US20200140974A1

US20200140974A1 - Method of removing iron ions from a solution containing neodymium, praseodymium, dysprosium and iron

Info

Publication number: US20200140974A1
Application number: US16/406,174
Authority: US
Inventors: Suiyi ZHU; Zhan Qu; Xue Lin; Ge DONG; Dejun BIAN; Mingxin HUO
Original assignee: Northeast Normal University
Current assignee: Northeast Normal University
Priority date: 2018-11-07
Filing date: 2019-05-08
Publication date: 2020-05-07
Also published as: CN109593977A; CN109593977B

Abstract

The present invention discloses a method of removing iron ions from a solution containing neodymium, praseodymium, dysprosium and iron, in which glucose is added into an acid solution containing neodymium, praseodymium, dysprosium and iron, at a molar ratio of iron/glucose at 0.2-2, and mixed evenly, and the solution is then hydrothermal treated, and after that an iron-containing precipitate is formed at the bottom, and the residual concentration of iron in the supernatant is less than 20 mg/L, and the retention rate of the rare earth elements is more than 97%. The present invention may separate iron from a solution containing neodymium, praseodymium, dysprosium and iron efficiently, which solves the pollution problem of iron to the extraction agent during the purification of the rare earth solution, and enhances the purity and utility value of the rare earth elements in the solution; the present invention is applicable to treat a rare earth solution containing a high concentration of iron or an acid solution of wastes, in which the retention rate of the rare earth elements is high, and the residual concentration of iron in the solution is low, with a simple operation and a low cost.

Description

TECHNICAL FIELD

The present invention relates to the field of waste resource utilization, particularly relates to method of removing iron ions from a solution containing neodymium, praseodymium, dysprosium and iron.

BACKGROUND

Iron is a metal commonly found in neodymium-containing rare earth wastes, which is high in content, similar to the rare earths in terms of chemical valences, and difficult to be separated from the rare earths. It is the key to find a high-efficiency and stable iron separation method for recovering precious rare earth elements in rare earth wastes to obtain rare earth products in high-purity. Currently, in the reported iron separation methods from rare earth wastes, wet separation methods include hydrochloric acid optimal solution method, sulfuric acid double salt precipitation, full extraction, phosphate precipitation, sulfide precipitation and the like.
(1) The primary steps of hydrochloric acid optimal solution method include oxidizing roasting (making the rare earth elements and iron to be the highest valence) and separation for removing impurities (controlling the pH at 4-4.5, the rare earths in the roasting products are dissolved preferentially). However, the pH controlling step is complex, and iron oxides may be dissolved during the dissolution of the rare earths, such that the final solution may contain iron, which need to be further removed before extraction. Otherwise, the life of the extraction agent is inclined to be reduced during the extraction of the rare earth solution containing iron.
(2) The primary steps of sulfuric acid double salt precipitation are: roasting (as above), dissolution (sulfuric acid dissolution, generating a solution containing the rare earths and ferrous sulfate), double salt precipitation (adding sodium sulfate into the solution, generating a complex salt of sodium sulfate and neodymium sulfate). This method would generate ferrous sulfate when sulfuric acid is added for dissolution, Fe element would be wasted during the recovery of the rare earths, and it would contaminate the environment after the discharge of ferrous sulfate solution, making it hard to implement industrialization production.
(3) The primary steps of full extraction include: dissolving and leaching (adding hydrochloric acid to dissolve the wastes, and adding hydrogen peroxide to oxidize ferrous ions), extraction to remove iron (extracting iron into the organic phase with N₅₀₃extraction agent) and extraction and separation of the rare earths (separating the single rare earth element with P₅₀₇extraction agent). For iron-containing solution with high concentration, the consumption of the extraction agent N₅₀₃is high, with high loss and cost.
(4) In the phosphate precipitation that has been reported, the rare earth waste containing iron is first dissolved, into which a reductive agent is added to reduce ferric in the solution to ferrous, and then phosphate is added to generate a rare earth phosphate precipitate. The rare earth phosphate precipitate produced by this method is not only insoluble in acid, but also insoluble in alkali, thus it is difficult to be processed to products with high added value.
(5) The primary steps of sulfide precipitation include adding acid to dissolve the rare earth waste containing iron, then adding hydrogen peroxide or air aeration to oxidize ferrous, and then adding Na₂S to generate a rare earth sulfide precipitate. There also would be iron sulfide precipitate generated in the rare earth precipitate, making the controlling conditions on obtaining the rare earths with high purity complex and difficult to implement.
(6) The primary steps of hydroxide precipitation include dissolving and leaching, ferrous oxidation and pH regulation. The key step is to oxidize the ferrous in the acid leaching solution and to control the pH of the solution within a range of 4-4.5 strictly, thus removing 98% of iron in the supernatant. However, there is a drawback that there were a plenty of coordination sites on the surface of ferric hydroxide precipitate, which may absorb the rare earth ions in water, causing about 30%-50% of the rare earth ions co-precipitate with iron, thus decreasing the recovery rate of the rare earths.
(7) With regard to oxalic acid precipitation, its basic steps are the same as those in hydroxide precipitation, in which it also need to control pH value strictly to generate a complex of oxalic acid—the rare earths. However, iron needs to be removed in advance when it is present in a high concentration.
In the above various methods, when the rare earth wastes containing iron were recycled, the first step is to dissolve the wastes with an acid, generating a solution containing iron and rare earth elements, and then to recycle the rare earths with an extraction agent. The processes of separating different rare earth elements using extraction techniques were sufficiently mature, while the extraction efficiencies tend to be influenced by iron ions in the solution, causing the extraction agent to be poisoned after the combination of iron and the extraction agent, thus decreasing the extraction efficiency of the rare earths. Against the hazard of iron in the extraction, some special iron extraction agents have been developed, while they are expensive, and due to the high concentration of iron in the solution, the application amount of the extraction agent is high, and the loss is also high.
Therefore, the prior art needs to be further improved and developed.

