Characterization of Sidr Leaf-Derived Colloidal Gas Aphrons Using Dimensionless Numbers for Flotation Applications

Colloidal Gas Aphrons (CGAs) generated from Sidr leaf extracts offer a novel froth-flotation route for removing heavy metals, dyes, and aromatic compounds from aqueous solutions. The flow behavior of the CGAs was characterized using several dimensionless numbers, namely the capillary, Reynolds, and Weber numbers. These numbers were selected because they are directly relevant to the forces and dynamics that govern CGA stability and are well-suited to describing the flow. The capillary number was found to be directly proportional to the CGA loading rate. At higher loading rates, the CGAs moved through the column more rapidly, causing viscous forces to dominate surface-tension forces. Similarly, the Reynolds number increased linearly with the CGA loading rate, indicating that CGA velocity was the dominant factor governing the flow behavior. Meanwhile, the foam's effective viscosity remained relatively constant. For the Weber number, a linear increase in CGA velocity produced a quadratic increase in inertial forces, leading to pronounced CGA deformation and eventual structural collapse.

The removal of mixed Cu²⁺ and Pb²⁺ from aqueous solution was investigated at four CGA loading rates. At a CGA loading rate of 6.1 cm/min, 94.0% Cu²⁺ removal was achieved at a V_CGA/V_feed ratio of 1.8. As the CGA loading rate increased, the residence time of the CGAs in the column decreased, and more bulk water was carried over. Therefore, a lower CGA loading rate of 1.0 cm/min was used for the removal of dyes and aromatics. Fresh CGAs removed 78.8% of methylene blue and 37.0% of Congo red at an initial concentration of 50 mg/L. For the aromatic compounds, removal reached 85.3% for fluorene, compared with 64.6% for naphthalene. Overall, Sidr leaf extract serves as an effective, biodegradable surfactant for CGA-based flotation, supporting its potential use in sustainable water treatment.