With the rapid development of electric vehicles and renewable energy, battery technology has become more and more important as a key way to store and release energy. In battery manufacturing, battery-grade lithium carbonate as a crucial material for lithium-ion battery cathode material, its preparation process and production process has a direct impact on battery performance. Therefore, in this blog, we will introduce the preparation process of battery grade lithium carbonate in detail.
The process involves roasting natural lithium concentrate to convert it into a usable form, followed by sulfuric acid extraction to transform lithium ore into a liquid lithium sulfate state. Lithium carbonate is prepared by adding solutions of calcium carbonate and caustic soda to elemental lithium, filtering out impurities to obtain crude lithium carbonate. The crude carbonate undergoes a carbonation reaction with water and carbon dioxide, resulting in a lithium bicarbonate solution. Thermal decomposition is then applied to extract lithium carbonate from the lithium hydrogen carbonate solution.
This project's production system mainly consists of three subsystems. The first one is the raw material pre-processing system, which includes processes such as crystalline conversion roasting process and acid roasting process. The second one is a lithium carbonate preparation system, which includes processes such as leaching, purification, lithium precipitation, carbonation, thermal decomposition, refining, and fine grinding. The last one is the by-product sodium sulfate preparation system, including processes such as neutralization, evaporation crystallization, centrifugation, and drying, etc.
First, transport the lithium ores to the raw material warehouse. Additionally, the particles of the lithium ores need to meet the process requirements through crushing and screening. Then, the lithium ores are transported by reclaimer and belt conveyor to the raw materials silo. After weighing by the quantitative feeder, it is then conveyed to the kiln tail feed chute through a conveyor belt and bucket elevator. Last but not least, the raw materials are dropped through a pipe to the end of the rotary kiln to begin the transformation process.
In this process, the raw material is calcined at high temperature to convert a-lithium pyroxene to β-lithium pyroxene. The entire crystal conversion roasting is a continuous production process using natural gas as the main fuel. The following are the detailed steps:
Raw Materials: A-lithium pyroxene, is fed into the process.
Fuel Supply: Natural gas, as fuel, is depressurized and metered at the on-site gas station and then enters the kiln head of rotary kiln.
Kiln Reaction: a-lithium pyroxene is transformed into β-lithium pyroxene by high temperature calcination in a rotary kiln. It is ignited and combusted by low nitrogen burner to ensure that material temperature in the high-temperature section is controlled at 1050~1150℃.
Continuous Production: After the material reaction is finished, the product is continuously discharged from the kiln head to maintain the continuity of production.
Industrial Waste Gas Treatment: While the product is discharged, the dust is led out from the kiln tail and collected by bag collector. Then followed by wet desulfurization and SCR denitrification to ensure that the exhaust gas meets the environmental standards, and is finally discharged high in the air.
Heat exchange and cooling: The clinker material from the kiln head ( about 1,000°C) is directly exchanged with the cold air in the grate cooler. The hot material is discharged from the rotary kiln to the grate bed of the grate cooler. Under the reciprocating motion of the cross-pushing rod, a certain thickness of bed is formed. The cooling fan provides cooling air to cool the hot roasted material.
Heat recovery: The cooled cooling air becomes high-temperature hot air (about 800°C), which re-enters the kiln system as combustion air, realizing heat recovery and reducing the energy consumption of the system.
Product transportation: After the roasted material is cooled to <100°C through the screening and cooling machine, it is conveyed through a sealed conveyor belt to enter the next process step.
The entire process achieves continuous transformation from α-spodumene to β-spodumene by controlling temperature, time, and smoke treatment. Additionally, thermal recovery is conducted throughout the process to enhance energy utilization efficiency.
The roasted materials are conveyed to the vertical mill for grinding through conveyor belts and elevators. After the fine grinding process, the proportion of material under the 200-mesh sieve is not less than 85%. The fine roasted material is screened by the powder selector and the dust is collected by dust collector. Finally, the fine roasted material that meets the requirements is transported to the fine roasted material silo for storage by using elevator or silo pump.
