A method for producing a rare earth concentrate from a rare earth salt solution

Abstract

The application provides a method for preparing a rare earth concentrate from a rare earth salt solution, which comprises the following steps: using an electrolyte solution as an electrolyte of an anode region, using a rare earth salt solution as an electrolyte of a cathode region, and separating the cathode region from the anode region by using a diaphragm; introducing a gas into the cathode region, and performing electrolysis, so that the pH of the electrolyte of the cathode region is increased, and rare earth ions are precipitated, thereby obtaining the rare earth concentrate; and the gas comprises carbon dioxide gas. The method provided by the application enriches rare earth by electrolysis, and carbon dioxide gas is introduced into the cathode region during the electrolysis process, so that the over-alkaline phenomenon on the electrode surface is inhibited, the problem of co-precipitation of impurities such as sulfur, calcium and magnesium with rare earth ions in the process of electrochemical enrichment of rare earth is solved, the grade of the rare earth concentrate is improved, and only carbon dioxide needs to be introduced, without adding other chemical reagents, so that the method is green and environment-friendly, and efficient utilization of carbon dioxide is achieved.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology and relates to a method for preparing rare earth enrichments from rare earth salt solutions. Background Technology

[0002] In the process of enriching and extracting rare earth elements from rare earth salt solutions, especially from low-concentration rare earth sulfate solutions containing calcium and magnesium, chemical reagents are inevitably introduced into the system, which can easily lead to water pollution and problems related to the discharge and treatment of saline wastewater. In addition, the co-extraction of impurity elements also reduces the enrichment efficiency of rare earth elements and increases production costs. Therefore, the green and efficient enrichment and extraction of rare earth ions from solutions has become one of the important research directions for the future.

[0003] In industry, chemical precipitation is a common method for enriching or extracting rare earth ions from rare earth salt solutions. The principle of chemical precipitation is to add an excess of chemical precipitant, such as ammonium salts, alkalis, or alkali metal compounds, to the rare earth salt solution, causing the rare earth ions to convert into compounds with low solubility, thereby enriching the rare earth elements. As a highly efficient enrichment method, chemical precipitation has advantages such as simple process and large throughput. However, the process requires the addition of excessive chemical reagents to the solution, which can easily introduce a large number of impurity ions, generating saline wastewater. Furthermore, some reagents do not participate in the reaction and co-precipitate with the rare earth ions, reducing the grade of the enriched product.

[0004] Compared to traditional chemical precipitation methods, electrochemical precipitation has the advantages of being green and producing no high-salt wastewater. Its main principle is that during water electrolysis, hydroxide ions generated in situ on the cathode surface adjust the pH of the solution to a certain range, converting rare earth ions in the solution into precipitates with low solubility. This process converts electrical energy into chemical energy, achieving green and efficient separation and enrichment of rare earth elements without introducing chemical reagents.

[0005] For example, CN120060931A proposes an electrolysis method for rare earth ion solutions, which has advantages such as no chemical reagents required, being green and pollution-free, and having a controllable alkali production rate. However, during the electrolysis process, a strongly alkaline region is generated near the cathode due to the hydrogen evolution reaction. In this region, impurities such as calcium and magnesium in the water easily deposit on the electrode surface, thereby reducing the enrichment efficiency of rare earths and increasing energy consumption. In addition, during the formation of rare earth electrochemical hydrolysis, impurity anions such as sulfate are also prone to co-precipitation, reducing product purity.

[0006] Therefore, there is an urgent need to provide an electrochemical precipitation method that is simple to operate and can effectively suppress the co-precipitation of impurity ions and rare earth elements, thereby improving the grade of rare earth enrichments. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing rare earth enrichment from rare earth salt solutions. The method enriches rare earths by electrolysis. During the electrolysis process, carbon dioxide gas is introduced into the cathode area to suppress the phenomenon of excessive alkalinity on the electrode surface. This solves the problem of co-precipitation of impurities such as sulfur, calcium, and magnesium with rare earth ions during the electrochemical enrichment of rare earths, thereby improving the grade of the rare earth enrichment. Furthermore, only carbon dioxide needs to be introduced, without the addition of other chemical reagents, making it green and environmentally friendly, and achieving efficient utilization of carbon dioxide.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a method for preparing rare earth enrichments from rare earth salt solutions, the method comprising the following steps:

[0010] An electrolyte solution is used as the electrolyte in the anode region, a rare earth salt solution is used as the electrolyte in the cathode region, and a diaphragm separates the cathode region from the anode region.

