Introduction to extracting lithium from natural lithium ore to produce battery grade lithium hydroxide monohydrate

The process of extracting lithium from lithium ore to produce battery grade monohydrate 

lithium hydroxide mainly includes raw material storage and transportation, roasting conversion, roasting acidification, 

lithium sulfate process (three steps of slurry leaching, solid-liquid separation and washing, purification), 

and lithium hydroxide process (four steps of concentration and causticization, freezing, two evaporation, drying and packaging).

The storage and transportation of raw materials, roasting conversion, 

and roasting acidification do not involve the evaporation and crystallization of salt solution. 

This article will not describe it here. If you want to know, you can read other articles in the author's official account. 

This article mainly introduces the processes of lithium sulfate and lithium hydroxide.

1、 Lithium sulfate slurry leaching process

The acidified clinker cooled to room temperature during the roasting and acidification stage, containing 3-5% sulfuric acid, 

is sent from a hopper to a slurry mixing tank by a conveyor, and calcium carbonate powder is added. 

The calcium carbonate powder is measured by a bottom measuring device and enters the slurry mixing tank. 

A certain amount of water is added to the slurry mixing tank for slurry treatment, 

so that soluble lithium sulfate in the clinker dissolves into the liquid phase. 

The liquid-solid ratio of the slurry is controlled at 1.5-2.5:1. 

Calcium carbonate reacts with sulfuric acid in the acid clinker to produce calcium sulfate precipitate and CO2 gas. 

When the pH value reaches 6.5, the neutralized slurry is pumped to the solid-liquid separation process by the slurry pump.

H2SO4+CaCO3=CaSO4+CO2+H2O

2、 Lithium sulfate solid-liquid separation and washing

The neutralizing slurry is filtered by a diaphragm filter press, and after 3 times of countercurrent washing, wet lithium slag (silicon calcium slag), 

lithium sulfate filtrate, and lithium slag washing solution are obtained. 

The wet lithium slag (leaching residue) is transported to the storage yard by a belt conveyor, 

and the filtrate is sent to the leaching solution storage tank in the purification and impurity removal process. 

The lithium slag washing solution from three counter current washes is stored and recycled separately: 

the first wash solution enters the slurry water storage tank, the second wash solution enters the first wash solution storage tank, 

the third wash solution enters the second wash solution storage tank, and the water source for the third wash solution is steam condensate and fresh water.

3、 Lithium sulfate purification

The solution in the lithium sulfate solution storage tank is pumped into the leaching solution heating tank for preheating (40 ℃) through a pipeline, 

and then pumped into the purification kettle through the leaching solution pump. 

Sodium hydroxide solution is added to adjust the pH value to 11-12, remove iron ions, aluminum ions, magnesium ions, etc. from the solution, heat up to 90 ℃, 

and add sodium carbonate to remove calcium. 

The purified solution is pumped into a plate and frame filter press for filtration, obtaining wet silicon calcium slag and purified solution. 

The purified solution enters the purification solution feeding tank, and the obtained calcium slag is sent to slurry leaching. 

fter the slag removal process of the above lithium sulfate device, the acidified clinker obtains a relatively pure lithium sulfate solution. 

The reaction in this process is as follows:

Fe3++30H-→Fe(OH)3↓

Fe2++2OH-→Fe(OH)2↓

Mg2++2OH-→Mg(OH)2↓

Al3++30H-→Al(OH)3↓

Ca2++Na2CO3→CaCO3↓+2Na+

4、 Lithium hydride concentration and causticization

The lithium sulfate solution after impurity removal is pumped to the causticization tank, 

and the required concentration of the solution entering the causticization tank is (LiO=40-50g/1). 

It can first enter the MVR evaporator to concentrate the solution.

Add sodium hydroxide (1:1.05-1) in a certain proportion to obtain a caustic solution, 

mainly composed of lithium hydroxide monohydrate and sodium sulfate. 

The reaction of this process is as follows:

Li2SO4+2NaOH+10H2O=2LiOH+Na2SO4.10H2O

The caustic solution is filtered through a plate and frame before entering the caustic solution storage tank.

5、 Freezing process

The indirect heat exchange temperature between the caustic solution and the frozen mother liquor is reduced by about 30-40 degrees. 

After being pumped into the freezing system and subjected to freezing and cryogenic processes, 

the temperature is lowered to about -10 ℃. 

By utilizing the different solubility of sodium sulfate and lithium hydroxide at low temperatures,

most of the sodium sulfate in the solution crystallizes as decahydrate sodium sulfate. 

The by-product Na2SO4.10H2O obtained by centrifugal separation of 

the frozen liquid is sent to the preparation process of sodium silicate powder, 

and the filtrate is sent to the evaporation process.

6、 Two evaporation processes

After freezing, the liquid is filtered by a plate and frame filter press 

and then pumped to the MVR evaporator for a first evaporation (discharge density: 1.28-1.30g/cm3). 

After cooling and centrifugation, a first mother liquor and a first crude lithium hydroxide (LiOH ≥ 55%) are obtained. 

The first mother liquor is sent to the causticization process, and the first crude lithium hydroxide is redissolved (redissolved LisO=60-80g/1), 

then filtered by a plate and frame filter press and pumped to the MVR evaporator for a second evaporation (discharge density: 1.20-1.24g/cm3). 

After cooling and centrifugation, the second mother liquor and refined lithium hydroxide are obtained. 

The second mother liquor is returned to the freezing process, and a part of the refined lithium hydroxide is sent to the drying and packaging process, 

while another part is sent to the drying and packaging process. Decarbonization process of lithium hydroxide.

7、 Drying and packaging process of lithium hydroxide

Premium lithium hydroxide is transported by a spiral conveyor to a disc dryer 

(drying temperature 50-70 degrees, indirect drying with hot water) to ensure uniform and stable feeding. 

After drying, the material is transported to a crusher (drying LiOH ≥ 56.5%) for crushing, and then to an electromagnetic iron remover for iron removal. 

After that, it is packaged into finished battery grade lithium hydroxide by an automatic weighing machine, belt conveyor, automatic sewing machine, 

inkjet printer, automatic bagging machine, mechanical hand code stamping machine, and automatic winding machine.