Method for preparing lithium carbonate by utilizing waste lithium iron phosphate positive electrode material

Abstract

The invention discloses a method for preparing lithium carbonate by using a waste lithium iron phosphate positive electrode material, which comprises the following steps: pulverizing the waste lithium iron phosphate positive electrode material, sieving, fully mixing the pulverized waste lithium iron phosphate positive electrode material with concentrated sulfuric acid, and carrying out dump leaching for 6-12 hours; primary leaching: raw materials come from secondary leaching residues, acid is adjusted to the pH value of 1.5-2.0, sodium ferrate is added, stirring leaching is performed at the temperature of 60-70 DEG C, leaching liquid serves as secondary leaching liquid, and leaching residues are recycled to be used for preparing iron phosphate raw materials; and secondary leaching: the solution comes from the primary leaching solution, acid is consumed by using heap leaching raw materials, the end point PH is controlled to be 3.0-3.5, sodium ferrate is added, and stirring leaching is performed under the condition of 45-55 DEG C. No hazardous waste is generated in the whole process, leaching residues are used as raw materials for preparing iron phosphate, calcium carbonate can be recycled for acid adjustment, and harmless treatment is truly achieved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium carbonate preparation, and in particular to a method for preparing lithium carbonate by utilizing waste lithium iron phosphate positive electrode materials. Background Art

[0002] Battery-grade lithium carbonate is mainly used to prepare lithium cobalt oxide, lithium manganese oxide, ternary materials and lithium iron phosphate and other lithium-ion battery positive electrode materials. The main raw material of lithium batteries is battery-grade lithium carbonate. With the advancement of new energy technology, there have been progress and breakthroughs in the field of transportation. Among them, lithium-ion batteries are the core energy of new energy vehicles and have played a decisive role in the development of new energy vehicles. The use of battery-grade lithium carbonate to prepare lithium batteries has better quality and performance, can reduce interference from the outside world, and thus extend its service life and increase the actual endurance time, which plays a vital role in the development of the new energy vehicle field.

[0003] There are currently two methods for preparing lithium carbonate:

[0004] As attached Figure 1 As shown, sulfuric acid + oxidation leaching method: waste lithium iron phosphate positive electrode material is leached with high-concentration sulfuric acid and oxidant, and the leachate is purified by impurities removal, and lithium carbonate is prepared by soda ash precipitation. The main defects of this method are large consumption of sulfuric acid and oxidant, high-temperature leaching, large amount of washing water after leaching, high leaching impurities, difficulty in impurity removal, and uneven loss of Fe and P in the leached slag, which has a great impact on the subsequent recovery of iron phosphate.

[0005] As attached Figure 2 As shown, lithium iron phosphate powder positive electrode material + sulfate roasting method: waste lithium iron phosphate positive electrode material is mixed with concentrated sulfate, roasted at high temperature, and lithium is extracted by water. After the leaching solution is impurities removed, lithium carbonate is prepared by soda ash precipitation. The main drawback of this method is that after the sulfate is mixed with the lithium iron phosphate positive electrode material, it needs to be roasted at high temperature, which has high cost and great impact on the environment. At the same time, in order to improve the recovery rate of lithium metal, a large amount of excess sulfate needs to be added, resulting in an increase in the subsequent cost of recovering sulfate.

[0006] Therefore, in order to solve the above problems, a method for preparing lithium carbonate using waste lithium iron phosphate positive electrode material is proposed. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing lithium carbonate using waste lithium iron phosphate positive electrode material, the steps comprising:

[0008] Step 1: Powdering and screening the waste lithium iron phosphate cathode material, fully mixing the powdered waste lithium iron phosphate cathode material with concentrated sulfuric acid, and heap leaching for 6-12 hours;

[0009] Step 2: Primary leaching: The raw material comes from the secondary leaching residue, and the acid is adjusted to pH 1.5-2.0, sodium ferrate is added, and leaching is carried out under stirring at 60-70°C. The leachate is used as the secondary leaching liquid, and the leaching residue is recovered for the preparation of iron phosphate raw materials;

[0010] Step 3: Secondary leaching: The solution comes from the primary leaching solution, and the heap leaching raw material is used to consume acid, and the end point pH is controlled at 3.0-3.5. Sodium ferrate is added, and leaching is carried out under stirring at 45-55°C. The leached residue is used as the primary leaching raw material. Fe and P are not leached during the leaching process. The leachate is directly adjusted to pH>10.5 for precipitation of lithium carbonate;

[0011] Step 4: Add soda ash solution to the alkaline lithium-containing solution obtained from the secondary leaching solution at a temperature of >90°C to prepare a battery-grade lithium carbonate product.

