Separation and recovery of Ni ²⁺ by foam separation using soapberry extract

BACKGROUND Foam separation is a low‐energy method for recovering dilute metal ions, but its practical use is often limited by reliance on synthetic surfactants. This study evaluated soapberry extract (SE), a biodegradable natural surfactant, for the separation and recovery of Ni 2+ from aqueous solution. RESULTS The critical micelle concentration of SE was 0.5 g/L, lower than those of SDS, DBS, and CTAB and close to that of SDBS. Single‐factor experiments showed that pH, air flow rate, collection time, liquid loading volume, SE concentration, and initial Ni 2+ concentration all affected recovery efficiency and enrichment ratio. The best single‐factor conditions were pH 8, 350 mL/min air flow, 5 min collection time, 300 mL liquid loading volume, 0.2 g/L SE, and 10 mg/L NiSO 4 · 6H 2 O, giving 84.7% recovery and an enrichment ratio of 8.2. Orthogonal optimization further improved recovery to 87.1% at pH 8.5, with an enrichment ratio of 6.9. CONCLUSION SE can serve as an environmentally benign collector for Ni 2+ foam separation and merits further testing in real wastewater matrices.