Lithium Carbonate Production Process

Wet treatment process of black mass of lithium iron ion battery 

1 wet process workshop for the preparation of iron phosphate. All types of acid leaching tanks in the workshop are covered. The liquid materials are transferred by pipeline pumping. The exhaust holes are set on the tank cover and directly connected to the collection pipeline. The black mass after the crushing of lithium iron phosphate single cells and the purchased black mass of lithium iron phosphate batteries are first temporarily stored in the black mass warehouse, and then anhydrous iron phosphate is produced after leaching, impurity removal and roasting in the wet process workshop for the preparation of iron phosphate. The specific production process is as follows:

1. Unpacking

Ton bags of lithium iron phosphate battery black mass are transported by forklift from the black mass warehouse to the closed unpacking room of the wet process workshop for preparing iron phosphate. In the unpacking room, the lithium iron phosphate battery black mass is unpacked manually and falls into the silo through the feed port, and then the pneumatic conveying pipeline directly transports the material from the silo to the slurry mixing tank. A negative pressure collection system with an air volume of 10,000 m³/h is installed above the unpacking room. The dust generated by unpacking is collected by negative pressure and then discharged through a 20m high exhaust pipe after being treated by a "three-stage bag" dust removal.

2. Slurry preparation

First, add a certain amount of condensed water into the slurry mixing tank, then add the lithium iron phosphate battery black mass into the slurry mixing tank, keep the solid-liquid ratio at 10:1, and stop stirring after 30 minutes. The slurry is directly pumped into the leaching tank through the pipeline.

3. Leaching

The raw material LiFePO4 undergoes a chemical reaction in the medium of sulfuric acid and hydrogen peroxide for about 12 hours, and the reaction temperature is controlled at 80°C. Lithium, iron, and phosphorus enter the solution, and insoluble substances such as carbon remain in the leaching residue. The leaching process mainly produces the following reactions:

4H₂SO₄+H₂O₂+2LiFePO₄=Li₂SO₄+Fe₂(SO₄)₃+2H₃PO₄+H₂O

2Al+3H₂SO₄=Al₂(SO₄)₃+3H₂↑

The slurry after pulping is transported to the leaching tank through a closed pipeline. After the raw materials are added, 98% sulfuric acid and 27.5% hydrogen peroxide are slowly added to the leaching tank as leaching agents. After the leaching time is reached, the leached slurry is pumped to the filter press for liquid-solid separation. The filtration time is 2 hours; the leaching liquid obtained by filtration is then pumped to the subsequent copper removal process; the leaching residue (carbon black) obtained by filtration has a moisture content of 50% after two-stage water washing and filtration, and is temporarily stored in the hazardous waste temporary storage warehouse in the factory area as solid waste to be identified. The acid mist generated during the leaching process is discharged through a 20m high exhaust pipe after being treated with "three-stage alkali solution spraying".

4. Copper removal

The leachate is transported to the copper removal tank through a closed pipeline, and iron powder is added to the copper removal tank, the reaction temperature is controlled at 80℃-90℃, and the reaction time is controlled to 9h. After the reaction time is reached, the copper removal slurry is pumped to the filter press for liquid-solid separation, and the filtration time is 2 hours. The copper slag obtained by filtration has a moisture content of about 30% after washing and filtration, and is sold as general solid waste; the filtrate is pumped into the slurry mixing tank through the pipeline as production supplementary water.

5. Aluminium removal

The leachate after copper removal still contains aluminum impurities, and further aluminum removal is required. Therefore, the leachate after copper removal is pumped into the aluminum removal tank through a pipeline. Sodium fluoride solution is added to the aluminum removal tank, and the reaction temperature is controlled at 50℃-80℃. After stirring and reacting for 2-3 hours, the reaction endpoint is considered when Al in the feed liquid is ≤0.20g/L.

After the aluminum removal reaction is completed, the leachate is pumped to the filter press for liquid-solid separation, and the filtration time is 2 hours; the aluminum slag obtained by filtration has a moisture content of about 30% after washing and filtration, and is sold as general solid waste; the filtrate is pumped into the slurry mixing tank through a pipeline as production supplementary water.

6. Iron phosphate crystals

The leaching solution after aluminum removal is pumped to the crystallization tank, and phosphoric acid is added to the crystallization tank to adjust the pH value of the solution to 1.5. The reaction temperature is controlled at 80°C. After about 6 hours of reaction, dihydrate iron phosphate crystallizes in the solution. The crystallization process reaction formula is as follows:

Fe₃++PO₄ 3- =FePO_4*2H₂O

FePO_4*2H₂O= FePO₄ +2H₂O

After the crystallization is completed, the slurry is pumped to the filter press for liquid-solid separation. The filter press time is 2 hours. The leachate obtained by the filter press is pumped to the dephosphorization tank. The dihydrate iron phosphate crystals obtained by the filter press are washed and filtered, and then sent to the roasting process to prepare anhydrous iron phosphate. The acid mist generated during the crystallization process is treated by "three-level alkali liquid spraying" and discharged through a 20m high exhaust pipe.

7. Phosphorus removal

After the crystallization is completed, the filtrate is pumped to the dephosphorization tank, and 32% sodium hydroxide solution and calcium sulfate solution are added to the dephosphorization tank, the pH of the solution is adjusted to 8.0, the reaction temperature is controlled to 80°C, and the reaction time is controlled to 4h. After the reaction time is reached, the dephosphorization slurry is pumped to the filter press for liquid-solid separation, and the filtration time is 2 hours. The dephosphorization liquid (filtrate) is pumped to the lithium precipitation workshop through a pipeline to produce lithium carbonate. The phosphorus slag obtained by filtration has a moisture content of about 30% after washing and filtration, and is sold as general solid waste; the filtrate is pumped into the slurry mixing tank through a pipeline as production supplementary water.

8. Drying and roasting

The free water of the dihydrate ferric phosphate crystals is removed in a dryer, and the crystal water is removed in a roasting kiln (not less than 500°C, 10 minutes) to produce anhydrous ferric phosphate.

The dryer uses steam as a heat source. The ferric phosphate dihydrate crystals are heated by indirect contact with high-temperature steam in the dryer to remove free water from the crystals. The heating temperature is 120°C and the drying time is 0.5h. The water vapor generated by drying is condensed and reused.

The roasting kiln uses natural gas as a heat source and adopts low-nitrogen combustion technology. The dihydrate ferric phosphate crystals are directly heated in contact with the hot air heated by the combustion of natural gas in the roasting kiln to remove the crystal water in the crystals; the heating temperature is 400℃-500℃, and the heating time is 2h. This process mainly produces roasting waste gas; the roasting waste gas is collected in a negative pressure sealed manner, and then discharged through a 20m high exhaust pipe after being treated with a "three-stage bag" dust removal.

9. Packing

The calcined anhydrous ferric phosphate is sent to the automatic baler through a vacuum feeder for packaging, and then transferred to the warehouse for temporary storage before being sold . The packaging waste gas generated in this process is collected in a closed negative pressure manner, and then discharged through a 20m high exhaust pipe after dust removal treatment by a "three-stage bag".