METHOD FOR RECOVERING VALUABLE METALS FROM POSITIVE ELECTRODE OF WASTE LITHIUM IRON PHOSPHATE

Abstract

Provided is a method for recovering valuable metals from a positive electrode of waste lithium iron phosphate. The method includes: subjecting a waste lithium iron phosphate battery to discharging and disassembly; subjecting a lithium iron phosphate positive plate obtained by the disassembly to breaking, followed by high temperature treatment; uniformly mixing a product obtained by the high temperature treatment with a carbon material, and roasting a mixture in a high-purity Cl.sub.2 atmosphere; subjecting a gas phase product obtained by the roasting to fractional quenching and condensation to recover ferric chloride and aluminum chloride separately; and subjecting a solid phase product obtained by the roasting to water leaching and filtration to obtain a lithium chloride aqueous solution, and then adding sodium carbonate to precipitate lithium carbonate. As a one-step carbothermal chlorination method is adopted in combination with a two-stage quenching and condensation process in the present invention, the use of acidic solutions during recovery of valuable metals from the lithium iron phosphate positive electrode can be avoided, and the use of large amounts of alkaline solutions or extraction agents to separate and recover chlorides step by step is also not required. The method of the present invention has the advantages of a high metal recovery rate, a low comprehensive cost and good economic benefits, social benefits and environmental protection benefits.

Claims

1. A method for recovering valuable metals from a positive electrode of waste lithium iron phosphate, sequentially comprising the following steps: (1) subjecting a waste lithium iron phosphate battery to discharging and disassembly to obtain a lithium iron phosphate positive plate; (2) subjecting the lithium iron phosphate positive plate to breaking, followed by high temperature treatment in an air atmosphere; (3) uniformly mixing a product obtained by the high temperature treatment with a carbon material by ball milling, then transferring a mixture to a sintering device, introducing high-purity Cl.sub.2 after vacuumizing the sintering device, and heating and roasting the mixture in the Cl.sub.2 atmosphere; (4) enabling a gas phase product produced in the roasting process to sequentially pass through a quenching and condensation separation device 1 and a quenching and condensation separation device 2; introducing SiCl.sub.4 that is preheated to 220-240 C. and flows backward with the gas phase product into a heat exchange tube of the quenching and condensation separation device 1, and recovering condensed FeCl.sub.3 in a deposition chamber of the quenching and condensation separation device 1; and introducing SiCl.sub.4 that is preheated to 100-120 C. and flows backward with the gas phase product into a heat exchange tube of the quenching and condensation separation device 2, and recovering condensed AlCl.sub.3 in a deposition chamber of the quenching and condensation separation device 2; and (5) subjecting a solid phase product obtained by the roasting in step (3) to water leaching, stirring and filtration to obtain a LiCl aqueous solution, and then adding sodium carbonate into the LiCl aqueous solution to recover and precipitate Li.sub.2CO.sub.3.

2. The method according to claim 1, wherein in step (2), the lithium iron phosphate positive plate has an average particle size of equal to or less than 3 mm after the breaking.

3. The method according to claim 1, wherein in step (2), the high temperature treatment is performed at a heating rate of 5-10 C./min and a temperature of 400-600 C., and the temperature is maintained for 3-6 h.

4. The method according to claim 1, wherein in step (3), the carbon material comprises at least one of graphite, carbon black, carbon fibers, carbon nanotubes and amorphous carbon.

5. The method according to claim 1, wherein in step (3), the mass ratio of the product obtained by the high temperature treatment to the carbon material is 10:1 to 5:1.

6. The method according to claim 1, wherein in step (3), the high-purity Cl.sub.2 is introduced at a rate of 10-50 mL/min.

7. The method according to claim 1, wherein in step (3), the roasting is performed in two stages; the roasting in the first stage is performed at a heating rate of 3-5 C./min and a temperature of 180-300 C., and the temperature is maintained for 1-3 h; and the roasting in the second stage is performed at a heating rate of 5-10 C./min and a temperature of 350-550 C., and the temperature is maintained for 3-6 h.

8. The method according to claim 1, wherein in step (4), before introduced into the heat exchange tube of the quenching and condensation separation device 2, the SiCl.sub.4 is preheated to 100-120 C. first, and the SiCl.sub.4 is introduced into the heat exchange tube of the quenching and condensation separation device 2 at a flow rate of 5-10 mL/min.

9. The method according to claim 1, wherein in step (4), before introduced into the heat exchange tube of the quenching and condensation separation device 1, the SiCl.sub.4 is preheated to 220-240 C. first, and the SiCl.sub.4 is introduced into the heat exchange tube of the quenching and condensation separation device 1 at a flow rate of 5-10 mL/min.

10. The method according to claim 1, wherein in step (5), water used in the water leaching is deionized water; and the water leaching and the stirring are performed for 1-4 h.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a flow chart of recovering valuable metals from a positive electrode of waste lithium iron phosphate used in an embodiment of the present invention.

