Sorption processes anionic surfactants

The partition coefficients for different LAS homologues (Table 5.4.2) are higher in the marine environment due to the higher ionic strength that promotes sorption of anionic surfactants [14] and an increase in the partition coefficient with the alkylic chain length has been observed (Table 5.4.2). The evolution of the concentration of the various homologues of LAS in solids in suspension (cf. Fig. 5.4.2) is similar to that found in water and, in the process of adsorption, an increase can be observed in line with the chain length, as commented on previously. 

The reversibility of sorption has considerable environmental relevance, because it permits the recovery of ecosystems after exposure to contamination, and makes possible the re-dissolution of chemicals that have been sorbed onto particulate material. For this reason, this aspect has been studied extensively, with results showing that sorption onto natural sediments is a reversible process for non-ionic [17] and anionic surfactants [8,20,30,45,46]. This desorption process, however, has not been confirmed by other authors [3,14]. 

In previous papers, we reported surfactant adsorption onto hydrotalcite-like compounds, i.e. Mg-AI-C03-LDHs [10, 11]. We showed that LDH efficiency in removing anionic surfactant from aqueous solution by adsorption was greater than that of alumina. We also showed that it is possible to use LDH in the calcined form to remove surfactants from aqueous solution, which in turn involves two processes, intercalation by regeneration of the LDH structure and adsorption on the regenerated material. The whole surfactant removal process is designed in this case as sorption. These results emphasised the recyclability of LDHs and their potential use as surfactant removers. 

Most of the results reported herein on the sorption of polycations by natural keratins have been obtained on simplified model systems. The rationale behind such an approach was to seek to determine the fate of sorbing polymer under well-defined conditions and so to obtain mechanistic insight. The results have clearly indicated that both adsorption and absorption processes can occur. They have also shown that the nature, extent, and consequences of polycation sorption can all be influenced by the presence of surfactant. In general, nonionic surfactants have a small effect on sorption, because of low interaction while cationic surfactants can have a very large effect because of competition for the sorption sites. Because of interaction and complex formation with cationic polyelectrolytes anionic surfactants can exercise an intermediate, but potentially very important, influence. 

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