Mg-Al layered double hydroxide intercalated with ethylene-diaminetetraacetate anion: Synthesis and application to the uptake of heavy metal ions from an aqueous solution

The development of a scavenger, which has a function of selective uptake of heavy metal ions from an aqueous solution with a high concentration, has been attempted by coupling Mg-Al layered double hydroxide (Mg-Al LDH) with ethylenediaminetetraacetate (edta) anion. edta·Mg-Al LDH that had an edta anion intercalated in the interlayer of Mg-Al LDH, could be synthesized by adding a solution of Mg(NO₃)₂ and Al(NO₃) ₃ to a solution of NaOH and edta-2Na (disodium dihydrogen edta dihydrate). The effect of the NaOH concentration in the solution on the formation of edta·Mg-Al LDH was examined to control the chemical species of the edta anion incorporated in the interlayer. The synthesized edta·Mg-Al LDH was found to have a capacity for rapid uptake of Cu ²⁺ and Cd²⁺ from an aqueous solution at the constant pH of 5.0. This capacity is attributed to the formation of the edta-metal complex in the interlayer of edta·Mg-Al LDH. This paper reports that the concentration of Cu²⁺ decreased from 64 mg/l to less than the effluent standards in Japan (3 mg/l) due to the edta·Mg-Al LDH in a short span of 10 min. Furthermore, the concentration of Cd²⁺ decreased from 112 mg/l to less than 1 mg/l within 15 min. The Cu²⁺ was observed to be preferentially uptaken from a Cu-Cd mixed chloride solution by the edta·Mg-Al LDH at the pH of 5.0. The function of edta anions as chelating agents is considered to be adequately active in the interlayer of edta·Mg-Al LDH.