Method for preparing rare earth hydroxide from alkali metal hydroxide and recycling rare earth hydroxide

Abstract

The invention discloses a method for preparing rare earth hydroxide from alkali metal hydroxide and recycling the rare earth hydroxide, which comprises the following steps: (1) mixing an alkali metal hydroxide solution and a rare earth chloride salt solution and reacting, after the reaction is finished, carrying out solid-liquid separation to obtain a precipitate and a mother solution, and washing the precipitate to obtain the rare earth hydroxide and a washing solution; (2) carrying out impurity removal and concentration on the mother liquor, and then electrolyzing to obtain an alkali metal hydroxide solution, Cl2 and H2; returning the obtained alkali metal hydroxide solution to the step (1), and recycling the alkali metal hydroxide solution as a precipitant; and (3) the Cl2 and H2 in the step (2) react to obtain hydrochloric acid, the hydrochloric acid is used for reverse extraction of the loaded organic phase to obtain a rare earth chloride salt solution, and the step (1) is returned. According to the method, the rare earth hydroxide can be obtained, and comprehensive recycling of the alkaline precipitant, the wastewater and the regenerated acid is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of rare earth metallurgy, and relates to a method for preparing rare earth hydroxide by using alkali metal hydroxide and recycling the same, and more particularly to a method for preparing rare earth hydroxide by using alkali metal hydroxide and recycling the alkali metal hydroxide, waste water and regenerated acid. Background Art

[0002] Rare earth hydroxides are important precursors to rare earth oxides and have significant applications themselves. For example, cerium-rich rare earth hydroxides are primarily used as glass decolorizers and clarifiers, and can also be used as a raw material for smelting cerium-rich rare earth ferrosilicon alloys. Lanthanum hydroxide can also be directly used in the glass, ceramic, and electronics industries. As a precursor to rare earth oxides, rare earth hydroxides, with a rare earth content of approximately 70% by weight, can significantly improve production efficiency. Furthermore, the calcination of rare earth hydroxides to obtain rare earth oxides requires low temperatures and consumes minimal energy.

[0003] CN105779792B discloses a method for preparing rare earth hydroxide with low impurity content. The method comprises adding a sodium hydroxide solution to a rare earth sulfate solution to carry out a precipitation reaction, then subjecting the solution to solid-liquid separation to obtain a precipitate product and a mother liquor. The precipitate product is then washed and dried to obtain a rare earth hydroxide having a sulfate content of less than 0.5 wt%. This method also uses sodium hydroxide as a precipitant, but the wastewater from the reaction is not treated, resulting in a large amount of sodium chloride wastewater. Industrial production is prone to environmental pollution.

[0004] CN119080047A discloses micron-sized lanthanum hydroxide particles and a preparation method thereof. Lanthanum salt solution and ammonia water are added dropwise to water in parallel at a reaction temperature of 30-90°C with stirring, to produce a suspension after the addition is complete. The relative dropwise addition rates of the lanthanum salt solution and ammonia water are controlled so that the molar ratio of NH3 in the ammonia water to lanthanum ions in the lanthanum salt solution is greater than 3, and the pH value of the reaction system is controlled to 7.5-9.5. The suspension is directly subjected to solid-liquid separation without aging to obtain a solid. The solid is then washed and dried to obtain micron-sized lanthanum hydroxide particles. However, the volume of the bottom liquid water during the reaction is 3-15% of the volume of the reaction vessel. The solid needs to be washed with a large amount of water until the pH of the washing liquid reaches 7.0, which produces a large amount of ammonium-containing wastewater, which is costly to treat and easily affects the environment when industrialized. Summary of the Invention

[0005] In light of this, the present invention provides a method for preparing rare earth hydroxide from alkali metal hydroxide and its recycling. This method, while producing rare earth hydroxide, also enables the comprehensive recycling of alkaline precipitants, wastewater, and regenerated acid. This method can further reduce energy consumption and save costs during the production of rare earth hydroxide. It also achieves recycling of regenerated acid and alkali metal ions through wastewater electrolysis, eliminating environmental pollution caused by alkali metal chloride wastewater.

