CN118833835A - CO (carbon monoxide)2Process and system for preparing lithium carbonate by gradient concentration and cooperation of lithium-containing minerals - Google Patents

Abstract

The present invention discloses a process and system for preparing lithium carbonate by gradient concentration of _{CO2 and} lithium-containing minerals, and the steps are as follows: limestone and lithium-containing minerals are prepared as raw material powder; the raw material powder is respectively fed into the _CO2 concentration system and the carbonization system for gas-solid heat exchange in proportion, and then all enters the decomposition furnace of the _CO2 concentration system, and then one path is calcined and cooled to obtain a lithium-based clinker product, and one path enters the carbonization furnace of the carbonization system and then enters the decomposition furnace; high-temperature kiln gas enters the carbonization system, and high-temperature tertiary air enters the _CO2 concentration system; the high _CO2 concentration flue gas discharged by the _CO2 concentration system is divided into three paths, one path enters the decomposition furnace, one path enters the carbonization furnace, and one path enters the mother liquor carbonation system to prepare lithium carbonate. The present invention independently sets up the _CO2 concentration system so that the flue gas generated by each system does not interfere with each other, and on the basis of preliminary concentration, sets up the carbonization system to further increase the _CO2 concentration in the flue gas of the _CO2 concentration system, so as to achieve gradient concentration and meet the carbonation demand of lithium-containing mother liquor.

Description

A process and system for preparing lithium carbonate by CO2 gradient concentration and lithium-containing minerals

Technical Field

The present invention relates to the technical field of preparing lithium carbonate from lithium-containing minerals, and in particular to a process and system for preparing lithium carbonate from lithium-containing minerals by gradient concentration of _CO2 .

Background Art

Lithium is a new type of energy and strategic resource, which is widely used in lithium batteries, ceramics, glass, medicine, metallurgy and other industries. In recent years, with the vigorous development of the power battery industry, the demand for lithium has shown explosive growth, which has also promoted the continuous advancement of lithium extraction technology. In nature, lithium mainly exists in the form of minerals. In China, lithium carbonate is mainly produced using spodumene as raw material.

At present, the technologies for producing lithium carbonate using lithium-containing minerals as raw materials mainly include limestone roasting method, soda ash pressure cooking method, transformation roasting-sulfuric acid method, etc. Among them, the practicability of limestone roasting method is very common and is suitable for decomposing almost all lithium minerals. The conventional production process of limestone roasting method is shown in Figure 1: limestone and lithium-containing minerals are mixed in a certain proportion, and the raw materials after mixing are fed into the raw material grinding system to prepare raw material powder with particle size meeting the requirements. The raw material powder with limestone and spodumene as the main raw materials is fed into the preheating and pre-decomposition system through the feeding point, and then enters the decomposition furnace for calcination and decomposition after gas-solid heat exchange in the multi-stage cyclone preheater, and then enters the kiln tail smoke chamber after gas-solid separation in the lowest stage cyclone preheater, and then enters the rotary kiln for solid phase reaction calcination to generate lithium-based compound clinker, and then the high-temperature clinker is cooled by the cooler to obtain lithium-based clinker products. After the lithium-based clinker product is ground by the grinding system, it enters the water leaching and filtration system to obtain lithium hydroxide leachate and waste residue (the main principle is that aluminum silicate minerals are roasted by limestone to make the main impurities silicon and aluminum generate compounds that are difficult to dissolve in water, while lithium and its associated valuable metals such as potassium and sodium generate compounds that are easily soluble in water, and then leached and separated by water to obtain lithium hydroxide). The lithium hydroxide leachate is evaporated and concentrated and then enters the mother liquor carbonation system to fully react with the purchased high-purity _CO2 gas. Subsequently, it undergoes multiple processes such as evaporation, separation, and crystallization to obtain lithium carbonate products. In addition, the low-temperature flue gas (flue gas with low _CO2 concentration) discharged from the outlet of the top-level cyclone preheater of the preheating and predecomposition system is partially recovered by the waste heat recovery and utilization system and then enters the flue gas treatment system. After the flue gas treatment, it enters the chimney and is discharged into the atmosphere.

The main reaction equations involved in the conventional production process of limestone roasting are:

Li ₂ O·Al ₂ O ₃ ·4SiO ₂ +8CaCO ₃ →Li ₂ Al ₂ O ₄ +4Ca ₂ SiO ₄ +8CO ₂ (1)

2Li(OH)+CO ₂ →Li ₂ CO ₃ +H ₂ O (2)

The main disadvantage of the conventional limestone roasting method is that the mother liquor carbonation process requires the provision of flue gas containing medium or high concentrations of _CO2 ( _CO2 wet basis concentration ≥40%, and the higher the _CO2 concentration, the higher the mother liquor carbonation efficiency) or pure _CO2 gas, while the conventional limestone roasting method uses conventional air as the combustion medium, resulting in a large amount of flue gas and a low _CO2 concentration ( _CO2 concentration is about 10-20%), which cannot meet the mother liquor carbonation requirements. Therefore, it is necessary to provide flue gas containing medium or high concentrations of _CO2 or purchase pure _CO2 gas, resulting in a significant increase in production costs; at the same time, a large amount of flue gas containing _CO2 is discharged from the preheating and predecomposition system, resulting in a significant increase in carbon emission reduction pressure.

Based on the above background, without purchasing additional pure _CO2 gas, the study optimized and improved the existing limestone roasting process so that the roasting system can produce lithium-based compound clinker normally while preparing flue gas containing medium and high concentrations of _CO2 required for the mother liquor carbonation process, thereby preparing lithium carbonate with higher efficiency and lower cost, while reducing the system's _CO2 emissions, which becomes the key to large-scale preparation of lithium carbonate by limestone roasting method.

Therefore, based on market demand and the key scientific and technological challenges faced, it is of great practical significance to provide a process and system for preparing lithium carbonate by _CO2 gradient concentration and coordinated lithium-containing minerals, which fully considers the carbonation demand of the mother liquor in the lithium carbonate preparation process and reduces carbon emissions in the lithium carbonate preparation process.

Summary of the invention

In order to solve the problems existing in the prior art, the present invention provides a process and system for preparing lithium carbonate by gradient concentration of _CO2 and coordinated use of lithium-containing minerals. The present invention solves the technical problems that a large amount of pure _CO2 gas needs to be purchased in the mother liquor carbonation process of the existing limestone roasting method, resulting in a significant increase in production costs, and a large amount of _CO2 -containing flue gas is discharged, resulting in a significant increase in carbon emission reduction pressure.

