Navegando por Assunto "Bauxita - Paragominas (PA)"

Agora exibindo 1 - 3 de 3

Acesso aberto (Open Access)
Bauxita, horizonte nodular e cobertura argilosa da região de Paragominas e Juruti, estado do Pará.
(Universidade Federal do Pará, 2011-12-20) CRUZ, Gilberto da Silva; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The hot and tropical climate during the Cenozoic resulted in the formation mainly lateritebauxite in the Amazon with the frequent occurrence of nodular and/or concretionary horizon consisting of both bauxite and/or ferro-aluminous crusts. The relationship between the nodular and/or concretionary horizon with lateritic profile and origin of the clay cover in the Amazon were the objectives of the present study, so did the selection of two lateritic profiles, located in the region of Paragominas (plateau Jabuti and PA-256 km 17) derived from rocks siliciclastics Ipixuna Formation and/or Itapecuru Group the late Cretaceous, and Juruti generated from the rocks siliciclastics of the Alter do Chão Formation, all in the state of Pará. This study applied the techniques of X-ray diffraction, optical microscopy, scanning electron microscopy and energy dispersive system (SEM/EDS), addition to chemical analysis. The lateritic profiles in the region Paragominas consist from bottom to top: Saprolitic horizon with laminar structures composed mainly of kaolinite beyond quartz grains fractured and corroded; Horizon mottled variegated coloration composed of kaolinite, goethite and hematite; bauxite lilac, look massive, porous, and cut by structures of clay columnar aspect in the plateau Jabuti, while in the PA-256 the bauxite is rosy, columnar and porous; Iron-aluminous crust with nucleous digested or no in the aluminous matrix; Concretionary horizon, consisting of a kaolinitic clay matrix, formed the basis for suesferic ferruginous concretions, porous, zoned, while the top consists particles porcelained aspect that displays a diffuse zoning outline in the outside by white or pink, then a yellow core and a more nucleous red color that sometimes has brown color; Clay cover formed mainly of kaolinite, gibbsitic nodules, quartz grains and fragments scattered laterite. The trace elements show a relationship with iron oxyhidroxides (Pb, V, As e Mo), anatase (Nb, Ta, W, Sn and Sc), zircon (Zr, Hf, Y and U) and gibbsite (Ga), while the rare earth elements exhibit the same behaviour along the profile which indicates a great genetic relationship between the horizons of the profile. The lateritic profile Juruti consists from bottom to top: Mottled horizon variegated color, Bauxite saccharoidal aspect formed by granules of gibbsite and quartz grains fractured and corroded, further bauxite with rounded ferrugious plasm immersed in aluminous matrix generating a feature breccia; Ferruginous crust massive look massive, porous with cavities filled by goethitic cutas and gibbsite, besides the occurrence of quartz grains fractured and corroded; Ferruginous nodules decreasing grain size toward the topo, looks massive porous with cavities filled by goethitic cutas and gibbsite, quartz grains, being immersed in the aluminous matrix of kaolinite; Bauxitic nodules decreasimg grain size toward the top, irregular aspect, porous with cavities filled by gibbsite already in the portion top the nodules are digested by aluminous matrix; Yellowish clay cover with gibbsitic nodules. Since the trace elements in the profile Juruti show concentrations lower than Paragominas and same chemical relationship with iron oxyhidroxides (Pb, V, As e Mo), anatase (Nb, Ta, W, Sn and Sc), zircon (Zr, Hf, Y and U) and gibbsite (Ga), while the rare earth elements occur in the V-shape when normalized to chondrites by enrichment of light rare earth elements (La and Ce) as heavy rareearth elements (Yb and Lu), and marked depression in the range of Nd, Sm, Eu and Gd, and the parallelism of the distribution curves shows that the same genetic relationship between the horizons as Paragominas. The evolutionof lateritic profiles in the two regions are characterized by the following stages: 1 – formation of the crust from the rocks of the Alter do Chão Formation from Juruti, Paragominas derived of the Ipixuna Formation and/or Itapecuru Group; 2 – bauxitization crust; 3 – degradation and partial dismantling of the crust, possibly followed by erosion and deposition for more recessed in the case of PA-256; bauxitization of the nodules and/or concretions and , finally; 5 – formation of Clay cover, called Belterra Clay. The mineralogical and characteristics of the profile studied possibly indicate that these profiles are formed from an evolution in situ for the concretionary and/or horizon and clay cover in relation to lateritic crusts. Periodic climatic variations and tectonic activations are mainly responsible for this evolution.
