CN112897557A

CN112897557A - Process for preparing high-purity lithium carbonate from lithium salt solution

Info

Publication number: CN112897557A
Application number: CN202110177058.3A
Authority: CN
Inventors: 戴梓宜; 戴晓宇; 袁中强
Original assignee: Hunan Yongshan Lithium Industry Co ltd
Current assignee: Hunan Yongshan Lithium Industry Co ltd
Priority date: 2021-02-07
Filing date: 2021-02-07
Publication date: 2021-06-04

Abstract

The invention discloses a process for preparing high-purity lithium carbonate from a lithium salt solution, which comprises the following steps: mixing and stirring a lithium salt solution to be treated and an oxalate solution, and precipitating to remove calcium; and filtering, finely removing impurities, thermally decomposing, centrifuging and drying the solution after calcium removal to obtain the high-purity lithium carbonate. The invention uses oxalate as a calcium removal reagent to replace the traditional Na₂CO₃Oxalate can form CaC with calcium₂O₄The effect of preliminary calcium removal is achieved, and due to C₂O₄ ^2‑Does not affect Li₂CO₃Ksp of (ii) does not cause Li₂CO₃Precipitate without producing Li₂C₂O₄The CaC can be generated by precipitation and subsequent thermal decomposition process₂O₄Precipitate, CaC₂O₄The precipitate enters a drying procedure, and can be pyrolyzed in the drying procedure and decomposed into CaO and CO₂Thereby reducing the amount of Li₂CO₃Influence of the principal content.

Description

Process for preparing high-purity lithium carbonate from lithium salt solution

Technical Field

The invention belongs to the technical field of lithium salt solution purification, and particularly relates to a process for preparing high-purity lithium carbonate from a lithium salt solution.

Background

LiHCO in lithium salt works₃In the purification of the solution, the fine impurity removal is generally accomplished by using a chelating agent or a resin system after the initial impurity removal (calcium removal) by using soda ash. In the precipitation of Ca using soda ash²⁺The process (2) often produces a large amount of COD (chemical oxygen demand) which cannot be treated and which cannot meet the emission standards. And due to Na₂CO₃The manufacturing process of (1) introduces a part of Cl into the system^-This fraction of Cl^-If the system cannot process and continuously concentrate, high corrosion phenomenon is formed on equipment; in addition, due to the addition of Na₂CO₃Greatly improve CO in lithium salt₃ ^2-Concentration, because Ksp is fixed, will lower Li⁺Concentration of resulting in L_i2CO₃Precipitate together with CaCO₃The precipitate is discharged, affecting the main content. In the fine impurity removal process, a part of free Ca can be remained in a solution system regardless of adopting a chelating agent or a resin system for impurity removal²⁺In the subsequent thermal decomposition step, this portion of free calcium forms CaCO₃Precipitation, final neutralization of Li₂CO₃Coprecipitation, and drying to affect the main content and impurity content of the finished product. Some researchers adopt an extraction method to carry out primary calcium removal, but the extraction method is complex in calcium removal operation, and although the lithium carbonate with high purity can be obtained, the extraction cost is high, so that the method is not suitable for industrial scale.

Therefore, the lithium salt factory at present lacks a low-cost lithium salt factory which can reduce LiHCO₃The calcium content in the solution can avoid introducing chloride ions and can also avoid the process that the main content is influenced by impurity precipitation.

Disclosure of Invention

The technical problem to be solved by the present invention is to overcome the above mentioned disadvantages and drawbacks of the background art and to provide a process for preparing high purity lithium carbonate from lithium salt solution.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

a process for preparing high-purity lithium carbonate from a lithium salt solution comprises the following steps:

(1) mixing a lithium salt solution to be treated with a precipitator, stirring, precipitating and removing calcium, wherein the precipitator is an oxalate solution;

(2) and (2) filtering, finely removing impurities, thermally decomposing, centrifuging and drying the solution subjected to calcium removal in the step (1) to obtain high-purity lithium carbonate.

In the above process, preferably, in the step (1), the oxalate solution is Na₂C₂O₄Solution of said Na₂C₂O₄The addition amount of the solution is 1.1 to 1.3 times of the theoretical molar weight (the theoretical molar weight refers to the amount of Ca in the solution²⁺Complete precipitation of the desired Na₂C₂O₄Theoretical amount of (c).

