KR20250001168A - Method for recovering lithium - Google Patents

Abstract

The present invention relates to a method for efficiently recovering valuable metals from waste resources containing lithium by a dry smelting method, and more specifically, to a method for recovering lithium by mixing a flux containing a Ca compound and a boron component with pulverized or crushed waste resources, melting the mixture at a high temperature of 1300°C or higher, and then obtaining a lithium-boron compound volatilized therefrom.

Description

Method for recovering lithium

The present invention relates to a method for efficiently recovering valuable metals from waste resources containing lithium by a dry smelting method, and more specifically, to a method for recovering lithium by mixing a flux containing a Ca compound and a boron component with pulverized or crushed waste resources, melting the mixture at a high temperature of 1300°C or higher, and then obtaining a lithium-boron compound volatilized therefrom.

A typical example of waste resources containing lithium is waste batteries. Waste batteries are generated when primary or secondary batteries, which are used as power sources for various electronic devices we use on a daily basis, such as cell phones, laptops, cassette toys, and emergency power supplies, reach the end of their lifespan.

These waste batteries contain hazardous metals such as lead, cadmium, and mercury, and also use KOH, NH4Cl, lithium salts, H2SO4, and organic solutions as electrolytes, so their impact on the environment cannot be ignored. In addition, they contain valuable metals such as silver, cobalt, nickel, zinc, manganese, and lithium, so recycling of waste batteries is required to protect the environment and efficiently use limited resources.

In particular, demand for lithium-ion batteries (LiBs) has been increasing along with the portable electronic device market since the 1990s, and demand has recently increased further worldwide due to the rapid expansion of the electric vehicle market.

This will soon far outstrip the amount of lithium that can be supplied from natural resources, which could lead to instability in the supply and demand of lithium resources. Furthermore, the continued accumulation of waste batteries could also cause major environmental problems.

To solve these problems, recycling of used lithium secondary batteries is very important. That is, if usable materials can be recovered from used batteries, less raw materials need to be extracted from limited underground sources. Also, if used lithium secondary batteries can be recycled, the serious negative environmental impact caused by mining and processing ores can be avoided.

Methods for recovering valuable metals contained in spent batteries include hydrometallurgy and pyrometallurgy.

Wet metallurgy involves additional purification and recovery technologies such as pretreatment, leaching and selective precipitation, ion exchange, and solvent extraction to extract valuable metals after pretreatment to recover cathode materials (see Patent Document 1). Some wet metallurgy processes have the disadvantages of relatively long leaching times and low leaching efficiencies due to the high valence state of cathode active materials and the strong binding force of organic binders. In addition, the extensive use of high-concentration acid solutions and reducing agents and the complex process steps generate considerable wastewater, which can cause secondary pollution due to wastewater and hazardous gas emissions during the leaching process. In particular, lithium can be dispersed during these separation and purification steps, which can lead to low lithium recovery rates.

To overcome these shortcomings and extract and refine metals, a dry refining method can be used (see Patent Documents 2 to 5). The dry refining recycling process has the advantage of being able to process large quantities through rapid chemical reactions, thereby reducing processing and process costs. In addition, the supply materials are relatively flexible, the process is simple, and the impact of dross on the environment is also minimal. Since mixed waste batteries are directly charged into the melting furnace without going through a sorting process, problems such as fire and explosion risks, especially when processing lithium batteries, can be solved, and there is no need to consider creating an inert atmosphere during the crushing process in the wet process.

However, the purity of the recovered metal is low through the above dry smelting process, and there is a limit to recovering high value-added metals. There is also a disadvantage in that the exhaust gas generated during the processing process needs to be treated. In particular, lithium, unlike other precious metals, is absorbed into the slag along with low-priced metals, so there is also the problem that an additional process is needed to effectively recover lithium.

Moreover, most research results on recycling of lithium-based batteries are focused on the separation and recovery of Co, Ni, and Cu, and currently, there is little research on Li.

Li is an ideal cathode material for high-voltage/high-energy batteries due to its high specific capacity (3.86 Ahg ^-1 ) and extremely low electrode potential (-3.04 V vs. standard hydrogen electrode), making it a very important rare metal.

Therefore, it is important to develop a groundbreaking recycling process to more efficiently extract and separate lithium among valuable metals from spent batteries containing high proportions of heavy metals and toxic electrolytes.