The present invention is implemented as follows: a process for preparing lithium carbonate by gradient concentration _{of CO2} in cooperation with lithium-containing minerals, comprising the following steps:

Raw material preparation:

Limestone and lithium-containing minerals are mixed in a certain proportion, and the mixed raw materials are ground to prepare raw material powder with particle size meeting the requirements;

Clinker preparation and high _CO2 concentration flue gas preparation:

The raw meal powder is fed into the _CO2 concentration system and the carbonization system at a predetermined feeding ratio, and then passes through the gas-solid heat exchange of each multi-stage cyclone preheater, and then all enters the decomposition furnace of the _CO2 concentration system for calcination and decomposition; the hot raw meal after decomposition is separated by cyclone and divided into two paths, the first path enters the rotary kiln through the kiln tail smoke chamber for calcination, and the second path enters the carbonization furnace of the carbonization system for _CO2 solidification absorption, and then enters the decomposition furnace of the _CO2 concentration system after cyclone separation; high-temperature kiln gas and high-temperature lithium-based compound clinker are generated in the rotary kiln, and the high-temperature lithium-based compound clinker is cooled by a cooler to obtain a lithium-based clinker product;

The high-temperature kiln gas enters the carbonization system to preheat the raw material inside it and provide _CO2 medium to the hot raw material undergoing _CO2 solidification absorption reaction. The flue gas discharged from the top outlet of the carbonization system is low-temperature and low- _CO2 concentration flue gas; the high-temperature tertiary air enters the _CO2 concentration system to preheat and pre-decompose the raw material inside it. The flue gas discharged from the top outlet of the _CO2 concentration system is low-temperature and high- _CO2 concentration flue gas. The temperature range of the low-temperature and high- _CO2 concentration flue gas is 240-380℃, and the wet-basis _CO2 concentration in the low-temperature and high- _CO2 concentration flue gas is 40-70%;

The low-temperature and high- _CO2 concentration flue gas is divided into three routes. The first route is reintroduced into the decomposition furnace after circulation; the second route is mixed with the high-temperature kiln gas from the rotary kiln and enters the carbonization furnace; the third route enters the mother liquor carbonation system for carbonation reaction to prepare lithium carbonate;

Lithium-based clinker carbonation:

The lithium-based clinker product is soaked in water and filtered to obtain lithium hydroxide leachate and waste residue. The lithium hydroxide leachate is evaporated and concentrated and then carbonated. During the carbonation, the lithium hydroxide leachate reacts with part of the high _CO2 concentration flue gas from the _CO2 concentration system to undergo carbonation reaction, and then evaporated, separated and crystallized to obtain a lithium carbonate product.

In the above technical solution, preferably, the lithium content in the lithium-containing mineral is 3-5%, and the ratio of the lithium-containing mineral to the limestone in the raw material is in the range of 1:3.05-3.2.

In the above technical solution, preferably, the raw material feeding ratio of the _CO2 concentration system and the carbonization system is preferably 2 to 2.5:1.

In the above technical solution, preferably, the material distribution ratio between the bottom cyclone preheater of the _CO2 concentration system entering the kiln tail smoke chamber and the carbonization furnace is 0 to 1.5:1.

In the above technical solution, preferably, in the _CO2 concentration system, the temperature at the outlet of the decomposition furnace is 880-900°C.

In the above technical solution, preferably, the reaction temperature window for the _CO2 solidification absorption reaction in the carbonization furnace is 650-700°C.

In the above technical solution, preferably, the high-temperature kiln gas and low-temperature high- _CO2 concentration flue gas exiting the rotary kiln are first separated from the fly ash before entering the carbonization furnace; a cyclone separator is used for fly ash separation.

In the above technical solution, preferably, the low-temperature and high- _CO2 concentration flue gases from the first and third paths are first dedusted before entering the decomposition furnace and the mother liquor carbonation system.

In the above technical solution, preferably, the low-temperature and low- _CO2 concentration flue gas discharged from the top outlet of the carbonization system recovers part of the heat through the waste heat recovery system and then enters the flue gas treatment system, and after the flue gas treatment, it enters the chimney and is discharged into the atmosphere.

A system for preparing lithium carbonate by gradient _CO2 concentration and synergistically using lithium-containing minerals, comprising a _CO2 concentration system, a carbonization system, a kiln tail smoke chamber, a rotary kiln, a cooler and a mother liquor carbonation system;

The _CO2 concentration system comprises a first row of multi-stage cyclone preheaters and a decomposition furnace, wherein the air inlet of the bottom cyclone preheater of the first row of multi-stage cyclone preheaters is connected to the air outlet pipe of the decomposition furnace, the air outlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters discharges low-temperature and high- _CO2 concentration flue gas, the feed inlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters is used for feeding raw material powder, the discharge port of the second-to-last cyclone preheater of the first row of multi-stage cyclone preheaters is connected to the decomposition furnace, and the discharge port of the bottom cyclone preheater of the first row of multi-stage cyclone preheaters is connected to the kiln tail smoke chamber and the carbonization furnace;

The carbonization system comprises a second row of multi-stage cyclone preheaters and a carbonization furnace, wherein the air inlet of the bottom cyclone preheater of the second row of multi-stage cyclone preheaters is connected to the air outlet pipe of the carbonization furnace, the air outlet of the top cyclone preheater of the second row of multi-stage cyclone preheaters discharges low-temperature and low- _CO2 concentration flue gas, the feed inlet of the top cyclone preheater of the second row of multi-stage cyclone preheaters is used for feeding raw meal powder, and the discharge port of the second-to-last cyclone preheater and the discharge port of the bottom cyclone preheater of the second row of multi-stage cyclone preheaters are both connected to the decomposition furnace;

The _CO2 concentration system further includes a first branch pipeline, a second branch pipeline and a third branch pipeline; the air inlets of the first branch pipeline, the second branch pipeline and the third branch pipeline are all connected to the air outlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters; the exhaust port of the first branch pipeline is connected to the circulating flue gas inlet of the decomposition furnace, the exhaust port of the second branch pipeline is connected to the flue gas inlet of the carbonization furnace, and the exhaust port of the third branch pipeline is connected to the mother liquor carbonation system;

The kiln tail smoke chamber, rotary kiln and cooler are connected in sequence, and the lithium-based clinker product outlet of the cooler is connected to the mother liquor carbonation system; the smoke outlet of the kiln tail smoke chamber is connected to the smoke inlet of the carbonization furnace, and the kiln door cover of the rotary kiln is connected to the tertiary air inlet of the decomposition furnace.

In the above technical solution, preferably, a cyclone separator is arranged between the smoke outlet of the kiln tail smoke chamber and the smoke inlet of the carbonization furnace, the air inlet of the cyclone separator is connected to the smoke outlet of the kiln tail smoke chamber and the exhaust port of the second branch pipe, the top air outlet of the cyclone separator is connected to the smoke inlet of the carbonization furnace, and the bottom discharge port of the cyclone separator is connected to the kiln tail smoke chamber; the stage number of the cyclone separator is one to two.

In the above technical solution, preferably, the air inlet of the first branch pipe and the air inlet of the third branch pipe are provided with a dust collector on the pipeline connected to the air outlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters.

In the above technical solution, preferably, the top cyclone preheater outlet of the second row of multi-stage cyclone preheaters is connected to a waste heat recovery system, and the flue gas outlet of the waste heat recovery system is connected to a flue gas treatment system.

