Adsorption of Pb(II) from aqueous solutions onto MgFeAl-CO3 LDH: thermodynamic and kinetic studies

The objective of this work is to determine the kinetic and thermodynamic properties of adsorption of Pb(II) from aqueous solutions by synthetically prepared MgFeAl-CO3 as layered double hydroxide (LDH) adsorbent. Compared to other adsorbents for heavy metal removal from aqueous solutions, LDH materials possessed many advantages such as nontoxic synthesis, chemical stability, environmentally friendly, and facile separation from the water solution. The synthesis of LDH was achieved by a co-precipitation method. The reaction products were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy with energy dispersive spectroscopy and N-2 sorption-desorption isotherm analysis. The adsorption rates were investigated. The effect of the parameters such as contact time, initial metal ion concentration, and temperature on the adsorption of the Pb(II) was studied. Equilibrium was achieved in 60 min and the equilibrium adsorption capacity was found to be increased with the increase in the Pb(II) initial concentration. The removal efficiency of Pb(II) increases from 59.50% to 71.15% when the temperature increases from 15 degrees C to 60 degrees C. The pseudo-first-order, pseudo-second-order, and Elovich kinetic models were tested and the first was found to fit better to the experimental data. The application of the intra-particle diffusion model demonstrates that the surface diffusion and the intra-particle diffusion occur in parallel during the adsorption of Pb(II) onto MgFeAl-CO3. The equilibrium adsorption data were analyzed by Langmuir, Freundlich, Redlich- Peterson, and Temkin isotherm models. The results indicated that the Redlich-Peterson and Langmuir isotherms were the most suitable models for the obtained experimental data and the Langmuir maximum adsorption capacity of the MgFeAl-CO3 is found to be 117.86 mg g(-1) at 298.15 K. The thermodynamic analysis of the adsorption of Pb(II) on MgFeAl-CO3 reveals that the present adsorption process is a spontaneous and endothermic reaction.