Mn2+]T[CO 32-]T These values have been fitted to the equation log Ksp* = -10.3 + 2.39 I0.5 - 0.69 I with a standard error of σ = 0.1 with I and concentrations in molalities. The extrapolated value of log Kspo (-10.3) in water is in good agreement with literature data (-10.1 to 10.8) determined in solutions of different composition and ionic strength. The measured values of the activity coefficient, γT(Mn2+) and γ T(CO32-), have been used to estimate the stability constant for the formation of the MnCO3 ion pair, K* (MnCO30). The value of K0(MnCO3 0) calculated from the values of K* (MnCO3) by the Pitzer equation (σ = 0.1) in this study (4.8 ± 0.1) is in reasonable agreement with literature data.

Original languageEnglish (US)
Pages (from-to)405-416
Number of pages12
JournalJournal of Solution Chemistry
Issue number5
StatePublished - May 2003


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

ASJC Scopus subject areas

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


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