A method for multi - level classification and recycling of rare earth elements

Abstract

The present invention provides a method for multi-stage classification and recovery of rare earth elements, which mainly uses humic acid, iron (hydr)oxide and inorganic phosphate to conduct multi-stage classification and recovery of a solution containing all partitioned rare earth elements, and solutions relatively rich in light rare earths, medium rare earths and heavy rare earths can be obtained respectively. The present invention can effectively separate and purify all partitioned rare earth ions into solutions rich in light rare earths, rich in medium rare earths and rich in heavy rare earths.

Description

Technical Field

[0001] The present invention relates to the separation and purification of rare earth elements in the ionic rare earth smelting process, and belongs to the technical field of rare earth ion separation and recovery. Background Art

[0002] Most of the existing extraction and separation technologies are ion exchange resins and solvent extraction methods, and the industrial method mostly adopts solvent extraction method: multi-stage extraction with different organic solvents (such as amines, esters, ethers, organophosphides, etc.). Generally speaking, these extractants have problems such as flammability, toxicity, high price, and easy environmental pollution. Therefore, aiming at the problem of effectively separating light rare earths, medium rare earths, and heavy rare earths, developing a cheap and pollution-free process method for enriching and separating these three types of rare earths is very important for improving the recovery rate of rare earth ions and simplifying the rare earth extraction process. Summary of the Invention

[0003] The purpose of the present invention is to solve the defects existing in the above-mentioned prior art, and provide a method for multi-stage classification and recovery of rare earth elements. Only cheap, environmentally friendly, pollution-free and recyclable humic acid, iron (hydro) oxide and inorganic phosphate are used to classify and recover all partitioned rare earth elements (15 kinds) in the solution, and solutions relatively rich in light rare earths, medium rare earths, and heavy rare earths can be obtained respectively.

[0004] The present invention can realize the classification and recovery in the mining and metallurgy process, or the specific and efficient recovery of trace elements in natural water bodies.

[0005] The present invention adopts the following technical solutions:

[0006] A method for multi-stage classification and recovery of rare earth elements, comprising:

[0007] Step (1). In the medium rare earth separation pool, iron oxide I is put in, and its mass concentration is 0.1 - 5 g / L. Then inorganic phosphate with a concentration of 20 - 100 μmol / L is added, and a certain amount of inorganic acid is used to adjust the pH of the suspension to 4 - 6. Stir for more than 8 hours. After the iron oxide I and phosphate react fully, the all-partitioned rare earth leaching solution is introduced into the medium rare earth separation pool, and stirred for more than 24 hours. Solid-liquid separation is carried out by suction filtration. Among them, the phosphated iron oxide I is recovered for the secondary recovery of medium rare earth elements, and the filtrate A is collected for standby;

[0008] Step (2). Iron oxide II is put into the heavy rare earth element separation pool, and its mass concentration is 0.1 - 5 g / L; the pH is adjusted to 7 - 8 with an inorganic base solution. The filtrate A in step (1) is introduced into the heavy rare earth separation pool, and stirred for more than 24 hours. The mixed filtrate is subjected to solid-liquid separation by suction filtration. Among them, the iron oxide II is recovered for the secondary recovery of heavy rare earth elements, and the filtrate B is collected for standby;

[0009] Step (3). In the light rare earth separation pool, first add humic acid with a mass concentration of 0.1 - 5 g / L, adjust the pH of the solution to 7 - 8 using inorganic acid, introduce filtrate B from step (2) into the light rare earth separation pool, stir well for more than 24 h and then perform solid-liquid separation. Among them, the recovered humic acid is used for the secondary recovery of light rare earth elements, and filtrate C flows into the heavy rare earth separation pool to achieve the recovery of heavy rare earth elements;

[0010] Step (4). Secondary recovery of medium rare earth elements: Place the recovered iron oxide I in the medium rare earth collection pool, add inorganic acid to adjust the pH of the suspension to 3 - 5, stir well for more than 24 h. After the rare earth ions adsorbed on iron oxide I are fully desorbed into the solution, perform solid-liquid separation on the suspension, collect the solution rich in medium rare earth elements, and obtain purified medium rare earth after drying. Iron oxide I is recycled, and the number of recycling times is 1 - 3 times.

