Navegando por Assunto "Hematita"

Agora exibindo 1 - 5 de 5

Acesso aberto (Open Access)
Influência de Gd e de elementos de transição nas propriedades físico-químicas da goethita (x-FeOOH)
(Universidade Federal do Pará, 1998-12-09) GANHEN, José Henrique de Melo; SCHELLER, Thomas; http://lattes.cnpq.br/5712304485190137
Goethite is a common mineral, easily found in surface environments, typically forming under oxidizing conditions as a product of chemical weathering of iron-bearing minerals. Several non-ferric metals have already been found in its structure, such as, for example, Cd, Co, Ni, V, Zn and Mn. The presence of these foreign elements in the structure of goethite can lead to variations in its physicochemical properties. To study variations in the following properties: unit cell dimensions, position of infrared bands, thermal properties, mineral color, degree of crystallinity and solubility product, synthetic goethite samples were prepared under mildly acidic conditions (pH ~ 4.5 ), incorporating Mn3+, Cd2+, V3+, Zr4+, Nb5+ and Gd3+ in its structure. The systematic changes in dimensions a, b and c of the unit cell, with the increase in the concentration of foreign elements in the structure, suggest that such elements replace Fe3+ in the octahedral structure of goethite and can be related to the ionic radius of the incorporated metals. The dispersion of values for the crystallographic axis a may result from distortion of the octahedron with the incorporation of non-ferric metals or structural defects. The crystallinity of the samples decreases with the increase in the concentration of foreign elements in the structure. The vibrations of the O-H bonds, out of plane, increased from 794 to 798 cm -1, indicating a slight shortening in the length of the M-OH bond (M = metal), with the increase in the concentration of incorporated metals. M-O bond vibrations, for M = Cd, Mn, V, Nb, Zr and Gd, were obtained in the region of 50 - 500 cm -1. The appearance of new vibration frequencies, compared to the pure synthetic goethite sample, and the disappearance of others, indicate the presence of metals other than iron in the structure. Data from differential thermal analysis (DTA) demonstrate that there is greater disorder in the structure, or less crystallinity of the samples, as the content of non-ferric metal in the octahedral structure of goethite increases.
Acesso aberto (Open Access)
Mineralogia e geoquímica de perfis lateríticos imaturos em Abel Figueiredo - Rondon do Pará, Amazônia Oriental.
(Universidade Federal do Pará, 2019-03-29) ABREU, Daiveson Serrão; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
Immature lateritic profiles are very common in Amazonia, such as in southern region of the state of Pará. However, these profiles are poorly researched their potential for hosting important mineral deposits, such as Au, Pt, Ni, Mn and mineralizations associated the resistate minerals (Sn, Nb-Ta, Y). In the Paragominas-Rondon do Pará region, these formations sometimes dominate the local landscape, both as autochthonous and as allochthonous deposits. To understand the process of formation of these profiles to contribute to the understanding of the geological evolution during the Cenozoic in the regions of Abel Figueiredo and Rondon do Pará is the objective of this work. Two autochthonous profiles located in the Abel Figueiredo region, southeast of Pará, one of them at km 137 of BR-222 and the other at km 138 of the same highway were selected for a textural, mineralogical and geochemical studies, besides characterizeation of the content heavy minerals and anatase for discussions of the source rock and evolution processes. Fieldwork, X-ray diffraction, optical and scanning electron microscopy and multielementary chemical analyzes were carried out. The profiles generally are equivalent in terms of succession of horizons, comprising from bottom to top by: clayey horizon, which is present only in the profile of km 138, is reddish brown in color with white patches and massive aspect; the partially dismantled columnar iron-aluminous crust, of dark reddish brown coloration, columnar structure, parallelized by channels filled by silt clayey material; partially dismantled nodular iron-aluminous crust of dark reddish brown coloration, with ochre tones, nodular structure, microporous to cavernous appearance; subspherolithic horizon of the profile of km 138 is represented by reddish brown subespheroliths, surrounded by a yellowish-brown clayey matrix, while the equivalent of the profile of km 137 is called the spherolithic to nodular horizon represented by spheroliths and nodules surrounded by matrix of brown color; topsoil, is of earthy consistency and homogeneous, correlated to the latosols of Amazonia. This structuring from the crust ferroaluminosa columnar shows increasing degree of biochemical and physical disaggregation marked by the dismantling and crustal fragmentation, by the occurrence of columnar pattern and nodules, and the comminution of the nodular fragments at the top giving rise to the