Ion flotation for heavy metal removal with biosurfactant sodium lauroyl methyl isethionate: Operational parameters and removal mechanism

The green surfactant Sodium Lauroyl Methyl Isethionate (SLMI) was employed for the first time in an ion flotation process to effectively remove heavy metal ions (HMs) from simulated wastewater. The HMs removal performance of SLMI was compared with the conventional surfactant, Sodium Dodecyl Sulfate (SDS). The operational parameters, such as surfactant concentration, flotation time, initial pH, and ionic strength, were investigated in the ion flotation process. Results showed that a surfactant concentration of 200 mg/L was particularly effective for Pb removal. A significant enhancement in HMs removal, especially for Ni and Cu, was observed with a flotation time of 30 min, achieving SLMI removal efficiencies up to 97.9 % and 97.8 % for Ni and Cu, respectively. The study also revealed that initial pH was crucial in HMs speciation and removal, with efficiencies exceeding 98 % at pH levels above 8. Additionally, at lower ionic strengths (0 to 0.5 g/L NaCl), HMs removal efficiency remained stable but declined at higher NaCl concentrations. Significant three-dimensional fluorescence spectra variations were observed due to the interactions between SLMI and HMs in ion flotation. Findings from this study suggest that SLMI could be a potential environmentally friendly alternative for conventional surfactant (e.g., SDS) in the ion flotation process for HMs removal.