[0011] Step (5). Secondary recovery of heavy rare earth elements: Place iron oxide II in the heavy rare earth recovery pool, add inorganic acid to adjust the pH to 3 - 5, stir well for more than 24 h. After the rare earth ions in filtrate C and adsorbed on iron oxide II are fully desorbed into the solution, perform solid-liquid separation on the suspension, collect the filtrate rich in heavy rare earth elements, and obtain purified heavy rare earth after drying. Iron oxide II is recycled, and the number of recycling times is 1 - 3 times.

[0012] Step (6). Secondary recovery of light rare earth elements: Place the recovered humic acid in light rare earth collection pool I, add inorganic acid to adjust the pH to 3 - 5, stir well for more than 24 h. After the rare earth ions adsorbed on the humic acid are completely desorbed into the solution, perform solid-liquid separation on the suspension, collect the solution rich in light rare earth elements, and obtain purified and separated light rare earth after drying. Humic acid is recycled, and the number of recycling times is 1 - 3 times.

[0013] Preferably, iron oxide I is ferrihydrite, and its synthesis method is: Slowly drip a 1 mol / L potassium hydroxide (KOH) solution into a 0.5 mol / L iron nitrate (Fe(NO3)3) solution while stirring well until the pH of the solution reaches 7 - 8, then quickly centrifuge. The obtained solid substance is repeatedly washed with deionized water until the conductivity is lower than 20 S cm -1 After that, freeze-dry to obtain pure-phase ferrihydrite. The specific surface area of the synthesized ferrihydrite is about 300 m 2 / g, pH zpc = 8.

[0014] Preferably, iron oxide II is goethite, and its synthesis method is as follows: Slowly drip a 2.5 mol / L potassium hydroxide (KOH) solution into a 0.2 mol / L iron nitrate (Fe(NO3)3) solution while stirring thoroughly until the solution pH reaches 12. Then, age the thoroughly stirred suspension in a water bath at 60 °C for 72 hours and then centrifuge at high speed. Repeatedly wash the solid with deionized water until the conductivity is lower than 20 S cm -1 After that, freeze-dry to obtain pure-phase goethite. The specific surface area of the synthesized goethite is about 60 m 2 / g, pH zpc = 9.

[0015] Preferably, in step (1), adjust the pH of the suspension to 5 - 5.5. The weakly acidic pH condition is favorable for the adsorption of ferrihydrite on inorganic phosphate, thereby enhancing the ternary complexation of rare earth ions and phosphate radicals, which is the key to the selective adsorption of medium rare earth ions. When pH < 3, ferrihydrite may dissolve to a certain extent, resulting in adverse effects. When 3 < pH < 5, the surface of ferrihydrite carries too much positive charge, generating a strong repulsive effect with rare earth cations, which is not conducive to the adsorption of rare earth ions. When pH > 5.5, the adsorption of ferrihydrite on phosphate radicals weakens, while the direct adsorption of rare earth ions strengthens, which is not conducive to the formation of ternary complexation of phosphate radicals and rare earth ions, reducing the selectivity for medium rare earth ions and producing adverse effects.

[0016] Preferably, in step (2), adjust the pH of the suspension to 7 - 7.5. Under the medium alkaline pH condition, the surface of goethite is negatively charged, which is favorable for the adsorption of positively charged rare earth cations. However, when pH > 7.5, rare earth ions are prone to form REE(OH)3 precipitates, which is not conducive to the selective adsorption of goethite on heavy rare earth ions and also unable to desorb and recover rare earth ions.

[0017] Preferably, in step (3), adjust the pH of the solution to 7 - 7.5. Under the medium alkaline pH condition, it is favorable for humic acid to adsorb rare earth cations. However, when pH > 7.5, rare earth ions are prone to form REE(OH)3 precipitates, which is not conducive to the selective adsorption of humic acid on light rare earth ions and also unable to desorb and recover rare earth ions.