[0006] The present invention adopts the following technical solutions to achieve the above-mentioned purpose.

[0007] The present invention provides a method for preparing rare earth hydroxide by using alkali metal hydroxide and recycling the same.

[0008] (1) mixing an alkali metal hydroxide solution and a rare earth chloride salt solution and reacting them, and after the reaction is completed, performing solid-liquid separation to obtain a precipitate and a mother liquor, and washing the precipitate to obtain rare earth hydroxide and a washing liquid;

[0009] (2) removing impurities and concentrating the mother liquor, and then electrolyzing it to obtain an alkali metal hydroxide solution, Cl2 and H2; returning the obtained alkali metal hydroxide solution to step (1) and recycling it as a precipitant;

[0010] (3) The Cl2 and H2 in step (2) are reacted to obtain hydrochloric acid, and the hydrochloric acid is used to strip the loaded organic phase to obtain a rare earth chloride salt solution, and then return to step (1). In this way, rare earth hydroxide can be obtained, and the generation of ammonia nitrogen wastewater can be avoided, and the comprehensive utilization of alkali metal hydroxide solution, wastewater, and regenerated acid can be achieved. Although the reactions of electrolysis and hydrochloric acid production are common when viewed separately, the inventors have comprehensively utilized them to achieve the comprehensive recycling of the mother liquor wastewater generated by the production of rare earth hydroxide while producing rare earth hydroxide. This is not a conventional option. In addition, the washing liquid produced is also recycled, and basically no external wastewater is generated.

[0011] In step (1), the alkali metal hydroxide solution is selected from one or both of sodium hydroxide solution and potassium hydroxide solution. The reaction temperature can be 40-90°C, preferably 50-85°C, more preferably 60-85°C, for example, 60°C, 70°C, 75°C, 80°C, or 85°C. Solid-liquid separation can be by centrifugation or filtration, preferably filtration. The precipitate is washed with water, which can be one of deionized water, purified water, and distilled water.

[0012] In step (1), the alkali metal hydroxide solution and the rare earth chloride salt solution can be preferably added dropwise to the reaction container in parallel for reaction.

[0013] In step (1), the mother liquor is a sodium chloride solution, and the washing liquid contains a trace amount of sodium chloride.

[0014] In step (2), the mother liquor is subjected to impurity removal (using a known method to remove organic matter). After the mother liquor is subjected to impurity removal, it is concentrated to obtain a concentrated sodium chloride solution. The concentrated sodium chloride solution can be a saturated sodium chloride solution. The concentrated sodium chloride solution is electrolyzed under the following conditions: a voltage of 2 to 3 V, preferably 2 to 2.5 V, and a current density of 200 to 230 A / m 2 , preferably 200~220A / m 2 The temperature is 40-60°C, preferably 45-50°C. The alkali metal hydroxide solution obtained by electrolysis is used to react with the rare earth chloride solution. In the present invention, the Cl2 and H2 obtained are both gases.

[0015] In step (3), Cl2 and H2 are sometimes ignited or photo-exposed to obtain HCl gas, which is then dissolved to obtain hydrochloric acid. However, if the gas purity is insufficient during ignition, it is easy to explode, and photo-exposed reactions also pose a safety hazard. When Cl2 and H2 react, a catalyst, such as activated carbon-supported copper chloride or activated carbon-supported ferric chloride, can be added to reduce the activation energy of the reaction, allowing the reaction to proceed under milder conditions (such as room temperature, or lower temperatures, such as below 10°C), thereby increasing the reaction rate and reducing side reactions and safety risks. Stripping is a key step in the rare earth solvent extraction and separation process. Its core is to add acid or alkali to the metal-loaded organic phase (i.e., the loaded organic phase) to allow the target metal ions to re-enter the aqueous phase, thereby achieving metal enrichment and extractant regeneration.

