Complexation with calixarenes and efficient supercritical CO2 extraction of Pb(II) from acidic medium

The present study describes the extraction of lead(II) from acidic medium with supercritical carbon dioxide using various calixarenes. It involves the investigation of the effect of temperature, acid molarity, and the metal to complexing agent molar ratio on supercritical fluid extraction efficiency. Efficient extraction of Pb(II) was observed for p-t-butylcalix(4) arene with (92 +/- 3)% extraction at 323 K, 20.27 MPa, 30 minute static time followed by 30 minute dynamic time and a metal to complexing agent molar ratio of 1 : 5. The complexing ability of Pb(II) with calixarene was established by absorption and energy dispersive spectroscopy. The scanning electron micrograph of calixarene and the lead-calixarene complex was studied. The structure of the Pb(II)-calixarene complex has been proposed based on solvent extraction in hexane and IR spectroscopic analysis of the extract. Thermodynamic aspects of extraction were also studied and the extraction reaction was found to be entropy driven. Interference from other metal ions, on Pb(II) extraction behaviour, has been investigated. The developed method has been utilized for extraction of Pb(II) from real samples viz. paints, batteries, tobacco and wastewater.