INTERACTIONS OF SODIUM DODECYLBENZENESULFONATE AND CALCITE IN 0.55-M-NACL-SOLUTION

Complex mutual interactions of calcite and sodium dodecylbenzene sulfo nate (NaDBS) were studied in 0.55 M NaCl solution, using several compl ementary techniques. Adsorption of NaDBS on calcite could be resolved from other processes such as adsorption onto the reaction vessel and/o r formation of solid crystalline phase, when a special a.c. voltammetr ic procedure was used below the critical micelle concentration (c.m.c. = = 9 x 10(-5) mol/L). A two-plateau type isotherm was obtained. Init ial adsorption of NaDBS occurs at Ca2+ ions on the calcite/solution in terface through electrostatic interactions. The second stage of adsorp tion was described as hydrophobic interaction between hydrocarbon chai ns 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 nu mber, n, the amount of adsorbed monomer, Gamma(1), the saturated adsor ption, Gamma(infinity), and the standard free energy of surface aggreg ate formation for one mole of surfactant, Delta G(hm)(0), were calcula ted.