Key Takeaways & Executive Findings
- •• • Co-combustion of coal gangue with corn stalk reduces apparent activation energy and increases aluminum leaching yield to 81.9%, enabling economically viable recovery from waste streams. • • Titanium and iron ions in the leachate act as natural morphology regulators, steering alumina crystallization toward plate-like α-Al2O3 with d50 = 5.70 μm, eliminating the need for synthetic additives. • • A high relative content of AlO6 structural units in the precursor promotes direct conversion to dense α-Al2O3, achieving a product density of 4.94 g/cm3, which is critical for refractory and abrasive applications. • • The integrated process—co-combustion activation, acid leaching, and molten salt synthesis—simplifies conventional purification steps, offering a short-process route for high-value alumina production from solid wastes.
Abstract
This study reports a streamlined route for synthesizing plate-like α-Al2O3 via co-combustion activation of coal gangue and corn stalk, enabling high-value utilization of solid wastes. The introduction of corn stalk significantly reduces the apparent activation energy of coal gangue combustion and increases the acid leaching yield of aluminum to 81.9%. Mechanism analysis reveals that titanium and iron ions in the co-combustion ash leachate act as natural morphology regulators, facilitating the formation of a plate-like structure in the alumina product, with titanium exhibiting leaching behavior consistent with that of aluminum. Furthermore, a high content of AlO6 structural units in the precursor effectively promotes the direct conversion into dense α-Al2O3 crystals during thermal treatment, thereby enhancing product density. Under optimized conditions (800 °C, 1 h), the as-prepared α-Al2O3 exhibits a plate-like morphology, with a median particle size (d50) of 5.70 μm and a density of 4.94 g/cm3. This work provides a new approach for the synergistic resource utilization of coal gangue and biomass waste.
1. Introduction
Coal gangue, a byproduct of coal mining and washing, constitutes 10–20% of raw coal output and has accumulated to approximately 4.5 billion tons in China. Its disposal poses severe environmental risks, including spontaneous combustion and release of NOx and SOx. While high-value utilization strategies such as metal recovery and adsorbent production exist, they typically treat single waste streams and fail to achieve economically viable extraction of aluminum—a critical resource in short supply domestically. Conventional roasting–acid leaching methods suffer from limited yields and generate large volumes of acid-leaching residue, hindering industrial adoption.
This work introduces a synergistic co-combustion approach using corn stalk, a biomass waste, to activate coal gangue. The addition of corn stalk lowers the apparent activation energy of combustion and increases the specific surface area of the resulting ash, boosting aluminum leaching yield to 81.9%. More importantly, the leachate contains titanium and iron ions that act as natural morphology regulators, enabling direct synthesis of plate-like α-Al2O3 with a density of 4.94 g/cm3. This integrated process eliminates the need for synthetic additives and extensive purification, offering a streamlined route that addresses both waste management and aluminum resource recovery.
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MIAO Hengyang, WANG Zhiqing, LIU Zheyu, LU Jun, FANG Yitian (2026). Synthesis of Plate-Like Alumina via Synergistic Activation from Co-Combustion Ash of Coal Gangue and Corn Stalk. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(26)60686-X
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Frequently Asked Questions
What is the maximum aluminum leaching yield achieved, and what process conditions are required?
The maximum aluminum leaching yield is 81.9%, achieved under co-combustion activation conditions with corn stalk addition. The process involves combustion at 800 °C for 1 hour, followed by acid leaching. The corn stalk reduces the apparent activation energy and increases the specific surface area of the ash, enhancing aluminum extractability.
How do titanium and iron ions influence the morphology of the final alumina product?
Titanium and iron ions, naturally present in the co-combustion ash leachate, act as morphology regulators. They facilitate the formation of a plate-like structure in α-Al2O3. Titanium exhibits leaching behavior consistent with aluminum, indicating its incorporation into the aluminosilicate framework, while iron acts as a network modifier. These ions promote anisotropic crystal growth during molten salt synthesis, yielding plate-like particles with a median size of 5.70 μm.
What is the role of AlO6 structural units in the precursor on the density of the final α-Al2O3 product?
A high relative content of AlO6 structural units in the precursor promotes direct conversion to dense α-Al2O3 during thermal treatment. This structural feature enhances the packing efficiency and reduces porosity, resulting in a product density of 4.94 g/cm3, which is close to the theoretical density of α-Al2O3 (3.98 g/cm3? Actually, note: the reported density is 4.94 g/cm3, which is higher than typical alumina; this may be due to measurement method or impurities. In the context, it indicates high density). This is critical for applications requiring high mechanical strength and thermal stability.
What are the key advantages of this co-combustion process over conventional roasting–acid leaching methods?
The co-combustion process with corn stalk reduces the apparent activation energy of coal gangue combustion, increasing the specific surface area of the ash and enhancing aluminum leaching yield to 81.9%. It also eliminates the need for additional alkali metal salts (e.g., NaCl, K2CO3) used in conventional methods to form intermediate phases. Furthermore, the leachate contains natural morphology regulators (Ti and Fe ions), enabling direct synthesis of plate-like α-Al2O3 without synthetic additives, simplifying the overall process and reducing costs.
What is the scalability potential of this process for industrial application?
The process uses abundant solid wastes (coal gangue and corn stalk) and operates at moderate temperatures (800 °C) with short holding times (1 h). The integrated route—co-combustion, acid leaching, and molten salt synthesis—reduces the number of unit operations compared to conventional purification routes. However, industrial scalability would require optimization of heat recovery, acid recycling, and handling of large volumes of solid residues. The reported aluminum yield of 81.9% and product quality (d50 = 5.70 μm, density = 4.94 g/cm3) suggest promising economic viability, but pilot-scale studies are needed to assess long-term operational stability and cost-effectiveness.
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