A method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer

Abstract

The present invention discloses a method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer. The method comprises pretreatment, roasting and activation, composite leaching, multi-stage extraction, stripping and activation, and slow-release fertilizer preparation. In the pretreatment stage, the phosphate ore is subjected to reverse flotation to remove gangue to improve the rare earth grade. In the roasting and activation stage, organic matter and fluorine in the phosphate ore are removed by staged roasting to activate the rare earths. In the composite leaching stage, the phosphate ore is decomposed by a mixed acid + microbial method to maximize the leaching of rare earths and increase the rare earth content in the leachate. In the extraction stage, ionic liquid is used to perform multi-stage extraction of the rare earths to improve the purity of the rare earth product. Finally, the slow-release fertilizer is prepared using the phosphate tailings, acid leaching residue, and insoluble potash ore powder as raw materials, forming a green, economical, and efficient integrated phosphate ore utilization process.

Description

Technical Field

[0001] The present invention relates to the field of rare earth recovery, and in particular to a method for recovering rare earth from rare earth-containing phosphate ore and co-producing slow-release fertilizer. Background Art

[0002] Rare earths are known as "industrial vitamins" and have excellent physical and chemical properties. They are widely used in high-tech fields such as new energy, electronic information, national defense and military industry, aerospace, etc. According to statistics, the global rare earth supply and demand gap is greater than 10% each year and is still increasing year by year.

[0003] In recent years, my country has implemented a series of policies restricting the mining and export of rare earth elements. However, facing growing downstream demand, it is imperative to enrich upstream sources by strengthening the utilization of associated resources. my country's phosphate rock has a low average grade and is primarily used to produce low-value-added slow-release fertilizers and phosphorus chemical products. However, the rare earth elements associated with phosphate rock are not effectively utilized, resulting in a waste of resources and a serious threat to environmental safety.

[0004] The extraction of rare earth elements associated with phosphate rock is usually done by acid leaching followed by extraction, which can be divided into the following categories: (1) leaching phosphate rock with sulfuric acid, with some rare earth elements entering the liquid phase. This method consumes a lot of acid, and rare earth elements are dissolved with iron and aluminum ions, resulting in a high impurity content in the rare earth product; (2) high-temperature roasting to activate phosphate rock, followed by selective complexation of rare earth elements with organic acids such as citric acid and oxalic acid. This method can improve the purity of rare earth products, but the rare earth leaching rate fluctuates greatly, and the cost of organic acids is high; (3) using microorganisms to decompose phosphate rock to release rare earth elements. This method takes a long time to decompose, and the strains have poor environmental tolerance. Therefore, it is urgent to develop an economical, efficient, and stable full-chain process flow of phosphate rock leaching-rare earth extraction-phosphorus resource recovery to achieve efficient utilization of phosphorus and rare earth resources in phosphate rock. Summary of the Invention

[0005] In response to the current problems of poor economic efficiency, low extraction efficiency, and low product purity of rare earths associated with phosphate rock, the present invention provides a method for recovering rare earths from rare earth-containing phosphate rock and co-producing slow-release phosphate fertilizer. The method specifically comprises pretreatment, roasting and activation, composite leaching, multi-stage extraction, stripping and activation, and slow-release fertilizer preparation. In the pretreatment stage, the phosphate rock is subjected to reverse flotation to remove gangue to improve the rare earth grade. In the roasting and activation stage, organic matter and fluorine elements in the phosphate rock are removed by staged roasting to activate the rare earth. In the composite leaching stage, the phosphate rock is decomposed by a mixed acid + microbial method to maximize the leaching of rare earths and increase the rare earth content in the leachate. In the multi-stage extraction stage, composite ionic liquid is used to perform multi-stage extraction of rare earths to improve the purity of the rare earth product. Finally, the slow-release fertilizer is prepared using phosphate tailings, acid leaching residue, and insoluble potassium ore powder as raw materials, forming a green, economical, and efficient integrated phosphate rock utilization process.

