Effective purification of graphite via low pulp density flotation-low temperature alkali roasting-acid leaching route: From laboratory-scale to pilot-scale

A typical flake graphite concentrate sampled from a graphite flotation plant was used to prepare high purity graphite. The carbon content of the concentrate was 85.6%, and silicate and iron-containing minerals were found principally in the concentrate. High-grade graphite concentrate with a carbon content of 95% was obtained in the flotation process with feed pulp of 5% solids by weight after regrinding by a low-speed ball milling system. A small amount of the flotation reagents such as caustic soda, water glass, kerosene, and pine oil were added. The resulting flotation concentrate was mixed with alkali and roasted at 500 °C for 90 min. During the alkali roasting, the silicate mineral was converted into the water- and acid-soluble materials. Afterward, the soluble materials and iron-containing minerals were dissolved by acid leaching. As a result, a product with a carbon content of 99.82% was prepared. According to the calculation results of Gibbs energy, the reactions between impurities and chemicals in alkali roasting and acid leaching processes were spontaneous. The purification route was very effective for high purity graphite production and has been successfully applied in the pilot-scale experiment.