Comparative analysis of lead and cadmium extraction capacities of hydrophobic deep eutectic solvents

In this study, a total of eight hydrophobic deep eutectic solvents (HDESs) were prepared and evaluated for their efficacy in extracting lead and cadmium from aqueous solutions. The physical and thermal properties of these HDESs were characterized. Among the HDESs tested, the thymol:decanoic acid system, with a molar ratio of 1:1, exhibited the highest distribution ratios for lead and cadmium, with values of 0.79 and 0.55, respectively. The extraction performance of the thymol:decanoic acid system was further investigated by considering various factors such as contact time, pH, mass ratio of water to HDES, and HDES molar ratio. After optimization, the thymol:decanoic acid HDES demonstrated significantly improved extraction efficiency for lead (up to 93.49 %) and cadmium (up to 76.70 %) at initial concentrations of 1000 ppm and 100 ppm, respectively. The extraction mechanism was found to be primarily driven by the complexation and partitioning effects of thymol:decanoic acid with lead or cadmium, as confirmed by the noticeable changes in harmonic frequencies (730, 1337, and 1515 cm-1) observed in the IR spectra analysis before and after extraction. Additionally, the performance of the thymol:decanoic acid HDES was evaluated through solvent regeneration using a multi-stage extraction and reuse approach.