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Secondary aluminum (Al) dross (SAD) is a hazardous waste discharged from Al production, processing and recycling. Over 6.7 million tons of SAD was discharged on the planet in 2023. SAD is consisted of 40–60 wt% of alumina (Al2O3), 10–30 wt% of AlN, 5–15 wt% of salts and 3–10 wt% of heavy metal oxides. Currently, recycling of SAD to make Al2O3by hydrometallurgy is a promising method for disposal of SAD. Hydrometallurgy method is mainly divided into acid leaching and alkali leaching. In acid leaching, Al, AlN and Al2O3react with acid to form aluminum sulfate and aluminum chloride. In alkali leaching, Al, AlN and Al2O3react with alkali to form sodium aluminate. High-purity Al2O3is obtained after precipitation, washing, drying and calcination from the leachate. Resource consumption and emission was calculated to evaluate the economic and environmental benefits. About 147.9 and 172.6 dollars was earned after making Al2O3from a ton of SAD by alkali and acid leaching process, respectively. And carbon emissions of a ton of Al2O3was risen about 596.5 and 2216.0 kg CO2, respectively, compared with the Bayer process with bauxite. We proposed a calcination pre-treatment with quicklime on SAD to reduce the carbon emission. The Al and AlN are oxidized into Al2O3after calcination, and the Al2O3reacts with CaO to form CaO·Al2O3. The Al in CaO·Al2O3can be leached out easily with a low concentration of alkali. This review provides a guidance for the recycling of SAD by hydrometallurgy, and proposes a novel idea for the energy and consumption reduction in alumina (Al₂O₃) production.

In the recycling process, aluminum scraps, characterized by a considerable specific surface area, yield a remelt abundant in inclusions. While advanced melt purification systems proficiently extract hydrogen and large inclusions, micron-sized inclusions remain challenging to remove. Despite previous findings suggesting nominal effects of inclusions on the microstructure and properties of aged 7xxx-series plates, the products' airworthiness demands further improvement. This research aims to decipher the influence of micron-sized inclusions on the microstructure and properties of recycled 7xxx aluminum alloy. We prepared thin sheets of varied cleanliness and utilized SEM, EBSD, and TEM to characterize their microstructure at different heat treatment stages. Additionally, high-temperature tensile and bending properties, together with exfoliation corrosion behaviors, were examined. Our results point to the causative role of inclusions in localized dislocation accumulation post-rolling, which annealing can mitigate but not fully eliminate; however, a solid solution can effectively address this issue. The inclusions significantly disrupt the microstructure and properties of the annealed recycled sheet, but their impact on the solid solution-aged recycled sheet is minor. This study's findings can guide the high-end transformation of recycled aluminum alloy and lay a theoretical foundation for sustainable aluminum recycling.

A facile and cost-effective approach for hierarchically porous ceramics has been proposed firstly, using coal fly ash as the main powder while secondary aluminum dross (SAD) as curing and foaming agents. Benefited from the hydrolysis of AlN and Al in SAD, gas and lamellar aluminum hydroxide sol attached to the surface of unreacted particles were produced, meanwhile pH value and viscosity increased, realizing foaming and coagulation casting simultaneously to fabricate porous green body. The increase of SAD amount could contribute to more intensive formation of flaky aluminum hydroxide sol, enhancing mechanical strength of green body, which has high compressive strength of 1.03 MPa at a bulk density of 0.68 g/cm3. Porous mullite-based ceramics could be sintered at a relatively low temperature of 1200–1250 °C owing to alkali metal oxide and amorphous SiO2in the solid wastes, which also help to form micropores on the pore wall due to partially sintering. Porous mullite-based ceramics possess hierarchical pores, bulk density of 1.00 g/cm3, open porosity of 66.15%, specific surface area of 2.24 m2/g and compressive strength of 9.14 MPa. Their removal rate of malachite green solution reaches 99.1% at a concentration of 100 mg/L and an adsorbent dosage of 100 g/L.

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% B2O3as a supplement, which contributed to the development of the liquid phase and a decrease in the melt's viscosity. The mechanism of in-situisothermal 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. Al2O3and 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.

ABSTRACT Geopolymer possesses good immobilization capacity for Pb. There are two rival interpretations regarding the immobilization mechanism of Pb. This research investigates the behavior of 3 Pb compounds in geopolymer [...]

