Method for removing impurity MgCl2 from lithium electrolyte KCl-LiCl

Abstract

The invention relates to a method for removing an impurity MgCl2 from a lithium electrolyte KCl-LiCl by an electrochemical method before carrying out electrolyzation for producing a metal Li. In the method, a deposition potential of a metal Mg in a LiCl-KCl-MgCl2 fused salt system is researched and obtained by cyclic voltammetry at the temperature of 450 DEG C; electrode liquid lead is used as a cathode; Ag/AgCl is used as a reference electrode; a spectroscopically pure graphite is used as an anode; constant potential electrolyzation is carried out under the deposition potential; and the electrolyzation time is between 4.2 and 10 hours, so that the metal Mg is deposited on the liquid lead cathode. The method is convenient to operate, and over 96 percent of Mg can be removed from fused salt by electrolyzation for five hours.

Description

technical field [0001] The invention relates to a purification process of alkali metal Li, belonging to the field of electrochemical metallurgy, in particular to a molten salt electrochemical method for removing impurity MgCl in lithium electrolyte KCl-LiCl 2 Methods. Background technique [0002] Currently, the only industrial production method for lithium metal is lithium chloride-potassium chloride molten salt electrolysis. The LiCl-KCl system is a simple binary eutectic system, and the composition of LiCl at the eutectic point is about 50 (wt)%. During industrial electrolysis, the lithium chloride content in the electrolyte is 55 (wt)%, the potassium chloride content is 45 (wt)%, the electrolysis temperature is between 390-450°C, and potassium chloride acts as a supporting electrolyte to stabilize and reduce the melting point. effect. The industrial lithium electrolyzer adopts graphite anode and low-carbon steel cathode under the action of direct current, the anode pr...

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Problems solved by technology

The vacuum distillation method is carried out in a stainless steel distillation furnace at 600-800°C. This method needs to evaporate most of the lithium, and each kilogram of pure lithium needs to consume 52 kWh of electricity, which consumes a lot of power and has low distillation efficiency; while the filtration method generally It is used to remove refractory impurities in lithium, but Mg, Al, Ca, etc., which are easy to form alloys with metal lithium, are difficult to remove; the biggest difficulty in purifying lithium by zone melting method is that liquid lithium will cause serious corrosion to the container, and the impurity calcium The purification effect is poor; these methods for purifying impurities in metallic lithium increase the production cost of high-purity metallic lithium. It is estimated that the purification of metallic lithium with a purity of 98.5wt% to 99.9wt% costs about 100,000 yuan / ton

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