Search Results (25)

With the rapid development of the global aluminum industry, the production of aluminum dross, as a hazardous solid waste generated in the aluminum production process, has increased annually. Aluminum dross contains not only substantial amounts of harmful substances, such as aluminum nitride, fluoride, and chloride, but also valuable resources such as metallic aluminum and alumina. This review summarizes the sources, composition, and hazards of aluminum dross to the environment and human health, with a focus on the harmless treatment and resource utilization technologies for aluminum dross. Harmless treatment technologies include denitrification, defluorination, and dechlorination, which are primarily classified into hydrometallurgical and pyrometallurgical methods. In terms of resource utilization, primary aluminum dross (PAD) was mainly used to extract metallic aluminum through heat treatment and cold treatment, while secondary aluminum dross (SAD) can be used to prepare refractory materials, building materials, water treatment agents, and extract alumina. This review also compares the advantages and disadvantages of current aluminum dross treatment technology and outlines future research directions, aiming to provide a reference for the sustainable development and environmental protection of the aluminum industry. Full article

Secondary aluminum dross (SAD) from the aluminum industry is a hazardous residue that restricts sustainable aluminum production. Residual aluminum nitride (AlN) and insoluble fluorides after conventional pretreatment are major barriers to the safe utilization of SAD. In this study, a low-temperature intensified roasting–alkaline leaching process was developed to remove harmful elements by using reaction heat and waste heat to expose enveloped AlN and fluoride phases, form soluble sodium-bearing compounds, and intensify AlN oxidation. Without additives, roasting at 750 °C for 3 h converted 91.65% of AlN, leaving 1.37% AlN in the roasted SAD. With Na₂O₂ as an oxygen donor in situ, NaF as a mineralizer to reduce roasting temperature, and sodium-bearing species as reactants for soluble NaAlO₂/Na₂SiO₃ formation, the AlN conversion increased up to 97.01% under 5% NaF and 2.5% Na₂O₂ at 750 °C for 3 h. Afterwards, higher temperature, longer duration, lower roasted SAD dosage, and higher caustic soda concentration all improved fluorine removal in the subsequent alkaline leaching. Under 100 g/L Na₂O, 20 g/L roasted SAD, and 100 °C, fluorine and chlorine removal efficiencies reached 92.52% and 99.47%, respectively. The final high-alumina residue contained 74% Al₂O₃, mainly in the forms of α-Al₂O₃, NaAl₁₁O₁₇, and MgAl₂O₄, with only 0.19% F and 0.03% Cl, making it suitable for the preparation of various alumina-bearing materials and alumina production. Full article

This study presents a material-level characterization of recycled aluminum briquettes produced by cold pressing Al–Si–Mg machining chips and investigates their behavior during subsequent remelting. The study evaluates density, porosity, chemical composition, and metallurgical yield before and after remelting, with the aim of assessing material-related prerequisites for potential metallurgical reuse applications. The cold-pressed briquette (Sample A) exhibited a bulk density of 2.29 g·cm⁻³ and an estimated porosity of 14.6%, attributed mainly to intergranular voids and residual surface contaminants. After melting and resolidification (Sample B), the density increased to 2.388 g·cm⁻³, while the estimated porosity decreased to 10.9%. Handheld ED-XRF analysis indicated no substantial compositional variation within the instrumental uncertainty range after remelting. SEM–EDS observations revealed Al-rich surface regions containing minor oxygen contributions associated with naturally formed surface oxides, while no pronounced intermetallic features were observed at the analyzed surface locations. The remelting process achieved a metallurgical yield of 94.2% with low dross generation. The results indicate that appropriately preprocessed and compacted aluminum machining chips can form mechanically stable briquettes with favorable remelting characteristics and potential applicability in secondary metallurgical processing. However, the present study does not evaluate deoxidation efficiency under molten steel conditions, which remains a subject for future investigation. Full article

