Mineração urbana: beneficiamento de componente catódico de pilhas para a síntese de catalisadores aplicados em processos de degradação

Abstract

Historically, the term "trash" has been used to refer to the byproducts of human activities and post-consumer products. However, in recent years, the understanding that these scraps can be reused, recycled, or transformed into valuable resources has led to a change in the terminology used to describe them. Instead of "trash," they are now referred to as "waste" or "recyclable materials," and a variety of technologies and practices are being developed to recover and reuse these materials more sustainably. Within this context, and considering the high volume of electronic waste generated annually, the main objective of this study was the modification of battery waste for application as catalysts in oxidation processes. The electrolyte paste, a component of the cathodic portion of common zinc-carbon batteries, rich in manganese oxides, underwent pretreatment steps such as homogenization and neutral leaching. This material was named BM and employed in the synthesis of the other catalysts. Two treatments were proposed to improve the catalytic activity of the BM precursor solid: thermal treatment in an inert atmosphere with a nitrogen flow (BM_N₂) and acid activation with sulfuric acid (H2SO4), followed by thermal treatment in an inert atmosphere with a nitrogen flow (BM_H+/N₂). The BM, BM_N₂, and BM_H+/N₂ materials were characterized for their chemical and textural properties using different techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Gas Adsorption/Condensation Porosimetry, X-ray Photoelectron Spectroscopy (XPS), among others. The results revealed different modifications in the pre-treated electrolytic paste after the performed treatments, especially regarding chemical composition and surface characteristics, such as increased porosity and specific surface area (BET). XRD analysis enabled the identification of different crystalline phases in the precursor solid (BM) and after the treatments (BM_N₂ and BM_H+/N₂), as well as the observation of differences in the crystalline profile. The catalytic activity of the materials was initially evaluated in the decomposition reaction of hydrogen peroxide (H2O2), which is an important step for the production of reactive oxygen species in Fenton-like reactions. The material subjected to acid activation (BM_H+/N₂) exhibited high activity in the studied reaction over multiple catalytic cycles compared to the other materials. Subsequently, the catalysts were applied in organic contaminant oxidation processes using methylene blue (MB) as a model molecule. Concurrently with this study, different molecules such as ascorbic acid (AA), citric acid (AC), formic acid (AF), and hydroquinone (HQ) were evaluated as co-catalysts in the degradation reaction of MB. It was observed that AC has an inhibitory effect on the degradation reaction of MB, resulting in a decrease in reaction efficiency. On the other hand, HQ and AF act synergistically with the prepared catalysts, promoting an increase in MB degradation. The promoting effect on catalytic activity was observed when HQ was used at concentrations of 1.65 mmol L-1 and 16.5 mmol L-1, and AF at a concentration of 57.9 mmol L-1.