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 center dot Li-Al LDH) was prepared by co-precipitation. HEDP center dot 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 center dot 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 center dot 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. (C) 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.