[0006] The present invention provides a method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer, comprising the following steps:

[0007] S1. Pretreatment: Add phosphate rock, water, and sodium hexametaphosphate into a ball mill and grind to 200-250 mesh. Then pour the slurry into a flotation machine and adjust the pH of the slurry to 5-6 with sulfuric acid. Then add inhibitors, flotation agents, and frothers for reverse flotation. Filter and dry the slurry in the tank and the foamed slurry separately to obtain phosphate concentrate and phosphate tailings.

[0008] S2. Calcination and activation: Add 5% by mass of sodium carbonate to the phosphate concentrate obtained in S1, calcine at 500°C for 1 hour, and then calcine at 1100°C for 2 hours to obtain activated phosphate concentrate.

[0009] S3. Composite leaching: Add a mixed acid consisting of sulfuric acid and an organic acid to the activated phosphate concentrate obtained in S2 at a liquid-to-solid ratio of (8-10):1. At the same time, inoculate the leaching system with Acidithiobacillus ferrooxidans at a ratio of 10%-20%. Control the leaching temperature at 30°C, the dissolved oxygen concentration in the system at 2.5-3.5 mg / L, and the leaching time for 6 hours. Then, perform solid-liquid separation to obtain a leachate and acid leaching residue.

[0010] S4. Multi-stage extraction: The leachate obtained in S3 is subjected to three-stage countercurrent extraction using [TBA]⁺[P507]⁻ extractant to obtain an extract.

[0011] S5. Stripping and purification: Stripping the extract obtained in S4 with 4-5 mol / L hydrochloric acid, followed by adding a precipitant to precipitate the rare earth, and obtaining rare earth oxides by calcination.

[0012] S6. Preparation of slow-release fertilizer: The phosphate tailings obtained in S1, the acid leaching residue obtained in S3, and the insoluble potassium ore powder were mixed with bentonite, calcined at 850° C. for 1 hour, and then granulated to obtain a slow-release fertilizer.

[0013] Preferably, in step S1, the inhibitor is sulfuric acid, the collector is dodecylamine, and the foaming agent is methyl isobutyl carbinol.

[0014] Preferably, in step S3, the concentration of sulfuric acid is 1.5-2 mol / L, the organic acid is citric acid or oxalic acid, and the organic acid concentration is 1 mol / L.

[0015] Preferably, the [TBA]⁺[P507]⁻ extractant in step S4 is prepared by the following method:

[0016] Step 1. React methyltributylammonium chloride with sodium hydroxide to prepare [TBA]⁺OH⁻;

[0017] Step 2. [TBA]⁺OH⁻ and P507 were reacted at a molar ratio of 1:1 at 60°C for 3 h to prepare [TBA]⁺[P507]⁻ ionic liquid;

[0018] Step 3. Add 30-40% n-dodecane to the [TBA]⁺[P507]⁻ ionic liquid and mix well to prepare the [TBA]⁺[P507]⁻ extractant.

[0019] Preferably, in the three-stage countercurrent extraction process in step S4, the ratio O / A=1.5 and the single-stage residence time is 5 min.

[0020] Preferably, in step S5, ascorbic acid is added to the hydrochloric acid in a mass ratio of 0.1% to 0.3%.

[0021] Preferably, the precipitant in step S5 is oxalic acid.

[0022] Preferably, the precipitation of rare earth in step S5 is divided into two stages: after adding oxalic acid, the pH is adjusted to 1.5-2.0 to precipitate light rare earth, and the pH is adjusted to 3.5-4.5 to precipitate heavy rare earth.

[0023] Preferably, the calcination temperature in step S5 is 900±20°C.

[0024] Preferably, the insoluble potassium ore powder in step S6 is one or more of potassium feldspar powder and mica powder.

