Caracterização Mineralógica de Caulins Provenientes de Pegmatitos das Regiões de Porciúncula – RJ e Patrocínio do Muriaé – MG Visando a Identificação de Halloysita

Abstract

Kaolin is an important industrial mineral and a geological indicator. The term kaolin refers to the kaolinite phyllosilicate group which comprises kaolinite itself, halloysite, dickite and nacrite. Halloysite is a polytype of kaolinite, having one more molecule of water in its structure and is distinguished mainly by its tubular shape, which gives the mineral a bigger surface area of contact, resulting in noble industrial applications. Due the morphology, the mineral has been studied for applications in the nanotechnology sectors, mainly in pharmaceuticals and fertilizers, as a carrier of active principles. Halloysite deposits can be classified as primary, when originated from the in situ alteration of silicates, or as secondary when originated from sedimentary processes. Recent researches report occurrences of the mineral in the south and southeast of Brazil, associated with primary deposits. The purpose of the study is to characterize their mineralogy aiming to identify the halloysite mineral. In order to achieve this objective, 4 samples of kaolin from 4 pegmatites were collected in the cities of Porciúncula - RJ and Muriaé - MG. The kaolin samples were characterized through X-ray diffractograms (XRD) of the raw, magnetic, non-magnetic and clay fractions of the 4 pegmatites. Images were generated by scanning electron microscope (SEM) in order to differentiate kaolinite from halloysite. Chemical analyzes were carried out aiming obtain the percentage of oxides in the studied samples. The analysis of density and whiteness index helped the mineralogical characterization process of the studied samples. XRD generated diffractograms that showed signs of the clay mineral studied together with kaolinite, quartz, muscovite, K-feldspar, goethite and gibbsite. The images generated by SEM shows kaolinite forming booklets and tubular halloysite. Chemical analyzes by X-ray fluorescence indicated the predominance of oxides of silicon, iron and potassium in the samples. With there results, Rio de Janeiro and Minas Gerais are studied states that can be targets for halloysite deposits.