[0011] Gas is introduced into the cathode region and electrolysis is performed to raise the pH of the electrolyte in the cathode region, causing rare earth ions to precipitate and obtain the rare earth enrichment.

[0012] The gas includes carbon dioxide.

[0013] The traditional electrochemical method for preparing rare earth concentrates relies on the hydrogen evolution reaction at the cathode surface. The in-situ generated hydroxide ions convert rare earth ions into hydroxide precipitates in the solution, thus achieving the separation and enrichment of rare earth ions. However, due to the limited convection environment at the electrode surface and the bulk solution interface, a large number of hydroxide ions cannot diffuse into the solution in time, hindering their reaction with the rare earth ions. This leads to an abnormally high pH at the electrode interface, causing other impurities to co-precipitate with rare earth ions, reducing current efficiency and the grade of the rare earth concentrate. Furthermore, anions in the rare earth salt solution, such as sulfate ions, readily co-precipitate during rare earth hydrolysis, further lowering the grade of the rare earth concentrate.

[0014] To address this issue, the present invention introduces carbon dioxide gas into the cathode region, thereby suppressing the excessive alkalinity of the cathode surface and promoting the precipitation of rare earth ions in the form of carbonates in the solution. This prevents the co-precipitation of rare earth ions with impurity ions such as calcium, magnesium, and sulfate ions, thus producing a high-grade rare earth carbonate concentrate. Therefore, the present invention overcomes the problems of impurity co-precipitation and the presence of a large amount of sulfur in the rare earth concentrate caused by poor mass transfer at the electrode surface in traditional electrolytic enrichment methods. Furthermore, the method described in this invention does not require the addition of other chemical reagents, making it green and environmentally friendly, and achieving efficient utilization of carbon dioxide.

[0015] It is understood that carbon dioxide gas is continuously introduced during the electrolysis process, and the carbon dioxide gas can be introduced into the rare earth salt solution.

[0016] The grade of the rare earth enrichment described in this invention refers to the percentage of the total amount of rare earth (calculated as rare earth oxides) contained in the rare earth enrichment by mass. A higher grade of rare earth enrichment indicates a higher rare earth recovery and enrichment rate and a lower impurity content.

[0017] Preferably, the ratio of the carbon dioxide gas flow rate to the effective electrode area of ​​the cathode region is 0.25 mL·min. -1 ·cm -2 -6.25 mL·min -1 ·cm -2 For example, it could be 0.25 mL·min -1 ·cm -2 0.5 mL·min -1 ·cm -2 1 mL·min -1 ·cm -2 1.5 mL·min -1 ·cm -2 2 mL·min -1 ·cm -2 2.5 mL·min -1 ·cm -2 3 mL·min -1 ·cm -2 3.5 mL·min -1 ·cm -2 4 mL·min -1 ·cm -2 4.5 mL·min -1 ·cm -2 5 mL·min -1 ·cm -2 5.5 mL·min -1 ·cm -2 6 mL·min -1 ·cm -2 Or 6.25 mL·min -1 ·cm -2 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0018] The ratio of the carbon dioxide gas flow rate to the effective area of ​​the cathode electrode in this invention reflects the amount of carbon dioxide gas on a unit area electrode. It is preferably within a specific range. If it is too small, the effect of carbon dioxide gas in suppressing the over-alkali phenomenon on the cathode surface will decrease, affecting the grade of rare earth enrichment. If it is too large, it will lead to a significant decrease in local pH, which is not conducive to the formation of high-grade rare earth carbonate dominant nucleation regions, reducing current efficiency and causing gas waste.

