Method for removing fluorine from ferrophosphorus acid solution in lithium iron phosphate battery recovery process

Abstract

The invention belongs to the technical field of ferrophosphorus recovery, and provides a method for removing fluorine from a ferrophosphorus acid solution in a lithium iron phosphate battery recovery process. The method comprises the following steps: introducing a ferrophosphorus acid solution into a device, then introducing air, nitrogen, argon, helium and other gases which do not react with sulfuric acid, phosphoric acid, ferric ions and water, enabling water to enter a gas phase from the solution through gas-liquid contact with the ferrophosphorus acid solution, and enabling HF to enter the gas phase along with the water through hydrogen-bond interaction force between the HF and water molecules. According to the method, the total amount of fluorine in the ferrophosphorus solution is reduced, the concentration is not changed, no impurity component is introduced, and the obtained acid-containing tail gas can be recycled and enriched to obtain an HF aqueous solution or a fluoride salt aqueous solution.

Description

Technical Field

[0001] The invention relates to the technical field of ferrophosphide recovery, and in particular to a method for removing fluorine from a ferrophosphide acid solution in a lithium iron phosphate battery recovery process. Background Art

[0002] Lithium iron phosphate wet batteries contain a large amount of fluorine, which can cause serious corrosion to metal equipment. In the wet process of recycling lithium iron phosphate batteries, part of the fluorine will enter the lithium recovery process system, and part of the fluorine will enter the ferrophosphorus recovery process system. The mainstream of the ferrophosphorus recovery process is to prepare battery-grade ferrophosphate. The ferrophosphorus slag left after lithium extraction is first dissolved in sulfuric acid, then precipitated and aged to obtain dihydrate ferrophosphate, and finally flashed and calcined. During calcination, fluorine will escape from the solid phase to the gas phase, thereby corroding the kiln.

[0003] At present, most of the defluorination methods in lithium recovery process are defluorination by adsorbent and precipitation. The only defluorination process in ferrophosphorus recovery process is defluorination by ferrophosphoric acid solution. However, the solution is highly acidic, and the defluorination adsorbent or precipitant cannot function normally in a strong acid environment. There is no effective defluorination method in ferrophosphorus recovery process.

[0004] Therefore, it is necessary to develop a method for defluorinating ferrophosphite solution in the recycling process of lithium iron phosphate batteries. Summary of the invention

[0005] The purpose of the present invention is to provide a method for removing fluorine from ferrophosphite solution in a lithium iron phosphate battery recycling process in view of the deficiencies in the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for defluorinating a ferrophosphite solution in a lithium iron phosphate battery recycling process, comprising the following steps:

[0008] A ferrophosphite solution is added to the bottom of the reaction device, and the ferrophosphite solution at the bottom is pumped to the top for spraying. Gas is introduced from the bottom of the reaction device, and the gas blows out the moisture in the ferrophosphite solution through gas-liquid contact. The moisture contains fluorine element, and the ferrophosphite solution after defluorination is obtained.

[0009] Preferably, the gas comprises one or more of air, nitrogen, argon and helium.

[0010] Preferably, the concentration of hydrogen ions in the ferrophosphite solution is ≤5 mol / L.

[0011] Preferably, the temperature of the ferrophosphite solution is 0 to 100°C.

[0012] Preferably, the temperature of the gas is 0 to 100°C.

[0013] Preferably, the reaction apparatus comprises a packed tower, a plate tower or a stirred reactor.

[0014] Preferably, the volume of the ferrophosphite solution after defluorination is 1 / 3 to 2 / 3 of the volume of the ferrophosphite solution.

[0015] Preferably, the gas blows out the water in the ferrophosphite solution to obtain tail gas containing fluorine element, and the tail gas is absorbed by water or alkali solution. The tail gas is absorbed by water to obtain hydrofluoric acid, and absorbed by alkali solution to obtain fluoride salt solution.

[0016] Preferably, the alkali solution comprises sodium hydroxide solution, ammonia water, potassium hydroxide solution or calcium hydroxide solution.

