Study on purification of waste cathode graphite by alkali roasting combined with hot pressing acid leaching

• KOH activation roasting opens up the internal pore channels of graphite. • The purity of regenerated graphite is 99.914%. • The mechanism of impurity removal is revealed in depth. Spent carbon cathode is a hazardous solid waste generated from aluminum electrolysis industry, which can be used as a potential resource for the preparation of high-purity graphite. This study aims to propose a purification method combining activation roasting and hot pressing acid leaching on the basis of the traditional methods for the purification of waste cathode graphite. The results show that KOH activated roasting can not only purify the waste cathode, but also leave a large number of holes and cracks on the surface of the waste cathode to increase the specific surface area and porosity, thus destroying its structure to open up the internal channels, which is conducive to the subsequent injection of high-temperature and high-pressure in-depth removal of the internal impurities of the mineral by hot pressing acid leaching. Under the optimal process conditions, the removal rate of fluoride ions can reach 99.933%, and the removal rates of sodium (Na), aluminum (Al), calcium (Ca), and silicon (Si) can reach 99.32, 99.74, 99.36, and 97.61%, respectively, and the purity of regenerated high-purity graphite products reaches 99.914%. At the same time, the reaction mechanism of KOH activated roasting and hot pressing acid leaching was investigated and analyzed, and this study can provide a new way of thinking for the recycling of aluminum electrolysis waste cathode to prepare high purity graphite, which is not only a simple and low-cost process compared to the traditional purification methods, but also can be applied to the recycling of other waste graphite, which has the potential prospects for industrial applications.