[0018] Preferably, in step (4), adjust the pH of the suspension to 3 - 3.5. Under the acidic pH condition, it is favorable for the desorption of rare earth ions from the surface of ferrihydrite to achieve the recovery of rare earth ions. When pH < 3, ferrihydrite may dissolve to a certain extent, thereby generating free Fe 3+ , forming impurities and reducing the purity of rare earth ions.

[0019] Preferably, in step (5), the pH of the suspension is adjusted to 3 - 3.5. Under acidic pH conditions, it is beneficial for rare earth ions to desorb from the goethite surface, realizing the recovery of rare earth ions. When pH < 3, ferrihydrite may dissolve to a certain extent, and then free Fe 3+ is formed, resulting in impurities and reducing the purity of rare earth ions.

[0020] Preferably, in step (6), the pH of the suspension is adjusted to 3 - 4. Under acidic pH conditions, it is beneficial for rare earth ions to desorb from the goethite surface, realizing the recovery of rare earth ions. When pH < 3, humic acid may partially dissociate or precipitate, resulting in the inability to recycle humic acid.

[0021] Advantages of the present invention:

[0022] 1. The present invention can effectively separate and purify all partition rare earth ions into light rare earth-rich, medium rare earth-rich, and heavy rare earth-rich solutions.

[0023] 2. The use of organic solvent extractants can be avoided, reducing environmental pollution. It can lighten the operation burden for subsequent single-element purification processes.

[0024] 3. The adsorption and desorption fillers used, including iron oxide I and humus, etc., can be recycled, reducing costs. The extractant of the present invention is green, environmentally friendly, pollution-free, and is natural minerals and natural humus, with low prices. Note: The adsorption reaction refers to the fixation of metal ions or acid radical ions on the surface of the adsorption material through electrostatic attraction (physical adsorption) or through complexation reactions (chemical adsorption), which is a common, cheap, and energy-free recovery and classification method. Different adsorption materials combined with different solution environments (such as pH, ionic strength, etc.) can efficiently and selectively separate target ions.

[0025] 4. Microscopic mechanism: (1) Under acidic conditions, the iron hydroxyl groups on the ferrihydrite surface (including isolated iron hydroxyl group FeOH, twin iron hydroxyl group Fe2OH, and tricoordinated iron hydroxyl group Fe3OH) will undergo protonation to form a positively charged FeOH2 surface group, which helps to adsorb free phosphate (H2PO4 - , which is the main form of inorganic phosphate under acidic conditions). At this time, phosphate undergoes inner-sphere adsorption on the ferrihydrite surface to form a protonated bidentate binuclear configuration (Fe2O2PO2H). When rare earth ions are added to the solution, they will interact with the phosphate adsorbed on the ferrihydrite surface, and then form a stable ternary complex bridged by phosphate. Under acidic conditions, the ternary complex generally presents a monodentate ternary complex configuration (Fe2O2POOREE + ), while under neutral conditions, it transforms into a bidentate ternary complex configuration (Fe2O2PO2REE +) This ternary complexation mechanism not only significantly enhances the adsorption capacity of rare earth ions, but also exhibits selectivity for medium rare earth ions during the macroscopic adsorption process because the monodentate ternary complexation configuration has a lower adsorption energy for medium rare earth elements (MREE).

[0026] (2) Goethite has a needle-like morphology, and its main exposed crystal planes are (101) and (210) crystal planes, among which the (210) crystal plane exhibits higher reactivity. Both of these crystal planes are rich in isolated iron hydroxyl groups (FeOH), which are prone to form a bidentate adsorption configuration (Fe2O2REE) with rare earth ions. Due to the smaller ionic radius of heavy rare earth ions (HREE), hydrolysis is more likely to occur, and thus complexation with isolated iron hydroxyl groups is easier. Therefore, goethite shows significant selective adsorption for heavy rare earth ions.

[0027] (3) The surface of humic acid is usually rich in various functional groups such as carboxyl (-COOH), hydroxyl (-OH), and phenolic hydroxyl groups. Its complex structure and diverse functional groups can provide multiple adsorption sites for the formation of rare earth ions and form various coordination configurations. The ionic radius of light rare earth ions is relatively large, and the steric hindrance of the formed complex is small, enabling it to form stable multidentate complexes with multiple coordination groups of humic acid. Therefore, humic acid has selective adsorption for light rare earth ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart for the separation and collection of light, medium, and heavy rare earth elements of the present invention.