In the above technical scheme, preferably, the mother liquor carbonation system includes a water immersion and filtration device, an evaporation concentration device and a mother liquor carbonation device, the lithium-based clinker outlet of the cooler is connected to the feed inlet of the water immersion and filtration device, the leachate outlet of the water immersion and filtration device is connected to the liquid inlet of the evaporation concentration device, the liquid outlet of the evaporation concentration device is connected to the liquid inlet of the mother liquor carbonation device, and the exhaust port of the first branch pipeline is connected to the air inlet of the mother liquor carbonation device.

In the above technical scheme, it is further preferred that the mother liquor carbonation system also includes a grinding system, which is located between the cooler and the water immersion and filtering device, the lithium-based clinker outlet of the cooler is connected to the material inlet of the grinding system, and the material outlet of the grinding system is connected to the feed inlet of the water immersion and filtering device.

In the above technical solution, preferably, the number of stages of the first row of multi-stage cyclone preheaters is four to seven; the number of stages of the second row of multi-stage cyclone preheaters is four to seven.

The principle of the present invention is:

Limestone and lithium-containing minerals are mixed in a certain proportion, and the mixed raw materials are fed into the raw material grinding system to prepare raw material powder with required particle size; the raw material powder with limestone and lithium-containing minerals as the main raw materials is fed into the _CO2 concentration system and the carbonization system in sequence, and the raw material is all fed into the decomposition furnace of the _CO2 concentration system for calcination and decomposition after gas-solid heat exchange in the multi-stage cyclone preheater, and then enters the kiln tail smoke chamber after gas-solid separation in the bottom cyclone preheater of the _CO2 concentration system, and then enters the rotary kiln for solid phase reaction and calcination to generate lithium-based compound clinker, and then the high-temperature lithium-based compound clinker is cooled by a cooler to obtain a lithium-based clinker product. After the lithium-based clinker product is ground by the grinding system, it enters the water leaching and filtering device to obtain lithium hydroxide leaching solution and waste residue. After the lithium hydroxide leaching solution is evaporated and concentrated, it enters the mother liquor carbonation device. Part of the high _CO2 concentration flue gas from the _CO2 concentration system enters the mother liquor carbonation device for carbonation reaction, and then undergoes multiple processes such as evaporation, separation, and crystallization to obtain lithium carbonate products. In addition, the low-temperature flue gas (low _CO2 concentration flue gas) discharged from the outlet of the top cyclone preheater of the carbonization system is partially recovered by the waste heat recovery system and then enters the flue gas treatment system. After the flue gas treatment, it enters the chimney and is discharged into the atmosphere. The low-temperature flue gas (high _CO2 concentration flue gas) discharged from the outlet of the top cyclone preheater of the _CO2 concentration system is divided into three routes. The first route is reintroduced into the decomposition furnace as circulating flue gas to ensure the cross-sectional wind speed in the offline _CO2 concentration system and prevent the _CO2 concentration system from collapsing. The second route is mixed with the high-temperature flue gas leaving the rotary kiln, and the temperature of the mixed flue gas is adjusted to meet the optimal reaction temperature for the _CO2 solidification absorption reaction entering the carbonization furnace. At the same time, the _CO2 concentration of the flue gas leaving the rotary kiln is increased, which can accelerate the carbonization reaction rate, improve the carbon capture efficiency, and reduce the _CO2 concentration in the flue gas leaving the carbonization system. According to the air volume requirements of the first and second routes, the amount of _CO2 flue gas in the third route can be indirectly adjusted to allow _CO2 to enter the mother liquor carbonation system for a carbonation reaction to prepare lithium carbonate.

The kiln tail smoke chamber, rotary kiln and cooler are connected in sequence to form a firing system. A tertiary air duct is arranged on the kiln door cover of the rotary kiln, and a first burner is arranged in the rotary kiln. The _CO2 concentration system includes a first row of multi-stage cyclone preheaters and a decomposition furnace, and the carbonization system includes a second row of multi-stage cyclone preheaters and a carbonization furnace. The first row of multi-stage cyclone preheaters and the second row of multi-stage cyclone preheaters respectively allow high-temperature flue gas and raw materials to fully exchange heat in the cyclone separators of each stage. The connecting pipe between the second stage cyclone preheater of the first row of multi-stage cyclone preheaters and the top cyclone preheater is provided with a feed port for feeding raw materials composed of limestone and lithium-containing minerals. The decomposition furnace is provided with a second burner, a tertiary air inlet and a circulating flue gas inlet. The tertiary air inlet is connected to the tertiary air duct, and the high-temperature tertiary air for cooling the hot clinker is used to provide combustion-supporting gas for fuel combustion in the decomposition furnace. The outlet of the decomposition furnace is connected to the air inlet of the bottom cyclone preheater of the first row of multi-stage cyclone preheaters, and the feed outlet of the bottom cyclone preheater is controlled by a material distribution valve to be divided into two routes: one route is connected to the kiln tail smoke chamber to feed the material undergoing carbonate decomposition in the decomposition furnace into the kiln tail smoke chamber through a connecting pipeline; the other route is connected to the inlet of the carbonization furnace through a pipeline to feed part of the material into the carbonization furnace to undergo _CO2 solidification absorption reaction to regenerate carbonate (CaO+ _CO2 → _CaCO3 ). The flue gas pipeline of the top cyclone preheater outlet of the _CO2 concentration system is divided into two routes, one route is connected to the dust collector; the other route is introduced into the cyclone separator through the second circulating fan, and mixed with the kiln flue gas to adjust the temperature of the mixed flue gas to the optimal carbonization temperature. The flue gas pipeline connected to the dust collector outlet is divided into two routes. One route is from the dust collector outlet through the first circulation fan to reintroduce part of the medium and high concentration _CO2 into the decomposition furnace, so that there is sufficient air volume and cross-sectional wind speed in the decomposition furnace, ensuring that the offline _CO2 concentration system does not collapse; the other route is introduced from the dust collector outlet through the tail exhaust fan into the mother liquor carbonation system, providing medium and high concentration _CO2 for the carbonation reaction _of 2LiOH+ _CO2 → _Li2CO3 + _H2O , increasing the gas ^phase driving force of _CO2 in the slurry, accelerating the formation of _CO32- in the slurry, and increasing the carbonization rate and sedimentation volume of alkaline lithium.

The outlet of the kiln tail smoke chamber is connected to the cyclone separator through the smoke pipeline, and the gas-solid separation is achieved through the cyclone separator. The fly ash out of the kiln tail smoke chamber is separated and sent to the rotary kiln again. The top smoke outlet of the cyclone separator is connected to the carbonization furnace, and a solidification absorption reaction occurs with the low-concentration _CO2 out of the kiln tail smoke chamber in the carbonization furnace. The air inlet of the bottom cyclone preheater of the carbonization system is connected to the carbonization furnace, and the bottom cyclone preheater discharge pipe is connected to the decomposition furnace, and the material that undergoes carbon fixation reaction is circulated back to the decomposition furnace to undergo carbonate decomposition reaction, so that the _CO2 concentration in the flue gas of the decomposition furnace is increased. The top cyclone preheater outlet of the second row of multi-stage cyclone preheaters is low-concentration _CO2 flue gas. In order to effectively utilize the enthalpy in the low-concentration _CO2 flue gas, a feed port is set to feed a certain proportion of raw materials into the connecting pipe between the second-stage cyclone preheater and the top cyclone preheater of the carbonization system. The raw materials are fully heat-exchanged with the low-concentration _CO2 flue gas in the cyclone preheaters except the bottom cyclone preheater. The preheated raw materials are introduced into the decomposition furnace of the _CO2 concentration system through the discharge pipe of the penultimate cyclone preheater of the carbonization system. After sufficient heat exchange, the low-temperature and low- _CO2 concentration flue gas exiting the carbonization system enters the flue gas waste heat utilization system to recover the available enthalpy, and the low-grade flue gas is discharged after treatment.

