Methods for producing valuable metals

Abstract

To provide a method capable of accurately determining a terminal point of a reductive melting reaction in a step of subjecting a raw material containing a waste lithium-ion battery to reductive melting treatment.SOLUTION: A method for producing a valuable metal from a raw material containing at least a waste lithium-ion battery includes a melting step of loading the raw material into a melting furnace, and introducing a reducer containing carbon to conduct reductive melting treatment. A gas analyzer installed in the melting furnace monitors the change with the lapse of time of a carbon dioxide (CO2) concentration in a gas discharged from the melting furnace, and determines a terminal point of a reaction in reductive melting treatment.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing valuable metals, which separates and recovers valuable metals from raw materials including at least discarded lithium batteries. [Background technology]

[0002] In recent years, lithium batteries (also called "lithium ion batteries") have become popular as lightweight, high-power secondary batteries. Known lithium batteries are those that contain a negative electrode material in which a negative electrode active material such as graphite is fixed to a negative electrode current collector made of copper foil, a positive electrode material in which a positive electrode active material such as lithium nickel oxide or lithium cobalt oxide is fixed to a positive electrode current collector made of aluminum foil, a separator made of a porous resin film such as polypropylene, and an electrolyte solution containing an electrolyte such as lithium hexafluorophosphate (LiPF6) inside an exterior can made of metal such as aluminum (Al) or iron (Fe).

[0003] One of the main uses of lithium-ion batteries is in hybrid and electric vehicles. For this reason, it is expected that a large amount of lithium-ion batteries installed in these vehicles will be discarded in the future according to their life cycle. In addition, some lithium-ion batteries are discarded as defective products during manufacturing. There is a demand for recycling such used batteries and defective batteries generated during manufacturing (hereinafter referred to as "waste lithium-ion batteries") as resources.

[0004] As a method of recycling, a pyrometallurgical process has been proposed in which all used lithium-ion batteries are melted in a high-temperature furnace. In this process, crushed used lithium-ion batteries are melted in a high-temperature furnace, and valuable metals such as nickel (Ni), cobalt (Co), and copper (Cu) are recovered as metals while controlling oxidation-reduction.

[0005] For example, Patent Document 1 discloses a method for recovering valuable metals from waste batteries, in which a preliminary oxidation process is performed prior to a dry process, thereby making it possible to stably control the degree of oxidation in the melting process, which was previously difficult, and thereby recovering valuable metals stably at a high recovery rate.

[0006] However, the melting process of waste lithium-ion batteries (melting process) requires high-temperature processing, which results in a large amount of energy consumption. In addition, excessive processing reactions can cause problems such as melting of refractories in the furnace. Therefore, there is a need for a method to determine the end point of the reaction in the melting process with high accuracy and prevent an increase in energy consumption and melting of refractories. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2012-172169 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been proposed in consideration of the above-mentioned circumstances, and aims to provide a method for accurately determining the end point of a reduction melting reaction in a process of performing a reduction melting treatment on raw materials including waste lithium-ion batteries. [Means for solving the problem]

[0009] As a result of extensive research, the inventors discovered that when raw materials including waste lithium-ion batteries are charged into a melting furnace and a reducing agent containing carbon is introduced to perform a reducing melting process, the end point of the reaction can be accurately determined by monitoring the change over time in the carbon dioxide (CO2) concentration in the gas discharged from the melting furnace, and thus completed the present invention.

[0010] (1) A first aspect of the present invention is a method for producing valuable metals from raw materials including at least waste lithium-ion batteries, the method including a melting step of charging the raw materials into a melting furnace and introducing a reducing agent including carbon to perform a reducing melting treatment, and a gas analyzer is provided in the melting furnace to monitor the change over time in the carbon dioxide (CO2) concentration in the gas discharged from the melting furnace to determine the reaction end point of the reducing melting treatment.

[0011] (2) A second aspect of the present invention is a method for producing valuable metals according to the first aspect of the present invention, wherein the reaction of the reducing melting treatment is determined to be completed when the CO2 concentration in the gas discharged from the melting furnace becomes 2% or less.