SUMMARY

In view of disadvantages of the above prior art, the present invention aims to provide a method of removing iron ions from a solution containing neodymium, praseodymium, dysprosium and iron, without the need of controlling the pH range at the end of reactions, allowing a high retention rate of the rare earths, and decreasing the residual concentration of iron in the solution.
To dissolve the above technical problems, the schemes of the present invention include:
Method of removing iron ions from a solution containing neodymium, praseodymium, dysprosium and iron, including the following steps:
A. taking a solution containing neodymium, praseodymium, dysprosium and iron, with a pH value between 0.1-3.5;
B. adding glucose to the solution from step A, and mixed evenly;
C. heating the mixed solution obtained from step B to 60° C.-350° C., keeping the temperature constant for 5 minutes-72 hours;
D. after the solution from step C is cooled, a precipitate is formed at the bottom, and the concentration of iron in the supernatant is less than 20 mg/L, the retention rate of the rare earth elements is more than 97%.
The above described method, wherein, the solution from step A comprised, but not limited to, the solution generated after extraction of rare earth materials by an acid, wherein the acid refers to hydrochloric acid or nitric acid.
The above described method, wherein, the content of iron in the solution from step A is between 0.15 g/L-300 g/L.
The above described method, wherein, the content of iron in the solution from step A is between 4.2 g/L-300 g/L, in which ethylene glycol or ascorbic acid is employed instead of glucose.
The above described method, wherein, the additive amount of ethylene glycol is based on the molar ratio of iron/ethylene glycol at 0.5-3.8, after treatment with ethylene glycol, the residual concentration of iron in the supernatant is less than 500 mg/L.
The above described method, wherein, the additive amount of ascorbic acid is based on the molar ratio of iron/ascorbic acid at 0.1-1.5, after treatment with ascorbic acid, the residual concentration of iron in the supernatant is less than 800 mg/L.
The above described method, wherein, after collected, the supernatant is aerated with air for 10 minutes-2 hours, and then adjusted to pH 4 with ammonia water, generating an iron precipitate, while the rare earths also co-precipitating to generate a precipitate, the content of iron in the supernatant is less than 15 mg/L, and the retention rate of rare earth elements is between 30%-52%.
The above described method, wherein, after the above precipitate is dissolved with hydrochloric acid or nitric acid according to the solid-to-liquid ratio of 40%-70%, the concentration of iron in the solution is more than 1500 mg/L, then it is treated according to step B, step C and step D, successively.
The above described method, wherein, the above step B particularly further included: the additive amount of glucose is based on the molar ratio of iron/glucose at 0.2-2, the glucose is mixed with wastes containing neodymium, praseodymium, dysprosium and iron, into which then an acid is added, and finally the glucose is heat treated according to step C.
The above described method, wherein, the heating in the above step C employs a programmed heating, the heating conditions are confined as follows: when the temperature is between 60° C.-120° C., the duration of heating is not less than 10 hours; when the temperature is between 300° C.-350° C., the duration of heating may less than 30 minutes.
The present invention provides a method of removing iron ions from a solution containing neodymium, praseodymium, dysprosium and iron, in which glucose is added in the solution containing iron and rare earths, and the solution is heat treated to generate a precipitate, thus removing iron from the solution efficiently. Compared with other methods for separating iron, the present invention may control the generation of precipitates without the need of regulating the pH, and there is no significant effect for the resulting precipitate on the concentration of rare earth elements in the solution; the method of removing iron by adding ethylene glycol or ascorbic acid instead of glucose, proposed in the present invention, may also remove iron from the rare earth solution efficiently, while the residual concentration of iron in the supernatant is higher than that in the method in which glucose is added; and after removing iron by adding ethylene glycol or ascorbic acid, there remains a portion of iron in the supernatant, which may be oxidized, and further the pH may be adjusted with ammonia water, thus removing iron by converting it into ferric hydroxide precipitate; the generated precipitate contains a large amount of iron and a few rare earth elements, after dissolution with an acid, a high concentration of iron in the dissolved solution could be removed by the method proposed in the present invention, to obtain a rare earth solution with a high purity; that is, iron could be separated from a solution containing neodymium, praseodymium, dysprosium and iron efficiently, which solves the pollution problem of iron to the extraction agent during the purification of the rare earth solution, and enhances the purity and utility value of the rare earth elements in the solution, the retention rate of the rare earths is high, and the residual concentration of iron in the solution is low, with a simple operation and a low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the concentration of iron in the solution after the addition of glucose, ethylene glycol and ascorbic acid according to the present invention;