Compared with the prior art, the present invention has the following advantages and effects:

1. The conventional limestone roasting process system is usually an online system, in which the flue gas in the rotary kiln enters the decomposition furnace, resulting in a low _CO2 concentration (20% to 30%) in the flue gas at the outlet of the preheating and pre-decomposition system. The system's native low _CO2 concentration flue gas is used as a raw material to supply the subsequent mother liquor carbonation reaction, resulting in a slow carbonation reaction rate, so that the existing carbonation process mainly relies on the purchase of high-purity _CO2 gas as a reaction gas source. The present invention uses an independently arranged firing system and a _CO2 concentration system to prevent the flue gases generated by each system from interfering with each other. The kiln flue gas generated by the firing system does not enter the decomposition furnace in the _CO2 concentration system, avoiding the low-concentration _CO2 flue gas from the kiln from further diluting the _CO2 concentration in the flue gas in the decomposition furnace, and thus the _CO2 concentration of the flue gas out of the _CO2 concentration system can be increased to more than 40%. On the basis of preliminary concentration, the present invention introduces the decomposed raw material in the _CO2 concentration system into the carbonization furnace through the carbonization system, so that the flue gas out of the firing system undergoes a mineralization reaction in the carbonization furnace, and the mineralized product is then introduced into the decomposition furnace of the _CO2 concentration system through the bottom cyclone preheater of the carbonization system to undergo a carbonate decomposition reaction, and the solidified _CO2 is released again, so that the _CO2 in the flue gas out of the kiln is enriched in the decomposition furnace, and the _CO2 concentration in the flue gas of the _CO2 concentration system is further increased to 40% to 70%, thereby achieving _CO2 gradient concentration and meeting the carbonation requirements of the lithium-containing mother liquor.

2. The present invention circulates the low-temperature and high- _CO2 concentration flue gas from the _CO2 concentration system through the cyclone separator and mixes it with the high-temperature flue gas from the kiln through the second circulating fan, and adjusts the temperature of the mixed flue gas to meet the optimal reaction temperature of _CO2 solidification and absorption; at the same time, the medium and high concentration _CO2 flue gas from the _CO2 concentration system is introduced into the carbonization furnace to increase the _CO2 concentration of the mixed flue gas, thereby achieving the purpose of accelerating the carbonization reaction rate, making the _CO2 in the flue gas carbonize as much as possible, improving the capture efficiency, and reducing the _CO2 concentration in the flue gas from the carbonization system.

3. The present invention comprehensively considers the main system functions involved in the conventional limestone roasting production process. On the basis of the conventional system, only a carbonization system needs to be added, and the conventional system needs to be modified less, and the modification cost is low. In addition, _CO2 in the system flue gas can be effectively enriched without high-energy carbon capture measures such as full oxygen combustion and chemical absorption. The circulating air volume of the first and second circulating fans can adjust the _CO2 flow supplied to the mother liquor carbonation system, so that the carbonation demand and supply are matched to avoid unnecessary waste.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of an existing process for preparing lithium carbonate using a limestone roasting method using lithium-containing minerals as raw materials;

FIG2 is a process flow chart of preparing lithium carbonate by gradient concentration _{of CO2} in cooperation with lithium-containing minerals provided in an embodiment of the present invention;

3 is a flow chart of a system for preparing lithium carbonate by gradient concentration of CO ₂ in coordination with lithium-containing minerals provided in an embodiment of the present invention.

Among them, 1. Cooler; 2. Rotary kiln; 201. Tertiary air duct; 202. First burner; 3. Kiln tail smoke chamber; 4. _CO2 concentration system; 4-1. First row of multi-stage cyclone preheaters; 4-2. Decomposition furnace; 4-201. Second burner; 5. Carbonization system; 5-1. Second row of multi-stage cyclone preheaters; 5-2. Carbonization furnace; 6. Dust collector; 7. First circulation fan; 8. Second circulation fan; 9. Cyclone separator; 10. Tail exhaust fan.

DETAILED DESCRIPTION

In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

Example

The embodiment of the present invention provides a process for preparing lithium carbonate by gradient concentration _{of CO2} and synergistically using lithium-containing minerals, comprising the following steps:

Raw material preparation:

Limestone and lithium-containing minerals are mixed in a certain proportion, and the mixed raw materials are ground to prepare raw material powder with particle size meeting the requirements;

Clinker preparation and high _CO2 concentration flue gas preparation:

The raw meal powder is fed into the _CO2 concentration system 4 and the carbonization system 5 at a predetermined feeding ratio, respectively, and is respectively subjected to gas-solid heat exchange in the first multi-stage cyclone preheater 4-1 and the second multi-stage cyclone preheater 5-1, and then all enters the decomposition furnace of the _CO2 concentration system for calcination and decomposition; the hot raw meal after decomposition is separated by cyclone in the bottom cyclone preheater of the first multi-stage cyclone preheater 4-1 and then divided into two paths, the first path enters the rotary kiln 2 for calcination through the kiln tail smoke chamber 3, and the second path enters the carbonization furnace 5-2 of the carbonization system 5 for _CO2 solidification absorption, and then enters the decomposition furnace 4-2 of the _CO2 concentration system after cyclone separation in the bottom cyclone preheater of the second multi-stage cyclone preheater 5-1; high-temperature kiln gas and high-temperature lithium-based compound clinker are generated in the rotary kiln 2, and the high-temperature lithium-based compound clinker is cooled by the cooler 1 to obtain a lithium-based clinker product;

The high-temperature kiln gas enters the carbonization system 5 to preheat the raw material inside it and provide _CO2 medium to the hot raw material undergoing _CO2 solidification absorption reaction. The flue gas discharged from the top outlet of the carbonization system 5 is low-temperature and low- _CO2 concentration flue gas, and the temperature range of the low-temperature and low- _CO2 concentration flue gas is 200-320°C; the high-temperature tertiary air in the tertiary air duct 201 enters the _CO2 concentration system to provide combustion-supporting gas, and the raw material inside the decomposition furnace 4-2 undergoes a decomposition reaction. The flue gas discharged from the top outlet of the _CO2 concentration system 4 is low-temperature and high- _CO2 concentration flue gas, and the temperature range of the low-temperature and high- _CO2 concentration flue gas is 240-380°C, and the wet-based _CO2 concentration in the low-temperature and high- _CO2 concentration flue gas is 40-70%;

The low-temperature and high- _CO2 concentration flue gas is divided into three routes. The first route is circulated back to the decomposition furnace 4-2 through the first circulation fan 7; the second route is mixed with the high-temperature kiln gas from the rotary kiln 2 through the second circulation fan 8 and enters the carbonization furnace 5-2; the third route enters the mother liquor carbonation system to undergo carbonation reaction to prepare lithium carbonate;

Lithium-based clinker carbonation:

The lithium-based clinker product is soaked in water and filtered to obtain lithium hydroxide leachate and waste residue. The lithium hydroxide leachate is evaporated and concentrated and then carbonated. During the carbonation, the lithium hydroxide leachate reacts with part of the high _CO2 concentration flue gas from the _CO2 concentration system to undergo carbonation reaction, and then evaporated, separated and crystallized to obtain a lithium carbonate product.