[0012] (3) The third invention of the present invention is a method for producing valuable metals according to the first or second invention, wherein, prior to starting the reducing melting treatment, the atmosphere in the melting furnace is replaced with an inert gas to set the oxygen (O2) concentration in the melting furnace to 1% or less. Effect of the Invention

[0013] According to the present invention, a method can be provided that can accurately determine the end point of a reduction melting reaction in a process of performing a reduction melting treatment on raw materials including waste lithium ion batteries. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a graph showing the change in CO2 concentration in exhaust gas accompanying a reduction melting reaction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An embodiment of the present invention (hereinafter, referred to as "the present embodiment") will be described below. Note that the present invention is not limited to the following embodiment, and various modifications are possible without departing from the scope of the present invention.

[0016] The method for producing valuable metals according to the present embodiment is a method for separating and recovering valuable metals from raw materials including at least waste lithium-ion batteries. Therefore, it can also be said to be a method for recovering valuable metals. The method according to the present embodiment is mainly a method using a dry smelting process, but may be composed of a dry smelting process and a wet smelting process.

[0017] Waste lithium-ion batteries contain lithium (Li) and valuable metals (Cu, Ni, Co), as well as low-value metals (Al, Fe) and carbon components. Therefore, by using raw materials that contain at least waste lithium-ion batteries, valuable metals can be efficiently separated and recovered.

[0018] The term "waste lithium ion batteries" refers not only to used lithium ion batteries, but also to waste materials from the manufacturing process of lithium ion batteries, such as defective products, residues from the manufacturing process, and scraps, which are generated during the manufacturing process of the positive electrode material that constitutes the battery. Therefore, waste lithium ion batteries can also be called lithium ion battery waste. Valuable metals are copper (Cu), nickel (Ni), cobalt (Co), and combinations thereof, and are at least one metal or alloy selected from the group consisting of copper (Cu), nickel (Ni), cobalt (Co), and combinations thereof.

[0019] Specifically, the method according to the present embodiment includes a melting step in which raw materials including at least waste lithium ion batteries are charged into a melting furnace, and a reducing agent including carbon is introduced to perform a reducing melting process.The method is characterized in that a gas analyzer is provided in the melting furnace, and the reaction end point of the reducing melting process is determined by monitoring the change over time in the carbon dioxide (CO2) concentration in the gas discharged from the melting furnace.

[0020] In the melting process for the reduction melting treatment, the raw material is charged into a melting furnace, a reducing agent containing carbon is introduced, and nickel (Ni) and cobalt (Co) in the positive electrode material of the waste lithium-ion batteries in the raw material are recovered as metals by proceeding with the following reduction reaction. At this time, the reaction shown in the following reaction formula proceeds, generating carbon dioxide (CO2) gas and carbon monoxide (CO) gas. Note that this reduction reaction starts and ends rapidly. 2LiCoO2+2C → Li2O+2Co+CO2+CO 2LiNiO2+2C → Li2O+2Ni+CO2+CO

[0021] In order to melt the raw materials and recover the metals, it is necessary to remove the impurities as oxides, and in order to separate and remove them as molten slag, it is preferable to add a flux such as calcium oxide and melt the slag at a temperature close to the melting temperature of the metals. The calcium oxide flux can be added as calcium carbonate, which has the advantage that it is inexpensive, and the following decomposition reaction occurs: CaCO3 → CaO+CO2

[0022] All of the reactions mentioned above involve CO2, and when there is almost no CO2 gas being generated, it can be said that the reactions that should be taking place in the melting furnace have almost finished, which means that the melting process is being carried out properly.

[0023] The operating temperature for the reduction melting process varies depending on the type of melting furnace and the slag composition, etc. For example, when an arc furnace or induction furnace is used and a reducing agent containing carbon is used, the melting points of the slag and metal are each around 1350°C to 1400°C, so it is necessary to control the melting temperature to at least 1400°C or higher.

[0024] In the past, in order to determine whether the reaction (reduction melting reaction) in the reduction melting process was complete and the material was in a molten state, the inside of the melting furnace was visually inspected to determine the timing of casting. However, when the material was not yet molten, the holding time was sometimes excessive in order to promote melting by holding it further. If the molten state was held for an excessive amount of time, the melting temperature was likely to rise, and the operation time of the batch operation was sometimes extended. In addition, the extended operation time caused problems such as increased energy consumption and the tendency for the refractories that make up the melting furnace to melt. In addition, the work of monitoring from the top of the furnace had the risk of molten material blowing up, and in the summer, the risk of heat stroke was also high, which resulted in disadvantages in the working environment.

