Potential-pH Diagrams for Iron and Nickel in High Salinity Geothermal Brine Containing Low Concentrations of Hydrogen Sulfide

Potential-pH diagrams are reported for iron and nickel in sulfide containing high salinity geothermal brine at 25 and 250 C. Metal sulfides, as well as dissolved chloride complexes, were considered in deriving the diagrams, and the potential-pH relationships for those equilibria involving dissolved H₂S or its anions are plotted for a constant total dissolved sulfide content of 10 ppm. The diagrams are used to analyze the general features of the thermodynamic behavior of iron and nickel in geothermal systems, and to identify processes that might be expected to occur in high temperature sulfide containing brines.