[0025] In the present invention, reverse flotation is performed on phosphate rock in a pretreatment stage to remove gangue ore and improve the rare earth grade; in the roasting and activation stage, staged roasting is performed to remove organic matter and fluorine element in the phosphate rock to activate the rare earth; in the composite leaching stage, a mixed acid + microbial method is used to jointly decompose the phosphate rock to leach rare earth to the maximum extent, thereby increasing the rare earth content in the leachate; in the extraction stage, ionic liquid is used to perform multi-stage extraction on the rare earth to improve the purity of the rare earth product; finally, the phosphate tailings, acid leaching residue and insoluble potassium ore powder are used as raw materials to prepare a slow-release fertilizer, thereby forming a green, economical and efficient integrated phosphate rock utilization process. DETAILED DESCRIPTION

[0026] The technical scheme of the present invention will be clearly and completely described below in conjunction with specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0027] <Example 1>

[0028] A method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer comprises the following steps:

[0029] S1. Pretreatment: Add phosphate rock, water, and sodium hexametaphosphate to a ball mill and grind to 200 mesh. Then pour the slurry into a flotation machine, adjust the slurry pH to 5 with sulfuric acid, and then add sulfuric acid, dodecylamine, and methyl isobutyl carbinol for reverse flotation. Filter and dry the slurry in the tank and the foam slurry separately to obtain phosphate concentrate and phosphate tailings.

[0030] S2. Calcination and activation: Add 5% by mass of sodium carbonate to the phosphate concentrate obtained in S1, calcine at 500°C for 1 hour, and then calcine at 1100°C for 2 hours to obtain activated phosphate concentrate.

[0031] S3. Composite leaching: A mixed acid consisting of 1.5 mol / L sulfuric acid and 1 mol / L oxalic acid was added to the activated phosphate concentrate obtained in S2, the volume ratio of sulfuric acid to oxalic acid was 3:1, and the liquid-solid ratio of the mixed acid to the phosphate concentrate was 10:1. At the same time, Acidithiobacillus ferrooxidans was inoculated in the leaching system at a ratio of 20%. The leaching temperature was controlled at 30°C, the dissolved oxygen concentration in the system was 3 mg / L, the leaching time was 6 h, and then solid-liquid separation was performed to obtain a leachate and acid leaching residue.

[0032] S4. Multi-stage extraction: The leachate obtained in S3 was subjected to three-stage countercurrent extraction using [TBA]⁺[P507]⁻ extractant, with an O / A ratio of 1.5 and a single-stage residence time of 5 minutes to obtain an extract. [TBA]⁺[P507]⁻ extractant was prepared by the following method:

[0033] Step 1. React methyltributylammonium chloride with sodium hydroxide to prepare [TBA]⁺OH⁻;

[0034] Step 2. [TBA]⁺OH⁻ and P507 were reacted at a molar ratio of 1:1 at 60°C for 3 h to prepare [TBA]⁺[P507]⁻ ionic liquid;

[0035] Step 3. Add 30% n-dodecane to the [TBA]⁺[P507]⁻ ionic liquid and mix well to prepare the [TBA]⁺[P507]⁻ extractant.

[0036] S5. Stripping and purification: The extract obtained in S4 was stripped with 4 mol / L hydrochloric acid. 0.3% by mass of ascorbic acid was added to the hydrochloric acid. Subsequently, oxalic acid was added to precipitate the rare earths. Light rare earths were precipitated at pH 1.5. Heavy rare earths were precipitated at pH 3.5. Rare earth oxides were then calcined at 900°C.

[0037] S6. Preparation of slow-release fertilizer: The phosphate tailings obtained in S1, the acid leaching residue obtained in S3, and potassium feldspar powder were mixed with bentonite, calcined at 850° C. for 1 h, and then granulated to obtain a slow-release fertilizer.

