Adsorção de antibiótico cefazolina sódica em argila organofílica Spectrogel tipo C

Abstract

Emerging contaminants have been widely investigated due to their potential risk to human health and the environment, even at low concentrations. Antibiotics are one of the most used classes of pharmaceuticals in the world, and have been continuously discarded into the environment and detected in effluents and aqueous matrices. Cefazolin (CFZ) is an antibiotic widely used in both human and veterinary medicine, and leaves a high residual value in the environment. Conventional treatments have been shown to be inefficient or costly to remove these contaminants at low concentrations. Thus, this dissertation evaluated the removal of cefazolin from aqueous matrices by adsorption. For this purpose, adsorbent affinity tests were carried out with a variety of adsorbent materials and biomaterials, with the Spectrogel type C organophilic clay being selected as the most promising material. The experimental design of a rotational central composite design was carried out to evaluate the best conditions of initial concentration (0.132 mmol/L), adsorbent mass (0.448 g/50 mL solution) and adsorbent diameter (0.655 nm). Batch tests indicated that the resistance to external film mass transfer is the limiting step of the process and the Sips model best described the system at equilibrium. The maximum adsorption capacity (Langmuir fit) was 0.877 mmol/g at 25°C. The batch tests achieved an 80% removal at an equilibrium time of 72 hours. Through the thermodynamic study, it was possible to observe that the process is endothermic and spontaneous. Thermal regeneration was evaluated, as well as a simplified batch design, which indicated the need for 112 g of Spectrogel for a volume of 10 L of CFZ solution, with a maximum removal of 90%. Adsorption in a continuous dynamic system was also analyzed. The tests took place in a fixed bed column packed with Spectrogel. The system operating with the condition of initial concentration of 0.5 mmol/L and flow rate of 0.1 mL/min provided the highest adsorption capacity of cefazolin (20 µmol/g), but the system with the condition of initial concentration of 0.3 mmol/L and flow rate of 0.1 mL/min promoted the lowest mass transfer zone value (5.88 cm). The DualSD model was the one that best described the process rupture curves. The molecular modeling of CFZ was evaluated, indicating a stable and poorly reactive molecule when compared to other drugs. The clay characterization analyzes before and after the adsorption process indicate that it is a predominantly amorphous, non-porous clay, with low surface area and stable, without major modifications after the process.