[0017] The beneficial effects of the present invention include:

[0018] The invention introduces a ferrophosphite solution into a device, and then introduces inert gases such as air, nitrogen, argon, helium, etc. that do not react with sulfuric acid, phosphoric acid, trivalent iron ions and water, and allows water to enter the gas phase from the solution through gas-liquid contact with the ferrophosphite solution. The hydrogen bond force between HF and water molecules allows HF to enter the gas phase together with the water. The method of the invention reduces the total amount of fluorine elements in the solution while keeping the concentration unchanged, and does not introduce any impurity components. The obtained acid-containing tail gas can be recycled and enriched to obtain an HF aqueous solution or a fluoride salt aqueous solution. DETAILED DESCRIPTION

[0019] The present invention provides a method for defluorinating a ferrophosphite solution in a lithium iron phosphate battery recycling process, comprising the following steps:

[0020] A ferrophosphite solution is added to the bottom of the reaction device, and the ferrophosphite solution at the bottom is pumped to the top for spraying. Gas is introduced from the bottom of the reaction device, and the gas blows out the moisture in the ferrophosphite solution through gas-liquid contact. The moisture contains fluorine element, and the ferrophosphite solution after defluorination is obtained.

[0021] In the present invention, the gas preferably comprises one or more of air, nitrogen, argon and helium.

[0022] In the present invention, the concentration of hydrogen ions in the ferrophosphite solution is preferably ≤5 mol / L, and more preferably 1 to 2 mol / L.

[0023] In the present invention, the temperature of the ferrophosphite solution is preferably 0 to 100°C, more preferably 10 to 50°C, and even more preferably 20 to 35°C.

[0024] In the present invention, the temperature of the gas is preferably 0 to 100°C, more preferably 20 to 50°C, and even more preferably 25 to 30°C.

[0025] In the present invention, it is preferred that the gas is introduced from the bottom side of the reaction device by means of a blower, and the gas does not react with sulfuric acid, phosphoric acid, trivalent iron ions and water.

[0026] In the present invention, the gas blows out the water containing fluorine in the ferrophosphite solution by gas-liquid contact, thereby reducing the total amount of fluorine in the ferrophosphite solution.

[0027] In the present invention, the reaction apparatus preferably comprises a packed tower, a plate tower or a stirred reactor.

[0028] In the present invention, the volume of the ferrophosphite solution after defluorination is preferably 1 / 3 to 2 / 3 of the volume of the ferrophosphite solution, and more preferably 1 / 2 of the volume of the ferrophosphite solution.

[0029] In the present invention, the gas blows out the water in the ferrophosphite solution to obtain tail gas containing fluorine element, and the tail gas is preferably absorbed by water or alkali solution, wherein the tail gas is absorbed by water to obtain hydrofluoric acid, and absorbed by alkali solution to obtain fluoride salt solution.

[0030] In the present invention, the alkali solution preferably comprises sodium hydroxide solution, ammonia water, potassium hydroxide solution or calcium hydroxide solution.

[0031] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0032] Example 1

[0033] At normal pressure, add 1m 3 The ferrophosphite solution (hydrogen ion concentration is 1 mol / L) is pumped to the bottom of the tower at a rate of 1m 3 / h flow rate is pumped to the top of the tower for spraying, and the temperature of the ferrophosphite solution is maintained at 20℃ through a heat exchanger. The air is blown by a fan at a speed of 1m 3 / h gas flow rate from the bottom of the tower side into the 25 ℃ air, through the gas-liquid contact, moisture into the air, HF and water molecules hydrogen bonding effect so that HF ​​and water into the air together, so that the water in the ferrophosphite solution (including HF) blow out until 1m bottom of the tower 3 The remaining 0.5m of ferrophosphite solution 3 The blowing time is 4 hours. The tail gas is collected and absorbed with water to obtain hydrofluoric acid.

[0034] The element contents in the iron phosphate solution before and after ventilation in this example are shown in Table 1.

[0035] Table 1 Element contents in ferrophosphite solution before and after blowing in Example 1

[0036] Fe(g / L) P(g / L) F(g / L) S(g / L) Before blowing 51.3 28.5 0.05516 52.9 After blowing 101.6 55.2 0.05492 106.3

[0037] As shown in Table 1, the F element concentration of the ferrophosphite solution remains almost unchanged after blowing, but the total amount is halved, and about 50% of the fluorine is removed.

[0038] Example 2

[0039] At normal pressure, add 1m 3 The ferrophosphite solution (hydrogen ion concentration is 1.5 mol / L) is pumped to the bottom of the tower at a speed of 1m 3 / h flow rate is pumped to the top of the tower for spraying, and the temperature of the ferrophosphite solution is maintained at 30℃ through a heat exchanger. The air is blown by a fan at a speed of 1m 3 / h gas flow rate from the bottom of the tower side into the 20 ℃ air, through the gas-liquid contact mode, moisture into the air, HF and water molecules hydrogen bonding effect so that HF ​​and water into the air together, so as to blow out the water in the ferrophosphate solution (including HF), until 1m bottom of the tower 3 The remaining 0.5m of ferrophosphite solution 3 The tail gas is collected and absorbed with water to obtain hydrofluoric acid.

