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As indicated in Chapters 1 and 2, coal combustion products (CCPs) include fly ash, bottom ash, boiler slag (furnace bottom ash) and flue gas desulfurisation material (FGD). The latter, however, is not produced by Australian coal-fired power stations. Fly ash represents the largest component of the group, accounting for up to 90% of the CCPs produced. The chemical composition of fly ash generally reflects the mineral matter of the parent coal, while the physical features (size and shape) of the particles often make it suited as an alternative material in applications that use sand, gravel or gypsum. Fly ash is made up of fine (1.0- 100 pm), powdery particles, composed of crystalline minerals, amorphous aluminosilicates, and small proportions of unburnt carbon. The texture of fly ash is comparable to that of "silt and fine sand" soils (Adriano et al. 1980; Aitken et al. 1984; Palumbo et al. 2004). It is these general characteristics, both in terms of elemental composition and physical properties, which have generated increasing interest in fly ash as a viable product for soil management in crop and pasture production systems in Australia and in many other parts of the world. |
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