Method for recovering rare earth and byproduct hydrogen from nitric acid decomposed phosphorite acidolysis solution
By electrolyzing phosphate rock acid electrolyte in a diaphragm electrolyzer using an electrochemical method and controlling the pH value in the cathode area, the problem of efficient recovery of rare earth elements in phosphate rock was solved. This achieved selective precipitation of rare earth elements and hydrogen byproduct, reduced fluoride ion concentration, reduced pollution, and promoted the high-value utilization of phosphate rock resources.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-22
- Publication Date
- 2026-03-27
AI Technical Summary
Existing technologies are difficult to efficiently recover rare earth elements from phosphate rock, especially in the nitric acid leaching solution of fluorine-containing phosphate rock where rare earth separation is difficult. Furthermore, traditional methods consume a lot of reagents, generate many by-products, are costly, and cause serious pollution.
An electrochemical method is used to electrolyze nitric acid to decompose phosphate rock acid solution in a diaphragm electrolytic cell. By controlling the pH value change in the cathode area, rare earth ions react with phosphate and fluoride ions to form insoluble compounds and precipitate, achieving selective precipitation and recovery of rare earths, and producing hydrogen as a byproduct.
It achieves efficient separation and recovery of rare earth elements, reduces the concentration of free fluoride ions, reduces secondary pollution, promotes the high-value utilization of phosphate rock resources, and eliminates the need for external chemical precipitants.
Smart Images
Figure CN121737488A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of rare earth element separation and resource utilization, and particularly relates to a method for recovering rare earth elements from a nitric acid decomposition phosphate ore acidolysis solution and by-product hydrogen. BACKGROUND
[0002] Phosphate rock is abundant in reserves, widely distributed and generally associated with rare earth elements (REEs). Utilizing phosphate rock to extract rare earths will be an important direction for realizing a green supply chain of rare earths. However, rare earth elements in phosphate rock are often present in the form of heterogeneous solid solution or phosphate, which is difficult to recover directly and often needs to be converted into a soluble form by acid leaching. Nitric acid leaching is one of the common treatment methods at present, and the product is a complex acidic solution containing a large amount of Ca 2+ , Mg 2+ , Fe 3+ , Al 3+ , K + , P, F - and other ions, with complex chemical composition and strong acidity, which poses great challenges to subsequent separation and purification.
[0003] Traditional rare earth recovery processes usually include multiple steps such as chemical precipitation, solvent extraction, ion exchange, etc. For example, in the chemical neutralization and coprecipitation method, rare earths are precipitated in the form of hydroxide or phosphate by gradually adjusting the pH, but this method has high reagent consumption and generates many by-product precipitates (such as calcium phosphate, iron hydroxide, etc.), with high cost of subsequent rare earth purification and heavy burden of waste liquid treatment; although the solvent extraction method has good selectivity, it is complex and has problems of extractant loss and secondary pollution. Overall, these traditional methods are difficult to meet the requirements of efficient recovery of rare earths from systems containing multiple impurities and high acidity (such as phosphate nitric acid leaching solution).
[0004] The electrochemical one-step precipitation method proposed in the present application is aimed at fluorine-containing phosphate ore acid leaching solution system, and there is no similar public report or patent at home and abroad at present. SUMMARY
[0005] The present application aims to provide a method for recovering rare earth from nitric acid decomposition of phosphate rock acid hydrolysis solution and by-product hydrogen, to overcome the shortcomings of the prior art, which adjusts the chemical environment of the cathode region in situ in an electrochemical system, electrolyzes the acid hydrolysis solution obtained by nitric acid decomposition of phosphate rock in the cathode pool of a diaphragm electrolytic cell, and through the generation of hydrogen gas and the increase of pH during the electrolysis process, the rare earth ions combine with phosphate ions, fluoride ions and other ions in the system to form insoluble rare earth compounds and precipitate, realizing the selective precipitation and recovery of rare earth elements, effectively separating the rare earth elements, and significantly reducing the concentration of free fluoride ions in the system; at the same time, hydrogen gas is recovered during the electrolysis process, realizing efficient utilization of energy and resources. This process does not require additional chemical precipitants or complex solvent extraction systems, avoiding secondary pollution problems. After electrochemical treatment, the acidity and free fluoride ion concentration of the acid hydrolysis solution are significantly reduced, providing conditions for the subsequent comprehensive utilization of phosphate or fluoride by-products, thereby promoting the high-value and clean utilization of phosphate rock resources.
