Industrial & Engineering Chemistry Research, Vol.54, No.15, 3933-3941, 2015
Studies on Complexation and Supercritical Fluid Extraction of Cd2+ with Calixarenes
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 formation and to establish the stoichiometry of the complex of the type [Cd(calixarene)](2+). The present method was utilized for the supercritical fluid extraction of cadmium from real samples of battery, paint, tobacco, and wastewater.