Influence of waste products from electricity and cement industries on the thermal behaviour of Estonian clay from Kunda deposit

The influence of two different oil shale ashes formed, respectively, at pulverized firing and at circulated fluidized bed combustion of Estonian oil shale (OS) at electricity production, and clinker dust (CD) formed at cement production on the thermal behaviour of Estonian clay from Kunda deposit, and, for comparison, on the illitic clay from Fuzerradvany (Hungary) was studied. Composition of clay with 40% of previously fired at 1050 °C clay (grog) was used as a basement one. In the blends studied the fired clay was partly or totally replaced with OS ash or CD additives. Experiments were carried out under non-isothermal condition up to 1050 °C using a Setaram Setsys 1750 thermoanalyzer coupled with Pfeiffer Omnistar Spectrometer at the heating rates of 1.25, 2.5, 5 and 10 °C min−1 in an oxidizing atmosphere containing 79% of Ar and 21% of O2. The differential isoconversional method of Friedman was applied to calculate the kinetic parameters. Depending on the origin of the additive the thermal behaviour of blends following the two-step route differentiated remarkably from the same characteristics of clays. The value of activation energy along the reaction progress varied for illitic clay and its blends with OS ash and CD additives more than based on Kunda clay, but, contrary, the average activation energy values for blends based on Kunda clay are, as a rule, bigger than based on illitic clay.