Kinetic and equilibrium studies on the uptake of Nd3+ and Sr2+ by Li–Al layered double hydroxide intercalated with 1-hydroxyethane-1,1-diphosphonic acid

1-Hydroxyethane-1,1-diphosphonic acid intercalated Li–Al layered double hydroxide (HEDP·Li–Al LDH) was prepared by co-precipitation. HEDP·Li–Al LDH was found to take up Nd3+ and Sr2+ ions from aqueous solutions; this can be attributed to the metal-chelating functions of the HEDP ions in the interlayers of HEDP·Li–Al LDH. Sr2+ uptake by HEDP·Li–Al LDH was larger than Nd3+ uptake. This is probably because the uptake of one mole of Nd3+ by HEDP·Li–Al LDH requires two times the number of moles of HEDP ions than the uptake of one mole of Sr2+. The mass-transfer-controlled shrinking core model described the uptake behavior better than the surface reaction-control model. HEDP ions in the HEDP·Li–Al LDH interlayer rapidly form chelate complexes with Nd3+ or Sr2+, as a result of which the transfer of Nd3+ or Sr2+ through the product layer is rate limiting. Furthermore, this reaction mechanism can be described by a Langmuir-type adsorption phenomenon, indicating that this reaction involves chemical adsorption; this is consistent with the formation of chelate complexes between Nd3+ or Sr2+ and HEDP ions in the interlayers of HEDP·Li–Al LDH. The control of chelate ions in the interlayer of Li–Al LDH leads to the control of the preferential uptake of metal ions.

Recommended molecular orientation of HEDP intercalation to the interlayer of Li–Al LDH.Figure optionsDownload as PowerPoint slide