NiFe-Layered Double Hydroxide Nanocomposites with Functionalized Bentonite Clay to Attenuate Lead Ions in Wastewater: Isothermal and Kinetic Studies

In this study, the efficiency of NiFe-layered double hydroxide (LDH), functionalized bentonite clay (F-bentonite) and their composites as adsorbents to remove lead ions (Pb2+) in aqueous solution was investigated. Batch tests revealed 60 min as the equilibrium contact time with a maximum removal efficiency of nearly 99%, and maximum adsorption capacity of 151 mg g(-1) was observed when using the composite adsorbent of LDH and functionalized bentonite. A maximum uptake capacity of 97.40 mg g(-1) for the LDH-F/bentonite composite was estimated at an optimum pH value of 6-7. A 99% removal efficiency by using 0.2 g of LDH-F/bentonite adsorbent and a maximum adsorption capacity of 177 mg g(-1) at an optimum Pb2+ concentration of 60 mg L-1 were also estimated. A best-fit of the Langmuir isotherm to the adsorption data of Pb2+ suggested a monolayer adsorption process while a physical adsorption system based on the findings of Dubinin-Radushkevich isotherm was proposed in addition to both homogeneous and heterogeneous adsorptions of Pb2+ as suggested by Sips and Redlich-Peterson models. The best-fit of the pseudo-second-order kinetic model proposed chemisorption as controlling mechanism of adsorption. The images of scanning electron microscopy and the weight percentage values in energy-dispersive X-ray analysis confirmed the adsorption of Pb2+ on the studied adsorbents. Moreover, the formation of a nanocomposite and the exchange of Pb2+ with anions on the adsorbent surfaces were suggested by both elemental analysis and FTIR spectroscopy.