A large quantity of scrap aircraft aluminum alloys in retired aircraft was used to produce cast aluminum alloys as raw material, resulting in a decrease of the value. In this work, the mixture of scrap aircraft aluminum alloys has been grade-maintaining recycled into 7075 aluminum alloy to maximize its recovery value. After melting, composition adjusting, refining and casting, the composition of recycled AA7075 ingots meet the requirements of GB/T 3190-2008, and the final melt is of great cleanliness. Four kinds of recycled AA7075 profiles were prepared by extrusion and T6/T73 heat treatment. The mechanical properties of all recycled profiles are superior to ASTM B209-14 and B221M-13 requirements. The T6-treated bars have the highest tensile strength (591 MPa), yield strength (534 MPa), elongation (10.0%), and stress-corrosion susceptibility factor (44.8). Nevertheless, the stress corrosion cracking, exfoliation corrosion and inter-granular corrosion resistance of the T6-treated bars still meet the requirements of aviation aluminum alloys. Scrap aircraft aluminum alloys can be regarded as master alloys for containing Zn, Mg, Cu, etc., and they have low melting point, fast melting speed, and uniform microstructure. Thus, high-quality 7075 aluminum alloys can be obtained by recycling the scrap aircraft aluminum alloys. Furthermore, the recycling process can provide some guidance for the industrial application of recycling scrap aircraft aluminum alloys.

As a kind of hazardous solid waste, the resource utilization of secondary aluminum ash (SAA) has become a worldwide challenge. The powdered Al and AlN contained in SAA will release a significant amount of heat during thermal treatment, making SAA have the potential to be used as a secondary energy resource. The thermogravimetric analysis (TG/DTG) coupled to a Fourier transform infrared spectrometer (FTIR) was carried out to evaluate the thermal degradation behavior and thermodynamic of SAA from room temperature to 1300 °C at three different heating rates (5, 10, 20 °C/min). The activation energy was calculated by model-free methods, showing that the activation energy of SAA during pyrolysis ranged from 39.99 to 552.3 kJ/mol for conversion rate (α) = 0.1–0.4. The FTIR results displayed gas products including O–H, C–H, N–H, and N=O groups. The increase in temperature from 1100 °C to 1500 °C will make the phase intensity of chloride and AlN gradually decrease, while the Al2O3is opposite. However, submicron-sized aggregates can still be observed in the sintered samples at 1100 °C and 1200 °C. After calcination at 1500 °C for 3 h, the micro morphology of SAA is basically dominated by large granular Al2O3and spinel, which verifies the possibility of slag as the raw material for ceramics and refractories. This research provides a novel idea of employing SAA as a secondary energy resource as well as the theoretical basis data on thermodynamics.

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.

Source and mask optimization (SMO) is a widely used computational lithography technology that greatly improves the image fidelity of lithography systems. This paper develops an efficient informatics-based SMO (EISMO) method to improve the image fidelity of lithography systems. First, a communication channel model is established to depict the mechanism of information transmission in the SMO framework, where the source is obtained from the gradient-based SMO algorithm. The manufacturing-aware mask distribution is then optimized to achieve the best mutual information, and the theoretical lower bound of lithography patterning error is obtained. Subsequently, an efficient informatics-based method is proposed to refine the mask optimization result in SMO, further reducing the lithography patterning error. It is shown that the proposed EISMO method is computationally efficient and can achieve superior imaging performance over the conventional SMO method.

For nanofibrous aerogels, a three-dimensional porous structure with interwoven nanofibers as a pore wall has become an urgent demand, and it remains to be a challenge to ensure the mechanical stability and thermal insulation. Other than the reported nanofiber as raw materials to generate three-dimensional cellular nanofibrous aerogels, an alternative low-cost and facile procedure has been proposed here via tactfully utilizing polymer sponge as a template attached with reactive particles, followed by a carbothermal reduction process to realize nanowire growth and their replacement of the original framework. The resulting spongy aerogels with numerous interlaced SiC/Si3N4nanowires as a skeleton exhibit an ultrahigh porosity of 99.79%. Meanwhile, compressive elasticity after a compression at strain of 35% for 400 cycles, a low thermal conductivity of 23.19 mW/(m K), an excellent absorption capacity of 33.9–95.3 times for varied organic solvents removal, along with flexibility in shape design favored by the initial organic sponge make this nanofibrous aerogel an ideal material for heat shielding, absorption, or catalyst support.

