Sectional defluorination method for fluorine-containing lithium sulfate solution

Abstract

The invention discloses a segmented fluorine removal method for a fluorine-containing lithium sulfate solution, and relates to the technical field of chemical purification. The method specifically comprises the following steps: A1, adding a PH regulator into fluorine-containing lithium sulfate liquid to regulate the PH; the segmented fluorine removal method for the fluorine-containing lithium sulfate solution comprises the following steps: step 1, adding a precipitator into F <->-containing lithium sulfate feed liquid, fully reacting and precipitating, and filtering to remove filter residues after complete precipitation to obtain a primarily defluorinated lithium sulfate solution; 2, adding a fluorine removal agent at a certain depth into the lithium sulfate solution subjected to primary fluorine removal, carrying out sufficient adsorption and ion exchange reaction precipitation, and filtering to remove filter residues after the precipitation is complete, so as to obtain a qualified lithium sulfate solution; and defluorination residues obtained by secondary defluorination are washed with water to obtain corresponding qualified byproducts respectively. The method has the advantages of simple process, no introduction of new impurity ions, low cost, no generation of fluorine-containing hazardous wastes, and easy industrial production and application.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical purification, and particularly to a method for removing fluorine in stages from a lithium fluorosulfate solution. Background Art

[0002] Lithium sulfate solution is one of the most common solutions for preparing lithium carbonate, especially in recent years with the application of the technology for the comprehensive recovery of all components from waste lithium iron phosphate battery materials.

[0003] According to the patent document, titled: A method for purifying and removing impurities from a lithium sulfate solution (patent publication number: CN110451535A, patent publication date: November 15, 2019), the lithium sulfate solution contains F⁻, and contains at least one impurity ion among Fe²⁺, Ni²⁺, Co²⁺, and Mn²⁺. This includes the following steps: adding calcium peroxide to the lithium sulfate solution, stirring for reaction, and filtering after the reaction is completed to obtain a filter residue and a filtrate; adding a pH regulator to the filtrate to adjust the pH value of the filtrate in stages, stirring for reaction, and filtering after the reaction is completed to obtain a filter residue and a purified lithium sulfate solution. It can simultaneously achieve the dissociation and oxidation of fluorine complexes of impurity ions such as Ni²⁺, Co²⁺, Mn²⁺, and Fe²⁺, effectively reduce the contents of impurity elements Co, Mn, Fe, and F in the solution, and reduce the influence of fluorine in the solution on purification and impurity removal. The method of the present invention can also prevent the formation of colloidal substances during the purification process, and avoid the non-selective adsorption of lithium by the colloidal substances formed during the impurity removal process.

[0004] Based on the description in the above document, generally, the removal of fluoride ions in the lithium feed solution is to add an excessive amount of calcium chloride salt to form calcium fluoride precipitate for removal. While removing fluorine, calcium impurities and chloride ions are introduced. This introduces new processes for removing calcium and chloride, significantly increasing the cost. Therefore, it is difficult to efficiently and low-costly reduce the fluoride ions in the solution to below 30 ppm using this method. For this reason, the present invention provides a method for removing fluorine in stages from a lithium fluorosulfate solution. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides a method for removing fluorine in stages from a lithium fluorosulfate solution, solving the problem that generally, the removal of fluoride ions in the lithium feed solution is to add an excessive amount of calcium chloride salt to form calcium fluoride precipitate for removal. While removing fluorine, calcium impurities and chloride ions are introduced. This introduces new processes for removing calcium and chloride, significantly increasing the cost. Therefore, it is difficult to efficiently and low-costly reduce the fluoride ions in the solution to below 30 ppm using this method.

[0006] To achieve the above objectives, the present invention is realized through the following technical solutions: A method for removing fluorine in stages from a lithium fluorosulfate solution, specifically including the following steps:

[0007] A1. Add a pH regulator to the lithium fluoride-containing sulfuric acid solution to adjust the pH.

[0008] A2. Add a defluorinating agent, start stirring, and after reacting for a period of time, perform solid-liquid separation to obtain a primary defluorinated solution and primary defluorination slag.

[0009] A3. Add a second defluorinating agent to the primary defluorinated solution, start stirring, and after reacting for a period of time, perform solid-liquid separation again to obtain a secondary defluorinated solution and secondary defluorination slag.

[0010] A4. Wash the primary defluorination slag and secondary defluorination slag countercurrently twice, and return the washing water to the system.

[0011] Preferably, the pH regulator in A1 is one of sodium carbonate, sodium hydroxide, calcium oxide or their aqueous solutions.

[0012] Preferably, the pH is controlled between 6 and 9 during the pH adjustment process.

[0013] Preferably, the stirring time in A1 and A2 is controlled between 0.5 and 1.5 h.

[0014] Preferably, after the primary defluorination of the filtrate, the fluoride ion removal rate is 90.1%.

[0015] Preferably, after the primary defluorination of the filtrate, the fluoride ion removal rate is further increased to 97.7%. The fluoride ion concentration at the reaction end point is in ppm level.

[0016] Preferably, the temperature of the defluorination process is from room temperature to 75 °C.

