Method for recovering boron and lithium in wastewater through electrochemical-membrane concentration coupling

Abstract

The invention provides a method for recovering boron and lithium in wastewater through electrochemical-membrane concentration coupling, which comprises the following steps: S1, adjusting the pH value of wastewater containing boron and lithium to be alkaline to obtain lithium-boron wastewater after the pH value is adjusted; s2, performing primary reverse osmosis treatment on the lithium-boron wastewater after the pH value is adjusted to obtain primary RO concentrated water and primary RO fresh water; s3, carrying out secondary reverse osmosis treatment on the primary RO fresh water to obtain secondary RO concentrated water and secondary RO fresh water, returning the secondary RO concentrated water to S2, mixing the secondary RO concentrated water with the lithium-boron wastewater subjected to pH value regulation, and carrying out primary reverse osmosis treatment; s4, adjusting the pH value of the primary RO concentrated water to be acidic; and S5, carrying out boron and lithium separation on the primary RO concentrated water after the pH value is adjusted by adopting an electrochemical adsorption-separation technology to obtain a lithium-rich solution and a boron-containing solution. According to the method, efficient separation and recovery of lithium and boron can be achieved, and comprehensive recovery of lithium, boron and fresh water resources is achieved.

Description

Technical Field

[0001] This invention relates to the fields of resource recycling and lithium extraction from salt lakes, and particularly to a method for electrochemical-membrane concentration coupling to recover boron and lithium from wastewater. Background Technology

[0002] Electrodialysis desalination water is a type of wastewater high in boron and low in lithium. Traditional adsorption-membrane separation coupling processes for lithium extraction from salt lake brine require further integration with electrodialysis to remove boron ion impurities. However, electrodialysis suffers from extremely low current efficiency and poor cost-effectiveness in terms of investment and operation when used for deep separation and enrichment of low-concentration lithium, resulting in the generation of large quantities of electrodialysis desalination water. Generally, recovering one ton of lithium carbonate generates 25-40 m³ of this wastewater. 3 Boron-containing electrodialysis desalination water typically contains 120-600 ppm of lithium, resulting in a 2%-5% lithium loss.

[0003] For the aforementioned electrodialysis desalination water with a high boron-to-lithium ratio, Chinese patent CN112897544B employs an ion exchange resin-nanofiltration combination technology for the stepwise recovery of lithium and boron from boron-containing wastewater. However, nanofiltration does not have a good separation effect on lithium, which leads to some lithium entering the boron recovery system, reducing the lithium recovery rate. In addition, this method involves a multi-stage nanofiltration combination, and the resulting freshwater contains a certain concentration of boron, making it difficult to utilize comprehensively. The overall technology is relatively complex, and the recycling effect is poor. Chinese patent CN116177557B proposes a method for preparing borax by recovering boron-containing wastewater from electrodialysis using a two-stage reverse osmosis process. However, reverse osmosis cannot effectively separate boron and lithium, and the resulting borax contains a large amount of lithium borate. Furthermore, the freshwater recovered from reverse osmosis also contains some boron, making it difficult to obtain high-quality freshwater and achieve comprehensive recovery and utilization of lithium and boron. Chinese patent application CN118878130A proposes a method for separating boron and lithium using a bipolar membrane. However, due to the low solubility of lithium borate, the current efficiency of the bipolar membrane electrolysis process is low, and electrolysis wastewater is generated. The primary recovery rate of lithium and boron is low. In addition, the byproduct lithium hydroxide contains a certain concentration of boron due to concentration diffusion, resulting in poor quality.

[0004] In summary, current lithium and boron-containing wastewater recovery processes still have many shortcomings, and there is an urgent need for a high-value-added method to achieve the comprehensive recovery and utilization of lithium, boron, and freshwater resources. Summary of the Invention

[0005] To address the problems of poor separation efficiency and low recovery rate of boron and lithium in the existing technologies, this invention provides a method for electrochemical-membrane concentration coupling recovery of boron and lithium from wastewater.

