The effect of furnace and flash heating on COx argillite for the synthesis of alkali-activated binders

Abstract

A considerable quantity of Callovo-Oxfordian (COx) argillite will be excavated due to deep geological radioactive waste disposal. Till now, there is no viable solution to make use of the excavated argillite. This paper investigates the possibility of producing alkali-activated materials based on argillite. The raw argillite is mainly composed of illite, smectite, muscovite and traces of kaolinite and chlorite. In addition, it contains carbonates, quartz, plagioclase and pyrite.At first, argillite was ground and thermally treated at different temperatures ranging from 600 °C to 800 °C and from 600 °C to 750 °C with furnace and flash processes, respectively. Then, a comparative study of the effect of the two heating processes on the physical, chemical and structural characteristics of argillite was undertaken. It was shown that in the case of furnace heat treatment, a heating between 700 °C and 800 °C leads to the full dehydroxylation of clay minerals (illite-smectite, illite/mica, kaolinite and chlorite) and the total transformation of octahedral aluminum to tetrahedral one. However, flash treatment induces partial structural dehydroxylation of argillite clay minerals regardless of the temperature. Finally, it was demonstrated that it is possible to produce alkali-activated materials from a mixture comprising of 50% of raw argillite and 50% of metakaolin and from calcined argillite regardless of the heat treatment process and the applied temperature.