A method for refining crude lithium

Abstract

The present invention provides a method for refining crude lithium, and belongs to the technical field of metal purification. The present invention melts the crude lithium material and then performs a first static sedimentation to obtain a supernatant melt 1, a low-impurity crude lithium melt, and a high-impurity crude lithium melt from top to bottom; the supernatant melt 1 is subjected to vacuum distillation under the condition of electromagnetic stirring without a paddle to volatilize low-boiling impurities, and then subjected to a second static sedimentation to form a bottom lithium melt and a supernatant melt 2; the supernatant melt 2 is separated to obtain purified lithium. The present invention performs vacuum distillation under the condition of electromagnetic stirring without a paddle, which not only realizes dynamic distillation of materials, reduces the distillation temperature, and improves the direct recovery rate of lithium, but also prevents the occurrence of cold zones inside to cause condensation and reflux of Na and K, thereby reducing the distillation efficiency and preventing secondary contamination of the product.

Description

Technical Field

[0001] The invention relates to the technical field of metal purification, and in particular to a method for refining crude lithium. Background Art

[0002] In recent years, with the development of the solar cell field, the preparation technology and equipment of high-purity lithium have been taken as a key research direction. The more commonly used method for purifying metallic lithium is the low-temperature vacuum distillation furnace. Its main mechanism is to heat-melt the crude lithium into liquid lithium in a protective medium, then remove the protective medium by a vacuum removal method, and then separate the volatile impurities from the metallic lithium by vacuum distillation.

[0003] This method has the problem that stirring is required when separating impurities, and the temperature near the stirring shaft is low, which will cause the impurities to continuously flow back into the lithium liquid and require repeated removal of impurities, and the direct recovery rate of lithium is low. Summary of the invention

[0004] The object of the present invention is to provide a method for refining crude lithium, by melting and purifying the crude lithium raw material under argon protection to remove high melting point and high density impurities, and distilling to remove low boiling point impurities, so as to prepare a product whose purity meets the national standard 3N refined lithium standard, which can improve the distillation efficiency, prevent secondary pollution of the product, and has a high direct recovery rate of lithium.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for refining crude lithium, comprising the following steps:

[0007] After the crude lithium material is melted, a first static sedimentation is performed to obtain a supernatant melt 1, a low-impurity crude lithium melt, and a high-impurity crude lithium melt in sequence from top to bottom;

[0008] The supernatant melt 1 is subjected to vacuum distillation under the condition of electromagnetic stirring without a paddle to volatilize low-boiling impurities, and then allowed to settle to form a bottom lithium melt and a supernatant melt 2; the supernatant melt 2 is separated to obtain purified lithium.

[0009] Preferably, the melting temperature is 250-330° C. and the holding time is 0.5-1 h.

[0010] Preferably, the melting is carried out without vortex stirring.

[0011] Preferably, the temperature of the first static sedimentation is 250-330° C., and the time is 1-6 hours.

[0012] Preferably, after obtaining the high-impurity crude lithium melt, the process further includes returning the high-impurity crude lithium melt as a crude lithium material to the melting process, and then opening the circuit after repeated use.

[0013] Preferably, the vacuum distillation pressure is 0.1-10 Pa, the temperature is 450-500° C., and the insulation time is 3-5 h.

[0014] Preferably, the rotation speed of the paddleless electromagnetic stirring is 50-500 r / min.

[0015] Preferably, the temperature of the second static sedimentation is 250-330° C., and the time is 1-2 hours.

[0016] Preferably, after obtaining the bottom lithium melt, the method further includes returning the bottom lithium melt to the melting process.

[0017] Preferably, after obtaining the purified lithium, the method further comprises casting the purified lithium into ingots.

[0018] The present invention performs vacuum distillation under the condition of electromagnetic stirring without a paddle, which not only realizes dynamic distillation of materials, reduces distillation temperature, and improves direct recovery of lithium, but also prevents the occurrence of cold zones inside to cause condensation and reflux of Na and K, thereby reducing distillation efficiency and preventing secondary contamination of products.