[0006] This invention is achieved through the following technical solution: A method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater includes: S1, adjust the pH of the wastewater containing boron and lithium to alkaline to obtain the pH-adjusted lithium-boron wastewater; S2, the lithium boron wastewater after pH adjustment is subjected to primary reverse osmosis treatment to obtain primary RO concentrate and primary RO desalination; S3, the primary RO desalination is treated by secondary reverse osmosis to obtain secondary RO concentrate and secondary RO desalination. The secondary RO concentrate is returned to S2 and mixed with the lithium boron wastewater after pH adjustment for primary reverse osmosis treatment. S4 adjusts the pH of the primary RO concentrate to acidity; S5, the concentrated RO water after pH adjustment is subjected to electrochemical adsorption-separation technology to separate boron and lithium, resulting in a lithium-rich solution and a boron-containing solution.

[0007] Preferably, in S1, the pH value of the boron and lithium-containing wastewater is adjusted to 8.0-10.5.

[0008] Preferably, in S2, the operating pressure of the first-stage reverse osmosis treatment is 1-3 MPa, and the water recovery rate is 60%-90%.

[0009] Preferably, in S3, the operating pressure of the secondary reverse osmosis treatment is 0.8-2.5 MPa, and the water recovery rate is 80%-95%.

[0010] Preferably, in S4, the pH value of the primary RO concentrate is adjusted to 4.0-7.0.

[0011] Preferably, in S5, the current density used in the electrochemical adsorption-separation technology is 5-50 A / m. 2 The operating voltage is 0.1-0.5V.

[0012] Preferably, in S5, the cathode and anode of the electrochemical adsorption-separation technology are symmetrical electrodes formed by lithium manganese oxide, lithium iron phosphate, or lithium nickel cobalt manganese oxide and their derivatives, and the anion exchange membrane used is a concentrated anion exchange membrane.

[0013] Preferably, in S5, the lithium-rich solution is concentrated and debored with resin to obtain lithium carbonate.

[0014] Preferably, in step S5, the boron-containing solution is adjusted to a certain pH value and then concentrated by evaporation to obtain borax.

[0015] Furthermore, in S5, the boron-containing solution is adjusted to pH 8.0-10.0 and then concentrated by evaporation to obtain borax.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for electrochemical-membrane concentration coupling recovery of boron and lithium from wastewater. First, the pH of the boron- and lithium-containing wastewater is adjusted, followed by two-stage reverse osmosis treatment to achieve high retention of boron and lithium, yielding high-purity freshwater while simultaneously achieving efficient recovery of lithium and boron. Next, the pH of the first-stage RO concentrate is adjusted to control borate ions to exist in the form of boric acid. Then, electrochemical adsorption-separation technology is used to separate boron and lithium. Under certain voltage and current densities, a reduction reaction occurs at the cathode to selectively extract lithium, while an oxidation reaction occurs at the anode to remove and enrich lithium, resulting in a high-purity lithium-rich solution in the anode chamber. The anion exchange membrane allows only selective passage of chloride ions. Since borate ions exist in the form of boric acid and are retained on the lithium-poor side (cathode chamber), a high-purity boron-containing solution is obtained. Because the cathode and anode are symmetrical electrodes, periodic separation and enrichment of lithium and boron are achieved through electrode switching. The method of this invention can achieve comprehensive recovery of lithium, boron and freshwater resources. The resulting lithium-rich solution has high purity and can be processed into commercial-grade lithium carbonate. The prepared freshwater has low impurity content, which meets the requirements of most working conditions. The obtained boron-containing solution can be adjusted to pH value and then concentrated by evaporation to obtain high-purity borax, which has high economic value. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of the electrochemical-membrane concentration coupled recovery method for boron and lithium in wastewater according to the present invention. Detailed Implementation

