The recovery of valuable elements from rare earth molten salt electrolytic slag by the fluorination-vacuum distillation method

Abstract

Rare earth molten salt electrolytic slag is a valuable secondary resource rich in rare earth elements, lithium and fluorine. Current recovery methods can achieve the comprehensive resource recovery and manageable costs. However, some drawbacks still need to be handled, such as excessive wastewater generation and prolonged processing times. Aiming to address these limitations, a fluorination-vacuum distillation method was proposed for recovering rare earth molten salt electrolytic slag. Initially, ammonium bifluoride was applied to fluorinate rare earth molten salt electrolytic slag at 773 K for 1.5 h, converting rare earth oxyfluorides and rare earth oxides into rare earth fluorides. The fluorinated slag was then compacted and distilled in a vacuum furnace, yielding two condensates: rare earth fluorides and a mixture of lithium fluoride and lithium cryolite. Under the optimal conditions, including distillation temperature of 1573 K, distillation time of 4 h and absolute pressure of 1 Pa, the recovery efficiencies of rare earth elements, lithium and aluminum reached 96.33 %, 99.99 % and 98.24 %, respectively. In this study, comprehensive resource recovery was achieved with a short process, and almost no wastewater or gas emission was generated due to the vacuum distillation method.