Harmless treatment significantly raises the alumina content of secondary aluminum dross (SAD), laying the foundation for the preparation of MgAl₂O₄ (MA) refractory bricks from SAD by doping MgO. Relevant research on different molding methods, as well as the effects of binder types and dosages on the physical properties (such as compressive strength, thermal conductivity, and thermal shock resistance) of sintered bricks, remains inadequate. In this study, 15 wt% MgO was first added to make the Al₂O₃/MgO mass ratio of SAD close to the theoretical value of 2.53 for MA formation, and the SAD-MgO premix was used as raw material. The influence of molding methods and binders on the properties of sintered bricks was investigated. The results indicate that dry pressing outperforms casting in physical performance. When calcium lignosulfonate (CL) was used as the binder for dry pressing, the average compressive strength reached a maximum of 102.12 MPa, the corresponding thermal conductivity was 2.24 W/(m·K), and the sample withstood 11 thermal shock cycles. Binder dosage experiments showed that the optimal CL addition was 5 wt%, and the recommended upper limit was 10 wt%. This work provides a new perspective for the high-value utilization of SAD in the preparation of spinel refractory bricks. Full article

Secondary aluminum dross (SAD) is classified as hazardous waste (HW48) due to its content of toxic (e.g., heavy metals, fluorides) and highly reactive phases (e.g., aluminum nitride, AlN). This review systematically synthesizes the sources, heterogeneous composition, and environmental risks of SAD, and critically evaluates state-of-the-art hydrometallurgical and pyrometallurgical detoxification and resource-utilization technologies. Comparative, mechanism-oriented analyses are used to elucidate the respective advantages, limitations, and scalability of wet versus thermal routes. Particular emphasis is placed on the migration, transformation, and ultimate fate of key hazardous species (AlN, fluorides, chlorides, and heavy metals) during treatment and product valorization. An integrated hydro–pyro nexus is conceptualized as synergistic hybrid processing that transcends the trade-offs between efficiency, energy consumption, and product purity that currently limit standalone technologies. Emerging hybrid process concepts, advanced additives, and circular-economy-oriented product pathways are evaluated to address current technological bottlenecks. Finally, critical knowledge gaps and research priorities are identified to accelerate safe, low-carbon, and high-value utilization of SAD. Full article

The depletion of natural resources remains an acute global problem, highlighting the importance of developing sustainable technologies that enable the simultaneous extraction of metals and recycling of waste. This paper describes a study of a technology for recycling aluminum slag from foundries to produce secondary aluminum alloy and regenerated flux. Research and processing methods include X-ray phase and spectral analysis of slag composition, multi-stage grinding in a jaw crusher and planetary mill, screening for fraction separation, and selective dissolution of the oxide–salt phase in water or hydrochloric acid followed by filtration and evaporation; obtaining regenerated flux based on phase diagrams of chloride systems; and briquetting and remelting of the extracted aluminum. The technology ensures the extraction of up to 85% of the metallic aluminum from slag and the production of regenerated flux based on the NaCl–KCl–MgCl₂ system with a low melting point. Full article

To conserve natural resources and reduce waste generation, the effective valorization of industrial waste and byproducts in engineering applications is becoming increasingly important. Among these materials, aluminum production residues (APRs) offer a promising and sustainable solution for road pavement applications. Unlike previous reviews, this paper uniquely examines recent research on the use of various APRs in bituminous materials across multiple scales, with particular attention to their roles as additives and fillers. The APRs examined included red mud (RM), aluminum dross (AD), and spent pot lining (SPL) residues, as well as secondary aluminum waste (SAW). These materials have been employed as additives in asphalt binders (microscale), as fillers in asphalt mastics (mesoscale), and as additives or fillers in asphalt mixtures (macroscale). Overall, this review indicates that adopting appropriate treatment approaches for APRs as asphalt modifiers can enhance their dispersion, thermal stability, rheological behavior, and leaching performance. In particular, the use of RM has been shown to improve thermal stability, tensile strength, intermediate-temperature cracking resistance, and rutting resistance, largely due to the increased stiffness it imparts to asphalt mastic and mixture phases. However, there is no clear consensus among researchers regarding other properties, as performance outcomes depend strongly on multiple factors, particularly the physicochemical characteristics of the RM, filler–binder ratios, testing methods, and reference filler types. Other APRs—such as AD, SPL, and SAW—have also shown beneficial effects on the performance of asphalt mixtures. There is still limited research on the influence of APRs physicochemical variability on asphalt–filler interactions and the performance of bituminous materials. For the safe and large-scale adoption of APRs, it is essential to establish standardized characterization procedures, testing methods, and application guidelines while considering diverse climatic conditions. Comprehensive assessments of cost and environmental impacts should also be incorporated to support informed decision-making by engineers and industrial stakeholders. Full article

