Liquid–Liquid Extraction of Lithium Ions Using a Slug Flow Microreactor: Effect of Extraction Reagent and Microtube Material

ABSTRACT

Lithium ions were extracted from aqueous solutions into cyclohexane containing di-(2-ethylhexyl)phosphoric acid (D2EHPA) through slug flow in millimeter-diameter glass and polytetrafluoroethylene (PTFE) tubes. The PTFE tube produced a higher initial mass transfer coefficient than the glass tube by increasing internal circulation in the organic phase, and maintained its specific surface area. Slug flow occurred in the PTFE tube when the interfacial tension between the aqueous and organic phases exceeded 50–55 mN/m, which increased the rate of extraction owing to increased circulation in both phases. The addition of tributyl phosphate (TBP) enhanced the extraction efficiency, but did not affect the extraction rate.

KEYWORDS:

• Microchannel
• slug flow
• mass transfer coefficient
• wall film
• internal circulation flow

Acknowledgments

The authors sincerely thank Prof. Ryu of Osaka Prefecture University for suggestions regarding slug flow and the organic reaction. We are also grateful to Prof. Masuyama of Osaka Institute of Technology (OIT) for measuring the surface tension between the aqueous and organic phases. We would also like to thank Editage (www.editage.jp) for their help with editing the language used in the manuscript.