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Red mud is a waste discharged from alumina production by Bayer process. It contains iron and titanium resources. Secondary aluminum dross (SAD) is a waste discharged from aluminum smelting and processing. It contains hazardous reactive aluminum nitride (AlN). In this work, iron and titanium in red mud were reduced by AlN in SAD by pyrometallurgy, and slag was manufactured into glass ceramics. Recovery rates of iron and titanium were 97% and 75%, when addition amount of red mud was double of SAD. The reduced iron and titanium were in form of metal iron and titanium nitride (TiN). Reduction process consisted of two steps: AlN, iron and titanium entered aluminosilicate network of melt; AlN reduced iron and titanium. Density, water absorption and microhardness of the glass ceramics were 3.10 g cm−3, 0.03% and 1195 HV. Utilizing 1 ton of SAD to replace carbon for iron reduction could reduce carbon emissions by 407 kg. In addition, co-disposing 400 kg red mud and 200 kg SAD could gain profit of 293 dollars. This work realized the total recycling of both red mud and SAD. [ABSTRACT FROM AUTHOR]

Electrolytic manganese residue (EMR) is toxic industrial solid waste. Electrolytic manganese enterprises have established a desulfurization and sulfuric acid production process to address its storage risks leaving desulfurized EMR (DEMR). In this study, DEMR was used as a raw material to prepare glass-ceramics. A method of melting and one-stage heat treatment was used to realize controlled crystallization of diopside, with calcium fluoride sludge (FS) as a nucleating agent. The impact of CaF 2 on the glass network structure, as well as on the microstructure and performance of the glass-ceramics, are discussed. CaF 2 can greatly improve the nucleation ability of glass precursors. When the addition of FS is small, the phase transition of glass is dominated by the diffusion of atoms and growth of diopside, forming dendritic crystals. When introducing more FS, the glass-ceramics form smaller island-shaped crystals due to many nucleation sites. The prepared glass-ceramics show excellent mechanical properties and chemical stability. Its hardness exceeds 6.5 GPa, with bending strength over 110 MPa. The acid resistance of glass-ceramics is higher than 99.5%, and the toxic metals in the raw materials are stable solidified. This study perfects the technology of EMR desulfurization pretreatment, which provides an effective graded recycling approach for EMR. [ABSTRACT FROM AUTHOR]

CaO MgO SiO 2 (CMS) glass-ceramics preparation normally needs two-step heat treatment (nucleation and crystal growth). In this work, CMS glass-ceramics are successfully produced by one-step heat treatment by building Ca 2+ and Mg 2+ fast diffusion layer between the residual glass and diopside crystal. High-temperature X-ray diffraction (HTXRD) shows that diopside crystals formed during the crystallization of CMS glass. At the glass layer between diopside crystal and residual glass, an enrichment of Na + is observed by energy dispersive spectroscopy line scanning (EDSLS), which increases the Si O Na bonds that promote Ca 2+ and Mg 2+ ions diffusion. This layer eventually promotes further growth or ripening of the diopside crystals. Thus, nucleation and crystal growth of the CMS glass proceed continuously at the crystallization peak temperature (T nc ), detected by differential scanning calorimetry. Thereby, one-step crystallization of the CMS glass-ceramics becomes possible and practical. [ABSTRACT FROM AUTHOR]

Secondary aluminum dross (SAD) is a solid waste of aluminum dross after it is extracted aluminum. Soda-lime-aluminosilicate (SLAS) glass-ceramics with high alumina contents (over 30 wt%) were successfully manufactured from SAD using pyrometallurgy without additional nucleation agents. The nucleation process of SLAS glass was studied, and 670 °C was selected as the nucleation temperature according to differential scanning calorimetry and X-ray diffraction results. Field-emission transmission electron microscopy was applied to study the microstructure of the specimens thermally treated at 670 °C for 3 and 12 h. Nucleation consisted of two parts: iron oxide nucleation and jadeite nucleation. During iron oxide nucleation, when the thermal treatment time increased from 3 to 12 h, the iron oxides first congregated in an amorphous phase and a small amount of metastable crystal; then, the congregated iron oxides crystallized into hematite and magnetite, which acted as crystal nuclei. During jadeite nucleation, the jadeite spontaneously crystallized from the glass matrix after thermal treatment at 670 °C. When the thermal treatment time increased from 3 to 12 h, the size of the jadeite crystals increased from approximately 6 to 12 nm. Jadeite crystals with a diameter of 12 nm acted as crystal nuclei. For glass-ceramics with a high content of aluminum and sodium, jadeite crystals can act as crystal nuclei without additional nucleation agents. [Display omitted] [ABSTRACT FROM AUTHOR]

