Microencapsulation of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) in the microcapsules with hydrophilic wall were carried out using two-step crosslinking of sodium alginate by Ca2+ ion and polyvinyl alcohol by glutaraldehyde. The morphologies of the microcapsules prepared and during the preparation were investigated. The extraction properties of Co(II) in ammonium sulfate solution using the microcapsules were also investigated under various conditions. Spherical and oval microcapsules containing PC88-A droplets with the diameter around 3mm were successfully prepared. The inside of the microcapsules was observed darkly by a lot of small droplets of PC-88A. The extraction of Co(II) using the microcapsules containing PC-88A was sharply increased at pH higher than 4. It was confirmed that Co(II) ion was extracted by two molecules of PC-88A in the condition at high Co(II) concentration range from the analysis of the relationship between the maximum amount of Co(II) extracted and the PC-88A content in the microcapsule. The extraction of Co(II) was analyzed quantitatively by three-step reaction model that is stepwise reaction with the cluster of three PC-88A-dimer, and was able to explain successfully based on the analysis. Co(II) extracted in the microcapsules was successfully back-extracted at pH lower than 2. The microcapsules containing PC-88A could be used repeatedly for several times for the extraction and back-extraction processes of Co(II).