spherolites /subespherolites. This structural pattern expresses a typical granodecrescent process, culminating with the topsoil, predominantly silty-clayey; The mineralogy of the lateritic profiles and topsoils consist of hematite, goethite, kaolinite, quartz, and as accessory anatase and heavy minerals (zircon, rutile, tourmaline, kyanite and staurolite) that describe a classic lateritic succession. Hematite and goethite are the main iron-bearing minerals that capture highly mobile elements (V, Cr, As, Se, Mo, Ag, Sb, Hg and Bi) fixed on crusts and their degradation products (nodules, spheroliths and subespheroliths). Caulinite and al-goethite play less importance in the capture of elements, but they support that the lateritic profile was affected by tropical weathering. Zircon, a mineral of residual behavior as well as the anatase, shows affinity with Ta, Nb, Y and ETR and comes from a single source of granitic filiation. The mineralogy and geochemistry indicate a continuous evolution of the partially dismantled columnar iron-aluminous crust to partially dismantled nodular iron-aluminous crust and this to the subesferolithic horizon or spherolithic to nodular horizon and finally to the topsoil. The distribution of SiO2, Al2O3, Fe2O3 and TiO2 shows that the crusts, nodules and spheroliths are similar chemically. This similarity is also demonstrated by the same pattern of distribution curves of trace elements and REE. Hematite and ferric goethite decompose and form kaolinite, Al-goethite, with parallel residual quartz and residual anatase concentration, which is manifested by the increase of SiO2 and Al2O3 and TiO2 and the subsequent gradual loss of Fe2O3. The mineralogical and chemical similarity between the clay matrix and the topsoil testifies that this matrix generated by the degradation of crust is the likely source of the topsoil. The lateritic profile began its development from the Miocene, when it was exposed to intense tropical forest root activity that biochemically decomposed the preexisting crusts giving rise to the nodules and spheroliths / subespheroliths with generation of clay matrix and simultaneously forming kaolinite and Al-goethite. The topsoil was formed at the top of the hills of the lower surface under the warm and humid Amazon climate during the Pleistocene.
Acesso aberto (Open Access)
Mineralogia e geoquímica do perfil laterítico do depósito de ferro da Serra Leste, Carajás-PA
(Universidade Federal do Pará, 2020-07-17) SILVA, Rayara do Socorro Souza da; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The Carajás Province hosts one of the largest high-grade iron ore deposits in the world, distributed in the districts Serra Norte, Serra Sul and Serra Leste. The process of Fe mineralization in the region is still a stage of discussion, due to the textural complexity typical of the ore, which induces different interpretations regarding its genetic model. In this context, in order to better understand its origin, the present work evaluates the contribution of lateritic weathering to the formation of the iron deposit of Serra Leste. In the field, a profile of weathering and its substrate were described, through two drill holes provided by the company VALE S.A, followed by sampling. After that, about 20 samples were described, photographed and prepared for mineralogical and chemical analysis. The mineralogical phases were identified by X-Ray Diffraction (XRD) and the micromorphological images obtained by Scanning Electron Microscopy (SEM), accompanied by semi-quantitative analyzes by Energy-Disperse Spectroscopy (EDS). The textural aspects also involved optical microscopy by reflected and transmitted light. Analysis by Mössbauer spectroscopy were used in order to identify the oxidation states of Fe ions present in the samples, complementing the information obtained by the other techniques. Chemical analyzes were performed by Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES), and Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The investigated profile comprises two successions of lateritic alteration, one derived from jaspilites and the other derived from mafic composition rocks. The profile comprises jaspilites and chloritites at the base, followed by saprolitic horizons (thick saprolite and fine saprolite) and ferroaluminous crusts. The chemical composition shows that the SiO2 contents (chert/quartz) decreased drastically during the formation of the horizons from the base of the profile, with an increase in the levels of Fe2O3 (mainly hematite and goethite) and its substantial concentration in the saprolitic horizon (mineralized zone). From the top of the fine saprolite there is an increase in the contents of Al2O3, TiO2 and P2O5, related to the presence of gibbsite, aluminous goethite and anatase, in the same way trace elements (Ga, V, Cr, Ta, Nb, W, Zr, ETR and others) present in the structure of newly formed minerals. The data obtained in the investigated profile, therefore, shows a lateritic evolution, and are similar to the mature lateritic profiles of the Amazon.
