Method for recycling valuable metals in waste lithium ion batteries

Abstract

The invention discloses a method for recycling valuable metals in waste lithium ion batteries, and relates to the field of recycling of lithium batteries. According to the method for recycling the valuable metal in the waste lithium ion battery, the waste lithium battery black powder is subjected to reduction roasting through the coffee grounds and the metal chloride, lithium ions in the waste lithium battery can be converted into lithium chloride with high water solubility, the lithium chloride is efficiently leached and recycled in the subsequent water leaching process, and the leaching rate of the obtained lithium ions reaches 84%-97%. Meanwhile, precipitates rich in carbon elements and transition metals can be obtained in the water leaching process by the method provided by the invention, and the graphite carbon in the negative electrode of the waste lithium battery can be efficiently recycled by carrying out flotation on the precipitates.

Description

Technical Field

[0001] The present invention relates to the field of recycling of lithium batteries, and in particular to a method for recycling valuable metals in waste lithium-ion batteries. Background Art

[0002] Lithium-ion batteries (LIBs) have the advantages of high energy density, good cycle performance, long life, and small size. They are vital energy storage devices in the fields of electric vehicles, electronic equipment, and aerospace. With the continuous use of battery packs, the positive electrode materials of lithium-ion batteries will undergo phase changes, cation mixing, transition metal dissolution, etc., which will cause the battery performance to decline and the battery to age. It is estimated that by 2030, the number of retired LIBs in my country will reach 200 million to 500 million tons. Therefore, the resource utilization of discarded LIBs is particularly important, which can not only solve environmental problems, but also alleviate the shortage of mineral resources. In recent years, researchers have tried to effectively recycle waste LIBs using pyrometallurgy, hydrometallurgy, and biohydrometallurgy. Among them, the method of using biomass to assist the reduction roasting and water leaching of waste LIBs is a low-cost and reliable process that can effectively recover valuable metals in waste LIBs. Using cheap biomass, it can be thermally decomposed at a lower temperature to produce reducing substances (CH 4 , CO, H 2 , tar, etc.) can reduce the valuable metals in waste LIBs to low-valent states, effectively destroy the structure of waste lithium materials, and convert lithium into soluble salts, which can be selectively and efficiently recovered through water leaching. However, in the process of roasting waste LIBs with biomass reduction, some lithium is still converted into low-soluble lithium carbonate, which leads to a low lithium leaching rate and requires secondary treatment and leaching. Therefore, this method usually consumes a lot of water, and the roasting process generally requires a higher roasting temperature, which is not conducive to energy saving and environmental protection. Summary of the invention

[0003] In order to solve the problem that the existing process of recycling waste LIBs with biomass is difficult to efficiently recover lithium ions, the present invention provides a method for recovering valuable metals in waste lithium-ion batteries, wherein coffee grounds and metal chlorides are used to reduce and roast the waste lithium battery black powder, and the lithium ions in the waste lithium battery black powder are converted into highly water-soluble LiCl. In the subsequent water immersion, only a low liquid-to-solid ratio is used to achieve efficient and selective recovery of lithium ions.

[0004] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0005] A method for recovering valuable metals in waste lithium-ion batteries comprises the following steps:

[0006] S1. Mixing waste lithium battery black powder with coffee grounds and metal chloride and roasting to obtain a roasted product, wherein the roasting temperature is 500 to 700°C;

[0007] S2. Leaching the calcined product obtained in step S1 to separate the lithium-rich filtrate and the leached residue;

[0008] S3. Adding a carbonate source or CO to the lithium-rich filtrate obtained in step S2 2 , lithium carbonate is obtained.

