Leonardo Evangelista Lagoeiro

Crystallographic texture of the magnetite-hematite transformation: Evidence for topotactic relationships in natural samples from Quadrilátero Ferrífero, Brazil

Abstract The transformation of magnetite to hematite is described and analyzed in three natural samples of banded iron formation, from Quadrilátero Ferrífero, Brazil. In each sample, a particular microstructure related to the transformation process is described. In the first, magnetite crystals are large and euhedral, and they display the beginning of the transformation into hematite. In the second sample, a relict crystal of magnetite was found and the fabric of the transformed hematite was evaluated. In the last sample, the foliation was the main observed structure and the correlations of magnetite and hematite lattices were measured. All the microstructures were analyzed in a scanning electron microscope equipped with a detector for electron backscatter diffraction allowing the complete analysis of crystallographic orientations of hematite and magnetite on a local scale. The results show that the orientations of the basal planes of hematite coincide with the orientations of the octahedral planes of magnetite, indicating that the hematite crystals are a direct product from the magnetite transformation.

Phase and Microstructural Characterization of Iron Ore Pellet and their Relation with Cold Crushing Strength Test

ABSTRACT In the production of the pellets, phase identification for specific sintering condition is of prime importance in understanding the basis for the production and the required properties. The application of a methodology involving optical and scanning electron microscope equipped with an EBSD opened a broad possibility to establish a base for the relationship between heat-treated pellet microstructural features and cold crushing strength. The first results from the conjoined application of these techniques show that the cold crushing strength of the pellet increase with the decrease of porosity, the appearance of the fayalite, as well as the presence of magnetite-unoxidized.

Effects of hematite surface characteristicson filtration process

In iron ore pelletizing plants a range of process parameters such as particle size distribution, specific surface area, and moisture, must be controlled to achieve optimized operation conditions. Particle size distribution and specific surface area are controlled during the grinding operations. Moisture, however, is controlled during filtration of the ground products. This work investigates the relationship between particle morphology, filter cake moisture and filter capacity. The samples were taken during the filtration tests and referred to three different blends presenting distinct mineralogical features and similar chemical compositions in order to investigate the effects of only the hematite surface characteristics. Six types of morphology are distinguished: granular hematite, tabular hematite, martitic hematite, polycrystalline hematite, hematite-goethite aggregates and goethite. For each filtration test, the filter cloth product was characterised. The characterisation analysis revealed that blends containing martitic hematite concentration above 11.45 percent increased substantially the filter capacity. However, it had also caused an increasing in final moisture content that reached values around 10.0 % compared with industrial moisture specification that can vary on the range of 8.5 to 9.5 %.

SEM observation of grain boundary structures in quartz-iron oxide rocks deformed at intermediate metamorphic conditions

Muitos estudos tem demonstrado o efeito de uma segunda fase sobre a distribuicao de fase fluida e dissolucao de graos de quartzo. Entretanto, como a maioria das observacoes vem de agregados deformados sob condicoes de tensao hidrostatica e em rochas quartzosas ricas em mica, a distribuicao 3D de poros e bordas quartzo-quartzo (BQQ) e quartzo-hematita (BQH) tem sido estudada. Varias superficies de fraturas orientadas segundo o elipsoide de deformacao finita foram analisadas. A distribuicao dos poros caracteriza a porosidade e a forma dos graos como altamente anisotropicas, o que resulta da natureza e orientacao das bordas. BQH tem propriedades fisico/quimicas muito diferentes de BQQ, uma vez que as plaquetas de hematita tem forte efeito no comportamento do fluido, de maneira similar as micas em quartzitos. Elas sao superficies planas, livres de poros, normais a direcao de maximo encurtamento, sugerindo que estiveram, em um momento, cobertas por um filme continuo de fluido agindo como um caminho mais rapido de difusao. Nas BQQ, os poros sao facetados, isolados, concentrados nos limites das mesmas refletindo o controle cristalografico e uma rede interconectada de fluido ao longo das juncoes dos graos. As BQQ normais a direcao de maxima extensao sao sitios de concentracao de fluido. Como consequencia, a dissolucao anisotropica e o crescimento de graos foram responsaveis pela formacao de plaquetas de hematita e graos de quartzo tabulares contribuindo significativamente para a geracao da foliacao observada nas rochas estudadas.

Toward the influence of iron oxide morphology on the grinding and filtration processes and on the cold crushing strength (CCS) of heat-treated iron ore pellets

ABSTRACT The present study demonstrates the effect of the different morphological types on the cold crushing strength (CCS) of heat-treated iron ore pellets. Blends with different iron ore oxides morphologies were subjected to grinding, filtering and pot grate tests on industrial scale trials. Results of grinding tests showed the hematite-goethite aggregates the most influent one on energy consumption. The martitic-hematite content was straightly related to the final moisture and filtration productivity. The hematite-goethite aggregates, therefore the goethite content, influences CCS, being the lower the goethite content, the higher the values of CCS.

The rheology of banded iron formation: constraints from axial compression experiments

Samples of Banded Iron Formation (BIF) with different quartz and hematite contents were deformed in axial compression experiments in a Griggs-type apparatus, at T = 900oC, P =1.5 GPa and strain rates of 10 -5 and 10 -6 s -1 . The aim is to investigate the mineral phase that controls the rheology of multi-phase rocks and to determine the processes that control the observed rock strength. BIF samples from Quadrilatero Ferrifero region-Brazil were cored perpendicular to the foliation, which is defined by parallel bands of quartz and iron oxide. Sample strength decreases with increasing hematite content and decreasing strain rate. At a strain rate of 10 -5 s -1 , samples with well-developed compositional banding showed higher strength. At the slower strain rate of 10 -6 s -1 no difference between samples with or without compositional banding is observed. For comparison, at 10 -6 s -1 , the highest quartz content sample is as weak as the highest hematite content sample at 10 -5 s -1 . Strain is localized in hematite-rich layers. One intriguing observation is that quartz grains within the more deformed hematite-rich bands show more evidence for crystal-plastic deformation than grains in quartz-rich bands.