[0019] Preferably, the gas also includes other gases, including oxygen or air.

[0020] The method described in this invention can introduce pure carbon dioxide gas into the cathode region, or it can introduce a mixture of carbon dioxide gas and other gases.

[0021] Preferably, the flow rate ratio of the carbon dioxide gas to the other gases is (4-6):1, for example, it can be 4:1, 4.5:1, 5:1, 5.5:1 or 6:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, the pH of the electrolyte electrolyzed into the cathode region rises to 6-8, for example, it can be 6, 6.5, 7, 7.5 or 8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Because hydrogen evolution occurs at the cathode during electrolysis, the pH of the electrolyte at the cathode rises. When the pH of the electrolyte in the cathode region reaches 6-8 at the end point of electrolysis as described in this invention, if the pH is too low, rare earth precipitation will be incomplete. If the pH is too high, a large amount of magnesium impurities will easily co-precipitate, reducing the grade of the enriched material.

[0024] Preferably, the rare earth salt solution includes a rare earth sulfate solution containing calcium and magnesium.

[0025] The method described in this invention is designed for rare earth sulfate solutions containing calcium and magnesium, and can yield high-grade rare earth concentrates. Therefore, even if the rare earth salt solution contains impurities such as calcium and magnesium ions, as well as sulfate ions that can co-precipitate with rare earth ions, the method described in this invention can still avoid co-precipitation of rare earth ions with calcium, magnesium, and sulfate ions, and prepare high-grade rare earth concentrates.

[0026] Preferably, in the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 50 mg / L-3000 mg / L, for example, 50 mg / L, 100 mg / L, 500 mg / L, 1000 mg / L, 1500 mg / L, 2000 mg / L, 2500 mg / L, or 3000 mg / L; the concentration of calcium ions is ≥50 mg / L, for example, 50 mg / L, 75 mg / L, 100 mg / L, 125 mg / L, 175 mg / L, 200 mg / L, 225 mg / L, or 250 mg / L; and the concentration of magnesium ions is ≥500 mg / L, for example, 500 mg / L, 700 mg / L, 900 mg / L, 1100 mg / L, 1300 mg / L, 1500 mg / L, 1700 mg / L, 1900 mg / L, or 2000 mg / L. mg / L, the concentration of sulfate ions is ≥1000 mg / L, for example, it can be 1000 mg / L, 2000 mg / L, 3000 mg / L, 4000 mg / L, 5000 mg / L, 6000 mg / L, 7000 mg / L or 8000 mg / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Furthermore, even if the calcium and magnesium rare earth sulfate solution of the present invention contains low concentrations of rare earth ions, it still contains a large number of calcium ions, magnesium ions and sulfate ions that affect the grade of rare earth enrichment, and can still effectively enrich rare earth ions to prepare high-grade rare earth enrichment.

[0028] Preferably, the current density of the electrolysis is 40 A / m 2 -1000 A / m 2 For example, it could be 40 A / m 2 100 A / m 2 200 A / m 2 300 A / m 2 400 A / m 2 500 A / m 2 600 A / m 2 700 A / m 2 800 A / m 2 900 A / m 2 Or 1000A / m 2 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0029] Preferably, the anion type in the electrolyte solution is the same as the anion type in the rare earth salt solution.

[0030] For example, when the rare earth salt solution is a rare earth sulfate solution, the electrolyte solution is an acid or salt containing sulfate, such as an ammonium sulfate solution and / or a magnesium sulfate solution.

[0031] Preferably, the concentration of the electrolyte solution is 1-2 mol / L, for example, it can be 1 mol / L, 1.25 mol / L, 1.5 mol / L, 1.75 mol / L or 2 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the membrane comprises any one of anion exchange membrane, cation exchange membrane, or bipolar membrane.