After finely grinding the raw material through the impeller feeder and electronic belt weigher, and then added to the acid mixer. Adding sulfuric acid from the sulfuric acid tank according to the proportion, then mixing and introducing the mixture into the acidification kiln. The process involves acid roasting at a temperature of 250-280°C for a duration of 30-60 minutes. During the roasting process, the β-spodumene in the calcined product reacts with sulfuric acid. Hydrogen ions from sulfuric acid replace lithium ions in β-spodumene, forming water-soluble Li2SO4 and producing acidulated clinker. After cooling to below 50°C, the acidulated clinker is conveyed to the clinker storage bin for storage.
Powdered calcium carbonate is transported to the factory area by tank truck and conveyed to the FT powder feeding system through pneumatic transport. It is then transported to the slurry mixing tank via screw conveyor, where it is added in a ratio of around 30% solid content of calcium carbonate. After stirring for 15 minutes in the first water washing stage, the mixture is pumped to the calcium slurry buffer tank for further use.
Extraction Liquid Separation: Utilizing a membrane pressure filter, the slurry obtained from leaching is subjected to solid-liquid separation.
Treatment of Extraction Liquid: The extracted liquid is transferred to a storage tank for purification, with a lithium sulfate concentration of around 140g/L.
Leaching Residue Treatment: After washing and air blowing, measures are taken to ensure that the lithium oxide content in the residue complies with the standard of 0.3～0.35%.
Conveyance to Purification Vessel: The lithium sulfate solution from the leaching liquid is transported to the purification vessel.
Adjustment of Reaction Conditions: Within the purification vessel, pH is regulated to 10~12 by introducing caustic soda and soda ash solutions. Stirring reactions are conducted at a controlled temperature of around 80°C.
Precipitation Formation: Precipitation occurs, immobilizing impurities such as iron, magnesium, aluminum, and calcium within the precipitate.
Solid-Liquid Separation: Filtration using a plate and frame press separates the purified liquid phase from the solid components.
Purification Residue Treatment: Processing the purification residue involves a pre-treatment before returning it to the leaching phase, enhancing reusability.
The lithium precipitation process aims to efficiently and with high purity extract lithium carbonate from the solution. It involves the following key steps:
The purified liquid is mixed with a sodium carbonate solution and heated to boiling to generate lithium carbonate precipitation.
The resulting slurry containing lithium carbonate is separated using a centrifuge, yielding solid lithium carbonate and a lithium precipitation liquor.
The lithium precipitation liquor is directed to the powder system for further processing.
The separated lithium carbonate solid undergoes stirred washing to eliminate attached impurities.
The separated crude lithium carbonate product is introduced into a continuous pulping tank, along with the addition of water (mainly sourced from caustic soda mother liquor, recycled water systems, and sewage treatment stations), to create a slurry. The slurry is continuously fed into a carbonation reaction tower for ongoing carbonation. The resulting lithium hydrogen carbonate solution's filtered clear liquid is stored in a buffer tank.
Lithium bicarbonate solution is heated to over 90°C, decomposing into lithium carbonate precipitate, carbon dioxide, and water. After separation, part of the solution is cooled for impurity removal, while another part undergoes neutralization and proceeds to the refined lithium carbonate process.
Mix lithium carbonate crude with water (3:1 ratio), stir at 90°C for 15-20 mins. Centrifuge to get wet lithium carbonate for carbonization. Send the separated washing water to acidifying material pulping leaching.
The lithium carbonate slurry is separated using a centrifuge, dried in a drying machine, finely ground to 3μm≤d50≤8μm with an airflow ultrafine crusher, and then automatically packaged before being sent to the finished goods warehouse.
The sodium sulfate production process includes neutralization, where lithium and leaching solutions react with concentrated sulfuric acid to form a solution with adjusted pH. The neutralized liquid undergoes evaporative concentration, leading to sodium sulfate crystallization and the recovery of sodium precipitation mother liquor. Wet sodium sulfate is dried to obtain anhydrous sodium sulfate, which is then packaged as the final product.