Antonio Telesca

Flue gas desulfurization gypsum and coal fly ash as basic components of prefabricated building materials.

The manufacture of prefabricated building materials containing binding products such as ettringite (6CaO·Al2O3·3SO3·32H2O) and calcium silicate hydrate (CSH) can give, in addition to other well-defined industrial activities, the opportunity of using wastes and by-products as raw materials, thus contributing to further saving of natural resources and protection of the environment. Two ternary mixtures, composed by 40% flue gas desulfurization (FGD) gypsum or natural gypsum (as a reference material), 35% calcium hydroxide and 25% coal fly ash, were submitted to laboratory hydrothermal treatments carried out within time and temperature ranges of 2h-7days and 55-85°C, respectively. The formation of (i) ettringite, by hydration of calcium sulfate given by FGD or natural gypsum, alumina of fly ash and part of calcium hydroxide, and (ii) CSH, by hydration of silica contained in fly ash and residual lime, was observed within both the reacting systems. For the FGD gypsum-based mixture, the conversion toward ettringite and CSH was highest at 70°C and increased with curing time. Some discrepancies in the hydration behavior between the mixtures were ascribed to differences in mineralogical composition between natural and FGD gypsum.

Utilization of Coal Combustion Ashes for the Synthesis of Ordinary and Special Cements

Raw mixes containing pulverized coal fly ash (with limestone and silica sand) or fluidized bed coal combustion ash (fly and bottom, with added limestone, anodization mud, and, when necessary, flue gas desulfurization gypsum), aimed at generating ordinary Portland or calcium sulfoaluminate clinkers, respectively, were heated in a laboratory electric oven at temperatures ranging from 1150° to 1500°C and submitted to X-ray diffraction analysis. The former had the same qualitative phase composition as that of a reference mixture, composed by limestone and clay; furthermore, they exhibited an excellent burnability on the basis of their residual free lime contents, measured after heating at 1350°, 1400°, 1450°, and 1500°C. The latter showed very good results in terms of conversion of reactants and selectivity degree toward the main mineralogical constituent, calcium sulfoaluminate (4CaO·3Al2O3·SO3), even if the behavior of a reference mixture consisting of limestone, bauxite, and natural gypsum was slightly better. The introduction of a fluidized bed coal combustion ash in the raw mix generating calcium sulfoaluminate clinker implies a saving of bauxite and natural gypsum, which can be fully replaced through the addition of anodization mud and flue gas desulfurization gypsum, respectively.

Calcium looping spent sorbent as a limestone replacement in the manufacture of portland and calcium sulfoaluminate cements.

The calcium looping (CaL) spent sorbent (i) can be a suitable limestone replacement in the production of both ordinary Portland cement (OPC) and calcium sulfoaluminate (CSA) cement, and (ii) promotes environmental benefits in terms of reduced CO2 emission, increased energy saving and larger utilization of industrial byproducts. A sample of CaL spent sorbent, purged from a 200 kWth pilot facility, was tested as a raw material for the synthesis of two series of OPC and CSA clinkers, obtained from mixes heated in a laboratory electric oven within temperature ranges 1350°-1500 °C and 1200°-1350 °C, respectively. As OPC clinker-generating mixtures, six clay-containing binary blends were investigated, three with limestone (reference mixes) and three with the CaL spent sorbent. All of them showed similar burnability indexes. Moreover, three CSA clinker-generating blends (termed RM, MA and MB) were explored. They included, in the order: (I) limestone, bauxite and gypsum (reference mix); (II) CaL spent sorbent, bauxite and gypsum; (III) CaL spent sorbent plus anodization mud and a mixture of fluidized bed combustion (FBC) fly and bottom ashes. The maximum conversion toward 4CaO·3Al2O3·SO3, the chief CSA clinker component, was the largest for MB and almost the same for RM and MA.

Use of Fluidized Bed Combustion Ash and Other Industrial Wastes as Raw Materials for the Manufacture of Calcium Sulphoaluminate Cements

Calcium sulphoaluminate cements, mainly composed by 4CaO·3Al2O3·SO3 and 2CaO·SiO2, are special hydraulic binders which require limestone, bauxite and gypsum as natural raw materials for their manufacture. In order to save bauxite and natural gypsum, it has been explored the possibility of using, among the raw mix components, FBC waste together with pulverised coal fly ash or anodization mud and, when necessary, flue gas desulphurization gypsum. Mixtures containing limestone (29–39%), FBC waste (30–44%), pulverised coal fly ash (0–13%) or anodization mud (0–32%), bauxite (0–18%) and flue gas desulphurization gypsum (0–8%) were heated for 2 hours in a laboratory electric oven at temperatures ranging from 1150° to 1300°C. The X-ray diffraction patterns on the burnt products generally showed a good conversion of the reactants and a high selectivity degree towards 4CaO·3Al2O3·SO3, particularly at 1250°C.