Interaction mechanisms between anionic surfactant micelles and different metal ions in aqueous solutions

In its using or eliminating processes, surfactant solutions usually exhibit different behaviors because of the different species or concentrations of the encountered metal ions. Interactions between anionic surfactant (SDS) micellar solutions and several familiar metal salt solutions (Al-2(SO4)(3), FeCl3, CaCl2 and MgCl2) were investigated. Precipitates were formed in all systems except SDS-MgCl2 visually. Stoichiometric analysis reveals that, in SDS-Al-2(SO4)(3) system, the precipitation phenomenon is mainly owing to the effect of adsorption-charge neutralization between Al3+ ions and SDS micelles; in SDS-FeCl3 system, bridge connection effect of Fe(OH)(2+) ions among SDS micelles becomes the dominant mechanism; while in SDS-CaCl2 system, all SDS micelles are decomposed and solubility product of Ca(DS)(2) crystal results in the precipitation. SEM photographs of the precipitates can serve as additional vivid proofs of the above conclusion.