A new hydrotalcite-like absorbent FeMnMg-LDH and its adsorption capacity for Pb~(2+) ions in water

摘要

A new hydrotalcite-like material layered double hydroxide (FeMnMg-LDH) with potentials used as adsorbent was synthesized based on a co-precipitation method. The Fe/Mn/Mg molar ratio in its crystal structure is 1:1:2. Well lamellar structure of the synthesized FeMnMg-LDH has been proved by its transmission electron microscope (TEM) images and the diffraction peaks are similar to the characteristic peaks of typical LDHs. Its adsorption characteristics for heavy metals, taking Pb2+ as an example, were examined in this paper. The maximum Pb2+ adsorption capacity of FeMnMg-LDH was about 421.42 mg/g at 25 degrees C, which is much higher than those of the most other similar kind of absorbents. In addition, it could keep a Pb2+ removal efficiency higher than 97% from aqueous solution at a wide pH range (pH 3-6). Thermodynamic parameters Delta H degrees, Delta S degrees and Delta G degrees have been calculated. Positive value of Delta H and negative value of Delta G demonstrate an endothermic and spontaneous process of Pb2+ adsorption on the FeMnMg-LDH sample. The adsorption mechanisms mainly involve surface-induced precipitation and ion exchange. The coexisting divalent cations could compete with Pb2+ ions for the adsorption following a competing ability of Cu2+ Cd2+ Mg2+ Ca2+. The results suggested that the synthesized FeMnMg-LDH material could be served as a potential material for the remediation of heavy metal contamination in water.