Method for preparing expandable graphite by replacing solid and liquid oxidizing agents with gaseous oxidizing agents

The invention discloses a method for preparing expandable graphite by replacing solid and liquid oxidizing agents with gaseous oxidizing agents, and solves the problems that heavy metals in washing wastewater are not easily treated in the process of preparing the expandable graphite by the solid oxidizing agents at present, the sulfur content of the graphite is high, product purity is reduced, the liquid oxidizing agents are unstable in reaction, and expansion times cannot be controlled. The method includes the steps: firstly, mixing sulfuric acid and the graphite; secondly, mixing gas; thirdly, oxidizing and intercalating the graphite; fourthly, deacidifying and drying the graphite. Oxidation degree is adjusted by different temperatures and pressures, the expandable graphite with controllable expansion times and high quality is prepared, the washing dilute wastewater is easily treated, and the method is used for preparing the expandable graphite.