Pre-stage process for spodumene production of lithium carbonate: description on lithium sulfate brine production from spodumene ore. Pure dry cargo!

Pre-stage process for spodumene production of lithium carbonate: description on lithium sulfate brine production from spodumene ore. Pure dry cargo!

The spodumene production of lithium carbonate includes two relatively independent links, namely, preparing brine by roasting in the early stage and producing lithium carbonate by brine. The spodumene production of brine includes eight links: drying - roasting - cooling - crushing - grinding - acidizing - water immersion - solid-liquid separation.

Australian spodumene

1、 Drying: The water content of spodumene purchased for the Project is usually 8%. In order not to affect the subsequent roasting process, the materials shall be dried in a rotary drying kiln with a drying temperature of about 250 ℃ and a duration of about 15min. Hot air shall be in direct contact with the materials. The water content of spodumene after drying is about 6.5%, and the drying process can reduce the fuel gas volume in the subsequent roasting process. The drying heat source comes from the waste heat of rotary kiln tail gas (in order to save energy and reduce consumption, a part of the hot flue gas with waste heat of rotary roasting kiln of about 250 ℃ is led into the drying kiln by the fan). All the collected dust dried will be used in the roasting process.

2、 Roasting: after drying, the spodumene enters the high-temperature roasting chamber of the roasting rotary kiln through the kiln tail for roasting (with coke oven gas as the fuel, and a spray gun is set at the middle section of the tunnel roasting kiln for direct combustion). The rotary kiln uses coke oven gas as the fuel, and the raw materials are roasted at high temperature by direct heating. The sintering temperature is controlled at 1100~1200 ℃, and the roasting time lasts for about 2h.

Rotary kiln

The spodumene raw material will be α Type spodumene converted to β Type spodumene, which converts lithium from an acid-soluble structure to an acid-soluble structure with a conversion rate of 95-98%.

The transformation process equation is: α- Li2O · Al2O3 · 4SiO2 → β- Li2O · Al2O3 · 4SiO2

3、 Cooling: when the materials are roasted at high temperature, due to the melting of some materials, the sintered materials will have a certain strength, so they need to be cooled. After entering the cooling kiln, they are cooled to about 90 ℃ by forced air cooling. The cooling time after roasting is 1.5 hours.

4、 Crushing: the cooled clinker is conveyed to the crusher by the closed chain bucket conveyor for crushing, so as to prevent large clinker from entering the subsequent process. The clinker is crushed to about 10mm grain size. The clinker is conveyed to the vertical mill system by the closed belt conveyor.

5、 Grinding: in order to facilitate the subsequent leaching operation and make the clinker more fully dissolved, the crushed clinker shall be further ground. The materials are conveyed to the grinding plate of vertical grinding system by the metering balance of the feeding belt. Under the action of centrifugal force, the materials move to the periphery of the grinding plate. When the material passes between the grinding plate and grinding roller, it is crushed into powder under the action of pressing force. The grinded material powder particles continue to move outward and finally throw to the periphery of the grinding plate; Relying on the negative pressure formed by the main exhaust fan, the slightly heated desiccant gas enters the mill from the vertical mill air inlet and passes through the outer edge of the grinding plate from bottom to top; The material powder particles are carried up by the slightly hot desiccant gas, and the heavy and large material powder particles in the separator collide with the blade baffle of the separator and return to the grinding plate for grinding; Lighter fine material powder particles are collected by the dust collector through the separator; The separator at the upper part of vertical mill screens the grinded materials, and the material powder with unqualified fineness is separated from the cyclone along the inner wall of inner cone and returned to the grinding plate for further grinding. The grinded materials with particle size less than 100 meshes enter the next process.

6、 Acidification: Crushed to<100 mesh β Spodumene and 98% concentrated sulfuric acid are mixed and acidized on the mixer (ratio: 2.5-3.5:1). The mixture is conveyed to two acidizing kilns via the feed screw conveyor. The acidizing kilns are heated by the hot air furnace burning coke oven gas and heated by the external heating indirect heating method. The reaction temperature is controlled at 250~300 ℃ for about 10min, β Type spodumene will be fully salinized with sulfuric acid, and the reaction equation is as follows:

Li2O · Al2O3 · 4SiO2+H2SO4 → Li2SO4+H2O · Al2O3 · 4SiO2

The following side reactions also occur:

Na2O · Al2O3 · 4SiO2+H2SO4 → Na2SO4+H2O · Al2O3 · 4SiO2

K2O · Al2O3 · 4SiO2+H2SO4 → K2SO4+H2O · Al2O3 · 4SiO2

MgO · Al2O3 · 4SiO2+H2S → MgSO4+H2O · Al2O3 · 4SiO2

CaO · Al2O3 · 4SiO2+H2S → CaSO4+H2O · Al2O3 · 4SiO2

Fe2O3+3H2SO4 → Fe2 (SO4) 3+3H2O

ZnO+H2SO4 → ZnSO4+H2O

TlO2+H2SO4 → TlOSO4+H2O

When the material is salinized, resin impurities are removed between the aluminosilicate core of spodumene and sulfuric acid, and the exchange results in the replacement of lithium in the spodumene by hydrogen, while the mineral structure is not actually destroyed. The acidized material after salination reaction is sent to the cooling kiln by the screw conveyor, cooled to below 80 ℃ by indirect water cooling, and then enters the subsequent leaching process.

The acid roasting unit is designed into four parts: raw material unit, acid roasting unit, cooling storage unit, heat supply unit, etc.

(1) Raw material unit

① Fine roasting material spodumene blanking, weighing and metering procedures.