[0012] Preferably, in the step 1, the powder of the waste lithium iron phosphate positive electrode material is controlled to have a particle size of >80% within 200 mesh.

[0013] Preferably, in the step 1, the waste lithium iron phosphate positive electrode material is mixed with concentrated sulfuric acid, and the amount of mixed acid is controlled to be 3-5% of the lithium content.

[0014] Preferably, the amount of sodium ferrate added in step 2 is 0.3-0.5 times the theoretical content.

[0015] Preferably, the amount of sodium ferrate added in step three is 0.05-0.1 times the theoretical content.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The invention mixes concentrated sulfuric acid with waste lithium iron phosphate positive electrode materials for heap leaching, utilizes the oxidizing property of concentrated sulfuric acid to preferentially partially oxidize and improve the leaching rate during the heap leaching process, and reduces the sulfuric acid consumption at the same time; utilizes the strong oxidizing property of sodium ferrate to reduce the amount of oxidant used; and at the same time, increases the oxidation potential of the leaching process during the leaching process, reduces the leaching temperature and stirring time, and improves the lithium metal leaching rate. The total lithium metal leaching rate is greater than 99.5%. At the same time, sodium ferrate is a multifunctional, efficient and non-toxic new green water treatment agent, has excellent oxidative bleaching, efficient flocculation, and excellent bactericidal effects, can quickly and effectively remove odors in sludge, and degrade organic matter in the solution.

[0018] The present invention realizes the preparation of lithium phosphate through two-stage leaching. Phosphorus and iron are hardly leached during the leaching process, which reduces the impurity removal link, reduces the operation cost, improves the quality of leached slag iron phosphate, provides good raw materials for the preparation of iron phosphate, and no hazardous waste is generated in the whole process. The leached slag is the raw material for preparing iron phosphate, and calcium carbonate can be recycled for acid adjustment, thereby truly realizing harmless treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the traditional sulfuric acid + oxidation leaching method for preparing lithium carbonate;

[0020] Figure 2 This is a schematic diagram of the traditional lithium iron phosphate powder positive electrode material + sulfate roasting method to prepare lithium carbonate;

[0021] Figure 3 It is a schematic diagram of preparing lithium carbonate according to the present invention;

[0022] Figure 4 This is a schematic diagram of the analysis of waste lithium iron phosphate powder according to Example 1 of the present invention;

[0023] Figure 5 This is a schematic diagram of the first batch of leached residue data of Example 1 of the present invention;

[0024] Figure 6 is a schematic diagram of data of the second batch of leachate of Example 1 of the present invention;

[0025] Figure 7 is a schematic diagram of filtrate data of Example 1 of the present invention;

[0026] Figure 8 is a schematic diagram of the lithium carbonate product obtained in Example 1 of the present invention;

[0027] Fig. 9 This is a schematic diagram of the analysis of waste lithium iron phosphate powder according to Example 2 of the present invention;

[0028] Fig.10 This is a schematic diagram of the first batch of leached residue data of Example 2 of the present invention;

[0029] Fig.11 is a schematic diagram of data of the second batch of leachate of Example 2 of the present invention;

[0030] Fig.12 is a schematic diagram of filtrate data of Example 2 of the present invention;

[0031] Fig.13 This is a schematic diagram of the lithium carbonate product obtained in Example 2 of the present invention;

[0032] Fig.14 This is a schematic diagram of the analysis of waste lithium iron phosphate powder according to Example 3 of the present invention;

[0033] Fig.15 This is a schematic diagram of the first batch of leached residue data of Example 3 of the present invention;

[0034] Fig.16 is a schematic diagram of data of the second batch of leachate of Example 3 of the present invention;

[0035] Fig.17is a schematic diagram of filtrate data of Example 3 of the present invention;

[0036] Fig.18 This is a schematic diagram of the lithium carbonate product obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] As attached Figure 3 As shown, the present invention provides a method for preparing lithium carbonate using waste lithium iron phosphate positive electrode materials, characterized in that the steps include:

[0039] Step 1: Powder the waste lithium iron phosphate cathode material and sieve it, and control the powder to have a particle size of >80% at 200 mesh. Fully mix the waste lithium iron phosphate cathode material after pulverization with concentrated sulfuric acid, and control the amount of mixed acid to be 3-5% of the lithium content, and heap leaching for 6-12 hours;

