A method for scale prevention treatment of cation exchange membranes for the electrolytic production of rare earth hydroxides

Abstract

The application relates to a scale-preventing treatment method of a cation exchange membrane for preparing rare earth hydroxide by electrolysis, which comprises the following steps: arranging a cathode liquid, an anode liquid, a material liquid A and a material liquid B, and separating an electrolytic cell into a cathode chamber and an anode chamber by using a cation exchange membrane; adopting an inert electrode as the anode and an air cathode as the cathode; injecting electrolyte into the electrolytic cell to start electrolysis, and generating H2O2 by performing oxygen reduction reaction in the cathode chamber; adding the material liquid A into the cathode chamber, and performing polycarboxylic acid modification on the surface of the cation exchange membrane opposite to the cathode; turning the cation exchange membrane opposite to the anode to face the cathode, and performing polycarboxylic acid modification on the surface of the cation exchange membrane by using the same electrolysis process; and applying the cation exchange membrane with the surfaces both completed with polycarboxylic acid modification to membrane electrolysis for preparing rare earth hydroxide, and adding the material liquid B into the anode liquid, so that the scale phenomenon on the surface of the cation exchange membrane in the electrolysis process can be prevented.

Description

Technical Field

[0001] This invention relates to the field of rare earth processing, and more particularly to a method for preventing scale buildup in cation exchange membranes used in the electrolytic preparation of rare earth hydroxides. Background Technology

[0002] Membrane electrolysis is a device that uses ion exchange membranes to separate different ions in an electrolyte during electrolysis. The core of this device lies in its ability to selectively permeate the membrane, allowing only ions with specific charges to pass through, thus effectively separating the anode and cathode chambers within the electrolytic cell, enabling the separation and purification of electrolysis products. Membrane electrolysis devices utilizing cation exchange membranes are widely used in seawater desalination, industrial wastewater desalination, and electrolytic synthesis industries. They are characterized by high efficiency, environmental friendliness, and operational flexibility, and are gradually replacing traditional electrolysis methods in many industrial fields.

[0003] During electrolysis, cations in the anode chamber can selectively pass through the cation exchange membrane into the cathode chamber. However, when divalent or higher-valence cations are present in the anolyte, these cations deposit on the surface of the cation exchange membrane, forming corresponding metal hydroxides or metal oxides, resulting in scaling and a decrease or even loss of the membrane's exchange capacity. Existing descaling methods are mechanical, such as the apparatus and its application in the continuous electroconversion of rare earth chlorides to prepare rare earth compounds reported in patent CN117822003A, which uses an electric brush for automatic mechanical descaling of the cation exchange membrane. Patent CN220485414U also uses a brush to scrape off the contaminants on the ion exchange membrane, improving the performance and lifespan of both the cation and anion membranes. While mechanical descaling is effective, it requires additional descaling equipment, and the high-frequency scraping inevitably causes significant mechanical damage to the polymer-based ion exchange membrane, potentially even leading to its destruction. Therefore, it is necessary to develop a low-cost anti-scaling method to prevent the deposition of metal hydroxides and metal oxides on the surface of the cation exchange membrane. Summary of the Invention

[0004] To address the technical problems of high requirements for mechanical descaling equipment and significant mechanical damage to ion exchange membranes in existing technologies, this invention proposes a method and application for scale prevention of cation exchange membranes. This invention first performs electrochemical pretreatment on the cation exchange membrane by modifying the anolyte surface with polycarboxylic acid. Then, during application, a weak organic acid is added. During electrolysis, an organic weak acid solution is added to the anolyte, forming a weak acid buffer zone on the cation exchange membrane surface that continuously releases H₂. + The formation of metal hydroxides is inhibited, and the unsuccessfully inhibited metal hydroxides and metal oxides are dispersed by polycarboxylic acid modified on the anolyte surface, preventing their deposition on the cation membrane surface.