Acesso aberto (Open Access)
Cristaloquímica da sodalita Bayer derivada de bauxitas com alta sílica reativa de Paragominas-Pa
(Universidade Federal do Pará, 2016-05-24) MELO, Caio César Amorim de; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607
In the Paragomina’s region, as well as the whole Brazilian north, gibbisitic bauxite deposits commonly shows high amount of kaolinite. The processing of this bauxites (called as High Silica Bauxites - BASR) became a challenge because in the conventional conditions of the Bayer process, the kaolinite is undesirably leached by NaOH solution, and then precipitated as sodalite. The formation of this phase brings a significant increase in process costs, both by increasing the processing time as the irreversible loss of NaOH robbed from the system to form sodalite, which is then discarded in the red mud. Given this metallurgical problem this study aimed to investigate the crystal chemistry of sodalite formed in conventional conditions of the Bayer process, so that, from these results, studies to reduce these losses of the process and facilitate the processing of BARS can be developed in the future. The materials investigated were kaolinitic gangues from 4 lithologies of an exploration well in Miltonia 3 mine (BN, BNC, BC and BCBA), as well as a kaolin from IMERYS S.A. The digestions were carried out in Teflon-lined, stainless steel autoclaves, using 1 g of solid material, 25 mL of NaOH solution and at a temperature of 150ºC in an oven. The NaOH concentration and the reaction time ranged from 2,5 to 5,0 M and 60 to 420 min, respectively. Then the solid material was characterized by XRD, DTA/TG, FTIR, SEM and ICP-OES. The results of the starting materials showed that the kaolin sample is essentially constituted by kaolinite, which has a high structural ordering degree. All the samples of kaolinitic gangue showed the same minerals: gibbsite, kaolinite, hematite, goethite and anatase. By the observation of the XRD patterns and DTA curves can be noted that the BN and BNC samples are more reactive than the others, possibly due a lower structural ordering degree and particle size. In the experiments with kaolin, it can be observed that are formed not one, but two sodalite phases, which coexist practically throughout the whole process and tending to an equilibrium phase. These two phases differs themselves by the amount and behavior of the NaOH and H2O molecules within the framework. The results of the refinments showed that these phases were: basic sodalita with cell parameter (ao) ~ 8,96 Å, which is predominant in the initial stages of the transformation, and hydrosodalite with ao ~ 8,85 Å dominant in the secondary stage (mainly in 180 min). The XRD results from kaolinitic gangues showed that in 60 min there was no full kaolinite/sodalite conversion, and the sodalite patterns in BN and BNC were more intense and well defined than BC and BCBA, confirming that these samples have more reactive kaolinites. The increase of the reaction time and NaOH concentration provided a slight increase of the structural sodalite order. It may be noted that in almost all experiments the only phase formed was basic sodalite. The exceptions were the lithologies: BCBA and BC, which hydrosodalite was formed in the highest time of reaction and NaOH concentration, thus showing that this phase is directly associated with a higher time, concentration and crystallinity of kaolinite available in the reaction medium. It can be observed that throughout the reaction, in shorter time and concentration it is not possible to achieve a balance, which leads to a constant interchange of predominant phase in the system. In the higher time and concentration experiments, a balance is virtually reached, in order that it cannot be observed separated diffraction peaks. However there is no significant increase of the structural ordering even for extreme times as 3 days of reaction. The ammonium chloride experiments showed that this reaction medium allows the formation of more crystalline phases than all others achieved in this research. However, it did not result in the diminished of the sodium consumption.
