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The reactive AlN, heavy metal ions, and salts in secondary aluminum dross make them harmful to the environment and difficult to handle, and therefore categorized as hazardous solid waste. A novel, simple, and versatile technique has been proposed here to prepare hierarchically porous ceramics using secondary aluminum dross as the sole raw material, namely, the hydrolysis‐induced simultaneous foaming and coagulation casting method. As the main component, Al and AlN could be hydrolyzed to generate aluminum hydroxide sol, which can form three‐dimensional network and lead to the outstanding compressive strength of green body (7.03 MPa). Gas release during hydrolysis, high‐temperature oxidation of AlN, and metallic Al based on Kirkendall effect could account for the final multilevel pores. The utilization of harmful components in secondary aluminum dross, supplys an alternative colloidal forming way for porous green body with complex shape when combined with other ceramic powders or inorganic solid waste. Low sintering shrinkage of 1.38%–3.60% for hierarchically porous ceramics offers this highly effective and low‐cost method to be easily promoted for industrial production. [ABSTRACT FROM AUTHOR]

Herein, a simple, versatile, and low‐cost approach has been proposed to realize the green utilization of secondary aluminum dross, the hazardous solid waste, namely directly sintering dry‐pressed green bodies from secondary aluminum dross to fabricate porous ceramics according to high‐temperature foaming process spontaneously without adding spare foaming agents. Aluminum nitride (AlN) in secondary aluminum dross was employed to realize high‐temperature foaming due to its oxidation, which makes traditional AlN and salts removal process needless. Moreover, near‐zero shrinkage or even expansion during sintering of porous ceramics have occurred because in‐situ foaming process together with the oxidation of Al particles well offset the sintering shrinkage. After sintering at 1400°C for 2 h, porous ceramics composed of α‐Al2O3 and spinel phases with open porosity of 37.91%, sintering expansion rate of 1.13%, flexural strength of 45.67 MPa, and thermal conductivity of 0.97 W/(m·K) have been prepared. Cenospheres as pore‐forming agents have been added to further improve the porosity, and alumina‐based porous ceramics with open porosity of 28.39%–43.20% and flexural strength of 15.80–52.48 MPa have been obtained. This effective solution for recycling secondary aluminum dross could supply high‐performance porous ceramics, which is expected to be applied in the fields of light‐weight structural components and thermal insulations. [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]

Highlights: [•] The article provides a new method for recycling rare earth (RE) from waste phosphor. [•] When compared with the traditional methods, leach rate was much higher. [•] Y–Eu concentrate and Tb–Ce concentrate were obtained successively. [•] It would reduce the burden of later extraction, separation and purification. [ABSTRACT FROM AUTHOR]

• Highly porous ceramics were fabricated by particle-stabilized foams method. • Slags from smelting of spent automotive catalysts have been utilized. • Sintering temperature and dosage of slag determined the properties of porous ceramics. • The obtained porous ceramics show excellent physical properties. Spent automotive catalysts are the most crucial secondary resources of platinum group metals (PGMs). Currently, the iron-capturing method is one of the most promising technologies for PGMs recycling. The residual smelting slags contain large amounts of CaO, Al 2 O 3 , MgO, SiO 2 , Na 2 O, and the trace of heavy metals (e.g. Cr, Pb, Ni), which are classified as solid waste or even hazardous waste, which are typically treated by landfills, and poses severe threats to the environment. In this paper, based on the specific chemical composition of smelting slags, ceramic foams with high porosity, low density and good thermal insulation were fabricated by particle-stabilized foams method, where long-chain surfactant hexadecyltrimethylammonium chloride served as the hydrophobic modifier of slag particles and colloidal silica as binding agent. Herein, the influence of sintering temperature and the amount of smelting slag on the physical properties of obtained porous ceramics were systematically investigated. The results showed that porous ceramics with a bulk density of 0.40–0.64 g/cm3, open porosity of 74.7–83.4%, thermal conductivity of 0.10–0.21 W/(m∙K) and compressive strength of 1.04–4.01 MPa can be obtained with the mass ratio of slag: colloidal silica of 2:1, 3:1 and 4:1 sintered at 1000°C for 2 h. The porous ceramics with these unique properties are promising to be applied as thermal insulation materials. This convenient, facile and versatile approach is also expected to fabricate porous ceramics by using other solid waste as raw materials. [ABSTRACT FROM AUTHOR]

Municipal solid waste incineration (MSWI) has already been extensively applied to facilitate volume reduction and energy recovery. Known as toxic solid waste for high content dioxins, MSWI fly ash is accumulated accordingly. Dioxins in MSWI fly ash are primarily derived from homogeneous reaction and heterogeneous reaction in the range of 200–800 °C, including cyclization, chlorination, catalytic and de novo synthesis of precursors. Degradation of dioxins is considered necessary for the disposal of MSWI fly ash harmless. Among the alternative degradation technologies, plasma, mechanochemistry, hydrothermal, photocatalytic and biodegradation have demonstrated an excellent detoxification effect and are conducive to the application of MSWI fly ash as a sort of resource. In this paper, a systematic review is conducted of the mechanism and process parameters of these five methods, with the emphasis placed on their potential for the large-scale treatment of MSWI fly ash. The study aims at indicating the current research status for scholars, and at identifying a treatment for MSWI fly ash that can be performed in a safer and more efficient way. Finally, their respective characteristics, challenges and future improvements are discussed as well. Image 1 • Influence of factors on formation of dioxins in MSWI fly ash are commented. • Five degradation technologies and its mechanisms for dioxins are reviewed. • Plasma and hydrothermal technology have potential for treating MSWI fly ash. • Dechlorination is the most common degradation mechanism of dioxins. [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]

