Tratamento de efluentes laboratoriais por eletrocoagulação com eletrodos de alumínio e utilização dos resíduos gerados para aprimoramento de eletrodos de folha de grafite

Abstract

A considerable amount of aqueous residue is generated from volumetric experiments in teaching laboratories, and these residues are not properly treated. This study aimed the investigation of electrocoagulation (EC) using aluminum electrodes to remove contaminants present on wastewater from analytical chemistry teaching laboratories, according to the UN sustainable goals. EC is an electrochemical technique known for its efficiency in water contaminants removal by the formation of flakes, who act as coagulants. The obtained results demonstrated that pH variation through time causes changes in the aluminum hydroxide precipitation, and a pH from 6 to 8 the better media. The Chemical Oxygen Demand (COD) was considerably smaller after EC treatment, and the energy consumption (kWh) was monitored through the process, providing information about the energetic cost associated with the contaminants removal. Also, Scanning Electron Microscopy (SEM) and Dispersive Energy Spectroscopy (DES) was performed, revealing the formation of aluminum hydroxide flakes in the electrodes surface associated with electrodes corrosion. Additionally, the generated residue from EC techniques was used to modify Pyrolytic Graphite Sheet (PGS) electrodes by drop casting, intended to increase the electrode conductivity. The results in the presence of Potassium Ferricyanide presented smaller peak currents (both in oxidation and in reduction process), however, it is observed a higher reversibility relation for all modified surfaces. Also, PGS electrode without modification presented the highest resistance to the charge transfer among all surfaces, indicating that, in fact, the modification provided a higher conductivity to the electrode.