As a preferred embodiment, the lithium content in the lithium-containing mineral is 3-5%, and the ratio of the lithium-containing mineral to the limestone in the raw material is in the range of 1:3.05-3.2.

As a preferred embodiment, the raw material feeding ratio of the _CO2 concentration system and the carbonization system is preferably 2-2.5:1.

As a preferred embodiment, the material distribution ratio between the bottom cyclone preheater of the _CO2 concentration system and the carbonization furnace entering the kiln tail smoke chamber is 0 to 1.5:1.

As a preferred embodiment, in the _CO2 concentration system, the temperature at the outlet of the decomposition furnace is 880-900°C.

As a preferred embodiment, the reaction temperature window for the CO ₂ solidification absorption reaction in the carbonization furnace 5 - 2 is 650 to 700°C.

As a preferred embodiment, the high-temperature kiln gas and low-temperature high- _CO2 concentration flue gas exiting the rotary kiln 2 are first separated from the fly ash before entering the carbonization furnace 5-2; when separating the fly ash, a cyclone separator 9 is used for separation and dust removal.

As a preferred embodiment, the low-temperature and high- _CO2 concentration flue gases from the first and third routes are first dedusted and then introduced into the decomposition furnace 4-2 and the mother liquor carbonation system via the first circulation fan 7 and the tail exhaust fan 10 respectively.

As a preferred embodiment, the low-temperature and low- _CO2 concentration flue gas discharged from the top outlet of the carbonization system recovers part of the heat through the waste heat recovery system and then enters the flue gas treatment system. After the flue gas treatment, it enters the chimney and is discharged into the atmosphere.

The embodiment of the present invention also provides a system for preparing lithium carbonate by gradient concentration of CO ₂ and coordinated lithium-containing minerals, comprising a CO ₂ concentration system 4, a carbonization system 5, a kiln tail smoke chamber 3, a rotary kiln 2, a cooler 1 and a mother liquor carbonation system;

The _CO2 concentration system comprises a first row of multi-stage cyclone preheaters 4-1 and a decomposition furnace 4-2, wherein the air inlet of the bottom cyclone preheater of the first row of multi-stage cyclone preheaters 4-1 is connected to the air outlet pipe of the decomposition furnace 4-2, and the air outlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters 4-1 discharges low-temperature and high- _CO2 concentration flue gas, the feed inlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters 4-1 is used for feeding raw material powder, the discharge port of the second-to-last cyclone preheater of the first row of multi-stage cyclone preheaters 4-1 is connected to the decomposition furnace 4-2, and the discharge port of the bottom cyclone preheater of the first row of multi-stage cyclone preheaters 4-1 is connected to the kiln tail smoke chamber 3 and the carbonization furnace 5-2;

The carbonization system comprises a second row of multi-stage cyclone preheaters 5-1 and a carbonization furnace 5-2, the air inlet of the bottom cyclone preheater of the second row of multi-stage cyclone preheaters 5-1 is connected to the air outlet pipe of the carbonization furnace 5-2, the air outlet of the top cyclone preheater of the second row of multi-stage cyclone preheaters 5-1 discharges low-temperature and low- _CO2 concentration flue gas, the feed inlet of the top cyclone preheater of the second row of multi-stage cyclone preheaters 5-1 is used for feeding raw material powder, and the discharge port of the second-to-last cyclone preheater and the discharge port of the bottom cyclone preheater of the second row of multi-stage cyclone preheaters 5-1 are both connected to the decomposition furnace 4-2;

The _CO2 concentration system 4 also includes a first branch pipeline, a second branch pipeline and a third branch pipeline; the air inlets of the first branch pipeline, the second branch pipeline and the third branch pipeline are all connected to the air outlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters 4-1; the exhaust port of the first branch pipeline is connected to the circulating flue gas inlet of the decomposition furnace 4-2, the exhaust port of the second branch pipeline is connected to the flue gas inlet of the carbonization furnace 5-2, and the exhaust port of the third branch pipeline is connected to the mother liquor carbonation system;

The kiln tail smoke chamber 3, rotary kiln 2, and cooler 1 are connected in sequence, and the lithium-based clinker product outlet of the cooler 1 is connected to the mother liquor carbonation system; the smoke outlet of the kiln tail smoke chamber 3 is connected to the smoke inlet of the carbonization furnace 5-2, and the kiln door cover of the rotary kiln 2 is connected to the inlet of the tertiary air duct 201 of the decomposition furnace 4-2.

As a preferred embodiment, a cyclone separator 9 is arranged between the smoke outlet of the kiln tail smoke chamber 3 and the smoke inlet of the carbonization furnace 5-2, the air inlet of the cyclone separator 9 is connected to the smoke outlet of the kiln tail smoke chamber 3 and the exhaust port of the second branch pipe, the top air outlet of the cyclone separator 9 is connected to the smoke inlet of the carbonization furnace 5-2, and the bottom discharge port of the cyclone separator 9 is connected to the kiln tail smoke chamber 3; the level of the cyclone separator 9 is one to two.

As a preferred embodiment, the air inlet of the first branch pipe and the air inlet of the third branch pipe are provided with a dust collector 6 on the pipeline connected to the air outlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters 4-1.

As a preferred embodiment, the top cyclone preheater outlet of the second row of multi-stage cyclone preheaters 5-1 is connected to a waste heat recovery system, and the flue gas outlet of the waste heat recovery system is connected to a flue gas treatment system.

As a preferred embodiment, the mother liquor carbonation system includes a water immersion and filtration device, an evaporation concentration device and a mother liquor carbonation device, the lithium-based clinker outlet of the cooler 1 is connected to the feed inlet of the water immersion and filtration device, the leachate outlet of the water immersion and filtration device is connected to the liquid inlet of the evaporation concentration device, the liquid outlet of the evaporation concentration device is connected to the liquid inlet of the mother liquor carbonation device, and the exhaust port of the first branch pipeline is connected to the air inlet of the mother liquor carbonation device.

As a further preferred embodiment, the mother liquor carbonation system also includes a grinding system, which is located between the cooler 1 and the water immersion and filtering device, the lithium-based clinker outlet of the cooler is connected to the material inlet of the grinding system, and the material outlet of the grinding system is connected to the feed inlet of the water immersion and filtering device.