[0009] The method for recovering valuable metals in waste lithium-ion batteries provided by the present invention includes introducing coffee grounds and metal chloride MeCl into the mixture of waste lithium-ion batteries and roasting the black powder in step S1. x During the calcination process, as the temperature increases, the black powder of waste lithium battery LiNi x Co y Mn z O 2 It will first react with coffee grounds to generate pyrolysis, generating the corresponding monometallic oxides. At the same time, coffee grounds as biomass will pyrolyze to generate the reducing pyrolysis product CH 4 , CO, C, etc. These pyrolysis products can react quickly with monometallic oxides and further promote the pyrolysis of coffee grounds. x It will react with Li in the monometallic oxide 2 O reacts to produce highly water-soluble lithium chloride, and the transition metal Me itself is converted into an insoluble oxidized metal. The specific reaction mechanism is shown in the following formulas (1) to (13):

[0010] LiNi x Co y Mn z O 2 = Li 2 O+xNiO+yCoO+zMnO 2 +[1-(xy-2z) / 2]O 2 (g) (1);

[0011] CO(g)+NiO=Ni+CO 2 (g) (2);

[0012] CO(g)+CoO=Co+CO 2 (g) (3);

[0013] 4CO(g)+2MnO 2 =4MnO+3CO 2 (g) (4);

[0014] C+2NiO=2Ni+CO 2 (g) (5);

[0015] C+2CoO=2Co+CO2 (g) (6);

[0016] C+2MnO 2 =2MnO+CO 2 (g) (7);

[0017] CH 4 (g)+4NiO =4Ni+CO 2 +2H 2 O(g) (8);

[0018] CH 4 (g)+4CoO =4Co+CO 2 +2H 2 O(g) (9);

[0019] CH 4 (g)+8MnO 2 =4Mn 2 O 3 +CO 2 (g)+2H 2 O(g) (10);

[0020] H 2 (g)+NiO =Ni+H 2 O(g) (11);

[0021] H 2 (g)+CoO =Co+H 2 O(g) (12);

[0022] MeCl x +Li 2 O =2LiCl x +MeO (13).

[0023] The LiCl generated during the calcination process in step S1 can be efficiently leached out during the water leaching process in step S2 to obtain a lithium-rich filtrate. The water consumption during water leaching is small, which is beneficial to energy conservation and environmental protection. Step S3: CO is introduced into the lithium-rich filtrate. 3 2- source (usually a carbonate solution, such as sodium carbonate) or CO 2 , lithium ions can be converted into lithium carbonate precipitation to achieve the recovery of lithium ions in waste lithium batteries. At the same time, other metals contained in the waste lithium battery black powder are insoluble metal elements or metal oxides generated during the roasting reaction, so they can be removed in the form of leached slag during the water leaching process in step S2, and will not enter the physical phase of the leaching solution, resulting in the subsequent lithium carbonate to be further removed.

[0024] In a specific embodiment of the present invention, the waste lithium battery black powder used in step S1 is prepared by discharging, disassembling, crushing and sorting waste ternary lithium batteries.

[0025] In a specific embodiment of the present invention, the metal chloride MeCl in step S1 x Including NaCl, CaCl 2 、MnCl 2 、NiCl 2 、CoCl 2 At least one of .

[0026] In a specific embodiment of the present invention, the mass fraction of carbon in the waste lithium battery black powder in step S1 is 28-30%. More specifically, the carbon in the waste lithium battery black powder is graphite. Currently, most of the negative electrode materials of lithium batteries are graphite.

[0027] In a specific embodiment of the present invention, the calcination in step S1 can be performed in an inert atmosphere. More specifically, the inert atmosphere can be at least one of argon and nitrogen.

[0028] Preferably, the metal chloride in step S1 comprises MnCl 2 、NiCl 2 , CaCl 2 、CoCl 2 At least one of .

[0029] By using the metal chloride to assist in the carbonization of coffee grounds, a lithium ion leaching rate and a graphite carbon recovery rate of more than 92% can be achieved.

[0030] More preferably, the metal chloride in step S1 comprises MnCl 2 、NiCl 2 , CaCl 2 At least one of .

[0031] The above-mentioned metal chloride is used to assist coffee grounds in pyrolysis of waste lithium battery black powder, and the recovery rate of lithium ions is higher.

[0032] Preferably, the mass ratio of the waste lithium battery black powder, coffee grounds and metal chloride in step S1 is 1:(1-5):(0.01-1.2).

[0033] More preferably, the mass ratio of the waste lithium battery black powder, coffee grounds and metal chloride in step S1 is 1:3:(0.8-1).

