Foaming Characterization of Sodium Dodecyl Sulfate (SDS) in Binary Mixed Aqueous Solutions

Sodium dodecyl sulfate (SDS) is an organic surfactant commonly applied in foam based treatment of wastewater as an efficient collector for heavy metal species. SDS is used in combination with a frothing agent, usually alcohols, to control and improve bubble size, adsorption area, foam stability and solution recovery. To achieve optimum performance, a proper collector-to-frother ratio is required which is commonly determined by trial-and-error or statistical approaches. The aim of this paper is to survey the scientific background of the influence of frother type and concentration on foam flotation response. Equilibrium and dynamic frothability of individual and dual surfactant aqueous solutions of SDS and different frothing agents, including ethanol, n-butanol, isoamyl alcohol and methyl isobutyl carbinol (MIBC) was measured. Equilibrium frothing evaluations indicated that frothability of surfactants enhances by increasing their molecular weights due to the improvement of liquid film elasticity surrounding bubbles. Dynamic frothability index value for SDS, MIBC, isoamyl alcohol, n-butanol and ethanol was found to be 92061.3, 38724.3, 10783.1, 1696.4, and 1349.7 s.dm 3 /mol, respectively, confirming the results from equilibrium data. Comparing frothability values obtained from different frother-SDS blends revealed that mixtures containing isoamyl alcohol and MIBC produce more stable foam which is suitable for precipitate and colloid flotation; whereas, solutions of ethanol and n-butanol are more selective and recommended for ion flotation. Referring to dynamic frothability indices of binary solutions, a reference chart was proposed as a guideline for selection of proper collector/frother system and to estimate preliminary collector-to-frother ratio with respect to the foam flotation purpose.