Domestic Publication Patent No. 10-2019-0084081 (Published on July 15, 2019) Domestic Publication Patent No. 10-2021-0094615 (Published on July 29, 2021) Domestic registration patent No. 10-2313417 (registration date 2021.10.08.) Domestic registration patent No. 10-0717389 (registration date 2007.05.04.) Domestic Publication Patent No. 10-2015-0096849 (Published on August 26, 2015)

Park Eun-mi et al., “Research trends in recycling of lithium secondary batteries through dry process”, Resources Recycling, Vol. 31, No. 3, 2022, 27-39. Shin Seon-myeong et al., “Research and development trends in recovery of precious metal powder from waste batteries,” J. Kor. Powd, Met. Inst., Vol. 20, No. 1, 2013.

The present invention has been made to solve the above problems, and by introducing a dry smelting method for recycling waste resources containing lithium, it is intended to provide a method that is simple in process, fast in processing speed, environmentally friendly, and efficient in terms of process for recovering lithium compared to existing methods.

In order to solve the above problem, the present invention provides a method for recovering lithium, comprising: a pretreatment step (1) of crushing or pulverizing waste resources containing lithium; a step (2) of mixing flux containing a Ca compound and a boron component with the treated waste resources; a step (3) of charging the mixture into a heating furnace and melting it at a high temperature of 1,300°C or higher; and a step (4) of obtaining a lithium-boron compound volatilized from the molten slag in the form of dust by air-cooling.

The above boron component can be added after the step (3) of melting without mixing it with the flux.

The above waste resources include waste lithium batteries.

The above flux further comprises at least one of SiO2, FeO, MnO and Al2O3 together with a Ca compound.

The above boron component includes any one of borax, borate, boric acid (H3BO3), boric anhydride (B2O3), ester of boric acid, boride, magnesium boride, hydrogen boride, and borane.

The temperature of the above melting step is performed at 1,300°C to 1,800°C.

The above lithium-boron compound includes at least one of LiBO2, LiB3O5, Li2B4O7, Li2B8O13, Li3BO3, Li4B2O5, Li6B4O9, Li3B7O12, and Li3B11O18.

A device for recovering lithium according to the above lithium recovery method is provided.

As described above, since the present invention utilizes a dry smelting recycling process, there is no discharge of wastewater and environmental pollutants, and mass processing is possible through a rapid chemical reaction, thereby having the advantage of reducing processing and process costs.

In addition, the present invention has a problem that when lithium-containing waste resources are dry-melted and reduced in the conventional manner, the yield of lithium dust is low due to the high volatility point of lithium oxide, but when a boron-based volatile agent such as H3BO3 or B2O3 is used, lithium-boron-based compounds such as LiBO2, LiB3O5, Li2B4O7, Li2B8O13, Li3BO3, Li4B2O5, Li6B4O9, Li3B7O12, and Li3B11O18 are formed, thereby lowering the volatility point, so that more than 90% of lithium can be extracted in the form of dust.

Figure 1 is a flow chart illustrating a lithium recovery method step by step according to one embodiment of the present invention.
Figure 2 is a flow chart illustrating a lithium recovery method step by step according to another embodiment of the present invention.
FIG. 3 is a photograph of a lithium-boron compound obtained in the form of dust according to one embodiment of the present invention.
FIG. 4 is a photograph of a layer-separated metal alloy and slag according to one embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best manner.

The present invention relates to a method for efficiently recovering valuable metals from waste resources containing lithium by a dry refining method. An example of the waste resources is preferably a waste lithium battery whose lifespan has expired.

In this specification, the term ‘lithium battery’ is used to include all lithium-containing primary batteries, secondary batteries, or all-solid-state batteries. Lithium batteries that have reached the end of their lifespan or are discarded after use are collectively referred to as ‘waste lithium batteries.’

In general, primary batteries, unlike secondary batteries, are batteries that cannot be electrically recharged once used, so they are thrown away. Secondary batteries are energy storage devices that can be repeatedly charged and discharged approximately 500 times or more, and are batteries that can convert chemical energy into electrical energy or vice versa. Representative examples include lithium-ion, lithium polymer, nickel-cadmium, and nickel-hydrogen batteries. Among these, lithium-ion batteries have far superior energy storage capacity and lifespan compared to other secondary batteries.

