Synthesis of High-Quality Expanded Graphite from Flotation-Enriched Natural Graphite

Here we disclose a method for obtaining high-purity expanded graphite (EG) with a carbon content of $\mathbf{{\gt} 9 9. 5 \%}$ wt. from flotation-enriched graphite with a carbon content of 94-97% wt. It has been experimentally shown that this effect is produced by a combination of the synthesis process of oxidized graphite (intercalation of graphite by anodic treatment in concentrated sulfuric acid followed by hydrolysis) and chemical cleaning using solutions of ammonium bifluoride in sulfuric acid and Trilon B in an alkaline buffer as cleaning reagents. The methods of X-ray phase analysis and thermogravimetry show that the interaction of oxidized graphite with cleaning reagents does not reduce the ability to expand. The magnitude of the mass loss of oxidized graphite and the temperature range of such losses practically do not change. The main mineral impurities of graphite ore are aluminosilicates up to 60-80% wt., effectively interact with hydrofluoric acid. Iron, calcium and magnesium oxides are converted into a soluble state when interacting with Trilon B. Quantum-chemical calculations show that the Trilon B molecule is better physically sorbed on an oxidized graphene-like plane than on its native form, interaction energy (-412 $\mathrm{kJ} / \mathrm{mol}),(-188 \mathrm{~kJ} / \mathrm{mol})$, respectively. The interaction of Trilon B with $\mathrm{Ca}^{2+}$ and $\mathbf{M g}^{2+}$ cations, regardless of the nature of the cation, is thermodynamically more likely in an aqueous solution than in the adsorbed state on the surface of the oxidized graphene plane. The proposed method ensures high purity of EG, which significantly reduces the cost of the technology and reduces environmental pollution.