Lithium leaching solution nanofiltration membrane section concentrated water recovery method

Abstract

The application belongs to the technical field of lithium extraction and wastewater recovery, and particularly discloses a method for recovering concentrated water from nanofiltration membrane segments of lithium leaching solution of lepidolite ore. The method comprises the following steps: 1) heating concentrated water collected after treatment of the nanofiltration membrane segments at 90-100 DEG C to evaporate water; 2) adding sulfuric acid to the concentrated solution after preliminary water removal in step 1) and heating at 110-120 DEG C to evaporate and remove chloride ions; and 3) continuously adding sulfuric acid on the basis of step 2) and heating at 150-160 DEG C, and water is added during the heating process, and the amount of the added water is 25-30% of the mass of the concentrated water, and fluorine ions are evaporated and removed. The method can directly evaporate fluorine ions and chloride ions in the concentrated water segments in steps to obtain target products, and secondary extraction and purification are not needed, raw materials are easy to obtain, and the operation is simple. The method can not only simply recover and treat the concentrated water segments, but also directly obtain corresponding products in one step, and thus provides a good treatment strategy for recycling chloride ions and fluorine ions in the concentrated water.

Description

Technical Field

[0001] This invention belongs to the field of lithium extraction and wastewater recycling technology, and specifically discloses a method for recovering concentrate from the nanofiltration membrane section of lithium extraction leachate from lithium mica ore. Background Technology

[0002] Global lithium extraction primarily utilizes brine lake extraction and ore extraction. For ore-based lithium extraction processes, the main methods include limestone extraction, sulfuric acid extraction, sulfate extraction, chloride extraction, and pressure leaching. All of these methods employ leaching and crystallization for concentration. For example, the methods for preparing lithium carbonate from lepidolite ore mainly fall into three categories: acid extraction, alkaline extraction, and salt extraction. Acid extraction primarily uses sulfuric acid as the leaching agent, requiring pre-high-temperature defluorination roasting to break down the mica structure, or roasting with sulfuric acid before leaching. Alkaline extraction mainly involves high-temperature roasting with calcium carbonate followed by leaching, or high-temperature defluorination roasting followed by pressure leaching under alkaline conditions. Salt extraction involves mixing sulfates, chlorides, etc., with lepidolite and then calcining at high temperatures to extract lithium. The sulfate method generally uses potassium sulfate, which is expensive; the chloride method generates chlorine gas, which severely corrodes equipment, and the chloride content in the lithium carbonate product easily exceeds the standard, thus exhibiting many shortcomings or defects.

[0003] Patent CN 117210703 A discloses a method for extracting lithium from lithium-containing ore. The method utilizes mixed acid treatment to overcome the aforementioned problems. For example, it discloses that in step S1, lithium-containing ore powder is reacted with mixed acid and water to obtain an acidified slurry. The mixed acid includes 410 ml of 31% hydrochloric acid, 110 ml of 98% sulfuric acid, and 200 ml of 36% fluorosilicic acid. The mixture is reacted at 80°C for 10 hours to obtain the acidified slurry. The acidification treatment of the lithium-containing ore powder dissolves its main components in ionic form in the slurry. After filtration and washing, the filtrate is cooled and precipitated with alum, then treated with a membrane process to obtain a concentrated lithium-rich solution. Finally, lithium is extracted using an extraction process. Specifically, the membrane process can involve four-stage nanofiltration and reverse osmosis concentration of the precipitated mother liquor to remove polyvalent impurity ions, resulting in a lithium-rich solution. Simultaneously, the aforementioned impurity ions can be recovered. For example, if nanofiltration is used for impurity removal, the mixed solution after cooling and alum precipitation is usually stored in the raw solution tank. After passing through the primary pretreatment membrane, carbonate and sulfate ions are separated and discharged. The permeate from the primary pretreatment membrane, after removing carbonate and sulfate ions, is collected in the primary liquid tank. The primary pretreatment solution in the primary liquid tank then undergoes secondary pressure filtration to obtain the concentrate and concentrated water from the secondary nanofiltration stage. The anions in this concentrated water mainly include fluoride ions and chloride ions. The fluoride ions in the above-mentioned concentrated water can be used to prepare hydrofluoric acid, thus providing a route for the resource-based recovery of hydrofluoric acid. However, the above-mentioned route for effective resource recovery is not mentioned. In fact, how to recover the above-mentioned anions for reuse has always been a difficult problem in the concentrated water treatment of this step. For example, the existing technologies mainly use the following routes for the recovery and preparation of hydrofluoric acid: the first is to use an alkaline solution to absorb the acidic anions; the second is to use calcium ions to absorb fluoride ions. However, the above two methods cannot directly recover hydrofluoric acid. The salt solution or CaF after neutralization with alkali still needs to be treated again to obtain hydrofluoric acid. Therefore, the concentrated water from the above treatment section still has shortcomings in terms of operation and complicated steps in recovering hydrofluoric acid. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for recovering concentrate from the nanofiltration membrane stage of lithium extraction leachate from lepidolite ore. This application uses the concentrate obtained from a lithium extraction method for lithium-containing ore disclosed in patent CN 117210703 A as an example to solve the recovery problem existing in the aforementioned concentrate treatment.