[0040] Step 2: Primary leaching: The raw material comes from the secondary leaching residue, and the acid is adjusted to pH 1.5-2.0, and sodium ferrate is added. The amount of sodium ferrate added is 0.3-0.5 times the theoretical content. The mixture is stirred and leached at 60-70°C. The leaching solution is used as the secondary leaching solution, and the leaching residue is recovered for the preparation of ferric phosphate raw materials;

[0041] Step 3: Secondary leaching: The solution comes from the primary leaching solution, and the heap leaching raw material is used to consume acid. The end point pH is controlled at 3.0-3.5, and sodium ferrate is added. The addition amount of sodium ferrate is 0.05-0.1 times of the theoretical content. The leaching is stirred at 45-55°C. The leached residue is used as the primary leaching raw material. Fe and P are not leached during the leaching process. The leaching solution is directly adjusted to pH>10.5 for precipitation of lithium carbonate;

[0042] Step 4: Add soda ash solution to the alkaline lithium-containing solution obtained from the secondary leaching solution at a temperature of >90°C to prepare a battery-grade lithium carbonate product.

[0043] Embodiment 1:

[0044] Step 1: Take the waste lithium iron phosphate powder from a factory, the particle size is 80.5% controlled at 200 mesh 200Kg for use, at 1.0m 3 Add 200kg of waste lithium iron phosphate powder into the PE drum. Figure 4The content of waste lithium iron phosphate powder was obtained by testing as shown, stirring was started, 8 kg of concentrated sulfuric acid was slowly added, stirring was carried out for 30 minutes, and heap leaching was carried out for 8 hours.

[0045] Step 2: At 1.0m 3 Add 0.4m3 of PE into the tank 3 Tap water, slowly add 100 kg of lithium iron phosphate powder to complete the heap leaching, adjust the acid to PH1.5-2.0, slowly add 3 kg of sodium ferrate, continue for 2.5 hours, raise the temperature to 65 ° C, filter, and store the first batch of leachate separately. Figure 5 As shown, the Li content in the leached residue was 0.1%.

[0046] Step 3: At 1.0m 3 In the PE tank, add the leachate from step 2, add the remaining 100Kg, heap leaching waste lithium iron phosphate powder, slowly add 0.3Kg of sodium ferrate, heat to 50℃, end point PH3.1, as shown in the attached Figure 6 As shown, the leaching solution contains Fe: 0.016 g / l, P: 0.023 g / l, indicating that Fe and P are hardly leached.

[0047] Step 4: Add 1.0m 3 PE tank, equipped with heating coil, start stirring, raise the temperature to 75℃, add sodium hydroxide and a small amount of sodium carbonate to adjust the acidity to 10.5, filter, and set aside the filtrate. Figure 7 As shown, the filtrate data was obtained;

[0048] Step 4: Add 1.5% of theoretical amount of soda ash, and precipitate lithium carbonate product at >90℃. The data of lithium carbonate product is as attached. Figure 8 shown.

[0049] Embodiment 2:

[0050] Step 1: Take the waste lithium iron phosphate powder from a factory, the particle size of which is 83.5% controlled at 200 mesh and set aside 300 kg of waste lithium iron phosphate powder at 1.0 m 3 Add 300kg of waste lithium iron phosphate powder into the PE drum. Fig. 9 The content of waste lithium iron phosphate powder was obtained by testing as shown, stirring was started, 12 kg of concentrated sulfuric acid was slowly added, stirring was carried out for 30 minutes, and heap leaching was carried out for 10 hours;

[0051] Step 2: At 1.0m 3 Add 0.6m into the PE tank 3 Tap water, slowly add 150Kg of lithium iron phosphate powder to complete the heap leaching, adjust the acid to PH1.5-2.0, slowly add 2.5Kg of sodium ferrate, continue for 2.5 hours, heat to 70℃, filter, and store the first batch of leachate separately. Fig.10 As shown, the Li content in the leached residue was 0.08%;

[0052] Step 3: At 1.0m 3 In the PE tank, add the leachate from step 2, add the remaining 150 kg, heap leaching waste lithium iron phosphate powder, slowly add 0.3 kg of sodium ferrate, heat to 55 ° C, end point PH 3.45, as shown in the attached Fig.11 As shown, Fe: 0.01 g / l, P: 0.01 g / l in the leaching solution, indicating that Fe and P are almost not leached;

[0053] Step 4: Add 1.0m 3 PE tank, equipped with heating coil, start stirring, raise the temperature to 75℃, add sodium hydroxide and a small amount of sodium carbonate to adjust the acidity to 10.5, filter, and set the filtrate aside to obtain the attached Fig.12 Filtrate data shown;

[0054] Step 4: Add 1.5% theoretical amount of soda ash, and precipitate lithium carbonate product at >90℃. The data of lithium carbonate product is as attached. Fig.13 shown.

