A battery powder resource recycling method

Abstract

This invention discloses a method for the resource recovery of battery powder, belonging to the field of resource recycling technology. The method includes the following steps: adding a phosphorus-containing mixed acid solution and hydrogen peroxide to the battery powder for acid dissolution, filtering to obtain a metal leachate; adding a first pH adjuster to the metal leachate to adjust the pH to 1.5–2.7, filtering to obtain an iron-removed leachate and crude iron phosphate; adding a second pH adjuster to the iron-removed leachate to adjust the pH to 3.5–5.5, filtering to obtain a qualified leachate and hazardous iron-aluminum slag; mixing the hazardous iron-aluminum slag with a reducing agent, and then carrying out a solid-phase oxidation reaction under heating conditions to obtain a precursor; washing the precursor with hot water, filtering to obtain a metal sulfate solution and directly discardable iron-aluminum oxide slag; the method described has high recycling efficiency and can convert hazardous solid waste into general solid waste.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, specifically a method for the resource recycling of battery powder. Background Technology

[0002] With the booming development of the new energy electric vehicle market, a large number of retired power batteries are facing disposal problems. At present, power battery recycling is mainly carried out through three methods: pyrometallurgical, hydrometallurgical, and biological methods. Among them, pyrometallurgical has high energy consumption and cannot selectively recover precious metals, while biological methods are too costly and have long production cycles. Hydrometallurgical processes are favored by more and more manufacturers due to their low cost and high selective metal recovery. However, the wastewater, waste gas, and waste residue generated during the hydrometallurgical recycling process seriously restrict the large-scale promotion of the hydrometallurgical recycling process.

[0003] In the wet recycling process of power batteries, battery powder generally undergoes processes such as high acid leaching, impurity removal, extraction and separation, and synthesis to achieve selective recovery of nickel, cobalt, manganese and lithium. In the impurity removal process, the pH is usually adjusted to cause elements such as iron and aluminum to form corresponding hydroxide precipitates, which are discharged as iron-aluminum slag. During this process, because nickel and iron have similar properties, some nickel, cobalt and manganese will be mixed in the iron-aluminum slag due to co-precipitation, which leads to the generation of hazardous solid waste and a decrease in the recovery rate of precious metals.

[0004] Therefore, if precious metals such as nickel, cobalt, and manganese can be recovered from iron and aluminum slag, it will not only improve the metal recovery rate of the leaching process and increase economic benefits, but also convert hazardous solid waste into general solid waste, greatly reducing the cost of waste residue treatment. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for the resource recycling of battery powder, which has high recycling efficiency and can convert hazardous solid waste into general solid waste.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for recycling battery powder includes the following steps:

[0008] Add phosphorus-containing mixed acid and hydrogen peroxide to the battery powder for acid dissolution, filter, and obtain metal leachate;

[0009] Add a first pH adjuster to the metal leachate to adjust the pH to 1.5-2.7, filter, and obtain iron-removed leachate and crude ferric phosphate;

[0010] Add a second pH adjuster to the iron removal leachate to adjust the pH to 3.5-5.5, filter, and obtain qualified leachate and hazardous waste iron and aluminum slag;

[0011] Hazardous iron and aluminum slag is mixed evenly with a reducing agent, and then subjected to a solid-phase oxidation reaction under heating conditions to obtain a precursor. The precursor is washed with hot water and filtered to obtain a metal sulfate solution and iron and aluminum oxide slag that can be directly disposed of.