Acesso aberto (Open Access)
Mineralogia e geoquímica do perfil laterito bauxítico na serra Sul, Província Mineral de Carajás
(Universidade Federal do Pará, 2020-11-03) RODRIGUES, Paulo Ronny Soares; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The Amazon holds the largest reserves of bauxites in Brazil, located in Trombetas, Juruti, Paragominas and Rondon do Pará. The Carajás region, with large lateritic deposits, especially of iron, is also emerging with potential for bauxite deposits, with emphasis on those of Serra Norte. In Serras Sul, smaller occurrences were identified, which were investigated in this work. In this context, field activities were carried out with sample collection and textural, mineralogical and chemical analyzes and then a genetic discussion was presented. In four alteration profiles on a side road near the Serra Sul, after geological cartography, 23 samples were collected, which were described, photographed and prepared for mineralogical analysis (X-ray diffraction), textural (optical and scanning electron microscopy) and chemical (mass and optical emission spectrometry, with inductively coupled plasma). The bauxite laterite profile comprises from the base to the top of: 1) Kaolin Horizon (HC); 2) Mottled clay Horizon (HAM); 3) Nodular Bauxite Horizon (HBN); 4) Clayey Bauxite Horizon (HBA) and 5) Ferruginous crust Horizon (HF); and finally to the top 6) Dismantled crust ferruginous horizon (HFD. The chemical composition is essentially dominated by Al2O3, Fe2O3, SiO2 and TiO2, which compose the main minerals, kaolinite, gibbsite, hematite, goethite and anatase. The trace elements V, Cr, Cu, Ga, As, Zr, Cd, Hf, Bi and Th, whose concentrations are generally higher than those of the Upper Crust of the Earth, are more concentrated in the ferruginous horizons, related to Fe oxy-hydroxides (hematite and goethite) and also to zircon. On the other hand, the elements Co, Zn, Se, Rb, Sr, (Nb), Ag, (Sn), Cs, Ba and Pb are at lower levels than theUpper Continental Crust, and their concentrations are lower in ferruginous horizons, suggesting affinity with clay minerals.ETR at levels lower than UCC, are enriched in ETRP and present strong positive and negative C and positive Eu anomaly, and suggest distribution in zircon, oxy-hydroxides of Fe and other mineral phases. and mass clearly demonstrate a complete lateritic evolution, only partially modified in its upper portion. The bauxite zone, however, does not have local potential for ore, due to the low content of usable alumina and high in reactive silica. However, its occurrence opens an opportunity for further research in view of the geological and paleoenvironmental potential of the Mineral Province of Carajás.
Acesso aberto (Open Access)
O Refinamento de Rietveld como um método para o controle de qualidade de minérios de ferro
(2002-04) KONIG, Uwe; POELLMANN, Herbert; ANGÉLICA, Rômulo Simões
The Rietveld method is an innovative technique for quality control and processing. A Quantification of iron ores with 2 and more phases is possible in a fraction of the time needed till now. This paper shows the most essential bases to the conditioning, preparation and quantification of simple mixtures of hematite, magnetite, goethite and quartz as principle ingredients of iron ores. Special preparation methods are necessary due to the anisotropic hematite crystals. Different sample preparations parameters must be evaluated prior to Rietveld quantification, for instance, "side loading" or "back loading" are recommended. The duration of grinding depends on the respective ore and hematite variety, usually between 4 and 12 minutes. A quantification of a 3 phases mixture turned out well with a maximum relative standard deviation of 3%.