Introduction to the Recycling and Production of Lithium Carbonate or Lithium Hydroxide from Waste Lithium Batteries

Waste ternary lithium batteries and lithium iron phosphate batteries both contain lithium elements, 

and recycling the lithium containing substances in waste lithium batteries is an important step in the recycling of waste lithium batteries. 

Waste lithium batteries undergo a series of treatments to obtain the production solution of lithium carbonate and lithium hydroxide

The lithium carbonate and other lithium product recovery system includes three subsystems: pretreatment line, lithium carbonate refining line, 

and lithium hydroxide line. Pre treatment includes three units: oil removal, impurity removal, and crystallization concentration of the nickel residue.

 The lithium carbonate refining line includes five units: lithium precipitation, pulping, carbonization, 

thermal decomposition, aging, centrifugal washing, lithium carbonate drying, crushing, and packaging. 

The lithium hydroxide production line includes four units: causticization, frozen sodium precipitation, 

MVR evaporation concentration crystallization+recrystallization, and drying, crushing, and packaging. 

The pre-treatment line is different from lithium ore and salt lake lithium extraction due to raw material reasons, 

while the lithium carbonate refining line and lithium hydroxide line are basically the same as lithium ore and salt lake lithium extraction. 

The recycling and production of waste lithium batteries and lithium hydroxide are described as follows.

1、 Preprocessing line

1.1 Nickel extraction residue oil removal: In extraction production, due to the hydrophilicity of the organic phase and insufficient phase separation, 

the extraction residue may contain a small amount of oil substances (petroleum content 100-300mg/L), 

which can affect the purity and performance of the product. 

To improve the purity of refined grade products, 

the comprehensive recycling system for waste lithium batteries uses activated carbon oil removal to remove oil from the nickel extraction residue.

Activated carbon adsorption for oil removal: 

After ultrasonic oil removal, the feed solution is further used to adsorb residual oil and fat in the solution by activated carbon, 

which is a physical adsorption process. Control the concentration of petroleum after oil removal to be less than 1mg/L.

1.2 Removal of impurities

After oil removal, the feed liquid enters the impurity removal process and is treated with sodium hydroxide to remove a small amount of iron, 

manganese, nickel, aluminum ions, as well as some calcium and magnesium ions. 

Control the temperature and pH value according to the process parameters to precipitate the above ions. 

After the reaction is completed, filter and remove impurities to obtain a mixed solution of lithium sulfate and sodium sulfate, 

which enters the crystallization concentration process; 

The filter cake is washed with pure water to form impurities, and the washing water and filtrate enter the next crystallization and concentration process. 

Theoretical formula for impurity removal: Me++nOH -=Me (OH) n ↓ (Me+represents Ca, Mg, Fe). 

Operating conditions and control parameters: pH=8-10; Temperature: Normal temperature.

1.3 Multi effect or MVR crystallization concentration

After impurity removal, the liquid is a mixed solution of lithium sulfate and sodium sulfate. 

To improve the lithium precipitation efficiency, the temperature is controlled to precipitate sodium sulfate 

and increase the concentration of lithium ions in the solution. 

By using the method of evaporation concentration followed by cooling crystallization, 

sodium sulfate in the solution exists in the form of sodium sulfate decahydrate, 

which has a much lower solubility than lithium sulfate. 

It precipitates in the form of crystals, and the sodium sulfate decahydrate separated by centrifugation enters the sodium sulfate line. 

The main reaction is: Na2SO4+10H2O=Na2SO4 · 10H2O

After controlling the concentration of Li+in the solution to a certain level, some of the centrifuged liquid enters the lithium carbonate refining line, 

and some of the centrifuged liquid enters the lithium hydroxide line to produce lithium carbonate and monohydrate lithium hydroxide products, respectively.

2、 Lithium carbonate refining line

2.1 Lithium deposition

By utilizing the much lower solubility of lithium carbonate in aqueous solution compared to lithium sulfate and sodium sulfate, 

lithium in the solution is precipitated in the form of lithium carbonate. 

The solubility of all three decreases with increasing temperature, but at the same temperature, 

the solubility of lithium carbonate is much lower than that of lithium sulfate and sodium sulfate. 

Therefore, the temperature at which lithium tends to boil during lithium deposition can achieve a higher lithium deposition rate.

After centrifugation, a measured amount of sodium carbonate is added to the liquid to react and generate lithium carbonate precipitate. 

After the reaction is complete, the filter cake is filtered to obtain lithium carbonate precipitate. 

After washing with pure water, it enters the pulping process, and the washing water and filtrate are sent to the sodium sulfate line together. 

The main reaction is: 2Li++CO32+=Li2CO3 ↓. 

Operating conditions and control parameters: temperature ≥ 80 ℃ (steam indirect heating), reaction time 2h.

2.2 Slurry

Add the crude lithium carbonate (with a water content of~30%) obtained by lithium precipitation into the slurry mixing tank, 

while adding pure water and thermal decomposition mother liquor (for reuse), slowly stir to fully mix, complete the slurry, 

and dissolve the lithium carbonate to the maximum extent to obtain the lithium carbonate slurry.

2.3 Carbonization

At room temperature, carbon dioxide gas is introduced and subjected to carbonization treatment by countercurrent carbonation, 

converting slightly soluble lithium carbonate into easily soluble lithium bicarbonate. 

The main reaction is Li2CO3+CO2+H2O=2LiHCO3

Carbon dioxide gas is fed from the first tower, and lithium carbonate slurry is fed from the third tower. 

The countercurrent carbonization reaction is carried out to convert lithium carbonate into lithium bicarbonate, 

and the resulting bicarbonate solution is discharged from the first tower. 

