Geopolymer binder is expected to be an optimum alternative to Portland cement due to its excellent engineering properties of high strength, acid corrosion resistance, low permeability, good chemical resistance, and excellent fire resistance. To study the sulfuric acid corrosion resistance of geopolymer concrete (GPC) with different binding materials and concentrations of sodium hydroxide solution (NaOH), metakaolin, high-calcium fly ash, and low-calcium fly ash were chosen as binding materials of GPC for the geopolymerization process. A mixture of sodium silicate solution (Na₂SiO₃) and NaOH solution with different concentrations (8 M and 12 M) was selected as the alkaline activator with a ratio (Na₂SiO₃/NaOH) of 1.5. GPC specimens were immersed in the sulfuric acid solution with the pH value of 1 for 6 days and then naturally dried for 1 day until 98 days. The macroscopic properties of GPC were characterized by visual appearance, compressive strength, mass loss, and neutralization depth. The materials were characterized by SEM, XRD, and FTIR. The results indicated that at the immersion time of 28 d, the compressive strength of two types of fly ash-based GPC increased to some extent due to the presence of gypsum, but this phenomenon was not observed in metakaolin-based GPC. After 98 d of immersion, the residual strength of fly ash based GPC was still higher, which reached more than 25 MPa, while the metakaolin-based GPC failed. Furthermore, due to the rigid 3D networks of aluminosilicate in fly ash-based GPC, the mass of all GPC decreased slightly during the immersion period, and then tended to be stable in the later period. On the contrary, in metakaolin-based GPC, the incomplete geopolymerization led to the compressive strength being too low to meet the application of practical engineering. In addition, the compressive strength of GPC activated by 12 M NaOH was higher than the GPC activated by 8 M NaOH, which is owing to the formation of gel depended on the concentration of alkali OH ion, low NaOH concentration weakened chemical reaction, and reduced compressive strength. Additionally, according to the testing results of neutralization depth, the neutralization depth of high-calcium fly ash-based GPC activated by 12 M NaOH suffered acid attack for 98 d was only 6.9 mm, which is the minimum value. Therefore, the best performance was observed in GPC prepared with high-calcium fly ash and 12 M NaOH solution, which is attributed to gypsum crystals that block the pores of the specimen and improve the microstructure of GPC, inhibiting further corrosion of sulfuric acid.

Alkali fusion of granite sawdust at a high alkali dosage can significantly improve geopolymerization activity, but also result in a high alkali consumption and a poor geopolymer performance. In this work, quartz, the most inert component in granite sawdust, was selected to explore the effect of low-alkali activation on its reactivity and the compressive strength of geopolymer. It was found that the amount of activated quartz is mainly determined by the amount of alkali used for activation. The surface of a quartz particle can be effectively activated by an alkali fusion process at a low alkali dosage of 5%. The metakaolin-based geopolymer synthesized with quartz activated by an alkali dosage of 5% shows a high compressive strength of 41 MPa, which can be attributed to the enhanced interfacial interaction between quartz and the geopolymer gel, suggesting that low-alkali activation is a potential way to improve the geopolymerization ability of granite sawdust.

This study addresses the technical challenges of conventional coal slurry sedimentation equipment in handling fine coal particles, such as poor settling performance and strong dependence on chemical reagents, by designing a novel high-gravity sedimentation and dewatering device. Solid–liquid centrifugal separation was simulated on the CFD-Fluent platform using the Eulerian–Eulerian method, with the solid volume fraction and effective deposition thickness adopted as key indicators of particle settling performance. The settling behavior and flow field characteristics of particles with different sizes (0.045–0.5 mm) were elucidated under varying centrifugal radii (400–800 mm) and rotational speeds (400–1200 r·min⁻¹), thereby providing a solid theoretical foundation for the parameter optimization of centrifugal settling processes for fine particles. The results indicate that increasing the centrifugal radius and rotational speed strengthens the centrifugal field effect, markedly enhancing the dynamic pressure gradient and interphase slip velocity. Under high-speed (ω = 1200 r·min⁻¹) and large-radius (R = 800 mm) conditions, the dynamic pressure of fine particles (0.045 mm) reached 7.52 MPa with a radial velocity of 0.79 m·s⁻¹, effectively compensating for the settling disadvantage of fine particles, promoting solid–liquid separation, and ensuring the stable deposition of coal particles. Meanwhile, as particle size increases, a distinct deposition thickness can be formed under different operating conditions, demonstrating that particle size is the dominant factor governing deposition behavior. The study elucidates the intrinsic mechanism of how multiple parameters—rotational speed, centrifugal radius, and coal particle size—synergistically influence particle deposition characteristics. By regulating these parameters to accommodate different particle sizes, the findings provide valuable insights for the parameter optimization of centrifugal settling processes for fine particles.