Study on synergistic purification of microcrystalline graphite by ammonium fluoride/EDTA: response surface methodology optimization and kinetic control

The efficient purification of microcrystalline graphite is the key to its high-value applications. Therefore, this study proposes a synergistic purification method involving ammonium fluoride roasting and ethylenediaminetetraacetic acid (EDTA) complex leaching. Using natural microcrystalline graphite (MG) as the raw material, the ammonium fluoride roasting process was optimized by response surface methodology (RSM), and the fixed carbon content of the roasted purified microcrystalline graphite (RMG) was obtained at 97.76 %. After subsequent EDTA complex leaching, the fixed carbon content in the final ERMG product reached 99.86 %. The MgF 2 component in the impurities was used as a representative model system for kinetic analysis, which indicated that the leaching process occurred in two stages. The first stage was controlled by the pore volume diffusion model, while the second stage was jointly controlled by interfacial transfer and product layer diffusion. Structural characterization confirmed that this process introduced nitrogen/fluorine co-dopants, which increased the interlayer spacing of graphite and formed macropores and mesopores. This method reduced the reliance on highly corrosive reagents, providing a promising alternative for the high-value utilization of microcrystalline graphite.