Reusable bentonite clay: modelling and optimization of hazardous lead and p-nitrophenol adsorption using a response surface methodology approach

Abstract

In this work, bentonite clay (BC) calcined at 500 °C was used as an adsorbent (BC-500) for the adsorption of Pb²⁺ and p-nitrophenol. The ability of BC-500 for the removal of Pb²⁺ and p-nitrophenol has been investigated. The adsorption studies tailored well the pseudo-first-order and the Langmuir model for Pb²⁺ and p-nitrophenol both. In addition, the optimal removal of Pb²⁺ and p-nitrophenol was found at pH 5 for Pb²⁺ and pH 6 for p-nitrophenol. However, the change of temperature (20–60 °C) was found to have a negative effect on the adsorption process on BC-500. Based on the Dubinin–Radushkevich model the adsorption occurs via a physical process. Accordingly, the adsorption mechanism was proposed using N₂-physisorption analysis before and after adsorption of Pb²⁺ and p-nitrophenol. The reusability of BC-500 was examined and the outcomes recommended that BC-500 had good potential as an economic and proficient adsorbent for Pb²⁺ or p-nitrophenol from contaminated water. Finally, the experimental Pb²⁺ and p-nitrophenol removal efficiency were found to be 90.93 ± 2.15% and 98.06 ± 1.87% while the predicted value by model equals 91.28 ± 1.68 and 97.24 ± 2.54, respectively, showing that the predicted model values are in good agreement with the experimental value.