The above process, preferably, Na₂C₂O₄The solution is prepared by mixing Na₂C₂O₄Or Na prepared from hydrate powder and pure water (or other process water and condensed water)₂C₂O₄And (3) solution.

Preferably, in the step (1), the temperature in the calcium removal process is 10-60 ℃, the stirring speed is 30-60 rpm, and the stirring time is not less than 30 min.

The calcium removal process mainly comprises the following chemical reactions:

in the above process, preferably, in the step (2), the filtration process is to filter the solution after calcium removal sequentially through a primary filtration device, a primary filtration buffer tank, a secondary filtration device and a secondary filtration buffer tank, wherein the primary filtration device and the secondary filtration device are any one of a filter press, a microporous precise filter and a bag filter, more preferably, the pore of the primary filtration device is 2000 meshes, and the pore of the secondary filtration tube is less than or equal to 20 μm. Removing insoluble substances in the original lithium salt solution and subsequently generated CaC as much as possible by a multiple filtration device₂O₄And (4) precipitating.

In the above process, preferably, in the step (2), the fine impurity removal means impurity removal by a combination of an anionic resin (preferably, a macroporous chelating resin having a polyvalent alcohol group as a functional group) and a cationic resin (preferably, a macroporous chelating resin having an aminocarboxylic acid (more preferably, phosphoric acid) -type active group).

In the above process, preferably, in the step (2), the thermal decomposition is performed in a high-temperature reaction apparatus selected from any one of a steam coil type reaction vessel, a steam jacketed type reaction vessel, and a shell and tube type evaporator.

In the above purification process, preferably, in the step (2), the thermal decomposition temperature is not lower than 95 ℃ and the thermal decomposition time is not lower than 45 min.

The chemical reactions mainly produced by thermal decomposition are as follows:

in the above process, preferably, in the step (2), the centrifugation is performed by using one or more centrifuge combinations of a vertical flat scraper centrifuge, a siphon centrifuge, a sedimentation centrifuge and a double-push centrifuge.

Preferably, in the step (2), the drying includes pre-drying at a temperature of not less than 100 ℃ for not less than 20min, and then heating to 300-350 ℃ for drying for 30-90 min.

In the above process, preferably, the device used in the drying process comprises one or more of a vacuum dryer, a rotary dryer and a disc dryer. Further preferably, the drying process is carried out using an electric rotary kiln.

The main chemical reactions generated during the drying process are as follows:

compared with the prior art, the invention has the advantages that:

(1) the invention uses oxalate as a calcium removal reagent to replace the traditional Na₂CO₃Oxalate can form CaC with calcium₂O₄The effect of preliminary calcium removal is achieved, and due to C₂O₄ ^2-Does not affect Li₂CO₃Ksp of (ii) does not cause Li₂CO₃Precipitating; meanwhile, Li₂C₂O₄The solubility is 8g/100ml, under which Li is not produced₂C₂O₄The CaC can be generated by precipitation and subsequent thermal decomposition process₂O₄Precipitate, CaC₂O₄The precipitate enters a drying procedure, and can be pyrolyzed in the drying procedure and decomposed into CaO and CO₂Thereby reducing the amount of Li₂CO₃Influence of the principal content.

(2) The technical scheme of the invention can reduce the calcium impurities to 56% of the original process and improve the purity of the lithium carbonate, and the purity of the prepared calcium carbonate is up to more than 99.8%.

(3) The decomposition mother liquor generated in the process of the invention does not relate to the enrichment of COD, has the advantage of environmental protection, and can greatly save the production cost. Discarding a batch of mother liquor according to the requirement of 10t of lithium carbonate per manufacture according to the proportion of 1: calculating the solid-liquid ratio of 20, discarding 20t of mother liquor, wherein the Li content of the mother liquor is 2g/L, and the Li content is converted into Li₂CO₃211kg, according to the current market price of 60000 yuan/ton, 1266 yuan can be saved per 1 ton of purified lithium carbonate production line, 10000 ton/a of lithium carbonate production line can be saved, and 1266 ten thousand yuan per year can be saved.

Drawings

FIG. 1 is a process flow diagram of the present invention.