[0005] To achieve the above technical objectives, the technical solution adopted by this invention is as follows:

[0006] A method for recovering concentrate from a nanofiltration membrane stage of lithium extraction solution from lepidolite includes the following steps:

[0007] 1) The concentrated water collected after nanofiltration membrane treatment is heated and evaporated to remove some of the water;

[0008] 2) Add sulfuric acid to the concentrated solution after preliminary dehydration in step 1), wherein the amount of sulfuric acid added accounts for 10-15% of the mass of the concentrated solution in step 1); then heat at 110-120℃ to evaporate and remove chloride ions for 15-24 hours.

[0009] 3) Continue to add sulfuric acid based on step 2), wherein the amount of sulfuric acid added is 1.5 to 1.6 times the mass of the concentrated water in step 1); then heat at 150 to 160°C, and add water during the heating process to evaporate and remove fluoride ions, and the heating time is 18 to 36 hours.

[0010] Preferably, the sulfuric acid used has a volume fraction of 98%.

[0011] Preferably, the amount of deionized water added in step 3) is 25-30% of the mass of the concentrated water.

[0012] The applicant has found that the concentration and amount of sulfuric acid added in each step, the heating temperature used, and the amount of water added in step 3) all significantly affect the recovery of chloride and fluoride ions. The above processes need to be properly coordinated to obtain better recovery of fluoride and chloride ions so as to directly absorb hydrogen fluoride and hydrogen chloride.

[0013] Preferably, in step 1), the concentrated water collected after nanofiltration membrane treatment is heated at 90-100°C until 40-60% of the water is evaporated.

[0014] Preferably, the concentrated water is derived from lithium extraction using a mixed acid method from lepidolite ore, and the mixed acid includes hydrochloric acid, sulfuric acid, and fluorosilicic acid.

[0015] Preferably, the nanofiltration membrane segment includes multi-stage nanofiltration, and the concentrate is collected from any nanofiltration membrane segment or the concentrate after combining multiple nanofiltration stages.

[0016] This invention also provides a method for directly obtaining hydrogen chloride and hydrofluoric acid, which involves recovering lithium from lithium mica ore leaching solution, or recovering the concentrate after filtration of the lithium mica ore leaching solution through a nanofiltration membrane stage, comprising the following steps:

[0017] 1) The concentrated water collected from the lithium extraction leaching solution of lithium mica ore or its leaching solution after being treated by a nanofiltration membrane stage is heated and evaporated to remove some of the water;

[0018] 2) Add sulfuric acid to the concentrated liquid after preliminary dehydration in step 1), wherein the amount of sulfuric acid added accounts for 10-15% of the mass of the concentrated water in step 1); then heat at 110-120℃ for 15-24 hours, and collect the evaporating liquid to obtain hydrogen chloride;

[0019] 3) Continue to add sulfuric acid based on step 2), wherein the amount of sulfuric acid added is 1.5 to 1.6 times the mass of the concentrated water in step 1); then heat at 150 to 160°C, and add water for evaporation during the heating process. The heating time is 18 to 36 hours, and collect the evaporated liquid to obtain hydrogen fluoride.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] This invention utilizes a multi-step sulfuric acid treatment process on the concentrated water obtained from the nanofiltration stage, combined with assisted separation at different temperatures, to directly recover hydrogen chloride and hydrofluoric acid from the concentrated water. The method employed in this invention directly evaporates fluoride and chloride ions from the concentrated water to obtain the target substances (liquid), eliminating the need for secondary extraction and purification. The raw materials are readily available, and the operation is simple. This method not only provides a simplified recovery process for the concentrated water but also allows for the direct one-step acquisition of the corresponding products, offering an effective strategy for the resource-efficient recovery of chloride and fluoride ions from concentrated water. Attached Figure Description

[0022] Figure 1 A schematic diagram of a method for recovering concentrate from lithium extraction leaching solution using a nanofiltration membrane section, provided in this application;

[0023] Figure 2 The result is obtained by real-time detection in step 3) of Example 1. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods; unless otherwise specified, the materials and reagents used are commercially available.

