Method for extracting rare earth oxide from wastewater generated in production of aluminum oxide from fly ash

Abstract

The invention provides a method for extracting rare earth oxide from waste water generated in production of aluminum oxide from fly ash. The method comprises the following steps: S1, taking industrial wastewater in the process of producing aluminum oxide from fly ash as a raw material, and extracting the industrial wastewater to obtain an organic phase; s2, washing the organic phase to obtain a rare earth organic phase; s3, the rare earth organic phase is subjected to reverse extraction, and a solution containing a rare earth compound is obtained; s4, carrying out precipitation reaction on the solution containing the rare earth compound, and filtering to obtain a rare earth compound precipitate; and S5, roasting the rare earth compound precipitate to obtain the rare earth oxide. The method solves the problem of rare earth recovery in the fly ash aluminum extraction rare earth-containing waste liquid with high calcium chloride and medium aluminum chloride concentration, overcomes the negative influence of calcium and aluminum elements on the rare earth recovery rate and the rare earth purity, realizes high-efficiency rare earth recovery and obtains a high-purity rare earth product.

Description

Technical Field

[0001] The invention relates to the technical field of coal chemical industry, in particular to a method for extracting rare earth oxides from waste water in the production of alumina from fly ash. Background Art

[0002] Rare earths have excellent optical, electromagnetic and other physical properties and can be combined with other materials to form new materials with different properties and a wide variety of varieties. Therefore, they are widely used in high-tech fields such as hydrogen storage materials, magnetic materials, new energy, and special steels. In addition to existing in the form of fluorocarbon ore, monazite, ion-adsorbed rare earth ore, and phosphate ore in nature, rare earths are also dispersed in minerals such as coal and oil shale. With the increase in the use of rare earths and the development of rare earth resources, the enrichment and recovery of trace rare earths from the ash and slag of related mineral resources has become a research hotspot.

[0003] Current research shows that the inorganic components of coal in the Jungar mining area have a high content of valuable elements, and are rich in aluminum, gallium, lithium, and rare earths, which are important resources for the national economy and are far more valuable than coal itself. However, the methods for recovering rare earths disclosed in the prior art, such as the Chinese patent with publication number CN112981092A, which discloses a method for extracting gallium, lithium, and rare earth metals from fly ash, require a large amount of calcium carbonate and acid, and only two steps of roasting are required during the extraction process, which consumes a lot of energy. For example, the Chinese patent with application number CN201711376785.2 discloses a process for extracting rare earths from fly ash, and rare earths with a purity of more than 75% are recovered from fly ash acid leaching liquid. The fly ash produced in the Jungar mining area has high aluminum and rare earth content (the main mineral components of the coal in the Jungar mining area are kaolinite and boehmite, and the main chemical components are Al2O3 and SiO2. It also contains a small amount of Fe2O3, TiO2, CaO, MgO, P2O5, K2O and Na2O, among which the Al2O3 content is 50-60%, the SiO2 content is 30-38%, and the ignition loss is 3-5%. The trace element gallium content is 85g / ton, lithium is 300-350g / ton, and the total amount of rare earth is 0.09-0.12%); the industrial wastewater produced by the production of alumina from the fly ash in the Jungar mining area is rich in rare earth ions, but because the characteristics of the waste liquid composition and ion content are different from the existing technology, the existing method is not suitable for the extraction of rare earths in this waste liquid. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for extracting rare earth oxides from wastewater produced by producing alumina from fly ash, so as to solve the problem that the method of extracting rare earth elements in the prior art is not suitable for industrial wastewater produced by producing alumina from fly ash in Jungar mining area.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided a method for extracting rare earth oxides from waste water in the process of producing alumina from fly ash, the method comprising: step S1, using industrial waste water in the process of producing alumina from fly ash as raw material, extracting the industrial waste water to obtain an organic phase; step S2, washing the organic phase to obtain a rare earth organic phase; step S3, stripping the rare earth organic phase to obtain a solution containing rare earth compounds; step S4, performing precipitation reaction and filtering on the solution containing rare earth compounds to obtain a rare earth compound precipitate; step S5, roasting the rare earth compound precipitate to obtain rare earth oxides.