FIG. 2 is the concentration of neodymium in the solution after the addition of glucose, ethylene glycol and ascorbic acid according to the present invention;

FIG. 3 is the concentration of praseodymium in the solution after the addition of glucose, ethylene glycol and ascorbic acid according to the present invention;

FIG. 4 is the concentration of dysprosium in the solution after the addition of glucose, ethylene glycol and ascorbic acid according to the present invention;

FIG. 5 is the scanning electron microscope photograph of the precipitate produced according to the present invention.

DETAILED DESCRIPTION

The present invention provides a method of removing iron ions from a solution containing neodymium, praseodymium, dysprosium and iron. In order to make the objectives, technical solutions and effects of the present invention clearer and definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.
The present invention provides a method of removing iron ions from a solution containing neodymium, praseodymium, dysprosium and iron, including the following steps:
A. taking a solution containing neodymium, praseodymium, dysprosium and iron, with a pH value between 0.1-3.5.
It is found during the experiment that when pH was less than 0.1, iron precipitates could not occur after the hydrothermal reaction, and thus iron and the rare earths could not be separated.
When pH was greater than 3.5, ferric ions were precipitated in the form of ferric hydroxide in the hydrothermal reaction, thus causing two drawbacks: (1) the rare earth elements in water were absorbed on the surface of the new precipitated ferric hydroxide colloid; (2) the new generated ferric hydroxide colloid would enwrap the rare earth elements in the solution during the condensation phase. Being affected by these two drawbacks, the rare earth elements in the solution would return into the ferric hydroxide precipitate, thus significantly decreasing the separation efficiency.
Therefore, the pH of the solution containing neodymium, praseodymium, dysprosium and iron in the present invention is controlled between 0.1-3.5.
B. glucose is added to the solution from step A, and mixed evenly;
Glucose is added to further promote the ferric ions in the solution to precipitate, thus enhancing the separation efficiency of iron from the solution. Specifically, glucose is used as the reductive agent to reduce ferric iron on the surface of crystalline hematite to ferrous iron, in which ferrous iron may be bound with ferrous iron in the solution when being oxidized with nitrate, forming a Fe—O—Fe bond, thus making the hematite crystals grow and decreasing the concentration of iron ions in the solution.
C. the mixed solution obtained from step B is heated to 60° C.-350° C., keeping the temperature constant for 5 minutes-72 hours;
When the temperature increased, the hematite crystal nucleus is generated from the ferric iron in the solution under the complexation of nitrates, which crystallize and grow.
D. after the solution from step C is cooled, a precipitate is formed at the bottom, and the concentration of iron in the supernatant is less than 20 mg/L, the retention rate of the rare earth elements is more than 97%.
Further, the solution from step A comprised, but not limited to, the solution generated after extracting the rare earth materials by an acid, wherein the acid refers to hydrochloric acid or nitric acid. And, the content of iron in the solution from step A is between 0.15 g/L-300 g/L.
Alternatively, the content of iron in the solution from step A is between 4.2 g/L-300 g/L, in which ethylene glycol or ascorbic acid is employed instead of glucose. The additive amount of ethylene glycol is based on the molar ratio of iron/ethylene glycol at 0.5-3.8, after treatment with ethylene glycol, the residual concentration of iron in the supernatant is less than 500 mg/L. The additive amount of ascorbic acid is based on the molar ratio of iron/ascorbic acid at 0.1-1.5, after treatment with ascorbic acid, the residual concentration of iron in the supernatant is less than 800 mg/L. After the supernatant is collected, it is aerated with air for 10 minutes-2 hours, and then adjusted to pH 4 with ammonia water, making iron to precipitate, while the rare earths also co-precipitating to generate a precipitate, the content of iron in the supernatant is less than 15 mg/L, and the retention rate of rare earth elements is between 30%-52%.
In particular, after the above precipitate is dissolved with hydrochloric acid or nitric acid according to the solid-to-liquid ratio of 40%-70%, the concentration of iron in the solution is more than 1500 mg/L, then it is treated according to step B, step C and step D, successively.
