Regeneration and reuse of bio-surfactant to produce colloidal gas aphrons for heavy metal ions removal using single and multistage cascade flotation

Bio-surfactants are commonly used in the treatment of wastewaters due to their favorable characteristics such as biodegradability and low toxicity. In this work, the bio-surfactants are extracted from low cost substrates like Ziziphus spina-christi (ZSC) plant leaves to reduce the cost of production. Thereafter, the bio-surfactant extracts were used for the preparation of colloidal gas aphrons (CGAs) to remove heavy metal ions (Cu ²⁺ , Pb ²⁺ ) from aqueous solutions. The molecules extracted from the leaves induced the foaming and detergent properties of the solution. Surface tension and electric conductivity techniques confirmed the formation of critical micelle at 5 wt% surfactant concentration. CGA bubbles were generated using the bio-surfactant extracts and employed in single stage and multistage cascaded flotation units to remove Cu ²⁺ and Pb ²⁺ from aqueous solutions. In the single stage flotation, the removal of Pb ²⁺ and Cu ²⁺ from the single and equimolar mixed solution were low. However, in the multistage cascade flotation, the removal efficiency of Pb ²⁺ and Cu ²⁺ increased significantly to 90.7% and 88.2%, respectively. Interestingly, the collected foamate from the flotation columns was regenerated using calcium alginate adsorbent and reused further to prepare the CGAs. Bio-surfactant solution obtained from the leaves of ZSC proved to be useful in the preparation of CGAs and the treatment of heavy metal containing wastewater.