In addition, while lithium-ion batteries are composed of a cathode, anode, a separator, and an electrolyte, all-solid-state batteries are batteries in which the electrolyte is solid rather than liquid. Therefore, all-solid-state batteries do not require safety devices and separators to protect against temperature changes and external impacts, so they can be implemented at a lower cost and with a higher capacity in the same size, and they have the advantage of no risk of fire.

The core materials used in the positive electrode of lithium-ion batteries include LCO (LiCoO2), NCM (Li[Ni,Co,Mn]O2), NCA (Li[Ni,Co,Al]O2), LMO (LiMn2O4), and LFP (LiFePO4), depending on the composition of the metal salt. The negative electrode material is a carbonaceous material such as graphite or silica, and copper is used as the current collector.

NCM622 is the most commonly used cathode material, which means that the nickel-cobalt-manganese ratio is 6:2:2.

Smelting is the most effective and widely used dry process method used to extract expensive metals from spent lithium batteries. The smelting process is carried out at high temperatures, but the biggest difference from roasting is the process temperature. Roasting is a process by gas-solid (or solid-solid reaction), so it is carried out below the melting point of the raw material, while smelting is a process by reaction in the liquid state, so it requires a high temperature above the melting point of the raw material.

In the smelting process, the battery material is heated above the melting temperature, and then the liquid metal is separated by reduction to form a molten layer that is not mixed. The advantage of the smelting process is that it is possible to recycle spent batteries with various chemical compositions, and the cells and modules of the battery can be directly loaded into the high-temperature furnace without sorting and preprocessing steps.

Accordingly, the present invention uses a dry smelting method, which is one of the high-temperature heat treatment methods, to efficiently recover valuable metals such as cobalt, copper, aluminum, iron, and lithium among the above-mentioned constituent materials as waste resources with economic value.

The term smelting generally refers to the process of using heat and chemical reducing agents to break down ore and drive out other elements as gases or slag, leaving only the metal behind. The reducing agent is usually a source of carbon such as coke or initial charcoal, and the carbon and aluminum present in lithium batteries act as reducing agents. Carbon removes oxygen from the ore, leaving the elemental metal. Therefore, carbon (C) is oxidized to produce carbon dioxide.

Slag plays a very important role in the efficient smelting process by maximally oxidizing low-value metals in waste batteries and inducing them to be included in the slag, and suppressing the oxidation of valuable metals and inducing them to be included in the alloy layer. In addition, adding a flux component during the smelting process allows the design of low-viscosity and low-melting-point slag, which also improves the recovery rate of metal components.

After the reduction smelting process is completed, the reduced transition metal has a higher density than the slag, so it is concentrated into a molten alloy phase and moves to the bottom of the furnace to form a molten metal pool, thereby dividing into a metal alloy layer and a slag layer. Al, Si, Li, Ca and Mn that are not included in the metal alloy layer and are oxidized are included in the slag layer. In particular, lithium is more stable when it exists as an oxide, so lithium oxide is not reduced and is mostly distributed in the slag layer.

In addition, the gas generated during the above process is captured as dust through a bag filter and discharged as clean gas through a scrubbing device. At this time, a small amount of lithium is captured as dust, but most of the lithium is discharged (or discharged) as slag, requiring an additional recovery process. However, the present invention aims to volatilize and concentrate and recover the lithium in a melting process by using a boron component. Meanwhile, a sulfur component can also be used, but if a boron component is used, there is the characteristic that SO2 toxic gas is not generated and there is no problem of a mat caused by sulfur.

FIG. 1 is a flow chart illustrating a lithium recovery method according to one embodiment of the present invention, step by step, including a pretreatment step (1) of crushing or pulverizing waste resources containing lithium to recover lithium; a step (2) of mixing flux containing a Ca compound and a boron component with the treated waste resources; a step (3) of charging the mixture into a heating furnace and melting it at a high temperature of 1,400°C or higher; and a step (4) of obtaining a lithium-boron compound volatilized from the molten slag in the form of dust by air-cooling.