[0017] Preferably, the deep defluorinating agent contains an aluminum-iron-silicon composite salt and polyhydroxy cations.

[0018] Beneficial effects

[0019] The present invention provides a method for stepwise defluorination of a lithium fluoride-containing sulfuric acid solution. Compared with the prior art, it has the following beneficial effects:

[0020] In the method for stepwise defluorination of a lithium fluoride-containing sulfuric acid solution, in the first step, a precipitating agent containing Ca is added to the lithium fluoride-containing sulfuric acid solution, and after sufficient reaction, F reacts with Ca to form CaF precipitation. After the precipitation is complete, the filter residue is removed by filtration to obtain a preliminarily defluorinated lithium fluoride solution; in the second step, a certain deep defluorinating agent containing an aluminum-iron-silicon composite salt and polyhydroxy cations is added to the preliminarily defluorinated lithium fluoride solution, and after sufficient adsorption and ion exchange reaction, F reacts with the deep defluorinating agent to form an adsorption colloid and Al 2+ , fully react, F - reacts with Ca 2+ to form CaF 2 precipitation, and after the precipitation is complete, the filter residue is removed by filtration to obtain a preliminarily defluorinated lithium fluoride solution; in the second step, a certain deep defluorinating agent containing an aluminum-iron-silicon composite salt and polyhydroxy cations is added to the preliminarily defluorinated lithium fluoride solution, and after sufficient adsorption and ion exchange reaction, F - reacts with the deep defluorinating agent to form an adsorption colloid and Al 13Fn(OH) m Precipitate. After the precipitation is complete, filter to remove the filter residue to obtain a qualified lithium sulfate solution; the defluorination residue obtained from secondary defluorination is washed with water to obtain the corresponding qualified by-products. The process of the present invention is simple, does not introduce new impurity ions, has low cost and does not produce fluorine-containing hazardous waste, and is easy to industrialize production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the flowchart of the staged defluorination of the present invention;

[0022] Figure 2 is the flowchart of the method for staged defluorination of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] Please refer to Figure 1 - Figure 2 , the present invention provides a technical solution:

[0025] A method for staged defluorination of a fluorine-containing lithium sulfate solution, specifically including the following steps:

[0026] A1. Add a pH regulator to the fluorine-containing lithium sulfate feed liquid to adjust the pH;

[0027] A2. Add a defluorinating agent, start stirring, and after reacting for a period of time, perform solid-liquid separation to obtain a primary defluorinated liquid and a primary defluorination residue;

[0028] A3. Add a second defluorinating agent to the primary defluorinated liquid, start stirring, and after reacting for a period of time, perform solid-liquid separation again to obtain a secondary defluorinated liquid and a secondary defluorination residue;

[0029] A4. Wash the primary defluorination residue and the secondary defluorination residue countercurrently twice, and return the washing water to the system.

[0030] In this embodiment, the pH regulator in A1 is one of sodium carbonate, sodium hydroxide, calcium oxide or their aqueous solutions.

[0031] In this embodiment, the pH is controlled between 6 and 9 during the pH adjustment process.

[0032] Add a certain amount of pH regulator to 1000 ml of the fluorine-containing lithium sulfate feed liquid, and adjust the pH value to 6.5 - 10 to obtain a first lithium sulfate feed liquid.

[0033] In this embodiment, the stirring time between A1 and A2 is controlled between 0.5 - 1.5 h.

[0034] Measure 100 ml of the first lithium sulfate stock solution, add a certain amount of the first defluorinating agent, stir for 0.5 - 1.5 hours to obtain the first defluorinating agent slurry; add the first defluorinating agent slurry to the remaining first lithium sulfate stock solution, stir for 1 hour and then filter.

[0035] In this embodiment, the filtrate is defluorinated once, and the fluoride ion removal rate is 90.1%.

[0036] The filtrate is detected by a PXSJ - 216F ion concentration meter, and the fluoride ion removal rate is 90.1%, obtaining the second lithium sulfate solution after preliminary defluorination and the first defluorination residue;

[0037] Measure 100 ml of the second lithium sulfate stock solution, add a certain amount of the second defluorinating agent, stir for 0.5 - 1.5 hours to obtain the second defluorinating agent slurry;

[0038] Add the second defluorinating agent slurry to the remaining second lithium sulfate stock solution, stir for a certain time, add a pH regulator to adjust the pH value between 5.0 - 7.0, react at room temperature for 1 hour, let it stand and then filter

[0039] In this embodiment, the filtrate is defluorinated once, and the fluoride ion removal rate is further increased to 97.7%. The fluoride ion concentration at the reaction end point is at the ppm level.

[0040] The filtrate is detected by a PXSJ - 216F ion concentration meter, and the fluoride ion removal rate is further increased to 97.7%;

[0041] Finally, a lithium sulfate solution with qualified defluorination, the first defluorination residue and the second defluorination residue are obtained. The lithium sulfate solution can be used for the production of battery - grade lithium carbonate products; the first defluorination residue is added with condensed water according to a solid - liquid mass ratio of 1:5, stirred and washed, and the qualified calcium fluoride obtained by filtration is sold.

