Residuos sem purificação utilizados como matéria-prima para sintese de produtos destinados ao tratamento de efluentes

Abstract

Solid waste is considered one of the main contributors to environmental harm, making it necessary to develop research aimed at reintegrating waste into the production chain as a new material, enabling its use in various economic sectors. This research aimed to investigate the use of alternative residues, such as eggshells and post-consumer battery electrolyte paste, as raw materials for synthesizing products intended for effluent treatment. The application of the obtained products (CaO and ZnO) was evaluated for color removal and the degradation of the Ruby GDN dye in an aqueous solution. The use of calcium oxide (CaO) derived from calcined chicken eggshells (Residue 1) at 600, 700, 800, and 900 °C for 2 hours, and zinc oxide (ZnO) derived from post-consumer battery electrolyte paste (Residue 2) calcined at 500 °C for 4 hours, was assessed as alternative heterogeneous photocatalysts without purification, meaning without additional enhancement processes. The obtained products were characterized by X-Ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), Diffuse Reflectance for band gap calculation, Thermogravimetry (TG), and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). The catalysts were tested using a 22 factorial design and the kinetic degradation of the Ruby GDN dye and untreated textile effluent. XRD and FTIR characterization results showed that the main components are calcium oxides for the eggshell and zinc oxide for the electrolyte paste. Band gap analysis revealed that the materials possess energy values very close to 3.0 eV, similar to commercial catalysts like TiO2 and ZnO, thus having recognized optical properties for photocatalysis applications. The thermogravimetric curve indicated excellent stability of CaO and ZnO at high temperatures, reaching stability after 780 °C and 690 °C, respectively. Micrographs for CaO showed that as calcination temperature increased, the material developed more regular shapes. For ZnO, the micrographs indicated well-defined, regular shapes with low porosity. EDS analysis verified a chemical composition of approximately 75% CaO for the product synthesized from eggshells and 75% ZnO for the catalyst produced from battery residue. Testing with Ruby GDN showed that 1.0 g/L of CaO calcined at 900 °C achieved 57% color removal at an initial dye concentration of 20 mg/L after 120 minutes of solar radiation exposure. The use of ZnO positively influenced color removal of Ruby GDN, achieving a total removal of 28.5% after 120 minutes of solar radiation exposure with 1.0 g/L of ZnO. Finally, a 23 factorial design was conducted using untreated textile effluent with unpurified ZnO catalyst, reaching a maximum degradation efficiency of 31% (1.25 g/L catalyst, pH 12, and 120 minutes of exposure to radiation). It was concluded that alternative heterogeneous catalysts, even without purification processes for the alternative residues studied, can be a sustainable option for textile effluent color removal, based on the principles of the circular economy.