Efficient removal of Cr(VI) from aqueous solution using activated carbon synthesized from silver berry seeds: modeling and optimization using central composite design

Synthesized activated carbon from silver berry (Elaeagnus angustifolia L.) seeds (AC(SBS)) was used as a low-cost adsorbent for the removal of hexavalent chromium (Cr(VI)) in aqueous solutions via a batch process. In this study, three process parameters like pH (2.5-8.5), AC(SBS) dosage (0.5-2.5 g/L), and initial concentration of Cr(VI) (10-100 mg/L) were optimized using a three-factor, five-level central composite design (CCD) to assess their effects on the Cr(VI) removal efficiency (R%). Equilibrium adsorption isotherm and kinetic were investigated under the optimum conditions. Results showed a good predictability between experimental and predicted values of Cr(VI) removal efficiency by the quadratic model (R-2 > 0.98) with a high F-value (134.02) and a low P-value (< 0.05). Results also showed that the highest removal efficiency of 99.84% was achieved with a pH of 2.5, an AC(SBS) dosage of 2.27 g/L, and an initial Cr(VI) concentration of 99.09 mg/L. Results confirmed that the CCD has been a useful tool in optimizing the adsorption process. The adsorption equilibrium data were best fitted by the Langmuir model with a maximum monolayer adsorption capacity of 88.57 mg/g. The adsorption process showed a pseudo-second order kinetic model and the adsorption rate of Cr(VI) on the AC(SBS) was controlled by external film and intra-particle diffusion mechanisms. The activated carbon synthesized from silver berry seeds could be used as an alternative to commercial activated carbons for industrial water treatment.