Moreover, the above step B particularly further included: the additive amount of glucose is based on the molar ratio of iron/glucose at 0.2-2, the glucose is mixed with a solution containing neodymium, praseodymium, dysprosium and iron, into which then an acid is added, and finally the glucose is heat treated according to step C. The heating in the above step C employs a programmed heating, the heating conditions are confined as follows: when the temperature is between 60° C.-120° C., the duration of heating is not less than 10 hours; when the temperature is between 300° C.-350° C., the duration of heating may less than 30 minutes.
In order to further describe the present invention, more detailed embodiments will be listed below for illustration.
Step 1. Dissolution of Neodymium-Iron Waste
5 kg of neodymium-iron waste was taken, and 50 L concentrated nitric acid was added at a weight-bulk ratio of 10%, and a solution containing neodymium, praseodymium, dysprosium and iron was obtained after the waste was dissolved. Wherein, the pH value of the solution was 0.65, the concentration of iron in the solution was 87760 mg/L, and the concentrations of neodymium, praseodymium and dysprosium were 1882 mg/L, 347 mg/L and 111.3 mg/L, respectively, as shown in FIGS. 1, 2, 3, and 4.
Step 2. Addition of Glucose
Based on the molar ratio of iron/glucose at 1, 15.6 kg glucose was added with stirring at 220 rpm for 1 hour.
Step 3. Heat Treatment
The solution of step 2 was transferred into a reactor, the filling degree of which was 50%, and which was heated in a closed state for 10 hours at the heating temperature of 160° C. After completion of heating, the reactor was cooled to room temperature spontaneously. After the reactor was opened, it was found that the precipitate was separated well from the solution and there was a light yellow precipitate forming at the bottom. The morphology of the dry precipitate was shown in FIG. 5, being spherical particles with sizes of about 50 nm.
Step 4. Collection of the Supernatant
The top supernatant was pumped out of the reactor; the precipitate at the bottom was mixed with water, filtered over a 0.45 μm filter membrane, the filtrate was collected and mixed with the supernatant. The pH of the mixture was 1.01, the concentration of iron in the mixture was 17.2 mg/L (FIG. 1), and the concentrations of neodymium, praseodymium and dysprosium were 1878 mg/L, 334 mg/L and 110.2 mg/L, respectively (FIG. 2, FIG. 3 and FIG. 4).
Step 5. Using Ethylene Glycol Instead of Glucose
Ethylene glycol was used instead of glucose, the additive amount of which was based on the molar ratio of iron/ethylene glycol at 1.2, after treatment according to the methods of step 2 and step 3, the aqueous solution was collected. The concentration of iron in the aqueous phase was determined as 438 mg/L (FIG. 1), and the concentrations of neodymium, praseodymium and dysprosium were 1851 mg/L, 337 mg/L and 108.2 mg/L, respectively (FIG. 2, FIG. 3 and FIG. 4).
Step 6. Using Ascorbic Acid Instead of Glucose
Ascorbic acid was used to replace glucose, the additive amount of which was based on the molar ratio of iron/ascorbic acid at 1, after treatment according to the methods of step 2 and step 3, the aqueous solution was collected. The concentration of iron in the aqueous phase was detected as 842 mg/L (FIG. 1), and the concentrations of neodymium, praseodymium and dysprosium were 1812 mg/L, 326 mg/L and 106.9 mg/L, respectively (FIG. 2, FIG. 3 and FIG. 4).
Step 7. Cyclic Iron Removal and Purification of the Rare Earth Solution
The aqueous solution resulted from step 5 or step 6 was aerated with air for 10 min at an aeration intensity of 1 L/min Ammonia water was then added to adjust the pH to 4, generating a precipitate of ferric hydroxide. The precipitate was collected, into which concentrated nitric acid was added at a volume ratio of precipitate/nitric acid at 0.5, stirred at a stirring rate of 220 rpm for 1 h, and the precipitate was dissolved, the concentration of iron in the resulting solution was 7425 mg/L, the concentrations of neodymium, praseodymium and dysprosium were 215 mg/L, 56.6 mg/L and 25.5 mg/L, respectively. Then, ethylene glycol or ascorbic acid was used for treatment according to step 6 or step 7, the concentrations of iron in the supernatants were 414 mg/L and 895 mg/L, respectively, and the concentrations of the rare earth elements such as neodymium, praseodymium and dysprosium remain unchanged basically.
Of course, the above description was only the preferred embodiments of the present invention, which were not limited to the above embodiments. It should be noted that all the equivalent substitutions, obvious deformation forms made by any person skilled in the art under the teachings of the present specification all fall within the essential scope of the specification and should be protected by the present invention.