In summary, the present invention relates to a method for recovering lithium from waste resources containing lithium as a lithium-boron compound. The lithium-boron compound may be at least one selected from LiBO2, LiB3O5, Li2B4O7, Li2B8O13, Li3BO3, Li4B2O5, Li6B4O9, Li3B7O12, Li3B11O18, etc.

That is, most of the lithium is generated from the molten slag by adding boric acid (H3BO3) as a boron component in the above step, and when the lithium-boron compound is generated according to the volatilization mechanism of the chemical reaction formula below, it easily volatilizes into a gas and is then obtained in the form of dust by air cooling.

<Chemical reaction formula>

Li2O + 2H3BO3 = 2LiBO2 + 3H2O, △G: -66.795 kcal

Li2O + 6H3BO3 = 2LiB3O5 + 9H2O, △G: -99.968 kcal

Li2O + 4H3BO3 = Li2B4O7 + 6H2O, △G: -88.916 kcal

Li2O + 8H3BO3 = Li2B8O13 + 12H2O, △G: -112.273 kcal

In these reaction equations, the Gibbs free energy (1,300 ℃) and △G < 0, so it is a spontaneous reaction, and as the temperature increases, volatile lithium-boron compounds are more easily generated.

At this time, depending on the Al2O3 content of the slag or the composition of the slag, the melting temperature is preferably in the range of 1,300°C to 1,800°C, and the melting time is also preferably maintained at the melting temperature for 1 hour or more. Here, it is necessary to block oxygen during temperature increase, inject an inert gas such as _N2 or Ar, or control the oxygen partial pressure to prevent oxidation of the boron component.

In another embodiment of the present invention, the boron component may be added separately to the liquid slag during or after melting, rather than being added together with the flux in the mixing step after the pretreatment step (see Fig. 2).

The amount of boron component added at this time can be used based on stoichiometry for lithium in the slag. That is, 0.5 to 10 times the lithium equivalent can be mixed, and 1 to 5 times the lithium equivalent is preferable, but is not limited thereto.

The boron component mentioned above is a hard, black-gray solid with a metallic luster, has a specific gravity of 2.33, and melts at 2000 to 2500℃. It does not exist in nature as a simple element, but its compounds include, but are not limited to, borax, borate, boric acid (H3BO3), boric anhydride (B2O3), ester of boric acid, boride, magnesium boride, hydrogen boride, and borane. Here, boric acid (H3BO3) is most preferable.

The above-mentioned waste lithium battery may be a cell, a cell pack, a module, an assembly or scrap thereof.

The flux of the present invention may further include at least one of SiO2, FeO, MnO, and Al2O3 to lower the melting point of slag together with a Ca compound, which is introduced into a refining furnace in a fine particle or powder form. The composition ratio of the above components may be variously changed in consideration of the melting point, etc., and specific examples of the Ca compound may be CaO or CaCO3.

It is also recommended to use a CaO-based flux that contains SiO2, MnO, Al2O3, etc., which have high removal efficiency for aluminum, an impurity contained in large quantities in waste lithium batteries, and have sufficient viscosity at the melting temperature.

The amount of the above flux may vary depending on the type of the spent battery cell, but 0.5 to 10 times the weight of the spent lithium battery cell may be used, and 2 to 5 times is preferable.

Ultimately, by controlling the amount of boron component and flux in the above chemical reaction formula as well as the ratio of carbon as a reducing agent, the lithium-boron compound required for recycling waste lithium can be obtained in the form of dust by air cooling.

The lithium-boron compound that volatilizes into a gas after generation can be separated or collected using a scrubber, a baghouse filter, an electrostatic precipitator, a cyclone, etc. FIG. 3 is a photograph of a lithium-boron compound obtained in the form of dust according to one embodiment of the present invention.

Example

Lithium batteries (NCM622) discarded at the end of their life cycle were discharged and crushed to prepare flakes. Flux was evenly mixed into 452.3 g of the crushed flakes and placed in a 0.5 L alumina crucible. At this time, 7.8 g of sand with SiO2 component was used as flux and 174.49 g of CaCO3 was additionally mixed.

