L. Barbieri

Alkaline and alkaline-earth silicate glasses and glass-ceramics from municipal and industrial wastes

Municipal (bottom ash and glass cullet coming from the municipal solid waste incineration and a community glass recycling program, respectively) and industrial (steel fly ash) wastes are particularly suitable to be subjected to a vitrification/devitrification process, leading to the production of alkaline and alkaline-earth silicate differently colored glasses with good chemical properties, capable to be transformed into surface nucleated basaltic glass-ceramics. These materials were investigated by means of differential thermal analysis, durability and release tests, X-ray diffraction and scanning electron microscopy.

Bulk and sintered glass-ceramics by recycling municipal incinerator bottom ash

Abstract Glass-ceramics were produced using an Italian municipal incinerator bottom ash and glass cullet coming from a community glass recycling program. The capability of three different mixtures to be vitrified and subsequently devitrified by both bulk and sintering process was investigated by means of differential thermal analysis, X-ray diffraction, hot stage microscopy, firing shrinkage, water absorption and bulk density measurements, as well as scanning electron microscopy observations. High ash contents favour the growth of crystallised fraction volume and the formation of crystals of the pyroxene group, and anorthite in addition to wollastonite. Since the nucleation mechanism starts from the surface and sintering occurs before crystallisation, all the compositions humidified with a water solution are easily sinterable in dense materials at the relatively low temperature of about 850°C, in such way as to render the process economically advantageous

Vitrification of industrial and natural wastes with production of glass fibres

Abstract Solid wastes coming from the municipal incinerator of Reggio Emilia, Italy, and sludge excavated from the lagoon of Venice were successfully vitrified at 1350–1500°C. Glass cullet, coming from a community glass recycling program, was introduced in some of the batches as a melting aid. Several analyses performed on the glasses showed that the glass transition and devitrification temperatures shift to higher values with increasing amount of waste in the raw materials. The glasses obtained display a good durability. Two kinds of wastes tested in the experiments could be vitrified by themselves, with no addition of external raw materials. Glass fibres were drawn from the obtained glasses at various temperatures. Mechanical tests showed that the elastic modulus increases with the waste content, while it does not depend on the drawing temperature. The fibres possess a good tensile strength (a maximum value of 1.6 GPa was obtained).

Chemical stability of geopolymers containing municipal solid waste incinerator fly ash

Municipal solid waste incinerators every year produce tons of fly ashes which, differently from coal fly ashes, contain large amounts of toxic substances (heavy metals, dioxins, furans). The stabilization/solidification (S/S) technology known as geopolymerization is proposed with the purpose to bond physically and chemically incinerator fly ashes (IFA) in a solid matrix, in order to reduce pollutant mobility. The chemical stability of geopolymers with Si/Al ratio of 1.8-1.9 and Na/Al ratio of 1.0, synthesized by alkali activation of metakaolin and the addition of 20wt% of two different kinds of IFA, is presented. The concentration of the alkaline solution, water to solid ratio and curing process have been optimized. The room temperature consolidation of IFA containing geopolymers has been tested for leachability in water for 1day, accordingly to EN 12457 regulation and extended to 7days to increase the water attack on solid granules. Leachable metals in the test solution, determined by ICP_AES, fall within limit values set by regulation for non-dangerous waste landfill disposal. Geopolymeric matrix evolution with leaching time has been also evaluated in terms of pH and electrical conductivity increase in solution.

Glass matrix composites from solid waste materials

Abstract Glass matrix composites have been obtained by mixing and sintering “negative cost” materials coming from municipal solid waste incinerators (MSWIs) and from one aluminium foundry. The bottom ashes from two MSWIs were used to obtain the glass matrix and the solid wastes from an aluminium alloy industry were employed as a second phase. The bottom ashes were vitrified by heating at 1400°C without any additive. The vitrification process reduces the bottom ash initial volume by about 60%. The obtained glass has a Young modulus of 96 GPa and a Vickers hardness of 6 GPa. The composites were prepared in air by a low temperature pressure-less viscous phase sintering process (740–830°C) and were morphologically and mechanically characterised. The composites showed a bending strength up to 50 MPa at room temperature and could be proposed for applications in the field of tiles.

Effect of TiO2 addition on the properties of complex aluminosilicate glasses and glass-ceramics

The nucleating effect of titania during glass crystallization has been studied in a complex glassy system where some particular oxides, such as ZnO and MgO, which present chemical and thermodynamic affinity for titanium have been added. Such additions tend to produce phase separation in the glass and leads to titanate phases formation in the glass-ceramic. Moreover, the presence of lithia has a promoting effect on both mechanisms because the lowered viscosity increases cation diffusion. Various thermal, microscopic, and diffractometric techniques have been used to investigate the amorphous and the crystalline phase.