[0038] <Example 2>

[0039] A method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer comprises the following steps:

[0040] S1. Pretreatment: Add phosphate rock, water, and sodium hexametaphosphate to a ball mill and grind to 200 mesh. Then pour the slurry into a flotation machine, adjust the slurry pH to 5 with sulfuric acid, and then add sulfuric acid, dodecylamine, and methyl isobutyl carbinol for reverse flotation. Filter and dry the slurry in the tank and the foam slurry separately to obtain phosphate concentrate and phosphate tailings.

[0041] S2. Calcination and activation: Add 5% by mass of sodium carbonate to the phosphate concentrate obtained in S1, calcine at 500°C for 1 hour, and then calcine at 1100°C for 2 hours to obtain activated phosphate concentrate.

[0042] S3. Composite leaching: A mixed acid consisting of 2 mol / L sulfuric acid and 1 mol / L oxalic acid was added to the activated phosphate concentrate obtained in S2, the volume ratio of sulfuric acid to citric acid was 3:1, and the liquid-solid ratio of the mixed acid to the phosphate concentrate was 10:1. At the same time, Acidithiobacillus ferrooxidans was inoculated at a ratio of 10% in the leaching system. The leaching temperature was controlled at 30°C, the dissolved oxygen concentration in the system was 3 mg / L, the leaching time was 6 h, and then solid-liquid separation was performed to obtain a leachate and acid leaching residue.

[0043] S4. Multi-stage extraction: The leachate obtained in S3 was subjected to three-stage countercurrent extraction using [TBA]⁺[P507]⁻ extractant, with an O / A ratio of 1.5 and a single-stage residence time of 5 minutes to obtain an extract. [TBA]⁺[P507]⁻ extractant was prepared by the following method:

[0044] Step 1. React methyltributylammonium chloride with sodium hydroxide to prepare [TBA]⁺OH⁻;

[0045] Step 2. [TBA]⁺OH⁻ and P507 were reacted at a molar ratio of 1:1 at 60°C for 3 h to prepare [TBA]⁺[P507]⁻ ionic liquid;

[0046] Step 3. Add 30% n-dodecane to the [TBA]⁺[P507]⁻ ionic liquid and mix well to prepare the [TBA]⁺[P507]⁻ extractant.

[0047] S5. Stripping and purification: The extract obtained in S4 was stripped with 4 mol / L hydrochloric acid. 0.1% by mass of ascorbic acid was added to the hydrochloric acid. Oxalic acid was then added to precipitate the rare earths. Light rare earths were precipitated at pH 2. Heavy rare earths were precipitated at pH 4.5. Rare earth oxides were then calcined at 900°C.

[0048] S6. Preparation of slow-release fertilizer: The phosphate tailings obtained in S1, the acid leaching residue obtained in S3, mica powder and bentonite were mixed, calcined at 850° C. for 1 hour, and then granulated to obtain a slow-release fertilizer.

[0049] <Example 3>

[0050] A method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer comprises the following steps:

[0051] S1. Pretreatment: Add phosphate rock, water, and sodium hexametaphosphate to a ball mill and grind to 250 mesh. Then pour the slurry into a flotation machine, adjust the slurry pH to 6 with sulfuric acid, and then add sulfuric acid, dodecylamine, and methyl isobutyl carbinol for reverse flotation. Filter and dry the slurry in the tank and the foam slurry separately to obtain phosphate concentrate and phosphate tailings.

[0052] S2. Calcination and activation: Add 5% by mass of sodium carbonate to the phosphate concentrate obtained in S1, calcine at 500°C for 1 hour, and then calcine at 1100°C for 2 hours to obtain activated phosphate concentrate.

[0053] S3. Composite leaching: A mixed acid consisting of 1.5 mol / L sulfuric acid and 1 mol / L citric acid was added to the activated phosphate concentrate obtained in S2, the volume ratio of sulfuric acid to citric acid was 4:1, and the liquid-solid ratio of the mixed acid to the phosphate concentrate was 8:1. At the same time, Acidithiobacillus ferrooxidans was inoculated in the leaching system at a ratio of 20%. The leaching temperature was controlled at 30°C, the dissolved oxygen concentration in the system was 3.5 mg / L, the leaching time was 6 h, and then solid-liquid separation was performed to obtain a leachate and acid leaching residue.