[0029] Figure 2 It is a diagram showing the preferential selective adsorption of light rare earth by humus.

[0030] Figure 3 It is a diagram showing the selective adsorption of medium rare earth ions by ferrihydrite loaded with phosphate groups.

[0031] Figure 4 It is a diagram showing the selective adsorption of heavy rare earth ions by goethite.

[0032] Figure 5 It is a diagram showing the separation effect of light, medium, and heavy rare earth ions after the implementation of the scheme. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be described clearly and completely below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments in the present invention belong to the scope of protection of the present invention.

[0034] In the present invention, the preferential adsorption behavior of humus (HA) for light rare earth ions, the preferential adsorption behavior of goethite for heavy rare earth ions, and the preferential adsorption behavior of ferrihydrite loaded with phosphate (ferrihydrite loaded with phosphate groups) for medium rare earth ions are discovered and fully utilized. By constructing a suitable adsorption sequence, an economical, environmentally friendly, and efficient separation and purification scheme for light rare earths, medium rare earths, and heavy rare earths can be achieved. The adsorption rates of the three adsorption systems are as follows:

[0035] (1) As Figure 2 shown, under neutral pH conditions (pH = 7), humus has a higher adsorption rate for light rare earths (80% - 100%), while the adsorption rate of heavy rare earths is very low (less than 20%). Therefore, humus can separate light rare earth ions from medium and heavy rare earth ions. Only through a simple filtration operation, the humus adsorbed with light rare earth ions can undergo a desorption reaction by adjusting the pH (acidic, such as pH = 3), and finally a large amount of light rare earth ions can be released into the light rare earth collection pool.

[0036] (2) As Figure 3 shown, the ferrihydrite loaded with phosphate groups has a strong selective adsorption effect on medium rare earths. The adsorption rate for medium rare earths reaches 60%, while the adsorption rate for light rare earth ions is only 20% - 40%, and the adsorption rate of heavy rare earths is about 30%.

[0037] (3) As Figure 4 shown, from light rare earths to heavy rare earths, the adsorption rate of goethite increases almost linearly, and it is more enriched in heavy rare earth ions. Therefore, after the separation of medium rare earth and light rare earth ions in the front, the selective enrichment of goethite for heavy rare earths will be more obvious.

[0038] Example 1

[0039] Laboratory simulation was carried out for the purification and separation operation of a standard solution of rare earth ions with all partition ratios, and the commercial brand is Accustandard (the content of each rare earth ion is 100 ppb).

[0040] As Figure 1 、 Figure 5As shown, step (1). In the medium rare earth separation pool, first add ferrihydrite with a water-soil mass concentration of 1 g / L. Of course, a mass concentration in the range of 0.1 - 5 g / L is also suitable. Then add sodium dihydrogen phosphate with a concentration of 60 μmol / L. Of course, a concentration in the range of 20 - 100 μmol / L is also suitable. Use hydrochloric acid or nitric acid with a concentration of 0.1 mol / L to adjust the pH of the suspension to 5. Of course, a pH of 4 - 6 is also suitable. Stir well for 8 hours or more. Introduce the rare earth total partition solution (the concentration of each adsorbed ion is 100 ppb) into the medium rare earth separation pool, stir well for 24 h, and perform solid-liquid separation on the mixed liquor by suction filtration. Among them, the recovered phosphated iron oxide I (with rare earth ions adsorbed on the surface) is used for the secondary recovery of medium rare earth elements, and the filtrate A is collected for standby. The concentration of rare earth ions is measured by ICP-MS.

[0041] Step (2). Add iron oxide II with a mass concentration of 1 g / L to the heavy rare earth element separation pool. Of course, a mass concentration in the range of 0.1 - 5 g / L is also suitable. Use sodium hydroxide with a concentration of 0.1 - 1 mol / L to adjust the pH of the solution to 7.5. Of course, a pH of 7 - 8 is also suitable. Introduce the filtrate A from step (1) into the heavy rare earth separation pool, stir well for 24 h; perform solid-liquid separation on the mixed filtrate by suction filtration. Among them, the recovered iron oxide II is used for the secondary recovery of heavy rare earth elements, and the filtrate B is collected for standby.