Detailed Description

In order to facilitate an understanding of the invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of the invention is not limited to the specific embodiments below.

Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

Example 1:

the invention relates to a process for preparing high-purity lithium carbonate from a lithium salt solution, wherein the lithium salt solution is 20m³、Li⁺The content of the organic acid is 9-10 g/L, Ca²⁺The specific process flow diagram of the lithium bicarbonate solution with the content of 40-50 mg/L is shown in figure 1, and the method comprises the following steps:

(1) 134kg of sodium oxalate was put into a sodium oxalate dissolution tank, and ultrapure water was added to 1m³Stirring is started at 30rpm for 30min, and at the moment, the sodium oxalate solution is 1 mol/L;

(2) according to the dosage of 1.1 times of the sodium oxalate solution required by theoretical calcium removal, 27.5L of prepared sodium oxalate solution is pumped into a calcium removal tank (the calcium removal tank is filled with a lithium salt solution to be treated) for calcium removal, and the calcium removal conditions are as follows: the temperature is 20 ℃, the stirring speed is 60rpm, and the calcium removal time is 60 min;

(3) filtering the mixed solution after calcium removal by a plate-and-frame filter press, a primary filtering buffer tank, a microporous precise filter and a secondary filtering buffer tank in sequence, wherein Li in the filtrate⁺9-10 g/L of Ca²⁺The content is 10 mg/L;

(4) pumping the filtrate filtered in the step (3) into a resin impurity removal system (anion and cation resin combined impurity removal system), adsorbing and removing impurities, wherein the impurity removal liquid consists of Li⁺9-10 g/L of Ca²⁺The content is 2 mg/L;

(5) pumping the impurity-removing liquid obtained in the step (4) into a steam coil type reaction kettle for thermal decomposition reaction, wherein the reaction conditions are as follows: the temperature is 95 ℃, the stirring speed is 30rpm, and the reaction time is 60 min;

(6) carrying out solid-liquid separation on the slurry subjected to thermal decomposition in the step (5) by using a vertical flat scraper centrifuge to obtain a solid phase of a lithium carbonate wet material with the water content of about 10%, and a liquid phase of a thermal decomposition mother liquor, namely Li⁺Content 2g/L, Ca²⁺The content is 2 mg/L;

(7) transferring the lithium carbonate wet material to an electric rotary kiln for drying (the rotating speed of a hearth is 5rpm), preheating and drying at 100 ℃ for 20min, then heating to 350 ℃ for drying at constant temperature for 60min, and controlling the moisture to be 0.01% after drying is finished to obtain the high-purity lithium carbonate.

Ca content of 10% of maximum water content²⁺CaO is synthesized by folding, and the absolute mass of lithium carbonate generated by centrifugation is as follows: m ═ c ═ V ═ M ═ (10-2) × 20 ═ 14/74 ═ 845.7kg, plus 10% water content, total mass 845.7/(100% -10%) -939.68 kg, mass of CaO produced was: 939.68 × 10% × 2/1000 × 56/40 ═ 0.263 g; the purity of the dried lithium carbonate finished product can reach more than 99.8 percent.

Example 2:

the invention relates to a process for preparing high-purity lithium carbonate from a lithium salt solution, wherein the lithium salt solution is 20m³、Li⁺The content of the organic acid is 9-10 g/L, Ca²⁺The specific process flow diagram of the lithium bicarbonate solution with the content of 10mg/L is shown in figure 1, and comprises the following steps:

(1) 134kg of sodium oxalate was put into a sodium oxalate dissolution tank, and ultrapure water was added to 1m³Stirring is started at 30rpm for 30min, and at the moment, the concentration of the sodium oxalate solution is 1 mol/L;

(2) according to the dosage of 1.1 times of the sodium oxalate solution required by theoretical calcium removal, 5.5L of the sodium oxalate solution prepared in the step (1) is pumped into a calcium removal tank (the calcium removal tank is filled with a lithium salt solution to be treated) for calcium removal, and the calcium removal conditions are as follows: the temperature is 20 ℃, the stirring speed is 60rpm, and the calcium removal time is 60 min;

