Sorption of metal cations on layered double hydroxides

Layered double hydroxides (LDHs) are a class of ionic lamellar compounds made up of positively charged brucite-like layers with an interlayer region containing charge compensating anions and solvation molecules. In recent years, many studies have focused on the application of LDHs in environmental remediation of anion pollutant. Meanwhile many reports are devoted to investigating the ability of LDHs to remove metal cations such as Pb2+, Cd2+ and Cu2+ from aqueous solutions. This paper provides an overview of the recent advances achieved in sorption of metal cations on LDHs. Sorption behaviors of various cations on LDHs including sorption isotherms and kinetics have been comprehensively reviewed. Several essential factors such as pH, temperature, ionic strength that influence the sorption are discussed. The sorption mechanisms including precipitation, surface complexation, isomorphic substitution and chelation with the anions in the interlayer of LDHs are discussed in detail. Possible improvement and potential applications of LDHs in the future are also proposed.