Akademik Veri Yönetim Sistemi
JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, cilt.94, sa.2, ss.591-596, 2008 (SCI-Expanded)
A model was proposed to calculate some thermodynamic parameters for the acid dissolution process of a bentonite containing a calcium-rich smectite as clay mineral along with quartz, opal and feldspar as impurities. The bentonite sample was treated with H2SO4 by applying dry method in the temperature range 50-150 degrees C for 24 h. The acid content in the dry bentonite-sulphuric acid mixture was 45 mass%. The total content (x) of Al2O3, Fe2O3 and MgO remained in the undissolved sample after treatment was taken as an equilibrium parameter. An apparent equilibrium constant, K-a, was calculated for each temperature by assuming K-a=(x(m)-x)/x where x(m) is the total oxide content of the natural bentonite. Also, an apparent change in Gibbs free energy, Delta G(a)(o), was calculated for each temperature by using the K-a value. The graphs of lnK(a) vs. 1/T and Delta G(a)(o) vs. T were drawn and then the real change in both the enthalpy, Delta H-o and the entropy, Delta S-o, values were calculated from the slopes of the straight lines, respectively. Inversely, real Delta G(o) and K values were calculated from the real Delta H-o and Delta S-o values through Delta G(o) = -RT ln K = Delta H-o - T Delta S-o equation. The best Delta H-o and Delta S-o fittings to this relation were found to be 65687 J mol(-1) and 164 J mol(-1)K(-1), respectively.