[0006] Furthermore, the industrial wastewater contains 5-7 g / L of aluminum chloride, 20-30 g / L of calcium chloride, 2-3 g / L of magnesium chloride, 2-3 g / L of potassium chloride, 2-4 g / L of sodium chloride, 0.1-1 g / L of lithium chloride, and 1-2 g / L of rare earth chloride; preferably, the industrial wastewater contains 6 g / L of aluminum chloride, 24 g / L of calcium chloride, 2.2 g / L of magnesium chloride, 2.25 g / L of potassium chloride, 3 g / L of sodium chloride, 0.5 g / L of lithium chloride, and 1.8 g / L of rare earth chloride; preferably, the pH of the industrial wastewater is 4-5, and more preferably the pH of the industrial wastewater is 5.

[0007] Furthermore, in step S1, the extraction adopts an extractant and a diluent, and the extractant preferably includes an ester compound and / or an amine compound, and the extractant preferably includes one or more of di(2-ethylhexyl phosphoric acid), 2-ethylhexyl phosphate-2-ethylhexyl ester, tributyl phosphate, diisooctyl phosphate, secondary carbon primary amine, and methyltrialkylammonium chloride, and more preferably one or more of secondary carbon primary amine and / or tributyl phosphate; the diluent is preferably isooctyl alcohol and / or kerosene.

[0008] Furthermore, in step S1, the extraction method is cross-current extraction or countercurrent extraction, and the number of extraction stages is preferably 1 to 6, more preferably 3 to 4; the volume ratio of the extraction phase (O / A) in the extraction is preferably 1:1 to 1:20, more preferably 1:3 to 1:10; the extraction temperature is preferably 25 to 60°C, more preferably 25 to 40°C; the pH value of the organic phase is preferably 1 to 7, more preferably 1.5 to 5.

[0009] Furthermore, in step S2, washing is performed using a detergent, preferably the detergent is an ammonium salt, more preferably the ammonium salt is ammonium sulfate and / or ammonium chloride; preferably the mass concentration of the detergent is 1 to 10%, more preferably 2 to 4%; preferably during the washing process, the pH of the organic phase is maintained at 1 to 7, more preferably 1.5 to 5; preferably the washing time is 5 to 35 minutes, more preferably 10 to 20 minutes; preferably the washing volume ratio (O / A) of washing is 1:1 to 1:20, more preferably 1:3 to 1:10; preferably the number of washings is 1 to 4 times, more preferably 1 to 3 times.

[0010] Further, in step S3, a stripping agent is used for stripping, and preferably the stripping agent includes an acid solution, and more preferably the stripping agent includes one or more of sulfuric acid, nitric acid or hydrochloric acid; more preferably, the concentration of the stripping agent is 1 to 5 mol / L, preferably 2 to 4 mol / L; preferably, the stripping ratio (O / A) is 1:1 to 1:10, more preferably 1:3 to 1:8; preferably, the stripping method is cross-current extraction or countercurrent extraction, and preferably, the stripping stage is 1 to 6, preferably 3 to 4; preferably, the stripping temperature is 25 to 60°C, preferably 25 to 40°C.

[0011] Furthermore, in step S4, a precipitant is used in the precipitation reaction, and preferably the precipitant is one or more of oxalic acid, potassium oxalate, sodium oxalate and calcium oxalate.

[0012] Furthermore, in step S5, before calcination, the rare earth compound precipitate is first washed with softened water. The calcination temperature is preferably 600-1000° C., preferably 800-950° C., and the calcination time is preferably 1-3 h, more preferably 2-2.5 h.

[0013] Furthermore, the recovery rate of the rare earth oxide is above 80%, and preferably the purity of the rare earth oxide is greater than 90%.

[0014] In order to achieve the above object, according to one aspect of the present invention, a rare earth oxide is provided, and the rare earth oxide is extracted according to the above method.

[0015] The technical solution of the present invention is applied. This application is aimed at the wastewater produced by fly ash to produce aluminum oxide. The main inorganic salt component of the wastewater is calcium chloride. This application solves the problem of recovering rare earths from fly ash aluminum-containing rare earth wastewater with high calcium chloride and medium aluminum chloride concentrations, overcomes the negative effects of calcium and aluminum elements on the recovery rate and purity of rare earths, and achieves high-efficiency recovery of rare earths and obtains high-purity rare earth products. The method of the present application consumes less reagents in the process of extracting rare earth oxides, and only a small amount of acid, oxalic acid precipitant, etc. is required; at the same time, the above method is simple to operate and easy to achieve industrial scale-up. DETAILED DESCRIPTION

[0016] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0017] As analyzed in the background technology, since the chemical composition and phase composition of the fly ash produced in the Jungar mining area are different from those of the existing rare earth deposits, the existing rare earth element extraction method is not applicable to the fly ash in the mining area. In order to solve the above problems, this application provides a method for extracting rare earth oxides from the wastewater of fly ash production of alumina.

