Influence of metal ions on the aggregation of anionic surfactants. Studies on the interactions between environmental pollutants in aqueous solutions

Surfactants, which are environmental pollutants, are also used in processes dedicated to the removal of heavy metals from contaminated environment. Thus, to clarify surfactant/heavy metals effects occurring in water and soil and to successfully use amphiphiles for metal elimination, the information on the interactions between surfactants and metal ions are highly required. In this work the influence of Cd2+ and Zn2+ on the aggregation of anionic surfactants: sodium dodecyl sulfate (SDS) and Sarkosyl was investigated. The experiments involved electrical conductance and pH measurements as well as the flame atomic absorption spectrometry (FAAS) studies. The results evidenced that both studied metal ions form aggregates of different stability with SDS and Sarkosyl at the concentrations below critical micelle concentration and they are able to bind also to the negatively charged micelles. SDS was found to be more effective than Sarkosyl in binding metal ions, however, both surfactants manifested stronger binding capacity to Cd2+ as compared to Zn2+. It was also summarized that the ability of SDS and Sarkosyl to bind metal ions changes in the following order: Pb2+ > Cd2+ > Zn2+. The foregoing findings were discussed in the relation to the differences in the values of the hydrated ionic radii and the enthalpies of hydration of the studied metal ions. (C) 2017 Elsevier B.V. All rights reserved.