This paper endeavors to explore the impact of secondary aluminum dross (SAD) on the characteristics of sulfoaluminate cement mortar. Measurements were taken for the mortar’s slump flow, plastic viscosity, initial setting time, and drying shrinkage rate (DR). Additionally, the flexural, compressive, and bonding strengths were evaluated. The leached concentrations of chromium (Cr) and zinc (Zn) in the specimens were determined. Furthermore, the carbonation depth (Dc) and chloride ion migration coefficient (CMC) were calculated. Lastly, scanning electron microscope energy spectrum analysis (SEM-EDS) and X-ray diffraction (XRD) spectrum analysis were conducted to analyze the mortar’s performance. The findings revealed that the slump flow and plastic viscosity of fresh mortar exhibited negative and positive quadratic relationships, respectively, with the mass ratio of SAD. Specifically, SAD could reduce the slump flow by 1.57% to 2.72% and augment the plastic viscosity by 5.21% to 36.89%. The placement time contributed to a decrease in the slump flow of fresh mortar by up to 20.4% and an increase in plastic viscosity by up to 11.2%. The initial setting time, mechanical strength, and DR of the mortar demonstrated quadratic variations with the mass ratio of SAD. At a 15% SAD mass ratio, the mortar exhibited the highest initial setting time, mechanical strength, and DR. The inclusion of SAD could elevate the initial setting time, flexural strength, compressive strength, bonding strength, and DR of the mortar by 14.33% to 65.07%, −14.75% to 22.58%, −8.94% to 9.96%, −13.33% to 66.67%, and −13.33% to 26.67%, respectively. Full article

Aluminum is one of the most in-demand nonferrous metals in the world. The secondary aluminum dross (SAD) produced during aluminum smelting is a type of solid waste that urgently requires disposal. SAD, municipal solid waste incineration fly ash, and bottom slag were used as raw materials to prepare porous ceramsite in a laboratory in this study. Multi-factor design experiments were then used to explore the influence of the sintering condition on the compressive strength to provide a basis for ceramsite preparation using SAD. The results showed that, within a certain variation range, the levels of each factor showed overall positive correlations with the ceramsite compressive strength. The contributions of the ceramsite particle size, the silicon–aluminum ratio (Si/Al), the sintering temperature, and the sintering time to the compressive strength of the porous ceramsite then decreased. The factors had a synergistic effect. The interactive effect of multiple factors on the porous ceramsite compressive strength rose with an increase in the particle size and Si/Al ratio. The average compressive strength of the porous ceramsite prepared in this study was 4.06 ± 3.71 MPa, and the maximum compressive strength was 14.13 MPa. The highest ceramsite compressive strength was achieved under a sintering temperature of 1270 °C, a particle size of 2 cm, a sintering time of 30 min, and a silicon–aluminum ratio of 1.5. In addition, there was a reaction relationship between the multiple factors involved in the sintering of the SAD-based porous ceramsite. Pilot or industrial tests should be conducted in the future based on these experiments and the intended ceramsite use. Full article

