The hydrochloric acid-fluoride salt is useful for purifying graphite. Ultrasonic-assisted technique can significantly reduce the leaching time and improve the leaching efficiency. Compared with single-frequency, dual-frequency ultrasound has the advantages of high energy efficiency and wide cavitation area. In this study, the combination of a dual-frequency ultrasound-assisted technique and hydrochloric acid–potassium hydrogen fluoride leaching agent was proposed for the leaching of aphanitic graphite to remove impurity minerals. First, the effects of probe-type ultrasonic power, tank-type ultrasonic power, temperature, HCl concentration, ultrasonication time, and KHF concentration on the purification efficiency of impurities from aphanitic graphite with the assistance of dual-frequency ultrasound were investigated. It was found that the combination of dual-frequency ultrasound and hydrochloric acid–potassium hydrogen fluoride can reduce the ash content of aphanitic graphite from 13.02 % to 1.02 % with an ash removal rate of 94.17 %. Second, volumetric reaction models and unreacted shrinkage nucleation models were used to fit the kinetics of impurities from aphanitic graphite with dual-frequency ultrasound-assisted HCl-KHF leaching. Kinetic analysis shows that the volumetric reaction model with chemical control was better to fit the leaching process. This is consistent with the calculation results of the activation energy of the reaction ( = 58.13 kJ/mol). Finally, laser particle size analyzer, X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray fluorescence spectroscopy (XRF), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) were used to analyze the fugacity of impurity minerals during the process of dual-frequency ultrasound-assisted HCl-KHF leaching. It was revealed that combining ultrasonic cavitation fragmentation with chloric acid–potassium fluoride generated SiF4 with high solubility, thereby removing silica-bearing impurities more efficiently. The challenges in further reducing ash content from 1.02 % in the leached concentrate of aphanitic graphite could be attributed to the existence of titanium-bearing mineral impurities on the surface of graphite particles and the presence of silica-bearing minerals between graphite carbon layers.

中文翻译：

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双超声联合盐酸-氟化氢钾浸出隐晶质石墨灰渣杂质的动力学


盐酸-氟化物盐可用于纯化石墨。超声波辅助技术可以显着缩短浸出时间，提高浸出效率。与单频超声相比，双频超声具有能量效率高、空化面积大等优点。本研究提出将双频超声辅助技术与盐酸-氟化氢钾浸出剂相结合用于隐晶质石墨的浸出，以去除杂质矿物。首先，研究了探针式超声功率、槽式超声功率、温度、HCl浓度、超声处理时间和KHF浓度对双频超声辅助下隐晶质石墨杂质净化效率的影响。结果发现，双频超声波与盐酸-氟化氢钾联合使用，可以将隐晶质石墨的灰分含量从13.02%降低到1.02%，除灰率达到94.17%。其次，使用体积反应模型和未反应收缩成核模型来拟合双频超声辅助 HCl-KHF 浸出隐晶质石墨中杂质的动力学。动力学分析表明，化学控制的体积反应模型更适合浸出过程。这与反应活化能的计算结果（= 58.13 kJ/mol）一致。 最后，激光粒度分析仪、X射线衍射（XRD）、扫描电子显微镜-能量色散X射线光谱（SEM-EDS）、X射线荧光光谱（XRF）、透射电子显微镜-能量色散X射线光谱采用TEM-EDS技术对双频超声辅助HCl-KHF浸出过程中杂质矿物的逸度进行了分析。结果表明，超声波空化破碎与氯酸-氟化钾相结合可生成高溶解度的 SiF4，从而更有效地去除含二氧化硅的杂质。进一步降低隐晶质石墨浸出精矿中灰分含量 1.02% 的挑战可能归因于石墨颗粒表面存在含钛矿物杂质以及石墨碳层之间存在含硅矿物。