Development of nano-sized Mn3O4 magnetic composites: application in wastewater treatment

• Ano de defesa: 2012
• Autor(a) principal: Gabriela Cordeiro da Silva
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Materiais e de Minas; Engenharia Metalúrgica; Engenharia metalúrgica
• Link de acesso: http://hdl.handle.net/1843/BUBD-93CFKJ

Composites with magnetic properties have been successfully synthesized by means of the deposition of manganese oxide, Mn3O4, precipitated by using O2 (an ecofriendly oxidant), onto magnetite particles. The magnetite particles in the composites (~40m2.g-1) form agglomerates with Mn3O4 particles. Solid-liquid separation by means of the application of a magnetic field is possible. The application of the magnetic composite in the oxidative adsorption of As3+ was evaluated. The arsenic sorption isotherm fits return values of b>1 for the Langmuirconstant, demonstrating high affinity of the composites for As(III), which is desired for the removal of trace and sub-trace contaminants from water. The maximum adsorption capacity is ~14mgAs.gsolid -1 (0.0048mmolAs.m-2 solid). During the As oxidation-adsorption process, iron is not released and part of the Mn(II) released to solution is being adsorbed or precipitated, or both, which implies in a less contaminants release to solution. XANES of the As-loaded composites show thatthe arsenic adsorbed is in the oxidized arsenic form, As(V), emonstrating that As(III) is successfully oxidized by Mn3O4. Raman and IR spectral data of Asloaded (5.0 to 16mg.g-1) samples suggest the presence of As-O bands referring to the formation of inner-sphere monodentate and bidentate complexes, elucidating arsenic surface complexes on the composite. The magnetic Mn3O4 composite was also applied to oxidize and remove methylene blue (MB) from water. UV-vis results show that Mn3O4 composite is capable of oxidizing MB forming its partially and fully demethylated derivatives. Decolorization of 85% is achieved in 60min, atpH 3. For pH>3, oxidation does not occur and only 50% of the MB is adsorbed. Desorption by methanol of the organic compounds adsorbed in the composite have shown that the fully demethylated MB derivative, thionine, is the only adsorbed compound. Therefore, the present work simplifies the synthesis of a manganese oxide composite to be applied in environmental systems as both an oxidant and an adsorbent. Moreover, the work improves the knowledge about the mode of Asinteractions with Mn3O4 by using vibrational spectroscopic techniques.