This study investigates the synthesis of magnesia–hercynite-based refractories using blends of magnesia powder, aluminum dross (AD), mill scale (MS), and graphite, focusing on the effects of carbon concentration and heating temperature. The results demonstrate successful synthesis at 1550 °C and 1650 °C, with high magnesia content (C80 and D80) leading to the formation of distinct phases, including MgO, FeAl₂O₄, MgFeAlO₄, CaMg(SiO₄), and Ca₃Mg(SiO₄)₂, which influence the ceramic’s microstructure and mechanical properties. Increased magnesia content reduces porosity and enhances crushing strength, while heating to 1650 °C significantly improves densification and nearly doubles cold crushing strength, from 43.77–58.97 MPa at 1550 °C to 76.79–95.67 MPa at 1650 °C. These findings suggest that the synthesized refractories exhibit properties comparable to commercial magnesia–hercynite bricks, with potential for the further development for industrial rotary kiln applications. Full article

Secondary aluminum dross is a solid waste generated after removing aluminum from industrial aluminum slag (primary aluminum dross), which is included in the European Hazardous Waste List because of harmful substances such as aluminum nitride. More and more SAD is being directly disposed of in landfills, which will not only harm the ecological environment and human health, but also cause resources. Under the background of green and low-carbon circular economy, nitrogen removal and resource recycling of SAD are very important environmental pollution, resource and the economic benefits of the aluminum industry. In this study, a new method was introduced to explore the interaction between various factors in the denitrification process by using the response surface method, and the optimal denitrification process conditions were predicted and determined by a regression equation that is, the denitrification rate of SAD was 99.98% at the reaction time of 263 min, reaction temperature of 95 ℃ and concentration of 6.5 wt.%. Furthermore, the content of Al₂O₃ in SAD was successfully elevated to 98.43% through the reaction carried out in a 10 wt.% NaOH solution system at the controlled temperature of 90 °C for 5 h. It was summarized that the wet treatment methodology can efficiently eliminate aluminum nitride (AlN) from SAD and heighten the Al₂O₃ grade to meet metallurgical standards. This research is expected to eliminate the adverse impact of SAD on the environment and its safety risks, and provide an innovative method for the sustainable resource utilization of SAD. Full article

The production process of the metallurgical industry generates a significant quantity of hazardous waste. At present, the common disposal method for metallurgical hazardous waste is landfilling, which synchronously leads to the leaching of toxic elements and the loss of valuable metals. This paper presents a comprehensive review of the research progress in the harmless treatment and resource utilization of stainless steel dust/sludge (including stainless steel dust and stainless steel pickling sludge) and aluminum ash (including primary aluminum ash and secondary aluminum dross), which serve as representative hazardous wastes in ferrous metallurgy and nonferrous metallurgy, respectively. Additionally, the general steps involved in the comprehensive utilization of metallurgical hazardous waste are summarized. Finally, this paper provides a prospective analysis on the future development and research trends of comprehensive utilization for metallurgical hazardous waste, aiming to offer a basis for the future harmless, high-value, resource-based treatment of metallurgical hazardous waste and the realization of industrial applications in China. Full article

Secondary aluminum dross containing a large amount of active substance can be used to prepare concrete. The mechanical strengths, the mass loss rate (MR) and the relative dynamic modulus of elasticity (RME) of ultra-high-performance concrete with secondary aluminum dross are researched. The NaCl freeze–thaw cycles (F-Cs) and dry–wet alternation (D-A) effects with NaCl and Na₂SO₄ are considered. The corresponding permeability of chloride ions and the carbonation depth (D_c) are obtained. The scanning electron microscope (SEM) photos are researched to reveal the variation of the mechanical mechanism. Results show that after specimens’ suffering from the action of 20 NaCl D-As, the MR of ultra-high-performance concrete is the highest. Specimens exposed to 200 NaCl F-Cs show the lowest MR and CMC. The RME of UHPC under salt actions increase in the order of 20 NaCl D-As < 20 Na₂SO₄ D-As < 200 NaCl F-Cs. After suffering 200 NaCl F-Cs, 20 Na₂SO₄ D-As and 20 NaCl D-As, the corresponding D_c values are 1.86 mm to 2.31 mm, 1.79 mm to 2.23 mm and 2.11 mm to 2.76 mm. The flexural strength decreases at the rates of 0.99%–25%, 3.92%–27.84% and 1.47%–21.59% respectively. The MR increases and the RME decreases as the cubic function changes with the amount of salt erosion. After the secondary aluminum dross is added, the CMC decreases at the rates of 0% to 11.53%, 0% to 33.17% and 0% to 8.41% during the process of the salt action. The SAD can reduce the D_c with the decreasing rates of 19.48%, 23.55% and 19.73%. The SAD can increase the compactness of ultra-high-performance concrete. Ultra-high-performance concrete suffering from 20 NaCl D-As shows the largest number and the highest width of cracks. However, when the specimens are exposed to 20 Na₂SO₄ D-As, the number of cracks is the lowest and the width is the narrowest. Full article

