Search Results (51)

To evaluate the stability of fiber-reinforced cemented foamed backfill (FCFB) in complex underground mining environments, this study investigates the synergistic effects of fiber content and modified coal gangue (MCG) under acidic and high-temperature conditions. Through a systematic analysis of hydration processes, compressive strength, and deformation characteristics, the research identifies critical mechanisms for optimizing backfill performance. Calcination of MCG at 700 °C enhances gelling activity via amorphous phase formation, while modified aluminum dross (MAD) treated at 950 °C develops dense α-Al₂O₃ and spinel phases, significantly improving chemical stability. In acidic environments, the suppression of calcium silicate hydrate (C-S-H) is offset by the development of Al³⁺-driven C-A-S-H gels. These gels adopt a tobermorite-like structure, substantially increasing acid resistance. Mechanical testing reveals that while 1% fiber reinforcement promotes nucleation and densification, a 2% concentration hinders hydration. Compressive strength at 28 days shows constrained growth due to pore inhibition, and failure modes transition from multi-crack parallel failure (3-day) to single-crack tensile-shear failure. Under acidic conditions, strain concentration in the upper sample highlights a competitive mechanism between Al³⁺ migration and fiber anchorage. Ultimately, the coordinated regulation of MCG/MAD and fiber content provides a robust solution for roof support in challenging thermo-chemical mining environments. 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

Fiber reinforcement offers a promising solution to improve the mechanical performance and durability of cement-based foam backfill (CFB), addressing critical issues such as brittleness and poor crack resistance under high-stress conditions. This study investigates the effects of polypropylene and polyacrylonitrile fibers, at varying contents and lengths, on the mechanical and flow properties of CFB. A series of experiments, including slump tests, rheology analysis, uniaxial compressive strength (UCS) tests, pore structure analysis, and scanning electron microscopy (SEM), were conducted to comprehensively evaluate fiber reinforcement mechanisms. The results show that increasing fiber content and length reduced fluidity due to fiber entanglement, while significantly enhancing mechanical properties through anchoring effects and network formation. After 28 days of curing, UCS increased by 208.2% with 2 wt% polypropylene fibers and 215.3% with 1 wt% polyacrylonitrile fibers (both at 6 mm length). Fiber-reinforced CFB demonstrated improved structural integrity and crack resistance, with failure modes transitioning from brittle to ductile. These findings highlight the potential of fiber-reinforced CFB to deliver durable, crack-resistant, and efficient mine backfill solutions, contributing to enhanced safety and sustainability in underground mining operations. 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

Recycling and reusing industrial waste and by-products are topics of great importance across all industries, but they hold particular significance in the metal industry. Aluminum, the most widely used non-ferrous metal globally, generates considerable waste during production, including dross, salt slag, spent carbon cathode and bauxite residue. Extensive research has been conducted to recycle and re-extract the remaining aluminum from these wastes. Given their varied environmental impacts, recycling these materials to maximize residue utilization is crucial. The components of dross, salt slag, and bauxite residue include aluminum and various oxides. Through recycling, alumina can be extracted using processes such as pyrometallurgy and hydrometallurgy, which involve leaching, iron oxide separation, and the production of alumina salt. Initially, the paper will provide a brief introduction to the generation of aluminum residues—namely, dross, salt slag, and bauxite residue—including their environmental impacts, followed by an exploration of their potential applications in sectors such as environmental management, energy, and construction materials. 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

In the current work, aluminum dross from the aluminum industry and fired-clay brick waste (Homra) were combined with alkaline activators (Na₂SiO₃/NaOH) with varying molarities of NaOH to create insulating geopolymer bricks. An alkaline activator with an (S/L) ratio of 3/1 was combined with Homra to replace it partly. The mixture was then molded into 50 × 50 × 50 mm³ stainless steel molds. Water absorption, compressive strength, bulk density, and apparent porosity of the produced geopolymer were measured at various curing durations and NaOH molarities. The findings showed that adding more aluminum dross waste replacement leads to a decrease in bulk density and compressive strength and an increase in the creation of pores that improve the produced bricks’ ability to insulate against heat. Using 8 M of NaOH after 28 days, the findings revealed that 3% aluminum dross waste replacement has a compressive strength of about 8.6 MPa, water absorption of 14.6%, bulk density of 1.307 g/cm³, and thermal conductivity of 0.32 W/m·K. The Egyptian standard, ASTM C62, satisfies these outcomes. Using DesignBuilder energy simulation software version 6.1.06, the constructed insulating brick under ideal circumstances was utilized to calculate its contribution performance in energy consumption. The annual energy consumption was reduced by about 21% compared to traditional hollow cement bricks. Full article

