Study on ultrasonic leaching and recovery of fluoride from spent cathode carbon of aluminum electrolysis

Under the assistance of ultrasound, the fluoride in the spent cathode carbon of aluminum electrolysis was recovered by the process of washing first and then leaching. The effects of time, temperature, liquid-solid ratio, ultrasonic power, alkali amount and acid concentration on the leaching rate of fluoride were investigated. The useful components in the leaching solution were recovered by evaporation crystallization and cryolite regeneration. The tests of X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), and scanning electron microscopy combined with energy dispersive spectroscopy (SEM-EDS) showed that under the optimal experimental conditions (water washing: 50 s, 3 : 1, 420 W; alkaline leaching: alkali amount 1 g, 60 min, 70 degrees C, 7 : 1, 480 W; acid leaching: acid concentration 0.6 mol L-1, 60 min, 5 : 1, 70 degrees C, 480 W), the leaching rate of fluoride was 82.99%, and the fluoride contents recovered in the water washing and leaching processes are 94.67% and 95%, respectively. There is no solid waste and waste water in the whole experimental process.