Lithium Carbonate Production Process

Lithium deposition preparation 

1 lithium precipitation workshop, the lithium-rich solution prepared in the lithium extraction workshop and the dephosphorized solution in the iron phosphate preparation wet process workshop are sent to the lithium precipitation workshop through pipelines to extract the lithium element in the solution and prepare lithium carbonate. The lithium carbonate production process in the lithium precipitation workshop is as follows:

1、Fluoride removal

In order to further remove fluoride from the liquid after phosphorus removal, a defluoridation agent (with polyaluminum sulfate as the main component) is used for defluoridation. The liquid after phosphorus removal is pumped into the defluorination reaction tank through a pipeline, and the defluoridation agent is added. The materials after full mixing and reaction are separated into mud and water in an inclined tube sedimentation tank, and the upper clear liquid enters the pre-concentration liquid tank; the bottom mud produced by separation is washed with water and pumped to the filter press for filtration, and the filtrate obtained by filtration is all recycled to the slurry mixing tank of the wet process workshop for iron phosphate preparation, and is not discharged; the fluorine slag after filtration has a water content of 30% and is sold as general solid waste.

2、Evaporation concentration

The supernatant after the defluorination process is a lithium sulfate solution. The second phase project will carry out MVR evaporation and concentration treatment on the supernatant to increase the lithium sulfate content in the solution to 15g/L. The lithium-rich solution after evaporation and concentration enters the next resin impurity removal process.

3、Resin impurity removal

The concentrated lithium sulfate solution and the lithium-rich solution in the lithium extraction workshop contain a small amount of calcium and magnesium ions. The presence of high calcium ions can easily cause wall formation in the subsequent lithium sulfate solution evaporator and affect the quality of battery-grade lithium sulfate. Therefore, resin adsorption is used to remove  Ca²⁺ and Mg²⁺ in the solution. The backwash wastewater generated by resin regeneration is treated by a primary RO reverse osmosis device in the workshop, with a water yield of 80%; the concentrated water obtained by reverse osmosis is used as production supplementary water for the acidification process of lithium precipitation mother liquor and is not discharged; the resin regeneration backwash wastewater after reverse osmosis treatment is discharged into the sodium sulfate wastewater treatment system.

4、Lithium precipitation, washing, filter pressing

Sodium carbonate and recycled lithium carbonate washing wastewater are pre-added in the lithium precipitation reaction tank, stirred and heated to 90°C, and after reaching the temperature, lithium sulfate solution after resin impurities removal is gradually added to carry out lithium precipitation reaction. After the lithium sulfate solution is added, the reaction is continued for 2 hours. Lithium carbonate and lithium precipitation mother liquor are obtained by centrifugal separation, and the lithium precipitation mother liquor enters the acidification tank. The lithium carbonate is washed twice in countercurrent to obtain lithium carbonate wet material.

The main reaction equation is as follows: Li₂SO₄+Na₂CO₃→Na₂SO₄+Li₂CO₃↓

This process mainly produces lithium carbonate washing wastewater; part of the lithium carbonate washing wastewater is directly reused in the lithium precipitation reaction tank, and the remaining lithium carbonate washing wastewater is treated in the workshop by a primary RO reverse osmosis device, with a water yield of 80%. The concentrated water obtained by reverse osmosis is used as production supplementary water for the lithium precipitation mother liquor acidification process and is not discharged; the lithium carbonate washing wastewater after reverse osmosis treatment is discharged into the sodium sulfate wastewater treatment system.

5、Drying, screening, crushing, iron removal, packaging

The wet lithium carbonate is sent to the disc dryer through a screw conveyor for drying. Steam is used as the heat source and the drying temperature is between 100℃ and 120℃. The dried lithium carbonate is first separated from foreign matter by a vibrating screen. The large particles of lithium carbonate under the screen are crushed to the required particle size of the product by a jet mill. After being treated by an iron remover, they are sent to an automatic packaging machine through a vacuum feeder for packaging to obtain battery-grade lithium carbonate products. The packaging waste gas generated in this process is collected in a negative pressure sealed manner, and then discharged from a 20m high exhaust pipe after being treated by a "three-stage bag" dust removal.

6、Mother liquor acidification, concentration, freezing, centrifugation, drying, packaging

The main components of lithium precipitation mother liquor are sodium sulfate and lithium sulfate. The lithium precipitation mother liquor is pumped into the acidification tank, and concentrated sulfuric acid is added to adjust the pH to 1.5~2. The acidified mother liquor is pumped into the MVR evaporator for concentration, and the concentrated mother liquor is cooled by the rapid freezing system, and then centrifuged to obtain sodium sulfate crystals and sodium precipitation mother liquor. The sodium precipitation mother liquor returns to the MVR for concentration. After the sodium sulfate crystals are dried in the disc dryer, they are sent to the automatic packaging machine for packaging through a vacuum feeder to obtain anhydrous sodium sulfate. The packaging waste gas generated in this process is collected in a negative pressure sealed manner, and then discharged from a 20m high exhaust pipe after dust removal through a "three-stage bag" treatment.