CN102002730A

CN102002730A - Method for removing impurity MgCl2 from lithium electrolyte KCl-LiCl

Info

Publication number: CN102002730A
Application number: CN 201010578101
Authority: CN
Inventors: 李冰; 申淼; 楼经纬; 李素贞; 于建国
Original assignee: East China University of Science and Technology
Current assignee: East China University of Science and Technology
Priority date: 2010-12-08
Filing date: 2010-12-08
Publication date: 2011-04-06

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

Impurity MgCl among a kind of removal lithium electrolyte KCl-LiCl 2Method

Technical field

The present invention relates to the purifying technique of basic metal Li, belong to the electrochemistry field of metallurgy, particularly a kind of molten salt electrochemistry method is removed impurity MgCl among the lithium electrolyte KCl-LiCl ₂Method.

Background technology

The unique industrial process of current metallic lithium is lithium chloride-Repone K fused salt electrolysis process.The LiCl-KCl system is that simple two component eutectic is, LiCl's consists of about 50 (wt) % during eutectic point.During industrial electrolysis, lithium chloride content is 55 (wt) % in the ionogen, and KCE content is 45 (wt) %, and electrolysis temperature is between 390-450 ℃, and Repone K plays a part stable as supporting electrolyte and reduces fusing point.The industry lithium cell adopts graphite anode and soft steel negative electrode under the direct current effect, and anode produces chlorine, and negative electrode produces lithium.The product purity that electrolytic process obtains is about 95-99wt%, contains impurity such as K, Na, Al, Ca, Si, Fe, Mg, Ni.Yet, in numerous metallic lithium Application Areass, as lithium cell, contain the application of high-technology fields such as lithium structural alloy and nuclear energy power generation, the purity that all requires lithium is more than 99.9wt%, because impurity produces corrosion to container material, can't satisfy the requirement of reactor coolant in the nuclear industry, aircraft industry usefulness Al-Li alloy and high power lithium battery negative material.

The metallic lithium of production purity more than 99.9wt% need be taked other purification measure at present.The method of lithium of purifying metals has vacuum distillation method, filtration method, zone melting method, gettering, rectification method etc.Vacuum distillation method is to carry out in the stainless steel distilling furnace under 600-800 ℃, and this method need be with the most of evaporation of lithium, and the pure lithium of per kilogram need consume 52 degree electricity, and power consumption is big, and distillation efficiency is low; And filtration method generally is used for removing lithium infusible impurity, but easily then is difficult to remove with Mg, the Al of metallic lithium formation alloy, Ca etc.; The greatest difficulty of zone melting method purifying lithium is the generation heavy corrosion of liquid lithium to container, and is relatively poor to the refining effect of impurity calcium; The method of impurity has all increased the production cost of high-purity lithium in these lithiums of purifying metals, and is that the metallic lithium of 98.5wt% is purified and to be 99.9wt%, about 100,000 yuan/ton of its cost through estimation with purity.Based on above reason, be necessary fully the Impurity removal method is improved, to improve product purity.

Summary of the invention

At the defective of prior art, the present invention adopts electrochemical method, removes assorted MgCl2 before electrolysis obtains metallic lithium.This method is simple to operate, can carry out before the Li electrolysis, does not influence follow-up electrolysis process, effectively reduces the content of impurity MgCl2 among the lithium electrolyte KCl-LiCl, thereby has reduced the content of impurity Mg the follow-up metal Li electrolytic process from the source.

The present invention is achieved through the following technical solutions:

1, preparation ionogen: in LiCl-KCl, add MgCl ₂Preparation ionogen LiCl-KCl-MgCl ₂System, wherein, the mol ratio of LiCl: KCl is 1: 1, MgCl ₂Be LiCl-KCl-MgCl ₂1.0wt%～the 5wt% of total mass;

2, determine the deposition potential of Mg: adopt tungsten filament as working electrode, adopt Ag/AgCl as reference electrode, that is: the insertion of Ag silk is equipped with in the electrolytical vitrified pipe of LiCl-KCl-AgCl, wherein the mol ratio of LiCl: KCl is 1: 1, and the mole number of AgCl is 4% of a LiCl-KCl-AgCl total mole number; Spectroscopically pure graphite is a counter electrode; Under 450 ℃, utilize square wave voltammetry, with the sweep velocity scanning of 50mv/s, determine the deposition potential of Mg;