[0034] According to ICP-OES data, waste lithium battery black powder is basically completely pyrolyzed when the mass ratio of coffee grounds is 3. Continuing to increase the mass ratio of coffee grounds does not help much for the pyrolysis of waste lithium battery black powder. At the same time, when the mass ratio of metal chloride is too high, some metal ions will be leached together with lithium ions, making it difficult to remove impurities in the subsequent lithium carbonate.

[0035] Preferably, the calcination temperature in step S1 is 550-650°C.

[0036] Preferably, the calcination time in step S1 is 10 to 120 minutes.

[0037] More preferably, the time of step S1 is 30 to 60 minutes.

[0038] The calcination temperature is 550-650°C, and the leaching rate of lithium ions is higher during water immersion.

[0039] More preferably, the calcination temperature in step S1 is 600° C. and the calcination time is 45 min.

[0040] In a specific embodiment of the present invention, the heating rate of the calcination in step S1 can be 5-15° C. / min.

[0041] In a specific embodiment of the present invention, the water immersion in step S2 can be performed at room temperature.

[0042] In a specific embodiment of the present invention, the water immersion in step S2 is performed under stirring conditions, more specifically, the stirring speed is 300 to 600 rpm, preferably 450 to 500 rpm.

[0043] In a specific embodiment of the present invention, after water leaching in step S2, the lithium-rich filtrate and the leached residue are separated by suction filtration.

[0044] Preferably, the liquid-to-solid ratio in the water immersion in step S2 is 5 to 15 mL / g, and the time is 15 to 80 min.

[0045] The method provided by the present invention can efficiently leach lithium ions, so the liquid-to-solid ratio in the water leaching process of step S2 only needs to be 5 to 15 mL / g and the time only needs to be 15 to 80 min.

[0046] More preferably, the immersion time in step S2 is 30 to 60 minutes.

[0047] In a specific embodiment of the present invention, a saturated sodium carbonate solution is introduced into the lithium-rich filtrate in step S3. More specifically, after the saturated sodium carbonate solution is introduced into the lithium-rich filtrate to obtain a precipitate in step S3, the reaction system is evaporated and concentrated, and filtered while hot to obtain lithium carbonate.

[0048] Preferably, the method for recovering valuable metals from waste lithium-ion batteries of the present invention further comprises the following steps:

[0049] S4. The leached residue obtained in step S2 is mixed with a flotation agent, and the carbon material and the transition metal slag are separated after flotation stratification; the flotation agent includes hydrogen acid.

[0050] After the lithium element is recovered by leaching, the leached residue in step S2 is subjected to flotation, which can achieve efficient separation and recovery of graphite and other valuable metals in the lithium battery. When the flotation agent contains hydrogen acid, using hydrogen acid as an inhibitor can improve the flotation separation effect.

[0051] More preferably, the flotation agent in step S4 further includes at least one of n-dodecane and 4-methyl-2-pentanol.

[0052] More preferably, the mass ratio of the components in the flotation agent in step S4 is n-dodecane:4-methyl-2-pentanol; hydrogen acid=(10-15):(7.5-10):250.

[0053] More preferably, the mass ratio of the components in the flotation agent in step S4 is n-dodecane:4-methyl-2-pentanol:hydrogen acid=12:8.5:250.

[0054] More preferably, the concentration of the hydrogen acid in step S4 is 200-300 mg / L.

[0055] More preferably, the concentration of the hydrogen acid in step S4 is 250 mg / L.

[0056] More preferably, the pH of the flotation agent in step S4 is 8-10.

[0057] More preferably, the pH of the flotation agent in step S4 is 9.2±0.1.

[0058] More preferably, the flotation temperature in step S4 is 25-60°C.

[0059] More preferably, the flotation temperature in step S4 is 45°C.

[0060] In a specific embodiment of the present invention, the transition metal slag separated in step S4 includes at least one of the elements Ni, Co and Mn.