[0024] FIG. 2 is a schematic diagram of recovering valuable metals from a positive electrode of waste lithium iron phosphate used in an embodiment of the present invention.

[0025] FIG. 3 is a schematic diagram of a quenching and condensation separation device of the present invention.

[0026] Illustration symbols are as follows: [0027] 1, 2: quenching and condensation separation device; [0028] 3, 4: preheating device; [0029] 5: roasted solid phase product; [0030] 6: heat exchange tube of a quenching and condensation separation device; and [0031] 7: deposition chamber of a quenching and condensation separation device.

DESCRIPTION OF THE EMBODIMENTS

[0032] The present invention is further described below in combination with examples and comparative examples.

Example 1

[0033] A method in the present example includes the following steps.

[0034] A waste lithium iron phosphate battery was discharged and disassembled to obtain a lithium iron phosphate positive plate. The obtained lithium iron phosphate positive plate was directly broken to obtain particles with an average particle size of equal to or less than 3 mm, and then the material was placed in a Muffle furnace for high temperature treatment at 500 C. at a heating rate of 5 C./min for 3 h in an air atmosphere to remove a polymer binder and a residual electrolyte lithium salt. A product obtained by the high temperature treatment was uniformly mixed with graphite at a mass ratio of 5:1 by ball milling, and then a mixed material was transferred into a tube furnace. After the tube furnace was vacuumized, high-purity Cl.sub.2 was introduced at a flow rate of 30 mL/min, and the mixed material was heated and roasted in the Cl.sub.2 atmosphere, where the roasting process was carried out in two stages: the mixed material was heated to 300 C. at a heating rate of 5 C./min during the roasting in the first stage, and the temperature was maintained for 1 h; and the mixed material was heated to 550 C. at a heating rate of 5 C./min during the roasting in the second stage, and the temperature was maintained for 3 h.

[0035] A gas phase product produced in the roasting process was enabled to sequentially pass through a quenching and condensation separation device 1 and a quenching and condensation separation device 2. SiCl.sub.4 that was preheated to 220 C. and flowed backward with the gas phase product was introduced into a heat exchange tube of the quenching and condensation separation device 1 at a flow rate of 5 mL/min, and condensed FeCl.sub.3 was SiCl.sub.4 that was preheated to 120 C. and flowed backward with the gas phase product was introduced into a heat exchange tube of the quenching and condensation separation device 2 at a flow rate of 5 mL/min, and condensed AlCl.sub.3 was recovered in a deposition chamber of the quenching and condensation separation device 2.

[0036] A solid phase product obtained by the roasting was subjected to water leaching with deionized water and stirring for 1 h, followed by suction filtration to obtain a LiCl aqueous solution, and then sodium carbonate was added into the LiCl aqueous solution to recover and precipitate Li.sub.2CO.sub.3.

Example 2

[0037] A method in the present example includes the following steps.

[0038] A waste lithium iron phosphate battery was discharged and disassembled to obtain a lithium iron phosphate positive plate. The obtained lithium iron phosphate positive plate was directly broken to obtain particles with an average particle size of equal to or less than 3 mm, and then the material was placed in a Muffle furnace for high temperature treatment at 400 C. at a heating rate of 10 C./min for 6 h in an air atmosphere to remove a polymer binder and a residual electrolyte lithium salt. A product obtained by the high temperature treatment was uniformly mixed with carbon black at a mass ratio of 10:1 by ball milling, and then a mixed material was transferred into a tube furnace. After the tube furnace was vacuumized, high-purity Cl.sub.2 was introduced at a flow rate of 10 mL/min, and the mixed material was heated and roasted in the Cl.sub.2 atmosphere, where the roasting process was carried out in two stages: the mixed material was heated to 180 C. at a heating rate of 3 C./min during the roasting in the first stage, and the temperature was maintained for 3 h; and the mixed material was heated to 450 C. at a heating rate of 5 C./min during the roasting in the second stage, and the temperature was maintained for 3 h.

[0039] A gas phase product produced in the roasting process was enabled to sequentially pass through a quenching and condensation separation device 1 and a quenching and condensation separation device 2. SiCl.sub.4 that was preheated to 240 C. and flowed backward with the gas phase product was introduced into a heat exchange tube of the quenching and condensation separation device 1 at a flow rate of 10 mL/min, and condensed FeCl.sub.3 was SiCl.sub.4 that was preheated to 100 C. and flowed backward with the gas phase product was introduced into a heat exchange tube of the quenching and condensation separation device 2 at a flow rate of 10 mL/min, and condensed AlCl.sub.3 was recovered in a deposition chamber of the quenching and condensation separation device 2.

[0040] A solid phase product obtained by the roasting was subjected to water leaching with deionized water and stirring for 4 hours, followed by suction filtration to obtain a LiCl aqueous solution, and then sodium carbonate was added into the LiCl aqueous solution to recover and precipitate Li.sub.2CO.sub.3.