3, electrolysis: as negative electrode, is liquid at 450 ℃ of following lead electrodes with metallic lead; Adopt Ag/AgCl as reference electrode, that is: the Ag silk is inserted and be equipped with in the electrolytical vitrified pipe of LiCl-KCl-AgCl, wherein the mol ratio of LiCl: KCl is 1: 1, and the mole number of AgCl is 4% of a LiCl-KCl-AgCl total mole number; Spectroscopically pure graphite is as anode; Adopt the method for potentiostatic deposition to carry out electrolysis under the deposition potential of Mg, electrolysis time is 4.2～10 hours, and Mg promptly separates out on lead electrode, cools the temperature to 20～30 ℃ afterwards, shifts out negative electrode.

Beneficial effect

The present invention adopts lithium chloride-when the Repone K fused salt electrolysis process prepares metallic lithium, can before obtaining metallic lithium, electrolysis remove the impurity MgCl2 among the basic ionogen KCl-LiCl earlier, compare with more existing metal Li purifying techniques, present method is convenient and swift, has saved the loaded down with trivial details technical process of distillation method purification, can reduce the cost of high purity lithium preparation effectively, adopt plumbous simultaneously as the negative electrode of removing impurity, cost is low, and is easy to operate simple, need not special processing.

Description of drawings

Fig. 1 removal of impurities electrolyzer synoptic diagram.

Wherein, 1-cooling water outlet; The 2-air outlet; The 3-inlet mouth; The 4-lead-in wire; The 5-entrance of cooling water; 6-spectroscopically pure graphite counter electrode; 7-tungsten filament working electrode; The 8-Ag/AgCl reference electrode; 9-KCl-LiCl-MgCl ₂Fused salt; The 10-Pb negative electrode; 11-alumina crucible (bottom of which has holes); 12-spectroscopically pure graphite crucible; The 13-stainless steel reactor; The 14-process furnace.

Fig. 2 LiCl-KCl-MgCl ₂(2wt%) Mg in the system ²⁺Reductive square wave volt-ampere collection of illustrative plates on tungsten filament electrode;

Wherein: scanning speed: 50mv/s; T=450 ℃; Working electrode: W (0.1649cm ²); Reference electrode: Ag/AgCl (the Ag silk inserts and to be equipped with in the electrolytical vitrified pipe of LiCl-KCl-AgCl, and wherein the mol ratio of LiCl: KCl is 1: 1, the mole number of AgCl be the LiCl-KCl-AgCl total mole number 4%); Counter electrode: spectroscopically pure graphite

Embodiment:

It is basic ionogen that this impurity removal process adopts LiCl-KCl, adds the MgCl of different content ₂Prepare different LiCl-KCl-MgCl ₂Electrolyte system, MgCl ₂Account for LiCl-KCl-MgCl ₂The 3.0wt% of total mass; At LiCl-KCl-MgCl ₂(3.0wt%) in the system, adopt the potentiostatic deposition method to remove Mg, concrete operations are as follows:

Adopt square wave voltammetry to determine the deposition potential of Mg: with W (0.1649cm ²) be working electrode; Ag/AgCl (same as described above) is as reference electrode; Spectroscopically pure graphite is a counter electrode, utilizes 450 ℃ of following Mg of electrochemical workstation scanning ²⁺Circulation square wave collection of illustrative plates (as shown in Figure 2), be-1.5Vvs.Ag/AgCl with this deposition potential of establishing Mg;

Potentiostatic deposition is removed impurity Mg: as shown in Figure 1, in electrolyzer, the double crucible structure that adopts plumbago crucible to apply mechanically alumina crucible, wherein the alumina crucible bottom has the aperture of φ=3cm, in order to place metal Pb (removal of impurities lead flake), under 450 ℃ of electrolysis temperatures, metal Pb sinks to the ionogen bottom as negative electrode with the form of liquid state; Have the hole of φ=3mm on the top wall of plumbago crucible, in order to insert the stainless steel bar lead-in wire liquid cathode Pb of UNICOM.The removal of impurities lead flake can suitably be adjusted according to concrete cell construction and size.

