Ion flotation of heavy metal ions by using biodegradable biosurfactant as collector: Application and removal mechanism

Ion flotation was used to remove copper(II), lead(II) and chromium(III) from simulated wastewater using a new biodegradable biosurfactants, namely, sodium N-lauroylsarcosinate (LS), and the synthetic surfactant sodium dodecyl sulfate (SDS) as collectors. The use of LS resulted in better removal of metal ions than that achieved with SDS. It was found that the removal efficiency of single metal ions can reach more than 95%. The results showed that the complex formed by surfactant and metal ion was flocculent and loose in structure, which may be the main reason for the slow ion flotation speed. XPS and IR analysis showed that there was a complex reaction between the sulfonic group of SDS and the carboxyl group of LS with metal ions. These findings indicate that the new biosurfactant LS has a better treatment effect on wastewater containing heavy metal ions and compared with industrial surfactants (such as SDS), LS is degradable and environmentally friendly, potentially leading to better industrial application. DFT theory further confirmed the experimental results. The calculated results show that LS has higher complexation ability for Pb(II) than dose SDS. LS reacts with Pb to form a four-membered ring complex containing two O atoms, which has higher stability than the complex containing SDS.