HF-Free Synthesis of α-Zirconium Phosphate and Its Use as Ion Exchanger for Separation of Nd(III) and Dy(III) from a Ternary Co–Nd–Dy System

Abstract

The recovery of Nd and Dy from a ternary Co-Nd-Dy system using layered crystalline zirconium phosphate (alpha-ZrP) was investigated. alpha-ZrP was synthesized by the refluxing method, and subsequently characterized by sodium hydroxide titration, Fourier transform-infrared spectrometry, thermogravimetry, scanning electron microscopy, and X-ray diffraction. The selectivity and ion exchange kinetics of the alpha-ZrP material were determined with regard to the individual elements. The influence of solution pH on the uptake was studied in ternary 1 and 2 mM equimolar solutions. The results showed that in acidic solution (pH 1-3), very little Co was taken up, while Nd and Dy uptakes were at reasonable levels (0.5-0.6 meq/g). The uptake isotherms of Nd, Dy, and Co were measured separately at pH 2.5 and 4.5 in ternary equimolar solution series. At pH 4.5, the loading capacities were about 0.2 meq/g for Co, 1.1 meq/g for Nd, and 1.5 meq/g for Dy. Dy was thus clearly preferred over Nd by alpha-ZrP. The loading of an alpha-ZrP column showed a similar preferred pattern. Nitric acid eluent removed Co, Nd, and Dy, but there was no separation of the metals in the eluate. A mixture of nitric and phosphoric acids, however, produced a strong separation. Co was very weakly retained in the column, and the ratio Dy/Nd in the eluent was in the range of 2-7. Thus, the alpha-ZrP material showed encouraging ion exchange properties for the separation and recycling of Nd and Dy from a ternary Co-Nd-Dy system. Much more work is needed, however, to develop a practical separation flowsheet.