A systematic and green low-temperature sulfation roasting-water leaching strategy was put forward to achieve a very high fluorine removal rate of 97.82% for spent carbon cathode (SCC), which was believed as a hazardous solid waste. And the carbon could be recycled with a purity of 90.29 wt.% in the flaky microstructure. Thermodynamic analysis and the results of SEM, XRD and EDS indicate that most of the fluoride could convert into water-soluble sulfate at low temperature. And the highest fluorine removal rate could be obtained when <0.15 mm SCC particles were mixed with sulfuric acid at a liquid-to-solid ratio of 1:1, and then roasted at 300 °C for 0.5 h. The sulfate was removed to purify the carbon via water-leaching process. Avrami exponents and corresponding activation energy for the roasting and leaching process demonstrated that both processes are controlled by diffusion.