(3) the mixed solution after the calcium removal in the step (2) is sequentially processedFiltering with plate-and-frame filter press, primary filtering buffer tank, microporous precise filter, and secondary filtering buffer tank to obtain filtrate containing Li⁺9-10 g/L of Ca²⁺The content is 5 mg/L;

(4) pumping the filtrate obtained in the step (3) into a resin impurity removal system (anion and cation resin combined impurity removal), and removing Li in the impurity removal liquid⁺9-10 g/L of Ca²⁺The content is 1 mg/L;

(5) pumping the impurity-removing liquid into a steam jacket type reaction kettle, starting thermal decomposition reaction, wherein the reaction conditions are as follows: the temperature is 95 ℃, the stirring speed is 30rpm, and the reaction time is 60 min;

(6) performing solid-liquid separation on the slurry decomposed in the step (5) by using a siphon centrifuge, wherein the solid phase is lithium carbonate wet material with the water content of 6-10%, and the liquid phase is thermal decomposition mother liquor, namely Li⁺Content 2g/L, Ca²⁺The content is 1 mg/L;

(7) transferring the lithium carbonate wet material to an electric rotary kiln (the rotating speed of a hearth is 5rpm) for drying, wherein the parameters of the electric rotary kiln are as follows: preheating and drying at 100 ℃ for 20min, heating to 350 ℃, drying at constant temperature for 60min, and obtaining high-purity lithium carbonate after drying is finished and drying is finished, wherein the water content is controlled to be 0.01%.

Ca content of 10% of maximum water content²⁺CaO is synthesized by folding, and the absolute mass of lithium carbonate generated by centrifugation is as follows: m (c) V (M) (10-2) 20 (M) 14/74 (845.7 kg), 10% water content, and 939.68kg (total mass of 845.7/(100% -10%). The produced CaO has the following quality: 939.68 × 10% × 1/1000 × 56/40 ═ 0.132 g; the purity of the dried lithium carbonate finished product can reach more than 99.99 percent.

Claims

1. A process for preparing high-purity lithium carbonate from a lithium salt solution is characterized by comprising the following steps:

(1) mixing and stirring a lithium salt solution to be treated and a precipitator for precipitation and calcium removal, wherein the precipitator is an oxalate solution;

2. The process of claim 1, wherein in step (1), the oxalate solution is Na₂C₂O₄The amount of the solution added is 1.1 to 1.3 times of the theoretical molar weight.

3. The process according to claim 1, wherein in the step (1), the temperature in the calcium removal process is 10-60 ℃, the stirring speed is 30-60 rpm, and the stirring time is not less than 30 min.

4. The process according to claim 1, wherein in the step (2), the filtration process is to sequentially filter the solution after calcium removal through a primary filtration device, a primary filtration buffer tank, a secondary filtration device and a secondary filtration buffer tank, wherein the equipment of the primary filtration device and the secondary filtration device is any one of a filter press, a microporous microfilter and a bag filter.

5. The process as claimed in claim 1, wherein in the step (2), the fine impurity removal means impurity removal by adopting a combination of anion and cation resins;

the thermal decomposition is carried out in a high-temperature reaction device, and the high-temperature reaction device is selected from any one of a steam coil type reaction kettle, a steam jacketed type reaction kettle and a shell and tube evaporator;

the centrifugation is carried out by adopting one or more centrifuge combination devices of a vertical flat scraper centrifuge, a siphon centrifuge, a sedimentation centrifuge and a double-push centrifuge;

the device adopted in the drying process comprises one or more of a vacuum dryer, a rotary dryer and a disc dryer.

6. The process according to claim 1, wherein in the step (2), the thermal decomposition temperature is not lower than 95 ℃ and the thermal decomposition time is not lower than 45 min.

7. The process of claim 1, wherein in the step (2), the drying comprises pre-drying at a temperature of not less than 100 ℃ for not less than 20min, and then heating to 300-350 ℃ for drying for 30-90 min.

8. The process according to any one of claims 1 to 7, wherein the lithium salt solution to be treated is a lithium bicarbonate solution or a lithium sulfate solution, wherein the lithium salt solution to be treated has a lithium content of not less than 6g/L and a calcium content of not less than 5X 10^- ⁵mol/L。

9. The process of any one of claims 1 to 7, wherein the high purity lithium carbonate is obtained at a purity of not less than 99.8%.