[0033] Preferably, the electrode used in the cathode region includes any one of a titanium metal electrode, a copper electrode, a carbon felt electrode, a titanium electrode, a silver electrode, or a carbon paper electrode; the electrode used in the anode region includes any one of a titanium-plated ruthenium electrode, a graphite electrode, or a porous carbon paper electrode.

[0034] Preferably, the grade of the rare earth enrichment is ≥90% (after roasting, such as roasting at 900℃), for example, it can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%, and the mass percentage of sulfate ions in the rare earth enrichment is ≤5% (after roasting, such as roasting at 900℃), for example, it can be 5%, 4.5%, 3%, 3.5%, 3%, 2.5%, 2%, 1.5% or 1%, the mass percentage of calcium ions is ≤1% (after roasting, such as roasting at 900℃), for example, it can be 1%, 0.8%, 0.6%, 0.4%, 0.2% or 0.1%, and the mass percentage of magnesium ions is ≤1% (after roasting, such as roasting at 900℃), for example, it can be 1%, 0.8%, 0.6%, 0.4%, 0.2% or 0.1%, but it is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0035] As a preferred embodiment of the method described in this invention, the method includes the following steps:

[0036] An electrolyte solution is placed in the anode chamber, so that the electrolyte solution serves as the electrolyte in the anode region. The anion type in the electrolyte solution is the same as the anion type in the rare earth salt solution.

[0037] A rare earth salt solution is placed in the cathode chamber, and the rare earth salt solution is used as the electrolyte in the anode region. The rare earth salt solution is a calcium and magnesium rare earth sulfate solution. In the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 50 mg / L-3000 mg / L, the concentration of calcium ions is ≥50 mg / L, the concentration of magnesium ions is ≥500 mg / L, and the concentration of sulfate ions is ≥1000 mg / L.

[0038] The anode chamber and the cathode chamber are separated by a diaphragm;

[0039] Carbon dioxide gas is introduced into the cathode region at a rate of 40 A / m 2 -1000 A / m 2 Electrolysis is performed at a current density until the pH of the electrolyte in the cathode region rises to 6-8, rare earth ions precipitate, and the rare earth enrichment is obtained after solid-liquid separation.

[0040] During the electrolysis process, carbon dioxide gas is continuously introduced into the cathode region, and the ratio of the flow rate of the carbon dioxide gas to the effective electrode area of ​​the cathode region is 0.25 mL·min. -1 ·cm -2 -6.25 mL·min -1 ·cm -2 .

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] This invention suppresses the over-alkali phenomenon on the cathode surface by introducing carbon dioxide gas into the cathode region, promotes the precipitation of rare earth ions in the form of carbonates in the solution, and prevents the co-precipitation of rare earth ions with impurity ions such as calcium ions, magnesium ions, and sulfate ions. This results in the preparation of high-grade rare earth carbonate concentrates. Therefore, this invention overcomes the problems of impurity co-precipitation and the presence of a large amount of sulfur in rare earth concentrates caused by poor mass transfer on the electrode surface in traditional electrolytic enrichment methods. Furthermore, the method described in this invention does not require the addition of other chemical reagents, is green and environmentally friendly, and achieves efficient utilization of carbon dioxide. Detailed Implementation

[0043] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0044] Example 1

[0045] This embodiment provides a method for preparing rare earth enrichments from rare earth salt solutions, the method comprising the following steps:

[0046] Titanium metal electrode and titanium-plated ruthenium electrode were used as cathode and anode, respectively; a 1 mol / L ammonium sulfate solution was placed in the anode chamber, so that the ammonium sulfate solution was used as the electrolyte in the anode area;

[0047] A rare earth salt solution is placed in the cathode chamber, and the rare earth salt solution is used as the electrolyte in the anode region. The rare earth salt solution is a calcium and magnesium rare earth sulfate solution. In the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 3000 mg / L, the concentration of calcium ions is 50 mg / L, the concentration of magnesium ions is 500 mg / L, and the concentration of sulfate ions is 1000 mg / L.