Management of agricultural biomass wastes: preliminary study on characterization and valorisation in clay matrix bricks.

In this work the feasibility of using woody agricultural biomass wastes as grapes and cherries seeds, sawdust, as pore forming agent, and sugar cane ash, as silica precursor, in bricks, were reported. Sawdust and grapes and cherries seeds, thanks to their organic substances content, during their combustion, bring an energetic support in the bricks firing phase and act as pore forming agent. Usually the addition of this kind of waste is limited to 10wt.% in order to reach an equilibrium between positive (weight and shrinkage decrease and porosity increase) and negative (increase of water absorption and mechanical resistance decrease) effects. The results show that grapes and cherries seeds, added in a percentage of 5wt.% to a brick formulation, have better influence with respect to the sawdust, maintaining the mechanical properties of the fired brick (950°C), showing modulus of rupture around 21-23MPa with a weight reduction of 3-10% (respect to the standard one). Regarding the sugar cane ash, the addition of 5wt.% improves the mechanical properties (modulus of rupture around 27MPa) and no weight decrease is observed. These results confirmed the role played by this kind of agricultural waste, which thanks to its high silica content (61wt.%) is capable to demonstrate a filler and plasticity reducing effect on the brick bodies. Tests carried out highlighted that the addition of these by-products (5wt.%) do not change negatively the main technological properties measured (water absorption, linear shrinkage, flexural resistance, etc.) and permit to hypothesize their use to obtain bricks with both insulating and higher mechanical properties using a pore agent forming or silica carrier alternative raw materials, respectively.

Utilisation of municipal incinerator grate slag for manufacturing porcelainized stoneware tiles manufacturing

Porcelainized stoneware tiles containing up to 20 wt.% of municipal incinerator grate slag have been fabricated by cold uniaxial pressing and conventional fast firing cycles. The sinterability of these samples was investigated from density and shrinkage measurements together with mechanical (Vickers microhardness and Youngs modulus) and esthetical (spot resistance and colour parameters analysis) properties. The comparison with the porcelainized stoneware tiles containing no waste suggest a good compatibility between the ceramic body and the waste that does not significantly change the properties of the final products and the conditions of the firing cycle. Nevertheless, the porosity increase, proportional to the waste content, causes a decrease in density, shrinkage, spot resistance and whiteness.

Cathode ray tube glass recycling: an example of clean technology.

In this study the use of ‘cleaned’ end of life (EOL) cathode ray tube (CRT) glass as a raw material in ceramic glazes is described. At present, the recycling and industrial utilization of CRT, a glass material from TV and computer sets, is a subject of intense research with particular regard to the so-called open-loop recycling, namely cycles different from that of the origin. However, the use of CRT glass as a secondary raw material is strictly related to the demand of high-quality raw material. The good preliminary results reached by introducing clean TV and PC monitor panel and cone glass into ceramic glaze formulations pushed research toward the setting-up of a base glaze that is exploitable for the production of pigmented, silk-screened and flame-hardened glazes (products used industrially for coating floor tiles). The aesthetic and chemical characterization of the tiles glazed by this product showed an extremely similar behaviour to originals that did not contain CRT glass. The good technical results achieved have been supported by the life cycle assessment analysis, which has demonstrated a reduction of the environmental impact of the CRT glass-containing ceramic glaze with respect to the standard one.

Solubility, reactivity and nucleation effect of Cr2O3 in the CaO-MgO-Al2O3-SiO2 glassy system

The effect of Cr2O3 on some anorthite-diopside glass-ceramics has been investigated up to amounts of 5 mol%. The solubility in the glassy compositions analysed is total for the oxide, but for amounts higher than 0.5 mol%, an insoluble spinel form, MgCr2O4, precipitates. Ultraviolet-visible spectroscopy has proved to be the most sensitive technique to the presence of Cr(III) in a crystalline spinel site, followed by X-ray diffraction and scanning electron microscopy observations. Electron spin resonance and X-ray photoelectron spectroscopy techniques excluded any oxidation state, other than Cr3+. The influence of the transition cation on glass nucleation is that of an increasing bulk effect with chromium, and thus chromium-spinel, content. The magnesium content affects spinel formation, while heat treatments up to 1100 °C do not. The spinel formation influences the anorthite-diopside ratio in the glass-ceramic, with a large favour towards the pyroxene.