[0019] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0020] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0021] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not intended to limit the order of the method steps or define the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0022] The present invention provides a method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater, comprising the following steps: S1. In order to control the form of boron ions, the pH value of the wastewater containing boron and lithium is adjusted to alkaline to obtain the lithium-boron wastewater after pH adjustment. S2, the lithium boron wastewater after pH adjustment is subjected to primary reverse osmosis treatment to obtain primary RO concentrate and primary RO desalination; S3, the primary RO desalination is treated by secondary reverse osmosis to obtain secondary RO concentrate and secondary RO desalination. The secondary RO concentrate is returned to S2 and mixed with the lithium boron wastewater after pH adjustment for primary reverse osmosis treatment. S4 adjusts the pH of the primary RO concentrate to acidity; S5, the concentrated RO water after pH adjustment is subjected to electrochemical adsorption-separation technology to separate boron and lithium, resulting in a lithium-rich solution and a boron-containing solution.

[0023] This invention first adjusts the pH of boron- and lithium-containing wastewater, then treats the pH-adjusted lithium-boron wastewater using reverse osmosis. The reverse osmosis membrane has a high rejection rate for lithium and boron. Through two-stage reverse osmosis, the lithium-boron wastewater is deeply treated, achieving high rejection rates for boron and lithium, resulting in high-purity fresh water and efficient recovery of lithium and boron. Next, the pH of the first-stage RO concentrate is adjusted to control borate ions to exist in the form of boric acid. Then, electrochemical adsorption-separation technology is used to separate boron and lithium. The principle of this electrochemical adsorption-separation technology is to selectively extract lithium through electrochemical oxidation-reduction reactions. The electrochemical system used in this technology consists of a cathode electrode and cathode chamber, and an anion exchange system. The system consists of an exchange membrane, an anode electrode, and an anode chamber. The cathode and anode are symmetrical electrodes. The anion exchange membrane separates the cathode chamber from the anode chamber. The cathode chamber is used to hold wastewater, and the anode chamber is used to hold water or a low-concentration lithium solution. Under certain voltage and current densities, a reduction reaction occurs at the cathode to selectively extract lithium, while an oxidation reaction occurs at the anode to remove and enrich lithium, resulting in a high-purity lithium-rich solution in the anode chamber. The anion exchange membrane allows only selective passage of chloride ions. Since borate ions exist in the form of boric acid and are retained on the lithium-poor side (cathode chamber), a high-purity boron-containing solution is obtained. Because the cathode and anode are symmetrical electrodes, the separation and enrichment of lithium and boron are achieved periodically by switching the current direction.

[0024] This invention enables the comprehensive recovery of lithium, boron, and freshwater resources, achieving complete resource utilization. The resulting lithium-rich solution has high purity and can be processed into commercial-grade lithium carbonate. The prepared freshwater has low impurity content, meeting the requirements of most operating conditions. The obtained boron-containing solution, after pH adjustment and evaporation concentration, yields high-purity borax with significant economic value.

[0025] In some preferred embodiments of the present invention, in S1, the wastewater containing boron and lithium is desalination wastewater generated by ordinary electrodialysis or selective electrodialysis or boron-lithium wastewater with a similar composition. The main characteristic of this wastewater is that the boron ion concentration is high and the lithium ion concentration is low.

[0026] In some preferred embodiments of the present invention, in S1, the wastewater containing boron and lithium has a lithium ion concentration of 0.06-0.6 g / L, a boron ion concentration of 0.1-3 g / L, a sodium ion concentration of 0.01-0.8 g / L, and a pH of 3-10.

[0027] In some preferred embodiments of the present invention, in S1, sodium hydroxide is used to adjust the pH value to 8.0-10.5, and more preferably, the pH value is adjusted to 8.8-9.0.

[0028] In S2 of this invention, the appropriate concentration factor (or water recovery rate) is adjusted based on the concentration of boron ions and lithium ions in the boron- and lithium-containing wastewater to avoid the crystallization and precipitation of lithium borate. In some preferred embodiments, the water recovery rate is 60%-90% and the operating pressure is 1-3 MPa during the first-stage reverse osmosis treatment. More preferably, the water recovery rate is 85%-88% and the operating pressure is 1-2.5 MPa.

