Adsorption isotherms and kinetics of arsenic removal from aqueous solution by Mg-Al layered double hydroxide intercalated with nitrate ions

Arsenic contamination in groundwater is an environmental problem that affects large populations on the global scale. The anion exchange material, Mg-Al layered double hydroxide (Mg-Al LDH) intercalated with NO3 (-), is an effective adsorbent for removing As(V) from aqueous solutions. In this study, we prepared Mg-Al LDH with a high anion exchange capacity by the co-precipitation method, and investigated its adsorption isotherm and reaction kinetics with As(V). The adsorption process is well described by the Langmuir model. The maximum adsorption capacities were determined to be 142.86 and 76.92 mg/g for LDHs synthesized with initial Mg/Al molar ratios of 2 and 4, respectively. The reaction kinetics of As(V) with Mg-Al LDH is demonstrated to be pseudo-second order, which indicates that chemisorption (i.e., anion exchange of HAsO4 (2-) with the intercalated NO3 (-)) is the rate determining step. The values of the activation energy also indicate that anion exchange is the predominant adsorption mechanism.