RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

Potentiometric titrations of goethite (αFeOOH) have been performed in various concentrations of NaCl, KCl, MgCl₂, CaCl₂, Na₂SO₄ and a mixed electrolyte containing the major ions of seawater in their seawater proportions. From this data we have calculated apparent stability quotients. A method of double extrapolation has been used to calculate intrinsic acidity and surface complex equilibrium constants. Using these constants we calculate the titratable charge and surface species distribution of goethite in seawater. At pH 8 the calculated charge is −38.8 µcoul cm⁻² and 90% of the titratable charge.is due to FeO⁻MgOH⁺ surface complexes. The calculated charge over the pH range 5-9 is in excellent agreement with the measured charge in the seawater type electrolyte.