阅读说明：本技术 碳酸型盐湖卤水转化成氯化物型卤水的方法 (Method for converting carbonate type salt lake brine into chloride type brine ) 是由 曹建勇 杨荣 梅波 赵清 于 2020-07-01 设计创作，主要内容包括：一种碳酸型盐湖卤水转化成氯化物型卤水的方法,包括下述步骤：将碳酸型盐湖卤水通过离子交换树脂,去除所述卤水中的微量钙镁离子获得软化卤水；将软化卤水泵送入第一级纳滤膜系统中,在第一级纳滤膜的两侧施加压力,形成压差；软化卤水中的部分水、钠离子、钾离子、锂离子、以及氯离子从高压侧经第一级纳滤膜迁移到低压侧；高压侧的高价阴离子被富集,获得富含高价阴离子的卤水,将该富含高价阴离子的卤水泵送返回盐湖,所述高价阴离子包括硫酸根离子、碳酸根离子以及多硼酸根离子；低压侧获得含有少量高价阴离子的氯化物型卤水。(A method for converting carbonate type salt lake brine into chloride type brine comprises the following steps: passing carbonate type salt lake brine through ion exchange resin, and removing trace calcium and magnesium ions in the brine to obtain softened brine; pumping softened brine into a first-stage nanofiltration membrane system, and applying pressure on two sides of a first-stage nanofiltration membrane to form a pressure difference; part of water, sodium ions, potassium ions, lithium ions and chloride ions in the softened brine are transferred from the high-pressure side to the low-pressure side through the first-stage nanofiltration membrane; enriching high-valence anions at a high-pressure side to obtain brine rich in the high-valence anions, and pumping the brine rich in the high-valence anions back to the salt lake, wherein the high-valence anions comprise sulfate ions, carbonate ions and polyborate ions; the low pressure side obtains chloride brine containing a small amount of high valent anions.)

1. A method for converting carbonate type salt lake brine into chloride type brine is characterized by comprising the following steps:

passing carbonate type salt lake brine through ion exchange resin, and removing trace calcium and magnesium ions in the brine to obtain softened brine;

pumping softened brine into a first-stage nanofiltration membrane system, and applying pressure on two sides of a first-stage nanofiltration membrane to form a pressure difference;

part of water, sodium ions, potassium ions, lithium ions and chloride ions in the softened brine are transferred from the high-pressure side to the low-pressure side through the first-stage nanofiltration membrane;

enriching high-valence anions at a high-pressure side to obtain brine rich in the high-valence anions, and pumping the brine rich in the high-valence anions back to the salt lake, wherein the high-valence anions comprise sulfate ions, carbonate ions and polyborate ions;

the low pressure side obtains chloride brine containing a small amount of high valent anions.

2. The method of claim 1, wherein: in the salt lake brine, the carbonate ion content is 5-40g/L, the sulfate ion content is 5-40g/L, and the boron content is 3-20g/L calculated by boron trioxide.

3. The method of claim 2, wherein: the first-stage nanofiltration membrane is made of cellulose acetate and derivatives thereof, aromatic polyamide, polyimide, polysulfone, polyethersulfone, polypiperazine, polyethylene or polypropylene.

4. A method according to any one of claims 1-3, characterized in that: the pressure difference between the two sides of the first-stage nanofiltration membrane is 20-120kg/cm²。

5. The method of claim 4, wherein: adding pure water at the high-pressure side of the first-stage nanofiltration membrane, and transferring part of water, sodium ions, potassium ions, lithium ions and chloride ions from the high-pressure side to the low-pressure side through the first-stage nanofiltration membrane; by continuously adding pure water, monovalent ions on the high-pressure side are continuously diluted and migrate to the low-pressure side through the first-stage nanofiltration membrane, so that the separation between monovalent ions and high-valence anions is realized, wherein the monovalent ions comprise lithium ions, sodium ions and/or potassium ions.

