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Secondary aluminum ash (SAA) is a hazardous solid waste generated in the process of recycling aluminum. The preparation of glass ceramic foams from high content of SAA, used as nucleating and foaming agent, was proposed to achieve green and comprehensive utilization of SAA. With the help of thermodynamic phase diagram and viscosity calculation, a mixture of SAA and waste glass (WG) were transformed, at 1200 °C for 30 min, into glass ceramic foams with porosity of 45.49%–59.45%, respectively. The mean pore size of the samples decreased from 2.89 to 1.53 mm with the decrease of SAA addition. Through the adjustment of temperature, it was found that the mixture had a microporous region at 1100 °C. The expansion region was observed at 1180 °C and 1200 °C, because of the oxidation of AlN in SAA. The porosity of the samples could be raised to 64.51%, with 5–9% B2O3 as a supplement, which contributed to the development of the liquid phase and a decrease in the melt's viscosity. The mechanism of in-situ isothermal foaming, nucleation, and crystallization of SAA and WG was clarified. The crystal intensity dropped and the amorphous phase became the primary phase at 800 °C. Al2O3, sodium silicate and sodium aluminum silicate precipitated at 1000 °C. Al2O3 and spinel with high melting point were wrapped by silicate. Silicate turned into the melt again as the temperature continued to rise. With the further reduction of viscosity, the gas diffused in crystalline and amorphous phases, and finally forms glass ceramic foams with hierarchical pore structure.

Powder sintering and in–situ foaming are the primary treatments for the preparation of glass ceramic foams from solid wastes. However, variables such as crystallization and viscosity, which are difficult to regulate at high temperatures. Herein, a novel technology based on alkali activation–crystallization strengthening was developed for the fabrication of glass ceramic foams with hierarchical pores. Vitrified municipal solid waste incineration (MSWI) ashes as the main calcium and aluminum source and secondary aluminum ash (SAA) as a foaming agent were foamed in NaOH solution at room temperature. The effects of solid–liquid ratio and NaOH concentration on the pore structure, individual foam force, phase evolution and physical properties were investigated, including crystallization kinetics and hierarchical pore formation mechanism. The results indicated that the solid–liquid ratio decreased from 60:40 to 40:60, making the pore wall thin and eventually disappear. The pore size in the range of 0–1 mm reaches 99.5% in 3 mol/L NaOH sample, with the lowest mean size of 0.34 mm. The crystallization kinetics parameters of the basic glass at 5–20 K/min showed that grains were primarily precipitated as three–dimensional at 5 K/min, resulting in micropores. The prepared samples exhibit high porosity (79.23–88.35%), adequate compressive strength (0.36–5.55 MPa) and a bulk density of 0.68–0.76 g/cm3. This work develops the function of SAA as a foaming agent at room temperature, as well as a new idea for the preparation of glass ceramic foams from solid waste containing glass phase or needing vitrification.

Utilization of solid waste can be a preferable waste management solution. In this study, a type of self-foamed glass ceramic material was prepared using lead zinc mine tailings, red mud, and silica sand tailings through in-situ decomposition foaming. The effect of silica sand tailings content on the pore morphology, microstructure, and basic performances of the prepared specimen was analyzed. Meanwhile, the differences in the pore morphology and self-foaming behavior of the foamed glass ceramics were discussed. The obtained results indicated that the addition of silica sand tailings facilitated the formation of the glass phase in samples, and the composition, content, and viscosity of the glass phase could be changed by adjusting the content of silica sand tailings, resulting in a uniform distribution of the formed pores. Owing to their well-distributed pore structure, foamed glass ceramics exhibit excellent comprehensive properties (light weight and high strength), making them a potential non-load-bearing material. In this study, the comprehensive properties of the sample prepared with 40 wt% silica sand tailings were determined to be the best: exhibiting the lowest bulk density (0.63 g/cm3), highest porosity (72.6%), and an applicable mechanical strength (9.7 MPa). This study utilized three solid wastes through a reasonable combination based on their chemical composition, and proposed a novel technique for the preparation of self-foaming glass ceramics via the cooperative treatment of various wastes. [ABSTRACT FROM AUTHOR]

