Estimation of Surface Excess of Surfactant under Coexisting Salts in Foam Separation

抄録

Foam separation experiments were carried out by use of sodium dodecylbenzene sulphonate. In the presence of various coexisting salts, the dynamic surface excess of dodecylbenzene sulphonate ion (DES^–), Γ_DBS^–, at the dynamic gas–liquid interface of bubble was experimentally and theoretically examined. The Davies adsorption isotherm could be well applied to Γ_DBS^– in the range of surfactant concentrations of C_DBS^–/C_m ≤ 0.15: C_DBS^– and C_m mean bulk concentration of DBS^– and critical micelle concentration respectively. It was also found that the values of the ratio of adsorption constant to desorption constant in the Davies adsorption isotherm, B₁/B₂, have values in the two regions of electrical potential, φ₀: in the region of –φ₀ < 4.0 × 10^–4 esu, B₁/B₂ value is 6.85 × 10^–7 cm and in that of –φ₀ > 4.0 × 10^–4 esu, the value is 6.07 × 10^–6 cm. Moreover, the effect of various coexisting salts on the surface excess of DBS^– in static equilibrium determined by surface tension measurements could be thermodynamically interpreted by a two-dimensional state equation by use of reduced concentration of DBS^– based on CMC. Saturated surface excess of DBS^– in static equilibrium could also be correlated to the ionic strength of coexisting metal ions. Using the equation derived from both the Davies adsorption isotherm and the Gouy–Chapman theory of the diffuse double layer (G.C. model), Γ_DBS^– under various coexisting salts could be estimated within an error of about ±10%. Estimations of Γ_DBS^– in various solution systems were also carried out.