[0029] In some preferred embodiments of the present invention, in S3, the water recovery rate of the secondary reverse osmosis treatment is controlled at 80%-95%, and the operating pressure is 0.8-2.5 MPa; more preferably, the water recovery rate is 90%-92%, and the operating pressure is 1-1.5 MPa.

[0030] In some preferred embodiments of the present invention, hydrochloric acid or sulfuric acid is used in S4 to adjust the pH of the primary RO concentrate to 4.0-7.0, and more preferably, the pH is adjusted to 5.5.

[0031] The electrochemical system used in the electrochemical adsorption-separation technology of this invention has symmetrical electrodes at the cathode and anode, such as lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide and their derivatives. More preferably, the symmetrical electrodes in the embodiments of this invention are formed by lithium iron phosphate and its derivatives. The anion exchange membrane is a concentrated anion exchange membrane.

[0032] In some preferred embodiments of the present invention, the current density of the electrochemical adsorption-separation technology is controlled at 5-50 A / m. 2 More preferably, the current density is 8-10 A / m 2 The operating voltage is controlled at 0.1-0.5V, more preferably at 0.4V; the cross-sectional flow velocity of the chamber is 0.5-10cm / s, more preferably at 3-4cm / s.

[0033] In some preferred embodiments of the present invention, the lithium-rich solution obtained in S5 is concentrated and debored with resin to obtain lithium carbonate.

[0034] In some preferred embodiments of the present invention, the boron-containing solution obtained in S5 is adjusted to pH value and then concentrated by evaporation (e.g., atmospheric pressure evaporation or vacuum evaporation) to obtain borax (sodium borate). Specifically, sodium hydroxide can be used to adjust the pH value to 8.0-10.0, and more preferably, the pH value is adjusted to 9.5.

[0035] Example 1 Reference Figure 1 This embodiment 1 includes the following steps: S1, In this embodiment, electrodialysis desalinated water is used as raw material with a pH of 5.0, and its composition is shown in Table 1; Table 1. Composition and pH of the electrodialysis desalinated water used in Example 1

[0036] In the above-mentioned electrodialysis demineralized water, chloride ions act as anions to maintain charge balance. The pH of the electrodialysis demineralized water was adjusted using a 30wt% sodium hydroxide solution, with the final pH value controlled at 8.8.

[0037] S2, the electrodialysis desalinated water with pH adjusted to 8.8 is concentrated by first-stage reverse osmosis. The operation is carried out at room temperature, the pressure is controlled at 1.5-2.5 MPa, and the freshwater recovery rate is controlled at 85%. The specific composition of the first-stage RO concentrate and the first-stage RO desalination after first-stage reverse osmosis is shown in Table 2.

[0038] Table 2. Composition and pH of Primary RO Concentrate and Primary RO Distillate

[0039] S3, the above-mentioned primary RO desalination is further treated by secondary reverse osmosis. The pressure during the operation is controlled at 1.0-1.5 MPa, and the desalination recovery rate is controlled at 92%. The specific composition of the secondary RO concentrate and secondary RO desalination obtained after secondary reverse osmosis is shown in Table 3.

[0040] Table 3. Composition and pH of Secondary RO Concentrate and Secondary RO Distillate

[0041] The secondary RO concentrate can be returned to the primary RO concentrate for further boron and lithium recovery. Therefore, based on Tables 2 and 3, the recovery rates of lithium and boron in the reverse osmosis section can be calculated as follows: Lithium / Boron recovery rate = 1 - Primary RO lithium / Boron loss rate × Secondary RO lithium / Boron loss rate.