[0040] In this embodiment, air is introduced to make 1m 3 The remaining 0.5m of ferrophosphite solution 3 The blowing time is 1 hour less than that in Example 1. The element contents in the ferric phosphate solution before and after aeration in this example are shown in Table 2.

[0041] Table 2 Element contents in ferrophosphite solution before and after blowing in Example 2

[0042] Fe(g / L) P(g / L) F(g / L) S(g / L) Before blowing 57.39 32.61 0.05146 59.19 After blowing 113.58 65.12 0.04938 119.01

[0043] It can be seen from Table 2 that the F element concentration of the ferrophosphite solution remains almost unchanged after blowing, but the total amount is halved, and about 50% of the fluorine is removed.

[0044] Example 3

[0045] At normal pressure, add 1m 3 The ferrophosphite solution (hydrogen ion concentration is 2 mol / L) is pumped to the bottom of the tower at a rate of 1m 3 / h flow rate is pumped to the top of the tower for spraying, and the temperature of the ferrophosphite solution is maintained at 35℃ through a heat exchanger. The air is blown by a fan at a speed of 1m 3 Air is introduced from the side of the tower bottom at a gas flow rate of / h. The air temperature is maintained at 45°C through a heat exchanger. Water enters the air through gas-liquid contact. The hydrogen bonding between HF and water molecules causes HF to enter the air along with the water, thereby blowing out the water (including HF) in the ferrophosphite solution until 1m below the tower bottom. 3 The remaining 0.5m of ferrophosphite solution 3The tail gas was collected and absorbed by a 10 g / L sodium hydroxide aqueous solution to obtain a sodium fluoride aqueous solution.

[0046] In this embodiment, air is introduced to make 1m 3 The remaining 0.5m of ferrophosphite solution 3 The blowing time is 1 hour less than that in Example 1. The element contents in the ferric phosphate solution before and after aeration in this example are shown in Table 3.

[0047] Table 3 Element contents in ferrophosphite solution before and after blowing in Example 3

[0048] Fe(g / L) P(g / L) F(g / L) S(g / L) Before blowing 56.4 31.3 0.04864 58.2 After blowing 113.5 62.9 0.04801 117.3

[0049] It can be seen from Table 3 that the F element concentration of the ferrophosphite solution remains almost unchanged after blowing, but the total amount is halved, and about 50% of the fluorine is removed.

[0050] The present invention utilizes ventilation in the ferrophosphite solution to allow gas-liquid contact, thereby allowing water to enter the gas phase. HF has hydrogen bonding forces with water molecules, and HF will also enter the gas phase due to the hydrogen bonding forces and be discharged from the system, thereby effectively removing the total amount of fluorine in the ferrophosphite solution.

[0051] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for defluorinating ferrophosphite solution in a lithium iron phosphate battery recycling process, characterized in that: The steps include: A ferrophosphite solution is added to the bottom of the reaction device, and the ferrophosphite solution at the bottom is pumped to the top for spraying. Gas is introduced from the bottom of the reaction device, and the gas blows out the moisture in the ferrophosphite solution through gas-liquid contact. The moisture contains fluorine element, and the ferrophosphite solution after defluorination is obtained.

2. The method according to claim 1, characterized in that: The gas includes one or more of air, nitrogen, argon and helium.

3. The method according to claim 1 or 2, characterized in that: The concentration of hydrogen ions in the ferrophosphite solution is ≤5 mol / L.

4. The method according to claim 3, characterized in that The temperature of the ferrophosphite solution is 0 to 100°C.

5. The method according to claim 3, characterized in that: The temperature of the gas is 0 to 100°C.

6. The method according to claim 4 or 5, characterized in that: The reaction apparatus comprises a packed tower, a plate tower or a stirred reactor.

7. The method according to claim 6, characterized in that The volume of the ferrophosphite solution after defluorination is 1 / 3 to 2 / 3 of the volume of the ferrophosphite solution.

8. The method according to claim 7, characterized in that The gas blows out the moisture in the ferrophosphite solution to obtain tail gas containing fluorine element, and the tail gas is absorbed by water or alkali solution. The tail gas is absorbed by water to obtain hydrofluoric acid, and the tail gas is absorbed by alkali solution to obtain fluoride salt solution.

9. The method according to claim 8, characterized in that The lye includes sodium hydroxide solution, ammonia solution, potassium hydroxide solution or calcium hydroxide solution.