With the liquid Pb is negative electrode; Ag/AgCl (the Ag silk inserts and to be equipped with in the electrolytical vitrified pipe of LiCl-KCl-AgCl, and wherein the mol ratio of LiCl: KCl is 1: 1, the mole number of AgCl be the LiCl-KCl-AgCl total mole number 4%) as reference electrode; Spectroscopically pure graphite is as anode, in 450 ℃, under the deposition potential of Mg, to LiCl-KCl-MgCl ₂(3.0wt%) system is carried out potentiostatic deposition, and Mg promptly separates out on lead electrode, and the electrolysis time scope is 4.2h-10h.Explanation as a comparison, electrolysis time adopts 4.2h, 5h, 10h respectively, with the impurity-eliminating effect of contrast different time.Electrolysis is isolated ionogen and negative electrode lead after finishing, and ionogen can be used for follow-up electrochemical electrolysis technology.

Impurity-eliminating effect is analyzed: 1. electrochemistry atlas analysis: as can be seen, before the electrolysis removal of impurities tangible Mg is arranged under-1.7V vsAg/AgCl current potential from the square wave voltammogram ²⁺The peak is separated out in reduction, and this shows Mg in the fused salt ²⁺Ionic exists.When adopting metal Pb to be negative electrode, electrolysis under this current potential, a large amount of Mg separates out with Pb and forms the Pb-Mg alloy, greatly reduces the activity of metal M g and the solubleness in molten salt system.After the electrolysis, there is not tangible Mg to separate out the peak in the square wave collection of illustrative plates.

2. chemical analysis results: after impurity removal process finishes, adopt the content of Mg in the residue ionogen that obtains behind fluorescence flame spectrum ICP-AES (Varian 710-ES) analytical separation, relatively the difference of Mg content in the ionogen before and after the electrolysis sees table 1 for details

Table 1 impurity Mg content ICP-AES analytical results

From embodiment as can be seen: MgCl in ionogen ₂When content is 3wt%, can remove 96.4% Al through electrolysis in 5 hours.From embodiment as can be seen: MgCl in ionogen ₂When content was 1wt%, after electrolysis 8 was little, its impurities removing efficiency reached 99.5wt%.When MgCl2 content was increased to 3wt% in the molten salt system, the electrolysis impurities removing efficiency of process 4.2h and 5h had reached more than 94%, improved temperature and was expected to further improve impurities removing efficiency.

Claims

1. remove impurity MgCl among the lithium electrolyte KCl-LiCl for one kind ₂Method, it is characterized in that described method steps is as follows:

1), preparation ionogen: in LiCl-KCl, add MgCl ₂Preparation ionogen LiCl-KCl-MgCl ₂System, wherein, the mol ratio of LiCl: KCl is 1: 1, MgCl ₂Be LiCl-KCl-MgCl ₂1.0wt%～the 5wt% of total mass;

2), determine the deposition potential of Mg: adopt tungsten filament as working electrode, adopt Ag/AgCl as reference electrode, spectroscopically pure graphite is a counter electrode; Under 450 ℃, utilize square wave voltammetry, with the sweep velocity scanning of 50mv/s, determine the deposition potential of Mg;

3), electrolysis: as negative electrode, is liquid at 450 ℃ of following lead electrodes with metallic lead; Adopt Ag/AgCl as reference electrode, spectroscopically pure graphite is as anode; Adopt the method for potentiostatic deposition to carry out electrolysis under the deposition potential of Mg, electrolysis time is 4.2～10 hours, and Mg promptly separates out on lead electrode, cools the temperature to 20～30 ℃ afterwards, shifts out negative electrode;

Wherein, described reference electrode Ag/AgCl preparation method is: the Ag silk is inserted be equipped with in the electrolytical vitrified pipe of LiCl-KCl-AgCl, wherein the mol ratio of LiCl: KCl is 1: 1, and the mole number of AgCl is 4% of a LiCl-KCl-AgCl total mole number.