Spent hydrogenation catalysts are strategic resources due to the high contents of Ni, Mo, and V. These metals were reduced and enriched as NiMoV alloy through pyrometallurgical smelting. However, it is a technical bottleneck for the separation of Ni, Mo and V from the polymetallic alloy. Hence, this paper proposed the atmospheric oxidation leaching of NiMoV alloy and separation of Ni, Mo and V through solvent extraction. The mixed solution of HCl and HNO3was employed as the leaching reagent for the dissolution of the alloy. The leaching efficiencies of Ni, Mo and V were all exceed 99.5% under the optimal conditions: c(HCl) of 3.0 mol/L, c(HNO3) of 2.5 mol/L, S/L of 1:10 (g/mL), temperature of 95 °C for 3.0 h. N235 was used as the extractant for the synergistic extraction of V and Mo, while TBP and sulfonated kerosene was used as modifier and diluent. The extraction efficiencies of V and Mo were 99.2% and 99.9% under three-stage extraction of the following conditions: pH of 1.2, c(N235) of 25 vol%, and O/A of 1:1. It was found that only 0.01% Ni and 9.7% Fe entered the organic phase and can be removed by washing, which showed excellent selectivity for V and Mo. Then, based on the principle of ion exchange, H2SO4and NH3·H2O were used to selectively strip V and Mo. Finally, V2O5, MoO3and Ni(OH)2were obtained after precipitation and calcination.

The aviation grade-maintained recycling of 7XXX aluminum alloy has been achieved. However, there is still a lack of research on the optimization of the microstructure and properties of recycled aviation alloy. This work explores the effect of solid solution treatment on the microstructure and properties of recycled 7050-T7451 plate and its mechanism. The mechanism of "solid solution synergistic regulation of mechanics and corrosion resistance" was elucidated. After the solid solution of recycled aviation aluminum plates, the incomplete dissolution of Al2CuMg caused stress concentration and deteriorated the mechanical properties. In addition, the Cu clusters promoted the anodic dissolution of Al, reducing the corrosion resistance. Therefore, the solution temperature of recycled 7050 sheet was increased from 470 °C to 480 °C for 100 minutes. And the residual Al2CuMg was reduced by 56.6%, which synergistically improved the mechanical and corrosion resistance properties of recycled 7050 plates. The mechanical properties of two sets of recycled 7050-T7451 plates reached 516.3 MPa and 522.0 MPa, with elongation 17.5% and 17.3%, and there was no intergranular corrosion. This work explored the regulation mechanism of microstructure and properties of recycled 7050-T7451 plate, laying the foundation for the application of recycled aviation aluminum alloys.

The effect of Cu, Fe, Co, Ni, Cr and Zn on Mn–Zr–Ti mixed oxides catalysts introduced by co-precipitation was investigated. The Mn–Co catalyst showed the highest NO conversion near 100% and a good N2selectivity > 90% at 200–300 °C. Comparing with the Mn–non catalyst, the Mn–Co catalyst presented a higher reaction rate constant at 120 °C with 23.3 ml s−1g−1. The Mn–Co catalyst possesses a high concentration of Mn4+and surface labile oxygen, which should improve the redox property and increase catalytic activity. Additionally, the Mn–Co showed the highest ratio of Lewis acid sites. The resistance to SO2was improved by incorporation of Co. In summary, the Mn–Zr–Ti mixed oxides catalyst have a better N2selectivity than other Mn-based catalysts and could be improved by doping with Co.

