Abstract
Kaolin is widespread as a result of the alteration in the San José Sn-Ag deposit located in Oruro, Bolivia. This study presents a chemical, mineralogical and thermal characterization of the San José kaolinitic deposit, which is necessary to determine their optimal applications. Mineral phases of these white silty kaolinitic materials were determined by X-ray diffraction (XRD) and are quartz, kaolinite, K-feldspar, muscovite, illite and minor halloysite, dickite, plagioclase, jarosite, rutile, alunite and gypsum. The fraction < 63 µm contains 20–27 mass% of kaolinite. Differential thermal analysis (DTA) shows an endothermic peak at 520 °C associated with the dehydroxylation of kaolinite and an exothermic peak at ~ 980 °C related to the crystallization of mullite. TG curves show a total mass loss up to 1300 °C of about 8 mass%. The dilatometric curves show a shrinkage at about 890 °C produced by the collapse of metakaolinite into a spinel-like structure, and another shrinkage starts at 1010 °C, at the beginning of the sintering, when the spinel-like phase is transformed to mullite and amorphous SiO2. Lightness L* is 80–92, but only the mined materials have b* < 4, suitable for paper filling applications.
Highlights
A significant source of primary kaolin comes from the alteration of host rocks produced during the circulation of hydrothermal fluids responsible to the formation of metallic deposits [1, 2]
They are abundant in the tropical regions of the east part of the country, where they formed from supergene processes, such as the active exploitations of kaolin in the departments of Santa Cruz [4] and Cochabamba [5, 6]
The aim of this study is to present a mineralogical and thermal characterization of kaolinitic rocks located in the vicinity of the San José mine (Oruro, Bolivia) to determine their possible industrial applications
Summary
A significant source of primary kaolin comes from the alteration of host rocks produced during the circulation of hydrothermal fluids responsible to the formation of metallic deposits [1, 2]. Other kaolinitic deposits are related to degradation of materials of Devonian age in Bolivia [3] They are abundant in the tropical regions of the east part of the country, where they formed from supergene processes, such as the active exploitations of kaolin in the departments of Santa Cruz [4] and Cochabamba [5, 6]. The aim of this study is to present a mineralogical and thermal characterization of kaolinitic rocks located in the vicinity of the San José mine (Oruro, Bolivia) to determine their possible industrial applications. This kaolinitic area was formed as result of the alteration of volcanic rocks by hydrothermal fluids during the formation of the San José ore deposit. An economic valuation of the exploitation of this deposit indicated the occurrence of 318,892 tons of kaolinitic material in this deposit [8]
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