The selective and sustainable separation of Cd(II) using C6MImT/[C6MIm]PF6 extractant

Cadmium has been classified as a kind of human carcinogens, and has a strong mobility in the water environment and this can result in serious harm to human health and environmental safety. Here, a new selective and efficient extraction-recovery strategy for Cd purification is provided by using C₆MimT/[C₆Mim]PF₆ as the green extractant. Due to the high compatibility between C₆MimT and [C₆Mim]PF₆, C₆MimT-Cd was efficiently separated from the aqueous phase. When the concentration of Cd(II) was 1000 mg/L, the extraction rate could reached 99.9 %. By comparing [C₆MIm]BF₄ with [C₆MIm]PF₆, the hydrophobicity restrained the ion exchange between cation and Cd and significantly reduced the loss of extractant. The extracted Cd(II) was separated in the form of precipitation after stripping. The extraction system of C₆MimT/[C₆Mim]PF₆ was stable after several extraction-stripping cycles. The extraction of Cd(II) by C₆MimT/[C₆Mim]PF₆ system mainly realized by forming a neutral and extractable cadmium complexes between Cd(II) and thione. Based on the natural complexation mechanism between metal and C₆MImT, Cd exists as obvious competitive advantage in coordination with C₆MimT compare to Pb, Zn, Mg, Cr, Fe. This work overcomes the problems of extractant loss and organic pollution caused by volatile or ion exchange, which can only reduce environmental hazards, but also promote the recovery of cadmium and other valuable resources.

Kinetic and equilibrium studies of the removal of cadmium ions from acidic chloride solutions by hydrophobic pyridinecarboxamide extractants

Liquid-liquid extraction of cadmium(II) from acidic chloride solutions was carried out with alkyl derivatives of pyridinecarboxamide in toluene with addition of 2-ethylhexan-1-ol as modifier. Equilibrium as well as kinetic studies was performed. The kinetic studies of a Cd(II) extraction process were carried out with a Lewis cell having a constant interfacial area. Cadmium(II) concentration in the aqueous phases was determined by atomic absorption spectroscopy (Varian SPECTR AA800). The results of equilibrium experiments showed that cadmium(II) was quantitatively extracted with N,N-dihexylpyridine-3-carboxamide whereas the derivative N,N-dihexylpyridine-2-carboxamide was not able to transfer Cd(II) ions from the aqueous phase to the organic one. Thus, the kinetics of extraction and the initial extraction rate were examined only in the systems with N,N-dihexylpyridine-3-carboxamide. The obtained experimental data as well as the calculated values of mass transfer coefficients suggest that the investigated process of extraction of Cd(II) by means of pyridinecarboxamide as extractant occurs in the mixed diffusion-kinetic region. Moreover, the results of adsorption studies indicated that the extraction of Cd(II) with a hydrophobic extractant should be considered as an interfacial process.