| Popis: |
Complex mutual interactions of calcite and sodium dodecylbenzenesulfonate (NaDBS) were studied in 0.55 M NaCl solution, using several complementary techniques. Adsorption of NaDBS on calcite could be resolved from other processes such as adsorption onto the reaction vessel and/or formation of solid crystalline phase, when a special a.c. voltammetric procedure was used below the critical micelle concenntration (c.m.c. = 9x10^-5 mol/L. A two-plateau type isotherm was obtained. Initial adsorption of NaDBS occurs at Ca^2+ ions on the calcite/solution interface through electrostatic interactions. The second stage of adsorption was described as hydrophobic interactions between hydrocarbon chains from bulk solution and those electrostatically adsorbed on calcite, forming surface aggregates. The results of adsorption were analyzed by a two-step adsorption model. The equilibrium constants k_1 and k_2 for the first and second adsorption step, the surface aggregation number, n, the amount of adsorbed monomer, Gama_1, the saturated adsorption, Gama_inf, and the standard free energy of surface aggregate formation for one mole of surfactant, deltaG^0_hm, were calculated. |