Safety and efficient dispose of municipal solid waste incineration (MSWI) fly ash with high toxicity has emerged as a worldwide challenge. Vitrification provides the advantages of capacity reduction, detoxification, and solidification of heavy metals, which has the potential to dispose of hazardous waste on a large scale. Herein, co–vitrification of MSWI fly ash and bottom slag has been accomplished based on the characteristics of calcium and silicon composition. A novel approach for producing glass ceramic foams by alkaline activation–crystallization was developed to realize the disposal of the obtained glass. The effect of MSWI fly ash/bottom slag ratios on the glass network, crystallization ability of the basic glass, pore structure, and physical properties of the porous green body was investigated. The results revealed that with increasing MSWI fly ash proportion, the Si–O of [SiO4] in the basic glass changed significantly and the crystallization ability steadily reduced. Si–O and Al–O in basic glass are easy to corrode under alkaline conditions, releasing Ca2+ and forming a low solubility product, calcium silicate hydrate. When the crystallization temperature increases from 950 ℃ to 1150 ℃, it is more conducive to the precipitation of the gehlenite phase. Extending the crystallization time promotes three–dimensional growth of crystals that are coupled with each other to form a network structure and a multi–stage pore structure. The pore structure was developed with the help of NH3 and H2 generated by the secondary aluminum ash (SAA). Through the preparation of glass ceramic foams, the raw materials were detoxified. The toxic heavy metals showed extremely low leaching concentrations, which were smaller than the limit of TCLP. The prepared samples had 70.22–80.61% of porosity, 0.78–1.19 g/cm3 of low bulk density, and 0.54–7.86 MPa of compressive strength.

Municipal solid waste incineration products of bottom ash (BA), fly ash (FA), and pickling sludge (PS), causing severe environmental pollution, were transformed into glass ceramic foams with the aid of CaCO3 as a pore-foaming agent during sintering. The effect of the BA/FA mass ratio on the phase composition, pore morphology, pore size distribution, physical properties, and glass structure was investigated, with results showing that with the increase in the BA/FA ratio, the content of the glass phase, Si-O-Si, and Q3Si units decrease gradually. The glass transmission temperature of the mixture was also reduced. When combined, the glass viscosity decreases, causing bubble coalescence and uneven pore distribution. Glass ceramic foams with uniform spherical pores are fabricated. When the content of BA, FA, and PS are 35wt%, 45wt%, and 20wt%, respectively, contributing to high performance glass ceramic foams with a bulk density of 1.76 g/cm3, porosity of 56.01%, and compressive strength exceeding 16.23 MPa. This versatile and low-cost approach provides new insight into synergistically recycling solid wastes. [ABSTRACT FROM AUTHOR]

The search for the possibility of expanding the resource base through the use of local rocks, as well as reducing the cost of final product, is one of the scientific research areas in the field of obtaining foam glass-based building materials. The aim of the research is the development of compositions and recommendations for the production of silicic rock-based glass ceramic foams. These studies will allow to create strong and durable building materials with low density and thermal conductivity, as well as increased biological stability. The results of studying the phase transformations occurring in the charge (tripoli : soda ash) during heating, obtained by thermal analysis methods are presented as well as the production technology, physico-mechanical and thermophysical properties of the developed glass ceramic foams. As a result, construction materials resistant to aggressive media with a density of 200 to 600 kg/m3, thermal conductivity from 0.053 to 0.115 W/m∙°C, compressive strength from 1.2 to 9.8 MPa, have been developed. Due to its properties, developed glass ceramic foams will be used primarily as insulants for the construction of nuclear power plants, in the gas and oil industries, industrial and civil engineering.

Abstract In this contribution, we presented a systematical investigation and prepared partially vitrified ceramic foam materials using polymetallic ore tailings (POTs) and other waste as raw materials. More importantly, six different POTs were evaluated in terms of bloating behavior, besides, the effects of sintering temperature and fly ash (FA) content on the structure, physical-mechanical properties and chemical stability were investigated. Our results revealed that among all selected POTs, the BT2 sample exhibits the best bloating ability due to the formation of appropriate liquid content, which is favorable for forming stable pore structure. Increased sintering temperature can accelerate the liquid phase formation and the increase in pore size, resulting in higher porosity and lower bulk density. And the pore structure varies with the addition of FA relatively uniform pore size distribution, high porosity and high compressive strength can be well achieved in this way. Besides, the partial vitrification of ceramic foam materials contributes to an increase in chemical stability while also reducing the risk of environmental pollutions. Here, an excellent performance combination (low bulk density at 0.63 g/cm3, high porosity at 73.6%, high compressive strength at 9.1 MPa) can be obtained in an optimized condition (15 wt% FA additions, sintering temperature at 1120 °C). The finding in this work, we believe, would provide guidance for rational utilization industrial wastes, which based on the synergistic complementarity effect between chemical components. Highlights • Partially vitrified ceramic material was prepared by rational composition design. • The bloating behavior and foaming mechanism of samples were analyzed. • A new glass ceramic foam with high porosity and high strength was prepared. [ABSTRACT FROM AUTHOR]

