Chromium(VI) removal by bone char–ZnO composite: Parameters optimization by response surface methodology and modeling

Abstract

This study presents the efficiency of bone char‐ –ZnO for eliminating chromium(VI) from aqueous solutions. The bone char‐ –ZnO composite was provided using sol‐–gel method. The elemental, morphology, surface analysis of bone char‐ –ZnO were fully studied. The prepared composite was mostly composed of Ca5(PO4)3OH and had a specific surface area of 28.09 m2/g. Results indicated that central composite design (CCD) has a desirable ability (R2 > 0.87) to predict chromium(VI) removal by bone char‐ –ZnO. Furthermore, the results suggest that the removal efficiency increased with the elevation of adsorbent dose, shaking rate, temperature, and contact time. Isotherm and kinetics investigation indicated that chromium adsorption process follows Langmuir model (R2 > 0.97 and Qm= 84.03 mg/g) and second‐ order kinetic model (R2 > 0.999). The values of ΔH° and ΔS° of the chromium adsorption reaction by bone char‐ –ZnO were obtained as 580 kJ/mol and 5.5 kJ/mol K, respectively, suggesting spontaneity and endothermicity of the reaction. Desorption study was also performed by two desorbent agents of distilled water and nitric acid. Overall, it can be concluded that the bone char‐ –ZnO composite is an efficient and potential adsorbent to be used in water and wastewater treatment plants. © 2018 American Institute of Chemical Engineers Environ Prog, 37: 1684–1695, 2018