Uptake of Nd³⁺ and Sr²⁺ by Li-Al layered double hydroxides intercalated with ethylenediaminetetraacetate

A Li-Al layered double hydroxide intercalated with ethylenediaminetetraacetate (EDTA·Li-Al LDH) was prepared by the drop-wise addition of an Al solution to a Li-EDTA solution at a constant pH of 8.0. EDTA·Li-Al LDH was found to take up Nd³⁺ and Sr²⁺ ions from aqueous solutions, which can be attributed to the metal-chelating functions of the EDTA ions in the interlayers of EDTA·Li-Al LDH. However, EDTA·Li-Al LDH was found to be inferior to Li-Al LDH intercalated with triethylenetetramine-hexaacetic acid (TTHA·Li-Al LDH) for both Nd³⁺ and Sr²⁺ uptake. This may be explained by the fact that the Nd-EDTA and Sr-EDTA complexes are less stable than the Nd-TTHA and Sr-TTHA complexes, respectively, leading to the lower uptake of Nd³⁺and Sr²⁺, respectively. Further, EDTA·Li-Al LDH was found to take up Nd³⁺ ions preferentially over Sr²⁺ ions from aqueous solutions, which may be caused by the fact that the Nd-EDTA complex is more stable than the Sr-EDTA complex. It should be noted that the Nd³⁺/Sr²⁺ uptake selectivity in the case of EDTA·Li-Al LDH was higher than that in the case of TTHA·Li-Al LDH. In other words, EDTA·Li-Al LDH was found to be superior to TTHA·Li-Al LDH in selectively taking up metal ions.