Claims

1. Method of removing iron ions from a solution containing neodymium, praseodymium, dysprosium and iron, which is characterized in that, including the following steps:

A. taking a solution containing neodymium, praseodymium, dysprosium and iron, with a pH value between 0.1-3.5;

B. adding glucose to the solution from step A, and mixed evenly;

C. heating the mixed solution obtained from step B to 60° C.-350° C., keeping the temperature constant for 5 minutes-72 hours;

D. after the solution from step C is cooled, a precipitate is formed at the bottom, and the concentration of iron in the supernatant is less than 20 mg/L, the retention rate of the rare earth elements is more than 97%.

2. The method according to claim 1, which is characterized in that, the solution from step A comprised, but not limited to, the solution generated after extracting the rare earth materials by an acid, wherein the acid refers to hydrochloric acid or nitric acid.

3. The method according to claim 1, which is characterized in that, the content of iron in the solution from step A is between 0.15 g/L-300 g/L.

4. The method according to claim 1, which is characterized in that, the content of iron in the solution from step A is between 4.2 g/L-300 g/L, in which ethylene glycol or ascorbic acid is employed instead of glucose.

5. The method according to claim 4, which is characterized in that, the additive amount of ethylene glycol is based on the molar ratio of iron/ethylene glycol at 0.5-3.8, after treatment with ethylene glycol, the residual concentration of iron in the supernatant is less than 500 mg/L.

6. The method according to claim 4, which is characterized in that, the additive amount of ascorbic acid is based on the molar ratio of iron/ascorbic acid at 0.1-1.5, after treatment with ascorbic acid, the residual concentration of iron in the supernatant is less than 800 mg/L.

7. The method according to claim 5, which is characterized in that, after collected, the supernatant is aerated with air for 10 minutes-2 hours, and then adjusted to pH 4 with ammonia water, making iron to precipitate, while the rare earths also co-precipitating to generate a precipitate, the content of iron in the supernatant is less than 15 mg/L, and the retention rate of rare earth elements is between 30%-52%.

8. The method according to claim 7, which is characterized in that, after the above precipitate is dissolved with hydrochloric acid or nitric acid according to the solid-to-liquid ratio of 40%-70%, the concentration of iron in the solution is more than 1500 mg/L, then it is treated according to step B, step C and step D, successively.

9. The method according to claim 1, which is characterized in that, the above step B particularly further included: the additive amount of glucose is based on the molar ratio of iron/glucose at 0.2-2, the glucose is mixed with wastes containing neodymium, praseodymium, dysprosium and iron, into which then an acid is added, and finally the glucose is heat treated according to step C.

10. The method according to claim 1, which is characterized in that, the heating in the above step C employs a programmed heating, the heating conditions are confined as follows: when the temperature is between 60° C.-120° C., the duration of heating is not less than 10 hours; when the temperature is between 300° C.-350° C., the duration of heating may less than 30 minutes.