[0061] In a specific embodiment of the present invention, after separation in step S4, the transition metal slag is further subjected to baking. After baking, the transition metal slag is transformed into Ni-Co-Mn ternary oxide, which can be recycled after further processing.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] The method for recovering valuable metals from waste lithium-ion batteries provided by the present invention uses coffee grounds and metal chlorides to reduce roast and water-leach waste lithium battery black powder, thereby improving the leaching rate of lithium ions in waste lithium battery black powder. The liquid-solid ratio of water used in water leaching to the roasted product is only 5-15 mL / g, and the leaching recovery rate can also reach 84-97%. In addition, by adding a flotation step later, the carbon element in the negative electrode of the lithium battery can also be recovered, with a recovery rate of more than 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 The present invention provides a flow chart of a method for recovering valuable metals from waste lithium-ion batteries.

[0065] Figure 2 The lithium ion leaching rate of the method for recovering valuable metals in waste lithium ion batteries provided by Examples 1 to 5 of the present invention and Comparative Example 2, wherein CG represents coffee grounds.

[0066] Figure 3 It is the lithium ion leaching rate of the method for recovering valuable metals in waste lithium ion batteries provided by Examples 3, 6 to 8 and Comparative Examples 7 to 8 of the present invention. DETAILED DESCRIPTION

[0067] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents. Among them, the raw material information used in each embodiment and comparative example is as follows:

[0068] Coffee grounds: provided by Changzhou Kangruize Supply Chain Management Co., Ltd.

[0069] Embodiments 1 to 5

[0070] This embodiment provides a series of methods for recovering valuable metals from waste lithium-ion batteries using different metal chlorides, comprising the following steps:

[0071] S1. Mix waste lithium battery black powder with coffee grounds and metal chloride in a mass ratio of 1:3:1, wherein the mass fraction of graphite in the waste lithium battery black powder is 28.42%; after obtaining the mixture, transfer it to a tube furnace, introduce an inert gas for 15 minutes to place the reaction system in an inert atmosphere, continue to introduce the inert gas and heat the mixture to 600°C at a heating rate of 10°C / min for roasting, and obtain a roasted product after roasting for 60 minutes;

[0072] S2. The calcined product obtained in step S1 was immersed in water with a liquid-to-solid ratio of 10 mL / g under stirring conditions, the stirring speed was 450 rpm, the immersion time was 60 min, the immersion temperature was 25 ° C, and after immersion, the lithium-rich filtrate and the leached residue were separated by suction filtration;

[0073] S3. A saturated sodium carbonate solution is passed into the lithium-rich filtrate obtained in step S2, and the precipitate is evaporated and concentrated, and filtered while hot to obtain lithium carbonate;

[0074] S4. The leached residue obtained in step S2 is mixed with a flotation agent, wherein the flotation agent contains 15 mg / L n-dodecane, 8.0 mg / L MIBC, 250 mg / L hydrochloric acid, and the pH value is 9.2±0.1; after stirring and standing for stratification at 45°C, the supernatant is taken to obtain the carbon material, and the precipitate is the transition metal slag; the transition metal slag is baked to obtain the Ni-Co-Mn ternary oxide.

[0075] The metal chlorides specifically used in Examples 1 to 5 are shown in Table 1 below:

[0076] Table 1. Metal chlorides used in Examples 1 to 5

[0077] Group Metal chlorides Example 1 NaCl Example 2 <![CDATA[CaCl 2 ]]> Example 3 <![CDATA[MnCl 2 ]]> Example 4 <![CDATA[NiCl 2 ]]> Example 5 <![CDATA[CoCl 2 ]]>

[0078] Embodiments 6 to 8

[0079] This embodiment provides a series of methods for recovering valuable metals in waste lithium-ion batteries with different roasting temperatures in step S1, wherein the difference from embodiment 3 is only in the roasting temperature. The specific roasting temperatures of embodiments 3, 6 to 8 are shown in Table 2 below:

[0080] Table 2. Calcination temperature of Examples 3, 6 to 8

[0081]

[0082]

[0083] Example 9

[0084] A method for recovering valuable metals in waste lithium-ion batteries, which differs from Example 3 only in that:

[0085] In step S1, the waste lithium battery black powder, coffee grounds, MnCl 2 The mass ratio of waste lithium battery black powder is 1:3:0.8, and the mass fraction of graphite in waste lithium battery black powder is 28.39%.

[0086] Example 10

[0087] A method for recovering valuable metals in waste lithium-ion batteries, which differs from Example 9 only in that:

[0088] In step S1, the mass fraction of graphite in the waste lithium battery black powder is 28.54%, and the calcination temperature is 650°C.

