Synthesis and Characterization of Nano-scale Clay Anion Exchanger and Its Application in Removing Arsenic from Aqueous System

Abstract

Layered double hydroxides (LDHs) have a great potential in arsenic removal due to their large surface areas and high anion exchange capacities. In this study, a new synthesis method involving fast coprecipitation followed by hydrothermal treatment has been used to synthesize stable homogeneous nano-scale MgAl-LDHs for As (V) removal. The products have been characterized using CHN, BET, XRD, FTIR, SEM, and TEM. The nano-scale LDHs synthesized in this study showed a poorer crystallinity, higher interlayer space, and smaller crystallite size than the commercial LDHs. The photon correlation spectroscopy showed that the nano-scale LDHs have a narrow particle size distribution with an equivalent hydrodynamic diameter of 122 nm. The adsorption isotherm of As (V) on the nano-scale LDHs with initial As (V) concentration 0.2-8 mg·dm-3 was best fitted by Freundlich model, while the isotherm with initial As (V) concentration 12-200 mg·dm-3 was best described by Langmuir model. The maximum adsorption capacity of As (V) on nano-scale LDHs was 78.1 mg/g, which was about 10 times higher than that of commercial LDHs. As (V) adsorption on nano-scale LDHs was a rapid process that achieved 92% adsorption equilibrium in 10 min. The adsorption of As (V) on nano-scale LDHs was confirmed by EDX analysis, and FTIR by showing a typical FTIR band at 830 cm-1. As (V) adsorbed on the nano-scale LDHs was effectively desorbed using 5 w/v% NaOH solution and the LDHs were successfully regenerated using 20 w/v% Mg (NO3) 2.6H2O solution. The results suggest that nano-scale LDHs as potential adsorbent for As (V) from waters, and that its reusability is possible.