• The leaching efficiency of Mn in EMR exceeded 99% under optimal conditions. • The leaching kinetics of Mn accords with the basic hypothesis of the Avrami model. • The leaching of Mn is controlled by a mixture of diffusion and reaction. • The EMR leachate was reused for the leaching step of rhodochrosite ore. • Battery-grade manganese sulfate was prepared from the secondary leaching solution. Electrolytic manganese residue (EMR) is a hazardous solid waste, while it also contains resources of Mn over 7 %. In this study, sulfuric acid with high concentration was used to leach Mn from EMR, and the leaching solution was reused and purified to produce battery-grade manganese sulfate. The optimal leaching conditions for EMR were determined through single-factor experiments and response surface methodology. Under the conditions of H 2 SO 4 concentration at 5.4 mol/L, liquid–solid ratio at 4.8 mL/g, and temperature at 80 °C, the highest Mn leaching efficiency of 99.12 % was achieved. The kinetics of leaching Mn from EMR follows the Avrami model. The leaching characteristics were described according to the basic hypothesis made by the Avrami equation and the fitted Avrami index. The kinetic process is macroscopically regarded as the inverse process of non-equilibrium crystallization. According to the Arrhenius equation, the leaching of Mn is controlled by the mixture of diffusion and reaction with an apparent activation energy of 19.8 kJ/mol. The EMR leaching solution was then reused for the leaching step of rhodochrosite ore to simulate actual production. The secondary leaching solution was purified using neutralization, sulfide precipitation, and fluoride precipitation, and manganese sulfate with high purity was produced from it by evaporative crystallization. This study provides a low-cost and high-efficiency process for leaching and recovering Mn from EMR, which can also reduce the environmental risk. [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 (SAD) and pickling sludge were hazardous wastes. In this work, aluminum nitride (AlN) from SAD was used to reduce heavy metals from pickling sludge by pyrometallurgy. Reaction mechanism was studied after exploring transformation of heavy metals and AlN during reaction process. It was found that reduction reaction between heavy metals and AlN was homogeneous reduction reaction. When mixture was heated to 1000 °C, heavy metals and AlN were distributed independently, and reduction reaction had not occurred. When mixture was heated to 1300 °C, heavy metals and AlN entered aluminosilicate network, and homogeneous reduction reaction occurred. Half of the heavy metals were reduced into metallic state and mixed with the dross. When the mixture was heated at 1400 °C for 1 h, metal block separated from dross. Reduction rates of Fe, Cr and Ni were 94%, 88% and 100%. Like water solution, aluminosilicate melt could dissolve heavy metal oxides, aluminum compound (AlN, Al 4 C 3 , etc.) and silicon compound (Si 3 N 4 , SiC, etc.). This work proposed a novel homogeneous reaction environment, aluminosilicate melt 'solution' environment, which had a significant effect not only on heavy metals reduction, but also on other high temperature oxidation-reduction. [Display omitted] • AlN in SAD was used to reduce heavy metals by pyrometallurgy. • Reduction rates of Fe, Cr and Ni were 94%, 88% and 100%. • Reaction mechanism was studied by exploring AlN and heavy metals transformation. • Reaction between AlN and heavy metals was homogeneous reduction reaction. • Aluminosilicate melt 'solution' was proposed for homogeneous reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe, Cr and Ni were reduced by AlN in SAD. • Reduction rates of Fe, Cr and Ni were up to 97, 91 and 100% • Using a ton SAD for chromium metallurgy could reduce carbon emission of 3961 kg. Secondary aluminum dross (SAD) is a hazardous solid waste due to containing aluminum nitride (AlN). In this work, AlN was used to reduce heavy metals in pickling sludge by pyrometallurgy. Reduction extent of Fe, Cr and Ni was up to 97, 91 and 100%. However, it was found that some AlN was oxidized by oxygen. AlN oxidization could be decreased by shortening melting process. The AlN oxidization would be restricted after aluminosilicate was melted. Reduction extent of heavy metals increased from 51% to 86%, when treatment temperature was increased from 1350 to 1400 °C. Meanwhile, AlN oxidization could be exacerbated by increasing CaF 2 and soda. The CaF 2 and soda could corrode the alumina protective layer on AlN and promote AlN oxidization. Reduction extent of heavy metals decreased from 48% to 19% after adding soda. The AlN oxidization could be restrained by cutting down the air during melting process. After covering the crucible, reduction extent of heavy metals was increased from 48% to 92%, and reduction extent of Fe, Cr and Ni was increased from 58, 18 and 83% to 97, 91 and 100%. After evaluating environment benefit of AlN reducing heavy metals, it was found that utilizing a ton SAD replacing carbon to reduce heavy metals in pickling sludge could reduce carbon emissions of 279 kg. In addition, SAD could be used as reductant to replace Al for chromium metallurgy. Using a ton SAD to replace Al for chromium metallurgy could reduce carbon emission of 3961 kg. [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]