Example 3

[0041] A method in the present example includes the following steps.

[0042] A waste lithium iron phosphate battery was discharged and disassembled to obtain a lithium iron phosphate positive plate. The obtained lithium iron phosphate positive plate was directly broken to obtain particles with an average particle size of equal to or less than 3 mm, and then the material was placed in a Muffle furnace for high temperature treatment at 600 C. at a heating rate of 10 C./min for 3 h in an air atmosphere to remove a polymer binder and a residual electrolyte lithium salt. A product obtained by the high temperature treatment was uniformly mixed with carbon fibers at a mass ratio of 10:1 by ball milling, and then a mixed material was transferred into a tube furnace. After the tube furnace was vacuumized, high-purity Cl.sub.2 was introduced at a flow rate of 50 mL/min, and the mixed material was heated and roasted in the Cl.sub.2 atmosphere, where the roasting process was carried out in two stages: the mixed material was heated to 250 C. at a heating rate of 5 C./min during the roasting in the first stage, and the temperature was maintained for 2 h; and the mixed material was heated to 350 C. at a heating rate of 10 C./min during the roasting in the second stage, and the temperature was maintained for 6 h.

[0043] A gas phase product produced in the roasting process was enabled to sequentially pass through a quenching and condensation separation device 1 and a quenching and condensation separation device 2. SiCl.sub.4 that was preheated to 230 C. and flowed backward with the gas phase product was introduced into a heat exchange tube of the quenching and condensation separation device 1 at a flow rate of 10 mL/min, and condensed FeCl.sub.3 was SiCl.sub.4 that was preheated to 110 C. and flowed backward with the gas phase product was introduced into a heat exchange tube of the quenching and condensation separation device 2 at a flow rate of 10 mL/min, and condensed AlCl.sub.3 was recovered in a deposition chamber of the quenching and condensation separation device 2.

[0044] A solid phase product obtained by the roasting was subjected to water leaching with deionized water and stirring for 3 hours, followed by suction filtration to obtain a LiCl aqueous solution, and then sodium carbonate was added into the LiCl aqueous solution to recover and precipitate Li.sub.2CO.sub.3.

Comparative Example

[0045] A waste lithium iron phosphate battery was discharged and disassembled to obtain a lithium iron phosphate positive plate. The obtained lithium iron phosphate positive plate was directly broken to obtain particles with an average particle size of equal to or less than 3 mm, and then the material was placed in a Muffle furnace for high temperature treatment at 500 C. at a heating rate of 5 C./min for 3 h in an air atmosphere to remove a polymer binder and a residual electrolyte lithium salt. A product obtained by the high temperature treatment was uniformly mixed with graphite at a mass ratio of 5:1 by ball milling, and then a mixed material was placed in a tube furnace. After the tube furnace was vacuumized, high-purity Cl.sub.2 was introduced at a flow rate of 30 mL/min, and the mixed material was heated and roasted in the Cl.sub.2 atmosphere, where the mixed material was heated to 300 C. at a heating rate of 5 C./min in the roasting process, and the temperature was maintained for 4 h.

[0046] A gas phase product produced in the roasting process was enabled to pass through a condensation device, and AlCl.sub.3 was recovered in the condensation device.

[0047] A solid phase product obtained by the roasting was subjected to water leaching with deionized water and stirring for 1 h, followed by suction filtration to obtain an aqueous solution of a mixed metal chloride salt containing LiCl and FeCl.sub.3, then ammonia was added into the aqueous solution of a mixed metal chloride salt to adjust the pH of the solution to 3.5, and the solution was subjected to suction filtration to obtain a ferric hydroxide precipitate and a filtrate.

[0048] Then, sodium carbonate was added into the filtrate to recover and precipitate Li.sub.2CO.sub.3.

Test of the Recovery Rate:

[0049] The recovery rate is calculated by the following formula: recovery rate=actual mass of a product/theoretical mass of the product100%, in which the theoretical mass of the product is obtained by determining the content of various elements in a broken product of a lithium iron phosphate positive plate using an inductively coupled plasma (ICP) method and then calculating the theoretical mass value of the product that is completely converted thereto.

[0050] Test results of the recovery rate of various elements in Examples 1-3 and Comparative Example are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Li (%) Fe (%) Al (%) Example 1 99.3 97.2 95.6 Example 2 98.6 97.8 94.3 Example 3 98.8 96.9 96.2 Comparative Example 71.6 82.6 94.5

[0051] As can be seen from Table 2, compared with Comparative Example, Examples 1-3 have the advantage that the recovery rate of Li can be significantly improved as a mixed chloride salt of Li and Fe is not required to be recovered step by step. In addition, the recovery rate of the metallic Fe and the metallic in Examples 1-3 is higher, indicating that the recovery purity of lithium carbonate in Examples 1-3 is also higher than that in Comparative Example.