[0025] Therefore, in the method according to the present embodiment, a gas analyzer is provided in the melting furnace, and the end point of the reaction of the reducing melting process is determined by monitoring the change over time in the carbon dioxide (CO2) concentration in the gas discharged from the melting furnace. In this way, by monitoring the CO2 concentration in the exhaust gas and checking the CO2 concentration and the time since the CO2 gas was generated, it is possible to accurately grasp the extent to which the reaction has progressed. Finally, the end of the above-mentioned reaction can be determined by the fact that the CO2 concentration in the exhaust gas has significantly decreased.

[0026] Figure 1 is a graph showing the transition of the CO2 concentration in the exhaust gas accompanying the reduction melting reaction, measured in the examples described later. Regarding the transition of the CO2 concentration, since the reduction melting reaction starts and ends rapidly, as shown in Figure 1, the CO2 concentration in the exhaust gas increases rapidly from the start of the reaction, remains at almost the same value due to the rate-limiting movement at the reaction interface, and then finally decreases rapidly. This makes it easy to determine the end of the reaction.

[0027] In addition, as shown in Figure 1, the CO2 concentration increases rapidly when the reduction melting reaction begins. Therefore, by monitoring the CO2 concentration in the exhaust gas, the start time of the reaction can be accurately determined.

[0028] Regarding the determination of the end point of the reduction melting reaction, for example, the end of the reaction in the melting furnace can be determined when the CO2 concentration in the exhaust gas is preferably 2% or less, more preferably 1% or less. As explained with reference to Figure 1, the change in the CO2 concentration over time increases rapidly at the start of the reaction, and then the reduction reaction of LiCoO2 and LiNiO2 and the decomposition reaction of CaCO3 proceed as shown in the reaction formula. During the progress of this reaction, the concentration of the generated CO2 gas remains roughly the same and does not change, and then, when the reduction reaction and the decomposition reaction are completed, the concentration of the CO2 gas rapidly decreases to a level of 2% or less.

[0029] In this way, the reaction end point can be determined by the CO2 concentration in the exhaust gas being preferably 2% or less, more preferably 1% or less, so that a uniform determination can be made. Furthermore, the metals recovered by determining the reaction end point based on the CO2 concentration in the exhaust gas will contain valuable metals at a high distribution rate.

[0030] Here, in the reduction melting process, it is preferable to replace the atmosphere in the melting furnace with an inert gas before the reduction melting process starts, so that the oxygen (O2) concentration in the melting furnace is 1% or less. In order to accurately control the degree of reduction in the reduction melting process, it is important to reduce the influence of oxidation, for example, due to oxidizing gases. In this regard, by replacing the atmosphere in the melting furnace with an inert gas before the reduction melting reaction starts, it is possible to maintain the sealing performance of the melting furnace and suppress the inflow of oxygen from the outside air. This makes it possible to more accurately control the degree of reduction.

[0031] The inert gas is not particularly limited, and nitrogen, argon, etc. can be used. The amount of inert gas supplied is also not particularly limited, as long as it can replace the inside of the melting furnace and ensure sealing properties that can suppress the inflow of oxygen.

[0032] Furthermore, the supply of the inert gas need not necessarily be carried out prior to the start of the reducing melting reaction, but may be carried out when the temperature is raised to the reducing temperature or continuously after the start of the reaction.

[0033] As described above, in the method for producing valuable metals according to this embodiment, when raw materials including waste lithium-ion batteries are charged into a melting furnace and subjected to a reducing melting treatment using a reducing agent containing carbon, a gas analyzer is provided in the melting furnace and the change over time in the carbon dioxide (CO2) gas concentration in the gas discharged from the melting furnace is monitored to determine the reaction end point of the reducing melting treatment.

[0034] According to this method, valuable metals can be produced in high concentrations while appropriately determining the completion of the reduction melting reaction, and the extension of operation time due to excessive holding time can be prevented. This effectively reduces energy consumption and prevents melting damage to refractories in the melting furnace. In addition, while in the past, frequent visual checks and melting status checks using a measuring stick were required to determine the reaction end point, this method makes these tasks unnecessary, allowing the end point to be determined efficiently with high safety, significantly improving workability.

