Spherical gamma-alumina macroscopic beads as easy to remove adsorbents for water remediation: Modeling of indigo carmine case study

[Display omitted] •Synthesis of millimetric gamma-alumina beads by a sol-gel-based route.•Modeling the indigo carmine removal from wastewater by γ-alumina beads.•Successful removal of indigo carmine with a maximum adsorption capacity of 126 mg/g.•Easy removal of millimeter-sized alumina beads after treatment. In light of the constantly increasing need for health and environmental preservation, in this study, alumina beads, with economic advantages and the benefit of being easily removed and recovered by the treated wastewater, were synthesized and investigated for the removal of Indigo Carmine (IC), selected as a representative of polluting organic dyes. The structure and physical properties of the adsorbent were characterized by Simultaneous Thermal Analysis (STA), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), and Energy Filtered Transmission Electron Microscopy (EFTEM). To maximize the efficiency of IC dye removal from wastewater by γ-alumina beads, control parameters like dye concentration, adsorbent amount and contact time were modified. The optimal operational conditions were assessed via the D-optimal design of response surface methodology (RSM-D-optimal). The maximum adsorption capacity of alumina beads was found to be 126 mg/g. Langmuir and Freundlich models were applied to adsorption isotherms with an R2 value of 0.956 and 0.9901, respectively, pointing to multilayer adsorption phenomena. Millimeter-sized beads of the loaded adsorbent were finally easily removed by the treated water and tested in a subsequent run of water remediation. The results reveal that γ−alumina beads can be considered a potential adsorbent for IC removal from wastewater, as they combine satisfactory remediation features with easy collection and removal after the treatment, eventually more efforts are required to make beads reusable.