Characterization of clays used in the ceramic manufacturing industry by reflectance spectroscopy: An experiment in the Sao Simao ball-clay deposit, Brazil

Abstract

The characterization of clays from the physical, chemical, and ceramic standpoint in pre-and-within mining stages is a necessary step. However, succinct mining planning, lack of industry-oriented standards and the usual bond to empirical discrimination of clays as regards their use, imply in mixing chemically and technologically different materials, with serious consequences to the mining and manufacturing process. Taking the alluvium-derived, ball-clay deposit of Sao Simao (SS) as a case study, this works aims to evaluate the potential of reflectance spectroscopy (RS) as a method to define types, purity and crystallinity of clays and to seek a possible relation between spectral characteristics of clays and their use in the ceramic industry. The SS deposit hosts three types of clays that were spectrally set apart based on RS. The technique indicated that the white clays comprise highly ordered kaolinite, mica, smectite and lepidocrosite (first finding in Brazilian alluviums). The brown clays are also rich in well-ordered kaolinite and contain abundant Fe-bearing minerals, as goethite, hematite and siderite (rarely found in alluviums). The gray clays are kaolinite-poor and are abundant in organic matter and smectites. Each of the clay classes typified in the SS deposit has a specific application in the fine ceramic industry, indicating the prominent potential of RS to characterize industrial materials. (V) 2007 Elsevier B.V. All rights reserved.