A new approach was applied to the description of acid-base properties and heavy and alkaline earth metal adsorption on the oxide-solution interface. The acid-base properties of hematite have been determined at different temperatures. The adsorption of protons and hydroxyl ions on the hematite surface has a temperature independent character. The proton and hydroxyl ion adsorption in NaCl media was explained by the reactions =H2O + H3O+ + Cl- = =H2OHCl + H2O =OH2 + OH- + Na+ = =OHNa + H2O. The modified equation of the Frumkin-Fouler-Guggenheim isotherm was used to simulate the experimental data (theta, relative adsorption) : log[theta(HCl)/(1 - theta(HCl))] - log[H+] -log[Cl-] =log KHCldegrees + logBH[N thetaHCl/(1 + (N - 1)thetaHCl)]; log[thetaNaOH/(1 - thetaNaOH)] -log[Na⁺] - log[OH^-] =log K(NaOH)degrees + log B-OH[N theta(NaOH)/(1 + (N - 1)theta(NaOH))]. The model parameters were log B-H = -4.92 +/- 0.1, log B-OH = -2.61 +/-0.05, N = 3.25 +/- 0.2. The site density of the hematite surface was determined to be 3.8 +/- 0.1 mu moles/m(2). The values of the constants were log KO(HCl)degrees (25-100 degrees C) = 9.50 +/- 0.1; log K(NaOH)degrees (25-100 degrees C) = 5.93 +/- 0.1.