Kinetics and equilibrium studies on the uptake of rare earth ions from aqueous solution using a Cu-Al layered double hydroxide intercalated with ethylenediaminetetraacetate

A Cu-AI layered double hydroxide intercalated with edta ions (edta•Cu-Al LDH) was able to take up rare earth ions from an aqueous solution. To determine the reaction mechanism, we have conducted kinetics and equilibrium studies on the uptake of rare earth ions such as Y³⁺, Sc³⁺, and La³⁺ from aqueous solution using edta•Cu-Al LDH. The uptake is more adequately described by the mass-transfer-controlled shrinking core model than by the surface-reaction-controlled model. The apparent activation energies were 19.6, 28.8, and 36.0 U mol^-1 for Sc ³⁺, Y³⁺, and La³⁺, respectively, confirming that the reaction involved in the uptake of M³⁺ by edta•Cu-Al LDH proceeds under mass transfer control. This reaction can also be expressed by Langmuir-type adsorption, suggesting the formation of a 1:1 chelate complex between rare earth ions and edta ions in the edta•Cu-Al LDH interlayer. The equilibrium adsorption constants were 4.4, 0.89, and 0.41 and the maximum adsorption amounts were 1.4, 0.3, and 0.5 mmol g^-1 for Sc ³⁺, Y³⁺, and La³⁺, respectively.