Extraction of rare earth elements from fluoride molten salt electrolytic slag by mineral phase reconstruction

There is no environmentally efficient process to extract rare earth elements from the slag of fluoride molten salt electrolysis. An extraction method was developed by drawing on the experience of extracting rare earths from gadolinite by hydrochloric acid decomposition. Sodium silicate roasting was used to reconstruct the phases of the rare earth electrolysis slag in a fluoride molten salt. The rare earth fluoride in the slag was transformed into a rare earth silicate that is easily dissolved by acid. A novel process of extracting rare earths from slag by sodium silicate roasting, washing, and acid leaching was developed. The effects of roasting time, mass ratio of sodium silicate to molten salt electrolytic slag, roasting temperature, leaching time, hydrochloric acid concentration, acid leaching temperature, and leaching liquid-solid ratio on the extraction of rare earths were examined. Under conditions of a roasting time of 1.5 h, roasting temperature of 850 °C, mass ratio of 1.5:1, leaching time of 2 h, hydrochloric acid concentration of 4 mol L-1, leaching temperature of 80 °C, and liquid-solid leaching ratio of 12:1, a leaching efficiency of rare earths from the slag of 98.96% was achieved.