[0048] An anion exchange membrane (Jinqiu Environmental Protection JQA-81) is used to separate the anode chamber and the cathode chamber;

[0049] Carbon dioxide gas is introduced into the cathode region, and the ratio of the flow rate of the carbon dioxide gas to the effective electrode area of ​​the cathode region is 6.25 mL·min. -1 ·cm -2 and at 1000A / m 2 Electrolysis was performed at a current density, and the pH of the electrolyte in the cathode region rose to 6.5, rare earth ions precipitated, and the rare earth enrichment was obtained after solid-liquid separation.

[0050] Example 2

[0051] This embodiment provides a method for preparing rare earth enrichments from rare earth salt solutions, the method comprising the following steps:

[0052] Copper and graphite electrodes were used as cathodes and anodes, respectively; a 2 mol / L ammonium sulfate solution was placed in the anode chamber, making the ammonium sulfate solution the electrolyte in the anode region;

[0053] A rare earth salt solution is placed in the cathode chamber, and the rare earth salt solution is used as the electrolyte in the anode region. The rare earth salt solution is a calcium and magnesium rare earth sulfate solution. In the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 1000 mg / L, the concentration of calcium ions is 200 mg / L, the concentration of magnesium ions is 1500 mg / L, and the concentration of sulfate ions is 6500 mg / L.

[0054] An anion exchange membrane (Jinqiu Environmental Protection JQA-81) is used to separate the anode chamber and the cathode chamber;

[0055] Carbon dioxide gas is introduced into the cathode region, and the ratio of the flow rate of the carbon dioxide gas to the effective electrode area of ​​the cathode region is 6.25 mL·min. -1 ·cm -2 and at 40 A / m 2 Electrolysis was performed at a current density, and the pH of the electrolyte in the cathode region rose to 6.6, rare earth ions precipitated, and the rare earth enrichment was obtained after solid-liquid separation.

[0056] Example 3

[0057] This embodiment provides a method for preparing rare earth enrichments from rare earth salt solutions, the method comprising the following steps:

[0058] Carbon felt electrode and titanium-plated ruthenium electrode were used as cathode and anode, respectively; a 1 mol / L magnesium sulfate solution was placed in the anode chamber, and the magnesium sulfate solution was used as the electrolyte in the anode area;

[0059] A rare earth salt solution is placed in the cathode chamber, and the rare earth salt solution is used as the electrolyte in the anode region. The rare earth salt solution is a calcium and magnesium rare earth sulfate solution. In the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 1000 mg / L, the concentration of calcium ions is 200 mg / L, the concentration of magnesium ions is 20000 mg / L, and the concentration of sulfate ions is 80000 mg / L.

[0060] The anode chamber and cathode chamber are separated by a cation exchange membrane (TWDDA3S).

[0061] Carbon dioxide gas is introduced into the cathode region, and the ratio of the flow rate of the carbon dioxide gas to the effective electrode area of ​​the cathode region is 2.5 mL·min. -1 ·cm -2 and at 100 A / m 2 Electrolysis was performed at a current density, and the pH of the electrolyte in the cathode region rose to 7.0, rare earth ions precipitated, and the rare earth enrichment was obtained after solid-liquid separation.

[0062] Example 4

[0063] This embodiment provides a method for preparing rare earth enrichments from rare earth salt solutions, the method comprising the following steps:

[0064] Titanium electrode and porous carbon paper electrode were used as cathode and anode, respectively; a 1 mol / L magnesium sulfate solution was placed in the anode chamber, and the magnesium sulfate solution was used as the electrolyte in the anode area.

[0065] A rare earth salt solution is placed in the cathode chamber, and the rare earth salt solution is used as the electrolyte in the anode region. The rare earth salt solution is a calcium and magnesium rare earth sulfate solution. In the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 1000 mg / L, the concentration of calcium ions is 200 mg / L, the concentration of magnesium ions is 1500 mg / L, and the concentration of sulfate ions is 6000 mg / L.