[0018] In a typical embodiment of the present application, a method for extracting rare earth oxides from wastewater in the production of alumina from fly ash is provided, the method comprising: step S1, using industrial wastewater in the process of producing alumina from fly ash as raw material, extracting the industrial wastewater to obtain an organic phase; step S2, washing the organic phase to obtain a rare earth organic phase; step S3, stripping the rare earth organic phase to obtain a solution containing rare earth compounds; step S4, performing precipitation reaction and filtering on the solution containing rare earth compounds to obtain a rare earth compound precipitate; step S5, roasting the rare earth compound precipitate to obtain rare earth oxides.

[0019] The present application extracts rare earth elements by an extraction-stripping method, and then obtains rare earth oxides by precipitation and roasting reaction. The extraction method of the present application is simple and easy to operate, and the rare earth oxides obtained by extraction have a high recovery rate and high purity, providing a new way for the high-value utilization of fly ash in the Jungar mining area.

[0020] The main mineral components of coal in the Jungar mining area are kaolinite and boehmite, and the main chemical components are Al2O3 and SiO2. It also contains a small amount of Fe2O3, TiO2, CaO, MgO, P2O5, K2O and Na2O, among which the Al2O3 content is 50-60%, the SiO2 content is 30-38%, and the ignition loss is 3-5%. The trace element gallium content is 85g / ton, lithium is 300-350g / ton, and the total amount of rare earth is 0.09-0.12%. In the process of acid-based alumina production, these valuable elements are enriched in aluminum extraction wastewater. The present application uses the above-mentioned wastewater as raw material, and the industrial wastewater includes 5-7 g / L of aluminum chloride, 20-30 g / L of calcium chloride, 2-3 g / L of magnesium chloride, 2-3 g / L of potassium chloride, 2-4 g / L of sodium chloride, 0.1-1 g / L of lithium chloride, and 1-2 g / L of rare earth chloride; preferably, the industrial wastewater includes 6 g / L of aluminum chloride, 24 g / L of calcium chloride, 2.2 g / L of magnesium chloride, 2.25 g / L of potassium chloride, 3 g / L of sodium chloride, 0.5 g / L of lithium chloride, and 1.8 g / L of rare earth chloride; preferably, the pH value of the industrial wastewater is 4-5, and more preferably, the pH value of the industrial wastewater is 5. Compared with the mother liquor of aluminum extraction from fly ash in the prior art, this application targets the wastewater of fly ash production of aluminum oxide, the main inorganic salt component of which is calcium chloride. This application solves the problem of recovering rare earths from fly ash aluminum extraction containing rare earth wastewater with high calcium chloride and medium aluminum chloride concentrations, overcomes the negative effects of calcium and aluminum elements on the recovery rate and purity of rare earths, and achieves high-efficiency recovery of rare earths and obtains high-purity rare earth products. The method of this application consumes less reagents in the process of extracting rare earth oxides, and only requires a small amount of acid, oxalic acid precipitant, etc.; at the same time, the above method is simple to operate and easy to achieve industrial scale-up.

[0021] If oxalate acetone is added to waste water according to the method in the prior art, a large amount of calcium oxalate precipitation is generated, resulting in too high consumption of oxalate acetone, and calcium oxalate needs to be separated from rare earth oxalate again. In some embodiments, in step S1, extraction is carried out using an extractant and a diluent, so that the rare earth element is fully dissolved in the extractant to achieve the purpose of extraction and separation, preferably the extractant includes one or more of an ester compound and / or an amine compound, preferably the extractant includes di(2-ethylhexyl phosphoric acid) (P204), 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (P507), tributyl phosphate (TBP), diisooctyl phosphate (P350), secondary carbon primary amine (N1923), methyl trialkyl ammonium chloride (N263), preferably one or more of secondary carbon primary amine (N1923) and tributyl phosphate (TBP), more preferably one or more of secondary carbon primary amine (N1923) and / or tributyl phosphate (TBP). The use of the above-mentioned extractant can avoid the use of the acid leaching method in the prior art. Since the aluminum content in the wastewater is relatively high, if the acid leaching method is used to extract rare earths, aluminum and rare earth elements will compete for extraction, which will lead to a decrease in the extraction rate of rare earth elements and low rare earth purity.

