The mineralogical characteristics of underground coal gasification (UCG) residuals are closely related to the gasification conditions. The study of the mineral composition and transformation of ash and slag under different gasification conditions has important scientific significance for understanding the real gasification conditions, improving the utilization efficiency of coal, and identifying and controlling the environmental impact. In this paper, the sequential transformation of minerals under different temperature and atmosphere are studied by X-ray diffraction (XRD) and FactSage software, and the elemental composition of the surface of the UCG ash and slag is characterized by SEM-EDX. The results show that the main minerals in the semicoke are quartz (SiO₂), illite (K_1.5Al₄(Si_6.5Al_1.5)O₂₀(OH)₄), and sanidine (KAlSi₃O₈). In the 900–1300°C reduction, ash, quartz, sanidine, hercynite (FeAl₂O₄), anorthite (CaAl₂Si₂O₈), and mullite (Al₆Si₂O₁₃) are the main minerals. The minerals in the oxidation residuals (1100–1500°C) are quartz, anorthite, hematite (Fe₂O₃), hercynite, cordierite (Fe₂Al₄Si₅O₁₈), and cristobalite. The reaction temperature has a significant effect on the changes in mineralogy. The reaction temperature is low during the pyrolysis process, and most changes involve only structural changes. With the reaction temperature increases, a series of reactions occur between different minerals. The reaction atmosphere also has a significant effect on the mineralogy. The research on the transformation of minerals in UCG residues can indirectly reflect the actual process of UCG, which can provide suggestions for the stable operation of the UCG process.

中文翻译：

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煤炭地下气化过程中矿物序贯转化研究：有望间接反映实际反应条件

煤炭地下气化残渣的矿物学特征与气化条件密切相关。研究不同气化条件下灰渣的矿物成分及转化情况，对于了解真实气化条件、提高煤炭利用效率、识别和控制环境影响具有重要的科学意义。本文利用X射线衍射（XRD）和FactSage软件研究了不同温度和气氛下矿物的序贯转变，并利用SEM-EDX表征了UCG灰渣表面的元素组成。结果表明，半焦中的主要矿物为石英（SiO ₂）、伊利石（K _1.5 Al₄ (Si _6.5 Al _1.5 )O ₂₀ (OH) ₄ )和sanidine (KAlSi ₃ O ₈ )。在 900-1300°C 还原过程中，主要矿物有灰分、石英、闪长石、辉长岩（FeAl ₂ O ₄）、钙长石（CaAl ₂ Si ₂ O ₈）和莫来石（Al ₆ Si ₂ O ₁₃）。氧化残渣 (1100–1500°C) 中的矿物有石英、钙长石、赤铁矿 (Fe ₂ O ₃ )、辉长岩、堇青石 (Fe ₂ Al ₄ Si ₅ O ₁₈) 和方石英。反应温度对矿物学的变化有显着影响。热解过程中反应温度较低，大部分变化仅涉及结构变化。随着反应温度的升高，不同矿物之间会发生一系列反应。反应气氛对矿物学也有显着影响。对UCG渣中矿物质转化的研究可以间接反映UCG的实际过程，可以为UCG工艺的稳定运行提供建议。