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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]

[Display omitted] • Heavy metals in MSWI fly ash were reduced into alloy by SAD. • Reduction rates of iron and zinc were 67 and 100% • Transparent glass for building was made from MSWI fly ash. • 115 ∼ 213 dollars were earned after disposing of 500 kg of MSWI fly ash. Municipal solid waste incineration (MSWI) fly ash is a hazardous waste containing heavy metals. Secondary aluminum dross (SAD) is a hazardous waste discharged from aluminum smelting, containing active aluminum nitride (AlN). In this work, heavy metals from MSWI fly ash were reduced into alloy by AlN from SAD, and the slag was manufactured into transparent glass for building. Reduction of iron and zinc was 67 and 100 %, respectively. Reduction mechanism was explored after applying XRD, XRF and thermodynamics analysis. It was found that the reduction reaction was an ion reaction. The AlN and heavy metal oxide transformed into anionic group containing nitrogen and heavy metal cation, after entering slag. The heavy metals were reduced into alloy after electron was transferred from anionic group to cation. In addition, the reduced iron and zinc could merge into alloy, which inhibited evaporation of zinc. Yellow transparent glass was obtained after the reduction process. Yellow was come from titanium oxide, which could not be reduced by AlN. Microhardness, density and water absorption of the transparent glass were 741 HV, 2.86 g·cm−3 and 0.04 %, respectively. Leaching content of Ni, Cu, Zn and Pb of the glass were 0.1, <0.1, 0.6 and < 0.1 mg/L, respectively, all below the TCLP limit. About 115 ∼ 213 dollars were earned after manufacturing 500 kg of MSWI fly ash into transparent glass. This work provided a novel idea of recycling solid waste into alloy and transparent glass for building. [ABSTRACT FROM AUTHOR]

Secondary aluminum dross (SAD) and red mud (RM) are solid waste discharged from aluminum industry. SAD contains 10–25 wt% aluminum nitride (AlN) and RM contains 20–50 wt% iron oxide. In this work, porous metal-ceramic composite was in-situ made from SAD and RM. Iron oxide was reduced into Fe 2 Si by AlN, and the generated nitrogen created pores. It was studied that effect of raw material and thermal treatment on pore structure and properties of the composite. Porosity, bulk density and compressive strength of composite were 65.78%, 1.03 g/cm3 and 17.77 MPa, when SAD content was 40 wt% and sintering temperature was 1450 °C. About 95.9% of malachite green in waste water was adsorbed by composite after 24 h. The composite could be recycled by magnetic separation after adsorption, attributed to the magnetic Fe 2 Si. This work proposed a novel idea of making recyclable porous material for adsorption of organics in waste water. [Display omitted] • Porous metal-ceramic composite was in-situ made from SAD and RM. • Porosity and bulk density of composite were 65.78% and 1.03 g/cm3. • 95.9% of malachite green in waste water was adsorbed by composite after 24 h. • The composite could be recycled by magnetic separation after adsorption. [ABSTRACT FROM AUTHOR]

This paper takes the recycled 7075 aluminum alloy as the object to study its smelting, extrusion and heat treatment processes. The composition, microstructure, mechanical properties and corrosion properties of recycled 7075 aluminum alloys were characterized by spectrometer, optical metallographic microscope, universal tensile testing machine, scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results showed that the composition distribution of recycled 7075 aluminum alloy ingots was more uniform and the microstructure was more optimized. The tensile strength, yield strength and elongation of recycled 7075 aluminum alloy plates were higher than American Society of Testing Materials (ASTM) standard. The recycled 7075-T6 aluminum alloy plates had good corrosion resistance to salt spray. This paper aims to provide guidance for the smelting, extrusion and heat treatment processes of scrap aircraft aluminum alloy regeneration process, and to lay the foundation of the recovery and reutilization of scrap aircraft aluminum alloys. • We obtain the recycled 7075 aluminum alloy using scrap aircraft aluminum alloys. • A method is proposed to prepare the recycled 7075 aluminum alloy ingot. • The level-maintained reuse of scrap aircraft aluminum alloys is realized. • The extruded plates are obtained with one-step extrusion. • The mechanical properties of the extruded plates are better than ASTM standard. [ABSTRACT FROM AUTHOR]