[0006] The present application provides a method for recovering rare earth from nitric acid decomposition of phosphate rock acid hydrolysis solution and by-product hydrogen, which utilizes an electrochemical method to electrolyze the acid hydrolysis solution obtained by nitric acid decomposition of phosphate rock in the cathode pool of a diaphragm electrolytic cell, through the generation of hydrogen gas and the increase of pH during the electrolysis process, the rare earth ions combine with phosphate ions, fluoride ions and other ions in the system to form insoluble rare earth compounds and precipitate, and the rare earth compounds are separated and hydrogen gas is collected. The specific method includes the following steps:
[0007] (1) Phosphate rock pretreatment
[0008] The phosphate rock is crushed to a particle size of ≤ 0.075 mm;
[0009] (2) Nitric acid leaching of rare earth in phosphate rock powder
[0010] The phosphate rock powder is thoroughly mixed with nitric acid and fully reacted, and then the insoluble material is separated to obtain the acid hydrolysis solution.
[0011] (3) Neutralization of nitric acid decomposition of phosphate rock acid hydrolysis solution
[0012] The acid hydrolysis solution obtained in (2) is thoroughly stirred while slowly adding alkali for neutralization to prevent local pH from being too high; at the same time, the pH of the acid hydrolysis solution is monitored, and when the pH rises to 1.0-1.8, the neutralization is stopped to obtain the neutralized acid hydrolysis solution.
[0013] (4) Electrochemical precipitation and recovery of rare earth and collection of hydrogen gas
[0014] The neutralized acid hydrolysis solution is placed in a cathode pool of a diaphragm electrolytic cell device as a cathode solution, and an anode solution is an inert electrolyte solution, and an anion exchange membrane is used to separate the electrolytic cell into the cathode pool and an anode pool; the cathode solution is stirred, and electricity is passed to make rare earths precipitate on the surface of the cathode and in the cathode pool; the pH of the cathode solution is monitored, and when the pH reaches 2.1-2.8, the electrolysis is ended; and high-content rare earth enrichment is obtained through collection, filtration and drying. Hydrogen gas generated in the cathode pool during the electrolysis is collected at the same time.
[0015] In the step (3) of the above method, the base is one or more of liquid ammonia, ammonia gas, ammonia water, sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, potassium carbonate solution or lime milk.
[0016] In the step (4) of the above method, the anode solution is an inert electrolyte solution, and is one or more of 0.1-3.0 mol / L of a salt solution of sodium nitrate, sodium sulfate, potassium nitrate or potassium sulfate; the anode material is graphite, lead alloy or a titanium-based coated electrode; the cathode material is graphite, a titanium-based coated electrode or a platinum-gold coated electrode; the stirring rate of the cathode pool is 50-600 r / min, the cathode current density is 0.05-10 A / dm 2 , the electrolysis time is 20-240 min, and the electrode spacing is 0.5-10.0 cm.
[0017] The principle of the application is that in an acidic system, the main existing form of rare earth ions and the type of precipitates are significantly affected by pH, anion composition and complexation balance. Generally, rare earths will be precipitated in the form of rare earth phosphate REPO4 or hydroxide RE(OH)3. However, if the solution contains a high concentration of fluoride ions F - , the situation will be significantly different. Fluoride ions not only form stable fluoride REF3 with rare earth ions, and the solubility of the fluoride is extremely low, but also form coordination complexes with rare earths. The existence of these fluorides or coordination compounds will competitively change the precipitation balance, leading to the formation of fluorides as the main path of REE from the acidic solution. Since the composition of the phosphate ore is mainly fluorapatite Ca5(PO4)3F, after nitric acid decomposition of the phosphate ore, the fluorine element mainly exists in the form of fluoride F - , fluorosilicate SiF6 2- , etc., and thus can provide fluoride ions for the precipitation of rare earths.
[0018] The present application shows through a large amount of research that in a fluorine-containing system, when the F - / REE 3+ ratio is high and the pH is lower than 3, the formation of REF3 is more favorable; and when the F - concentration is low or the PO4 3-In systems with higher fluorine content, REPO4 formation is dominant. In other words, the presence of fluorine gives rare earth precipitation a distinct dual-phase competition mechanism: it can form fluorides or co-precipitate with phosphate. The alteration of the thermodynamic and kinetic behavior of the solution system by fluoride ions affects not only the type of precipitate phase but also the nucleation rate, particle morphology, and separation performance.
[0019] In electrochemical methods, in-situ precipitation and enrichment of rare earth ions can be achieved by inducing a local pH rise near the cathode by applying current. This method does not require the addition of large amounts of alkali or precipitating agents and can precisely control the local chemical environment in an acidic system, enabling efficient rare earth separation and recovery. When fluoride ions are present in the electrochemical system, the local pH rise in the cathode region alters the competitive relationship between fluoride ions, phosphate ions, and rare earth ions, potentially leading to the simultaneous formation of mixed precipitates of rare earth fluorides, rare earth phosphates, and rare earth hydroxides. In this case, the proportion and purity of different precipitate phases can be controlled by adjusting parameters such as current density, charge quantity, temperature, stirring rate, and membrane partitioning structure.