[0026] The concentrate from the nanofiltration membrane stage of the lithium mica ore lithium extraction leachate in this embodiment can be referenced from the concentrate obtained through the nanofiltration membrane stage in patent CN 117210703 A. The following embodiment focuses on the recovery of this concentrate. Using the above-mentioned patented method, this embodiment obtained 2N concentrate, the composition of which is shown below:

[0027] Types of ions <![CDATA[F - / ppm]]> <![CDATA[Cl - / ppm]]> <![CDATA[SO4 2- / ppm]]> Al / ppm Ca / ppm Fe / ppm K / ppm concentration 25724.48 53325.47 1734.89 24600.75 204.34 4711.75 425.24 Types of ions Li / ppm Mg / ppm Mn / ppm Na / ppm Rb / ppm Si / ppm concentration 35.21 279.45 652.12 5.18 47.51 0

[0028] As can be seen from the above concentrated water, the concentrations of fluoride and chloride ions, which are present as anions, are very high, necessitating resource recovery. This application utilizes the aforementioned concentrated water section for recovery treatment. The above also applies to the direct recovery and extraction of lithium from lithium mica ore leaching solutions, and this application does not limit this application to this aspect.

[0029] Example 1

[0030] like Figure 1 As shown, a method for recovering concentrate from a nanofiltration membrane stage of lithium extraction solution from lepidolite includes the following steps:

[0031] 1) The concentrated water collected after nanofiltration membrane treatment is heated at 95°C until 50% of the water is evaporated and removed;

[0032] 2) Add sulfuric acid to the concentrated solution after preliminary dehydration in step 1), wherein the amount of sulfuric acid added accounts for 11% of the mass of the concentrated solution in step 1), and the volume fraction of sulfuric acid is 98%; then heat at 115℃ to evaporate and remove chloride ions for 18 hours.

[0033] 3) Continue to add sulfuric acid based on step 2), wherein the amount of sulfuric acid added is 1.5 times the mass of the concentrated water in step 1), and the volume fraction of sulfuric acid is 98%; then heat at 160℃, and add water during the heating process. The amount of deionized water added is 30% of the mass of the concentrated water. This process is used to evaporate and remove fluoride ions, and the heating time is 24 hours.

[0034] Example 2

[0035] A method for recovering concentrate from a nanofiltration membrane stage of lithium extraction solution from lepidolite includes the following steps:

[0036] 1) The concentrated water collected after nanofiltration membrane treatment is heated at 90°C until 40% of the water is evaporated and removed;

[0037] 2) Add sulfuric acid to the concentrated solution after preliminary dehydration in step 1), wherein the amount of sulfuric acid added accounts for 12% of the mass of the concentrated solution in step 1), and the volume fraction of sulfuric acid is 98%; then heat at 110℃ to evaporate and remove chloride ions for 24 hours.

[0038] 3) Continue to add sulfuric acid based on step 2), wherein the amount of sulfuric acid added is 1.6 times the mass of the concentrated water in step 1), and the volume fraction of sulfuric acid is 98%; then heat at 150°C, and add water during the heating process. The amount of deionized water added is 25% of the mass of the concentrated water. This process is used to evaporate and remove fluoride ions, and the heating time is 36 hours.

[0039] Example 3

[0040] A method for recovering concentrate from a nanofiltration membrane stage of lithium extraction solution from lepidolite includes the following steps:

[0041] 1) The concentrated water collected after nanofiltration membrane treatment is heated at 100°C until 60% of the water is evaporated and removed;

[0042] 2) Add sulfuric acid to the concentrated solution after preliminary dehydration in step 1), wherein the amount of sulfuric acid added accounts for 10% of the mass of the concentrated solution in step 1), and the volume fraction of sulfuric acid is 98%; then heat at 120℃ to evaporate and remove chloride ions for 15 hours.

[0043] 3) Continue to add sulfuric acid based on step 2), wherein the amount of sulfuric acid added is 1.55 times the mass of the concentrated water in step 1), and the volume fraction of sulfuric acid is 98%; then heat at 155℃, and add water during the heating process. The amount of deionized water added is 28% of the mass of the concentrated water. This process is used to evaporate and remove fluoride ions, and the heating time is 18h.

