Kinetics and the difference for extraction of praseodymium and neodymium from nitrate aqueous solution by [A336][NO₃] using the single drop technique

The kinetics and the difference for Pr(III) and Nd(III) extraction from nitrate aqueous solution using trialkylmethylammonium nitrate ([A336][NO₃]) as extractant were investigated by the single drop technique. The dependence of the extraction rate of Pr(III) and Nd(III) on the concentrations of free Pr(III) and Nd(III) ions, the concentrations of NaNO₃ and H⁺ in aqueous solutions, and the concentrations of [A336][NO₃] in kerosene solutions were discussed and the corresponding extraction rate equations for Pr(III) and Nd(III) were obtained. These equations demonstrated that the reaction rate constant of Pr(III) with [A336][NO₃] was double than that of Nd(III). The effect of the addition of diethylenetriaminepentaacetic acid (DTPA) on the difference in the extraction rate of Pr(III) and Nd(III) by [A336][NO₃] was also investigated. It was revealed that the difference in the complex formation rates of Pr(III) and Nd(III) with DTPA made a significant impact on the difference in the extraction rates of Pr(III) and Nd(III) with [A336][NO₃]. The ratio of extraction rates of Pr(III) to Nd(III) with [A336][NO₃] was in proportion to the ratio of complex formation rates of Pr(III) to Nd(III) with DTPA. The extraction rate difference for Pr(III) and Nd(III) with [A336][NO₃] increased due to a higher complex formation rate constant of DTPA with the free and un-complexed Nd(III) ions in the aqueous nitrate solution than that with Pr(III) ions. Therefore, the addition of DTPA in the aqueous nitrate solution is an effective method to intensify the separation of Pr(III) and Nd(III) in kinetics. The study on the extraction mechanism indicated that both the extraction of Pr(III) and Nd(III) by [A336][NO₃] were diffusion controlled, and the reactions obeyed S_N2 mechanism. The present work highlights a possible approach to strengthen the kinetic separation of Pr(III) and Nd(III).