[0042] First-stage RO lithium loss rate =

[0043] First-stage RO boron loss rate =

[0044] Among them, V 一级RO淡水 C represents the volume of first-stage RO freshwater. 一级RO淡水-Li V represents the volume concentration of lithium in primary RO desalination water. 一级原水 C represents the volume of primary raw water. 一级原水-Li The volume concentration of lithium in primary raw water; C 一级RO淡水-B C represents the volume concentration of boron in primary RO desalination water. 一级原水-BLet represent the boron concentration in the primary RO raw water. Based on this, the lithium loss rate for primary RO is calculated to be 1.7%. Similarly, the lithium loss rate for secondary RO is calculated to be 18.4%, and the total lithium recovery rate = 1 - 1.7% * 18.4% = 99.7%. Likewise, the boron loss rate for primary RO is 7.7%, and for secondary RO it is 9.2%, and the total boron recovery rate = 1 - 7.7% * 9.2% = 99.2%. These two recovery rates are defined as the total recovery rate of the reverse osmosis process. Furthermore, for the reverse osmosis process, the water recovery rate = total volume of secondary RO desalinated water / total volume of primary RO raw water = 78.2%.

[0045] S4. Since the reverse osmosis section processes a small amount of water at a time, a total of 10L of RO concentrate is obtained after multiple treatments. The RO concentrate is then adjusted to pH 5.5 with 31wt% hydrochloric acid and used as the feed solution for the electrochemical system. Its specific composition is shown in Table 4.

[0046] Table 4. RO concentrate composition containing lithium and boron

[0047] S5, the lithium- and boron-containing RO concentrate, after pH adjustment, was used as the feed solution for electrochemical adsorption-separation. The electrochemical system used FePO4 / LiFePO4 as the anode and cathode, and employed a concentrated anion exchange membrane (AIM). The operating voltage during the experiment was 0.4V, and the current density was 10A / m³. 2 The circulating flow rate in the cathode / anode chamber was controlled at 1 L / min, and the flow rate at the control cross section was 3 cm / s. After treatment, lithium-rich solution and boron-containing solution were obtained, and their specific compositions are shown in Table 5.

[0048] Table 5 Composition and pH of the electrochemical adsorption-separation solution

[0049] Referring to Table 5, the lithium recovery rate in the electrochemical adsorption-separation section = V 富锂溶液 ×C 富锂溶液-Li / (V) 原料液 ×C 原料液-Li The recovery rate of lithium was calculated to be 97.4%; similarly, the recovery rate of boron was calculated to be 97.0%.

[0050] S6. The boron-containing solution obtained in S5 above is added to a 30wt% sodium hydroxide solution to adjust the pH value to 9.5. After vacuum evaporation, the crystallization rate is controlled at 95% to obtain the borax product, the composition of which is shown in Table 6 below.

[0051] Table 6 Composition of Borax Products

[0052] Based on Table 6 above, the borax prepared by the method of the present invention fully meets the quality requirements of Grade I sodium tetraborate decahydrate in GB / T-537-2009.

[0053] The method achieves a water recovery rate of 78.2%, a lithium recovery rate of 97.1% (reverse osmosis section lithium recovery rate * electrochemical adsorption-separation section lithium recovery rate), and a boron recovery rate of 91.4% (reverse osmosis section boron recovery rate * electrochemical adsorption-separation section boron recovery rate * crystallization rate).

[0054] Example 2 Reference Figure 1 This embodiment 2 includes the following steps: S1, In this embodiment, electrodialysis desalinated water is used as raw material, and its composition is shown in Table 7; Table 7. Composition and pH of the electrodialysis desalinated water used in Example 2

[0055] In the above-mentioned electrodialysis demineralized water, chloride ions act as anions to maintain charge balance. The pH of the electrodialysis demineralized water was adjusted using a 30wt% sodium hydroxide solution, with the final pH value controlled at 9.0. S2, the electrodialysis deionized water with pH adjusted to 9.0 is concentrated by first-stage reverse osmosis. The operation is carried out at room temperature, the pressure is controlled at 1.0-2.5 MPa, and the freshwater recovery rate is controlled at 88%. The specific composition of the first-stage RO concentrate and the first-stage RO desalination after first-stage reverse osmosis is shown in Table 8.

