Solubility of Rhodochrosite (MnCO3) in NaCl Solutions

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 MnCO3(s) for the reaction \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$\begin{gathered} {\text{MnCO}}_{\text{3}} ({\text{s}}) + 2{\text{H}}^{\text{ + }} = {\text{Mn}}^{{\text{2 + }}} + {\text{CO}}_{\text{2}} ({\text{g}}) + {\text{H}}_{\text{2}} {\text{O}} \hfill \\ {\text{ K}}_{{\text{so}}}^{\text{*}} = [{\text{Mn}}^{{\text{2 + }}} ]{\text{p(CO}}_{\text{2}} {\text{)/[H}}^{\text{ + }} {\text{]}}^{\text{2}} \hfill \\ \end{gathered} $$ \end{document}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 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${\text{K}}_{{\text{sp}}}^{\text{*}} = [{\text{Mn}}^{{\text{2 + }}} ]_{\text{T}} {\text{[CO}}_{\text{3}}^{{\text{2}} - } {\text{]}}_{\text{T}}$$ \end{document}These values have been fitted to the equation \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${\text{log K}}_{{\text{sp}}}^{\text{*}} = - 10.3 + 2.39\left| {^{0.5} - \;0.69} \right|$$ \end{document}with a standard error of σ = 0.1 with Iand concentrations in molalities. The extrapolated value of log Kosp(−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 γT(CO32−), have been used to estimate the stability constant for the formation of the MnCO3ion pair, K*(MnCO30). The value of K0(MnCO30) 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.