Modeling and Optimization of Cr(VI) Adsorption onto Algerian Montmorillonite Using Response Surface Methodology

This work aims to remove hexavalent chromium from aqueous solutions by adsorption onto Algerian montmorillonite, a bentonite type from Maghnia (N.W. Algeria). The efficiency of the process was evaluated and optimized using Response Surface Methodology (RSM). Raw and activated samples have been characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy techniques (FTIR), scanning electron microscopy (SEM), X-ray fluorescence (XRF) and BET surface area analysis. The obtained results revealed that the acid-activated bentonite; is mainly composed of montmorillonite and exhibits a more uniform and homogeneous surface with a specific surface area (SSA) of 111 m2/g. The value of the specific surface area (SSA) for natural clay is 63.17 m2/g. The effects of physico-chemical parameters such as pH, adsorbent mass, contact time and initial concentration on the adsorption properties of Cr (VI) ions onto clays was investigated at room temperature. The obtained results revealed that the removal percentage of Cr(VI) ions from aqueous solution was 98% for 40 min and optimal pH 4. A central composite design (CCD) was used to optimise the adsorption conditions. The statistical model obtained is reliable (R2 = 0.993). Under optimal conditions, a Cr(VI) removal efficiency of 98% was achieved. The kinetics of Cr(VI) ions adsorption fitted well with the pseudo-second-order model. Langmuir and Freundlich adsorption isotherms were used to evaluate their potential fit to the experimental data.