6. The method of claim 1, wherein the chloride brine is a sodium chloride potassium chloride lithium chloride composite solution containing a small amount of high valence anions and a small amount of bicarbonate ions, the chloride brine is subjected to secondary separation by using a secondary nanofiltration membrane, a concentrated solution on the high pressure side of the secondary nanofiltration membrane is returned to be mixed with the softened brine and enters the primary nanofiltration membrane for primary filtration, and a filtrate obtained on the low pressure side of the secondary nanofiltration membrane is a sodium chloride, potassium chloride and lithium chloride composite solution containing a small amount of bicarbonate ions, a small amount of polyborate ions and a small amount of carbonate ions and a small amount of sulfate ions; preferably, in the primary nanofiltration filtrate, Li⁺：0.31-0.8g/L，Na⁺：30-72g/L，K⁺：6.7-16g/L，B₂O₃：0.8-2g/L；SO₄ ^2-：0.3-0.8g/L，CO₃ ^2-：0.3-0.7g/L，HCO₃ ^-: 0.11-0.25g/L, 40-96g/L of chloride ion; preferably, in the secondary nanofiltration filtrate, Li⁺：0.31-0.8g/L，Na⁺：30-72g/L，K⁺：6.7-16g/L，B₂O₃：0.25-0.4g/L；SO₄ ^2-：0.015-0.04g/L，CO₃ ^2-：0.015-0.03g/L，HCO₃ ^-: 0.08-0.2g/L and 40-96g/L of chloride ions.

7. The method according to claim 6, wherein the filtrate obtained from the low pressure side of the second stage nanofiltration membrane is subjected to three-stage separation by using a third stage nanofiltration membrane, the concentrated solution from the high pressure side of the third stage nanofiltration membrane is returned to be combined with the chloride type brine obtained from the low pressure side of the first stage nanofiltration membrane, and the filtrate obtained from the low pressure side of the third stage nanofiltration membrane is a sodium chloride, potassium chloride or lithium chloride composite solution containing trace carbonate ions and trace polyborate ions; preferably, in the three-stage nanofiltration filtrate, Li⁺：0.31-0.8g/L，Na⁺：30-72g/L，K⁺：6.7-16g/L，B₂O₃：0.08-0.1g/L；SO₄ ^2-：0.001-0.005g/L，CO₃ ^2-：0.001-0.003g/L，HCO₃ ^-: 0.02g/L and 40-96g/L of chloride ions.

8. The method of claim 7, wherein a small amount of sodium hydroxide is added to the filtrate obtained from the low pressure side of the second nanofiltration membrane to adjust the pH to between 9.0 and 10.0, to convert a small amount of bicarbonate ions in the solution to carbonate ions, to convert a small amount of boric acid to polyborate ions, and to increase the removal efficiency of the third nanofiltration membrane for bicarbonate ions and boron.

9. A large-scale continuous production method for extracting lithium from carbonate type salt lake brine is characterized by comprising the following steps: treating carbonate type salt lake brine by adopting the method of any one of claims 1 to 8, obtaining corresponding filtrate on the low-pressure side of the nanofiltration membrane, crystallizing and evaporating the filtrate, and realizing the potassium-lithium co-production.

10. The process according to claim 9, characterized in that the filtrate is evaporated by crystallization by means of radiation, multiple effect evaporation, MVR and/or TVR.

Technical Field

The invention relates to a method for converting carbonate salt lake brine into low-valence chloride brine by a nanofiltration method.

Background

The carbonic acid type salt lakes in Tibet and south America are rich in lithium ions and carbonate ions, have high natural endowment, and can form lithium carbonate after being concentrated by a salt pan. However, these carbonate lakes contain a large amount of sulfate ions, polyborate ions, bicarbonate ions, chloride ions, sodium ions, and potassium ions.

Through continuous research of the applicant, the salt field radiation efficiency is low due to the existence of a large amount of polyborate ions, and meanwhile, a large amount of salts such as mirabilite, sodium carbonate decahydrate, sodium chloride, halite, sylvine, potassium chloride, sodium tetraborate and the like formed in the concentration process of the salt field cause the loss of a large amount of entrained lithium ions, so that the lithium ion yield is low, meanwhile, the phase diagram of a multi-element system is complex, valuable elements such as potassium ions and the like cannot be separated, and the resource waste is greatly caused. In addition, the precipitation of lithium carbonate is accompanied by the precipitation of various impurity salts such as sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, etc., and the purity of the obtained lithium carbonate is low and the purification cost is high. Due to the existence of a large amount of carbonate ions, sulfate ions and polyborate ions, continuous, high-efficiency, stable and high-yield co-production of potassium and lithium resources can not be realized.

The following methods are common in the brine treatment.

1. The salt lake brine directly adopts an adsorption process:

1) aluminum adsorbent:

the aluminum adsorbent is a molecular sieve adsorbent. In the adsorption process, because the bulk solution is a saturated solution, lithium chloride enters a laminated structure of the adsorbent under the action of osmotic pressure (other molecules such as sodium chloride, sodium carbonate and the like cannot enter the laminated structure). When the adsorbent is saturated, pure water is needed for washing, and brine in the adsorbent sphere and the adsorbent gap is washed away, so that the content of impurity ions entering the eluent is reduced. And finally, eluting by using fresh water, wherein the osmotic pressure in the solution of the body outside the laminated structure of the adsorbent is lower, and the osmotic pressure of the lithium chloride in the laminated structure is higher, so that the lithium chloride can be released from the laminated structure into the solution of the body.

