Crystallization of (Na₂O–MgO)–CaO–Al₂O₃–SiO₂ Glassy Systems Formulated from Waste Products

Abstract

Aluminosilicate and silicate glass-ceramics were obtained from controlled devitrification of CaO-Al 2 O 3 -SiO 2 glassy systems starting from Spanish and Italian coal fly ash or Italian municipal incinerator slag mixed with other byproducts, such as glass cullet and dolomite. The nucleation mechanism and the crystallization kinetics were investigated by thermal, diffractometric, and microstructural measurements. Moreover, the experimentally observed devitrification and the identification of the crystalline phases formed were compared with the indications derived from Ginsberg, Raschin-Tschetveritkov, and Lebedeva diagrams used for petrological glass-ceramics. All the glasses showed a good crystallization tendency with the formation of dendritic pyroxene and acicular wollastonite together with feldspar and iron spinels starting from the surface. The activation energy values for crystallization ranging from 472 to 832 kJ⅐mol ؊1 were found to be close to those typical for aluminosilicate glasses; moreover, the possibility to vitrify and devitrify up to 100 wt% of slag and up to 40 -50 wt% of ash mixed with glass cullet and dolomite makes the vitrification treatment a suitable disposal procedure.

Plasma treatment of air pollution control residues

“…This . The most frequent crystallisation mechanism, the one at the surface, has proved to be quite an effective method for enhancing the strength of glass (Barbieri et al, 2000b). It is concluded that plasma treatment of APC residues produces a highly inert and stable glass which is suitable for disposal in inert landfill or use in bulk civil engineering applications.…”

Glass-ceramics: Their production from wastes—A Review

“…Barbieri and co-workers have published a series of papers [103][104][105] on glass-ceramics produced from fly ash mixed with other waste materials. The other wastes were mainly float dolomite (CaMg(CO 3 ) 2 ) from mineral extraction operations, which was used to increase CaO and MgO content, and glass cullet to increase the amount of SiO 2 , Na 2 O and CaO present in the parent glass.…”

“…Barbieri and co-workers were able to produce a series of glass-ceramics containing different phases [103][104][105]. For example glass-ceramics from fly ash with only glass cullet as an additive had acicular wollastonite as the crystalline phase whereas, with the further addition of dolomite, this phase was only found after heat treatment in a narrow temperature range around 1000°C and most heat treatments resulted in a microstructure with dendritic pyroxene (diopside) and a small amount of acicular feldspar (anorthite).…”

Nucleation and crystal growth of glasses produced by a generic plasma arc-process

“…Therefore, this must be considered as the optimum crystallisation treatment to transform the PG glass into a glass-ceramic material. It is well known that wollastonite is a common crystalline phase in glass-ceramics formulated with high CaO content 6,16,19, and in conventional ceramic tiles manufactured by a fast-firing process. Wollastonite crystallisation gives high mechanical resistance to tile products and a high content of this phase in a sintered glass-ceramic will imply higher strength of the final products.…”

“…In thermal plasma vitrification, the heat generated is used to treat hazardouswastes containing metals, inorganic oxides and/or organics at temperatures above 1500ºC, at which point metal containing wastes are melted and organic contaminants are thermally destroyed. The plasma vitrification yields a leach-resistant monolithic glassy slag, which is environmentally safe for landfill disposal or can be reused as glassceramic for construction materials [4][5][6][7][8] .…”