Remoção de poluentes orgânicos em sistemas aquosos por materiais à base de ferro

Abstract

The use of iron-based materials to remove organic pollutants refractory to conventional water and wastewater treatment methods is a compelling alternative since iron has low commercial value, wide availability, and low toxicity. In this context, this work evaluated the use of an iron ore tailings sample (RMF) and nanoscale zero valent iron (nZVI), obtained by a “green” synthesis process, for the removal of organic pollutants from aqueous solutions. According to the characterization analyses, the RMF sample was predominantly composed of hematite and quartz, with a point of zero charge of 5.64 and a specific area of 4.3 m2 g-1. The RMF was able to remove two dyes, one anionic (Direct Red 80 - VD80) and the other cationic (Methylene Blue -AM) , from aqueous solutions. The initial pH of the medium (pH0) had a strong influence on the efficiency of the process, indicating that electrostatic forces directly affect this process. The adsorption of VD80 by RMF was well described by the pseudo-second order kinetic (PSO) and Langmuir isotherm models. The synthesis of nZVI by reducing iron in solution using an extract from Eucalyptus grandis leaves was well succeeded. The characterization results of the synthesized material (EGnZVI), indicated that Fe0 was formed and, however, that a parcel was oxidized. In addition, organic compounds from the extract, including polyphenolics, were incorporated into the structure of the material, giving rise to an amorphous material. The EGnZVI were very efficient for the removal of VD80 and Dicamba in the presence of H2O2 (nZVI-Fenton process) under slightly acidic conditions (pH0 of 4 and 5.5), and followed a PSO kinetics. Furthermore, under these conditions, this process was more efficient than the classic Fenton using Fe2+. In the presence of UV light, the process was very efficient for the degradation of VD80 in a wide pH0 interval (2.5-8.5). Finally, the post-treatment Dicamba solution presented greater toxicity to Ceriodaphnia dubia than the original compound, which can be attributed to the by-products formed. It was also observed that EGnZVI were less toxic than the Fe in its ionic form.