The carbonic acid type brine does not have obstacles when being adsorbed by adopting the aluminum adsorbent, but lithium chloride diffuses outside the layered structure due to the reduction of osmotic pressure in the bulk solution in the water washing process, and particularly, the lithium chloride released from the layered structure due to the existence of mass transfer resistance of adsorbent spheres can not be rapidly dispersed in the bulk solution. Therefore, high-concentration lithium chloride in the adsorbent sphere and carbonate ions in the sphere precipitate lithium carbonate to block the adsorbent pore, so that the analysis work cannot be smoothly carried out.

Therefore, the aluminum adsorbent cannot directly adsorb the carbonate type salt lake brine.

2) Manganese-based, titanium-based or manganese-titanium composite adsorbents:

aluminum, titanium and manganese are all amphoteric substances and can be dissolved under acid and alkali conditions. The manganese series or titanium series adsorbent is an ion sieve, lithium ions exchange with hydrogen ions on the adsorbent in the adsorption process, and one hydrogen ion can be released when the adsorbent adsorbs one lithium ion. When in desorption, one hydrogen ion needs to be adsorbed every time one lithium ion is released.

Therefore, firstly, the adoption of manganese-based and titanium-based adsorbents inevitably needs to consume a large amount of hydrochloric acid or sulfuric acid; secondly, after brine is adsorbed, hydrogen ions are released from the adsorbent to cause the pH value of the adsorbed brine to change, the brine cannot be directly discharged, and alkali is added to adjust the pH value, so that a large amount of sodium hydroxide is consumed; and thirdly, the manganese-based and titanium-based adsorbents are eluted in an acidic environment, so that the service life of the adsorbents is reduced, the process stability is poor and the cost of the adsorbents is high.

2. The calcining process comprises the following steps:

the calcining process is suitable for salt lake of magnesium sulfate subtype, and includes the steps of drying sodium chloride in the sun through salt pan process to obtain potash fertilizer, spray drying the solid bittern comprising magnesium chloride, polyborate and lithium chloride, and calcining at 1000 deg.c. The process is not suitable for carbonate salt lakes.

3. An electrodialysis process:

the electrodialysis method process is suitable for the magnesium sulfate subtype salt lake, firstly, sodium chloride is sunned and removed through the salt pan process, potash fertilizer is sunned, at the moment, the main components in brine are magnesium chloride, magnesium polyborate and lithium chloride, the magnesium chloride and the magnesium polyborate are intercepted through selective electrodialysis, and the lithium chloride penetrates through an electrodialysis membrane, so that the process is not suitable for the carbonate type salt lake.

4. The extraction method comprises the following steps:

the extraction method has the problems of large acid and alkali consumption, environmental pollution risk and the like when applied to the carbonate salt lake, particularly the carbonate salt lake mostly exists at the altitude of more than 4000, the ecological environment of the regions is fragile, the self-cleaning capability of the environment is poor, and a pollution-free zero-emission process is required to be adopted.

Therefore, there is a need to develop a method for converting carbonate type salt lake brine into chloride type brine to solve one or more of the above technical problems.

Disclosure of Invention

In order to solve at least one of the above technical problems, according to an aspect of the present invention, a method for converting carbonate salt lake brine into chloride brine is provided, in which a membrane separation technology is used to convert carbonate salt lake brine into chloride brine with a low valence state, so as to provide a basis for large-scale continuous production of extracting lithium from carbonate salt lake brine, and make it possible to apply an adsorption technology and simplify a phase diagram for crystallization and evaporation and realize co-production of potassium and lithium.

Specifically, the method for converting carbonate type salt lake brine into chloride type brine is characterized by comprising the following steps:

passing carbonate type salt lake brine through ion exchange resin, and removing trace calcium and magnesium ions in the brine to obtain softened brine;

pumping softened brine into a first-stage nanofiltration membrane system, and applying pressure on two sides of a first-stage nanofiltration membrane to form a pressure difference;

part of water, sodium ions, potassium ions, lithium ions and chloride ions in the softened brine are transferred from the high-pressure side to the low-pressure side through the first-stage nanofiltration membrane;

enriching high-valence anions at a high-pressure side to obtain brine rich in the high-valence anions, and pumping the brine rich in the high-valence anions back to the salt lake, wherein the high-valence anions comprise sulfate ions, carbonate ions and polyborate ions;

the low pressure side obtains chloride brine containing a small amount of high valent anions.