[0019] In the vacuum distillation step, only the lithium at the top (i.e., the supernatant melt 2) is taken as the product, which can effectively reduce the impurities such as Ca, Mg, and Si in the distillation product. The impurities are reduced by high-temperature sedimentation again (i.e., the second static sedimentation), and the high-impurity material at the bottom (i.e., the bottom lithium melt) is returned to the melting process again, thereby ensuring the recovery rate of lithium and the operation is simple and reliable;

[0020] The entire process of the present invention is completed in a sealed environment, thereby reducing the pollution of the lithium ingot by air and water vapor.

[0021] During the whole process of the present invention, all substances are converted into products (K, Na ingots, high-purity lithium ingots) without waste residue discharge, thus meeting environmental protection requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The following is a flow chart of the method for refining crude lithium in an embodiment;

[0023] Figure 2 This is a schematic diagram of the layers after the first static sedimentation of the present invention. DETAILED DESCRIPTION

[0024] The present invention provides a method for refining crude lithium, comprising the following steps:

[0025] After the crude lithium material is melted, a first static sedimentation is performed to obtain a supernatant melt 1, a low-impurity crude lithium melt, and a high-impurity crude lithium melt in sequence from top to bottom;

[0026] The supernatant melt 1 is subjected to vacuum distillation under the condition of electromagnetic stirring without a paddle to volatilize low-boiling impurities, and then allowed to settle to form a bottom lithium melt and a supernatant melt 2; the supernatant melt 2 is separated to obtain purified lithium.

[0027] The present invention melts the crude lithium material and then performs a first static sedimentation to obtain a supernatant melt 1, a low-impurity crude lithium melt and a high-impurity crude lithium melt in sequence from top to bottom.

[0028] In the present invention, the purity of the crude lithium material is preferably ≥99%, that is, the mass content of Li is ≥99%.

[0029] In the present invention, the crude lithium material preferably includes solid crude lithium ingots and / or liquid crude lithium.

[0030] In the present invention, the melting temperature is preferably 250-330°C, more preferably 280-300°C; the holding time is preferably 0.5-1h. In the present invention, the melting is preferably carried out under vortex-free stirring conditions; the vortex-free stirring is preferably achieved by a U-shaped stirring paddle. The present invention adopts vortex-free stirring to accelerate melting while preventing the upper, middle and lower layers of lithium liquid from disturbing each other.

[0031] In the present invention, the temperature of the first static sedimentation is the same as the melting temperature, and the time is preferably 1 to 6 hours, more preferably 2 to 5 hours, and further preferably 3 to 4 hours.

[0032] In the present invention, the melting and the first static sedimentation are preferably carried out in the same equipment.

[0033] The melting point of lithium is 180.5℃. At 250-330℃, Li, K and Na in crude lithium have become melts. The remaining impurities will exist in solid form due to their high melting points (such as Ca, Mg, Si and other impurities with high melting points and high density). During stirring, due to the centrifugal force, these solid impurities with high density will be thrown to the outer circle. After the first static state, under the action of gravity, the impurities with high density will settle to the lower layer. Therefore, the impurity content in the melt near the bottom of the equipment is higher, and the upper lithium liquid (i.e., the supernatant melt 1) has a higher purity. The impurity content of the lithium liquid in the intermediate buffer zone is between the two, which can prevent the supernatant melt 1 from disturbing the high-impurity crude lithium. The melting points and densities of lithium and various impurities in the crude lithium are shown in Table 1 below:

[0034] Table 1 Melting point and density of lithium and impurities in crude lithium

[0035]

[0036] like Figure 2As shown, after the first static sedimentation, the present invention obtains the supernatant melt 1 (Ⅰ product zone), low-impurity crude lithium melt (Ⅱ buffer zone) and high-impurity crude lithium melt (Ⅲ high-impurity crude lithium zone) from top to bottom. In the present invention, the height of the buffer zone is preferably 200mm. The present invention can ensure the quality of the purification process product by setting a buffer zone and vortex-free stirring, and at the same time, it can also minimize the lithium content in the purified high-impurity crude lithium, and reduce the number of times the crude lithium with high lithium content that does not meet the standard is returned to the furnace due to discharging or judgment errors.

[0037] After obtaining the supernatant melt 1, the low-impurity crude lithium melt and the high-impurity crude lithium melt, the present invention preferably returns the high-impurity crude lithium melt as the crude lithium material to the melting process, and opens the circuit after repeated use; the low-impurity crude lithium melt remains in the equipment to continue to separate the upper and lower layers of the melt; the supernatant melt 1 is transported to the vacuum distillation system, and vacuum distillation is performed under the condition of no-paddle electromagnetic stirring to volatilize the low-boiling impurities.