[0066] The anode chamber and cathode chamber are separated by a dual-stage membrane (Fumasep-FBM-PK);

[0067] A mixture of carbon dioxide and air (flow rate ratio of carbon dioxide to air of 4:1) is introduced into the cathode region, wherein the flow rate of the carbon dioxide gas is 0.25 mL / min. -1 ·cm -2 and at 100 A / m 2 Electrolysis was performed at a current density until the pH of the electrolyte in the cathode region rose to 6.0, rare earth ions precipitated, and the rare earth enrichment was obtained after solid-liquid separation.

[0068] Example 5

[0069] This embodiment provides a method for preparing rare earth enrichments from rare earth salt solutions, the method comprising the following steps:

[0070] Carbon felt electrode and titanium-plated ruthenium electrode were used as cathode and anode, respectively; a 1 mol / L magnesium sulfate solution was placed in the anode chamber, and the magnesium sulfate solution was used as the electrolyte in the anode area;

[0071] A rare earth salt solution is placed in the cathode chamber, and the rare earth salt solution is used as the electrolyte in the anode region. The rare earth salt solution is a calcium and magnesium rare earth sulfate solution. In the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 1000 mg / L, the concentration of calcium ions is 200 mg / L, the concentration of magnesium ions is 1500 mg / L, and the concentration of sulfate ions is 6000 mg / L.

[0072] An anion exchange membrane (Jinqiu Environmental Protection JQA-81) is used to separate the anode chamber and the cathode chamber;

[0073] A mixture of carbon dioxide and oxygen gas (with a flow rate ratio of 6:1) is introduced into the cathode region, and the flow rate of the carbon dioxide gas is 1.25 mL / min to the effective electrode area of ​​the cathode region. -1 ·cm -2 and at 100 A / m 2 Electrolysis was performed at a current density, and the pH of the electrolyte in the cathode region rose to 6.6, rare earth ions precipitated, and the rare earth enrichment was obtained after solid-liquid separation.

[0074] Example 6

[0075] This embodiment provides a method for preparing rare earth enrichments from rare earth salt solutions, the method comprising the following steps:

[0076] Silver electrode and titanium-plated ruthenium electrode were used as cathode and anode, respectively; a 1 mol / L magnesium sulfate solution was placed in the anode chamber, and the magnesium sulfate solution was used as the electrolyte in the anode area;

[0077] A rare earth salt solution is placed in the cathode chamber, and the rare earth salt solution is used as the electrolyte in the anode region. The rare earth salt solution is a calcium and magnesium rare earth sulfate solution. In the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 1000 mg / L, the concentration of calcium ions is 200 mg / L, the concentration of magnesium ions is 1500 mg / L, and the concentration of sulfate ions is 6000 mg / L.

[0078] An anion exchange membrane (Jinqiu Environmental Protection JQA-81) is used to separate the anode chamber and the cathode chamber;

[0079] Carbon dioxide gas is introduced into the cathode region, and the ratio of the flow rate of the carbon dioxide gas to the effective electrode area of ​​the cathode region is 1 mL·min. -1 ·cm -2 and at 100 A / m 2 Electrolysis was performed at a current density, and the pH of the electrolyte in the cathode region rose to 6.6, rare earth ions precipitated, and the rare earth enrichment was obtained after solid-liquid separation.

[0080] Example 7

[0081] This embodiment provides a method for preparing rare earth enrichments from rare earth salt solutions, the method comprising the following steps:

[0082] Carbon paper electrode and titanium-plated ruthenium electrode were used as cathode and anode, respectively; a 1 mol / L magnesium sulfate solution was placed in the anode chamber, and the magnesium sulfate solution was used as the electrolyte in the anode area;

[0083] A rare earth salt solution is placed in the cathode chamber, and the rare earth salt solution is used as the electrolyte in the anode region. The rare earth salt solution is a calcium and magnesium rare earth sulfate solution. In the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 1000 mg / L, the concentration of calcium ions is 200 mg / L, the concentration of magnesium ions is 1500 mg / L, and the concentration of sulfate ions is 6000 mg / L.

