Transformations of calcium sulphates in solidified carbonated volatile fluidized ashes

Abstract

Abstract Carbonation of volatile fluidized ashes with the use of carbon dioxide can be a means to their transformation into a product with a possible application as an additive to cement and concrete. Currently, due to its physical-chemical characteristics and particularly because of the high concentration of free calcium oxide, the possible applications of this product are highly limited, perhaps even none existent. A significant reduction or even the complete elimination of CaO can be achieved by its transformation into calcium carbonate. In carbonated volatile fluidized ashes, two components relevant to the binding time of mortar, as well as its durability, can be found: calcium carbonates and calcium sulphates. During the investigation it was assumed that calcium carbonate, being poorly water-soluble, would not react with the remaining components of the porous water of the volatile fluidized ash. Crystalline phases of calcium sulphates, anhydrite, gypsum and bassanite occurring in bound volatile fluidized ashes after carbonation demonstrate the possibility of crystallization in the presence of calcium carbonate. In particular, a change in the concentration of bassanite indicates that this phase, as a precursor to the crystallization of gypsum, may play a significant role in the process of binding carbonated volatile ashes.