[0055] Embodiment 3:

[0056] Step 1: Take the waste lithium iron phosphate powder from a factory, the particle size of which is 83.5% controlled at 200 mesh and set aside 400 kg of waste lithium iron phosphate powder, as shown in the attached Fig.14 The test results show that the content of waste lithium iron phosphate powder is 1.0m 3 Add 400kg of waste lithium iron phosphate powder into the PE drum, start stirring, slowly add 20kg of concentrated sulfuric acid, stir for 30min, and heap leaching for 10h;

[0057] Step 2: At 1.0m 3 Add 0.8m into the PE tank 3 Tap water, slowly add 200Kg of lithium iron phosphate powder to complete the heap leaching, adjust the acid to PH1.5-2.0, slowly add 4.5Kg of sodium ferrate, continue for 2.5 hours, heat to 70℃, filter, and store the first batch of leachate separately. Fig.15 As shown, the Li content in the leached residue was 0.08%;

[0058] Step 3: At 1.0m 3 In the PE tank, add the leachate from step 2, add the remaining 200 kg, heap leaching waste lithium iron phosphate powder, slowly add 0.5 kg of sodium ferrate, heat to 55 ° C, end point PH345, as shown in the attached Fig.16 As shown, Fe: 0.01 g / l, P: 0.01 g / l in the leachate, indicating that Fe and P are almost not leached;

[0059] Step 4: Add 1.0m 3PE tank, equipped with heating coil, start stirring, raise the temperature to 75℃, add sodium hydroxide and a small amount of sodium carbonate to adjust the acidity to 10.5, filter, and set aside the filtrate. Fig.17 As shown, the filtrate data was obtained by detection;

[0060] Step 4: Add 1.5% theoretical amount of soda ash, and precipitate lithium carbonate product at >90℃. The data of lithium carbonate product is as attached. Fig.18 shown.

[0061] Utilizing the technical solution described in the present invention, or those skilled in the art designing a similar technical solution inspired by the technical solution of the present invention to achieve the above-mentioned technical effects, all fall within the protection scope of the present invention.

Claims

1. A method for preparing lithium carbonate using waste lithium iron phosphate positive electrode material, characterized in that: include: Step 1: Powdering and screening the waste lithium iron phosphate cathode material, fully mixing the powdered waste lithium iron phosphate cathode material with concentrated sulfuric acid, and heap leaching for 6-12 hours; Step 2: Primary leaching: The raw material comes from the secondary leaching residue, and the acid is adjusted to pH 1.5-2.0, sodium ferrate is added, and leaching is carried out under stirring at 60-70°C. The leachate is used as the secondary leaching liquid, and the leaching residue is recovered for the preparation of iron phosphate raw materials; Step 3: Secondary leaching: The solution comes from the primary leaching solution, and the heap leaching raw material is used to consume acid, and the end point pH is controlled at 3.0-3.

5. Sodium ferrate is added, and leaching is carried out under stirring at 45-55°C. The leached residue is used as the primary leaching raw material. Fe and P are not leached during the leaching process. The leachate is directly adjusted to pH>10.5 for precipitation of lithium carbonate; Step 4: Add soda ash solution to the alkaline lithium-containing solution obtained from the secondary leaching solution at a temperature of >90°C to prepare a battery-grade lithium carbonate product.

2. The method for preparing lithium carbonate using waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: In the step 1, the powder of the waste lithium iron phosphate positive electrode material is controlled to have a particle size of >80% within 200 mesh.

3. The method for preparing lithium carbonate using waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: In the step 1, the waste lithium iron phosphate positive electrode material is mixed with concentrated sulfuric acid, and the amount of mixed acid is controlled to be 3-5% of the lithium content.

4. The method for preparing lithium carbonate using waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: The amount of sodium ferrate added in step 2 is 0.3-0.5 times the theoretical content.

5. The method for preparing lithium carbonate using waste lithium iron phosphate positive electrode material according to claim 1, characterized in that: The amount of sodium ferrate added in step 3 is 0.05-0.1 times the theoretical content.

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