Thaumasite formation in stabilized coal combustion by-products

The by-products of the desulfurization process in a spray drier usually contain a mixture of hannebachite (CaSO3 . 1/2H(2)O), gypsum (CaSO4. 2H(2)O), and the finer fraction of the fly ash. This material was mixed with an additional fly ash and stabilized by adding about 3 wt% lime kiln dust (LKD). The stabilized product was used either as a structural fill or was left in the storage yard for several years. Samples extracted from these sites were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The analytical results show the formation of thaumasite (Ca3Si(OH)(6)(CO3)(SO4) . 12H(2)O), ettringite (Ca6Al2(SO4)(3) (OH)(12) . 26H(2)O), and an intermediate phase with varying chemical composition of calcium, aluminum, silicon, and sulfur. (C) 2002 Elsevier Science Ltd. All rights reserved.