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Structure-guided tuning of the SiO2/Al2O3 mass ratio enables low-temperature fiberization of red mud slags
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DOI：10.1016/j.jclepro.2026.149078.png)
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Abstract
En 中文
Producing high-quality inorganic fibers from red mud is an effective route for its high-value utilization; however, the high-alumina, high-alkali nature of red mud gives rise to melts with limited fluidity and a strong crystallization tendency, thereby impairing fiberization performance. To enable the production of high-quality fibers from red-mud-derived slag, this study combines thermodynamic calculations, crystallization-kinetics analysis, and structural characterization by Raman spectroscopy, MAS NMR, and XPS to elucidate how the SiO2/Al2O3 mass ratio governs the minimum suitable fiber-forming conditions and melt structure; these findings are further validated by centrifugal fiberization experiments. The results show that increasing the SiO2/Al2O3 mass ratio from 0.8 to 2.8 markedly improves melt fluidity, lowering the flow temperature by 92 °C. During melting, the coexisting mineral phases evolve from Al-rich refractory phases to Ca-Mg silicate phases, substantially narrowing the temperature interval between the deformation and flow points. During cooling, the primary crystalline phase precipitating from the melt is nepheline (NaAlSiO4). With increasing SiO2/Al2O3 mass ratio, the crystallization driving force (Ran) decreases by 0.177%/K, whereas the crystallization activation energy (Ec) increases by 141.1 kJ/mol, indicating a substantially reduced crystallization propensity. Moreover, the crystallization process is surface-crystallization-dominated (n = 0.9-2.3). The minimum suitable fiber-forming temperature decreases by approximately 200 °C as the SiO2/Al2O3 mass ratio increases, and the controlling factor shifts from crystallization-limited to fluidity-limited behavior at SiO2/Al2O3 = 1.8. Structural analysis at the minimum suitable fiber-forming temperature shows that increasing the SiO2/Al2O3 mass ratio raises the fractions of Q3+Q4 units and bridging oxygen, increases the proportion of [AlO5]7- species, and enhances network polymerization. Meanwhile, the tendency toward local ordering weakens, leading to a gradual improvement in the glass-forming ability of the red-mud-derived melt. Centrifugal fiberization experiments demonstrate that increasing the SiO2/Al2O3 mass ratio reduces the average fiber diameter by approximately 41% and the slag-shot content by 5.7 percentage points. At SiO2/Al2O3 = 1.8, the fiber properties meet the relevant national standards, supporting the synergistic improvement in fiber performance arising from the optimized melt structure and enhanced amorphous-forming ability at this composition. Collectively, these results demonstrate that tuning the SiO2/Al2O3 mass ratio to synergistically regulate network polymerization, Al coordination, and the local Si-O-Al configuration enhances the glass-forming ability of red-mud-derived melts, thereby providing a mechanistic basis for compositional redesign and process optimization toward high-quality inorganic fibers.
Keywords:
Red mud
High-quality inorganic fibers
SiO2/Al2O3 mass ratio
Minimum suitable fiber-forming temperature
Melt structure
Journal
IF:
10
Papers:
4.6W
Citations:
36.8W
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