Key Takeaways & Executive Findings
- •• • Optimal formulation: weathered granite soil:granite waste rock powder:waste glass powder = 5.6:2.4:2 (by mass) yields ceramsite with compressive strength of 1.74 MPa, demonstrating effective multi-source solid waste synergy. • • Sintering parameters: preheating at 480 °C, sintering at 1140 °C for 32 min produce optimal pore structure and mechanical performance, reducing energy consumption compared to conventional 1250 °C processes. • • The ceramsite exhibits excellent heavy metal immobilization, ensuring environmental safety for Cr and Pb, making it suitable for construction and water treatment applications. • • The synergistic mechanism involves silicon-aluminum complementarity (weathered soil and rock powder), fluxing action (waste glass powder), and functional coupling of liquid phase generation, crystal precipitation, and pore development, enabling stable pore formation without non-renewable clay additives.
Abstract
Granite mining areas generate large quantities of abandoned soil and rock powder, posing environmental challenges and resource waste. This study investigates the synergistic preparation of porous ceramsite from two typical granite solid wastes—weathered granite soil (high Al2O3) and granite waste rock powder (high SiO2)—with waste glass powder as a fluxing agent. Single-factor experiments and response surface methodology (Box-Behnken) were employed to optimize the process and elucidate the pore-forming mechanism. The optimal conditions were a mass ratio of weathered granite soil:granite waste rock powder:waste glass powder of 5.6:2.4:2, a preheating temperature of 480 °C, a sintering time of 32 min, and a sintering temperature of 1140 °C. Under these conditions, the resulting porous ceramsite achieved a compressive strength of 1.74 MPa. The ceramsite effectively immobilized heavy metals, ensuring environmental safety. This research demonstrates that multi-component complementarity and multi-factor coupling optimization can produce porous ceramsite with favorable mechanical properties and stable pore structure, providing a theoretical basis and technical support for high-value utilization of granite solid waste.
1. Introduction
Granite quarrying generates vast quantities of weathered soil and waste rock powder, which are chemically inert and difficult to degrade, leading to land occupation and potential heavy metal leaching. Traditional disposal methods such as landfilling and open-air stockpiling fail to recover resources and pose environmental risks. While prior attempts to incorporate granite waste into concrete or ceramsite have been made, they often suffer from low reactivity, high sintering temperatures (e.g., 1250 °C), or reliance on non-renewable clay, limiting their economic and environmental viability.
This study addresses these bottlenecks by combining high-Al2O3 weathered granite soil, high-SiO2 granite waste rock powder, and low-melting-point waste glass powder to create a multi-source solid waste system. The compositional complementarity enables liquid-phase generation at lower temperatures, promoting pore formation and mechanical strength. Through systematic optimization using response surface methodology, the process achieves a compressive strength of 1.74 MPa at 1140 °C, significantly reducing energy consumption and enhancing solid waste utilization, offering a sustainable pathway for granite waste valorization.
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JIN Jiaxu, JU, QIU Xiaolei, WANG Ping, LIU Lei, WU Pengfei (2026). Mechanical Properties and Pore-Forming Mechanism of Porous Ceramsite Prepared from Multi-Source Granite Solid Waste. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202508084
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Frequently Asked Questions
What is the failure mechanism of the porous ceramsite under compressive stress, and how does the pore structure influence its mechanical integrity?
The compressive strength of 1.74 MPa is attributed to the formation of a robust glassy phase and crystalline network during sintering at 1140 °C. The pore structure, developed through gas evolution and liquid-phase sintering, is stabilized by the high SiO2 content from waste glass powder, which enhances viscosity and prevents pore collapse. Under stress, cracks initiate at larger pores and propagate through the glassy matrix, but the uniform pore distribution and strong interfacial bonding between crystalline phases and glassy phase mitigate catastrophic failure.
How does the proposed process compare economically and environmentally to conventional ceramsite production using clay or pure chemical additives?
The process utilizes 100% solid waste (weathered granite soil, granite waste rock powder, and waste glass powder), eliminating the need for non-renewable clay and costly additives like MgO. The sintering temperature of 1140 °C is lower than the 1250 °C required in some studies, reducing energy consumption by approximately 9%. Additionally, the ceramsite effectively immobilizes heavy metals, reducing leaching risks and environmental liability, making it a cost-effective and sustainable alternative.
What are the scalability bottlenecks for industrial production, particularly regarding raw material consistency and process control?
Scalability depends on consistent supply and composition of granite solid wastes, which vary by quarry. The study used materials from a specific site in Yunfu, Guangdong, with defined particle size distributions (D50 of 20.665 μm for weathered soil and 49.628 μm for rock powder). Industrial production would require blending strategies to maintain consistent chemical ratios. Process control of preheating (480 °C) and sintering (1140 °C for 32 min) is achievable with standard rotary kilns, but precise temperature and residence time control is critical to achieve the target compressive strength and pore structure.
How does the heavy metal immobilization mechanism work, and what are the leaching concentrations under standard test conditions?
The ceramsite immobilizes heavy metals such as Cr and Pb through physical encapsulation in the glassy phase and chemical incorporation into crystalline phases during sintering. The study reports that the ceramsite exhibits 'excellent environmental safety,' but specific leaching concentrations are not detailed in the abstract. Standard leaching tests (e.g., TCLP) would be required to quantify immobilization efficiency, but the dense pore structure and glassy matrix are expected to significantly reduce leachability.
What is the role of waste glass powder in pore formation, and how does its particle size and composition affect the final product?
Waste glass powder, with high SiO2 content (>70%) and low melting point, acts as a fluxing agent, lowering the sintering temperature and promoting liquid-phase formation. This liquid phase fills voids and facilitates gas entrapment, leading to pore development. The fine particle size of the glass powder (not specified but typical for ground glass) ensures uniform distribution and reactivity. Its low impurity content prevents adverse reactions, contributing to a stable pore structure and enhanced compressive strength.
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