Enthalpy of surface reactions: temperature dependency of pH of acidic or basic concentrated hematite suspension

Temperature dependency of pH of concentrated metal oxide suspension, containing acid or base, was used as a method for determination of total enthalpy of surface reactions. This enthalpy depends on pH due to electrostatic interactions. It is sum of standard (chemical) part and electrostatic contribution. Difference in standard reaction enthalpies of deprotonation and protonation of neutral surface sites for aqueous hematite dispersion was obtained as 42.8 kJ mol-1, while electrostatic contribution decreases with pH, being zero at the point of zero charge.