[0084] An anion exchange membrane (Jinqiu Environmental Protection JQA-81) is used to separate the anode chamber and the cathode chamber;

[0085] Carbon dioxide gas is introduced into the cathode region, and the ratio of the flow rate of the carbon dioxide gas to the effective electrode area of ​​the cathode region is 0.75 mL·min. -1 ·cm -2 and at 200 A / m 2 Electrolysis was performed at a current density until the pH of the electrolyte in the cathode region rose to 8.0, rare earth ions precipitated, and the rare earth enrichment was obtained after solid-liquid separation.

[0086] Example 8

[0087] This embodiment provides a method for preparing rare earth enrichments from rare earth salt solutions, wherein the method, except that the ratio of the carbon dioxide gas flow rate to the effective electrode area of ​​the cathode region is 0.1 mL·min -1 ·cm -2 Except for the above, everything else is the same as in Example 1.

[0088] Example 9

[0089] This embodiment provides a method for preparing rare earth enrichments from rare earth salt solutions, wherein the method, except that the ratio of the carbon dioxide gas flow rate to the effective electrode area of ​​the cathode region is 7 mL·min -1 ·cm -2 Except for the above, everything else is the same as in Example 1.

[0090] Example 10

[0091] This embodiment provides a method for preparing rare earth enrichments from rare earth salt solutions. The method is the same as in Example 1, except that the pH of the electrolyte in the cathode region is 5.5.

[0092] Example 11

[0093] This embodiment provides a method for preparing rare earth enrichments from rare earth salt solutions. The method is the same as in Example 1, except that the pH of the electrolyte in the cathode region is 8.5.

[0094] Example 12

[0095] This embodiment provides a method for preparing rare earth enrichment from rare earth salt solution. The method is the same as in Example 1, except that the concentration of rare earth ions is 50 mg / L.

[0096] Comparative Example 1

[0097] This comparative example provides a method for preparing rare earth enrichments from rare earth salt solutions, the method comprising the following steps:

[0098] Carbon felt electrode and titanium-plated ruthenium electrode were used as cathode and anode, respectively; a 1 mol / L magnesium sulfate solution was placed in the anode chamber, and the magnesium sulfate solution was used as the electrolyte in the anode area;

[0099] A rare earth salt solution is placed in the cathode chamber, and the rare earth salt solution is used as the electrolyte in the anode region. The rare earth salt solution is a calcium and magnesium rare earth sulfate solution. In the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 1000 mg / L, the concentration of calcium ions is 200 mg / L, the concentration of magnesium ions is 1500 mg / L, and the concentration of sulfate ions is 6000 mg / L.

[0100] An anion exchange membrane (Jinqiu Environmental Protection JQA-81) is used to separate the anode chamber and the cathode chamber;

[0101] At 100 A / m 2 Electrolysis was performed at a current density, and the pH of the electrolyte in the cathode region rose to 6.6, rare earth ions precipitated, and the rare earth enrichment was obtained after solid-liquid separation.

[0102] The precipitation rates of rare earth ions obtained by the methods described in the above embodiments and comparative examples are shown in Table 1; the grade, sulfate ion content, magnesium ion content, and calcium ion content of the rare earth enrichments obtained by the methods described in the above embodiments and comparative examples are also shown in Table 1.

[0103] Table 1

[0104]

[0105] As can be seen from Table 1 above:

[0106] As shown in Examples 1-11 and Comparative Example 1, the present invention, by introducing carbon dioxide gas into the cathode region, can prevent rare earth ions from co-precipitating with other impurities, thereby improving the grade of rare earth enrichment and reducing the impurity content in the rare earth enrichment. As shown in Examples 1-3, 6-7, and 4-5, the present invention can introduce pure carbon dioxide gas or a mixture of carbon dioxide gas and other gases into the cathode region. As shown in Examples 1 and 8-9, the present invention preferably uses a ratio of the flow rate of the carbon dioxide gas to the effective electrode area of ​​the cathode region within a specific range, thereby further promoting the effect of carbon dioxide gas and improving the grade of rare earth enrichment. As shown in Examples 1 and 10-11, the present invention preferably uses an electrolyte pH that rises to a specific range in the cathode region, thereby further improving the precipitation rate of rare earth ions and the grade of rare earth enrichment. As shown in Examples 1 and 12, the method of the present invention can still effectively enrich rare earth ions even at extremely low concentrations.

