Uptake of heavy metal ions from aqueous solution using Mg-Al layered double hydroxides intercalated with citrate, malate, and tartrate

Mg-Al layered double hydroxide (Mg-Al LDH) was modified with organic acid anions using a coprecipitation technique, and the uptake of heavy metal ions from aqueous solution by the Mg-Al LDH was studied. Citrate.Mg-Al LDH, malate.Mg-Al LDH, or tartrate.Mg-Al LDH, which had citrate(3-) (C6H5O73-), malate(2-) (C(4)H(4)o(5)(2-)), or tartrate(2-) (C4H4O62-) anions intercalated in the interlayer, was prepared by dropwise addition of a mixed aqueous solution of Mg(NO3)(2) and Al(NO3)(3) to a citrate, malate, or tartrate solution at a constant pH of 10.5. These Mg-Al LDHs were found to take up Cu2+ and Cd2+ rapidly from an aqueous solution at a constant pH of 5.0. This capacity was mainly attributable to the formation of the citrate-metal, malate-metal, and tartrate-metal complexes in the interlayers of the Mg-Al LDHs. The uptake of Cu2+ increased in the order malate.Mg-Al LDH < tartrate.Mg-Al LDH < citrate.Mg-Al LDH. The uptake of Cd2+ increased in the order malate.Mg-Al LDH < tartrate.Mg-Al LDH = citrate.Mg-Al LDH. These differences in Cu2+ and Cd2+ uptake were attributable to differences in the stabilities of the citrate-metal, malate-metal, and tartrate-metal complexes. These results indicate that citrate(3-), malate(2-), and tartrate(2-) were adequately active as chelating agents in the interlayers of Mg-Al LDHs. (C) 2008 Elsevier B.V. All rights reserved.