The SIT model parameters for interactions of carbonate compounds with sodium and potassium ions accounting for association

Abstract

The current study is devoted to the determination of the SIT coefficients at 298.15 K for interactions, involving $C{O}_2\left(\text{aq}\right)$, $\text{HC}{O}_3^{-}$, and $C{O}_3^{2‐}$, with mostly Na⁺ and K⁺ ions. The SIT model is a simple yet physically sound model for activity coefficients in aqueous solutions, that has just one parameter for each cation-anion or a dissolved gas – electrolyte interaction. Among the issues that were met for carbonate systems are the side reactions of hydrolysis and disproportionation in the carbonate solutions, that complicate the analysis of data and lead to unusually large difference, up to 9%, in the values of activity coefficients, determined in different authoritative laboratories. For ${\text{Na}}_{2}C{O}_3$ and $K_{2}C{O}_3$ solutions, it was necessary to take into account the reaction of formation of the ionic pair $M^{+}+C{O}_3^{2‐}=\text{MC}{O}_3^{-}$, with the equilibrium constants ${\beta }_1^o$ equal to ${\log }_{10}{\beta }_1^o=$ 0.75 ± 0.08 for $M^{+}=N{a}^{+}$ and to ${\log }_{10}{\beta }_1^o=$ 0.67 ± 0.11 for $M^{+}=K^{+}$. In all, there are values for more than 20 binary SIT interaction coefficients. All results are valid at 298.15 K, 0.1 MPa.