Comparative study on As(III) and As(V) adsorption by CO32--intercalated Fe/Mn-LDHs from aqueous solution

Arsenic pollution prevails in rivers and reservoirs in nonferrous metal mining areas, especially in lead–zinc mining areas, which affects the health of the people residing in such areas. Arsenic usually exists as As(III) and As(V) in water, and the adsorption of As(III) and As(V) changes with the type of adsorbent used. In this work, we report a novel adsorbent Fe/Mn–CO3-layered double hydroxide (Fe/Mn–CO3-LDH) composite that can efficiently remove both As(III) and As(V) from water. When the initial concentrations of As(III) and As(V) were 5, 10 and 50 mg/L, the adsorption capacities were 10.12–53.90 and 10.82–48.24 mg/g in the temperature range of 25–45 °C, respectively. The adsorption kinetics conformed well to the pseudo-second-order kinetic model, with all of the fitted correlation coefficients being above 0.998 for all the three initial concentrations (5, 10 and 50 mg/L) tested, suggesting a chemisorption-dominated process. The adsorption isotherms of As(III) and As(V) by Fe/Mn–CO3-LDHs conformed better to the Freundlich model than to the Langmuir one, indicating a heterogeneous reversible adsorption process. The theoretical maximum adsorption capacity increased with the increase in temperature. During adsorption, As(III) was partially converted to As(V), which was further interacted with intralayer anions. While the electrostatic attraction played an important role in the adsorption of As(V).