[0022] The present application has no particular limitation on the type of diluent, and any diluent commonly used in the art can be applied to the present application. The preferred diluent is isooctyl alcohol and / or kerosene.

[0023] The present application has no particular restrictions on the extraction method. In some embodiments, in step S1, the extraction method is cross-current extraction or countercurrent extraction, and the number of extraction stages is preferably 1 to 6, and more preferably 3 to 4. The cross-current extraction and countercurrent extraction of the present application both utilize the difference in solubility of each component in the liquid mixture in a certain solvent to achieve the purpose of separation of the mixture. Multi-stage cross-current extraction is a series process of multiple single-stage extractions. In multi-stage countercurrent extraction, the direction of movement of the feed liquid is opposite to the direction of movement of the extractant. Compared with the same-stage cross-current extraction, countercurrent extraction can obtain a higher yield at the same point extractant dosage; relative to multi-stage cross-current extraction, the amount of countercurrent extractant is small and the extract concentration is high. Cross-current extraction is generally selected in laboratories; multi-stage countercurrent extraction is generally selected for industrialization.

[0024] In order to separate the rare earth elements in the solution as much as possible, the extraction phase ratio (O / A) in the extraction is preferably 1:1 to 1:20, and more preferably 1:3 to 1:10; if the extraction phase ratio is higher than this range, the content of impurity ions such as calcium, iron and other elements will be too high, thereby reducing the purity of the rare earth elements; if the extraction phase ratio is lower than this range, the rare earth elements will be insufficiently extracted, thereby reducing the extraction rate of the rare earth elements.

[0025] In order to avoid the poor solubility of rare earth elements due to too low extraction temperature, and to avoid the structure of the compounds in the solution being damaged by too high temperature, the extraction temperature is preferably 25-60°C, more preferably 25-40°C.

[0026] The pH value will affect the extraction efficiency. In order to improve the extraction efficiency, the pH value of the organic phase is preferably 1 to 7, more preferably 1.5 to 5. If the pH is too low, H + It will combine with organic molecules and compete with rare earth ions, resulting in a decrease in the extraction rate. If the pH is too high, Al 3+ It is easy to form Al(OH)2 with OH- ions + For aluminum hydroxide with colloidal properties (very fine solid particles) such as Al(OH)2 and Al(OH)3, tiny solid particles are easily emulsified in the organic phase. Incomplete solid-liquid separation directly affects the rare earth extraction rate and purity.

[0027] In some embodiments, in step S2, washing is performed with a detergent. In order to fully remove impurities in the solution (such as impurity ions such as calcium and iron, and aqueous solution entrained in the organic phase, etc.) and improve the purity of the rare earth elements, the detergent is preferably an ammonium salt, and more preferably the ammonium salt is ammonium sulfate and / or ammonium chloride; the mass concentration of the detergent is preferably 1 to 10%, and more preferably 2 to 4%.

[0028] The preferred washing time is 5 to 35 minutes, more preferably 10 to 20 minutes; the preferred washing ratio (O / A) is 1:1 to 1:20, more preferably 1:3 to 1:10; the preferred number of washings is 1 to 4 times, more preferably 1 to 3 times.

[0029] In some embodiments, the stripping agent is used for stripping, and the stripping agent preferably includes an acid solution, and the stripping agent preferably includes one or more of sulfuric acid, nitric acid or hydrochloric acid; more preferably, the concentration of the stripping agent is 1 to 5 mol / L, preferably 2 to 4 mol / L; preferably, the stripping ratio (O / A) is 1:1 to 1:10, more preferably 1:3 to 1:8; preferably, the stripping method is cross-current extraction, and preferably, the stripping stage is 1 to 6, preferably 3 to 4; preferably, the stripping temperature is 25 to 60°C, preferably 25 to 40°C. The stripping agent is an acid solution, and H in the acid solution is + Combined with the extractant, it forms a competitive relationship with the rare earth ions in the organic phase, that is, it combines with H + Releases rare earth ions.

