ISSN 1008-5548

CN 37-1316/TU

2024年30卷  第3期
<返回第3期

优化碱酸法提纯石墨

Optimizing alkaline-acid method for graphite purification


刘云泽1,孟繁荣2,4,崔学民1,王林杰3,何振全5,李仁涛5,盖国胜2,3,4

(1. 广西大学 化学化工学院,广西 南宁 530004;2. 清华大学无锡应用技术研究院,江苏 无锡214100;3. 山东石油化工学院 化学工程学院,山东 东营 257061;4. 山东省粉体材料中试示范基地,山东 东营 257061;5. 淄博清大粉体材料工程有限公司,山东 淄博 255086)


引用格式:

刘云泽,孟繁荣,崔学民,等. 优化碱酸法提纯石墨[J]. 中国粉体技术,2024,30(3):76-87.

LIU Y Z, MENG F R, CUI X M, et al.Optimizing alkaline-acid method for graphite purification[J]. China Powder Science and Technology,2024,30(3):76−87.

DOI:10.13732/j.issn.1008-5548.2024.03.007

收稿日期:2024-02-03,修回日期:2024-04-01,上线日期:2024-04-26。

基金项目:国家重点研发计划项目,编号:2021YFC2902900;广西自然科学基金项目,编号:2022GXNSFDA035062。

第一作者简介:刘云泽(1998—),男,硕士生,研究方向为材料化工。E-mail:liuyz@st.gxu.edu.cn。

通信作者简介:崔学民(1971—),男,研究员,博士,广西自然科学基金创新团队带头人,广西高校卓越学者,广西高校优秀人才,博士生导师,研究方向为材料化工。E-mail:cuixm@gxu. edu. cn。


摘要:【目的】 优化天然石墨提纯效果,降低酸在提纯过程中的过多使用对环境造成的影响,满足各行各业对高品质石墨的需求,实现更环保、高效的石墨提纯效果。【方法】 以鳞片石墨为原料,采取 NaOH-HCl-HF 联合处理的工艺对石墨进行提纯研究,提高石墨的固定碳含量(质量分数,下同),降低石墨中的主要杂质元素如Si、 Fe、 Al、 Cu等的含量。详细考察 NaOH 的用量以及焙烧温度 2 个关键因素对该工艺提纯效果的影响;通过扫描电子显微镜(SEM)观察石墨形貌特征,X射线荧光光谱仪(XRF)和电感耦合等离子体原子发射光谱仪(ICP)测定提纯处理前后石墨的杂质含量,X射线衍射仪(XRD)确定石墨及其灰分的晶体结构。【结果】 当焙烧温度为500 ℃、焙烧时间为2.5 h,HCl的体积与石墨的质量比为2∶1,氢氟酸的体积与石墨的质量比为2∶1时,石墨的平均固定碳含量从原来的95. 3%提高到99.93%;当NaOH与石墨的质量比分别为 0.5∶1和 0.6∶1时,石墨的平均固定碳含量为 99.91% 和 99.93%。考虑到成本效益等因素,确定当 NaOH与石墨的质量比设定为0.5∶1时为理想工艺条件。XRD、SEM、XRF、ICP测试结果表明:经过提纯处理后的石墨层结构并不会出现明显的变化,基本性能不变;提纯处理后的石墨相比于提纯处理前的石墨,杂质含量明显地降低。【结论】 该碱酸工艺不仅能有效地去除石墨中的杂质,盐酸和氢氟酸的组合还可以显著地提升提纯效果,可有望应用在石墨提纯处理和新能源材料领域。

关键词:石墨;碱酸法;加碱焙烧;固定碳;纯化

Abstract

Objective To enhance the purification effect of natural graphite and reduce the environmental impact of excessive acid use,while meeting the continuous demand for high-quality graphite, a more environmentally friendly and efficient graphite purification process is required.

Methods The NaOH-HCl-HF combined treatment process was used to purify flake graphite, increasing its fixed carbon content and reducing impurities such as Si, Fe, Al, and Cu. The experiment investigated the influence of sodium hydroxide dosage and roasting temperature on the purification effect of the process. The study utilised scanning electron microscopy (SEM) to observe the morphological characteristics of graphite. X-ray fluorescence spectrometry (XRF) and inductively coupled plasma atomic emission spectrometry (ICP) were used to detect impurity content in the graphite before and after purification. Additionally, the crystal structure of the graphite and its ash was determined using X-ray diffraction (XRD).

Results and Discussion The majority of the graphite structure exists in the form of flakes, which can reach lengths of over 100 μm and have a relatively thin thickness. Following purification with HCl and HF,the flake structure of the graphite sample remains unchanged, and the edges of the layered structure do not curl due to high-temperature heating. Following the purification treatment,the XRD spectrum of the flake graphite displays diffraction peaks of graphite carbon at 2θ=26.6°,54.8°,and 87.3°. The peak intensities and widths remain essentially unchanged compared to the raw graphite material. This indicates that the alkali-acid purification process does not alter the intrinsic structure of the graphite itself. When roasting for 2.5 hours,use roasting temperatures of 450 ℃,500 ℃,and 550 ℃ respectively,and a hydrochloric acid(mL)to graphite(g)ratio of 2∶1. Use the NaOH-HCl method to purify graphite, resulting in an average fixed carbon content of 97.35%,97.98%, and 97.86%,respectively. If the roasting temperature is too high,NaOH reacts with Al2O3,SiO2, and other substances to form aluminosilicates with poor solubility. This aluminosilicate exhibits strong resistance to acid, making it difficult to dissolve through acid leaching. The average fixed carbon content of graphite increases with the mass ratio of NaOH to graphite, reaching 97.52%,97.55%, and 98.13% at ratios of 0.4∶1,0.5∶1, and 0.6∶1, respectively. However, increasing the mass ratio beyond 0.4 does not significantly improve the fixed carbon content of graphite. Based on cost and energy consumption, a mass ratio of NaOH to graphite of 0.4∶1 is recommended when roasting at 500 ℃. The fixed carbon content of graphite increases gradually as roasting time increases, reaching a maximum value at 2.5 hours before gradually decreasing. At this point, the carbon content of graphite is 98. 26%. The fixed carbon content in graphite may decrease due to excessive roasting time and oxidation of a small amount of graphite. It is important to note that the language used in this text is clear, objective, and value-neutral, adhering to the characteristics outlined in the assignment. The NaOH-HCl purification method was used to reduce the SiO2 content to 0.26% and 0.62%,Fe2O3 content to 0.07% and 0.2%, Al2O3 content to 0.21% and 0.15%, and CuO content to 0.001% and 0.002%, respectively. The results indicate that the impurity content of graphite significantly decreases after purification. The average fixed carbon contents of graphite are 99.91% and 99.93% respectively when the mass ratios of NaOH and graphite are 0.5∶1 and 0.6∶1. However, based on factors such as cost and efficiency,it has been determined that a mass ratio of 0.5∶1 for NaOH and graphite is the standard that meets the ideal process conditions.

Conclusion The alkaline-acid process can effectively remove impurities in graphite and reduce the environmental harm caused by excessive use of hydrofluoric acid. Additionally, the combination of hydrochloric acid and hydrofluoric acid can significantly improve the purification effect. This method is expected to be used in the fields of graphite purification treatment and new energy materials.

Keywords:graphite; alkali-acid process; alkaline roasting; fixed carbon; purification


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