Navegando por Assunto "Birnessita"

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Caracterização química e mineralógica de birnessita natural da Mina do Azul (Província Mineral de Carajás, Brasil) e seu análogo sintético (K-OL-1) obtido pelo método sol-gel
(Universidade Federal do Pará, 2016-06) FIGUEIRA, Bruno Apolo Miranda; ANGÉLICA, Rômulo Simões; COSTA, Marcondes Lima da; MERCURY, José Manuel Rivas; SANTOS, Manoel Roberval Pimentel dos; POELLMANN, Herbert
This paper presents a comparative chemical and mineralogical study of birnessite (BIR-AZ) collected from Azul mine (Carajás Province, Brazil) and its synthetic analogous synthesized by sol-gel method. The products were characterized by X-ray diffraction, FT-Raman spectroscopy, thermal analysis (TG-DTA), scanning electron microscopy (SEM) and ICP-MS techniques. The results obtained confirm the presence of well-defined layer structures having monoclinic system, C2/m space group and the unit cell parameters are: BIR-AZ, a = 5.148 Å; b=2.843 Å, c=7.175 Å, and β = 100.75º; K-OL-SG, a = 5.150 Å; b = 2.846 Å, c = 7.214 Å, and β= 101.29º. The birnessite from Azul mine ores shows thermal stability up to 600 ºC, whereas its synthetic analogous, above 900 ºC. FT-Raman bands at 635, 570 and 410 cm-1 were identified and attributed to the Mn-O and K-O bond deformations in the birnessite structure. SEM images reveals that the manganese oxide mineral consist of platy packed particles of about 1 to 5 µm. By contrast, the morphology of the synthetic compound displays randomly arranged globules (<1 µm).
Acesso aberto (Open Access)
Síntese e caracterização de óxido hidróxido de manganês do tipo manganita (γ -MnOOH)
(2008-06) FIGUEIRA, Bruno Apolo Miranda; ANGÉLICA, Rômulo Simões; SCHELLER, Thomas
Manganese oxyhydroxide (g - MnOOH) of the manganite type has been synthesized by a simple route with K-birnessite prepared by the sol-gel method. The hydrothermal treatment of the lamellar birnessite type structure facilitates the formation of tunnel structures where the size of the tunnels depends on the synthesis conditions (pH, temperature and time). The evidence of manganite formation under the synthesis conditions were made by X-ray diffraction, scanning electron microscopy, thermogravimetry, differential thermal analysis and infrared spectroscopy.
Acesso aberto (Open Access)
Síntese e caracterização de óxidos de manganês: transformação de estruturas em camada para estruturas em túnel
(Universidade Federal do Pará, 2007-04-24) FIGUEIRA, Bruno Apolo Miranda; SCHELLER, Thomas; http://lattes.cnpq.br/5712304485190137
This work describes the preparation, characterization e application of manganese oxides with layer structure like - birnessite with alkaline ions interlayer Na+ e K+. These structures are made of the octahedron MnO6 shared by edges and/or corners as basic building block, with oxidation states +2, +3 e +4, giving vacancies in the structure and a resulting negative charge neutralized by interlayer cations. The methods already known in literature to synthesize birnessite were: reduction (K, Na-birnessite) and sol - gel (Kbirnessite). Later, this layer structures synthesized were applied to the attainment of structures in tunnel: manganite, K-hollandite, and todorokite. From the synthetic methods, the most practical and efficient for the preparation of layer structures were chosen for study with the idea of making these compounds accessible to those interested in studying their different aspects. Some modifications were introduced into the original synthesizing route in order to adapt it to the possibilities and necessities of laboratory of geosciences, UFPA, as well as to overcome the problems which appeared during the experimental work.
Acesso aberto (Open Access)
Transformação de minérios e rejeitos de óxidos de Mn da região Amazônica em nanomateriais com estrutura Lamelar (OL-1).
(Universidade Federal do Pará, 2012-03-09) FIGUEIRA, Bruno Apolo Miranda; POLMANN, Herbert; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607; 7501959623721607
This work represents a novel study about the synthesis of manganese oxides based in materials with controlled properties (structure) from new sources of Mn: ores and residues of manganese oxides from the Amazon Region. The first step of was the chemical and mineralogical characterization of minerals K-birnessite, K-hollandite, and Ba-hollandite isolated by micropreparation from the Azul (Carajás mining district, Pará state), Urucum (Mato Grosso do Sul satate) and Apuí (Amazon state, area under prospecting) mines. In the second step of the study, ore samples from the old mine of Serra do Navio (Amapá state) and residues from Azul (Carajás) were used to obtain a K-birnessite (K-OL) structure. Preliminary studies on the characterization of raw materials indicated the presence of manganite and nsutite phases for the ore, while for the residues, kaolinite, gibbsite, quartz, hematite, rutile, todorokite, pyrolusite and K-birnessite were identified. The starting materials were converted to Mn2O3 phase (550 ºC), that after hydrothermal treatment with 7.5 mol.L-1 of KOH (15 mL) for 4.5 days, was converted to the lamellar compound with K+ cations in the interlamellar space. The final products showed similar properties to the lamellar products obtained by commercial reagents described in the literature. K- birnessite synthesized from the ores was stable up to 500 °C. At 650 °C, the lamellar phase suffered a tunneling process and was transformed to K-OMS-2, which exhibiteds K-hollandite (cryptomelane) type structure. The tunneling process was not observed to K-birnessite obtained from residues, but the structure remained stable up to 800 °C. The Stretching vibrations of the Mn-O bonds in the MnO6 octahedra were characterized by Raman and IR spectroscopy. On the third and last part, the synthesis of the Na-birnessite (Na-OL) was verified, starting from the ores of the Azul mine. Initially, the manganese oxides minerals containing cryptomelane, vernadite, nsutite and pyrolusite were transformed into a single phase, hausmannite (Mn3O4), at the temperature of 1000 ºC. By hydrothermal treatment of Mn3O4 with NaOH, varying the time, a compound with properties similar to Na-OL (Na-birnessite) was synthesized. To achieve the optimal synthesis conditions were used 0.05 g of Mn3O4, 5.5 mol.L-1 of NaOH (30 mL), 170 °C and 5.5 days. The lamellar product has excellent degree of crystallinity, thermal stability above 650 °C and platy morphology. Images obtained by transmission electron microscopy revealed the presence of nanobelts with crystallite size of 200 nm.