[0012] This invention involves acid dissolving battery powder using a phosphorus-containing mixed acid solution and hydrogen peroxide. The use of hydrogen peroxide improves metal leaching efficiency and oxidizes ferrous ions. The addition of the phosphorus-containing mixed acid solution provides phosphorus during acid dissolution. After the initial pH adjustment to 1.5–2.7, an iron-removing leachate and crude ferric phosphate are obtained, ensuring iron is produced as crude ferric phosphate, effectively improving economic value. A second pH adjustment to 3.5–5.5 yields a qualified leachate and hazardous iron-aluminum slag. The qualified leachate can then undergo subsequent extraction processes to sequentially treat valuable metals such as nickel, cobalt, and manganese. The hazardous waste iron and aluminum slag needs further transformation. This invention creatively mixes the hazardous waste iron and aluminum slag with a reducing agent and then carries out a solid-phase oxidation reaction, which transforms the water-insoluble nickel-cobalt-manganese hydroxide into the water-soluble nickel-cobalt-manganese sulfate, while part of the iron and aluminum hydroxide is transformed into the even more insoluble iron and aluminum oxides. This allows for the efficient recovery of precious metals nickel, cobalt, and manganese from the iron and aluminum slag, improving production efficiency while also transforming the hazardous waste iron and aluminum slag into general solid waste, reducing waste residue treatment costs. After hot water washing, a metal sulfate solution and directly discardable iron and aluminum oxide slag (general waste, which can be directly disposed of) are obtained.

[0013] It should be noted that the battery powder is obtained by dismantling used power batteries and then crushing and calcining them.

[0014] In a preferred embodiment of the present invention, the molar ratio of phosphorus in the phosphorus-containing mixed acid solution to the molar ratio of iron in the battery powder is 1 to 1.2:1, and the hydrogen ion concentration in the phosphorus-containing mixed acid solution is 1 to 2 mol / L.

[0015] For example, the phosphorus-containing mixed acid is prepared by mixing phosphoric acid with other acids (such as hydrochloric acid or sulfuric acid), as long as it meets the requirements of a phosphorus molar ratio of 1 to 1.2:1 and a hydrogen ion concentration of 1 to 2 mol / L.

[0016] In a preferred embodiment of the present invention, the amount of hydrogen peroxide added is 0.5 to 1.5 times the molar amount of iron in the battery powder. At this amount, the hydrogen peroxide is in excess, which can both improve the metal leaching efficiency and oxidize ferrous ions, facilitating subsequent iron recovery.

[0017] For example, the temperature during acid dissolution is controlled between 50 and 70°C, and the acid dissolution time is controlled between 2 and 4 hours.

[0018] In a preferred embodiment of the present invention, a first pH adjuster is added to the metal leachate to adjust the pH to 2-2.7. When the pH is adjusted to between 2 and 2.7, the conversion rate of crude ferric phosphate is higher.

[0019] In a preferred embodiment of the present invention, the first pH adjuster includes at least one of sodium carbonate, sodium hydroxide, and ammonia.

[0020] For example, the first pH adjuster includes at least one of a sodium carbonate solution with a mass fraction of 20-40%, a sodium hydroxide solution with a mass fraction of 5-20%, and an ammonia solution with a mass fraction of 5-20%.

[0021] In a preferred embodiment of the present invention, a second pH adjuster is added to the iron removal leachate to adjust the pH to 4-5.5. In particular, when the pH is adjusted to between 4 and 5.5, the removal rates of aluminum and iron are higher.

[0022] In a preferred embodiment of the present invention, the second pH adjuster includes at least one of sodium carbonate, sodium hydroxide, and ammonia.

[0023] For example, the second pH adjuster includes at least one of a sodium carbonate solution with a mass fraction of 20-40%, a sodium hydroxide solution with a mass fraction of 5-20%, and an ammonia solution with a mass fraction of 5-20%.

[0024] In a preferred embodiment of the present invention, the mass ratio of the hazardous waste iron and aluminum slag to the reducing agent is 1:0.1-2, and the reducing agent includes at least one of ammonium sulfate, ammonium chloride, and urea. The addition of the reducing agent can effectively improve the leaching effect on metals (e.g., nickel, cobalt, manganese, iron, and aluminum).

[0025] In a preferred embodiment of the present invention, the mass ratio of the hazardous waste iron-aluminum slag to the reducing agent is 1:0.5 to 1.5. In particular, the leaching effect is better when the mass ratio of the hazardous waste iron-aluminum slag to the reducing agent is within this range.

[0026] In a preferred embodiment of the present invention, the solid-phase oxidation reaction is carried out at a temperature of 400–800°C for a time of 1–4 hours.

