Transformação de minérios e rejeitos de óxidos de Mn da região Amazônica em nanomateriais com estrutura Lamelar (OL-1).

Abstract

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.