Purification mechanism of microcrystalline graphite and dissolution of non-carbon impurity during alkali autoclave-acid leaching

IF 1.2 4区地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY

Physics and Chemistry of Minerals Pub Date : 2024-07-18 DOI:10.1007/s00269-024-01290-9

Zhang Xiyue, Sun Hongjuan, Peng Tongjiang, Zeng Li, Liu Bo

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Abstract

Low impurity content is crucial for graphite applications and microcrystalline graphite is an important candidate material. In this study, natural microcrystalline graphite, with a fixed carbon content of 76.65%, was purified by an alkaline autoclave-acid leaching method. The effects of the mole ratio of NaOH to Si and Al in graphite, the liquid–solid ratio of NaOH solution and graphite, alkali autoclave temperature and reaction time on the purity of microcrystalline graphite were studied. Results showed that the dissolution and phase transformation of non-carbon impurities were closely related to the purification process. During the alkali autoclave stage, complete dissolution of quartz was observed. The Si–O tetrahedra and Al–O octahedra structures in aluminosilicate minerals were damaged and [Al (OH)₄]⁻, [H₂SiO₄]²⁻ and [SiO₂ (OH)₃]⁻ were released. The soluble silicate and aluminate ions underwent recrystallization, producing cancrinite and sodalite that could be dissolved by acid leaching, resulting in purified microcrystalline graphite. The purity of microcrystalline graphite was further improved due to the autoclave treatment allowed NaOH solution to penetrate into the cracks of microcrystalline graphite aggregates under high pressure. In addition, the acid solution could enter the micropores left by alkali etching to dissolve the residual impurities. The fixed carbon content of microcrystalline graphite could be increased to 99.9% through the alkaline autoclave-acid leaching method.

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碱高压釜-酸浸出过程中微晶石墨的净化机理和非碳杂质的溶解

低杂质含量对石墨的应用至关重要，而微晶石墨是一种重要的候选材料。本研究采用碱性高压釜-酸浸法提纯了固定碳含量为 76.65% 的天然微晶石墨。研究了 NaOH 与石墨中 Si 和 Al 的摩尔比、NaOH 溶液与石墨的液固比、碱高压釜温度和反应时间对微晶石墨纯度的影响。结果表明，非碳杂质的溶解和相变与提纯过程密切相关。在碱高压釜阶段，观察到石英完全溶解。铝硅酸盐矿物中的 Si-O 四面体和 Al-O 八面体结构遭到破坏，[Al (OH)4]-、[H2SiO4]2- 和 [SiO2 (OH)3]- 被释放出来。可溶性硅酸根离子和铝酸根离子发生重结晶，生成可通过酸浸法溶解的硅灰石和钠长石，从而得到纯化的微晶石墨。由于高压釜处理可使 NaOH 溶液在高压下渗入微晶石墨聚集体的裂缝中，因此微晶石墨的纯度进一步提高。此外，酸溶液还能进入碱蚀刻留下的微孔，溶解残留的杂质。通过碱性高压釜-酸浸出法，微晶石墨的固定碳含量可提高到 99.9%。

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来源期刊

Physics and Chemistry of Minerals 地学-材料科学：综合

CiteScore

2.90

自引率

14.30%

发文量

审稿时长

3 months

期刊介绍： Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are: -Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.) -General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.) -Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.) -Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.) -Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems -Electron microscopy in support of physical and chemical studies -Computational methods in the study of the structure and properties of minerals -Mineral surfaces (experimental methods, structure and properties)