Use of central composite design and surface modeling for cadmium (ii) ions removal from aqueous environment using novel modified layer double hydroxide

In this work, Zn2Al-layered double hydroxide (LDH) that modified with Ponceau 4R (E 124) as food coloring, (Zn2Al-LDH/Ponceau) was synthesized and characterized  using different techniques including, X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray (EDX) spectroscopy. Zn2Al-LDH/Ponceau was then applied for Cd2+ removal from aqueous solution. The response surface methodology (RSM) approach using central composite design (CCD) was applied to develop a mathematical model and optimize process parameters for Cd2+ removal from aqueous solution using a chemically modified Zn2Al-LDH/Ponceau. The optimal conditions to remove Cd2+ from aqueous solution were found to be initial Cd2+ concentration of 76 mg.L-1, pH value of 4.22, adsorbed amount of 0.04 g, temperature of 30.3 °C, and the contact time of 46 min. The isotherm and kinetics and thermodynamics of the adsorption were investigated in detail. The obtained results suggested the adsorption of Cd2+ onto Zn2Al-LDH/Ponceau follow Langmuir isotherm and the kinetic data are in good agreement with the Elovich kinetic model. In addition, the results of thermodynamic parameters indicated that the adsorption process was instantaneous nature and exothermic.