[0020] Beneficial effects: Compared with existing technologies, the method of this invention uses an electrochemical method to recover rare earth elements from the acid hydrolysis solution of phosphate rock decomposed by nitric acid, producing hydrogen as a byproduct. This is more economical and environmentally friendly than using chemical precipitation methods to recover rare earth elements. The rare earth elements recovered by this method have higher purity, reduce the concentration of free fluoride ions in the system, reduce secondary pollution problems, and are more conducive to the high-value and clean utilization of phosphate rock resources. Attached Figure Description
[0021] Figure 1 This is a flowchart of the process flow of the method of the present invention. Detailed Implementation
[0022] Example 1:
[0023] The acid hydrolysis solution obtained from the decomposition of 1 ton of phosphate rock with nitric acid has a phosphoric acid content of 9.31%, a total nitrogen content of 3.2%, a total rare earth content of 0.054% (TRE2O3), and free F. - The content is 0.55%, F - / REE 3+ The ratio of ammonia to ammonia solution is 10.2:1. Ammonia solution is slowly added dropwise to the acid hydrolysate while stirring it thoroughly to prevent local pH from becoming too high, which could lead to irreversible precipitation. During the neutralization process, the pH of the neutralized acid hydrolysate is measured multiple times to prevent excessive ammonia. When the pH is neutralized to 1.1, the addition is stopped.
[0024] 0.5 tons of neutralized acid hydrolysate were placed in the cathode cell of the diaphragm electrolytic cell as the catholyte, and 0.5 tons of 2 mol / L sodium nitrate were used as the anolyte. An anion exchange membrane separated the anode and cathode. The stirring rate was 100 r / min and the current density was 229 A / m. 2, the end point pH is 2.5, the electrode interval is 5.8 cm, and the reaction is carried out for 180 min, 6.43 kg of rare earth-rich precipitate is collected, the rare earth content is 529.2 g, more than 98% of the rare earth in the solution is precipitated, and 20.5 L of hydrogen is collected at the same time. The free F - content in the solution is reduced to 0.15%.
[0025] Example 2:
[0026] Take 1 ton of acid hydrolysis solution obtained by decomposing phosphate rock with nitric acid, the phosphoric acid content is 9.68%, the total nitrogen content is 3.3%, the total rare earth content is 0.059% (TRE2O3), the free F - content is 0.35%, the ratio of F - / REE 3+ is 5.9:1, ammonia water is slowly added to the acid hydrolysis solution, and the acid hydrolysis solution is fully stirred to prevent local pH from being too high to cause the formation of irreversible precipitate; during the neutralization process, the pH of the neutralized acid hydrolysis solution is measured multiple times to prevent excessive ammonia water, and the dropping is stopped when the pH is neutralized to 1.1.
[0027] 0.5 tons of neutralized acid hydrolysis solution is placed in the cathode pool of the diaphragm electrolytic cell device as the cathode solution, and the anode solution is 0.5 tons of 2 mol / L sodium nitrate, and the anode and cathode are separated by anion exchange membrane; under the conditions of stirring rate of 100 r / min, current density of 229 A / m 2 , end point pH of 2.5, electrode interval of 5.8 cm, reaction for 180 min, 6.67 kg of rare earth-rich precipitate is collected, the rare earth content is 548.7 g, more than 93% of the rare earth in the solution is precipitated, and 21.3 L of hydrogen is collected at the same time. The free F - content in the solution is reduced to 0.09%.
[0028] Example 3:
[0029] Take 1 ton of acid hydrolysis solution obtained by decomposing phosphate rock with nitric acid, the phosphoric acid content is 9.31%, the total nitrogen content is 3.2%, the total rare earth content is 0.054% (TRE2O3), the free F - content is 0.28%, the ratio of F - / REE 3+ is 5.2:1, ammonia water is slowly added to the acid hydrolysis solution, and the acid hydrolysis solution is fully stirred to prevent local pH from being too high to cause the formation of irreversible precipitate; during the neutralization process, the pH of the neutralized acid hydrolysis solution is measured multiple times to prevent excessive ammonia water, and the dropping is stopped when the pH is neutralized to 1.1.
[0030] 0.5 tons of neutralized acid hydrolysis solution was placed in the cathode pool of the diaphragm electrolytic cell device as the cathode solution, the anode solution was 0.5 tons of 2 mol / L sodium nitrate, and the anode and cathode were separated by anion exchange membrane; under the conditions of stirring rate of 100 r / min, current density of 229 A / m 2 , end point pH of 2.5, electrode spacing of 5.8 cm, reaction for 180 min, 6.43 kg of rare earth-rich precipitate was collected, the rare earth content was 480.6 g, more than 89% of the rare earth in the solution was precipitated, and 19.9 L of hydrogen was collected at the same time. The free F - in the solution was reduced to 0.08%.