In consideration of recycling solid waste to achieve high value-added products, glass-ceramics have been fabricated from municipal solid waste incineration (MSWI) fly ash, pickling sludge (PS), and waste glass (WG) by melting at 1450 °C firstly to achieve parent glass and then crystallizing at 850 °C. Results demonstrated that heavy metals have been well solidified in the prepared glass-ceramics, and relatively/extremely low leaching concentrations of heavy metals have been detected. The synthetic toxicity index of heavy metals has been greatly reduced from 7-18 to <3.2 after crystallization treatment, and the leaching concentrations of Cr, Ni, Zn, Cu, and Pb are 0.15, 0.05, 0.26, 0.12, 0.19 mg L-1 respectively. Chemical morphology analysis, principal component analysis, TEM and EPMA were utilized to clarify the migration, transformation, and solidification mechanism of heavy metals from the as-received solid wastes. The major heavy metals, Cr and Ni which is responsible for the most toxicity, mainly exist in form of the oxidation state and residual state in parent glass, while the residual state in the glass-ceramics. The solidification performance was mostly positively correlated with the form of residue state, which the stability of heavy metals in glass-ceramics is improved. The solidification mechanism of heavy metals in glass-ceramics could be explained by the combination of chemical solidification/stabilization and physical coating. The TEM and EPMA confirmed that Cr and Ni mainly exist in the spinel crystalline (NiCr 2 O 4 , Fe 0.99 Ni 0.01 Fe 1.97 Cr 0.03 O 4) by solid solution or chemical substitution, and a small amount of Cr in the diopside phase. Pb, Cu, and Zn are homogenously dispersed in the glass-ceramics, which is considered as physical coating solidification. [Display omitted] [ABSTRACT FROM AUTHOR]

As a hazardous waste, municipal solid waste incineration (MSWI) fly ash poses a serious threat to the environment, and considerable efforts have been made to achieve its harmless treatment. Herein, a novel approach for handling MSWI fly ash has been proposed to prepare porous glass–ceramics by alkali activation–crystallization, which overcomes the difficulty of controlling air bubbles under high temperatures. MSWI bottom ash rich in Al 2 O 3 and SiO 2 are co-treating as raw material to develop glass framework structure. The alkali activation mechanism shows that the development of MSWI ashes based basic glass from monomer to silica–aluminate gel under alkaline condition. The influence of H 2 O 2 addition on the morphology and physical properties of porous glass–ceramics were evaluated. Porous glass–ceramics with uniform hierarchical pore structure have been fabricated at 3 mol/L NaOH, a solid loading of 55 wt%, and 1–4 wt.% H 2 O 2 , then crystallization treatment at 1150 °C for 2 h, the porosity and the bulk density of which varies from 77.22 to 82.94% and 0.68–0.91 g/cm3 respectively, while their relatively high compressive strength ranges from 1.62 MPa to 3.85 MPa. Attributed to the hierarchical porous structure, uniform distribution of pores and excellent physical properties, porous glass–ceramics has potential applications in construction, filtration, and adsorption materials, providing a convenient and feasible method for the efficient and comprehensive utilization of MSWI ashes. [Display omitted] • A novel method for developing hierarchically porous glass ceramics is proposed. • The alkali-activation mechanism of basic glass prepared by MSWI ashes has been studied. • Hydration products can promote the formation of sub-micron pore. • The porous glass-ceramics has excellent properties and environmentally acceptable. [ABSTRACT FROM AUTHOR]

