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Two main pathways have been identified for the desorption of metal ions from contaminated land using biosurfactants [31]. In the first pathway, there is a complex formation between the free, non‐ionic form of metal and biosurfactant molecules. In this interaction, using the principle of Le Chatelier, the solution phase activity of the metal ions is reduced and thus its desorption from the medium increases. In the second pathway, it is proposed that there is an accumulation of biosurfactants at the solid–solution interface and absorption of metal ions occurs as the interfacial tension reduces between the two.

According to Rufino et al. [32], ion exchange, precipitation dissolution, counter‐ion association, and electrostatic interaction are some of the chief mechanisms that govern metal–biosurfactant binding in the contaminated environment. Studies reveal that the complex formation capability of the biosurfactant with the metal ions is the chief cause for their usefulness in metal ion remediation. Precisely, ionic bonds formed in between metal ions and anionic biosurfactants lead to a generation of stronger stabilizing forces as nonionic complexes form, which, of course, are stronger as compared to metal and soil interaction. Because of the neutral charge of the complex with a subsequent amalgamation of the metal into micelles, the complex form of metal–biosurfactants desorb from the soil matrix and move into the soil solution. A detailed study of the proposed mechanism reveals that either an outer‐sphere surface complex formation occurs in between negatively charged surfaces and metals due to strong electrostatic attraction or an inner‐sphere surface complex formation is established between the metal ions and biosurfactant molecules due to chemical bonding in which hydroxide groups serve as ligands. The mechanism of metal binding through both pathways is smoothed in the presence of water molecules and easy protonation and deprotonation of oxide functional groups. The mechanism of metal–biosurfactant interaction is represented in Figure 4.1.

Figure 4.1 Biosurfactant mediated heavy metal remediation.