As a preferred embodiment, the number of stages of the first-row multi-stage cyclone preheaters 4-1 is four to seven; the number of stages of the second-row multi-stage cyclone preheaters 5-1 is four to seven.

In order to better understand the above-mentioned embodiments of the present invention, they are further described below in conjunction with specific examples.

As shown in FIG. 2 , limestone and lithium-containing minerals are mixed in a certain proportion, and the mixed raw materials are fed into a raw material grinding system for grinding to prepare raw material powder with a particle size that meets the requirements.

The raw meal powder with limestone and lithium-containing minerals as main raw materials is fed into the _CO2 concentration system 4 and the carbonization system 5 in sequence. After gas-solid heat exchange in each multi-stage cyclone preheater, the raw meal is all fed into the decomposition furnace 4-2 of the _CO2 concentration system for calcination and decomposition. Then, after gas-solid separation in the bottom cyclone preheater 9 of the _CO2 concentration system 4, it enters the kiln tail smoke chamber 3, and then enters the rotary kiln 2 for solid phase reaction and calcination to generate lithium-based compound clinker. Then, the high-temperature lithium-based compound clinker is cooled by the cooler 1 to obtain the lithium-based clinker product.

The lithium-based clinker product is ground by the grinding system and then enters the water leaching and filtering device to obtain lithium hydroxide leaching solution and waste residue. The lithium hydroxide leaching solution enters the mother liquor carbonation device after the evaporation and concentration process. Part of the high _CO2 concentration flue gas from the _CO2 concentration system enters the mother liquor carbonation device for carbonation reaction, and then the lithium carbonate product is obtained through multiple processes such as evaporation, separation, and crystallization.

In addition, the low-temperature flue gas (low _CO2 concentration flue gas) discharged from the outlet of the top cyclone preheater of the carbonization system 5 is partially recovered by the waste heat recovery system and then enters the flue gas treatment system. After the flue gas treatment, it enters the chimney and is discharged into the atmosphere. The low-temperature flue gas (high _CO2 concentration flue gas) discharged from the outlet of the top cyclone preheater of the _CO2 concentration system 4 is divided into three routes. The first route is reintroduced into the decomposition furnace 4-2 as circulating flue gas to ensure the cross-sectional wind speed in the offline _CO2 concentration system so that the _CO2 concentration system 4 does not collapse; the second route is mixed with the high-temperature flue gas out of the rotary kiln 2, and the temperature of the mixed flue gas is adjusted to meet the optimal reaction temperature for the _CO2 solidification absorption reaction when entering the carbonization furnace 5-2. At the same time, the _CO2 concentration of the flue gas out of the rotary kiln is increased, which can accelerate the carbonization reaction rate, improve the carbon capture efficiency, and reduce the _CO2 concentration in the flue gas out of the carbonization system; the third route enters the mother liquor carbonation system for carbonation reaction to prepare lithium carbonate.

As shown in Fig. 3, the cooler 1, the rotary kiln 2 and the kiln tail smoke chamber 3 are connected in sequence to form a firing system, a tertiary air duct 201 is arranged on the kiln door cover of the rotary kiln 2, and a first burner 202 is arranged in the rotary kiln 2. The _CO2 concentration system 4 includes a first row of multi-stage cyclone preheaters 4-1 and a decomposition furnace 4-2, and the carbonization system 5 includes a second row of multi-stage cyclone preheaters 5-1 and a carbonization furnace 5-2.

The cyclone preheaters of the first multi-stage cyclone preheater 4-1 are connected in sequence, and the cyclone preheaters of the second multi-stage cyclone preheater 4-2 are connected in sequence. A feed port is set on the connecting pipe between the second stage cyclone preheater and the top cyclone preheater of the first multi-stage cyclone preheater 4-1, and a feed port is set on the connecting pipe between the second stage cyclone preheater and the top cyclone preheater of the second multi-stage cyclone preheater 5-1. Raw materials composed of limestone and lithium-containing minerals are fed to the feed ports in a front-to-back order. The lithium content of the lithium-containing minerals is 3-5%, and the ratio of the lithium-containing minerals to the limestone in the raw materials is in the range of 1:3.05-3.2. The preferred number of stages of the multi-stage cyclone preheater of the _CO2 concentration system 4 is four to seven, and the preferred number of stages of the multi-stage cyclone preheater of the carbonization system 5 is four to seven. The raw meal and the high-temperature flue gas fully exchange heat in the cyclone preheaters of each level of the _CO2 concentration system 4. The outlet temperature of the top cyclone preheater of the _CO2 concentration system 4 ranges from 240 to 380°C.

The furnace wall of the decomposition furnace 4-2 is provided with a tertiary air inlet, which is connected to the tertiary air duct 201, and the high-temperature tertiary air used to cool the hot clinker is used to provide combustion-supporting gas for the fuel combustion in the decomposition furnace 4-2. A circulating flue gas inlet is arranged at the bottom of the decomposition furnace 4-2, and a part of the medium and high concentration CO ₂ from the CO ₂ concentration system 4 is successively introduced into the decomposition furnace 4-2 after passing through the dust collector 6 and the first circulating fan 7, so that there is sufficient air volume and high cross-sectional wind speed in the decomposition furnace, ensuring that the offline CO ₂ concentration system 4 does not collapse. A second burner 4-201 is arranged above the tertiary air inlet. The outlet of the decomposition furnace 4-2 is connected to the inlet of the bottom cyclone preheater of the _CO2 concentration system 4. The discharge channel of the bottom cyclone preheater is divided into two paths. The first path is connected to the kiln tail smoke chamber 2 through a material pipe, and the raw material that has undergone carbonate decomposition in the decomposition furnace 4-2 is fed into the material pipe. The second path is connected to the inlet of the carbonization furnace 5-2 through a material pipe. A part of the material is fed into the carbonization furnace 5-2 through a material dividing valve to generate a _CO2 solidification absorption reaction to regenerate carbonate (CaO+ _CO2 → _CaCO3 ). The material dividing valve arranged on the discharge pipe of the bottom cyclone preheater of the _CO2 concentration system 4 controls the ratio of the materials entering the kiln tail smoke chamber 3 and the carbonization furnace 5-2 to be 0 to 1.5:1. The decomposition furnace 4-2 is provided with a raw material inlet above the second burner 4-201, and the raw material inlet is connected to the discharge pipe of the penultimate cyclone preheater of the _CO2 concentration system 4, and the temperature of the outlet of the decomposition furnace 4-2 in the _CO2 concentration system 4 is controlled to be 880-900°C, so that the preheated raw material fed into the decomposition furnace 4-2 is fully decomposed (the _CO2 partial pressure in the decomposition furnace is relatively high, so the temperature is increased by 30-50°C compared with the conventional working condition). The present invention independently arranges the firing system and the _CO2 concentration system, so that the flue gas generated by each system does not interfere with each other, and the kiln flue gas generated by the rotary kiln 2 does not enter the decomposition furnace of the _CO2 concentration system, so as to avoid the low-concentration _CO2 flue gas out of the rotary kiln 2 from further diluting the _CO2 concentration in the flue gas in the decomposition furnace 4-2, and then the _CO2 concentration of the flue gas out of the _CO2 concentration system can be increased to more than 40%.

