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In the present study, we explored the extraction of Cd2+ by supercritical fluid carbon dioxide using calixarenes as complexing agents in acidic medium. The optimum conditions for the extraction of cadmium were found to be 30 min of static extraction followed by 30 min of dynamic extraction, a temperature of 323 K, a pressure of 20.27 MPa, a CO2 flow rate of 2 mL min–1, and a nitric acid concentration of 0.1 M. Among the studied calixarenes, hexaacetylcalix[6]arene gave the maximum extraction efficiency of (90 ± 2)% in acidic medium. The presence of fluorinated pentadecafluoro-n-octanoic acid led to the enhancement of the extraction efficiency. The formation of a cadmium–calixarene complex was supported by energy-dispersive X-ray spectrocopy and UV–visible absorbance spectrocopy. Calixarene and its complex with cadmium were found to have distinctly different features in their scanning electron microscopy images. A solvent extraction study was carried out to study the thermodynamic aspects of complex format...

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.

Various calixarenes were evaluated for the supercritical fluid extraction of uranium from nitric acid medium. The extraction efficiency was found to be affected by various parameters, namely pressure, temperature, CO2 flowrate, extraction time, and molarity of nitric acid. The addition of HPFOA (pentadecafluoro-n-octanoic acid) for the production of CO2-phillic fluorinated counter ion enhanced the extraction efficiency. Under optimized conditions (pressure of 200 atm, temperature of 323 K, 30 minutes of static time followed by 30 minutes of dynamic time, CO2 flowrate of 2 mL min−1, nitric acid molarity of 0.1 M) for uranium: calixarene: HPFOA mole ratio of 1:5:10, highest extraction efficiency could be obtained with p-tert.-butyl calix[6]arene (79.9%). Solvent extraction study with hexane as the organic phase indicated the formation of [UO2 (calixarene)]2+. In order to assess the suitability of the developed method to extract uranium in the presence of a host of other ions, extraction efficiency for other...