[0038] In the present invention, the rotation speed of the paddleless electromagnetic stirring is preferably 50-500r / min, more preferably 100-400r / min, and further preferably 200-300r / min. In the present invention, the pressure of the vacuum distillation is preferably 0.1-10Pa, more preferably 1-9Pa, and further preferably 3-7Pa; the temperature of the vacuum distillation is preferably 450-500°C, more preferably 460-490°C, and further preferably 470-480°C; the insulation time is preferably 3-5h, and more preferably 3.5-4.5h. The present invention performs vacuum distillation under the condition of paddleless electromagnetic stirring, which not only realizes dynamic distillation of materials, reduces distillation temperature, and improves direct recovery of lithium, but also prevents the occurrence of cold zones inside to cause condensation and reflux of Na and K, thereby reducing distillation efficiency and preventing secondary contamination of products.

[0039] The principle of the vacuum distillation of the present invention is: K, Na and Li are separated by utilizing the low boiling points of K and Na under vacuum conditions, and the distillation temperature is controlled within the range where Li has not yet started to evaporate but K and Na have completely evaporated, thereby avoiding a decrease in the direct yield of Li due to excessively high temperature. When the pressure in the system is at a vacuum degree of 0.1 to 10 Pa, the boiling points of K, Na and Li are shown in Table 2 below.

[0040] Table 2 Boiling points of K, Na and Li

[0041]

[0042] The present invention volatilizes low boiling point impurities (K, Na) by vacuum distillation. The present invention preferably condenses, collects and casts the volatilized low boiling point impurities into ingots to obtain K and Na ingots.

[0043] After the vacuum distillation is completed, the present invention performs a second static sedimentation to form a bottom lithium melt and a supernatant melt 2. In the present invention, the temperature of the second static sedimentation is preferably consistent with the temperature of the vacuum distillation. In the present invention, during the second static sedimentation process, high-density impurities will settle to the bottom of the vacuum distillation system to form a bottom lithium melt.

[0044] The present invention separates the supernatant melt 2 to obtain purified lithium. The present invention preferably casts the purified lithium into ingots to obtain purified lithium ingots. In an embodiment of the present invention, the supernatant pure lithium melt is specifically transported to a metal lithium ingot casting system. The pure lithium ingot obtained by the present invention is a product that meets the national standard 3N refined lithium standard.

[0045] The present invention returns the bottom lithium melt to the melting process. The present invention preferably presses the bottom lithium melt into the melting process through a pipeline by pressurization.

[0046] The present invention only takes the supernatant melt 2, which can effectively reduce impurities such as Ca, Mg, Si and the like in the distillation product. The impurities are reduced by high-temperature sedimentation again (i.e., the second static sedimentation), and the high-impurity material at the bottom (i.e., the bottom lithium melt) is returned to the melting process again, thereby ensuring the recovery rate of lithium and the operation is simple and reliable.

[0047] The entire process of the present invention is completed in a sealed environment, thereby reducing the pollution of the lithium ingot by air and water vapor.

[0048] The crude lithium refining method provided by the present invention is described in detail below in conjunction with the examples, but they should not be construed as limiting the scope of protection of the present invention.

[0049] Example 1

[0050] according to Figure 1 The process shown proceeds as follows:

[0051] (1) A solid crude lithium ingot containing ≥ 99% lithium (see Table 3 below for details) is melted.

[0052] Table 3 Composition of solid crude lithium ingot of Example 1 (wt%)

[0053] Element Li K Na Ca Fe Si Al Ni Cu Mg Cl N Pb raw material 99.0 0.260 0.58 0.035 0.0009 0.0013 0.0004 - 0.0002 0.009 - - -

[0054] (2) 25 kg of crude lithium material was melted (melting temperature 250°C, temperature error ≤ 1°C) and stirred at constant temperature for 0.5 h, then allowed to settle for 1 h to allow impurities such as Ca, Mg, Si, lithium oxide, and lithium nitride to settle to the bottom of the equipment. The material in the equipment was divided into three areas, namely, product area I located at the top of the equipment to obtain a supernatant melt 1, buffer area II located in the middle of the equipment to obtain a low-impurity crude lithium melt, and high-impurity crude lithium area III located at the bottom of the equipment to obtain a high-impurity crude lithium melt; the composition of each area is shown in Table 4 below.