This study investigates the potential of utilizing industrial by-products—mill scale (MS) and aluminum dross (AD)—as sources of Fe₂O₃ and Al₂O₃, respectively, for hercynite (FeAl₂O₄) production. Through combustion of MS-AD-graphite systems at 1550 °C under air atmosphere, hercynite-based refractory materials were synthesized. Results confirm the viability of this upcycling approach for hercynite synthesis. During the formation of hercynite, the development of a dendritic structure can be observed, which subsequently fuses into a grain shape. XRD phase analysis using the Rietveld method revealed that the major components of the product with a C/O ratio of 1 were 85.11% FeAl₂O₄, 10.99% Al₂O₃, and 3.9% C. For the product with a C/O ratio of 2, the composition was 82.4% FeAl₂O₄, 13.0% Al₂O₃, and 4.6% C. The combustion of raw pellets with a C/O ratio of 1 at 1550 °C for 1 h in a normal air atmosphere is economically viable for producing hercynite, yielding 85.11 wt%. This approach presents a sustainable and eco-friendly alternative to using commercial raw materials, potentially eliminating the need for virgin alumina and iron ore. By repurposing waste materials from the steel and aluminum industries, this study contributes to the circular economy and aligns with the goal of zero waste. 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

This study created ceramic preforms with a 3D network structure (TAD_3D) by using treated aluminum dross (TAD) and kaolin slurry, with 30 ppi polyurethane foam as a template via the sacrificial template method. TAD_3D/5A05Al composites were then produced via pressureless infiltration of 5A05Al aluminum alloy into TAD_3D. The corrosion behavior and resistance of TAD_3D/5A05Al in salt spray were assessed via neutral salt spray corrosion (NSS), scanning electron microscopy (SEM), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests. The results showed that after 24 to 360 h of NSS corrosion, the corrosion of the 5A05 matrix was primarily pitting, with pits expanding and deepening over time, and showing a tendency to interconnect. The main corrosion products were MgAl₂O₄, Al(OH)₃, and Al₂O₃. As corrosion progressed, these products increased and filled cracks, pits, and grooves at the composite interface on the material’s surface. Corrosion products transferred to the grooves at the composite interface and grew on the ceramic surface. Corrosion products on the ceramic framework and the Al matrix can form a continuous passivation film covering the composite surface. PDP and EIS results indicated that the composite’s corrosion resistance decreased by 240 h but increased after that time. After 240 h, the surface passivation film can weaken corrosion effects and enhance the composite’s resistance, although it remained weaker than that of the uncorroded samples. Additionally, grooves at the composite interface deepened over time, with loosely structured corrosion products inside, potentially leading to severe localized corrosion. Full article

Utilizing titanium diboride (TiB₂) inoculation for grain-refining purposes is a widely established practice in aluminum casthouses and foundries. Since this inoculation is usually implemented jointly with or between routine melt treatment steps ahead of casting, it is important to know whether and how other melt treatment processes affect the fade of TiB₂ particles. For the present study, we investigated the influence of degassing process on the separation behavior of TiB₂ particles in aluminum melt. Multiple sampling methods were employed and the samples were analyzed via spectrometer analysis. The removal efficiency of TiB₂ during the gas-purging process of 5083 aluminum melt was confirmed to be significant over 10 min of treatment time. The rate at which the TiB₂ content decays was found to increase with the impeller rotary speed from 400 rounds per minute (rpm) to 700 rpm. The separation rate of TiB₂ particles was obtained to be 0.05–0.08 min⁻¹ by fitting the experimental data. Particle mapping results suggest that the TiB₂ particles were separated to a dross layer. The obtained experimental results were used to quantitatively evaluate the conventional deterministic flotation model. The deviation between the conventional model and the experimental data was explained through the entrainment–entrapment (EE) model. Suggestions were made for future analytical and experimental works which may validate the EE model. Full article

This study utilizes desalted and denitrated treated aluminum dross (TAD) as a raw material, along with kaolin and 10 ppi (pores per inch) polyurethane foam as a template. The slurry is converted into an aluminum dross green body with a three-dimensional network structure using the impregnation method. A three-dimensional network aluminum dross ceramic framework (TAD_3D) is created at a sintering temperature of 1350 °C. The liquid 5A05 aluminum alloy at a temperature of 950 °C infiltrates into the voids of TAD_3D through pressureless infiltration, resulting in TAD_3D/5A05Al composite material with an interpenetrating phase composite (IPC) structure. The corrosion behavior of TAD_3D/5A05 composite material in sodium chloride solution was examined using the salt spray test (NSS) method. The study shows that the pores of the TAD3D framework, produced by sintering aluminum dross as raw material, are approximately 10 ppi. The bonding between TAD3D and 5A05Al interfaces is dense, with strong interfacial adhesion. The NSS corrosion time ranged from 24 h to 360 h, during which the composite material underwent pitting corrosion, crevice corrosion and self-healing processes. Results from Potentiodynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) indicate that, as corrosion progresses, the E_corr of TAD_3D/5A05Al decreases from −0.718 V to −0.786 V, and I_corr decreases from 0.398 μA·cm⁻² to 0.141 μA·cm⁻². A dense oxide film forms on the surface of the composite material, increasing the anodic Tafel slope and decreasing the cathodic Tafel slope, thus slowing down the rates of cathodic and anodic reactions. Factors such as lower interface corrosion resistance or a relatively weak passivation film at the interface do not significantly diminish the corrosion resistance of TAD_3D and 5A05Al. The corrosion resistance of the composite material initially decreases and then increases. 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