In the direction of dealing with solid hazards, preparing glass ceramic foam materials has become a practicable technique due to its environmental-friendly and economical characteristic. Here, we have successfully prepared glass ceramic foams with excellent combination of properties by utilizing lead-zinc mine tailings (LZMT), fly ash (FA) and red mud (RM) as the major component. The influence of sintering temperature on phase evolution, pore morphology, microstructure, physical properties and chemical stability of glass ceramic foam was investigated. The results reveal all above performances exhibit temperature-dependent character, with increasing sintering temperature, the performances enhance first and then deteriorate, the optimal porosity and compressive strength value for the prepared sample can be well achieved at the temperature of 980 °C. Liquid phase was formed during the heat treatment process and resulted in the variation of pore structure. According to SEM image and EDS spectra, the liquid phase may be the Ca-Al-Si-O system glass with less network modifier. The experiment results indicated that glass ceramic foams can be obtained by using solid wastes with different chemical compositions, better yet, it features with economic efficiency to solve the industrial solid wastes problems. [ABSTRACT FROM AUTHOR]

The here described investigation was essentially aimed at exploring the chemical stabilization and reutilization of iron-rich slag from copper metallurgy, by the manufacturing of glass-ceramic foams. The foams were developed according to a new method, recently reported for pure recycled soda-lime glass. Mixtures of soda-lime glass/slag powders (with slag content ranging from 10 to 30 wt%), suspended in alkaline aqueous solution, underwent progressive low temperature (80 °C) hardening, owing to the formation of hydrated calcium silicate compounds (C S H). Before complete setting, an extensive foaming could be achieved by vigorous mechanical stirring, with the help of a surfactant. After foaming, glass/slag mixtures could be sintered at 800–1000 °C; the mutual interaction caused an extensive crystallization, with precipitation of Ca Fe silicates and iron oxides (hematite and magnetite), promoting the mechanical properties (up to 4.4 MPa, with a porosity of about 80%). Leaching test confirmed the stabilization of pollutants, from the slag, in the final ceramics. Owing to the separation of iron oxides, particularly magnetite, the newly obtained foams exhibited a ferrimagnetic behavior, that could be exploited in electromagnetic shielding applications. [ABSTRACT FROM AUTHOR]

Glass ceramic foams were prepared by direct foaming method, using coal fly ash and waste glass as the main materials, borax and calcium carbonate as fluxing agent and foaming agent, respectively. The effects of coal fly ash additions, foaming time, heating rate and sintering temperature on the bulk density, porosity, mechanical properties and thermal conductivity were systematically investigated. The optimum parameters to prepare the glass ceramic foams were obtained at 800 °C for 45 min with 40 wt.% coal fly ash, 60 wt.% waste glass, 30 wt.% borax and 0.5 wt.% calcium carbonate. The specimens prepared this way have a low bulk density (as low as 0.46 g/cm 3 ), exhibiting considerable compressive strength (exceeding 5 MPa) and low thermal conductivity (about 0.36 (W/m K)). The energy saving effect using glass ceramic foams was evaluated by EnergyPlus software, indicating that the prepared glass ceramic foams show good energy conservation effect for building thermal insulation materials. The preparation of glass ceramic foams using solid wastes may provide a promising way to prepare thermal insulation material, considering the advantages in both economic and environmental aspects. [ABSTRACT FROM AUTHOR]

Safety and efficient dispose of municipal solid waste incineration (MSWI) fly ash with high toxicity has emerged as a worldwide challenge. Vitrification provides the advantages of capacity reduction, detoxification, and solidification of heavy metals, which has the potential to dispose of hazardous waste on a large scale. Herein, co–vitrification of MSWI fly ash and bottom slag has been accomplished based on the characteristics of calcium and silicon composition. A novel approach for producing glass ceramic foams by alkaline activation–crystallization was developed to realize the disposal of the obtained glass. The effect of MSWI fly ash/bottom slag ratios on the glass network, crystallization ability of the basic glass, pore structure, and physical properties of the porous green body was investigated. The results revealed that with increasing MSWI fly ash proportion, the Si–O of [SiO 4 ] in the basic glass changed significantly and the crystallization ability steadily reduced. Si–O and Al–O in basic glass are easy to corrode under alkaline conditions, releasing Ca2+ and forming a low solubility product, calcium silicate hydrate. When the crystallization temperature increases from 950 ℃ to 1150 ℃, it is more conducive to the precipitation of the gehlenite phase. Extending the crystallization time promotes three–dimensional growth of crystals that are coupled with each other to form a network structure and a multi–stage pore structure. The pore structure was developed with the help of NH 3 and H 2 generated by the secondary aluminum ash (SAA). Through the preparation of glass ceramic foams, the raw materials were detoxified. The toxic heavy metals showed extremely low leaching concentrations, which were smaller than the limit of TCLP. The prepared samples had 70.22–80.61% of porosity, 0.78–1.19 g/cm3 of low bulk density, and 0.54–7.86 MPa of compressive strength. [Display omitted] • Co-vitrification of high proportions of MSWI fly ash and bottom slag was studied. • The change of glass characteristics by different MSWI fly ash content was determined. • Secondary aluminum ash (SAA) was employed as a foaming agent at room temperature. • Co–detoxifying hazardous solid wastes was successfully realized. [ABSTRACT FROM AUTHOR]