Recovery and purification of kish graphite from steelmaking dust by using acid leaching with physical auxiliary methods

Abstract Graphite has been a critical raw material in recent years due to its high economic importance and high risk of supply disruptions. The traditional source of graphite is natural graphite ores; however, the production of natural graphite ores is controlled by few countries. It is thus important to find an alternative source of graphite, and steelmaking byproducts, such as dust and slag, can be considered because of their high potential for the recovery of kish graphite. The original kish graphite normally has a low carbon content and large amounts of impurities, and purification is necessary before using kish graphite in industry. The purpose of this study was to recover kish graphite from steelmaking dust by combining multi-stage froth flotation and acid leaching processes. The conditions of acid leaching were examined, and physical auxiliary methods (heating, microwave irradiation, and ultrasonication) were studied. After the multi-stage froth flotation process, the carbon content of the kish graphite was approximately 84 wt%, and Fe, Ca, Al, Na, K, Si, and Mg were the major elements of impurities. The acid leaching process was useful for enhancing the carbon content of the kish graphite and removing the impurities, particularly when using HCl and HBF 4 . However, HCl should be a more appropriate selection for acid leaching when considering the price of acids. The carbon content of the kish graphite reached ~ 95 wt% when using 1.0 N HCl with ≥ 30 min of reaction time and a ≥ 5 L kg −1 liquid-to-solid ratio. The physical auxiliary methods can further increase the carbon content of the kish graphite. The kish graphite purified by heating 1.0 N HCl at 80 °C for 5 min had the highest carbon content of approximately 97 wt%. The purified kish graphite and the natural graphite had similar crystallinity and lamellar structures, but the purified kish graphite had more structural defects. The recovery of kish graphite from steelmaking dust can obtain valuable materials and should have benefits for the environment.