[0054] S4. Multi-stage extraction: The leachate obtained in S3 was subjected to three-stage countercurrent extraction using [TBA]⁺[P507]⁻ extractant, with an O / A ratio of 1.5 and a single-stage residence time of 5 minutes to obtain an extract. [TBA]⁺[P507]⁻ extractant was prepared by the following method:

[0055] Step 1. React methyltributylammonium chloride with sodium hydroxide to prepare [TBA]⁺OH⁻;

[0056] Step 2. [TBA]⁺OH⁻ and P507 were reacted at a molar ratio of 1:1 at 60°C for 3 h to prepare [TBA]⁺[P507]⁻ ionic liquid;

[0057] Step 3. Add 30% n-dodecane to the [TBA]⁺[P507]⁻ ionic liquid and mix well to prepare the [TBA]⁺[P507]⁻ extractant.

[0058] S5. Stripping and purification: The extract obtained in S4 was stripped with 5 mol / L hydrochloric acid. 0.2% by mass of ascorbic acid was added to the hydrochloric acid. Oxalic acid was then added to precipitate the rare earths. Light rare earths were precipitated at pH 1.5. Heavy rare earths were precipitated at pH 3.5. Rare earth oxides were then calcined at 900°C.

[0059] S6. Preparation of slow-release fertilizer: The phosphate tailings obtained in S1, the acid leaching residue obtained in S3, mica powder and bentonite were mixed, calcined at 850° C. for 1 hour, and then granulated to obtain a slow-release fertilizer.

[0060] <Experimental Example 1>

[0061] Using Examples 1-3, rare earth recovery and co-production of slow-release fertilizer were carried out on the Fangmashan phosphate rock in Jingmen, Hubei Province. The P2O5 grade in the phosphate rock sample was 20.17%, and the rare earth grade was 0.21%. The contents of RE2O3, CaO, Al2O3, and Fe2O3 in the rare earth oxide sample were measured respectively.

[0062] Table 1 Rare earth oxide product quality

[0063]

[0064] It can be seen from the above table that the RE2O3 content in the rare earth oxides prepared by this technical method is 59.35%-62.31%, and the purity is relatively high.

[0065] <Experimental Example 2>

[0066] The slow-release fertilizer prepared in Experimental Example 1 was used as a raw material to measure its yield-increasing effect on wheat. The test site was selected in a wheat-growing area in Xiping, Henan Province. The basic physical and chemical properties of the soil were pH 7.45, organic matter content 1.71%, alkaline nitrogen 100.16 mg / kg, available phosphorus 61.08 mg / kg, and available potassium 127.66 mg / kg. The experiment adopted a randomized block design with an area of ​​1 mu. The wheat variety was "Zhengmai 158". This experiment had a total of 4 treatments, each with 3 replicates, namely, Examples 1-3. The comparative example was a farmer's customary fertilization of 24-10-10, with a total fertilizer application rate of 50 kg / mu. Except for the different types of fertilizers, other field measures such as sowing, irrigation, and weeding were all consistent. Wheat yield was measured during the wheat maturity period.

[0067] Table 2 Wheat yield under different treatments

[0068]

[0069] It can be seen from the above table that after applying the slow-release fertilizer produced by this technology, the number of wheat ears per mu, the number of grains per ear, the thousand-grain weight and the yield are all increased.

[0070] The above implementation cases are only for illustrating the technical solutions and features of the present invention, and their purpose is to enable people familiar with the technology to implement them better. They cannot be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention are within the scope of protection of the present invention. The ones not described in detail are prior art.