[0055] Table 4 Composition of components in each zone of Example 1 (wt%)

[0056]

[0057] (3) The high-impurity crude lithium is returned to the melting process feeding system and reused as crude lithium raw material, and the circuit is opened after repeated use;

[0058] (4) The supernatant melt 1 is transported to a vacuum distillation system, where K and Na impurities are evaporated by constant temperature stirring distillation (the speed of the propellerless electromagnetic stirring is 50 r / min, the pressure of the vacuum distillation is 0.1 Pa, and the distillation temperature is 450° C.). The K and Na vapors are collected by condensation to achieve the purpose of removal.

[0059] (5) After standing and settling for 3 hours, a bottom melt and a supernatant melt 2 are formed in the vacuum distillation system. The supernatant melt 2 with a purity of 99.93% (see Table 5 below) is transported to the metal lithium ingot casting system.

[0060] Table 5 Composition of supernatant melt 2 of Example 1 (wt%)

[0061] Element Li K Na Ca Fe Si Al Ni Cu Mg Cl N Pb Supernatant melt 2 99.93 0.005 0.002 0.018 0.0010 0.0009 0.0003 - 0.0004 0.0008 0.005 0.01 0

[0062] (6) The metallic lithium melt with slightly higher Ca and Mg impurities at the bottom of the vacuum distillation system is pressed into the melting process through a pipeline under liquid conditions and melted again.

[0063] The purity of the final product lithium is Li≥99.9%, and the direct recovery rate of metallic lithium in this embodiment is 99%.

[0064] Example 2

[0065] according to Figure 1 The process shown proceeds as follows:

[0066] (1) A solid crude lithium ingot containing ≥ 99% lithium (see Table 6 below for details) is melted.

[0067] Table 6 Composition of solid crude lithium ingot of Example 2 (wt%)

[0068] Element Li K Na Ca Fe Si Al Ni Cu Mg Cl N Pb raw material 99.0 0.350 0.42 0.0397 0.0008 0.0011 0.0005 - 0.0007 0.0085 - - -

[0069] (2) 30 kg of crude lithium material was melted (melting temperature 290°C, temperature error ≤ 1°C) and stirred at constant temperature for 0.75 h, and then allowed to settle for 3 h to allow impurities such as Ca, Mg, Si, lithium oxide, and lithium nitride to settle to the bottom of the equipment. The material in the equipment was divided into three areas, namely, product area I located at the top of the equipment to obtain a supernatant melt 1, buffer area II located in the middle of the equipment to obtain a low-impurity crude lithium melt, and high-impurity crude lithium area III located at the bottom of the equipment to obtain a high-impurity crude lithium melt; the composition of each area is shown in Table 7 below.

[0070] Table 7 Composition of components in each zone of Example 2 (wt%)

[0071]

[0072]

[0073] (3) The high-impurity crude lithium is returned to the melting process feeding system and reused as crude lithium raw material, and the circuit is opened after repeated use;

[0074] (4) The supernatant melt 1 is conveyed to a vacuum distillation system, where K and Na impurities are evaporated by constant temperature stirring distillation (the speed of the propellerless electromagnetic stirring is 300 r / min, the pressure of the vacuum distillation is 5 Pa, and the distillation temperature is 470°C). The K and Na vapors are collected by condensation to achieve the purpose of removal.

[0075] (5) After standing and settling for 4 hours, a bottom melt and a supernatant melt 2 are formed in the vacuum distillation system. The supernatant melt 2 with a purity of 99.96% (see Table 8 below) is transported to the metal lithium ingot casting system.

[0076] Table 8 Composition of supernatant melt 2 of Example 2 (wt%)

[0077]

[0078] (6) The metallic lithium melt with slightly higher Ca and Mg impurities at the bottom of the vacuum distillation system is pressed into the melting process through a pipeline under liquid conditions and melted again.

[0079] The purity of the final product lithium is Li≥99.9%, and the direct recovery rate of metallic lithium in this embodiment is 99%.

[0080] Example 3

[0081] according to Figure 1 The process shown proceeds as follows:

[0082] (1) A solid crude lithium ingot containing ≥ 99% lithium (see Table 9 below for details) is melted.