[0056] Table 8. Composition and pH of Primary RO Concentrate and Primary RO Distillate

[0057] S3. The primary RO desalination water in Table 8 above is further treated by secondary reverse osmosis. The pressure during the operation is controlled at 1.0-1.5 MPa, and the desalination water recovery rate is controlled at 90%. The specific composition of the secondary RO concentrate and secondary RO desalination water obtained after secondary reverse osmosis is shown in Table 9.

[0058] Table 9 Composition and pH of Secondary RO Concentrate and Secondary RO Distillate

[0059] The secondary RO concentrate can be returned to the primary RO concentrate for further boron and lithium recovery. Therefore, based on Tables 8 and 9, the recovery rates of lithium and boron in the reverse osmosis section can be calculated as follows: Lithium / Boron Recovery Rate = 1 - Primary RO Lithium / Boron Loss Rate × Secondary RO Lithium / Boron Loss Rate. For the specific formula, please refer to Example 1.

[0060] The calculated lithium loss rate for the first-stage RO is 3.1%, and the lithium loss rate for the second-stage RO is 15.0%. The total lithium recovery rate is 1 - 3.1% * 15.0% = 99.5%. Similarly, the boron loss rate for the first-stage RO is 9.8%, and the boron loss rate for the second-stage RO is 11.3%. The total boron recovery rate is 1 - 9.8% * 11.3% = 98.9%. These two recovery rates are defined as the total recovery rate of the reverse osmosis section. In addition, for the reverse osmosis section, the water recovery rate is calculated as: (total volume of second-stage RO desalinated water / total volume of first-stage RO raw water) = 79.2%.

[0061] S4. Since the reverse osmosis section processes a small amount of water per cycle, a total of 10L of RO concentrate is obtained after multiple treatments. The RO concentrate is then adjusted to pH 5.5 with 31wt% hydrochloric acid and used as the feed solution for the electrochemical system. Its specific composition is shown in Table 10.

[0062] Table 10 RO concentrate composition containing lithium and boron

[0063] S5. The lithium- and boron-containing RO concentrate, after pH adjustment, was used as the feed solution for electrochemical adsorption-separation. This electrochemical system used FePO4 / LiFePO4 as the cathode / anode and a concentrated anion exchange membrane (AIM). The operating voltage during the experiment was 0.4V, and the current density was 8A / m³. 2 The circulating flow rate in the cathode / anode chamber was controlled at 1.3 L / min, and the flow rate at the control cross section was 4 cm / s. After treatment, lithium-rich solution and boron-containing solution were obtained, and their specific compositions are shown in Table 11.

[0064] Table 11 Composition and pH of the electrochemical adsorption-separation solution

[0065] Referring to Table 11, the lithium recovery rate in the electrochemical adsorption-separation section = V 富锂液 ×C 富锂液-Li / (V) 原料液 ×C 原料液-Li The recovery rate of lithium was calculated to be 94.1%; similarly, the recovery rate of boron was calculated to be 95.0%.

[0066] S6. The boron-containing solution obtained in S5 above is added to a 30wt% sodium hydroxide solution to adjust the pH value to 9.5. After vacuum evaporation, the crystallization rate is controlled at 90% to obtain the borax product, the composition of which is shown in Table 12 below.

[0067] Table 12 Composition of Borax Products

[0068] Based on Table 12 above, the borax prepared by the method of the present invention fully meets the quality requirements of Grade I sodium tetraborate decahydrate in GB / T-537-2009.

[0069] The method achieves a water recovery rate of 79.2%, a lithium recovery rate of 93.6% (reverse osmosis lithium recovery rate * electrochemical adsorption-separation lithium recovery rate), and a boron recovery rate of 84.6% (reverse osmosis boron recovery rate * electrochemical adsorption-separation boron recovery rate * crystallization rate).