[0035] In the above description, the end point of the reaction is determined by monitoring the CO2 concentration in the exhaust gas. However, the end point may be determined by monitoring the carbon monoxide (CO) gas concentration in the exhaust gas. Specifically, as described above, CO gas is also generated in the reduction melting reaction of LiCoO2 and LiNiO2. While a portion of the CO gas contributes as a reducing agent to the reduction reaction of LiCoO2 and LiNiO2, the portion that does not contribute to the reduction reaction is distributed in the exhaust gas. Therefore, the start and end of the reduction melting reaction in the melting furnace can be determined by monitoring the change over time in the concentration of CO gas distributed in the exhaust gas. EXAMPLES

[0036] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0037] [Examples and Comparative Examples] An externally heated high-frequency induction furnace with a graphite crucible on the outside was used, and 50 kg of oxide powder particles with the mass ratio of main elements shown in Table 1 below was charged into an MgO-based refractory crucible placed inside the graphite crucible, and a reducing agent and flux were added to carry out a reduction melting test. Specifically, as the reducing agent, 2.35 kg of graphite powder was added in an appropriate amount to reduce Cu, Ni, and Co, i.e., 1.1 times the equivalent amount to reduce NiO2 and CoO2. As the flux, calcium carbonate was added in an appropriate amount to melt the amount of alumina in the sample by eutectic formation, i.e., 9.63 kg in the molar ratio of CaCO3:Al2O3 = 1:1.

[0038] [Table 1]

[0039] A lid was placed on the top of the induction furnace to prevent free air from entering from the outside, and an alumina N2 gas supply pipe with an inner diameter of 5 mm and an outer diameter of 8 mm was attached so that its end was about 5 cm from the top end of the MgO crucible with a depth of 100 cm, and N2 gas was continuously supplied into the crucible at a flow rate of 30 L / min from the time the temperature was raised to the time the molten metal was poured out. This allowed an inert atmosphere to be maintained. The supply rate of N2 gas was set to 30 L / min so that the gas inside the MgO refractory crucible with a capacity of 90 L could be replaced every 3 min.

[0040] In order to suck up the exhaust gas generated by the reaction, a suction tube was inserted into the furnace so that its end was 20 to 30 cm from the top of the MgO-based crucible, and connected to a gas analyzer (PG330P, manufactured by Horiba, Ltd.) and sucked in at 1 L / min. so that the fluctuations could be constantly monitored. A thermometer for controlling the inside of the furnace was placed so that it was in contact with the outside of the graphite crucible.

[0041] In Example 1, the carbon dioxide (CO2) concentration in the gas discharged from the furnace during the reducing melting treatment was monitored using a gas analyzer, and the end point of the reducing melting reaction was determined from the change over time. On the other hand, in Comparative Example 1, a melting test was performed using a similar device, but without a gas analyzer, and the end point of the reducing melting reaction was determined by visually observing the state of the furnace.

[0042] [result] Figure 1 shows the change over time in the temperature inside the furnace and the CO2 concentration in the exhaust gas in Example 1. Table 2 below shows the measured values ​​of the CO2 concentration in the exhaust gas at specific melting times in Example 1 and the visual confirmation results of the state inside the furnace at those times, and the visual confirmation results of the state inside the furnace at each melting time in Comparative Example 1. Regarding the visual confirmation of the state, an unmelted state is indicated by "x", an insufficiently melted state is indicated by "△", a state where melting is almost completed is indicated by "○", and a completely melted state is indicated by "◎".

[0043] [Table 2]

[0044] As shown in Figure 1, CO2 was generated in the exhaust gas when the temperature was raised to 800°C, and it can be seen that the reaction started at this point when the CO2 concentration rose sharply. After a period of time in which the CO2 concentration in the exhaust gas remained almost constant, it gradually decreased to below 1%. The O2 concentration in the furnace was 17.8% at 0.0h of melting time, 8.9% at 0.5h, and 1.6% at 1.0h, and had fallen below 1% to almost 0% 1.5h before the reaction began.

[0045] In addition, based on the transition of the CO2 concentration as shown in the graph of FIG. 1, as shown in Table 2, in Example 1, the CO2 concentration in the exhaust gas corresponds to the result of visual inspection inside the furnace, and therefore, it was found that the end point of the reaction can be appropriately determined by monitoring the CO2 concentration in the exhaust gas.