[0030] In order to precipitate the rare earth elements in the solution, in some embodiments, in step S4, a precipitant is used in the precipitation reaction, and preferably the precipitant is one or more of oxalic acid, potassium oxalate, sodium oxalate and calcium oxalate.

[0031] In step S5, the rare earth compound precipitate is first washed with softened water before being calcined. The present application has no particular restrictions on the calcination conditions, and the calcination conditions commonly used in the art can be applied to the present application. In order to fully convert the rare earth compound precipitate into rare earth oxides and avoid excessive temperature from damaging its own structure, the calcination temperature is preferably 600 to 1000° C., preferably 800 to 950° C., and the calcination time is preferably 1 to 3 hours, more preferably 2 to 2.5 hours.

[0032] The rare earth oxide of the present application has good recovery rate and purity. The recovery rate of the rare earth oxide is above 80%, and preferably the purity of the rare earth oxide is greater than 90%.

[0033] In another typical embodiment of the present application, a rare earth oxide is provided, which is extracted according to the above method.

[0034] The rare earth oxide obtained by the above method has higher purity.

[0035] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0036] The industrial wastewater used in the examples of the present application includes 6 g / L aluminum chloride, 24 g / L calcium chloride, 2.2 g / L magnesium chloride, 2.25 g / L potassium chloride, 3 g / L sodium chloride, 0.5 g / L lithium chloride, and 1.8 g / L rare earth chloride.

[0037] Example 1

[0038] (1) Extraction and enrichment of rare earths: Extraction agents are used to extract rare earth elements from industrial wastewater, with isooctyl alcohol and kerosene as diluents, and the extractant is secondary carbon primary amine (N1923). The organic phase ratio (O / A) is 1:10, the pH value is 5, the extraction temperature is 35°C, and the extraction level is 3; the extraction method is cross-current extraction.

[0039] (2) Washing of organic phase: The organic phase was washed with a sulfuric acid aqueous solution having a mass concentration of 3%, a pH value of 1, a washing time of 20 min, a washing ratio (O / A) of 1:5, and a washing frequency of 2 times.

[0040] (3) Organic back extraction: Use sulfuric acid aqueous solution as the back extraction agent to back extract the rare earth organic phase to obtain a pure rare earth sulfate solution. Back extraction stage 2, organic phase ratio (O / A) 1:8, back extraction temperature 40 ° C, extraction stage 2, extraction method cross-current extraction, back extraction agent concentration 3 mol / L;

[0041] (4) adding oxalic acid to a solution containing pure rare earth sulfate to generate a rare earth oxalic acid precipitate;

[0042] (5) Oxalic acid precipitation filtration: Filter the above precipitate using a filtration device. Vacuum filtration is selected for filtration.

[0043] (3) Preparation of rare earth oxides: The rare earth precipitate is washed with demineralized water, filtered and calcined at a certain temperature to obtain rare earth oxides. The calcination temperature of the rare earth precipitate is 800°C and the calcination time is 2h.

[0044] Example 2

[0045] (1) Extraction and enrichment of rare earths: Extraction agents are used to extract rare earth elements from industrial wastewater. Isooctanol and kerosene are used as diluents. The extractants are secondary carbon primary amine (N1923) and tributyl phosphate. The organic phase ratio (O / A) is 1:3, the pH value is 1, the extraction temperature is 60°C, and the extraction level is 4; the extraction method is cross-current extraction.

[0046] (2) Washing of organic phase: The organic phase was washed with an aqueous solution of ammonium chloride. The mass concentration of the aqueous solution of ammonium chloride was 3%, the pH value was 1, the washing time was 20 min, the washing ratio (O / A) was 1:20, and the number of washing times was 3 times.

[0047] (3) Organic back extraction: Use sulfuric acid aqueous solution as the back extraction agent to back extract the rare earth organic phase to obtain a pure rare earth sulfate solution. The extraction stage is 2, the organic phase ratio (O / A) is 1:10, the extraction temperature is 25°C, the extraction stage is 2, the extraction method is cross-current extraction, and the back extraction agent concentration is 3 mol / L;

[0048] (4) adding oxalic acid to a solution containing pure rare earth sulfate to generate a rare earth oxalic acid precipitate;

[0049] (5) Oxalic acid precipitation filtration: Filter the above precipitate using a filtration device. Vacuum filtration is selected for filtration.

