Removal of hexavalent chromium from aqueous solutions using nano-Fe3O4/waste banana peel/alginate hydrogel biobeads as adsorbent

Abstract In this study, the removal of Cr(VI), known as one of the most dangerous heavy metal pollutants, was investigated by adsorption method using magnetic alginate biopolymer-supported banana peel composite beads (MAB), which were synthesized for the first time. Using plant waste for this composite synthesis is both important in terms of utilization of plant waste and more environmentally friendly. Optimum conditions were determined by examining the parameters of concentration (10–300 ppm), adsorbent dose (1–8 g/L), mixing time (5–360 min), pH (2–8), and temperature (25–55 °C). Characterization of this new synthesized composite adsorbent, FTIR, XRD, SEM, and EDX mapping measurements were performed. The experimentally found adsorption data were modeled by applying Freundlich, Langmuir, Scharthard, Temkin, and D-R isotherm models, and isotherm constants were calculated. The adsorption data on MAB are more compatible with the Langmuir and Freundlich isotherm. In the shaking-batch system at 25 °C and pH = 2, the maximum adsorption capacity of the composite was calculated as 370.4 mg/g. Adsorption kinetics were found to be suitable for pseudo-second-order. Thermodynamic studies were realized to evaluate thermal changes of the adsorption process, and desorption processes were realized to determine the regeneration times of MAB. The temperature studies showed that adsorption capacity increased with increasing temperature, showing that the system was endothermic. As a result, it has been shown that MAB can be used as an efficient biocomposite adsorbent for the removal and recovery of Cr (VI) ions from aqueous media. Graphical Abstract