Application of Box-Behnken design for optimizing parameters of hexavalent chromium removal from aqueous solutions using Fe3O4 loaded on activated carbon prepared from alga: Kinetics and equilibrium study

In the present paper, the Response Surface Methodology (RSM) was evaluated for optimizing the Hexavalent Chromium (Cr (VI)) removal efficiency using our synthesized adsorbent, i.e., Fe3O4-NPs loaded on activated carbon (AC-Fe3O4-NPs). For studying the characteristics of synthesized catalyst, the different analyses, e.g., pHpzc, XRD, FE-SEM, and VSM was utilized. As detected in results, a suitable correlation could be perceived between the values obtained by experiments and the values predicted by the quadratic model (P 0.05). Results revealed that the efficiency of Cr (VI) adsorption decreases by an increase in pH values and an increase in the reaction time and adsorbent dosage was led to development of the process efficiency. Through employment of analysis of variance (ANOVA) for comparing acquired data, the optimum conditions was proposed; these conditions were pH of 3, pollutant concentration of 40 mg/L, the adsorbent concentration of 1 g/L, and time of 90. At these determined conditions, Cr (VI) adsorption efficiency was higher than 21.90 %. The Cr (VI) adsorption experimental data were superlatively fitted to the Freundlich isotherm model and the removal followed the pseudo-second-order kinetic model (R2 0.99). The experimentally obtained maximum adsorption capacity of AC-Fe3O4-NPs for Cr (VI) adsorption was estimated to be 15.24 mg/g.