[0031] The difference between Example 3 and Example 1 is that the ratio of F - / REE 3+ is different, which shows that under the same pH condition, a high ratio of F - / REE 3+ is conducive to the generation of REF3 in the electrolysis process, and the recovery rate of rare earth is higher.
[0032] Example 4:
[0033] Take 1 ton of acid hydrolysis solution obtained by nitric acid decomposition of phosphate rock, the phosphoric acid content is 9.31%, the total nitrogen content is 3.2%, the total rare earth content is 0.054% (TRE2O3), the free F - content is 0.55%, the ratio of F - / REE 3+ is 10.2:1, slowly add ammonia water to the acid hydrolysis solution, and fully stir the acid hydrolysis solution to prevent local pH from being too high to form irreversible precipitate; during the neutralization process, the pH of the neutralized acid hydrolysis solution is measured multiple times to prevent excessive ammonia water, and the dropping is stopped when the pH is neutralized to 1.4.
[0034] 0.5 tons of neutralized acid hydrolysis solution was placed in the cathode pool of the diaphragm electrolytic cell device as the cathode solution, the anode solution was 0.5 tons of 2 mol / L sodium nitrate, and the anode and cathode were separated by anion exchange membrane; under the conditions of stirring rate of 100 r / min, current density of 229 A / m 2 , end point pH of 2.5, electrode spacing of 5.8 cm, reaction for 150 min, 6.41 kg of rare earth-rich precipitate was collected, the rare earth content was 529.6 g, more than 98% of the rare earth in the solution was precipitated, and 18.5 L of hydrogen was collected at the same time. The free F - in the solution was reduced to 0.14%.
[0035] The difference between Example 4 and Example 1 is that the pH of neutralization is different. It is shown that the higher the pH of neutralization of the acid hydrolysis solution before electrolysis, the shorter the time required to reach the target pH without precipitation.
Claims
1. A method for recovering rare earth elements and producing hydrogen as a byproduct from the acid hydrolysis solution of phosphate rock decomposed by nitric acid, characterized in that, Includes the following steps: (1) Phosphate rock pretreatment The phosphate rock was crushed to a particle size ≤0.075 mm; (2) Leaching of rare earth elements from phosphate rock powder with nitric acid After thoroughly mixing and reacting the phosphate rock powder with nitric acid, the insoluble matter is separated to obtain the acid hydrolysis solution. (3) Neutralizing nitric acid to decompose phosphate rock acid hydrolysis solution While thoroughly stirring the acid hydrolysate obtained in step (2), slowly add alkali solution to neutralize it; at the same time, monitor the pH of the acid hydrolysate, and when the pH rises to 1.0 to 1.8, stop neutralization to obtain a neutralized acid hydrolysate; (4) Electrochemical precipitation recovery of rare earth elements and collection of hydrogen The neutralized acid electrolyte is placed in the cathode cell of the diaphragm electrolytic cell as the catholyte, while the anolyte is an inert electrolyte solution. An anion exchange membrane is used to separate the electrolytic cell into the cathode cell and the anolyte. The catholyte is stirred, and electricity is applied to precipitate rare earth elements on the cathode surface and in the cathode cell. The pH of the catholyte is monitored, and electrolysis is stopped when the pH reaches 2.1–2.
8. The rare earth enrichment is obtained by collection, filtration, and drying, while hydrogen gas generated in the cathode cell during electrolysis is also collected.
2. The method for recovering rare earth elements and producing hydrogen as a byproduct from the acid hydrolysis solution of phosphate rock decomposition with nitric acid, as described in claim 1, is characterized in that... In step (3), the alkaline solution is one or more of ammonia water, sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, potassium carbonate solution, or lime milk.
3. The method for recovering rare earth elements and producing hydrogen as a byproduct from the acid hydrolysis solution of phosphate rock decomposition with nitric acid as described in claim 1, characterized in that, In step (4), the anolyte is an inert electrolyte solution, which is a solution of one or more salts selected from sodium nitrate, sodium sulfate, potassium nitrate, and potassium sulfate at a concentration of 0.1–3.0 mol / L; the anode material is a graphite, lead alloy, or titanium-based coated electrode; the cathode material is a graphite, titanium-based coated electrode, or platinum-coated electrode; the cathode cell stirring rate is 50–600 r / min, and the cathode current density is 0.05–10 A / dm³. 2 The electrolysis time is 20–240 min, and the electrode spacing is 0.5–10.0 cm.