[0089] Comparative Example 1

[0090] A method for recovering valuable metals in waste lithium-ion batteries, which differs from Example 3 only in that:

[0091] In step S1, no coffee grounds or MnCl are added. 2 , the waste lithium battery black powder was roasted separately, and the mass fraction of graphite in the waste lithium battery black powder was 28.20%;

[0092] Step S4 is not performed.

[0093] Comparative Example 2

[0094] A method for recovering valuable metals in waste lithium-ion batteries, which differs from Example 3 only in that:

[0095] No MnCl was added in step S1 2 Only coffee grounds were added to assist the pyrolysis of waste lithium battery black powder. The mass ratio of waste lithium battery black powder to coffee grounds was 1:4, and the mass fraction of graphite in the waste lithium battery black powder was 28.24%.

[0096] Comparative Example 3

[0097] A method for recovering valuable metals in waste lithium-ion batteries, which differs from Example 3 only in that:

[0098] In step S1, no coffee grounds are added, only MnCl 2 Assisted pyrolysis of waste lithium battery black powder, waste lithium battery black powder and MnCl 2 The mass ratio of waste lithium battery black powder is 1:4, and the mass fraction of graphite in waste lithium battery black powder is 28.80%.

[0099] Comparative Example 4

[0100] A method for recovering valuable metals in waste lithium-ion batteries, which differs from Comparative Example 3 only in that:

[0101] In step S1, the calcination temperature is 500° C., and the mass fraction of graphite in the waste lithium battery black powder is 28.62%.

[0102] Comparative Example 5

[0103] A method for recovering valuable metals in waste lithium-ion batteries, which differs from Example 3 only in that:

[0104] In step S1, the obtained waste lithium battery black powder and sodium sulfate are mixed and roasted in a mass ratio of 1:4, and the mass fraction of graphite in the waste lithium battery black powder is 28.44%.

[0105] Comparative Example 6

[0106] A method for recovering valuable metals in waste lithium-ion batteries, which differs from Example 3 only in that:

[0107] In step S1, the coffee grounds are replaced with corn stalks, and the mass fraction of graphite in the waste lithium battery black powder is 28.43%.

[0108] Comparative Examples 7 to 8

[0109] This comparative example provides a series of steps S1 of a method for recovering valuable metals in waste lithium-ion batteries with different roasting temperatures, wherein the difference from Example 3 is only in the roasting temperature, wherein the roasting temperature in comparative example 7 is 300°C, and the roasting temperature in comparative example 8 is 400°C.

[0110] Performance Testing

[0111] The lithium-rich filtrate obtained in step S2 of the embodiment and the comparative example and the carbon material obtained in step S4 were tested to obtain the recovery rates of lithium ions and graphite carbon in waste lithium batteries by the methods of each embodiment and the comparative example as shown in Table 3 and Figures 2-3 As shown:

[0112] Table 3. Recovery rates of lithium ions and graphite carbon by the methods of the embodiments and comparative examples

[0113]

[0114]

[0115]

[0116] Note: “ / ” in Table 3 above means that step S4 was not performed, i.e. graphite carbon was not recovered.

[0117] As shown in Table 3 above and Figures 2-3 As shown in the figure, the method provided by the present invention can be used to recover lithium ions from waste lithium-ion batteries, and the leaching recovery rate can reach more than 84%. At the same time, after adding the flotation step, the graphite carbon in the lithium battery can also be recovered, and the recovery rate is as high as more than 95%. Among them, it can be seen from the data of Examples 1 to 5 that the use of CaCl 2 、MnCl 2 、NiCl 2 The leaching rate of lithium ions was higher after pyrolysis of waste lithium battery black powder by coffee grounds (Examples 2 to 4). 2Leaching (Example 5) can also achieve a lithium ion recovery rate and carbon recovery rate of more than 92%, so the present invention preferably uses CaCl 2 、MnCl 2 、NiCl 2 、CoCl 2 Assist coffee grounds to roast and recover the black powder of waste lithium batteries. At the same time, the leaching recovery rates of lithium ions and graphite carbon in each comparative example have decreased. According to the data of comparative examples 1 to 4, it can be seen that when no auxiliary agent is added during roasting in step S1 (comparative example 1), or only one of coffee grounds and metal chloride is added (comparative examples 2 to 4), the leaching recovery rate of lithium ions will be affected. When only metal chlorides are added to assist the roasting and pyrolysis of waste lithium batteries (comparative examples 3 to 4), the leaching rate of lithium ions will be higher than that of only adding coffee grounds (comparative example 2), but other metals will be leached.

