Abstract

Over the past several decades, kaolin has been used intensively in the paper industry as a coating and filler material. These applications require kaolin of a high brightness grade, which depends heavily on the level of impurities (mainly Fe-bearing minerals such as Fe oxides and hydroxides) and may be improved by beneficiation processes involving grain-size classification, magnetic separation and chemical treatments. This investigation was carried out on five Brazilian kaolin samples of different geographical and geological origins. Granulometric, mineralogical, chemical and physical characterizations were performed on all samples before and after the beneficiation process.

Chemical compositions were determined by X-ray fluorescence and the most important crystalline phases were identified using X-ray diffraction. Kaolinite is the dominant mineralogical phase with minor amounts of muscovite and quartz. The nature of Fe impurities was investigated by electron spin resonance and 57Fe Mössbauer spectroscopy. For all studied kaolin samples, Fe ions (Fe3+ and Fe2+) are present in variable amounts, in the kaolinite structure and also in Fe oxides (magnetite, hematite and goethite). The beneficiation procedure aims to remove these Fe oxides and was found to be most efficient for the Mogi das Cruzes kaolin. The Seridó kaolin had the best whiteness index observed among the analysed samples.

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