Adsorption of chromium (VI) on hydrotalcite-hydroxyapatite material doped with carbon nanotubes: Equilibrium, kinetic and thermodynamic study

Hexavalent chromium adsorption in aqueous solution was studied in a fixed bed column with a hydrotalcite-hydroxyapatite (HT-HAp) material doped with carbon nanotubes (CNT) at 333.15 K. Equilibrium, kinetic and thermodynamic behaviors were the focus of this work. The CNT doping was performed in two different proportions (5 and 15%wt.). Isotherm (Langmuir, Freundlich, Temkin, Redlich-Peterson, Sips, and Toth) and kinetics (Thomas, Yoon-Nelson, and Adams-Bohart) models were tested. HT-HAp/CNT15 sample presented the best Cr(VI) bated proportion (76.97%R). The adsorption behavior was fit by the Freundlich model, following a pseudo-second order kinetic mechanism confirmed by Thomas model. Thermodynamic parameters indicated a physisorption process.