Characterization at High Temperature of the Porcelanite Mineral Phases from the Gafsa-Metlaoui Basin and Valuation in the Ceramic Domain

In a bid to test the potential use of the porcelanites of the Gafsa-Metloui basin in the ceramic manufacturing domain, three porcelanites were collected from three different areas: the Kef el Ghiss, Oued Thelja and Kef Eddour. These porcelanites were treated at 800, 1000 and 1200 °C for three to six hours. The aim has been to understand their relating phase transformations at high-temperature, by simple calcination and activated calcination with an alkaline flux (Na2CO3). The treated and raw samples were analyzed through various techniques (XRD, X-ray Fluorescence). All samples were discovered to be opal C/T-rich. The Oued Thelja and Kef Eddour samples appear to be carbonate-rich, while the Kef el Ghiss’s sample turns out to be rather clayey and contain trace amounts of quartz, francolite and feldspars. Following calcination, all samples have appeared to lose a large part of their mineralogical constituents (clay minerals, calcite, dolomite, quartz, francolite, hematite and feldspars), while the opal C/T proved to transform into cristobalite and tridymite. Thus, the activated calcination, within the ranges of 1000–1200 °C, of the samples of Oued Thelja and Kef Eddour proved to yield cristobalite and tridymite. The same mineral phases were obtained with enstatite and/or diopside, following a simple 1200 °C calcination process. The administered ceramic tests appear to reveal that the Kef Eddour and Kef el Ghiss associated samples are not suitably fit for ceramic applications. As for the Oued Thelja relevant sample, it proves to display satisfactory properties (in terms of shrinkage, porosity and loss on ignition), and could therefore be valued in ceramics manufacture through applying it in formulas of up to 20% in range, in conformity with the following formula: 20% Opal C/T + 12% Tabarka clay + 30% feldspars + 38% clay from Ukraine.