The crucible containing the sample was heated at a rate of 5°C/min to 1400°C in an Ar inert atmosphere in an electric furnace and maintained for 1 hour to reduce CoO and NiO to Co and Ni metals, and a required amount of O ₂ was added at a rate of 0.97 L/min to oxidize excess C and Al. After completion of the O ₂ addition, the crucible was maintained at 1400°C for 1 hour while maintaining the inert atmosphere with Ar gas to allow layer separation of the alloy components and slag components. While continuously maintaining the Ar atmosphere and 1400°C in the slag layer, a total of 106.9 g of boric acid (H3BO3) as a lithium volatile agent was added over 1 hour. The reaction time was maintained at 1400°C for 1 hour, and the LiBO2 generated during this process was volatilized into vapor. After this reaction, the metal alloy and slag were obtained by slow cooling (see Fig. 4).

The weight of each alloy layer and slag layer remaining in the furnace was measured, and the content of each component was organized (see Table 1). It was confirmed that the generated metal alloy layer contained Co, Ni, Cu, Mn, B, etc., and the slag layer contained Li, Mn, Al, CaO, SiO2, B, etc.

In addition, lithium-boron compounds generated as high-temperature steam during the smelting process were collected in the form of dust in a bag filter at below 100℃ through a cooling device and dust collector connected to the electric furnace, and the exhaust gas was cleaned and discharged through a scrubbing device. The weight of the collected dust and the contents of the analyzed components are also summarized in Table 1.

Sample weight
(g) Content of ingredients (%) Li Co Ni Cu Mn Al Ca Si B Input
(input) Flake
(NCM
622) 452.3 2.2 4.3 12.9 7.0 4.2 8.4 - - - Sand 7.8 - - - - - - - 46.7 - Limestone 174.49 - - - - - - 37.1 - - H3BO3 106.9 - - - - - - - - 17.5 Output
(product) Metal Alloy 120.6 - 15.8 48.2 25.7 10.0 - - - 0.3 Slag 317.9 0.3 0.1 0.1 0.2 2.1 12.0 20.4 1.2 1.7 Dust 72 12.6 - - - - - - - 19.6

The weights of the metal alloy, slag, and dust of the above product were 120.6 g, 317.9 g, and 72 g, respectively, and the content of the constituent precious metal was analyzed and confirmed. In particular, the amount of dust recovered was calculated by reverse-calculating the amount excluding the Li content present in the alloy and slag using the analysis results of the captured dust, as the amount remaining in the device could not be confirmed.

For each product, the results of calculating the distribution ratio of valuable metals are summarized in Table 2. It was confirmed that the weight of Li contained in the dust was almost all of 90.8% of the weight of Li in the input raw material. In other words, it shows that more than 90% of lithium was recovered.

product Distribution ratio (%) Li Co Ni Cu Mn Al Ca Si B Alloy 0.0 98.5 99.5 97.8 63.8 0.0 0.0 0.0 1.7 Slag 9.2 1.5 0.5 2.2 36.2 100 100 100 28.3 Dust 90.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 70.0

As described above, it was confirmed that the present invention is very suitable for recovering lithium from spent lithium batteries with a high recovery rate of 90% or more by dry melting reduction.

Claims (8)

In a lithium recovery method,
Pretreatment step (1) of crushing or crushing waste resources containing lithium;
Step (2) of mixing a flux containing a Ca compound and a boron component into the above-mentioned treated waste resources;
Step (3) of charging the above mixture into a heating furnace and melting it at a high temperature of 1,300°C or higher; and
A method including a step (4) of obtaining a lithium-boron compound volatilized from the molten slag in the form of dust by air cooling; In claim 1, a method of adding the boron component after the step (3) of melting without mixing it with the flux A method according to claim 1 or claim 2, wherein the waste resource comprises a waste lithium battery. A method according to claim 1 or claim 2, wherein the flux further comprises at least one of SiO2, FeO, MnO and Al2O3 together with a Ca compound. A method according to claim 1 or claim 2, wherein the boron component comprises one of borax, borate, boric acid (H3BO3), boric anhydride (B2O3), ester of boric acid, boride, magnesium boride, hydrogen boride, and borane. In claim 1 or claim 2, the temperature of the melting step is performed at 1,300°C to 1,800°C A method according to claim 1 or claim 2, wherein the lithium-boron compound comprises at least one of LiBO2, LiB3O5, Li2B4O7, Li2B8O13, Li3BO3, Li4B2O5, Li6B4O9, Li3B7O12, and Li3B11O18. Device for recovering lithium according to the method of claim 1 or claim 2