Extracting metallic lithium and separating diffusion pump oil from lithium slag using a novel negative pressure distillation technology

Abstract

Lithium slag, an industrial by-product derived from oil refining systems during the extraction of metallic lithium via molten salt electrolysis, holds a substantial concentration of lithium metal, thus positioning it as a valuable secondary resource. However, disposal poses significant challenges due to the highly reactive nature of the oil and metallic lithium it contains. To address this, a dual-stage vacuum distillation method was employed to ensure safe handling. The process utilized distinct volatilization and condensation properties of the slag components. First, vacuum pump oil was distilled and recovered at a temperature of 300 °C under a pressure of 10 Pa. Second, at 700 °C, metallic lithium was volatilized and subsequently collected on a condenser. This approach achieved effective separation and recovery of valuable elements. Infrared spectra analysis of the oil extracted from lithium slag before and after distillation revealed significant similarity, thereby validating its successful recycling and reuse. Additionally, the collected metallic lithium achieved a purity level of ˃ 98 %. Computational analysis using Fluent software accurately predicted the condensation temperature and metallic lithium volume as well as oil under low-pressure and high-temperature conditions, thereby correlating with experimental results. Subsequent industrial-scale experiments conducted at a 5 kg level demonstrated the efficient and clean recovery of both metallic lithium and oil.