Transformação de solo rico em ferro para aplicação em reações de interesse ambiental

Abstract

Iron oxides of natural origin have been used in environmental and industrial remediation because they have different characteristics, ranging from their source in the earth's crust to their application in reactions. In this work, the soil sample (plintossolo type) was modified by heat treatment in the presence of H2 or charcoal at different temperatures (300, 400, 500 and 800 °C) for 1 h. The materials obtained were characterized and used in three types of reactions: (i) heterogeneous Fenton reactions for the degradation of the black textile dye remazol (PR) and hydrogen peroxide decomposition, (ii) Photo-Fenton reactions for the degradation of PR and (iii) reduction of Cr+6 to Cr+3. The results obtained in X-ray diffractograms (XRD) allowed to identify the following phases of iron oxides in the soil sample without heat treatment: gibbsite, goethite, hematite, magnetite and quartz. In the treated soil samples, the signals referring to goethite and hematite decrease in intensity, since with the increase in temperature there is the appearance of the magnetite phase, as well as the formation of metallic iron. Infrared (IR) spectra identified vibrations related to goethite, hydroxyls linked to metallic oxides and also the presence of silicon oxide. Thermogravimetric analysis (TG) shows mass loss events due to sample dehydration, dehydroxylation of goethite forming hematite, oxidation of carbon present in the sample, oxidation of magnetite forming hematite and a mass gain also confirms the presence of magnetite and metallic iron. In Scanning Electron Microscopy (SEM) a similar morphology was observed between the samples, presenting irregular surfaces with formation of agglomerates and by energy dispersive spectroscopy (EDS) they were found in the samples basically iron, oxygen, aluminum and silicon. In heterogeneous Fenton reactions, S-A300 was better in PR degradation, about 61%, which may be related to the formation of the Fe3O4 phase. Photolysis Reactions of H2O2 and Photo-Fenton were compared, as the concentration of hydrogen peroxide was increased, Photolysis presented better or similar results to Photo-Fenton, showing that the PR discoloration is due to the Photolysis reaction. The S-A800 was chosen to reduce the Cr+6 and within 30 minutes of reaction, it was able to degradation all the Cr+6 from the solution.