[0027] As a preferred embodiment of the present invention, the temperature of the solid-phase oxidation reaction is 400-600°C. At this temperature, the effect is better, further converting the water-insoluble nickel-cobalt-manganese hydroxide into the water-soluble nickel-cobalt-manganese sulfate, while the iron-aluminum hydroxide is partially converted into the more insoluble iron-aluminum oxide, so that the precious metals nickel, cobalt, and manganese in the iron-aluminum slag can be recovered efficiently.

[0028] In a preferred embodiment of the present invention, the temperature of the hot water during the hot water washing is 50-80°C, the mass ratio of hot water to precursor is 3-20:1, and the washing time is 15-30 minutes.

[0029] The beneficial effects of this invention are as follows: This invention dissolves battery powder in a phosphorus-containing mixed acid solution and hydrogen peroxide. The use of hydrogen peroxide can improve the metal leaching efficiency and oxidize ferrous ions. The addition of the phosphorus-containing mixed acid solution provides phosphorus element while dissolving the powder. By first adjusting the pH to 1.5-2.7, an iron-removing leachate and crude ferric phosphate are obtained, so that iron is produced in the form of crude ferric phosphate, effectively improving economic value. By second adjusting the pH to 3.5-5.5, a qualified leachate and hazardous iron-aluminum slag are obtained. At this point, the qualified leachate can be further processed through subsequent extraction processes. This invention creatively combines hazardous waste iron and aluminum slag with a reducing agent for solid-phase oxidation, which converts the sparingly soluble nickel-cobalt-manganese hydroxide into readily soluble nickel-cobalt-manganese sulfate. Meanwhile, some of the iron and aluminum hydroxide is converted into even less soluble iron and aluminum oxides. This process efficiently recovers the precious metals nickel, cobalt, and manganese from the slag, improving production efficiency while converting the hazardous waste into general solid waste, thus reducing waste treatment costs. After hot water washing, a metal sulfate solution and directly discardable iron and aluminum oxide slag (general waste) are obtained. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] In this invention, there are no particular limitations on the specific dispersion and stirring methods.

[0032] Unless otherwise specified, all reagents or instruments used in this invention are commercially available products.

[0033] Example 1

[0034] A method for recycling battery powder includes the following steps:

[0035] (1) After the waste power lithium battery is dismantled, it is crushed and calcined to obtain battery powder;

[0036] (2) Prepare a phosphorus-containing mixed acid solution with sulfuric acid and phosphoric acid, so that the hydrogen ion concentration in the phosphorus-containing mixed acid solution is 2 mol / L and the ratio of the molar amount of phosphorus element to the molar amount of iron element in the battery powder is 1.2:1. Prepare hydrogen peroxide with a mass fraction of 30%, sodium hydroxide solution with a mass fraction of 10%, and sodium carbonate solution with a mass fraction of 30%.

[0037] In this step, the formula for calculating the acid-soluble metal leaching rate is:

[0038]

[0039] In the formula: m is the mass of battery powder, α is the mass percentage of metal elements in battery powder, c is the mass concentration of metal elements in metal leachate, and V is the volume of metal leachate.

[0040] (3) Add phosphorus-containing mixed acid solution and hydrogen peroxide to the battery powder and dissolve it in acid at 65°C for 2 hours. Filter to obtain metal leachate, wherein the amount of hydrogen peroxide added is 1.2 times the molar amount of iron in the battery powder.

[0041] In this step, the formula for calculating the conversion rate of crude iron phosphate is:

[0042]

[0043] In the formula: C1 is the mass concentration of iron in the metal leaching solution, C2 is the mass concentration of iron in the iron removal leaching solution, and V is the volume of the metal leaching solution;

[0044] (4) Add sodium carbonate solution to the metal leachate, adjust the pH to 2.3, filter, and obtain iron-free leachate and crude iron phosphate. The qualified leachate can be separated into precious metals such as nickel, cobalt and manganese through the extraction process.

[0045] (5) Add sodium hydroxide solution to the iron removal leachate, adjust the pH to 4.8, filter, and obtain qualified leachate and hazardous iron-aluminum slag (hazardous solid waste, the heavy metal content still exceeds the standard, and cannot be directly discarded). The qualified leachate can be separated into precious metals such as nickel, cobalt and manganese through the extraction process.

