Reply to Dr. Stoessell’s Comment on Reaction paths and equilibrium end-points in solid-solution aqueous-solution systems

In this reply to the critical comment by R. K. Stoessell, the limiting activity coefficients of bromide in halite (Y_NaBr) have been calculated through least-squares fitting of data from the literature concerning bromide distribution coefficients in the NaCl-NaOH-H2O system at 35°C. The analysis produced coefficients of Y_NaBr = 7.4 for regular solid-solution models and 8.8 for subregular models. Based on these models, the bromide concentrations of halite in equilibrium with seawater at initial halite saturation were estimated to be 1.7 ppm and 14 ppm, respectively. A comprehensive review of existing literature illustrates a broad range of distribution coefficients for trace bromide in halite, with reported lower values of D_e = 0.01 and higher values of D_a = 0.03 by various authors. The measurement of stoichiometric saturation states for halite containing trace bromide is noted as impractical due to the insensitivity of solubility measurements with varying bromide mole fractions. It is emphasized that determination of distribution coefficients in equilibrium conditions is essential for understanding the thermodynamic mixing properties of both Na(Cl,Br) and K(Cl,Br) solid-solution series at low bromide concentrations, highlighting the need for careful interpretation of precipitation processes in relation to stoichiometric saturation.