Acesso aberto (Open Access)
Gênese das bauxitas nodulares do Platô Miltônia-3, Paragominas - PA
(Universidade Federal do Pará, 2017-12-12) CALADO, Waldirney Manfredi; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607
There are two distinct levels of bauxites on the Miltônia-3 plateau located at the Bauxite Province of Paragominas-PA. These levels are separated by a pseudopsolitic to concretionary ferruginous laterite (FL) horizon, marking a hiatus between two distinct cycles of the current bauxite profile formation. The bauxites of the upper level (2nd cycle of formation) have nodular to concrete characteristics whereas those of the basal level (1st cycle of formation) are composed by a more physically complete concrete bauxite (CB) added by another level of a more friable bauxite with clayey portions for its base (concrete bauxite with clayey bauxite - CBCB). It was noticeable the CNB located at the upper level of gibbsite-enriched horizon with low reactive silica and iron contents, which are very similar to those found on the horizon of the main bauxite ore (CB) of the profile. In field observations, on the survey fronts and in the drill holes it was found that this CNB is a gradation of the above Nodular Bauxite (NB) horizon. This gradation is observed by the increase in the size of the bauxite nodules, where their Fe-gibbsite pseudopsolites grows up by coalescence, decreasing the diffused iron and silica contents marked by the change in color from lilac-yellow to a red-orange color, to ocher, in higher depths. It is also noticeable a decrease until the complete disappearance of the Al-ferruginous pseudopsolites, in addition to the decrease of the volume of gibsytic-kaolinite clay at this level. Based on this study using macroscopic and microscopic petrography, SEM/EDS, XRD and chemical analysis, as well as Principal Component Analysis (PCA) and descriptive statistics, two evolution model proposals were developed on the genesis of the upper level of nodular bauxites of this lateritic-bauxite deposit, considering: Model (1) - Origin from the degradation of the original bauxites (1st Cycle), related to a 2nd Lateritization Cycle which consists of the preexistence of mature bauxite (CB), overlapped by FL, which was covered by "Belterra Clay". This new nodular level (NB) occurs through the coalescence process whereby the residual aluminous phase junction occurred, resulting from the migration of Fe and Si in solution out of this level and by the migration of the neighboring levels above the clayey overburden (CAP) and below that of FL and CB, forming and concentrating large scale gibbsitepreferably and secondarily to kaolinite. With the continuous evolution of this level of NB, a maturation of the basal portion of this level is observed, forming the CNB whose nodules are interincreased, connecting locally, consuming neighboring levels above NB and levels below FL and CB, up to the total consumption of these; Model (2) - Its origin from a 2nd Lateritization Cycle, however from a later sedimentary deposition on the lateritic profile of the 1st Cycle. With the exposure of a source rock as a granitoid pluton (Cantão, Japiim, Jonasa, Ourém and Ney Peixoto of Neoproterozoic granites), gneiss (Archaean crystalline basement) or siliciclastic sediments (Itapecuru and Ipixuna Formations of the Upper Cretaceous), whose weathering degradation made it possible the generation of sediments of clayey nature preferentially kaolinite during the Paleogene until the beginning of the Oligocene. Migration of Fe, Si, Ca, Na, etc. occurred outside this level, preserving and concentrating the Al and O in situ, in addition to the residual Si. The process of coalescence allowed for the addition of the residual aluminous phase, preferentially concentrating the gibbsite and secondarily kaolinite, closing the first cycle of bauxite formation. Thereafter, there was a regional upwelling, followed by erosive processes that allowed for the exposure of this previously formed bauxite profile, under a seasonal climate, with an abundance of meteoric water and intense intercalated insolation, where the FL developed, of regional occurrence marking a hiatus between the formation cycles of these bauxites. New regional retraction movement, which allowed for the deposition of sediments of siliciclastic origin, which served as source rock for a new bauxite formation cycle during the Upper Miocene. They may be the same rocks from which physical and chemical degradation provided sediments for the 1st cycle of bauxite formation. Repeating the coalescence process of the residual aluminous phase, with the large scale development preferably of the gibbsite and secondarily kaolinite, closing the second cycle of NB and CNB formation.