In the fine roasting bin β The spodumene enters the unit and is weighed and metered by the enclosed weighing feeder before being put into the double-screw mixer.

② Concentrated sulphuric acid conveying and metering process.

Concentrated sulphuric acid is delivered to the metering tank through pipes from the sulfuric acid tank farm in the plant area, and then sent to the double-screw mixer by the sulfuric acid feeding pump.

(2) Acid roasting unit

① β Spodumene fines (100 mesh) flow from the bottom outlet of the fines bin into the metering scale.

② The measuring scale is generally spiral scale, rotor scale, Corio force scale, etc. The Corio force scale is used in this project.

③ The outlet of the metering scale is connected to the screw conveyor, and the rotation speed of the screw conveyor is controlled through the reading of the Corio force scale, so as to control the feeding amount of spodumene powder.

④ Screw conveyor outlet connected to mixer.

⑤ Generally, single screw mixer, spiral belt mixer and double screw mixer are adopted. The Project adopts double screw mixer.

⑥ The 98% sulfuric acid is sent to the mixer from the storage tank through the fluorine lined magnetic pump.

⑦ Flow meter and control valve are set on the sulfuric acid pipeline.

⑧ Sulfuric acid mass flow is controlled by spodumene mass flow.

⑨ Sulfuric acid is sprayed into the mixer through the multipoint nozzle and mechanically mixed with spodumene fine powder. The mixture is called acid mixing material.

⑩ The mixed acid material is sent to the acidizing kiln through the kiln inlet screw and the kiln tail cover.

(3) Acid Clinker Cooling Storage Unit

The acidized material from the furnace tail is sent to the cooling kiln by the screw to be cooled to below 80 ℃. The cooling kiln adopts the indirect cooling form of chilled water. The cooled acidized clinker is sent to the wet process section in the plant.

(4) Heat supply unit

The heat supply system of the Project adopts the form of hot air circulation system (hot air circulation) supplied by coke oven gas hot air furnace.

The coke oven gas sent by the pipeline and the preheated air sent by the air fan are burned in the hot air furnace. The hot flue gas generated by combustion is mixed with the circulating hot flue gas sent by the high temperature circulating fan in the tail section of the hot air furnace. The hot air pipeline enters the jacket of the acidizing kiln through valve regulation to provide heat for the furnace body. Most of the hot flue gas is recycled in the heating system, and a part of the flue gas is discharged by the chimney after preheating the air. Each air duct in the system is provided with a regulating valve to meet different requirements for heating temperature of each section of the furnace body. The smoke exhaust duct is provided with a regulating valve to regulate the balance of air pressure of the system.

Operating conditions and control parameters: control the reaction temperature to 250 ℃ - 300 ℃. The feeding amount of sulfuric acid shall be determined according to the amount of effective component Li2O in the ore. Keep the content of free acid in the acid mixing material at 20-22%. The feed acid ratio is determined to be about 2.5-3.5, and the retention time of the material in the roasting furnace is about 30min. Free acid content in acid clinker is 2-6%, atmospheric pressure.

7、 Water immersion: The acid cooled spodumene acid clinker contains about 2~6% sulfuric acid, which is sent to the pulping tank via the buried scraper conveyor via the acid clinker bin, and the acid clinker slurry (the cooled acid clinker has a temperature of about 40 ℃, and enters below the liquid level of the closed leaching tank via the feeding channel) is prepared with lithium slag washing solution, resin regeneration water and condensate according to the liquid-solid ratio of about 1.6:1, and then sent to the neutralization tank Lime is used to neutralize residual sulfuric acid. Limestone and quicklime are sent to the neutralization tank by the feeder via the buried scraper conveyor, and the pH meter in the neutralization tank controls the feeder speed, so as to control the addition amount of limestone and quicklime. When the pH value reaches 6~6.5, stop feeding and the neutralization reaction lasts for 20min. Lithium enters the liquid phase (neutralization slurry) from the solid phase after leaching, and the lithium leaching rate reaches about 98%. Neutralizing slurry is sent to filter press by slurry pump for subsequent operation.

Reaction equation:

CaCO3+H2SO4 → CaSO4+CO2 ↑+H2O

CaO+H2SO4 → CaSO4+H2O

Operating conditions and control parameters: leaching temperature: 40 ℃, liquid-solid ratio: 1.6:1, leaching time: 2-3h, atmospheric pressure.

8、 Solid-liquid separation:

When the neutral slurry is pumped into the filter press, wet lithium residue, lithium sulfate filtrate and lithium residue washing solution are obtained respectively through filtration, washing, pressing, blowing, slag unloading and other processes.

Plate and frame filter press

Filtration: the neutral slurry is pumped into the filter press for solid-liquid separation. When the slurry pump flow slows down to about 5m3/h, the filter press stops feeding. The filtered filtrate is mainly lithium sulfate filtrate and enters the impurity removal process after being temporarily stored in the filtrate tank.

Washing: the lithium content in the filter residue obtained from solid waste separation is still high, and the lithium sulfate solution in the lithium residue is washed online by condensate as much as possible. The solution obtained from leaching is the lithium residue washing solution, which is returned to the leaching process for acid clinker slurry preparation.

Pressing: the lithium residue after leaching shall be pressed continuously, and the pressed filtrate shall be returned to the leaching process for acid clinker slurry preparation.

Dewatering: after pressing, the lithium residue is blown with 0.7MPa wet air to drain, and the drained water returns to the leaching process for acid clinker slurry preparation. The water content of lithium slag after dewatering shall be less than 20%.

Slag unloading: use the belt conveyor to treat the leaching residue completed by pressure filtration as solid waste.

Salt solution evaporator