Claims

1. A method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer, characterized in that: The following steps are involved: S1. Pretreatment: Add phosphate rock, water, and sodium hexametaphosphate into a ball mill and grind to 200-250 mesh. Then pour the slurry into a flotation machine, adjust the pH of the slurry to 5-6 with sulfuric acid, then add an inhibitor, a flotation agent, and a frother for reverse flotation. Filter and dry the slurry in the tank and the foam slurry separately to obtain phosphate concentrate and phosphate tailings. S2, roasting activation: adding 5% by mass of sodium carbonate to the phosphate concentrate obtained in S1, calcining at 500°C for 1 hour, and then calcining at 1100°C for 2 hours to obtain activated phosphate concentrate; S3, composite leaching: adding a mixed acid consisting of sulfuric acid and an organic acid to the activated phosphate concentrate obtained in S2 at a liquid-to-solid ratio of (8-10):1, and simultaneously inoculating the leaching system with Acidithiobacillus ferrooxidans at a ratio of 10%-20%, controlling the leaching temperature at 30°C, the dissolved oxygen concentration in the system at 2.5-3.5 mg / L, the leaching time for 6 hours, and then performing solid-liquid separation to obtain a leachate and acid leaching residue; S4, multi-stage extraction: using [TBA]⁺[P507]⁻ extractant to perform three-stage countercurrent extraction on the leachate obtained in S3 to obtain an extract; S5, stripping and purification: stripping the extract obtained in S4 with 4-5 mol / L hydrochloric acid, then adding a precipitant to precipitate the rare earth, and obtaining rare earth oxides by calcination; S6. Preparation of slow-release fertilizer: The phosphate tailings obtained in S1, the acid leaching residue obtained in S3, the insoluble potassium ore powder and bentonite are mixed, calcined at 850° C. for 1 hour, and then granulated to obtain a slow-release fertilizer.

2. The method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer according to claim 1, characterized in that: In step S1, the inhibitor is sulfuric acid, the collector is dodecylamine, and the foaming agent is methyl isobutyl carbinol.

3. The method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer according to claim 1, characterized in that: In step S3, the concentration of sulfuric acid is 1.5-2 mol / L, the organic acid is citric acid or oxalic acid, and the organic acid concentration is 1 mol / L.

4. The method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer according to claim 1, characterized in that: In step S4, the [TBA]⁺[P507]⁻ extractant is prepared by the following method: T1. React methyltributylammonium chloride with sodium hydroxide to prepare [TBA]⁺OH⁻; T2, reacting [TBA]⁺OH⁻ with P507 in a molar ratio of 1:1 at 60°C for 3 h to prepare [TBA]⁺[P507]⁻ ionic liquid; T3. Add 30-40% n-dodecane to the [TBA]⁺[P507]⁻ ionic liquid and mix well to prepare the [TBA]⁺[P507]⁻ extractant.

5. The method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer according to claim 1, characterized in that: During the three-stage countercurrent extraction in step S4, the O / A ratio was 1.5 and the single-stage residence time was 5 min.

6. The method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer according to claim 1, characterized in that: In step S5, ascorbic acid is added to the hydrochloric acid in a mass ratio of 0.1% to 0.3%.

7. The method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer according to claim 1, characterized in that: In step S5, the precipitant is oxalic acid.

8. The method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer according to claim 1, characterized in that: The precipitation of rare earth in step S5 is divided into two stages: after adding oxalic acid, the pH is adjusted to 1.5-2.0 to precipitate light rare earth, and the pH is adjusted to 3.5-4.5 to precipitate heavy rare earth.

9. The method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer according to claim 1, characterized in that: The calcination temperature in step S5 is 900±20°C.

10. The method for recovering rare earths from rare earth-containing phosphate ore and co-producing slow-release fertilizer according to claim 1, characterized in that: In step S6, the insoluble potassium ore powder is one or more of potassium feldspar powder and mica powder.

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