Tratamento de solução contendo bromazepam através de adsorção em hidrogel produzido a partir das cinzas de bagaço de cana-de-açúcar e alginato

Abstract

The development of sustainable adsorbent materials through the incorporation of agro-industrial residues into polymeric matrices represents a promising strategy for the treatment of emerging contaminants while promoting waste valorization. In this context, this study aimed to develop and evaluate an adsorbent hydrogel produced from sodium alginate and sugarcane bagasse ash (SCBA) for the removal of bromazepam from aqueous solution. The use of SCBA, a residue generated in large quantities by the sugar-energy sector, contributes to circular economy principles, while structuring the adsorbent as a hydrogel facilitates its application in aqueous media and its subsequent separation after treatment. The material was synthesized by ionic gelation using calcium chloride (CaCl₂) solution and characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis and differential scanning calorimetry (TG/DSC), scanning electron microscopy (SEM), determination of the point of zero charge (pHₚzc), and evaluation of elemental leaching by ICP-OES. The characterization analyses evidenced the formation of a material composed of an alginate matrix associated with the mineral fraction of SCBA, while maintaining its structural integrity after the adsorption process. The influence of operational variables was investigated using a Rotatable Central Composite Design (RCCD), considering pH, adsorbent mass, and initial bromazepam concentration. The pHₚzc of the material was 6.27, and the leaching assessment indicated low release of most of the analyzed elements, although manganese exhibited comparatively greater mobility and should therefore be considered when evaluating the chemical stability of the material. Statistical analysis showed that pH exerted the greatest influence on the adsorption process and exhibited a nonlinear effect. Under the evaluated adsorption conditions, the best performance was obtained at pH 4.0, an initial bromazepam concentration of 1.0 mg L⁻¹, and a hydrogel mass of 20 g, achieving removal efficiencies above 94% after 360 min of contact. In the reuse assays, the material maintained high removal efficiency over four consecutive cycles. Overall, the results indicate that the developed hydrogel has potential for bromazepam removal from aqueous media, combining the development of an adsorbent material with agro-industrial waste valorization and environmental sustainability.