Batch and Column Adsorption of Reactive Red 198 from Textile Industry Effluent by Microporous Activated Carbon Developed from Walnut Shells

Abstract

In this study, the adsorption potential of walnut shells (WNS) was investigated using batch and fixed-bed column. Activated carbons (ACs) were prepared from WNS as a precursor for by chemical activation with H3PO4 and KOH with different impregnation ratios for removing reactive red 198 from wastewater. The surface characteristics of the prepared ACs were determined by the analysis of N2 adsorption isotherms (BET), ultimate, proximate and elemental analysis, Fourier transform Infrared spectroscopy, scanning electron microscopy, and acid–base Boehm titration. BET measurements showed that AC-H3.5 has the highest BET surface area (1980 m2/g). Batch adsorption studies were performed to evaluate the effect of pH (3–9), adsorbent dosage (0.5–2.5 g/L), and contact time on the adsorption capacity of WNS for the ACs obtained under optimum conditions. The adsorption kinetics followed the pseudo-second-order model. The equilibrium analysis revealed that the adsorption data was successfully fitted with the Langmuir isotherm. The maximum adsorption capacity calculated by Langmuir isotherm was 79.15 mg/g. Also, enthalpy, entropy, and free Gibbs energy changes showed that the reaction was endothermic. The effects of different bed heights, flow rates and the initial concentrations of dye on the breakthrough characteristics in fixed-bed adsorption column were investigated. Moreover, the Thomas, Yan and bed depth service time (BDST) models were used to predict the breakthrough curves of each component. The R2 of Thomas and Yan model were more than 0.95 and the R2 of BDST model was more than 0.96, also, the adsorption capacity calculated by both models corresponded with experimental values. Also a decrease in flow rate resulted in an increase in the bed volumes with a higher empty bed residence time at the breakthrough.