Waste fly ash (WFA) and secondary aluminum dross (SAD) are common solid wastes inducing environmental pollution. These materials contain certain active substances that can be used in cement-based materials. Therefore, cement concrete can be used to solidify these solid wastes. In this study, the influence of the assembly unit of secondary aluminum dross (SAD) and waste fly ash (WFA) on the properties of ultra-high-performance concrete (UHPC) is investigated. The slump flow, the plastic viscosity, the yield shear stress, and the initial setting time of fresh UHPC are measured. Moreover, the flexural and compressive strengths and the dry shrinkage rate (DSR) are determined. The electrical resistance and reactance are tested. The electron microscopy spectroscopy (EDS), thermogravimetric analysis (TG), and X-ray diffraction spectrum (XRD) curves are obtained for revealing the mechanism of macroscopic performances. Results show that due to the optimal specific surface area and the volcanic ash effect, the UHPC with the assembly unit of 50% SAD and 50% WFA provides the highest slump flow, DSR, and mechanical strengths, while the corresponding plastic viscosity, yield shear stress, and electrical resistance are the lowest. The SAD can delay the setting time of UHPC. The relationship between the electrical resistance or the electrical reactance and the mass ratio of SAD accords with the quadratic function. The corresponding electrical resistance is the lowest. The relationship between the mechanical strengths and the electrical resistance fits with the cubic function. The leaching amounts of Z_n and C_r increase in the form of cubic function with the immersing time. Meanwhile, the SAD can decrease the Z_n and C_r by 0%–46.3% and 0%–45.2% respectively. As obtained from the EDS results, the element of Al is increased by adding SAD. The XRD curves show that the crystals of Al₂O₃ are increased and the SiO₂ crystals are decreased by the added SAD. UHPC with 50% SAD exhibits the highest compact microstructures and the least Ca(OH)₂ and 3CaO·S_iO₂ hydration products. The TG results show that UHPC with 50% SAD shows the lowest TG values of all the groups. This research will provide new UHPC materials and techniques applied in solidifying the WFA and SAD in the future. Full article

Although the use of primary aluminum dross as cement replacement has shown promising results in mortars and concretes, there is a knowledge gap between the effect of the secondary dross inactivation process and particle sizes on the mechanical properties and consistency. So, by using X-ray diffraction, laser granulometry, and scanning electron microscopy, this article describes first the inactivation process applied to a secondary aluminum dross. Second, this manuscript presents the fresh and hardened properties of mortar mixes containing 5, 10, and 20% inactivated secondary aluminum dross with three different particle sizes (i.e., fine, intermediate, and coarse). Mortar flow test results indicate that compressive and flexural strengths of mixes containing up to 20% fine and intermediate aluminum dross as cement replacement were satisfactory, respectively. These results have the potential to reduce the environmental and health impacts caused by cement production and secondary aluminum dross disposal, respectively. Moreover, the durability aspects of the mortar mixes, as well as the effectivity of the investigated inactivation process, are identified as future research topics. Full article