[0046] Here, in Example 1, based on the results of monitoring the CO2 concentration in the exhaust gas, the melting process was terminated 10.5 hours after the start of the melting process when the CO2 concentration reached 1% or less, and the pouring of the molten metal was started. Meanwhile, in Comparative Example 1, unlike Example 1, the end point of the reaction was determined only by visually checking the state inside the furnace, and therefore the timing at which complete melting was finally determined was 0.5 hours later than the timing at which the CO2 concentration in the exhaust gas reached 1% or less in Example 1 (in Comparative Example 1, the melting process was terminated 11.0 hours after the start of the melting process, and the pouring of the molten metal was started), and it became necessary to maintain the conditions inside the furnace, etc., during that time.

[0047] Table 3 below shows the results of pouring the molten material after the end of the melting treatment (Example 1: melting time 10.5 hours, Comparative Example 1: melting time 11.0 hours) in Example 1 and Comparative Example 1, removing the slag on the top surface of the solid material obtained thereafter, and analyzing the metal obtained to determine the amount of metal recovered (metal distribution rate). The amount of metal recovered shows the distribution rate to the metal obtained by comparing the amount of Cu, Ni, and Co in the recovered metal with the amount of each element in the raw material placed in the crucible before the reduction melting test.

[0048] Table 3 also shows, as Reference Example 1, the metal analysis values ​​at 9.5 hours of melting time in the test of Example 1. For the results of Reference Example 1, an iron rod was inserted into the molten metal to sample slag, the obtained slag was analyzed, and the amount of metal recovered was calculated from the analysis results to calculate the metal distribution ratio in the same manner.

[0049] [Table 3]

[0050] As shown in Table 3, valuable metals were effectively recovered at the same recovery rate in Example 1, in which the reaction end point was determined by the CO2 concentration in the exhaust gas, and Comparative Example 1, in which the reaction was terminated in a treatment time longer than that of Example 1. This result shows that the end point of the reduction melting reaction can be accurately determined by monitoring the CO2 concentration.

[0051] As described above, the results of Reference Example 1 are analysis values ​​at the time after 9.5 hours of melting time, and are results at the time when the material is not completely melted even by visual inspection, but the recovery amount was smaller for all elements of Cu, Ni, and Co than in Example 1. This indicates that the reduction melting reaction is not completely completed, as can be confirmed by visual inspection. As shown in Table 2, the CO2 concentration in the exhaust gas at the melting time of 9.5 hours is in the middle of the concentration reduction stage. In other words, even in light of the results of Reference Example 1, it is found that the end point of the reduction melting reaction can be accurately determined by monitoring the CO2 concentration in the exhaust gas, and valuable metals can be recovered at a high recovery rate by such determination.

[0052] Furthermore, from these results, it can be seen that the reaction end point can be determined more accurately and valuable metals can be recovered efficiently by setting the CO2 concentration in the exhaust gas at a threshold value of preferably 2% or less, more preferably 1%.

[0053] From the above examples, it was found that when a carbon-containing reducing agent is introduced to perform reduction melting treatment, the end point of the reduction melting reaction can be accurately determined from the change over time by monitoring the CO2 concentration in the exhaust gas. This makes it possible to suppress the extension of operation time, i.e., the melting time, which would otherwise be excessive, the resulting increase in energy consumption, and even the melting damage of refractories, and thus to efficiently produce valuable metals.

Claims

1. A method for producing valuable metals from raw materials including at least waste lithium ion batteries, The method includes a melting step of charging the raw material into a melting furnace, and introducing a reducing agent containing carbon and a flux containing calcium carbonate to perform a reduction melting process, A gas analyzer is provided in the melting furnace to measure carbon dioxide (CO ２ ) The change in concentration over time is monitored to determine the end point of the reduction melting treatment; When the CO 2 concentration in the gas discharged from the melting furnace becomes 2% or less, it is determined that the reaction of the reducing melting treatment is completed. A method for producing valuable metals.

2. Prior to the start of the reduction melting treatment, the inside of the melting furnace is replaced with an inert gas to reduce the amount of oxygen (O ２ ) concentration is 1% or less; The method for producing valuable metals according to claim 1.

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