[Display omitted] • Over 6.5 million tons of SAD is discharged on the planet annually. • Recycling SAD to make building materials is reviewed. • Recycling SAD to make ceramics possesses a better carbon reduction. • SAD can be made into metal/alumina ceramics with low carbon emission. Secondary aluminum dross (SAD) is consisted of alumina, aluminum nitride (AlN), salts and heavy metal oxides. Over 6.5 million tons of SAD is discharged in the world annually. Currently, recycling SAD to make building materials is a promising way of waste recovery. Building materials made from SAD can be divided into structure materials and insulation materials. Structure materials inherits the high strength, fire resistance and chemical stability of alumina in SAD. The products include cement, bricks, ceramics and glass ceramics. Insulation materials are manufactured by utilizing reactivity of AlN in SAD. AlN can hydrolyze or be oxidized to release gas. Insulation materials include porous bricks, porous ceramics and porous glass ceramics. Environmental and economic benefits analysis was conducted on structure materials and insulation materials made from SAD. Ceramics and porous ceramics were taken as evaluation objects. Manufacturing a ton of ceramics and porous ceramics from SAD attained profits of 370.2 and 388.2 dollars, and reduced carbon emissions of 746.2 and 261.5 kg. Therefore, recycling SAD to make ceramics possessed a better carbon reduction. In order to further reduce carbon emission and utilize AlN in SAD, we proposed a novel idea of manufacturing metal/alumina composite ceramics from SAD and metallurgical solid waste. AlN in SAD reduced the metal oxides into alloy, which can strengthen the alumina ceramics. We should clarify the thermodynamics and kinetics of AlN reducing metal oxides and strengthening mechanisms of metal/alumina composite ceramics. [ABSTRACT FROM AUTHOR]

[Display omitted] • High addition SAD is fully recycled and transformed into glass–ceramic foams. • Glass-ceramic foams exhibited excellent compressive strength and high porosity. • The application of glass–ceramic foams in adsorbent was verified. • The pore-forming mechanism is explained during thermal treatment. Porous ceramics with hierarchical pore and high strength were prepared by secondary aluminum dross and quicklime as main raw materials. The influence of quicklime content and thermal treatment on the porosity, pore morphology, compressive strength and bulk density of porous ceramics has been investigated. Scanning electron microscopy, computed tomography, x-ray diffraction and thermal analysis were used to characterize the microstructure, phase transition and high-temperature reaction of the samples. The formation temperature of the liquid phase in the micro-region starts at around 973 °C, close to the temperature at which the mixture starts to produce the liquid phase as calculated by FactSage7.1 software. The achieved porous ceramics exhibited excellent compressive strength of 12.4–51.0 MPa at a relatively high porosity of 63.7%-79.6%. Furthermore, the potential application of the obtained porous ceramics as adsorbent was verified by the adsorption of malachite green solution. Due to the high connectivity of the pores and the presence of a large number of thin lamellar crystalline phases, the adsorption rate of the sample to malachite green solution can be as high as 98.4%. [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]

• Glass ceramic foams with high strength is developed by multiple solid wastes. • Secondary aluminum ash as self-foaming material is proposed to prepare glass ceramic foams. • The self-foaming mechanism relies on the oxidation reaction of AlN. • The degree of polymerization in glass with different alkalinity is analyzed. Glass ceramic foam with high strength was developed using municipal waste incineration bottom ash, fly ash, pickling sludge and secondary aluminum ash as raw materials without foaming agent. The effect of the secondary aluminum ash content and alkalinity on the pore morphology, porosity, water absorption, compression strength and bulk density of glass ceramic foams has been evaluated. The results showed that the increase of secondary aluminum ash content is beneficial to gas generation, but it will reduce the formation of liquid phase, resulting in the variation of pore morphology. In the process of alkalinity adjustment, the degree of polymerization of glass decreased first and then increased, which is similar to the change of max pore size, providing guidance for quantitative analysis of pore formation. The optimized sample reached porosities up to 63.02%, bulk density of ~1.42 g/cm3, and excellent compressive strength ~41.93 MPa. The analysis of self-foaming mechanism proved that secondary aluminum ash can be used as a self-foaming waste results from the oxidation reaction of AlN. In this work, a clean and sustainable utilization method has been proposed for recycling multiple solid wastes by preparing glass ceramic foams with a potential application for construction insulation materials with load-bearing. Moreover, an innovative exploration of secondary aluminum ash as the self-foaming waste in high temperature environmental was proposed. [ABSTRACT FROM AUTHOR]