[0107] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing rare earth enrichments from rare earth salt solutions, characterized in that, The method includes the following steps: An electrolyte solution is used as the electrolyte in the anode region, a rare earth salt solution is used as the electrolyte in the cathode region, and a diaphragm separates the cathode region from the anode region. Gas is introduced into the cathode region and electrolysis is performed to raise the pH of the electrolyte in the cathode region, causing rare earth ions to precipitate and obtain the rare earth enrichment. The gas includes carbon dioxide.

2. The method according to claim 1, characterized in that, The ratio of the carbon dioxide gas flow rate to the effective electrode area of ​​the cathode region is 0.25 mL·min. -1 ·cm -2 -6.25 mL·min -1 ·cm -2 ; Preferably, the gas also includes other gases, including oxygen or air; Preferably, the flow rate ratio of the carbon dioxide gas to the other gases is (4-6):

1.

3. The method according to claim 1 or 2, characterized in that, The pH of the electrolyte electrolyzed into the cathode region rises to 6-8.

4. The method according to claim 1 or 2, characterized in that, The rare earth salt solution includes a rare earth sulfate solution containing calcium and magnesium.

5. The method according to claim 4, characterized in that, In the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 50 mg / L-3000 mg / L, the concentration of calcium ions is ≥50 mg / L, the concentration of magnesium ions is ≥500 mg / L, and the concentration of sulfate ions is ≥1000 mg / L.

6. The method according to claim 1 or 2, characterized in that, The current density of the electrolysis is 40 A / m 2 -1000A / m 2 .

7. The method according to claim 1 or 2, characterized in that, The anion type in the electrolyte solution is the same as the anion type in the rare earth salt solution; Preferably, the concentration of the electrolyte solution is 1-2 mol / L.

8. The method according to claim 1 or 2, characterized in that, The membrane includes any one of anion exchange membrane, cation exchange membrane, or bipolar membrane.

9. The method according to claim 1 or 2, characterized in that, The rare earth enrichment has a grade of ≥90%, and the mass percentage of sulfate ions, calcium ions, and magnesium ions in the rare earth enrichment is ≤5%, ≤1%, and ≤1%, respectively.

10. The method according to claim 1 or 2, characterized in that, The method includes the following steps: An electrolyte solution is placed in the anode chamber, so that the electrolyte solution serves as the electrolyte in the anode region. The anion type in the electrolyte solution is the same as the anion type in the rare earth salt solution. A rare earth salt solution is placed in the cathode chamber, so that the rare earth salt solution serves as the electrolyte in the anode region. The rare earth salt solution is a calcium and magnesium rare earth sulfate solution. In the calcium and magnesium rare earth sulfate solution, the concentration of rare earth ions is 50 mg / L-3000 mg / L, the concentration of calcium ions is ≥50 mg / L, the concentration of magnesium ions is ≥500 mg / L, and the concentration of sulfate ions is ≥1000 mg / L. The anode chamber and the cathode chamber are separated by a diaphragm; Carbon dioxide gas is introduced into the cathode region at a rate of 40 A / m 2 -1000 A / m 2 Electrolysis is performed at a current density until the pH of the electrolyte in the cathode region rises to 6-8, rare earth ions precipitate, and the rare earth enrichment is obtained after solid-liquid separation. During the electrolysis process, carbon dioxide gas is continuously introduced into the cathode region, and the ratio of the flow rate of the carbon dioxide gas to the effective electrode area of ​​the cathode region is 0.25 mL·min. -1 ·cm -2 -6.25 mL·min -1 ·cm -2 .

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