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

[0006] A method for preventing scale buildup on a cation exchange membrane used in the electrolytic preparation of rare earth hydroxides includes the following steps:

[0007] Step 1) Place the cation exchange membrane in the electrolytic cell and divide the electrolytic cell into a cathode chamber and an anode chamber;

[0008] Step 2) Add a methyl allyl polyoxyethylene ether solution to the cathode chamber; add a soluble salt solution to the anode chamber and perform electrolysis. During the electrolysis process, add feed solution A dropwise to the cathode chamber. Feed solution A contains acrylic acid and vitamin C.

[0009] Step 3) Flip the cation exchange membrane after electrolysis in Step 2) and place it back into the electrolytic cell. Divide the electrolytic cell into a cathode chamber and an anode chamber, and then repeat Step 2).

[0010] Step 4) Rare earth hydroxides are prepared by membrane electrolysis using the cation exchange membrane treated in Step 3; during the membrane electrolysis preparation of rare earth hydroxides, feed solution B is added dropwise to the anode chamber, the feed solution B containing organic acid, the organic acid being selected from at least one of lactic acid, maleic acid, and tartaric acid.

[0011] Optionally, the concentration of the methyl allyl polyoxyethylene ether solution added to the cathode chamber in step two) is 0.05–0.5 mol / L.

[0012] Optionally, in step two, a soluble salt solution with a concentration of 0.1–1.0 mol / L is added to the anode chamber.

[0013] Optionally, the soluble salt is at least one of sodium chloride, sodium nitrate, and sodium acetate.

[0014] Optionally, the concentration of acrylic acid in feed solution A is 0.1–1.0 mol / L; and the concentration of vitamin C is 0.01–0.1 mol / L.

[0015] Optionally, the concentration of organic acid in the feed solution B is 0.2–2.0 mol / L.

[0016] Optionally, in step two, the anode is an inert electrode and the cathode is an air cathode.

[0017] Optionally, in step two), the electrolysis current density is 50–500 mA / cm². 2 The electrolysis temperature is 10–70℃ and the time is 0.5–2.0h.

[0018] Optionally, in step two), the dropping rate of liquid A is 1.0 to 10.0 g / min.

[0019] Optionally, in step four), the dropping rate of liquid B is 1.0 to 10.0 g / min.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) This application achieves a high-efficiency anti-scaling effect of cation exchange membrane by chemically modifying the surface of the cation exchange membrane and combining it with the buffering effect of organic weak acid, thus avoiding the risks of large investment in physical and mechanical anti-scaling equipment and mechanical damage to the cation exchange membrane.

[0022] (2) The surface modification of the cation exchange membrane is carried out by electrolysis. The electrolysis process has a high degree of automation and is easy to realize industrial production. Therefore, the anti-scaling treatment method of the cation exchange membrane of the present invention is simple to operate, low in cost, and can be effectively applied to the electrolytic preparation of rare earth hydroxides. It has considerable economic benefits and meets the needs of large-scale commercial application. Attached Figure Description

[0023] The present invention will now be described in detail with reference to the embodiments and accompanying drawings, wherein:

[0024] Figure 1 The resistance during the membrane electrolysis preparation of rare earth hydroxides in each embodiment and comparative example;

[0025] Figure 2 This describes the current efficiency during the membrane electrolysis preparation of rare earth hydroxides in various embodiments and comparative examples. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0027] Example 1:

[0028] Step (1): Prepare a 0.05 mol / L methyl allyl polyoxyethylene ether (HPEG) solution as the cathode solution, a 0.1 mol / L NaCl solution as the anolyte, a mixed solution of 0.1 mol / L acrylic acid (AA) and 0.01 mol / L vitamin C as feed solution A, and a 0.2 mol / L maleic acid solution as feed solution B; use a cation exchange membrane to divide the electrolytic cell into a cathode chamber and an anode chamber; use an inert electrode for the anode and an air cathode;

[0029] Step (2): Inject catholy liquid and anoly liquid into the electrolytic cell in step (1) of Example 1, respectively, at a cathodic current density of 50 mA / cm². 2 Electrolysis begins at 25℃, with oxygen reduction reaction occurring in the cathode chamber to produce H2O2 (O2 + 2H+). + +2e － →H2O2); After electrolysis for 0.5 h, feed solution A is added dropwise to the cathode chamber at a rate of 1.0 g / min. Under the redox initiation system of feed solution A and H2O2 in the cathode solution, a free radical copolymerization reaction of methyl allyl polyoxyethylene ether and acrylic acid is carried out. Polycarboxylic acid is synthesized on the side of the cation exchange membrane facing the cathode and the surface is modified. The cation exchange membrane facing the anode is turned around to face the cathode, and the same electrolysis process is used to modify the cation exchange membrane on this side with polycarboxylic acid.

