Effect of iron sulfides on the physicochemical processes occurring during solidification of synthetic calcium aluminosilicate monolith

Abstract

Phase formation processes occurring during solidification of two samples of silicate materials obtained by filtration combustion of a mixture of fly ash, limestone, and sand were studied. During the solidification of the material produced in the combustion mode in which impurity pyrite FeS₂ completely decomposed by the interaction with atmospheric CO₂ and water, dicalcium silicate, melilite, and glass phase gradually transformed into a mixture of serpentine-type binder (Ca, Fe, Mg)₃[(Si, Al)₂O₅](OH)₄ · nH₂O and calcium carbonates. The narrowing of the combustion wave front allows one to preserve pyrite particles encapsulated in the glass phase. In this case, the mechanism of solidification of the combustion product changes: the expose to sulfuric acid released by pyrite oxidation of the silicate components of the material results in the formation of gypsum and hydrosilicates filling the pore space. This enables one to reach high strength characteristics of the material without prepressing. The presence of a lower-pH medium in the pore space inhibits ettringite crystallization, thus preventing mechanical destruction.