Absorption spectroscopic study of synergistic extraction of praseodymium with benzoyl acetone in presence of crown ether

The extraction behaviour of Pr(III) from aqueous nitric acid medium employing benzoylacetone has been studied in presence of two crown ethers, viz., 15-crown-5 and benzo-15-crown-5 in chloroform medium using UV-vis absorption spectroscopy. The binary equilibrium constant (log kex) for the complex [Pr(benzoylacetonate)(NO3−)2(H2O)] in organic phase was found to be 1.170. The overall equilibrium constants (log K) for the ternary species [Pr(benzoylacetonate)(crown ether)(NO3−)2] were estimated to be 4.01 and 4.41 for 15-crown-5 and benzo-15-crown-5, respectively. The trend in the equilibrium constant values were very much in accordance with the nature of substitution of the donor moiety. The extraction of Pr(III) by the benzoylacetone-crown ether combination was maximum at pH 3.0 and extraction decreases with increase in pH. It has been found that the extent of extraction of Pr(III) in organic phase as the binary as well as ternary complex [Pr(benzoylacetonate)(NO3−)2(H2O)] and [Pr(benzoylacetonate)(crown ether)(NO3−)2], increases with increase in concentration of the ligand. Similar trend is observed in the extraction by only donors. Enthalpies and entropies of formation for the ternary extraction process have been estimated. In addition, the effect of NaNO3 as foreign salt was also studied and it was observed that with increase in ionic strength, percentage extraction increases.