[0030] Step (3): The cation exchange membrane modified with polycarboxylic acid on both sides in step (2) of Example 1 is applied to an electrolytic cell. 0.1 mol / L CeCl3 solution is added to the anode and cathode chambers respectively as the electrolyte. The anode current density is 100 mA / cm². 2 Electrolysis begins under the following conditions: feed solution B is added dropwise to the anode chamber at a rate of 1.0 g / min to prepare Ce(OH)3 by membrane electrolysis.

[0031] Example 2

[0032] Step (1): Prepare a 0.25 mol / L methyl allyl polyoxyethylene ether (HPEG) solution as the cathode liquid, a 0.5 mol / L NaNO3 solution as the anolyte, a 0.5 mol / L acrylic acid (AA) and 0.05 mol / L vitamin C mixed solution as feed solution A, and a 1.0 mol / L lactic acid solution as feed solution B; use a cation exchange membrane to divide the electrolytic cell into a cathode chamber and an anode chamber; use an inert electrode for the anode and an air cathode;

[0033] Step (2): Inject catholy liquid and anoly liquid into the electrolytic cell in step (1) of Example 2, respectively, at a cathodic current density of 250 mA / cm². 2Electrolysis begins at 45℃, with oxygen reduction reaction generating H2O2 in the cathode chamber. After 2.5 hours of electrolysis, feed solution A is added dropwise to the cathode chamber at a rate of 5.0 g / min. Under the redox initiation system of feed solution A and H2O2 in the cathode solution, a free radical copolymerization reaction of methyl allyl polyoxyethylene ether and acrylic acid is carried out, synthesizing polycarboxylic acid on the side of the cation exchange membrane facing the cathode and performing surface modification. Polycarboxylic acid modification is then performed on the surface of the cation exchange membrane facing the cathode. The cation exchange membrane facing the anode is then reversed to face the cathode, and polycarboxylic acid modification is performed on this side of the cation exchange membrane using the same electrolysis process.

[0034] Step (3): The cation exchange membrane modified with polycarboxylic acid on both sides in step (2) of Example 2 is applied to an electrolytic cell. 0.5 mol / L LaCl3 solution is added to the anode and cathode chambers respectively as the electrolyte. The anode current density is 300 mA / cm². 2 Electrolysis was started under the following conditions, and feed solution B was added to the anode chamber at a dropping rate of 5.0 g / min to prepare La(OH)3 by membrane electrolysis.

[0035] Example 3

[0036] Step (1): Prepare a 0.5 mol / L methyl allyl polyoxyethylene ether (HPEG) solution as the cathode solution, a 1.0 mol / L sodium acetate solution as the anolyte, a 1.0 mol / L acrylic acid (AA) and 0.1 mol / L vitamin C mixed solution as feed solution A, and a 2.0 mol / L tartaric acid solution as feed solution B; use a cation exchange membrane to divide the electrolytic cell into a cathode chamber and an anode chamber; use an inert electrode for the anode and an air cathode;

[0037] Step (2): Inject catholy liquid and anoly liquid into the electrolytic cell in step (1) of Example 3, respectively, at a cathodic current density of 500 mA / cm. 2 Electrolysis begins at 70℃, with oxygen reduction reaction generating H2O2 in the cathode chamber. After 2.5 hours of electrolysis, feed solution A is added dropwise to the cathode chamber at a rate of 10.0 g / min. Under the redox initiation system of feed solution A and H2O2 in the cathode solution, a free radical copolymerization reaction of methyl allyl polyoxyethylene ether and acrylic acid is carried out, synthesizing polycarboxylic acid on the side of the cation exchange membrane facing the cathode and performing surface modification. Polycarboxylic acid modification is then performed on the surface of the cation exchange membrane facing the cathode. The cation exchange membrane facing the anode is then reversed to face the cathode, and polycarboxylic acid modification is performed on this side of the cation exchange membrane using the same electrolysis process.

