Accurate thermodynamic model for the calculation of H2S solubility in pure water and brines

A thermodynamic model calculating the solubility of hydrogen sulfide (H2S) in pure water and in aqueous NaCl solutions (0-6 M, 273-500 K, 0-200 bar) is presented. The model is based on a specific particle interaction theory for the liquid phase and a highly accurate equation of state for the vapor phase. With this specific interaction approach, this model is able to predict H2S solubility in other systems, such as H2S-H2O-Na2SO4, H2S-H2O-CaCl2, H2S-H2O-KCl, and H2S-seawater, without fitting experimental data from these systems. Comparison of the model predictions with experimental data indicates that the model is within or close to experimental uncertainty, which is about 7% in H2S solubility. The model is programmed and can be downloaded from the website: www.geochem-model.org/programs.htm. Online calculation is also made available on the website: www.geochem-model.org/models.htm. The H2S solubility model can be used together with numerical speciation-solubility modeling codes such as PHREEQC to calculate sulfide mineral solubility in H2S saturated brines. An example calculation for galena solubility is given.