[0070] Example 3 S1, In this embodiment, electrodialysis desalinated water is used as raw material with a pH of 7.5, and its composition is shown in Table 13; Table 13 Composition and pH of the electrodialysis desalinated water used in Example 3

[0071] In the above-mentioned electrodialysis demineralized water, chloride ions act as anions to maintain charge balance. The pH of the electrodialysis demineralized water was adjusted using a 30wt% sodium hydroxide solution, with the final pH value controlled at 9.0.

[0072] S2, the electrodialysis deionized water with pH adjusted to 9.0 is concentrated by first-stage reverse osmosis. The operation is carried out at room temperature, the pressure is controlled at 1.0-2.5 MPa, and the freshwater recovery rate is controlled at 80%. The specific composition of the first-stage RO concentrate and the first-stage RO desalination after the first-stage reverse osmosis is shown in Table 14.

[0073] Table 14 Composition and pH of Primary RO Concentrate and Primary RO Distillate

[0074] S3. The above-mentioned primary RO desalination water is further treated by secondary reverse osmosis. The pressure during the operation is controlled at 1.0-1.5 MPa, and the desalination water recovery rate is controlled at 90%. The specific composition of the secondary RO concentrate and secondary RO desalination water obtained after secondary reverse osmosis is shown in Table 15.

[0075] Table 15 Composition and pH of Secondary RO Concentrate and Secondary RO Distillate

[0076] The secondary RO concentrate can be returned to the primary RO concentrate for further boron and lithium recovery. Therefore, based on Tables 14 and 15, the recovery rates of lithium and boron in the reverse osmosis section can be calculated as follows: Lithium / Boron recovery rate = 1 - Primary RO lithium / Boron loss rate × Secondary RO lithium / Boron loss rate.

[0077] First-stage RO lithium loss rate =

[0078] First-stage RO boron loss rate =

[0079] Among them, V 一级RO淡水 C represents the volume of first-stage RO freshwater. 一级RO淡水-Li V represents the volume concentration of lithium in primary RO desalination water. 一级原水 C represents the volume of primary raw water. 一级原水-Li The volume concentration of lithium in primary raw water; C 一级RO淡水-B C represents the volume concentration of boron in primary RO desalination water. 一级原水-B Let represent the boron concentration in the primary RO raw water. Based on this, the lithium loss rate for primary RO is calculated to be 4.0%. Similarly, the lithium loss rate for secondary RO is calculated to be 22.5%, and the total lithium recovery rate = 1 - 4.0% * 22.5% = 99.1%. Likewise, the boron loss rate for primary RO is 5.8%, and for secondary RO it is 6.9%, and the total boron recovery rate = 1 - 5.8% * 6.9% = 99.6%. These two recovery rates are defined as the total recovery rate of the reverse osmosis process. Furthermore, in the reverse osmosis process, the water recovery rate = total volume of secondary RO desalinated water / total volume of primary RO raw water = 72%.

[0080] S4. Since the reverse osmosis section processes a small amount of water at a time, a total of 10L of RO concentrate is obtained after multiple treatments. The RO concentrate is then adjusted to pH 5.5 with 31wt% hydrochloric acid and used as the feed solution for the electrochemical system. Its specific composition is shown in Table 16.

[0081] Table 16 RO concentrate composition containing lithium and boron

[0082] S5, the lithium- and boron-containing RO concentrate, after pH adjustment, was used as the feed solution for electrochemical adsorption-separation. The electrochemical system used FePO4 / LiFePO4 as the anode and cathode, and employed a concentrated anion exchange membrane (AIM). The operating voltage during the experiment was 0.4V, and the current density was 8A / m³. 2 The circulating flow rate in the cathode / anode chamber was controlled at 1 L / min, and the flow rate at the control cross section was 3 cm / s. After treatment, lithium-rich solution and boron-containing solution were obtained, and their specific compositions are shown in Table 17.