[0083] Table 9 Composition of solid crude lithium ingot of Example 3 (wt%)

[0084] Element Li K Na Ca Fe Si Al Ni Cu Mg Cl N Pb raw material 99.0 0.470 0.35 0.04 0.001 0.0008 0.0003 0.0007 0.0002 0.0077 - - -

[0085] (2) 35 kg of crude lithium material was melted (melting temperature 330°C, temperature error ≤ 1°C) and stirred at constant temperature for 1 hour, then allowed to settle for 6 hours to allow impurities such as Ca, Mg, Si, lithium oxide, and lithium nitride to settle to the bottom of the equipment. The material in the equipment is divided into three areas, namely, product area I located at the top of the equipment to obtain a supernatant melt 1, buffer area II located in the middle of the equipment to obtain a low-impurity crude lithium melt, and high-impurity crude lithium area III located at the bottom of the equipment to obtain a high-impurity crude lithium melt; the composition of each area is shown in Table 10 below.

[0086] Table 10 Composition of components in each zone of Example 3 (wt%)

[0087]

[0088] (3) The high-impurity crude lithium is returned to the melting process feeding system and reused as crude lithium raw material, and the circuit is opened after repeated use;

[0089] (4) The supernatant melt 1 is conveyed to a vacuum distillation system, where K and Na impurities are evaporated by constant temperature stirring distillation (the speed of the propellerless electromagnetic stirring is 500 r / min, the pressure of the vacuum distillation is 10 Pa, and the distillation temperature is 500° C.), and the K and Na vapors are collected by condensation to achieve the purpose of removing impurities.

[0090] (5) After standing and settling for 5 hours, a bottom melt and a supernatant melt 2 were formed in the vacuum distillation system. The supernatant melt 2 with a purity of 99.94% (see Table 11 below) was transported to the metal lithium ingot casting system.

[0091] Table 11 Composition of supernatant melt 2 of Example 3 (wt%)

[0092] Element Li K Na Ca Fe Si Al Ni Cu Mg Cl N Pb Supernatant melt 2 99.94 0.005 0.002 0.012 0.0006 0.0009 0.0003 0.0006 0.0007 0.0004 0.005 0.01 0

[0093] (6) The metallic lithium melt with slightly higher Ca and Mg impurities at the bottom of the vacuum distillation system is pressed into the melting process through a pipeline under liquid conditions and melted again.

[0094] The purity of the final product lithium is Li≥99.9%, and the direct recovery rate of metallic lithium in this embodiment is 99%.

[0095] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for refining crude lithium, characterized in that: The following steps are involved: After the crude lithium material is melted, a first static sedimentation is performed to obtain a supernatant melt 1, a low-impurity crude lithium melt, and a high-impurity crude lithium melt in sequence from top to bottom; The supernatant melt 1 is subjected to vacuum distillation under the condition of electromagnetic stirring without a paddle to volatilize low-boiling impurities, and then allowed to settle to form a bottom lithium melt and a supernatant melt 2; the supernatant melt 2 is separated to obtain purified lithium.

2. The method according to claim 1, characterized in that The melting temperature is 250-330° C. and the heat preservation time is 0.5-1 h.

3. The method according to claim 1 or 2, characterized in that: The melting is carried out without vortex stirring.

4. The method according to claim 1, characterized in that: The temperature of the first static sedimentation is 250-330° C., and the time is 1-6 hours.

5. The method according to claim 1, characterized in that After obtaining the high-impurity crude lithium melt, the method further includes returning the high-impurity crude lithium melt as a crude lithium material to the melting process, and opening the circuit after repeated use.

6. The method according to claim 1, characterized in that The vacuum distillation has a pressure of 0.1-10 Pa, a temperature of 450-500° C., and a heat preservation time of 3-5 h.

7. The method according to claim 1, characterized in that The rotation speed of the paddleless electromagnetic stirring is 50-500 r / min.

8. The method according to claim 1, characterized in that The temperature of the second static sedimentation is 250-330° C., and the time is 1-2 hours.

9. The method according to claim 1, characterized in that: After obtaining the bottom lithium melt, the method further includes returning the bottom lithium melt to the melting process.

10. The method according to claim 1, characterized in that After obtaining the purified lithium, the method further includes casting the purified lithium into ingots.

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