[0042] Step (3). In the light rare earth separation pool, first add 1 g / L of humus (HA). Of course, a mass concentration in the range of 0.1 - 5 g / L is also suitable. Use hydrochloric acid or nitric acid with a concentration of 0.1 - 1 mol / L to adjust the pH of the suspension to 7 - 8. Introduce the filtrate B from step (2) into the light rare earth separation pool, stir well for 24 h and then perform solid-liquid separation by suction filtration. Among them, the recovered humus (containing rare earth) is used for the secondary recovery of light rare earth elements, and the filtrate C flows into the heavy rare earth element recovery pool to achieve the recovery of heavy rare earth elements. Table 1 shows the rare earth ion concentrations of the adsorbent and the filtrate:

[0043] Table 1 Rare earth ion concentrations of the adsorbent and the filtrate in each stage of separation:

[0044]

[0045]

[0046] Step (4). Secondary recovery of medium rare earth elements: Place the recovered iron oxide I in the medium rare earth collection pool, add hydrochloric acid or nitric acid with a concentration of 0.1 - 1 mol / L to adjust the pH of the suspension to 3 (of course, a pH of 3 - 5 is also suitable), stir well for 24 h. After the rare earth ions are completely desorbed into the solution, the suspension is separated by solid-liquid separation through suction filtration, and the solution rich in medium rare earth elements is collected. After simple evaporation and drying, purified medium rare earth is obtained. The iron oxide I is recycled, and the number of cycles is 1 - 3 times. The measured concentrations of adsorbed medium rare earth ions and recovered medium rare earth ions are shown in Table 2 below:

[0047] Table 2 Concentrations of adsorbed medium rare earth ions and recovered medium rare earth ions ppb (rich medium rare earth pool)

[0048]

[0049] Step (5). Secondary recovery of heavy rare earth elements: Place the iron oxide II in the heavy rare earth recovery pool, add hydrochloric acid or nitric acid with a concentration of 0.1 mol / L to adjust the pH of the suspension to 3 (of course, a pH of 3 - 5 is also suitable), stir well for 24 h. After the rare earth ions adsorbed on the iron oxide II and in filtrate C are desorbed into the solution, the suspension is separated by solid-liquid separation through suction filtration, and the filtrate rich in heavy rare earth elements is collected. After simple evaporation and drying, purified heavy rare earth is obtained. The iron oxide II is recycled, and the number of cycles is 1 - 3 times. The concentrations of adsorbed heavy rare earth ions and recovered heavy rare earth ions are shown in Table 3:

[0050] Table 3 Concentrations of adsorbed heavy rare earth ions and co-recovered heavy rare earth ions ppb (rich heavy rare earth pool)

[0051]

[0052] Step (6). Secondary recovery of light rare earth elements: Place the recovered humus in the light rare earth collection pool I, add hydrochloric acid or nitric acid with a concentration of 0.1 mol / L to adjust the pH of the suspension to 3 (of course, a pH of 3 - 5 is also suitable), stir well for 24 h. After the rare earth ions are completely desorbed into the solution, the suspension is separated by solid-liquid separation through suction filtration, and the solution rich in light rare earth elements is collected. After simple evaporation and drying, purified and separated light rare earth is obtained. The humus is recycled, and the number of cycles is 1 - 3 times. The concentrations of adsorbed light rare earth ions and recovered light rare earth ions are shown in Table 4:

[0053] Table 4 Concentrations of adsorbed light rare earth ions and recovered light rare earth ions ppb (rich light rare earth pool)

[0054]