A Mn/Ti–Si catalyst was synthesized and investigated using the NH3selective catalytic reduction (NH3-SCR) of NO in a dry flow and in the presence of H2O or SO2. In particular, the effect of H2O and SO2was studied in several model reactions to obtain a deeper insight into the impact of poisoning compounds on N2O formation. The adsorption behavior of NO and NH3indicated that H2O and SO2decreased the adsorption capacity for NO and increased the adsorption capacity for NH3. The formation of N2O from the disproportionation of NO was negligible. The increase in the adsorption capacity for NH3caused by H2O and SO2did not result in an increase in N2O formation. The formation of N2O from the reaction of NO with NH3was significantly inhibited by H2O and SO2, which could be attributed to the inhibition of the pathway viathe Langmuir–Hinshelwood mechanism. The SCR measurements indicated that the formation of N2O primarily originated from the oxidation of NH3and was suppressed in the presence of H2O or SO2, with a stronger observable effect in the presence of H2O. The formation of N2O is influenced by both the acid–base properties and the redox properties. A mechanism for N2O formation and the suppression effect of H2O and SO2over the Mn/Ti–Si catalyst was proposed, which suggested that the NH3adsorbed on the Brønsted acid sites could inhibit the formation of N2O.

The implementation of extended producer responsibility (EPR) promotes upgrading and standardization of the recycling of waste electrical and electronic equipment (WEEE) in China, reducing the risk of environmental pollution. This paper discusses China's WEEE management via EPR and identifies the four phases and their features of the development of WEEE recycling since the fund subsidy scheme was implemented in 2012. Using GEM Co., Ltd. as an example, this paper explains how the recycling company closed the loop on WEEE recycling, improved the added value of dismantling WEEE through technological innovation, recycled high-quality secondary materials, established a whole waste plastics traceability system, and explored the non-fund subsidies for recycling WEEE. It is suggested that the government take new measures to eliminate outdated enterprises and promote a WEEE disposal industry in the direction of company groups. China might also vigorously advocate for new technologies and equipment to reduce labor costs and enhance the added value of dismantled products. Such efforts would encourage all enterprises to actively participate in EPR, strengthen their ability and willingness to recycle WEEE and reuse recycled materials, and build a closed-loop green supply chain for electrical and electronic products.

There are 45%-71% machining chips generated during the manufacturing process of aviation components. Most of these MCs are down-grade recycled as cast alloy, causing resource waste. In this work, aviation MCs were added into the melt for grade-maintaining recycling. A systematic evaluation was conducted on the melt quality, microstructure evolution, and properties of industrial recycled 7050-T7451 plates with a capacity of 60t/furnace, as well as a comparison with the primary plates. The composition of the recycled 7050 melt is qualified, and the hydrogen content is below 0.075ml/100gAl. The results of PoDFA and LiMCA show that the inclusions in the recycled 7050 melt are mainly below 40μm in diameter, and the number of inclusions is 3 times that of the primary melt. TEM shows that the dispersed phase particles of the recycled plate are more uniform and finer. EBSD shows that the recrystallization ratio of recycled 7050-T7451 plate is 8.3%, much lower than the 23.9% of the primary plate. The mechanical and corrosion properties of the recycled 7050-T7451 all meet the AMS 4050 standard. The cost of grade-maintaining recycling can be saved by 6,130,000 USD per year for a production line with an annual output of 20,000 tons of plates. This work clarified the process, cost, microstructure, and properties of recycled 7050-T7451 plate, laying a foundation for the application of grade-maintaining recycled aviation aluminum alloys.

The refining of aluminum scraps commonly employs nitrogen-fluxes to eliminate impurities. However, the aluminum nitride (AlN)generated by the reaction between nitrogen and the aluminum melt, along with residual fluxes, contribute to low cleanliness of the recycled aluminum melt and pose difficulties for the disposal of secondary aluminum dross (SAD) . Our innovative research has resulted in the recycling of aerospace-grade clean aluminum alloy melts. The results indicate that the argon bubble floating process adsorbs inclusions and hydrogen, achieving an aerospace-grade ultra-clean melt. The solid-liquid interface between the tube wall and the melt provides a diffusion channel for hydrogen atoms, and the bubbles rising up along the wall lead to a higher hydrogen content in the melt. The argon refining dross is primarily composed of Al and Al2O3, which can be recycled as a raw material for aluminum electrolysis. Argon refining can decrease the hydrogen content and the number of inclusions with particle size ≥40μm in the recycled aluminum melt to the level of aerospace aluminum alloy melt. Nonetheless, the particle size ≥20μm remains 1.5-2.5 times that of primary aluminum.