According to another aspect of the invention, the salt lake brine has 5-40g/L carbonate ion content, 5-40g/L sulfate ion content and 3-20g/L boron content calculated by boron trioxide.

According to another aspect of the present invention, the material of the first stage nanofiltration membrane comprises cellulose acetate and its derivatives, aromatic polyamide, polyimide, polysulfone, polyethersulfone, polypiperazine, polyethylene or polypropylene.

According to another aspect of the invention, the pressure difference between the two sides of the first-stage nanofiltration membrane is 20-120kg/cm²。

According to another aspect of the invention, pure water is added to the high-pressure side of the first-stage nanofiltration membrane, and part of water, sodium ions, potassium ions, lithium ions and chloride ions migrate from the high-pressure side to the low-pressure side through the first-stage nanofiltration membrane; by continuously adding pure water, monovalent ions on the high-pressure side are continuously diluted and migrate to the low-pressure side through the first-stage nanofiltration membrane, so that the separation between monovalent ions and high-valence anions is realized, wherein the monovalent ions comprise lithium ions, sodium ions and/or potassium ions.

According to another aspect of the invention, the chloride-type brine is a sodium chloride potassium chloride lithium chloride composite solution containing a small amount of high-valence anions and a small amount of bicarbonate ions, the chloride-type brine is subjected to secondary separation by using a secondary nanofiltration membrane, a concentrated solution on the high-pressure side of the secondary nanofiltration membrane is returned to be mixed with the softened brine and enters the primary nanofiltration membrane for primary filtration, and a filtrate obtained on the low-pressure side of the secondary nanofiltration membrane is a sodium chloride, potassium chloride and lithium chloride composite solution containing a small amount of bicarbonate ions, a small amount of polyborate ions and a small amount of carbonate ions and a small amount of sulfate ions.

According to another aspect of the invention, the filtrate obtained from the low-pressure side of the second-stage nanofiltration membrane is subjected to three-stage separation by using a third-stage nanofiltration membrane, the concentrated solution at the high-pressure side of the third-stage nanofiltration membrane is returned to be combined with the chloride type brine obtained from the low-pressure side of the first-stage nanofiltration membrane, and the filtrate obtained from the low-pressure side of the third-stage nanofiltration membrane is a sodium chloride, potassium chloride and lithium chloride composite solution containing trace carbonate ions and trace polyborate ions.

According to another aspect of the invention, a small amount of sodium hydroxide is added into the filtrate obtained at the low-pressure side of the second-stage nanofiltration membrane, the pH is adjusted to 9.0-10.0, a small amount of bicarbonate ions in the solution are converted into carbonate ions, a small amount of boric acid is converted into polyborate ions, and the removal efficiency of the third-stage nanofiltration membrane on the bicarbonate ions and the boron is increased.

According to another aspect of the invention, a large-scale continuous production method for extracting lithium from carbonate type salt lake brine is provided, which is characterized in that: the carbonate type salt lake brine is treated by adopting the method, corresponding filtrate is obtained at the low-pressure side of the nanofiltration membrane, and the filtrate is crystallized and evaporated to realize the co-production of potassium and lithium.

According to yet another aspect of the invention, the method of crystallizing evaporating the filtrate comprises irradiation, multiple effect evaporation, MVR and/or TVR.

The invention can obtain one or more of the following technical effects:

the carbonate type salt lake brine is converted into low-valence chloride type brine by adopting a membrane separation technology, so that a foundation is provided for large-scale continuous production of extracting lithium from the carbonate type salt lake brine;

the adsorption method technology is applied, the phase diagram is simplified to carry out crystallization and evaporation, and the co-production of potassium and lithium becomes possible;

the salt pan radiation efficiency is improved; the loss of lithium ions caused by a large amount of salts is reduced; the lithium ion yield is improved;

the phase diagram of the multivariate system is simplified; the lithium carbonate has high purity and less impurities; the refining cost is reduced.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a schematic diagram of a process for converting carbonate lake brine to chloride brine according to a preferred embodiment of the present invention.

Detailed Description

The best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings, wherein the detailed description is for the purpose of illustrating the invention in detail, and is not to be construed as limiting the invention, as various changes and modifications can be made therein without departing from the spirit and scope thereof, which are intended to be encompassed within the appended claims.