Obtenção de nanocompósitos de piroaurita de rejeito de mineração imobilizado em fibras de poliestireno reciclado para adsorção de polifenóis da agroindústria cafeeira

Abstract

The generation of liquid waste from agribusiness containing phenolic compounds, such as caffeic acid (CAF) and chlorogenic acid (CGA), represents a significant environmental challenge. Although these polyphenols have relevant bioactive properties, they become toxic to the environment when present in high concentrations in water bodies. In this scenario, the use of waste as a raw material for the development of adsorbent materials emerges as a promising strategy. A very abundant waste product is that from bauxite mining, which contains high levels of aluminum and iron oxides, which can be used in the synthesis of double lamellar hydroxides (HDLs). Among these materials, pyroaurite (Mg-Fe-Al DHL) stands out, characterized by its high surface area, anion exchange capacity, and strong affinity for organic compounds. Despite its potential, the application of adsorbent nanoparticles in aqueous systems faces practical limitations, mainly due to the difficulty of separating and recovering the material after use. In this context, the immobilization of adsorbent particles in polymer matrices has proven to be a viable alternative. Expanded polystyrene (EPS) is one of the main urban plastic wastes and can be reused as a support for functional particles by incorporating them into EPS fibrous membranes obtained by the solution blow spinning (SBS) technique. Polycaprolactone (PCL) is a biodegradable and flexible polymer that can provide these characteristics to the materials to which it is added. Thus, the present study aimed to synthesize pyroaurite from bauxite mining waste (Porto Trombetas, PA) and immobilize it in EPS and PCL fibers (EPS:PCL) obtained by SBS. There are no reports in the literature on the use of pyroaurite obtained from bauxite mining waste immobilized in EPS fibers recycled by SBS for the adsorption of polyphenols, highlighting the novelty and original contribution of this work. The synthesized pyroaurite presented a high specific surface area (146.91 m² g-1) and structure confirmed by XRD. The incorporation of pyroaurite into EPS fibers was successful, with thermogravimetric analysis indicating approximately 7.85% inorganic load in the final material and evidence of modification of the chemical composition of the matrix by EDS. In adsorption tests performed with pyroaurite particles, high efficiency in the removal of polyphenols was observed: 91.98% for ACG and 93.83% for CAF in just 30 minutes. The kinetic data were adjusted to the pseudo-second-order model (R² = 1), and the Langmuir isotherm allowed the calculation of qmax of 90.90 mg g−1 for ACG and 294.12 mg g−1 for CAF. When applying the resulting composite material obtained by immobilizing pyroaurite in EPS:PCL fibers, the removal rates were 59.8% for ACG and 74.9% for CAF after 24 hours, and qmax calculated by the Langmuir isotherm was 77.52 mg g−1 for ACG and 357.14 mg g−1 for CAF. The results obtained in this study demonstrate the potential of pyroaurite immobilized in polymer fibers, applicable for several adsorption cycles, as a viable technology for environmental applications, especially in the treatment of wastewater from the coffee agroindustry.