Secondary aluminum dross is a solid waste discharged during aluminum processing and melting. Calcium aluminate glass-ceramics was manufactured from secondary aluminum dross without adding nucleating agent. Phase transition of glass-ceramics was studied. Nucleation temperature was set at 846 ℃ according to differential scanning calorimetry and X-ray diffraction results. Field-emission transmission electron microscopy was applied to observe microstructure of the thermally treated parent glass. During nucleation process, omphacite grew from glass network. Omphacite growth consisted of two steps: migration of silicon group and cation; growth of omphacite. After parent glass was thermally treated at 846 ℃ for 3 h, silicon group and cation migrated and formed silicon enrichment field. A little of omphacite crystal formed in silicon enrichment field. When thermal treatment time was increased to 12 h, more independent omphacite crystals grew in silicon enrichment field. The independent omphacite crystals grew larger and contacted with each other to form a large omphacite crystal. The large omphacite crystal became nucleus of glass-ceramics. Omphacite nucleation had two effects on crystallization of glass-ceramics. First, omphacite crystal became nucleus, which provided surface for growing crystals. Second, omphacite growth consumed silicon group in glass network, which decreased polymerization degree of glass network and promoted crystallization. In calcium aluminate glass-ceramics with silicon, omphacite crystal could act as the nucleus without additional nucleation agents. [Display omitted] • Calcium aluminate glass ceramics was made from the secondary aluminum dross. • Nucleation was attributed to omphacite growth. • Nucleation consisted of silicon groups migrating and omphacite growing. • Omphacite nucleation consumed silicon groups and promoted crystallization. • Omphacite acted as a novel nucleus in calcium aluminate glass ceramics with silicon. [ABSTRACT FROM AUTHOR]

Secondary aluminum dross (SAD) from aluminum industry is classified as a hazardous solid waste due to containing aluminum nitride (AlN). In this work, AlN was first used to reduce heavy metals by pyrometallurgy. The reduction rates for iron, chromium and nickel were up to 90%, 80% and 100%, respectively. However, the reduction from AlN and oxygen oxidization of AlN occurred simultaneously. AlN which formed solid solution with alumina could reduce heavy metals, while the rest was oxidized by oxygen. In addition, the reduction rates for iron and chromium could be increased with increasing CaF 2 from 6.7 to 9.0 wt%. CaF 2 could decreased viscosity of molten slag, which favored the ion migration, and then increased the reduction rates. After the reduction, glass ceramics were manufactured from the molten slags. The bending strength, microhardness and alkali resistance of the glass ceramics were up to 77 MPa, 1011 HV and 98.7%, respectively. According to XRD and SEM results, glass ceramics with CaAl 2 SiO 6 crystal phase, crosslinked network structure grains and smaller pores exhibited better bending resistance. In addition, glass ceramics with CaAl 2 SiO 6 crystal phase possessed the highest microhardness and alkali resistance. After this process, hazardous pickling sludge and SAD were totally recycled. [Display omitted] • Hazardous pickling sludge and SAD were totally recycled by pyrometallurgy. • AlN in SAD was first used to reduce heavy metals. • Reduction rates for iron, chromium and nickel were 90%, 80% and 100%. • Bending strength and microhardness of the glass ceramics were 77 MPa and 1011 HV. [ABSTRACT FROM AUTHOR]

Municipal solid waste incinerated (MSWI) fly ash and pickling sludge contain heavy metals such as Cr, Pb, Ni, etc., which are harmful to the environment but also suitable to be the nucleating agents in glass-ceramics preparation. In this paper, MSWI fly ash, pickling sludge, and waste glass were melted at 1400 °C for 3 h, and the obtained parent glass was nucleated and crystallized at 800 °C for 0.5 h. Glass-ceramics was successfully prepared by the one-step process. The effects of the content of pickling sludge on crystalline properties of parent glass and the physicochemical properties of glass-ceramics have been systematically discussed. The gap between nucleation temperature (T n) and crystallization temperature (T c) can be narrowed with higher content of pickling sludge, which caused fracture of the glass network (Si-O) and generation of the nonbridging oxygen (NBO), promoting the formation of diopside phase. As a result, nucleation and crystallization can be finished at the same temperature, called one-step process. The sample PS22 with 22 wt% pickling sludge added performed the best crystallization ability for having the narrowest gap (ΔT = 177 °C) between T c and glass transition temperature (T g) and the highest ratio of NBO to total oxygen (T) (NBO/T = 1.72). The Vickers' hardness and bending resistance of the products are 13.11 GPa and 135.84 MPa, respectively. The glass-ceramics are composed of homogeneously distributed diopside, donathite-spinel and glass phase. The toxic heavy metals are effectively stabilized by glass-ceramics. This study provides insights into more efficient and cleaner utilization of MSWI fly ash, pickling sludge and waste glass as glass-ceramic materials. Image 1 • Glass-ceramics were made from MSWI fly ash and pickling sludge and waste glass. • Properties of glass-ceramics by one-step were satisfied with the industrial standard. • Pickling sludge is an efficient nucleating agent in terms of glass crystallization. • Pickling sludge depolymerizes the glass network and decreases the thermal stability. [ABSTRACT FROM AUTHOR]