The filtered lithium bicarbonate solution is temporarily stored in the intermediate feed tank and then enters the thermal decomposition process. 

The filter cake mainly contains a small amount of unreacted lithium carbonate and impurities (such as silica, alumina, calcium sulfate, etc.). 

The filter cake is washed with pure water, and the washing water and filtrate enter the next thermal decomposition process. 

Operating conditions and control parameters: temperature at room temperature, time of about 2 hours, pH=6-7.

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2.4 Thermal decomposition aging centrifugation washing

Transfer the lithium bicarbonate solution into a thermal decomposition tank, 

and use a jacket heating method to maintain the temperature of the solution in the tank (95 ℃) for thermal decomposition reaction. 

Lithium bicarbonate decomposes and regenerates into lithium carbonate. 

During the reaction, continuously stir the solution to prevent solid wall hanging and boiling during heating, 

and at the same time, improve the heat dissipation of the solution, allowing lithium carbonate to slowly crystallize and precipitate. 

The main reaction is: 2LihCO3=Li2CO3 ↓+CO2 ↑+H2O.

The thermal decomposition slurry enters the aging process. Operating conditions and control parameters: temperature of 80-90 ℃, reaction time of 2 hours.

In order to increase the growth of lithium carbonate crystals generated by thermal decomposition reaction 

and make their particle size distribution uniform, 

the reacted slurry is slowly stirred in a stirring tank through a pipeline for about 2 hours to age. 

After aging, the lithium carbonate slurry is sent to a centrifuge for solid-liquid separation to obtain 

the thermal decomposition mother liquor and refined lithium carbonate wet product. 

The wet product is further removed of impurities such as K+, Na+, Ca2+, Mg2+by backwashing with pure water. 

The thermal decomposition mother liquor and washing water are reused in the pulping process.

2.5 Lithium carbonate drying crushing packaging

The washed lithium carbonate wet product is sent to a disc dryer for drying, 

and indirectly heated for drying (temperature 180 ℃) to reduce the moisture content of lithium carbonate from 5% to below 0.25%. 

Further crushing and packaging to obtain the final battery grade sodium sulfate product.

3、 Lithium hydroxide line

3.1 Cautiousness

Part of the centrifuged liquid produced in the crystallization and concentration process is pumped into a sealed caustic soda mixing tank, 

and a certain proportion of caustic soda is added. 

The reaction is carried out at room temperature and pressure for 20-30 minutes, 

and the caustic solution (lithium hydroxide and sodium sulfate solution) is filtered. 

The caustic residue is washed with pure water, and the washing water enters the frozen sodium precipitation process. The main reaction is:

Li2SO4+2NaOH=Na2SO4+2LiOH

Mg2++2OH-=Mg(OH)2↓

Ca2++2OH-=Ca(OH)2↓

3.2 Freezing Crystallization of Sodium

After causticization, the liquid is cooled to~45 ℃ by indirect heat exchange with circulating water, 

and then cooled to~25 ℃ by indirect heat exchange with sodium sulfate mother liquor that has been subjected to cryogenic centrifugation. 

By utilizing the different solubility of Na2SO4 and LiOH at low temperatures,

most of the sodium sulfate in the solution is separated into decahydrate sodium sulfate crystals, 

which are then centrifuged to obtain decahydrate sodium sulfate and enter the sodium sulfate system.

After centrifugation, the liquid is indirectly cooled to -8 ℃ by using ice salt water in a freezing station. 

The sodium sulfate in the solution further crystallizes to form a solid, which is then separated by secondary centrifugation. 

The centrifuged crystals are sodium sulfate decahydrate, 

which is added to condensed water to prepare sodium sulfate mother liquor for intermediate cooling. 

The frozen liquid is a lithium hydroxide solution, which is transported to the evaporation and concentration process.

3.3 Evaporation concentration crystallization recrystallization

One time evaporation crystallization: After freezing, the liquid is concentrated by MVR evaporation. 

After one time evaporation, the liquid (temperature 85 ℃) is cooled and crystallized, 

and then centrifuged to obtain one time mother liquor (returned to freeze for sodium precipitation) and crude lithium hydroxide.

Crude heavy dissolution+secondary concentration crystallization: 

Crude lithium hydroxide is added to condensed water and secondary evaporation mother liquor for re dissolution. 

The re solution is filtered and refined before being concentrated by secondary MVR evaporation.

 After the second evaporation, the liquid is cooled and crystallized, 

and then centrifuged to obtain the second evaporation mother liquor and wet lithium hydroxide. 

The second mother liquor is returned for dissolution, and the wet lithium hydroxide is sent to the drying process.

Control the evaporation concentration ratio and adjust it based on the measurement results of sulfate concentration in the mother liquor. 

Control the concentration of sodium sulfate at saturation concentration so that it does not precipitate with lithium hydroxide crystals, 

ensuring the purity of the crude lithium hydroxide product.

3.4 Drying crushing packaging

Wet premium lithium hydroxide is sent to a disc dryer for drying (temperature 90 ℃, indirectly heated by water vapor) through a screw conveyor. 

The feeding amount is quantitatively controlled to ensure the uniformity and stability of the material. 

After drying, the material is sieved by a vibrating screen, and the material on the screen is re dissolved. 

The material on the screen is then transported by a screw conveyor to a permanent magnet demagnetizer 

and sent to the material bin through a vacuum feeder. 

It is then transported by a conveyor screw to a cooling machine, 

where it is indirectly cooled by circulating cooling water to ensure that the material temperature is less than 35 ℃. 

After cooling, it is transported by a screw conveyor to a packaging machine and packaged as finished lithium hydroxide monohydrate.