The outlet of the kiln tail smoke chamber 3 is connected to the cyclone separator 9 through a flue gas pipeline, and gas-solid separation is achieved through the cyclone separator 9. The fly ash leaving the kiln tail smoke chamber 3 is separated and then sent back to the rotary kiln 2. The top flue gas outlet of the cyclone separator 9 is connected to the carbonization furnace 5-2 through a flue gas pipeline, and a solidification absorption reaction occurs with the low-concentration _CO2 flue gas leaving the kiln tail smoke chamber in the carbonization furnace 5-2. The preferred stage of the cyclone separator 9 is one to two, and the optimal reaction temperature window for the _CO2 solidification absorption reaction in the carbonization furnace 5-2 is 650 to 700°C. The air inlet of the bottom cyclone preheater of the carbonization system 5 is connected to the carbonization furnace 5-2, and the carbonization product is separated into gas and solid in the bottom cyclone preheater. The raw material that undergoes carbon fixation reaction is circulated back to the decomposition furnace 4-2 through the connecting material pipe between the bottom cyclone preheater and the decomposition furnace 4-2 for decomposition, and the _CO2 in the flue gas leaving the rotary kiln 2 is enriched in the decomposition furnace, so that the _CO2 concentration of the flue gas of the _CO2 concentration system 4 is improved. The wet basis concentration of _CO2 in the flue gas of the _CO2 concentration system 4 is 40% to 70%. Feeding a certain proportion of raw materials into the feed port set at the connecting pipe of the second-stage cyclone preheater and the top cyclone preheater of the carbonization system 5 can effectively recover and utilize the heat enthalpy in the low-concentration _CO2 flue gas, and fully exchange heat with the low-concentration _CO2 flue gas in the cyclone preheaters other than the bottom cyclone preheater. The preheated raw materials enter the decomposition furnace 4-2 through the discharge pipe of the penultimate cyclone preheater of the carbonization system 5. The raw material feeding ratio of the _CO2 concentration system 4 and the carbonization system 5 is preferably 2 to 2.5:1. After sufficient heat exchange, the low-temperature and low- _CO2 concentration flue gas exiting the carbonization system 5 enters the flue gas waste heat utilization system to recover the available heat enthalpy, and the low-grade flue gas is discharged after treatment. The air outlet temperature range of the top cyclone preheater of the carbonization system 5 is 200 to 320°C.

The air outlet of the top cyclone preheater of the _CO2 concentration system 4 is connected to the second circulation fan 8 through a flue gas pipeline, and is introduced into the kiln flue gas pipeline through the second circulation fan 8. The medium and high concentration _CO2 is mixed with the kiln flue gas and the temperature of the mixed flue gas is adjusted to the optimal carbonization temperature. The optimal reaction temperature window for the _CO2 solidification absorption reaction in the carbonization furnace 5-2 is 650-700°C. The mixed flue gas enters the carbonization furnace after the fly ash is separated by the cyclone separator 9, and the _CO2 concentration of the flue gas out of the rotary kiln is increased at the same time, which can accelerate the carbonization reaction rate, improve the carbon capture efficiency, and reduce the _CO2 concentration in the flue gas out of the carbonization system.

The tail exhaust fan 10 introduces the medium and high concentration _CO2 dedusted by the dust collector into the mother liquor carbonation system, provides medium and high concentration _CO2 for the carbonation reaction of _2LiOH + _CO2 → _Li2CO3 + _H2O , increases the gas phase driving force of _CO2 in the slurry, accelerates the formation ^of _CO32- in the slurry, and increases the carbonization speed and sedimentation volume of alkaline lithium. The circulating air volume of the tail exhaust fan 10, the first circulating fan 7, and the second circulating fan 8 can adjust the _CO2 flow rate supplied to the mother liquor carbonation system, so that the _CO2 consumption required for carbonation matches the supply amount, avoiding unnecessary waste.

It should be noted that those skilled in the art can make settings according to actual needs. The cooler can be a grate cooler, a single-drum cooler or a multi-drum cooler, and the fan can be a combination of existing multiple fans.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (16)