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for multi-stage classification and recycling of rare earth elements, characterized in that, It includes the following steps: Step (1): In the medium rare earth separation pool, an iron oxide I solution with a mass concentration of 0.1 - 5 g / L is put in, and then an inorganic phosphate with a concentration of 20 - 100 μmol / L is added. A certain amount of inorganic acid is used to adjust the pH of the suspension to 4 - 6, and it is stirred for more than 8 hours. After the iron oxide I solution and the inorganic phosphate react fully, the total partition rare earth leaching solution is introduced into the medium rare earth separation pool and stirred for more than 24 hours. Solid-liquid separation is carried out by suction filtration. Among them, the phosphated iron oxide I is recycled for the secondary recovery of medium rare earth elements, and the filtrate A is collected for standby; Step (2): An iron oxide II solution with a mass concentration of 0.1 - 5 g / L is put into the heavy rare earth element separation pool; the pH is adjusted to 7 - 8 using an inorganic base solution. The filtrate A in step (1) is introduced into the heavy rare earth separation pool and stirred for more than 24 hours. The mixed filtrate is subjected to solid-liquid separation by suction filtration. Among them, the iron oxide II is recycled for the secondary recovery of heavy rare earth elements, and the filtrate B is collected for standby; Step (3): In the light rare earth separation pool, first, a humic acid solution with a mass concentration of 0.1 - 5 g / L is put in, and the pH of the solution is adjusted to 7 - 8 using an inorganic acid. The filtrate B in step (2) is introduced into the light rare earth separation pool. After fully stirring for more than 24 hours, solid-liquid separation is carried out by suction filtration. Among them, the humic acid is recycled for the secondary recovery of light rare earth elements, and the filtrate C flows into the heavy rare earth separation pool to achieve the recovery of heavy rare earth elements; Step (4): Secondary recovery of medium rare earth elements: The recycled iron oxide I is placed in the medium rare earth collection pool, and an inorganic acid is added to adjust the pH of the suspension to 3 - 5. It is fully stirred for more than 24 hours. After the rare earth ions attached to the iron oxide I are fully desorbed into the solution, the suspension is subjected to solid-liquid separation by suction filtration. The solution rich in medium rare earth elements is collected, and after evaporation and drying, purified medium rare earth is obtained. The iron oxide I returns to step (1) for reuse; Step (5): Secondary recovery of heavy rare earth elements: The iron oxide II is placed in the heavy rare earth recovery pool, and an inorganic acid is added to adjust the pH to 3 - 5. It is fully stirred for more than 24 hours. After the rare earth ions attached to the iron oxide II and in the filtrate C are fully desorbed into the solution, the suspension is subjected to solid-liquid separation by suction filtration. The filtrate rich in heavy rare earth elements is collected, and after evaporation and drying, purified heavy rare earth is obtained. The iron oxide II returns to step (2) for reuse; Step (6): Secondary recovery of light rare earth elements: The recycled humic acid is placed in the light rare earth collection pool I, and an inorganic acid is added to adjust the pH to 3 - 5. It is fully stirred for more than 24 hours. After the rare earth ions adsorbed on the humic acid are completely desorbed into the solution, the suspension is subjected to solid-liquid separation by suction filtration. The solution rich in light rare earth elements is collected, and after simple evaporation and drying, purified and separated light rare earth is obtained; the humic acid returns to step (3) for reuse.

2. The method according to claim 1, characterized in that, In step (1), the iron oxide I is ferrihydrite; in step (2), the iron oxide II is goethite.

3. According to the method described in claim 1, in step (1), the inorganic phosphate is sodium dihydrogen phosphate.

4. The method according to claim 1, wherein The cycle number of iron oxide Ⅰ in step (4) is 1 - 3 times; the cycle number of iron oxide Ⅱ in step (5) is 1 - 3 times; the cycle number of humic acid in step (6) is 1 - 3 times.

5. The method according to claim 1, characterized in that, In step (1), adjust the pH of the suspension to 5 - 5.

5.

6. The method according to claim 1, characterized in that, In step (2), adjust the pH of the suspension to 7 - 7.

5.

7. The method according to claim 1, characterized in that, In step (3), adjust the pH of the solution to 7 - 7.

5.

8. The method according to claim 1, characterized in that In step (4), adjust the suspension to pH = 3 - 3.

5.

9. The method according to claim 1, characterized in that In step (5), adjust the pH of the suspension to 3 - 3.

5.

10. The method according to claim 1, characterized in that, In step (6), adjust the pH of the suspension to 3 - 4.

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