[0016] Preparation of the catalyst activated carbon-supported copper chloride or activated carbon-supported ferric chloride: Using activated carbon as a carrier, copper chloride solution (or ferric chloride solution) is impregnated onto the carrier, and the concentration (15-25wt%) of the impregnation solution copper chloride solution (or ferric chloride solution), the impregnation time (40-90 minutes) and the impregnation ratio (the volume mass ratio of the impregnation solution to the carrier is 4-6mL:1g) are controlled to achieve efficient loading of copper ions or iron ions. The impregnation temperature is room temperature. There is no particular restriction on the source of the activated carbon. According to one embodiment of the present invention, the activated carbon is selected from the columnar activated carbon of Fujian Xinsen Carbon Industry Co., Ltd. The concentration of the impregnation solution is preferably 20-23wt%. The impregnation time is preferably 60-70 minutes. The impregnation ratio is preferably 5-5.5mL:1g.

[0017] According to the method of the present invention, preferably, in step (1), the alkali metal hydroxide in the alkali metal hydroxide solution is sodium hydroxide, potassium hydroxide or a mixture of sodium hydroxide and potassium hydroxide. According to a specific embodiment of the present invention, the alkali metal hydroxide in the alkali metal hydroxide solution is sodium hydroxide.

[0018] According to the method of the present invention, preferably, in step (1), OH in the alkali metal hydroxide solution -The molar ratio of rare earth metal ions to the rare earth chloride salt solution is 3 to 3.3, preferably 3.1 to 3.3. This helps to fully react and precipitate the raw materials, which helps to ensure the yield and purity of rare earth hydroxide.

[0019] According to the method of the present invention, preferably, in step (1), OH in the alkali metal hydroxide solution - The molar ratio of the rare earth metal ions to the rare earth chloride salt solution is 3.2 to 3.3.

[0020] According to the method of the present invention, preferably, in step (1), the rare earth in the rare earth chloride salt solution is a single element or a mixed element.

[0021] The rare earth in the rare earth chloride solution refers to lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, and yttrium, preferably lanthanum, cerium, praseodymium, and neodymium.

[0022] In some specific embodiments, the rare earth chloride solution is a praseodymium-neodymium chloride solution. In other specific embodiments, the rare earth chloride solution is a lanthanum chloride solution. In still other specific embodiments, the rare earth chloride solution is a lanthanum-cerium chloride solution.

[0023] According to the method of the present invention, preferably, in step (1), the reaction temperature is 40-90° C. This is conducive to the complete reaction of the raw materials.

[0024] According to the method of the present invention, preferably, in step (1), the pH value of the reaction system is controlled to be 7.5 to 8.5 during the reaction. The pH value is more preferably 8.0 to 8.5. At the end of the reaction, the pH value of the reaction system is 8.0 to 8.5.

[0025] According to the method of the present invention, preferably, in step (1), the pH value of the reaction system is controlled to be 8.0-8.5 during the reaction process.

[0026] According to the method of the present invention, preferably, the washing liquid of step (1) is used to dilute the alkali metal hydroxide solution of step (2), used for absorbing HCl in step (3), or used as the bottom liquid of the reaction in step (1).

[0027] According to the method of the present invention, preferably, in step (3), the concentration of hydrochloric acid is 3 to 12 mol / L. The concentration of hydrochloric acid is preferably 3 to 6 mol / L, and more preferably 5 to 6 mol / L. This is beneficial for improving the stripping efficiency of the loaded organic phase.

[0028] The method of the present invention can produce rare earth hydroxides while avoiding the generation of ammonia nitrogen wastewater. It also allows for the reuse of precipitant (alkali metal hydroxide), wastewater, and regenerated acid (hydrochloric acid), resulting in zero solid waste emissions. Compared to thermal decomposition processes, the electrolytic alkali production process consumes less energy and offers greater economic benefits. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0030] Preparation of activated carbon-supported copper chloride catalyst used in the following examples: Using activated carbon as a carrier, a copper chloride solution was impregnated onto the carrier. The copper ion loading was achieved by controlling the concentration of the copper chloride solution (20 wt%), the impregnation time (60 minutes), and the impregnation ratio (the volume-to-mass ratio of the impregnation solution to the carrier was 5 mL:1 g).