[0046] In steps (4) and (5), the formulas for calculating the iron and aluminum removal rate are as follows:

[0047]

[0048] In the formula: C1 is the mass concentration of iron and aluminum elements in the iron removal leachate, C2 is the mass concentration of iron and aluminum elements in the qualified leachate, and V is the volume of the iron removal leachate.

[0049] (6) Mix the hazardous waste iron and aluminum slag with ammonium sulfate at a mass ratio of 1:1, put them into a 500℃ heating furnace, and carry out a high-temperature solid-phase oxidation-reduction reaction for 1 hour to convert the water-insoluble nickel cobalt manganese hydroxide into water-soluble nickel cobalt manganese sulfate, while the iron and aluminum hydroxide is partially converted into even more insoluble iron and aluminum oxides to obtain the precursor.

[0050] (7) Wash the precursor with 10 times its mass of 60°C hot water for 30 min to obtain hot water leachate, filter it to obtain metal sulfate solution and iron and aluminum oxide slag (general solid waste) that can be directly discarded.

[0051] In steps (6) and (7), the formula for calculating the metal leaching rate is as follows:

[0052]

[0053] In the formula: m is the mass of hazardous waste iron and aluminum slag, α is the mass percentage of metal elements in the hazardous waste iron and aluminum slag, c is the mass concentration of metal elements in the hot water leachate, and V is the volume of the hot water leachate.

[0054] Example 2

[0055] The difference between Example 2 and Example 1 is that the amount of hydrogen peroxide added is 0.5 times the molar amount of iron in the battery powder, while everything else is the same.

[0056] Example 3

[0057] The difference between Example 2 and Example 1 is that the amount of hydrogen peroxide added is 1.5 times the molar amount of iron in the battery powder, while everything else is the same.

[0058] Example 4

[0059] The difference between Example 4 and Example 1 is that in step (4), the pH is adjusted to 1.5, but everything else is the same.

[0060] Example 5

[0061] The difference between Example 5 and Example 1 is that in step (4), the pH is adjusted to 2, but everything else is the same.

[0062] Example 6

[0063] The difference between Example 6 and Example 1 is that the pH is adjusted to 2.5 in step (4), but everything else is the same.

[0064] Example 7

[0065] The difference between Example 7 and Example 1 is that the pH is adjusted to 3.5 in step (5), but everything else is the same.

[0066] Example 8

[0067] The difference between Example 8 and Example 1 is that the pH is adjusted to 4.5 in step (5), but everything else is the same.

[0068] Example 9

[0069] The difference between Example 9 and Example 1 is that the pH is adjusted to 5.5 in step (5), but everything else is the same.

[0070] Example 10

[0071] The difference between Example 10 and Example 1 is that in step (6), the hazardous waste iron and aluminum slag and ammonium sulfate are mixed in a mass ratio of 1:0.1, while all other steps are the same.

[0072] Example 11

[0073] The difference between Example 11 and Example 1 is that in step (6), the hazardous waste iron and aluminum slag and ammonium sulfate are mixed in a mass ratio of 1:0.5, while all other steps are the same.

[0074] Example 12

[0075] The difference between Example 12 and Example 1 is that in step (6), the hazardous waste iron and aluminum slag and ammonium sulfate are mixed in a mass ratio of 1:1.5, while all other steps are the same.

[0076] Example 13

[0077] The difference between Example 13 and Example 1 is that in step (6), the ratio of hazardous waste iron and aluminum slag to ammonium sulfate is 1:2 by mass, while all other steps are the same.

[0078] Example 14

[0079] The difference between Example 14 and Example 1 is that the high-temperature solid-phase oxidation-reduction reaction temperature in step (6) is 400℃ (i.e., the temperature of the heating furnace is 400℃), while all other aspects are the same.

[0080] Example 15

[0081] The difference between Example 15 and Example 1 is that the high-temperature solid-phase oxidation-reduction reaction temperature in step (6) is 600℃ (i.e., the temperature of the heating furnace is 600℃), while all other aspects are the same.