[0044] Comparative Example 1

[0045] Other experimental steps are the same as in Example 1, except that: in step 2), sulfuric acid is added to the concentrated solution after the preliminary dehydration in step 1), wherein the amount of sulfuric acid added accounts for 5% of the mass of the concentrated water in step 1), and the volume fraction of sulfuric acid is 98%; then it is heated at 115°C to evaporate and remove chloride ions, and the heating time is 18h.

[0046] Comparative Example 2

[0047] The other experimental steps are the same as in Example 1, except for step 3): sulfuric acid is added on the basis of step 2), wherein the amount of sulfuric acid added is 1 times the mass of the concentrated water in step 1), and the volume fraction of sulfuric acid is 98%; then it is heated at 160°C, and water is added during the heating process. The amount of deionized water added is 30% of the mass of the concentrated water. This process is used to evaporate and remove fluoride ions, and the heating time is 24 hours.

[0048] Comparative Example 3

[0049] The other experimental steps are the same as in Example 1, except for step 3): sulfuric acid is added on the basis of step 2), wherein the amount of sulfuric acid added is 1.5 times the mass of the concentrated water in step 1), and the volume fraction of sulfuric acid is 98%; then it is heated at 120°C, and water is added during the heating process. The amount of deionized water added is 30% of the mass of the concentrated water. This process is used to evaporate and remove fluoride ions, and the heating time is 24 hours.

[0050] Comparative Example 4

[0051] The other experimental steps are the same as in Example 1, except for step 3): sulfuric acid is added on the basis of step 2), wherein the amount of sulfuric acid added is 1.5 times the mass of the concentrated water in step 1), and the volume fraction of sulfuric acid is 98%; then it is heated at 160°C, and water is added during the heating process. The amount of deionized water added is 15% of the mass of the concentrated water. This process is used to evaporate and remove fluoride ions, and the heating time is 24 hours.

[0052] Comparative Example 5

[0053] The other experimental steps are the same as in Example 1, except that the sulfuric acid volume fraction used is 50%.

[0054] Efficacy Verification: The concentrated water extraction effects of the examples and comparative examples were tested using an ion chromatograph (Shenghan CIC-D100). The analytical conditions were as follows: column type: SH-AC-23 (4.0mm*m²50mm); eluent: 15mM NaOH; flow rate: 1.0mL / min; injection volume: 25uL; pressure: 10.6MPa; column temperature: 35℃; detector: suppressed conductivity current: 50mA.

[0055] one, Figure 2 Table 1 shows the results obtained from the real-time detection in step 3) for Example 1:

[0056] Table 1

[0057] Compound Name Retention time [min] Peak area [(μS / cm)*min] Peak height [μS / cm] Resolution Tail Factor fluorine 3.30 5.55 36.63 14.21 2.08 chlorine 4.82 ND (Not detected, same below) ND ND ND

[0058] II. The chloride ion concentrations obtained in each embodiment and comparative example were compared before and after treatment. Specifically, ① chloride absorption percentage = (mass of chloride ions absorbed after each treatment step / mass of chloride ions in the concentrated water taken in step 1) × 100%; ② fluoride absorption percentage = (mass of fluoride ions absorbed after each treatment step / mass of fluoride ions in the concentrated water taken in step 1) × 100%. Specific test and calculation data are shown in Table 2 below:

[0059] Table 2

[0060]

[0061] As can be seen from Table 2, after step 2), the chloride ion absorption in Examples 1 to 3 was good, reaching over 95%, meaning that almost all of them could be recovered. Although step 2) affected fluorine absorption, i.e., fluorine ions were simultaneously carried out of the absorbent in step 2), the amount carried out was small; fluorine could be completely absorbed in step 3) without mutual interference, thus directly obtaining hydrogen fluoride and hydrogen chloride solutions with good purity and extraction concentration, completing the recovery.

[0062] In addition, in Comparative Example 1, the amount of sulfuric acid added in step 2) was 5% of the mass of the concentrated water in step 1). The amount of sulfuric acid used was relatively small, which affected the complete absorption of chloride ions in this process. As a result, chloride ions and fluoride ions in subsequent steps were still mixed together in large quantities, and the separation and recovery effect was not good. At the same time, fluoride ions could not be completely extracted after step 3), which affected the recovery effect.

[0063] Comparative Example 2 added sulfuric acid at a rate of 1 times the mass of the concentrate from Step 1) during the extraction process in Step 3). This amount also affected the complete extraction of fluoride ions in Step 3, and the fluoride ion concentration obtained in the final treatment was 39.00%, which could not achieve a good recovery effect.

