Removal of Cr(VI) from water using pineapple peel derived biochars: Adsorption potential and re-usability assessment

In the present study, biochar was prepared using waste pineapple peel biomass with slow pyrolysis at 350, 450, 550 and 650 °C to explore the effect of temperature treatment on characteristic properties of biochars. Various characterization parameters were analyzed to elucidate the temperature driven changes. Pyrolysis temperature had a significant impact on the properties of the developed biochar, leading to morphological and physiochemical changes. The relationship between pyrolysis temperature and induced physicochemical properties with Cr(VI) adsorption onto biochars was also investigated. Various adsorption parameters as pH (1.5–8), initial Cr(VI) concentration (10–500 mg/L), biochar dose (0.5–10 g/L) and adsorption time (0–96 h) were studied. Freundlich isotherm (R2 = 0.957–0.972) and pseudo-second-order kinetics model (R2 = 0.981–0.994) best fitted the experimental data suggesting multilayer adsorption with chemical interactions between Cr(VI) ions and biochar surface. Biochar prepared at 350 °C was found to have the highest adsorption capacity of 41.67 mg/g among biochars. Complete Cr(VI) removal was achieved at 10 mg/L Cr(VI) concentration with all the biochars. Rather than surface area polarity of biochar was found to be the influencing character of biochar for Cr(VI) adsorption. Feasibility of produced biochars for reuse was also explored. The study suggested that pineapple peel residue can be recycled to biochars with high carbon stability and can be used as a low-cost alternative adsorbent for wastewater treatment.