[0082] Example 16

[0083] The difference between Example 16 and Example 1 is that the high-temperature solid-phase oxidation-reduction reaction temperature in step (6) is 700℃ (i.e., the temperature of the heating furnace is 700℃), while all other aspects are the same.

[0084] Example 17

[0085] The difference between Example 17 and Example 1 is that the high-temperature solid-phase oxidation-reduction reaction temperature in step (6) is 800℃ (i.e., the temperature of the heating furnace is 800℃), while all other aspects are the same.

[0086] Example 18

[0087] The difference between Example 18 and Example 1 is that the hot water temperature in step (7) is 50°C, while everything else is the same.

[0088] Example 19

[0089] The difference between Example 19 and Example 1 is that the hot water temperature in step (7) is 80°C, while everything else is the same.

[0090] Comparative Example 1

[0091] The difference between Comparative Example 1 and Example 1 is that hydrogen peroxide was not added during acid dissolution in Comparative Example 1, but everything else is the same.

[0092] Comparative Example 2

[0093] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses only sulfuric acid for acid dissolution, that is, the acid solution of Comparative Example 2 has a hydrogen ion molar concentration of 2 mol / L.

[0094] Comparative Example 3

[0095] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 does not perform step (4), that is, Comparative Example 3 does not adjust the pH to 2.3, but everything else is the same.

[0096] Comparative Example 4

[0097] The difference between Comparative Example 4 and Example 1 is that Ammonium sulfate was not added to Comparative Example 4, but everything else is the same.

[0098] Comparative Example 5

[0099] The difference between Comparative Example 5 and Example 1 is that Comparative Example 5 was washed with room temperature pure water (25°C), but everything else was the same.

[0100] Test case

[0101] 1. The acid-soluble metal leaching rates of Examples 1 to 3 and Comparative Example 1 are shown in Table 1.

[0102] Table 1

[0103] Metal leaching rate Ni Co Mn Fe Al Example 1 99.6％ 99.8％ 99.9％ 99.9％ 99.9％ Example 2 81.3％ 85.9％ 89.5％ 91.2％ 90.1％ Example 3 99.8％ 99.6％ 99.8％ 99.9％ 99.9％ Comparative Example 1 42.6％ 55.3％ 41.2％ 69.3％ 73.8％

[0104] As can be seen from Table 1, the addition of hydrogen peroxide can significantly improve the metal leaching rate.

[0105] 2. The conversion rates of crude iron phosphate in Examples 1, 4-6, and Comparative Examples 2-3 are shown in Table 2.

[0106] Table 2

[0107] Example 1 Example 4 Example 5 Example 6 Comparative Example 2 Comparative Example 3 crude iron phosphate conversion rate 95.7％ 5.6％ 68.8％ 96.4％ none none

[0108] As can be seen from Table 2, adjusting the pH to 1.5–2.7 in the first stage and adding phosphoric acid are necessary to promote the conversion of iron into crude ferric phosphate. Furthermore, the conversion rate of crude ferric phosphate is higher when the pH is adjusted to between 2 and 2.7.

[0109] 3. The aluminum and iron removal rates of Examples 1 and Examples 7-9 are shown in Table 3.

[0110] Table 3

[0111] Example 1 Example 7 Example 8 Example 9 Iron removal rate 98.7％ 32.3％ 90.5％ 99.3％ Aluminum removal rate 97.6％ 12.7％ 81.1％ 98.5％

[0112] As can be seen from Table 3, adjusting the pH to between 4.5 and 5.5 results in a higher removal rate of aluminum and iron.

[0113] 4. The metal leaching rates of Examples 1, 10-19, and Comparative Examples 4-5 are shown in Table 4.

