Removal of Cu, Pb and Zn by foam fractionation and a soil washing process from contaminated industrial soils using soapberry-derived saponin: A comparative effectiveness assessment

• Contaminated soil of heavy metals was remedied using biosurfactants, saponin and surfactin.
• Foam fractionation and soil washing process were studied.
• Removal efficiency was strongly influenced by concentration, pH and incubation time.
• The removal efficiencies were noticed in the order of Pb > Cu > Zn.
• We report an environment friendly and applicable for metal removal.

The feasibility of using the eco-friendly biodegradable surfactant saponin (a plant-based surfactant) from soapberry and surfactin from Bacillus subtilis (BBK006) for the removal of heavy metals from contaminated industrial soil (6511 mg kg−1 copper, 4955 mg kg−1 lead, and 15 090 mg kg−1 zinc) by foam fractionation and a soil flushing process was evaluated under variation of fundamental factors (surfactant concentration, pH, temperature and time). The results of latter process showed that 1–2% Pb, 16–17% Cu and 21–24% Zn was removed by surfactin after 48 h, whereas the removal of Pb, Cu and Zn was increased from 40% to 47%, 30% to 36% and 16% to 18% in presence of saponin with an increase from 24 to 72 h at room temperature by the soil washing process at pH 4. In the foam fractionation process, the metal removal efficiencies were increased with increases in the saponin concentration (0.075–0.15 g L−1) and time (24–72 h), whereas the efficiency was decreased with increasing pH (4–10) and temperature (>40 °C). The removal efficiencies of Pb, Cu and Zn were increased significantly from 57% to 98%, 85% to 95% and 55% to 56% with an increase in the flow rate from 0.2 to 1.0 L min−1 at 0.15 g L−1 saponin (pH 4 and 30 °C). The present investigation indicated that the foam fractionation process is more efficient for the removal of heavy metal from contaminated industrial soil in comparison to the soil washing process. The plant-based eco-friendly biodegradable biosurfactant saponin can be used for environmental cleanup and pollution management.