实验技术与管理

粉煤灰-CO₂低矿化效率是制约粉煤灰高效矿化封存CO₂的核心问题，而揭示粉煤灰-CO₂矿化反应过程的微观机制及重要影响因素，是解决低矿化效率问题的关键。文章针对此问题，利用自主研发装置开展了粉煤灰常规浸泡、浸泡-矿化和微观结构测定表征实验，探究了浸泡时间对碱金属离子浸出扩散特征、离子浸出对粉煤灰微观结构和CO₂矿化效率的影响机制。实验表明：pH值的增长速率随浸泡时间呈现负指数衰减，浸泡24 h后的矿化效率和矿化封存量最高分别为12.855%和12.91 kg/t，与未浸泡的矿化封存量相比提高了25%。CaCO₃的衍射峰强度随浸泡时间增加先增大后减小，浸泡24 h的CaCO₃质量分数最大为1.10%。与原始粉煤灰相比，浸泡处理的矿化粉煤灰会发生团聚胶结现象，且浸泡24 h时的团聚胶结程度最深，表面附着有无定型CaCO₃。矿化粉煤灰中C元素占比随浸泡时间(≤24 h)的增加而增加，而C元素占比越高，表明粉煤灰的矿化程度越高。

[Objective] The global greenhouse effect is escalating, leading to the progressive deterioration of ecosystems and climate worldwide. As the primary greenhouse gas, reducing CO₂ emissions is crucial for effectively mitigating this effect. Fly ash–CO₂ mineralization and sequestration technology represents a promising approach for carbon fixation and emission reduction. However, the low carbonation efficiency of fly ash–CO₂ remains the central constraint hindering effective CO₂ mineralization and sequestration. Thus, elucidating the microscopic mechanisms and key influencing factors of fly ash–CO₂ carbonation is essential toward addressing this limitation. [Methods] To investigate these issues, a custom-designed setup was used to conduct experiments, including conventional immersion, immersion–carbonation, and microstructural characterization tests to examine the effects of immersion time on alkaline metal ion leaching and diffusion, as well as the impact of the microstructures of fly ash and CO₂ on the carbonation efficiency. [Results] Results show that the p H increase rate exhibited a negative exponential decay relative to immersion time. After 24 hours of immersion, the carbonation efficiency and sequestration capacity reached peak values of 12.855% and 12.91 kg/t, respectively, representing a 0.25-fold increase over non-immersed fly ash. Raw, unmineralized fly ash contains amorphous silica(SiO₂), mullite(Al₂ Si O₅), and amorphous silica hydrate(SiO₂·x H_2O). No diffraction peaks were detected for calcium carbonate, calcium hydroxide, or magnesium hydroxide, confirming the absence of calcium carbonate in the original sample. Conversely, the mineralized sample contained phases such as amorphous silica hydrate(SiO₂·x H_2O), quartz(SiO₂), mullite(Al₂ Si O₅), calcium carbonate(CaCO₃), and hydroxides(Ca(OH)₂ and Mg(OH)₂). The absence of the magnesite diffraction peak indicated that magnesium did not participate in the mineralization reaction. Furthermore, the observed low-intensity diffraction peaks were broad, indicating low sample purity and small crystal size, confirming the predominantly amorphous composition of the matrix. The diffraction-peak intensity of calcium carbonate initially increased and then decreased with increasing immersion time, with the maximum mass fraction(1.10%) observed at the 24-hour mark. Raw fly ash particles were spherical and dispersed. By comparison, the carbonated samples exhibited agglomeration and cementation, peaking at the 24-hour mark, with amorphous calcium carbonate deposited on the particle surface. Additionally, the carbon content of the carbonated fly ash increased with immersion time(within 24 hours), indicating a higher carbonation degree. The frequencies of larger and smaller particles increased and decreased, respectively, with the immersion time(≤ 24 h), suggesting positive and negative correlations between larger and smaller particles and the carbonation degree, respectively. [Conclusions] This study investigated the leaching and diffusion characteristics of fly ash–derived alkaline metal ions and their impacts on the microphysicochemical properties of fly ash, as well as their relationship with CO₂ mineralization efficiency. Through a series of experiments involving fly ash immersion across different durations, followed by mineralization tests and microstructural characterization of the mineralized fly ash, the influences of soaking time on the leaching and diffusion behavior of alkaline metal ions were evaluated. Additionally, the effects of leaching on the microstructure of fly ash, as well as the efficiency of CO₂ mineralization, were examined. Overall, these findings provide theoretical guidance for optimizing reaction parameters and enhancing mineralization efficiency in fly ash–CO₂ mineralization processes.