Vacuum Distillation Of Crude Lithium To Eliminate Sodium

With the extensive application of Li battery, more and more high-purity lithium metal are needed. While preparation of lithium metal by vacuum thermal reduction is studied, the main industrial method of Lithium is molten salt electrolysis method. Lithium ingot prepared by this method with high impurity sodium doesn't meet the challenge of Li battery; we may use vacuum distillation method to eliminate all kinds of impurities in it. Therefore, Lithium refining focuses on how to enhance the purity of lithium metal.In this thesis, the feasibility of separation of all kinds of impurities from lithium metal is investigated theoretically and the experiment conditions are determined. The small-scale experiments are carried through in internal-heating vacuum furnace, with the conditions of about 10g crude Lithium and below 10Pa vacuum degree, and the influence of temperature and time upon eliminating sodium are inspected. The results are satisfying. The content of sodium in crude lithium is reduced from 0.66% to 0.0018% in a single stage distillation process with residual gas pressure below 10 Pa, distillation temperature of 400℃ and distillation time of 2 hours.With the quality of crude lithium increased, argon is used to stir lithium liquid tostrengthen distillation effect. In theory, the mechanism of lithium liquid surface removing sodium and the role of argon bubble removing sodium are studied. When argon enters lithium liquid, creates lithium liquid movement and forms circulating flow, the content and temperature of lithium liquid are homogeneous, heat-transfer coefficient and mass-transfer coefficient are enhanced, thermodynamic equilibrium conditions in the interface of gas and liquid are changed, impurity metals with high vapor pressure are easy to be separated from lithium liquid and distillation aim is achieved.The kilogram-scale experiments are carried through in external-heating vacuum furnace, and the influence of argon, crude lithium, distillation temperature, distillation time and the content of sodium in crude lithium upon eliminating sodium are inspected. The results are preferable. The content of sodium in crude lithium, which weighs 448.2g, is reduced from 0.69% to 0.0080% in a single stage distillation process with distillation temperature of 520℃ and distillation time of 8 hours, and coefficient of recovery is 84.45%. The kilogram-scale experiments of eliminating calcium are also carried through, with the adding of boron-oxide, in the furnace and the results aren't perfect.The crude lithium has been detected by scanning electron microscopy and we have observed impurity sodium is distributed homogeneously in crude lithium, the diameter of sodium particle is 1~2 u m, and other impurities are irregular shape, with the diameter above 15 u m. So we have selected corrosion resistance steel filter pipe with 10 u m filter pore size to do filtering separation experiments. After filtering, the content of all kinds of impurities in lithium liquid are all reduced to different degrees and the quality of lithium ingot is improved.At last, a new technology of purifying crude lithium is brought forth and a new vacuum furnace with argon stirring is designed for lithium metal distillation.