[0083] Table 17 Composition and pH of Electrochemical Adsorption-Separation Solution

[0084] Referring to Table 17, the lithium recovery rate in the electrochemical adsorption-separation section = V 富锂溶液 ×C 富锂溶液-Li / (V) 原料液 ×C 原料液-Li The recovery rate of lithium was calculated to be 80.0%; similarly, the recovery rate of boron was calculated to be 97.1%.

[0085] S6. The boron-containing solution obtained in S5 above is added to a 30wt% sodium hydroxide solution to adjust the pH value to 9.5. After vacuum evaporation, the crystallization rate is controlled at 90% to obtain the borax product, the composition of which is shown in Table 18 below.

[0086] Table 18 Composition of Borax Products

[0087] Based on Table 18 above, the borax prepared by the method of the present invention fully meets the quality requirements of Grade I sodium tetraborate decahydrate in GB / T-537-2009.

[0088] The method can achieve a water recovery rate of 72%, a lithium recovery rate of 79.3% (reverse osmosis section lithium recovery rate * electrochemical adsorption-separation section lithium recovery rate), and a boron recovery rate of 87.0% (reverse osmosis section boron recovery rate * electrochemical adsorption-separation section boron recovery rate * crystallization rate).

[0089] In summary, this invention can comprehensively recover lithium, boron, and fresh water, with good separation effect of lithium and boron and high recovery rate.

[0090] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater, characterized in that, include: S1, adjust the pH of the wastewater containing boron and lithium to alkaline to obtain the pH-adjusted lithium-boron wastewater; S2, the lithium boron wastewater after pH adjustment is subjected to primary reverse osmosis treatment to obtain primary RO concentrate and primary RO desalination; S3, the primary RO desalination is treated by secondary reverse osmosis to obtain secondary RO concentrate and secondary RO desalination. The secondary RO concentrate is returned to S2 and mixed with the lithium boron wastewater after pH adjustment for primary reverse osmosis treatment. S4 adjusts the pH of the primary RO concentrate to acidity; S5, the concentrated RO water after pH adjustment is subjected to electrochemical adsorption-separation technology to separate boron and lithium, resulting in a lithium-rich solution and a boron-containing solution.

2. The method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater according to claim 1, characterized in that, In S1, the pH value of the boron and lithium-containing wastewater is adjusted to 8.0-10.

5.

3. The method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater according to claim 1, characterized in that, In S2, the operating pressure of the first-stage reverse osmosis treatment is 1-3 MPa, and the water recovery rate is 60%-90%.

4. The method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater according to claim 1, characterized in that, In S3, the operating pressure of the secondary reverse osmosis treatment is 0.8-2.5 MPa, and the water recovery rate is 80%-95%.

5. The method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater according to claim 1, characterized in that, In S4, the pH value of the primary RO concentrate is adjusted to 4.0-7.

0.

6. The method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater according to claim 1, characterized in that, In S5, the current density used in the electrochemical adsorption-separation technology is 5-50 A / m. 2 The operating voltage is 0.1-0.5V.

7. The method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater according to claim 1, characterized in that, In S5, the electrochemical adsorption-separation technology uses symmetrical electrodes formed by lithium manganese oxide, lithium iron phosphate, or lithium nickel cobalt manganese oxide and their derivatives as the cathode and anode, and a concentrated anion exchange membrane is used.

8. The method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater according to claim 1, characterized in that, In S5, the lithium-rich solution is concentrated and boron is removed by resin to obtain lithium carbonate.

9. The method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater according to claim 1, characterized in that, In S5, the boron-containing solution is adjusted to pH value and then concentrated by evaporation to obtain borax.

10. The method for electrochemical-membrane concentration coupled recovery of boron and lithium from wastewater according to claim 9, characterized in that, In S5, the boron-containing solution is adjusted to pH 8.0-10.0 and then concentrated by evaporation to obtain borax.

Images