[0038] Step (3): The cation exchange membrane modified with polycarboxylic acid on both sides in step (2) of Example 3 is applied to an electrolytic cell. A 1.0 mol / L yttrium acetate solution is added to the anode and cathode chambers respectively as the electrolyte. The anode current density is 500 mA / cm². 2 Electrolysis begins under the following conditions: feed solution B is added to the anode chamber at a dropping rate of 10.0 g / min to prepare Y(OH)3 by membrane electrolysis.

[0039] Comparative Example 1

[0040] Unmodified cation exchange membranes were used in an electrolytic cell. A 1.0 mol / L yttrium acetate solution was added to both the anode and cathode chambers as electrolytes. The anode current density was 500 mA / cm². 2 Electrolysis was started under certain conditions to prepare Y(OH)3.

[0041] Comparative Example 2

[0042] Unmodified cation exchange membranes were used in an electrolytic cell. A 1.0 mol / L yttrium acetate solution was added to both the anode and cathode chambers as electrolytes. The anode current density was 500 mA / cm². 2 Electrolysis was started under the following conditions, and 2.0 mol / L tartaric acid solution was added dropwise to the anode chamber at a rate of 10.0 g / min to prepare Y(OH)3 by membrane electrolysis.

[0043] Comparative Example 3

[0044] The cation exchange membrane modified with polycarboxylic acid in Example 3 was applied to an electrolytic cell. A 1.0 mol / L yttrium acetate solution was added to both the anode and cathode chambers as the electrolyte. The anode current density was 500 mA / cm². 2 Electrolysis was started under certain conditions to prepare Y(OH)3.

[0045] The resistance and current efficiency in the above embodiments and comparative examples were tested, and the results are as follows: Figure 1 and Figure 2 As shown.

[0046] Depend on Figure 1It can be seen that the initial resistance (at electrolysis time = 0 min) of the polycarboxylate-modified cation exchange membranes (Examples 1-3 and Comparative Example 3) is slightly higher than that of the untreated membrane. In Comparative Example 1, the resistance value increases rapidly with electrolysis time, indicating severe scaling on the surface of the cation exchange membrane, suggesting that the unmodified cation exchange membrane itself does not have anti-scaling ability. In Comparative Examples 2-3, the resistance value increases slowly with electrolysis time, and scaling also occurs on the surface of the cation exchange membrane, but the resistance value is much lower than that of Comparative Example 1, indicating that the polycarboxylate-modified cation exchange membrane alone and the addition of a weak acid solution alone can alleviate the scaling phenomenon of the cation exchange membrane, but cannot prevent scaling. In Examples 1-3, the resistance value decreases slowly with electrolysis time because the polycarboxylate modified on the surface of the cation exchange membrane can effectively disperse the metal cations at the liquid membrane interface, accelerating their passage rate through the cation exchange membrane, thereby reducing the membrane resistance. In addition, no scaling phenomenon appears on the surface of the cation exchange membrane, indicating that the use of polycarboxylate-modified cation exchange membrane combined with a weak acid solution can effectively prevent scaling.

[0047] Depend on Figure 2 It can be seen that the current efficiency of rare earth hydroxide preparation in Comparative Example 1 was the lowest, at 40.2%. However, the current efficiency was increased to 70.8% and 55.1% respectively by the polycarboxylate-modified cation exchange membrane alone and the addition of a weak acid solution alone, indicating that both polycarboxylate modification and the addition of a weak acid solution can improve current efficiency. Furthermore, the current efficiencies in Examples 1-3 were all close to 100%, demonstrating that the use of polycarboxylate-modified cation exchange membranes combined with weak acid solutions can be effectively applied to the electrolytic preparation of rare earth hydroxides.

