Selectivity Sequence of Multivalent Lanthanides for their Separation on Antimonate Based Exchangers

Abstract

The adsorption of trivalent lanthanide ions, Ln3+ (La3+, Pr3+, Nd3+, Gd3+, and Er3+), using two antimonate based exchangers, namely, silicon antimonate (SiSb) and poly(acrylamide titanium antimonate), PAmTA, was studied from their nitrate solutions at pH 3.5 ± 0.1. The formation constants in Ln3+/SiSb and Ln3+/PAmTA systems, logK S1 and logK S2 , were calculated for the above mentioned lanthanides. The K d values of the selected lanthanides were calculated at 30, 40, 50, and 60°C reaction temperatures. A fractionation is observed that due to the selective sorption between the heavy rare earths (HREEs) and the light rare earths (LREEs) at various reaction temperatures, the HREEs are being more sorbed than the LREEs. The selectivity order increased with increasing atomic number of these ions. Log K d -Z plots revealed the presence of the M-type tetrad phenomenon in the system. Furthermore, the calculated separation factors showed that, binary separations for Er+3/La+3, Er+3/Pr+3, Er+3/Nd+3, and Gd+3/La+3 on SiSb, while, Er+3/Gd+3, Gd+3/Pr+3, Gd+3/Nd+3, Nd+3/La+3, and Nd+3/Pr+3, side by side to the mentioned separations could be accomplished on PAmTA at 30°C. The separation efficiency was found to increase with increasing in reaction temperatures. On PAmTA (at 40°C and 50°C) and on SiSb (at 50°C), Er+3/(La+3, Pr+3, Nd+3, Gd+3), Gd+3/(La+3, Pr+3, Nd+3), Nd+3/(La+3, Pr+3) fractionations were also noticed, while on the surface of SiSb at 40°C, Gd+3/La+3 and Gd+3/Pr+3 could be added to the list of binary separations at 30°C. Nevertheless, La+3/Pr+3 break through could not be obtained at any reaction temperature. Kinetic investigations were carried out; drawing an analogy, the pseudo second-order model was more agreeable to fit the data.