Accurate Thermodynamic Model for the Calculation of H2S Solubility in Pure Water and Brines

A thermodynamic model calculating the solubility of hydrogen sulfide (H 2 S) 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 H 2 S solubility in other systems, such as H 2 S−H 2 O−Na 2 SO 4, H 2 S−H 2 O−CaCl 2, H 2 S−H 2 O−KCl, and H 2 S−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 H 2 S 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 H 2 S solubility model can be used together with numerical speciation-solubility modeling codes such as PHREEQC to calculate sulfide mineral solubility in H 2 S saturated brines. An example calculation for galena solubility is given.