[0064] Comparative Example 3 (in step 3) involves heating at 120°C during extraction. This temperature does not achieve a good synergistic effect with sulfuric acid, resulting in a fluoride ion concentration of 28.00% in the final treatment, indicating very low fluoride ion absorption.

[0065] Comparative Example 4 uses 15% of the mass of the concentrated water added in step 3). As can be clearly seen from Table 2, this amount of added water cannot be well combined with sulfuric acid to extract fluoride ions. The fluoride ion concentration obtained after step 3) is 58.50%, and a large amount of fluoride ions still cannot be extracted.

[0066] When the process using sulfuric acid with a volume fraction of 50% was applied to the sample provided in Example 5, it was found that the extraction concentration of chloride ions was only 40.39%, which also affected the subsequent extraction of fluoride ions, resulting in poor performance.

[0067] Operational test:

[0068] The method of this invention is used to collect the concentrate from the nanofiltration membrane. Combined with the method of Example 1, it is recycled in real time. The industrial continuous recycling process is stable in all process indicators and can directly recover hydrogen fluoride and hydrogen chloride, which has good industrial recycling value.

[0069] The specific implementation schemes described above are merely a further detailed explanation of the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are only specific examples of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering concentrate from a nanofiltration membrane stage of lithium extraction solution from lepidolite ore, characterized in that, Includes the following steps: 1) The concentrated water collected after nanofiltration membrane treatment is heated and evaporated to remove some of the water; 2) Add sulfuric acid to the concentrate after preliminary dehydration in step 1), wherein the amount of sulfuric acid added accounts for 10-15% of the mass of the concentrate in step 1); then heat at 110-120℃ for 15-24 hours to evaporate and remove chloride ions. 3) Continue to add sulfuric acid based on step 2), wherein the amount of sulfuric acid added is 1.5 to 1.6 times the mass of the concentrated water in step 1); then heat at 150 to 160°C for 18 to 36 hours to evaporate and remove fluoride ions; In step 3), water is added during the heating process to evaporate and remove fluoride ions. The amount of water added is 25-30% of the mass of the concentrated water in step 1); the volume fraction of sulfuric acid used is 70-98%.

2. The method for recovering concentrate from the nanofiltration membrane stage of lithium extraction solution from lithium mica ore according to claim 1, characterized in that, In step 1), the concentrated water collected after nanofiltration membrane treatment is heated at 90-100°C until 40-60% of the water is evaporated.

3. The method for recovering concentrate from the nanofiltration membrane stage of lithium extraction solution from lithium mica ore according to claim 1, characterized in that, The concentrated water comes from lithium extraction using the mixed acid method from lepidolite ore. The mixed acid includes hydrochloric acid, sulfuric acid, and fluorosilicic acid.

4. The method for recovering concentrate from the nanofiltration membrane stage of lithium extraction solution from lithium mica ore according to claim 3, characterized in that, The nanofiltration membrane segment includes multiple nanofiltration stages, and the concentrate is collected from any nanofiltration membrane segment or the concentrate after combining multiple nanofiltration stages.

5. A method for directly obtaining hydrogen chloride and hydrofluoric acid, characterized in that, The lithium is obtained by extraction using lithium mica ore leaching solution, or by filtration of lithium mica ore leaching solution through a nanofiltration membrane and subsequent concentrate recovery, including the following steps: 1) The concentrated water collected from the lithium extraction leaching solution of lithium mica ore or its leaching solution after being treated by a nanofiltration membrane stage is heated and evaporated to remove some of the water; 2) Add sulfuric acid to the concentrated liquid after preliminary dehydration in step 1), wherein the amount of sulfuric acid added accounts for 10-15% of the mass of the concentrated water in step 1); then heat at 110-120℃ for 15-24 hours, and collect the evaporating liquid to obtain hydrogen chloride; 3) Continue to add sulfuric acid based on step 2), wherein the amount of sulfuric acid added is 1.5 to 1.6 times the mass of the concentrated water in step 1); then heat at 150 to 160°C, and add water to evaporate during the heating process. The heating time is 18 to 36 hours, and collect the evaporated liquid to obtain hydrogen fluoride. In step 3), water is added during the heating process to evaporate and remove fluoride ions. The amount of water added is 25-30% of the mass of the concentrated water in step 1); the volume fraction of sulfuric acid used is 70-98%.

6. The method for directly obtaining hydrogen chloride and hydrofluoric acid according to claim 5, characterized in that, The liquids collected from hydrogen chloride and hydrogen fluoride in steps 2) and 3) are water.

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