Hydroxyl Removal in Muscovite by Heating for Low-Fluoride Purification of Natural Flake Graphite

Abstract

To reduce the amount of hydrofluoric acid in the purification process of natural flake graphite and increase the utilization rate of spherical graphite tailing, high-purity spherical graphite tailing was prepared by hydrochloric acid leaching, heat treatment, and hydrofluoric acid leaching. After hydrochloric acid leaching, the purity of spherical graphite tailing was increased from 97.05 to 97.72%, and the remaining impurities were mainly muscovite and quartz. Compared with uncalcined graphite, 99.9% high-purity graphite was obtained by heat treatment at 900 °C, and the ratio of hydrofluoric acid to spherical graphite tailing was decreased from 1.6 to 0.6 mL g −1 . In the process of heat treatment, the chlorite structure decomposes at 800 °C to form forsterite, enstatite, and spinel. As the −OH group of muscovite was removed, the intermediate layer of muscovite was opened, making it easier to react with hydrofluoric acid and reducing the amount of hydrofluoric acid. The high-purity spherical graphite tailing obtained was used as an anode material for lithium-ion batteries, with a reversible capacity of up to 400 mAh g −1 after 400 cycles, which had a wide application prospect in energy storage.