[0118] According to the data of Comparative Examples 5-6, when only sodium sulfate is added during roasting (Comparative Example 5), although sodium sulfate can also assist in the pyrolysis of waste lithium battery black powder and increase the leaching rate of lithium ions and graphite carbon, it will also lead to the leaching of other metals. After replacing coffee grounds with corn stalks and then coordinating with metal chlorides to assist in roasting black powder (Comparative Example 6), the leaching recovery rate of lithium ions is poor, indicating that the selection of biomass raw materials is extremely critical.

[0119] By comparing the data of Examples 3, 6-8 with Comparative Examples 7-8, it can be seen that when the roasting temperature is lower than 500°C (Comparative Examples 7-8), the lithium ion content in the obtained lithium-rich filtrate is low, indicating that the roasting in step S1 needs to be carried out at a temperature of 500°C or above, and the method provided by the present invention can have an excellent leaching recovery rate for lithium ions. The roasting temperature in step S1 is 500-650°C (Examples 3, 6-8), and a high lithium ion recovery rate of about 95% can be obtained. In this range, the roasting temperature continues to increase, and the leaching recovery rate shows a trend of first rising and then falling. For comprehensive consideration of energy consumption and lithium ion recovery rate, the preferred roasting temperature of the present invention is 550-650°C (Examples 3, 7-8).

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for recovering valuable metals from waste lithium-ion batteries, characterized in that: The steps include: S1. Mixing waste lithium battery black powder with coffee grounds and metal chloride and roasting to obtain a roasted product, wherein the roasting temperature is 500 to 700°C; S2. Leaching the calcined product obtained in step S1 to separate the lithium-rich filtrate and the leached residue; S3. Add a carbonate source or CO2 to the lithium-rich filtrate obtained in step S2 to obtain lithium carbonate.

2. The method for recovering valuable metals from waste lithium-ion batteries according to claim 1, characterized in that: The metal chloride in step S1 includes at least one of MnCl2, NiCl2, CaCl2, and CoCl2.

3. The method for recovering valuable metals from waste lithium-ion batteries according to claim 1 or 2, characterized in that: In step S1, the mass ratio of waste lithium battery black powder, coffee grounds and metal chloride is 1:(1-5):(0.01-1.2).

4. The method for recovering valuable metals from waste lithium-ion batteries according to claim 1, characterized in that: The calcination temperature in step S1 is 550-650°C.

5. The method for recovering valuable metals from waste lithium-ion batteries according to claim 1, characterized in that: The liquid-to-solid ratio in the water immersion in step S2 is 5 to 15 mL / g, and the time is 15 to 80 min.

6. The method for recovering valuable metals from waste lithium-ion batteries according to claim 1, characterized in that: The following steps are also included: S4. The leached residue obtained in step S2 is mixed with a flotation agent, and the carbon material and the transition metal slag are separated after flotation stratification; the flotation agent includes hydrogen acid.

7. The method for recovering valuable metals from waste lithium-ion batteries according to claim 6, characterized in that: The flotation agent in step S4 further includes at least one of n-dodecane and 4-methyl-2-pentanol.

8. The method for recovering valuable metals from waste lithium-ion batteries according to claim 7, characterized in that: The mass ratio of each component in the flotation agent in step S4 is n-dodecane:4-methyl-2-pentanol; hydrogen acid=(10-15):(7.5-10):

250.

9. The method for recovering valuable metals from waste lithium-ion batteries according to claim 6, characterized in that: The concentration of the hydrogen acid in step S4 is 200-300 mg / L.

10. The method for recovering valuable metals from waste lithium-ion batteries according to claim 6, characterized in that: The pH of the flotation agent in step S4 is 8-10.

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