EXTRACTION OF HEXAVALENT CHROMIUM IONS WITH POLYUREA MICROCAPSULES

The extraction of metal ions from aqueous solutions has been studied using polyurea microcapsules. Experimental results showed that when N235 was used as an extractant encapsulated with the microcapsules, the extraction rate for chromium(VI) was much faster than that for cobalt(II) and copper(II). Among the extractants tested, trioctylamine (TOA) gave the best results. When tributyl phosphate (TBP) was used as an extractant, the mean diameter of the microcapsules was smaller due to the lower interfacial tension at the oil/water interface. The extraction rate increased with a decrease in pH in the feed solution, but increased with an increase in TOA concentration in the microcapsules. When the molar ratio of tolylene 2,4-diisocyanate to diethylene triamine for preparing the microcapsules was varied from 1/4 to 1/8, the extraction rate decreased, indicating that the membrane formulation had impact on the mass transfer across the membrane. The stripping of the chromium ions from the microcapsules can be promoted by raising the pH in the stripping solution.