Navegando por Assunto "Estilbita"

Agora exibindo 1 - 4 de 4

Acesso aberto (Open Access)
Atividade pozolânica de arenito zeolítico da região Nordeste do Brasil
(2012-06) PICANÇO, Marcelo de Souza; ANGÉLICA, Rômulo Simões; BARATA, Márcio Santos
In northeastern Brazil, sedimentary zeolites occur associated with sandstones of the Corda Formation (Parnaiba Paleozoic Basin), discovered in the 2000s. These sandstones are composed of quartz, natural zeolites (estilbite) and clay minerals (smectite). Preliminary studies have shown that this sandstone can be used as a pozzolanic material in Portland-cement-based systems after the material has been sieved to remove the quartz and after thermal activation because the estilbite has low pozzolanic activity. The main objective of this study was to determine the best particle size distribution that yields the highest smectite and zeolite concentration, besides the best temperature for higher pozzolanic activity. The experimental program employed the zeolitic sandstone passing through a #200 and #325 mesh sieve and calcination at the following temperatures: 150°C, 300°C and 500°C. Chemical analysis of the sieved samples was carried out by X-ray fluorescence spectroscopy and X-ray diffractometry, while mineralogical characterization was done by X-ray and thermogravimetric analysis and thermogravimetry..To assess reactivity, calorimetry driving and mechanical tests for pozzolanic activity in hydrated lime and cement Porltand were performed. The results showed that the sample sieved through at #200 mesh was the most suitable because it had a higher concentration of estilbite and a higher percentage of material seived compared to the sample sieved at #325 mesh, 15% and 2% respectively. The 500°C calcination temperature was accompanied by increased pozzolanic activity due to changes in estilbite and smectite cristalinity; the more moderate temperatures of 150°C and 300°C were not sufficient to achieve similar results. The mortars with sandstone sieved at #200 mesh and calcinated at 500°C reached the minimum limits required for a material to be considered as pozzolanic, i.e, 6 MPa for hydrated lime mortars and 75% for the pozzolanic index activity (PAI).
Acesso aberto (Open Access)
Avaliação preliminar do emprego de arenito zeolítico da região nordeste do Brasil como material pozolânico para cimento Portland
(2011-12) PICANÇO, Marcelo de Souza; ANGÉLICA, Rômulo Simões; BARATA, Márcio Santos
Natural zeolites usually exhibit pozzolanic activity without any additional treatment, e.g. thermal activation. They have been used for building since the ancient Roman Empire times in the production of hydraulic cements and concretes. Nowadays, there are many discussions involving the natural zeolites pozzolanic reactivity in the incorporation of the Portland cement composition. The appropriate use of pozzolans enables the production of special cements with lower manufacturing cost and with a greater durability in comparison with the corresponding cements without addition. In Brazil, zeolite consumption comes either from the importation of foreign countries or synthetic products. No zeolite mine is available in the country and only few geological occurrences were already described in the literature without any commercial interest. In northeast Brazil, the Geological Survey (CPRM) discovered zeolite-bearing sandstones related to Cretaceous sedimentary rocks of the Parnaíba Paleozoic Basin. The main purpose of this paper is to evaluate the possible use of such sandstones as pozzolan for using in Portland cements (CPI-S). A bulk sample of the zeolitic sandstone (AZ) was collected in the field. In the laboratory, preparation included drying, milling and sieving at the following grain-size fractions, in order to remove quartz and concentrate the zeolite: 100# (AZ-1), 200# (AZ-2) and 325# (AZ-3). After mineralogical evaluation, the AZ-2 fraction was selected for further analysis and assays. The experimental study was mainly based on mineralogical characterization, including: X-ray diffraction (XRD), chemical analysis and heat flow calorimetry, besides pozzolanic activity assay and compressive strength. The results show that the mineralogical composition of the zeolitic sandstone is mainly quartz, zeolite (stilbite) and smectite. Stilbite is the main pozzolanic phase, and the smectite can also play an important role. The hydration of the Portland cement was accelerated due to the very fine grained nature of the material. Meanwhile, the reactivity obtained was slightly below the standard requirements to be used in industrial scale. Additional studies should be carried out in order to evaluate if a further thermal treatment (between 300 °C and 500 °C) may increase the pozzolanic activity due to the stilbite destruction around this temperature. The same happens with kaolinite that needs thermal treatment above 550 ºC to convert to the amorphous phase metakaolin in order to be used as one of the most commons pozzolans in the cement industry. The main purpose was to contribute for the production of an alternative kind of cement which produces less pollution to the environment (CO2 decrease in the atmosphere) with cost saving. In addition, it is expected to contribute for the exploitation of the sedimentary zeolites occurrences which have been relatively well studied from a geological point, but are still not mined.
