Separation and recovery of valuable elements from acid leachate of spent carbon cathode by fractional precipitation method

Spent carbon cathode (SCC), a hazardous waste from aluminum electrolysis industry, has been confirmed that it can be direct treated and purified by hydrothermal acid leaching in the previous study. This work focuses on a hydrometallurgical process to separate and recover the valuable elements from the acid leachate of SCC by fractional precipitation method. Thermodynamic calculation, single factor experiment and characterization of the products are utilized to obtain the ion-transformation mechanism, optimize the conditions of process and confirm the physicochemical properties of the products. The results indicate that 92.6 % Si, 93.07 % Al and more than 99 % Fe, Ca are recovered from the acid leachate in the form of Na2SiF6, Na3AlF6, Fe(OH)3 and CaF2 respectively and concentration of F- in acid leachate decrease from 3115 mg/L to 6.6 mg/L when the conditions attach the optimal. Finally, Na and Cl in acid leachate is recovered in the form of NaCl via evaporation crystallization. The whole process completes the separation and recovery of all elements in acid leachate of SCC, which has no wastewater discharge and is a closed-cycle route.