Aplicação do pó de aciaria elétrica em reações de descontaminação ambiental e na agricultura

Abstract

In the present work, the waste from the steel industry, electric arc furnace dust (EAFD), rich in zinc oxide (46.0%) was used as a photocatalyst in degradation reactions of organic and inorganic contaminants and was also applied as a fertilizer in the cultivation of common beans. To evaluate the efficiency of the waste as a photocatalyst, different classes of organic contaminants were used, including the dye Reactive Black 5 (RB5), the drug Oxytetracycline (OTC) and the herbicide Atrazine (ATZ). Besides pure EAFD, other materials were used as photocatalysts. The EAFD also had its surface modified with different metallic silver contents (0.25; 0.5; 1.0; and 2.0% Ag/EAFD), to obtain more efficient materials. EAFD and silver-modified materials were characterized by X-ray fluorescence, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. These techniques confirmed the zinc content of the residue and the photodeposited silver in the materials (values close to those calculated). The results showed that the higher the silver content, the greater the photocatalytic efficiency. Since, in the degradation of PR5, the 2.0 Ag/EAFD material showed three times higher kinetic constant than when compared to EAFD. EAFD was also used in the reduction of Cr(VI) to Cr(III). For this, different parameters were evaluated, such as: the presence of sacrifice agent (formic acid (FA) and malonic acid (MA)), the pH of the reaction medium (2; 4; 6 and 8), mass of photocatalyst (0 .05; 0.1; 0.2 and 0.4 g) and initial concentration of Cr(VI) (5; 10 and 20 ppm). Metal reduction reactions showed that the best conditions are in the presence of the MA sacrifice agent, at pH 2, with 0.2 g EAFD and at a concentration of 5 ppm, reducing 100% Cr(VI) at approximately 130 min of reaction, with UVC radiation at 51 W. EAFD was also applied as fertilizer in the planting of common beans. It was submitted to a zinc extraction route, from which different fractions rich in this micronutrient were obtained. These were applied as a soil treatment and expressed potential as a Zn-based fertilizer. The application of PPT 5 and PPT 5C fractions presented results close to those obtained with comercial fertilizers. Thus, with the results obtained in the different applications of EAFD, it is observed that its recycling and use in environmental decontamination processes (photocatalyst) and in the soil (fertilizer), brings advantages since it provided a noble destination for a waste.