[0042] In this embodiment, the temperature of the defluorination process is from room temperature to 75 °C.

[0043] In this embodiment, the deep defluorinating agent contains an aluminum - iron - silicon composite salt and polyhydroxy cations.

[0044] Control example

[0045] In this control example, add a certain amount of pH regulator to 1000 ml of the fluorine - containing lithium sulfate stock solution to adjust the pH value to 6.5 - 10 to obtain the lithium sulfate stock solution.

[0046] In this control example, measure 100 ml of the first lithium sulfate stock solution, add an excessive amount of defluorinating agent, stir for 0.5 - 1.5 hours to obtain the defluorination slurry.

[0047] In this comparative example, the defluorination slurry was added to the remaining lithium sulfate liquor, stirred for 1 hour and then filtered.

[0048] In this comparative example, the filtrate was detected by a PXSJ-216F ion concentration meter, and the fluoride ion removal rate was 92.8%. The defluorinated lithium sulfate solution and defluorination slag were obtained.

[0049] When comparing the examples with the comparative example, the defluorination effect differed by 4.9%, and the dosage of the defluorinating agent used in the comparative example was larger.

[0050] In summary, a certain amount of pH regulator was added to 1000 ml of fluorine-containing lithium sulfate liquor, and the pH value was adjusted to 6.5 - 10 to obtain the first lithium sulfate liquor;

[0051] 100 ml of the first lithium sulfate liquor was measured, a certain amount of the first defluorinating agent was added, and stirred for 0.5 - 1.5 hours to obtain the first defluorinating agent slurry;

[0052] The first defluorinating agent slurry was added to the remaining first lithium sulfate liquor, stirred for 1 hour and then filtered.

[0053] The filtrate was detected by a PXSJ-216F ion concentration meter, and the fluoride ion removal rate was 90.1%. The second lithium sulfate solution after preliminary defluorination and the first defluorination slag were obtained;

[0054] 100 ml of the second lithium sulfate liquor was measured, a certain amount of the second defluorinating agent was added, and stirred for 0.5 - 1.5 hours to obtain the second defluorinating agent slurry;

[0055] The second defluorinating agent slurry was added to the remaining second lithium sulfate liquor, stirred for a certain time, the pH value was adjusted to between 5.0 - 7.0 by adding a pH regulator, reacted at room temperature for 1 hour, and filtered after standing;

[0056] The filtrate was detected by a PXSJ-216F ion concentration meter, and the fluoride ion removal rate was further increased to 97.7%;

[0057] Finally, a qualified lithium sulfate solution for defluorination, the first defluorination slag and the second defluorination slag were obtained. The lithium sulfate solution can be used for the production of battery-grade lithium carbonate products; the first defluorination slag was added with condensed water and stirred for washing according to the solid-liquid mass ratio of 1:5, and the qualified calcium fluoride obtained by filtration was sold.

[0058] Meanwhile, the content not described in detail in this specification belongs to the prior art well-known to those skilled in the art.

[0059] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device.

[0060] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for defluoridating a fluorine-containing lithium sulfate solution in stages, characterized in that: The specific steps include: A1. Add a pH regulator to the fluorine-containing lithium sulfate solution to adjust the pH; A2, add defluorinating agent, start stirring, and after a period of reaction, perform solid-liquid separation to obtain primary defluorinating liquid and primary defluorinating residue; A3, adding the second defluorinating agent to the primary defluorinating liquid, starting stirring, and after a period of reaction, performing solid-liquid separation again to obtain a secondary defluorinating liquid and a secondary defluorinating slag; A4. Wash the primary defluorination residue and the secondary defluorination residue twice in countercurrent, and return the washing water to the system.

2. The method for defluorination of a fluorine-containing lithium sulfate solution according to claim 1, characterized in that: The pH regulator in A1 is one of sodium carbonate, sodium hydroxide, calcium oxide or their aqueous solutions.

3. The method for defluorination of a fluorine-containing lithium sulfate solution according to claim 2, characterized in that: During the pH adjustment process, the pH is controlled between 6 and 9.

4. The method for defluorination of a fluorine-containing lithium sulfate solution according to claim 1, characterized in that: The stirring time in A1 and A2 is controlled between 0.5-1.5h.

5. The method for defluorination of a fluorine-containing lithium sulfate solution according to claim 1, characterized in that: The filtrate was defluorinated once, and the fluoride ion removal rate was 90.1%.

6. The method for defluorination of a fluorine-containing lithium sulfate solution according to claim 1, characterized in that: After the filtrate is defluorinated once, the fluoride ion removal rate is further increased to 97.7%. The fluoride ion concentration at the reaction end point is at the ppm level.

7. The method for defluorination of a fluorine-containing lithium sulfate solution according to claim 1, characterized in that: The temperature of the defluorination process is room temperature-75°C.

8. The method for defluorination of a fluorine-containing lithium sulfate solution according to claim 1, characterized in that: The deep defluorination agent contains aluminum-iron-silicon composite salt and polyhydroxy cation.

Images