1. A process for preparing lithium carbonate by gradient concentration of _CO2 in cooperation with lithium-containing minerals, characterized in that it comprises the following steps: Raw material preparation: Limestone and lithium-containing minerals are mixed in a certain proportion, and the mixed raw materials are ground to prepare raw material powder with particle size meeting the requirements; Clinker preparation and high _CO2 concentration flue gas preparation: The raw meal powder is fed into the _CO2 concentration system and the carbonization system at a predetermined feeding ratio, and then passes through the gas-solid heat exchange of each multi-stage cyclone preheater, and then all enters the decomposition furnace of the _CO2 concentration system for calcination and decomposition; the hot raw meal after decomposition is separated by cyclone and divided into two paths, the first path enters the rotary kiln through the kiln tail smoke chamber for calcination, and the second path enters the carbonization furnace of the carbonization system for _CO2 solidification absorption, and then enters the decomposition furnace of the _CO2 concentration system after cyclone separation; high-temperature kiln gas and high-temperature lithium-based compound clinker are generated in the rotary kiln, and the high-temperature lithium-based compound clinker is cooled by a cooler to obtain a lithium-based clinker product; The high-temperature kiln gas enters the carbonization system to preheat the raw material inside it and provide _CO2 medium to the hot raw material undergoing _CO2 solidification absorption reaction. The flue gas discharged from the top outlet of the carbonization system is low-temperature and low- _CO2 concentration flue gas; the high-temperature tertiary air enters the _CO2 concentration system to preheat and pre-decompose the raw material inside it. The flue gas discharged from the top outlet of the _CO2 concentration system is low-temperature and high- _CO2 concentration flue gas. The temperature range of the low-temperature and high- _CO2 concentration flue gas is 240-380℃, and the wet-basis _CO2 concentration in the low-temperature and high- _CO2 concentration flue gas is 40-70%; The low-temperature and high- _CO2 concentration flue gas is divided into three routes. The first route is reintroduced into the decomposition furnace after circulation; the second route is mixed with the high-temperature kiln gas from the rotary kiln and enters the carbonization furnace; the third route enters the mother liquor carbonation system for carbonation reaction to prepare lithium carbonate; Lithium-based clinker carbonation: The lithium-based clinker product is soaked in water and filtered to obtain lithium hydroxide leachate and waste residue. The lithium hydroxide leachate is evaporated and concentrated and then carbonated. During the carbonation, the lithium hydroxide leachate reacts with part of the high _CO2 concentration flue gas from the _CO2 concentration system to undergo carbonation reaction, and then evaporated, separated and crystallized to obtain a lithium carbonate product. 2. The process for preparing lithium carbonate by gradient concentration of _CO2 and coordinated use of lithium-containing minerals according to claim 1 is characterized in that the lithium content in the lithium-containing mineral is 3-5%, and the ratio of the lithium-containing mineral to limestone in the raw material is in the range of 1:3.05-3.2. 3. The process for preparing lithium carbonate by _CO2 gradient concentration and coordinated lithium-containing minerals according to claim 1 is characterized in that the raw material feeding ratio of the _CO2 concentration system and the carbonization system is preferably 2 to 2.5:1. 4. The process for preparing lithium carbonate by gradient _CO2 concentration and coordinated lithium-containing minerals according to claim 1 is characterized in that the material distribution ratio between the bottom cyclone preheater of the _CO2 concentration system entering the kiln tail smoke chamber and the carbonization furnace is 0 to 1.5:1. 5. The process for preparing lithium carbonate by _CO2 gradient concentration and coordinated lithium-containing minerals according to claim 1 is characterized in that: in the _CO2 concentration system, the temperature at the outlet of the decomposition furnace is 880-900°C. 6. The process for preparing lithium carbonate by gradient concentration of _CO2 and coordinated lithium-containing minerals according to claim 1 is characterized in that the reaction temperature window for the _CO2 solidification absorption reaction in the carbonization furnace is 650-700°C. 7. The process for preparing lithium carbonate by _CO2 gradient concentration and coordinated lithium-containing minerals according to claim 1 is characterized in that: the high-temperature kiln gas and low-temperature high- _CO2 concentration flue gas exiting the rotary kiln are first separated from the fly ash before entering the carbonization furnace; and a cyclone separator is used for fly ash separation. 8. The process for preparing lithium carbonate by gradient concentration of CO2 and coordinated _lithium- containing minerals according to claim 1 is characterized in that the low-temperature and high- _CO2 concentration flue gases from the first and third routes are first dedusted before entering the decomposition furnace and the mother liquor carbonation system. 9. The process for preparing lithium carbonate by gradient _CO2 concentration and coordinated lithium-containing minerals according to claim 1 is characterized in that the low-temperature and low- _CO2 concentration flue gas discharged from the top outlet of the carbonization system is partially recovered by the waste heat recovery system and then enters the flue gas treatment system, and after the flue gas treatment, it enters the chimney and is discharged into the atmosphere. 10. A system for preparing lithium carbonate by gradient _CO2 concentration and synergistically using lithium-containing minerals, characterized in that it comprises a _CO2 concentration system, a carbonization system, a kiln tail smoke chamber, a rotary kiln, a cooler and a mother liquor carbonation system; The _CO2 concentration system comprises a first row of multi-stage cyclone preheaters and a decomposition furnace, wherein the air inlet of the bottom cyclone preheater of the first row of multi-stage cyclone preheaters is connected to the air outlet pipe of the decomposition furnace, the air outlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters discharges low-temperature and high- _CO2 concentration flue gas, the feed inlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters is used for feeding raw material powder, the discharge port of the second-to-last cyclone preheater of the first row of multi-stage cyclone preheaters is connected to the decomposition furnace, and the discharge port of the bottom cyclone preheater of the first row of multi-stage cyclone preheaters is connected to the kiln tail smoke chamber and the carbonization furnace; The carbonization system comprises a second row of multi-stage cyclone preheaters and a carbonization furnace, wherein the air inlet of the bottom cyclone preheater of the second row of multi-stage cyclone preheaters is connected to the air outlet pipe of the carbonization furnace, the air outlet of the top cyclone preheater of the second row of multi-stage cyclone preheaters discharges low-temperature and low- _CO2 concentration flue gas, the feed inlet of the top cyclone preheater of the second row of multi-stage cyclone preheaters is used for feeding raw meal powder, and the discharge port of the second-to-last cyclone preheater and the discharge port of the bottom cyclone preheater of the second row of multi-stage cyclone preheaters are both connected to the decomposition furnace; The _CO2 concentration system further includes a first branch pipeline, a second branch pipeline and a third branch pipeline; the air inlets of the first branch pipeline, the second branch pipeline and the third branch pipeline are all connected to the air outlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters; the exhaust port of the first branch pipeline is connected to the circulating flue gas inlet of the decomposition furnace, the exhaust port of the second branch pipeline is connected to the flue gas inlet of the carbonization furnace, and the exhaust port of the third branch pipeline is connected to the mother liquor carbonation system; The kiln tail smoke chamber, rotary kiln and cooler are connected in sequence, and the lithium-based clinker product outlet of the cooler is connected to the mother liquor carbonation system; the smoke outlet of the kiln tail smoke chamber is connected to the smoke inlet of the carbonization furnace, and the kiln door cover of the rotary kiln is connected to the tertiary air inlet of the decomposition furnace. 11. The system for preparing lithium carbonate by gradient concentration of _CO2 and coordinated lithium-containing minerals according to claim 10 is characterized in that: a cyclone separator is arranged between the smoke outlet of the kiln tail smoke chamber and the smoke inlet of the carbonization furnace, the air inlet of the cyclone separator is connected to the smoke outlet of the kiln tail smoke chamber and the exhaust port of the second branch pipeline, the top air outlet of the cyclone separator is connected to the smoke inlet of the carbonization furnace, and the bottom discharge port of the cyclone separator is connected to the kiln tail smoke chamber; the cyclone separator has one to two stages. 12. The system for preparing lithium carbonate by gradient concentration of _CO2 and coordinated lithium-containing minerals according to claim 10 is characterized in that: the air inlet of the first branch pipeline and the air inlet of the third branch pipeline are provided with a dust collector on the pipeline connected to the air outlet of the top cyclone preheater of the first row of multi-stage cyclone preheaters. 13. The system for preparing lithium carbonate by gradient concentration of _CO2 and coordinated lithium-containing minerals according to claim 10 is characterized in that the air outlet of the top cyclone preheater of the second row of multi-stage cyclone preheaters is connected to a waste heat recovery system, and the flue gas outlet of the waste heat recovery system is connected to a flue gas treatment system. 14. The system for preparing lithium carbonate by gradient concentration of _CO2 and coordinated lithium-containing minerals according to claim 10, characterized in that: the mother liquor carbonation system comprises a water immersion and filtration device, an evaporation concentration device and a mother liquor carbonation device, the lithium-based clinker outlet of the cooler is connected to the feed inlet of the water immersion and filtration device, the leachate outlet of the water immersion and filtration device is connected to the liquid inlet of the evaporation concentration device, the liquid outlet of the evaporation concentration device is connected to the liquid inlet of the mother liquor carbonation device, and the exhaust port of the first branch pipeline is connected to the air inlet of the mother liquor carbonation device. 15. The system for preparing lithium carbonate by _CO2 gradient concentration and coordinated lithium-containing minerals according to claim 14 is characterized in that: the mother liquor carbonation system also includes a grinding system, the grinding system is located between the cooler and the water immersion and filtering device, the lithium-based clinker outlet of the cooler is connected to the material inlet of the grinding system, and the material outlet of the grinding system is connected to the feed inlet of the water immersion and filtering device. 16. The system for preparing lithium carbonate by gradient concentration of _CO2 and coordinated lithium-containing minerals according to claim 10, characterized in that: the number of stages of the first row of multi-stage cyclone preheaters is four to seven; the number of stages of the second row of multi-stage cyclone preheaters is four to seven.