Abstract
The thermal behavior of green clay samples from the Arumetsa and Füzérradvány deposits (Hungary) and the influence of two new types of Estonian oil shale (OS) ashes and cement bypass dust (clinker dust) additives on it were the objectives of this study. Thermal and thermo-dilatometric analysis methods were applied using a Setaram Setsys 1750 thermoanalyzer coupled with a Pfeiffer Omnistar spectrometer and a Setaram Setsys 1750 CS Evolution dilatometer. The kinetic parameters were calculated based on the differential isoconversional method of Friedman. The results of the thermal analysis of clays and blends indicated the emission of physically bound water at 200–250 °C. At temperatures from 200–250 °C to 550–600 °C the release of water is caused by oxidation of organic matter and dehydroxylation of different clay minerals like illite, illite-smectite, mica and kaolin. From blends, in addition, also from the decomposition of portlandite. The emission of CO2 at these temperatures was a result of the oxidation of organic matter contained in the clays. In the temperature range from 550–600 °C to 800–900 °C, the mass loss was caused by ongoing dehydroxylation processes in clay minerals but was mainly due to the decomposition of the carbonates contained in the OS ashes and clinker dust. These processes were accompanied by contraction and expansion of the ceramic bodies with the corresponding changes in the SSA and porosity values of the samples. Therefore, the decomposition of the clays took place in one step which blends in two steps. At first, dehydroxylation of the clay minerals occurs, followed by decomposition of the carbonates. The value of the conversion-dependent activation energy E along the reaction progress α varied for the Arumetsa and illitic clay between 75–182 and 9–206 kJ mol−1, respectively. For the blends based on Arumetsa and illitic clay, the activation energy of the first step varied between 14–193 and 5–205 kJ mol−1, and for the second step, it was between 15–390 and 135–235 kJ mol−1, respectively, indicating the complex mechanism of the processes.
Highlights
Licensee MDPI, Basel, Switzerland.Previously, the influence of new types of oil shale (OS) ashes and clinker dust on the thermal behavior of Estonian clay from Kunda deposits has been studied [1]
The results of the thermal analysis coupled with the mass-spectroscopic (MS) analysis of the evolved gaseous compounds indicated that the emission of hygroscopic and physically bound water at a heating rate of 5 ◦ C per min occurred up to 220 ◦ C, with corresponding peak minimums in the DTG curves at 86 ◦ C and 98 ◦ C and shoulders at 151 ◦ C and 153 ◦ C for the Arumetsa and illitic clay, respectively, (Figure 1a) and with corresponding maximums in the water emission profiles at 86 ◦ C and 78 ◦ C, respectively
The emission of carbon dioxide was more intensive for the Arumetsa clay, in which the content of organic carbon was on the level of 0.32%, and less intensive for the illitic clay, with the content of organic carbon being 0.06% (Table 2)
Summary
The influence of new types of OS ashes and clinker dust on the thermal behavior of Estonian clay from Kunda deposits has been studied [1]. The results of studying the influence of these ashes and clinker dust additives on the thermal behavior of Estonian clay from another big deposit (i.e., the Arumetsa deposit) is presented. The ashes used were formed through the circulated fluidized bed combustion of OS at the Auvere Power Plant (CFBC at temperatures 750–830 ◦ C; fly ash (FA)) and through. The total amount of OS ashes and clinker dust is decreasing, according to the reduction of OS-based electricity production in Estonia and improvements in the exploited technologies for OS combustion and cement production [2,3]. The amount of OS ashes formed in 2020 was on the level of
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