High Pressure Hydrothermal Purification of Natural Flake Graphite Based on Response Surface Methodology

Abstract

High-purity graphite is of significant interest because of its diverse range of industrial applications. The traditional HF purification method produces a large amount of fluorine-containing wastewater, harming the environment. The environmentally friendly alkali-acid purification method avoids the generation of fluorinated wastewater. Herein, natural flake graphite sourced from Linkou County, Heilongjiang Province, is utilized as the primary material to address the challenge of low purity encountered in conventional alkali-acid purification methods. In addition, the response surface method is used to optimize the temperature, mass concentration and liquid-to-solid ratio of the hydrothermal alkali dissolution step in the purification process. To enhance the purification process, an integrated alkaline-acid approach is proposed, including a pretreatment step, the incorporation of co-solvents and the implementation of multiple acid-leaching stages. The x-ray diffraction (XRD), scanning electron microscopy (SEM) and x-ray fluorescence spectroscopy (XRF) measurements were used to characterize the purification effect. Experimental results show that through combined pretreatment, alkali dissolution and acid leaching, the fixed carbon content of graphite can be increased from 94% to 99.96%. The alkali-acid purification method greatly improves the purity of graphite and provides good potential for graphite in various industrial applications.