[0031] Preparation of activated carbon-supported ferric chloride catalyst used in the following examples: Using activated carbon as a carrier, a ferric chloride solution was impregnated onto the carrier. The loading of iron ions was achieved by controlling the concentration of the ferric chloride solution (20 wt%), the impregnation time (60 minutes), and the impregnation ratio (the volume-to-mass ratio of the impregnation solution to the carrier was 5 mL:1 g).

[0032] The activated carbon used was columnar activated carbon produced by Fujian Xinsen Carbon Industry Co., Ltd.

[0033] Example 1

[0034] The method of preparing rare earth hydroxide by using alkali metal hydroxide and recycling it in this embodiment comprises the following steps:

[0035] (1) A 240 g / L sodium hydroxide solution and a praseodymium-neodymium chloride solution are mixed and reacted at 75° C. The pH value of the reaction system is controlled to be 8.0. After the reaction is completed, a precipitate and a sodium chloride solution (i.e., mother liquor) are obtained by solid-liquid separation. The precipitate is washed with water to obtain praseodymium-neodymium hydroxide (i.e., rare earth hydroxide) and a washing liquid (containing a trace amount of sodium chloride). The washing liquid can be recycled as the bottom liquid of the reaction in this step.

[0036] (2) The sodium chloride solution is impurity-removed (organic matter removed) and concentrated to obtain a concentrated sodium chloride solution, and then the concentrated sodium chloride solution is subjected to a voltage of 2.5 V and a current density of 220 A / m 2 , electrolysis is carried out at a temperature of 45° C. to obtain a sodium hydroxide solution (i.e., an alkali metal hydroxide solution), Cl2, and H2. The obtained sodium hydroxide solution is returned to step (1) and recycled as a precipitant.

[0037] (3) The Cl2 and H2 in step (2) are reacted in the presence of an activated carbon-supported copper chloride catalyst to obtain hydrochloric acid after absorption. The hydrochloric acid is used to strip the loaded organic phase to obtain a praseodymium-neodymium chloride solution, which is returned to step (1) and used as a raw material.

[0038] Example 2

[0039] The method of preparing rare earth hydroxide by using alkali metal hydroxide and recycling it in this embodiment comprises the following steps:

[0040] (1) 300 g / L sodium hydroxide solution and lanthanum chloride solution are mixed and reacted at 85° C. The pH value of the reaction system is controlled to be 8.0. After the reaction is completed, a precipitate and a sodium chloride solution (i.e., mother liquor) are obtained by solid-liquid separation. The precipitate is washed with water to obtain lanthanum hydroxide (i.e., rare earth hydroxide) and a washing liquid (containing a trace amount of sodium chloride). The washing liquid can be recycled as the bottom liquid of the reaction in this step.

[0041] (2) The sodium chloride solution (i.e., mother liquor) is subjected to impurity removal (removal of organic matter) and concentration to obtain a concentrated sodium chloride solution, and then the concentrated sodium chloride solution is subjected to a voltage of 2.5 V and a current density of 220 A / m 2 , electrolysis is carried out at a temperature of 45° C. to obtain a sodium hydroxide solution (i.e., an alkali metal hydroxide solution), Cl2, and H2. The obtained sodium hydroxide solution is returned to step (1) and recycled as a precipitant.

[0042] (3) reacting the Cl2 and H2 in step (2) in the presence of an activated carbon-supported ferric chloride catalyst, and using the washing liquid to absorb HCl to obtain hydrochloric acid, which is used to strip the loaded organic phase to obtain a lanthanum chloride solution, which is returned to step (1) and used as a raw material.

