Caracterização de argilas de novos jazimentos situados em Parelhas/RN, Brasil, visando aplicação na indústria cerâmica

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Abstract

RESUMO O Estado do Rio Grande do Norte, mais especificamente no município de Parelhas, Brasil, a indústria cerâmica já é bastante consolidada, crescendo ano após ano. Entretanto, o estímulo do setor tem provocado acelerada exaustão das jazidas de argilas locais utilizadas pela indústria e, por conseguinte, ameaçando a manutenção da indústria cerâmica no município e na região Seridó. Por esta razão, tem-se aprofundado o interesse de buscar novos jazimentos de argilas, a fim de suprir as suas demandas atuais e futuras. Recentemente, foram descobertos novos jazimentos no município, todavia, estas argilas não têm sido devidamente caracterizadas, causando prejuízos tanto a qualidade final do produto, como ao seu pleno aproveitamento industrial. Assim, este trabalho tem como objetivo caracterizar física, química e mineralogicamente argilas extraídas de três novos jazimentos do município de Parelhas/RN, com a finalidade de classificá-las visando sua aplicação na indústria de cerâmica vermelha da região. As amostras foram beneficiadas por secagem a 60 °C, seguida de moagem e peneiramento em malha de 200 mesh. Então, foram caracterizadas por fluorescência de raios-x, difração de raios-x, análise termogravimétrica e diferencial, análise granulométrica, perda ao fogo e plasticidade. Os constituintes das amostras identificados por fluorescência de raios X foram SiO2, Al2O3, Fe2O3, MgO, K2O, CaO e TiO2. Os difratogramas de raios-X revelaram a presença predominante dos argilominerais esmectita, feldspato, caulinita e quartzo nas amostras. A perda de massa total para as amostras variou entre 14% a 22,65%. A distribuição de partículas variou entre 0,2 a 40 µm, com diâmetro médio entre 6 e 16 µm. As amostras são classificadas como altamente plásticas e apresentam viabilidade para serem utilizadas na indústria de cerâmica vermelha.

Translated abstract

ABSTRACT The State of Rio Grande do Norte, more specifically in the municipality of Parelhas, Brazil, the ceramic industry is already well established, growing year after year. However, the industry stimulus has led to accelerated exhaustion of the local clay deposits used by the industry and, therefore, threatening the maintenance of the ceramics industry in the municipality and the Seridó region. For this reason, interest has been deepened in the search for new clay deposits in order to meet their current and future demands. Recently, new deposits have been discovered in the municipality, however, these clays have not been properly characterized, causing damage to both the final quality of the product and its full industrial use.Thus, this work aims to characterize physically, chemically and mineralogically clays extracted from deposits in the Parelhas/RN municipality, with the purpose of classifying them aiming to be applied in the ceramic industry of the region. The samples were beneficiated by drying at 60 °C, followed by milling and sieving in 200 mesh sieves. Then, they were characterized by x-ray fluorescence, x-ray diffraction, thermogravimetric and differential analysis, particle size analysis, ignition loss and plasticity. The constituents of the samples identified by X-ray fluorescence were SiO2, Al2O3, Fe2O3, MgO, K2O, CaO and TiO2. The X-ray diffractograms revealed the predominant presence of the clay minerals smectite, feldspar, kaolinite and quartz in the samples. The total mass loss for the samples ranged from 14% to 22.65%. The particle distribution ranged from 0.2 to 40 μm, with an average diameter between 3 and 7 μm. The samples are classified as highly plastic and are feasible for use in the red ceramic industry.

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Evaluation of the medicinal use of clay minerals as antibacterial agents.

Lynda Williams, Shelley E. Haydel (2010)

Natural clays have been used to heal skin infections since the earliest recorded history. Recently our attention was drawn to a clinical use of French green clay (rich in Fe-smectite) for healing Buruli ulcer, a necrotizing fasciitis ('flesh-eating' infection) caused by Mycobacterium ulcerans. These clays and others like them are interesting as they may reveal an antibacterial mechanism that could provide an inexpensive treatment for this and other skin infections, especially in global areas with limited hospitals and medical resources.Microbiological testing of two French green clays, and other clays used traditionally for healing, identified three samples that were effective at killing a broad-spectrum of human pathogens. A clear distinction must be made between 'healing clays' and those we have identified as antibacterial clays. The highly adsorptive properties of many clays may contribute to healing a variety of ailments, although they are not antibacterial. The antibacterial process displayed by the three identified clays is unknown. Therefore, we have investigated the mineralogical and chemical compositions of the antibacterial clays for comparison with non-antibacterial clays in an attempt to elucidate differences that may lead to identification of the antibacterial mechanism(s).The two French green clays used to treat Buruli ulcer, while similar in mineralogy, crystal size, and major element chemistry, have opposite effects on the bacterial populations tested. One clay deposit promoted bacterial growth whereas another killed the bacteria. The reasons for the difference in antibacterial properties thus far show that the bactericidal mechanism is not physical (e.g., an attraction between clay and bacteria), but by a chemical transfer or reaction. The chemical variables are still under investigation.Cation exchange experiments showed that the antibacterial component of the clay can be removed, implicating exchangeable cations in the antibacterial process. Furthermore, aqueous leachates of the antibacterial clays effectively kill the bacteria. Progressively heating the clay leads first to dehydration (200 degrees C), then dehydroxylation (550 degrees C or more), and finally to destruction of the clay mineral structure by (~900 degrees C). By identifying the elements lost after each heating step, and testing the bactericidal effect of the heated product, we eliminated many toxins from consideration (e.g., microbes, organic compounds, volatile elements) and identified several redox-sensitive refractory metals that are common among antibacterial clays. We conclude that the pH and oxidation state buffered by the clay mineral surfaces is key to controlling the solution chemistry and redox related reactions occurring at the bacterial cell wall.