Acesso aberto (Open Access)
Cimentos Portland aditivados com arenito zeolítico com propriedades pozolânicas
(2014-06) PICANÇO, Marcelo de Souza; ANGÉLICA, Rômulo Simões; BARATA, Márcio Santos
The proper use of pozzolans enables the production of special cements with lower manufacturing cost and higher durability in comparison with cements without mineral additions. It also enables significant gains in productivity and in equipment service life in the factory as well as reduce the CO2 emission into the atmosphere. Zeolites have been used as pozzolanic material in mixtures with Fuller's Earth and water in buildings from the ancient Roman Empire. Nowadays, there are many discussions involving pozzolanic reactivity of natural zeolites in the incorporation to Portland cement. In the Northeastern region of Brazil, sedimentary zeolites related to sandstones of the Parnaiba Basin were discovered by the Geological Survey of Brazil in the 2000s. These sandstones are mainly composed by quartz, natural zeolites (estilbity) and clay (smectite). Preliminary studies have pointed that this sandstone may be used as pozzolanic material in Portland cements. The material must be previously grinded to remove quartz and thermally activated, since stilbite is a zeolite with low pozzolanic activity. The aim of this study was to evaluate the ideal amount of thermally activated zeolitic sandstone to be incorporated in the Portland cement in order to improve its mechanical and mineralogical properties. In the laboratory, the < # 200 fraction of the zeolitic sandstone was calcined at 500 º C. Chemical and miner-alogical analysis were carried out by X-ray fluorescence spectroscopy (XRF) and X-ray Diffractometry (XRD), respectively. The hydration behavior of the cements was evaluated using heat-flow calorimetry, besides thermal analysis and XRD. To evaluate the physical properties, mechanical testing of compressive strength in cement mortar Portland with different proportions of sandstone was carried out. The results showed that the AZ2-3 zeolitic sandstone with the proportion of 10% incorporated in Portland cement type CPI-S, showed the best result of compressive strength and mineralogical properties of the samples suitable for the production of CPII-Z type commercial cement.
Acesso aberto (Open Access)
A zona zeolítica da Formação Corda, Bacia do Parnaíba
(Universidade Federal do Pará, 2002-02-14) REZENDE, Nélio das Graças de Andrade da Mata; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302; https://orcid.org/0000-0002-0134-0432
Since the occurrence of zeolites in the Parnaíba Basin were revealed, in the middle of the last decade, several works have been published addressing the main traces of geological conditioning, as well as the possibility of processing the ore. These investigations provided an overview of the mineralogical composition of the deposit and identified the presence of zeolites stilbite and laumontite occurring as cement in fluvial and eolian sandstones of the Corda Formation, associated with caucite and smectites. They also provided some data on the chemistry of the whole rock and one of the zeolite species (stilbite). They did not contain information about paragenesis and the hypotheses raised about genetic aspects were inconsistent. There was speculation about the possibility of a hydrothermal influence and the probable existence of a well-defined mineralogical zoning, which could favor eventual exploratory investments. The main objective of this dissertation was to systematically study two representative sections of the Zeolite Zone of the Corda Formation, to define the paragenesis and the spatial pattern of mineralogical distribution, as well as to elucidate the issue of genetic modeling for the accumulation of zeolites. Additionally, we tried to open perspectives for possible fields of application of this material. The work methodology involved an intensive bibliographic research on the geological conditioning of zeolite deposits in sedimentary rocks and on the physicochemical parameters that regulate the stability of stilbite and laumontite. This theoretical foundation was an important subsidy in the interpretation of the data obtained through various analytical resources, managing to assemble a table that provides a generic overview of the diagenetic environment of the Corda Formation, and its evolution, with emphasis on the conditions of pressure, temperature and chemistry of the zeolite zone, and the spatial distribution of the two zeolites, in addition to paragenesis relationships. The study of the isotopic compositions of carbon and oxygen was an important auxiliary tool in this interpretation The focus on Regional Geology admits the need for a review of the Mesozoic stratigraphic order of the basin, with the possibility of dissociating the Corda Formation into two distinct segments, and emphasizes the importance of the role played by basic volcanic rocks in this order, and their spatial and genetic link with zeolites. The local geological context reflects a broad sedimentary system, predominantly eolic and fluvial, developed over basaltic flows. Mineralogically, two distinct universes can be highlighted: a) a detrital one, containing grains of diverse composition in which quartz predominates and, subordinately, basalt fragments, in addition to feldspars, quartzite, chert and limestone, among others; b) an authigenic phase, with the paragenesis involving a ferruginous coating, the smectites (predominantly montmorillonites), and zeolites (stilbite and laumontite) and calcite. It is not possible to define the order of crystallization of zeolites among themselves, nor of these with calcite, as there is evidence that these minerals are cogenetic and formed from fluctuations in the chemical balance of the interstitial fluid, both in fluvial and aeolian facies. The texture of the sandstone, characterized by a predominantly floating and/or punctual packing, the isotopic composition of oxygen and carbon in the calcitic cement and the absence of albitization in the detrital plagioclase, in addition to the degree of preservation of the smectites and the absence of siliceous cement, provided subsidies to characterize a diagenesis dominated by temperature and pressure conditions compatible with surface conditions, with the zeolite process involving an open hydrological regime, developed in an arid and semi-arid environment. Adsorption tests for copper show that phases enriched in laumontite have a relatively high performance, compatible with some activated aluminas, which recommends carrying out more complete investigations of the industrial properties of the zeolite ore from the Corda Formation.