[0043] Example 3

[0044] The method for preparing rare earth hydroxide from alkali metal hydroxide and recycling it in this embodiment comprises the following steps:

[0045] (1) A 200 g / L sodium hydroxide solution and a lanthanum cerium chloride solution were mixed and reacted at 85° C. The pH value of the reaction system was controlled to be 8.0. After the reaction was completed, a precipitate and a sodium chloride solution (i.e., mother liquor) were obtained by solid-liquid separation. The precipitate was washed with water to obtain lanthanum hydroxide (i.e., rare earth hydroxide) and a washing liquid (containing a trace amount of sodium chloride). The washing liquid can be recycled as the bottom liquid of the reaction in this step.

[0046] (2) The sodium chloride solution (i.e., mother liquor) is subjected to impurity removal (removal of organic matter) and concentration to obtain a concentrated sodium chloride solution, and then the concentrated sodium chloride solution is subjected to a voltage of 2.5 V and a current density of 220 A / m2 , electrolysis is carried out at a temperature of 45°C to obtain a sodium hydroxide solution (i.e., an alkali metal hydroxide solution), Cl2, and H2. The washing liquid is used to dilute the sodium hydroxide solution, and the obtained diluted sodium hydroxide solution is returned to step (1) and recycled as a precipitant.

[0047] (3) reacting the Cl2 and H2 in step (2) in the presence of an activated carbon-supported ferric chloride catalyst to obtain hydrochloric acid after absorption, which is used to strip the loaded organic phase to obtain a lanthanum cerium chloride solution, which is returned to step (1) and used as a raw material.

[0048] The present invention is not limited to the above-mentioned embodiments. Any modification, improvement, or substitution that can be conceived by those skilled in the art without departing from the essential content of the present invention shall fall within the scope of the present invention.

Claims

1. A method for preparing rare earth hydroxide by using alkali metal hydroxide and recycling it, characterized in that: (1) mixing an alkali metal hydroxide solution and a rare earth chloride salt solution and reacting them, and after the reaction is completed, performing solid-liquid separation to obtain a precipitate and a mother liquor, and washing the precipitate to obtain rare earth hydroxide and a washing liquid; (2) removing impurities and concentrating the mother liquor, and then electrolyzing it to obtain an alkali metal hydroxide solution, Cl2 and H2; returning the obtained alkali metal hydroxide solution to step (1) and recycling it as a precipitant; (3) The Cl2 and H2 in step (2) are reacted to obtain hydrochloric acid, and the hydrochloric acid is used to strip the loaded organic phase to obtain a rare earth chloride salt solution, and the process returns to step (1).

2. The method according to claim 1, characterized in that In step (1), the alkali metal hydroxide in the alkali metal hydroxide solution is sodium hydroxide, potassium hydroxide or a mixture of sodium hydroxide and potassium hydroxide.

3. The method according to claim 1, characterized in that In step (1), the OH in the alkali metal hydroxide solution - The molar ratio of the rare earth metal ions to the rare earth chloride salt solution is 3 to 3.

3.

4. The method according to claim 1, wherein In step (1), the OH in the alkali metal hydroxide solution - The molar ratio of the rare earth metal ions to the rare earth chloride salt solution is 3.2 to 3.

3.

5. The method according to claim 1, wherein In step (1), the rare earth in the rare earth chloride salt solution is a single element or a mixed element.

6. The method according to claim 1, characterized in that In step (1), the reaction temperature is 40-90°C.

7. The method according to claim 1, characterized in that In step (1), the pH value of the reaction system is controlled to be 7.5 to 8.5 during the reaction process.

8. The method according to claim 1, characterized in that In step (1), the pH value of the reaction system is controlled to be 8.0-8.5 during the reaction process.

9. The method according to claim 1, characterized in that The washing liquid of step (1) is used to dilute the alkali metal hydroxide solution of step (2), used for absorbing HCl in step (3), or used as the bottom liquid of the reaction of step (1).

10. The method according to any one of claims 1 to 9, characterized in that In step (3), the concentration of hydrochloric acid is 3 to 12 mol / L.