Air-assisted solvent extraction: towards a novel extraction process

The air-assisted solvent extraction (AASX) concept uses a solvent-coated bubble to contact the organic and aqueous phases. Compared to conventional solvent extraction, a high contact area can be created using less solvent and the natural buoyancy provided by the air core promotes phase separation. A method of producing coated bubbles exploiting foaming properties of kerosene-based solvent is introduced. Coating thickness is estimated at ≈3 μm on a 0.44 cm diameter bubble giving a solvent specific surface area of ≈3000 cm2/cm3, equivalent to a solvent droplet of ≈20 μm. Such a droplet would have very poor phase separation properties. In extraction tests (500 mg/l Cu solution), high aqueous/organic ratios could be used (e.g., 75:1) while phase separation remained excellent. This shows the potential for AASX to treat large volume, low concentration streams such as acid mine drainage.