[0048] The above description of the embodiments is intended to enable those skilled in the art to understand and apply the technology of this invention. Those skilled in the art can easily make various modifications to these examples and apply the general principles described herein to other embodiments without creative effort. Therefore, this invention is not limited to the above embodiments. Modifications in the following situations should be within the scope of protection of this invention: ① New technical solutions implemented based on the technical solution of this invention and combined with existing common knowledge, where the technical effects of the new technical solution do not exceed the technical effects of this invention; ② Equivalent substitutions of some features of the technical solution of this invention using known technology, resulting in the same technical effects as those of this invention; ③ Extendable technical solutions based on the technical solution of this invention, where the substantive content of the extended technical solution does not exceed the technical solution of this invention; ④ Equivalent transformations made using the content of this specification and drawings, directly or indirectly applied to other related technical fields.

Claims

1. A method for preventing scale buildup on a cation exchange membrane used in the electrolytic preparation of rare earth hydroxides, characterized in that, Includes the following steps: Step 1) Place the cation exchange membrane in the electrolytic cell and divide the electrolytic cell into a cathode chamber and an anode chamber; Step 2) Add a methyl allyl polyoxyethylene ether solution to the cathode chamber; add a soluble salt solution to the anode chamber for electrolysis. During electrolysis, feed solution A, containing acrylic acid and vitamin C, is added dropwise to the cathode chamber. An air cathode is used, and the electrolysis current density is 50–500 mA / cm². 2 ; Step 3) Flip the cation exchange membrane after electrolysis in Step 2) and place it back into the electrolytic cell. Divide the electrolytic cell into a cathode chamber and an anode chamber, and then repeat Step 2). Step 4) Rare earth hydroxides are prepared by membrane electrolysis using the cation exchange membrane treated in Step 3; during the membrane electrolysis preparation of rare earth hydroxides, feed solution B is added dropwise to the anode chamber, the feed solution B containing organic acid, the organic acid being selected from at least one of lactic acid, maleic acid, and tartaric acid.

2. The method for preventing scale buildup in the cation exchange membrane used for electrolytic preparation of rare earth hydroxides according to claim 1, characterized in that, In step two), the concentration of the methyl allyl polyoxyethylene ether solution added to the cathode chamber is 0.05–0.5 mol / L.

3. The method for preventing scale buildup in the cation exchange membrane used for electrolytic preparation of rare earth hydroxides according to claim 1, characterized in that, In step two), a soluble salt solution with a concentration of 0.1–1.0 mol / L is added to the anode chamber.

4. The method for preventing scale buildup in the cation exchange membrane used for electrolytic preparation of rare earth hydroxides according to claim 1, characterized in that, The soluble salt is at least one of sodium chloride, sodium nitrate, and sodium acetate.

5. The method for preventing scale buildup in the cation exchange membrane used for electrolytic preparation of rare earth hydroxides according to claim 1, characterized in that, The concentration of acrylic acid in solution A is 0.1–1.0 mol / L; the concentration of vitamin C is 0.01–0.1 mol / L.

6. The method for preventing scale buildup in the cation exchange membrane used for electrolytic preparation of rare earth hydroxides according to claim 1, characterized in that, The concentration of organic acid in the feed solution B is 0.2–2.0 mol / L.

7. The method for preventing scale buildup in the cation exchange membrane used for electrolytic preparation of rare earth hydroxides according to claim 1, characterized in that, In step two), the anode is an inert electrode.

8. The method for preventing scale buildup in the cation exchange membrane used for electrolytic preparation of rare earth hydroxides according to claim 1, characterized in that, In step two), the electrolysis temperature is 10–70°C and the time is 0.5–2.0 h.

9. The method for preventing scale buildup in the cation exchange membrane used for electrolytic preparation of rare earth hydroxides according to claim 5, characterized in that, In step two), the dropping rate of liquid A is 1.0 to 10.0 g / min.

10. The method for preventing scale buildup in the cation exchange membrane used for electrolytic preparation of rare earth hydroxides according to claim 6, characterized in that, In step four), the dropping rate of liquid B is 1.0 to 10.0 g / min.

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