[0114] Table 4

[0115] Metal leaching rate Ni Co Mn Fe Al Example 1 99.2％ 99.5％ 99.8％ 94.3％ 35.2％ Example 10 13.3％ 21.0％ 15.4％ 5.6％ 3.1％ Example 11 81.9％ 82.6％ 89.5％ 60.3％ 11.2％ Example 12 99.5％ 99.6％ 99.7％ 98.5％ 37.6％ Example 13 99.4％ 99.5％ 99.8％ 98.9％ 42.4％ Example 14 85.6％ 87.3％ 70.5％ 23.6％ 15.5％ Example 15 92.7％ 90.5％ 93.2％ 40.9％ 16.3％ Example 16 21.1％ 16.1％ 22.5％ 6.6％ 3.4％ Example 17 2.5％ 1.7％ 3.6％ 0.4％ 0.9％ Example 18 96.3％ 95.6％ 95.5％ 91.7％ 30.7％ Example 19 99.3％ 99.5％ 99.7％ 94.5％ 35.5％ Comparative Example 4 33.5％ 25.2％ 20.8％ 2.1％ 1.3％ Comparative Example 5 89.8％ 93.4％ 91.8％ 88.6％ 31.7％

[0116] As can be seen from the table, the method of the present invention has an extremely high metal leaching rate.

[0117] Comparing Examples 1, 10-13 and Comparative Example 4, it can be seen that the addition of reducing agent can significantly improve the metal leaching rate. Moreover, when the mass ratio of reducing agent to hazardous waste iron and aluminum slag is between 0.5 and 2:1, the leaching effect is better and the metal leaching rate is higher.

[0118] Comparing Example 1 with Examples 14-17, it can be seen that when the high-temperature solid-phase oxidation-reduction reaction temperature is between 400 and 600°C, the leaching effect is better and the metal leaching rate is higher.

[0119] Comparing Example 1 with Examples 18-19 and Comparative Example 5, it can be seen that washing with hot water at 50-80°C results in better leaching effect and higher metal leaching rate.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for the resource recycling of battery powder, characterized in that, Includes the following steps: Add phosphorus-containing mixed acid and hydrogen peroxide to the battery powder for acid dissolution, filter, and obtain metal leachate; Add a first pH adjuster to the metal leachate to adjust the pH to 1.5-2.7, filter, and obtain iron-removed leachate and crude ferric phosphate; Add a second pH adjuster to the iron removal leachate to adjust the pH to 3.5~5.5, filter, and obtain qualified leachate and hazardous iron and aluminum slag; Hazardous iron and aluminum slag is mixed evenly with a reducing agent and then subjected to a solid-phase oxidation reaction under heating conditions to obtain a precursor. The precursor is washed with hot water and filtered to obtain a metal sulfate solution and iron and aluminum oxide slag that can be directly discarded. The reducing agent includes ammonium sulfate; the temperature of the solid-phase oxidation reaction is 400~800℃.

2. The method for resource recovery of battery powder according to claim 1, characterized in that, The ratio of the molar amount of phosphorus in the phosphorus-containing mixed acid solution to the molar amount of iron in the battery powder is 1~1.2:1, and the hydrogen ion concentration in the phosphorus-containing mixed acid solution is 1~2 mol / L.

3. The method for resource recovery of battery powder according to claim 1, characterized in that, The amount of hydrogen peroxide added is 0.5 to 1.5 times the molar amount of iron in the battery powder.

4. The method for resource recovery of battery powder according to claim 1, characterized in that, Add the first pH adjuster to the metal leaching solution to adjust the pH to 2-2.

7.

5. The method for resource recovery of battery powder according to claim 1, characterized in that, The first pH adjuster includes at least one of sodium carbonate, sodium hydroxide, and ammonia.

6. The method for resource recovery of battery powder according to claim 1, characterized in that, Add a second pH adjuster to the iron removal leachate to adjust the pH to 4-5.

5.

7. The method for resource recovery of battery powder according to claim 1, characterized in that, The second pH adjuster includes at least one of sodium carbonate, sodium hydroxide, and ammonia.

8. The method for resource recovery of battery powder according to claim 1, characterized in that, The mass ratio of the hazardous waste iron and aluminum slag to the reducing agent is 1:0.1~2.

9. The method for resource recovery of battery powder according to claim 1, characterized in that, The solid-phase oxidation reaction takes 1 to 4 hours.

10. The method for resource recovery of battery powder according to claim 1, characterized in that, During the hot water washing process, the temperature of the hot water is 50~80℃, the mass ratio of hot water to precursor is 3~20:1, and the washing time is 15~30min.

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