Preparation and Characterization of Immobilized Chelate Extractant in PVA Gel Beads for an Efficient Recovery of Copper(II) in Aqueous Solution

Abstract

To efficiently recover metals from aqueous solutions using solvent extractions, the various types of immobilized chelate extractants have been proposed because the conventional liquid−liquid extraction requires a large quantity of organic solvents and a complicated equipment system. As a basis of developing a safer, simpler, and more environment-friendly chelate extraction process, in the present work, a commercial chelate extractant, 5-dodecylsalicylaldoxime in kerosene (LIX860-I), was originally immobilized in the polyvinylalcohol (PVA) gel beads. The PVA gel beads prepared were used for recovering copper(II) in the aqueous solutions containing cupric sulfate (0.4−0.7 wt % in CuSO4·5H2O). The gel beads of 5 mm in mean diameter were packed in a column of 5.4 cm in diameter for extracting copper(II) from the solution to the gel beads without direct contact of the solvent with the aqueous solution. The extraction was carried out in an expanded bed 8.2 cm in height by circulating the copper(II)-containing solution upward through the column. Copper(II) in the solution could steadily be extracted into the gel beads, although the process required a relatively long time due to the diffusion resistance of copper(II) in the gel phase. The progressive change of the extractant in a bead was found to be elucidated by the shrinking core model. A practical extraction process was suggested to employ the earlier stage of the extraction process where the rate was relatively high. The estimated chelation equilibrium between copper(II) and the chelate extractant in the gel beads was almost the same as that in the liquid−liquid extraction. The sorption equilibrium of copper(II) into the bead was well-described by the Langmuir-type isotherm, suggesting almost perfect utilization of the extractant immobilized in the bead. The copper(II) extracted in the gel beads was completely recovered by stripping with an aqueous sulfuric acid solution of a high concentration of 225 g/L. The gel beads could be reused at least three times with negligible leakage of the LIX860-I and no damage to the beads. The PVA gel beads are recommended to be kept in the column and cyclically utilized by extracting copper(II) from the aqueous solution and then stripping it.