2011 Volume 18 Pages 123-135
2-Ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A), which is an effective extractant of Zn(II), was microencapsulated by in situ polymerization in a W/O/W emulsion system. Divinylbenzene was used as the wall material and polymerized in the organic phase by free radical polymerization. Microcapsules with large interconnected-spherical pores were successfully prepared. The pore size and the diameter of the microcapsules increased with increasing NaCl concentration in the inner aqueous phase. The diameter of the microcapsules was almost constant at around 230 μm and was independent of the concentration of PC-88A in the organic phase. The entrapment efficiency of PC-88A in the microcapsules was higher than 80% for all preparation conditions. The extraction of Zn(II) using the microcapsules containing PC-88A sharply increased at pH values greater than 2. Zn(II) extracted in the microcapsules was successfully back-extracted at pH values less than 2. It was confirmed that two molecules of PC-88A reacted with one Zn(II) ion by quantitative analysis of the relationship between the maximum amounts of Zn(II) extracted and the amount of PC-88A encapsulated in the microcapsules. The extraction rate of Zn(II) was accelerated by the formation of interconnected-spherical pores inside the microcapsules.