Herein, a novel method for hierarchically porous mullite ceramics with complex and fine structure was proposed, that is vat photopolymerization of multi-phase Pickering emulsion. Pickering emulsions stabilized by mixed particles features water in oil type, high solid content, suitable rheological properties and excellent ultraviolet-curing ability, making them appropriate pastes for vat photopolymerization. The printed components possess hierarchically porous structure involving interconnected mm-scale pores designed by three-dimensional model, uniform μm-scale pores derived from emulsion droplet and less voids generated by the removal of photosensitive resin in the location of continuous phase. Therefore, porous mullite ceramics with octet lattice structure possess excellent compressive strength up to 4.3MPa at high porosity of 74.08% compared to the counterparts from pure resin-based suspension. The products from this facile, universal and effective method could serve as ideal candidates for catalytic filters, biological scaffolds and electronic components owing to their designable structure and outstanding multifunctionality.

Knowledge of the kinetics and mechanism of BaMgAl10O17:Eu2+(BAM) fusion with sodium hydroxide will benefit recycling rare earth elements (REEs) from the waste phosphors. The reaction temperature range of 290–375 °C and the reaction mechanism were determined using X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Activation energy was determined by the four model-free methods, and calculated results showed that the Kissinger method value of 579.5 KJ/mol was close to the average value of the Kissinger-Akahira-Sunose (KAS) and the Flynn-Wall-Ozawa (FWO) methods of 563.5 kJ/mol. The calculated activation energy variation tendency versus conversion factor agreed with the proposed mechanism.

The thickness and porosity of TiO2mesoporous film were optimized for better distribution of quantum dots to enhance the performance of CdS/CdSe quantum dot cosensitized solar cells. The CdS and CdSe quantum dots were prepared on TiO2mesoporous film through a successive ion layer absorption and reaction (SILAR) method and a chemical bath deposition (CBD) method, respectively. It was found that the distribution of quantum dots was inhomogeneous from the surface to the interior of the TiO2film, being mainly concentrated at the upper layer of the TiO2film. As a result, simply increasing film thickness did not make significant contribution to improving solar cell efficiency since only a small portion of quantum dots might access the interior of the film, leading to an exposure of TiO2nanoparticles in electrolyte and thus reducing the electron lifetime due to increased charge recombination rate. Our study revealed that the efficiency could reach its maximum, ∼4.62%, with the TiO2film, the thickness of which was around 11 μm, and porosity was optimized by adding 12 wt % ethyl cellulose into the paste for making the TiO2film.

The CeO2, Ce-Nb-Oxand Nb2O5catalysts were synthesized by citric acid method to investigate the promotion effect of Nb on ceria for selective catalytic reduction (SCR) of NO with NH3. The catalytic activity measurements indicate that the mixed oxide Ce-Nb-Oxpresents a higher SCR activity than the single oxide CeO2or Nb2O5catalyst. In addition, the Ce-Nb-Oxcatalyst shows a high resistance towards H2O and SO2at 280 °C. The Raman, X-ray photoelectron spectra and temperature programmed reduction with H2results indicate that the incorporation of Nb provides abundant oxygen vacancies for capturing more surface adsorbed oxygen, which provides a superior redox capability and accelerates the renewal of active sites. Furthermore, the Fourier transform infrared spectra and temperature programmed desorption of NH3results suggest that niobium pentoxide shows high surface acidity, which is partly retained in the Ce-Nb-Oxcatalyst possessing a high content of Lewis and Brønsted acid sites. Therefore, the incorporation of Nb improves both the redox and acidic capacities of Ce-Nb-Oxcatalyst for the SCR reaction. Here, the redox behavior is primarily taken on Ce and the acidity is well improved by Nb, so the synergistic effect should exist between Ce and Nb. In terms of the reaction mechanism, in situDRIFT experiments suggest that both NH3on Lewis acid sites and NH4+on Brønsted acid sites can react with NO species, and adsorbed NO and NO2species can both be reduced by NH3. In the SCR process, O2as an important role primarily acts as the accelerant to improve the redox and acid cycles. This work proves that the combination of redox and acidic properties of different constituents can be feasible for catalyst design to obtain a superior SCR performance.

Mn0.5Zn0.5Fe2O4nanoparticles are prepared using spent alkaline batteries as raw materials by a multi‐step process including acid leaching, chemical treatment of iron shells, and citrate—nitrate precursor auto‐combustion.