[0050] (3) Preparation of rare earth oxides: The rare earth precipitate is washed with demineralized water, filtered and calcined to obtain rare earth oxides. The calcination temperature of the rare earth precipitate is 600° C. and the calcination time is 3 h.

[0051] Example 3

[0052] (1) Extraction and enrichment of rare earths: Extraction of rare earth elements in industrial wastewater was carried out using an extractant, isooctyl alcohol and kerosene as diluents, and TBP as the extractant. The organic phase ratio (O / A) was 1:7, the pH value was 3, the extraction temperature was 40°C, and the extraction level was 3; the extraction method was cross-current extraction.

[0053] (2) Washing of organic phase: The organic phase was washed with an aqueous solution of ammonium chloride. The mass concentration of the aqueous solution of ammonium chloride was 3%, the pH value was 1.5, the washing time was 20 min, the washing ratio (O / A) was 1:20, and the washing times were 2 times.

[0054] (3) Organic back extraction: Use hydrochloric acid aqueous solution as the back extraction agent to back extract the rare earth organic phase to obtain a pure rare earth chloride solution. The extraction stage is 2, the organic phase ratio (O / A) is 1:3, the extraction temperature is 40°C, the extraction stage is 2, the extraction method is cross-current extraction, and the back extraction agent concentration is 5 mol / L;

[0055] (4) adding oxalic acid to a solution containing pure rare earth chloride to generate a rare earth oxalic acid precipitate;

[0056] (5) Oxalic acid precipitation filtration: Filter the above precipitate using a filtration device. Vacuum filtration is selected for filtration.

[0057] (3) Preparation of rare earth oxides: The rare earth precipitate is washed with demineralized water, filtered, and calcined to obtain rare earth oxides. The calcination temperature of the rare earth precipitate is 1000° C. and the calcination time is 1 h.

[0058] Example 4

[0059] The difference from Example 1 is that in step (1), the organic phase ratio (O / A) is 1:1.

[0060] Example 5

[0061] The difference from Example 1 is that in step (3), the organic phase ratio (O / A) is 1:1.

[0062] Example 6

[0063] The difference from Example 1 is that in step (1), the pH is 7.

[0064] Example 7

[0065] The difference from Example 1 is that in step (2), the mass concentration of the detergent is 11%.

[0066] Example 8

[0067] Different from Example 1, in step (4), the concentration of the stripping agent is 6 mol / L.

[0068] Comparative Example 1

[0069] The rare earth elements were extracted according to the Chinese patent application number 201711376785.2. The extraction rate and purity of the rare earth elements in the above embodiments and comparative examples are shown in Table 1.

[0070] Table 1

[0071] Extraction rate (%) purity(%) Example 1 96.0 98.1 Example 2 91.2 97.1 Example 3 89.3 96.1 Example 4 88.6 95.2 Example 5 87.6 94.2 Example 6 87.2 92.3 Example 7 81.2 90.1 Example 8 84.1 91.2 Comparative Example 1 75.0 80.0

[0072] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: the present application extracts rare earth elements by the extraction-stripping method, and then obtains rare earth oxides by precipitation and roasting reaction. The extraction method of the present application is simple and easy to operate, and the rare earth oxides obtained by extraction have high recovery rate and high purity, which provides a new way for the high-value utilization of fly ash in the Jungar mining area.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for extracting rare earth oxides from wastewater produced from fly ash to produce alumina, characterized in that: The method comprises: Step S1, using industrial wastewater from the process of producing alumina from fly ash as raw material, extracting the industrial wastewater to obtain an organic phase; Step S2, washing the organic phase to obtain a rare earth organic phase; Step S3, stripping the rare earth organic phase to obtain a solution containing rare earth compounds; Step S4, performing precipitation reaction and filtering on the solution containing the rare earth compound to obtain a rare earth compound precipitate; Step S5, calcining the rare earth compound precipitate to obtain the rare earth oxide.

2. The method according to claim 1, characterized in that The industrial wastewater contains 5-7 g / L of aluminum chloride, 20-30 g / L of calcium chloride, 2-3 g / L of magnesium chloride, 2-3 g / L of potassium chloride, 2-4 g / L of sodium chloride, 0.1-1 g / L of lithium chloride, and 1-2 g / L of rare earth chloride; preferably, the industrial wastewater contains 6 g / L of aluminum chloride, 24 g / L of calcium chloride, 2.2 g / L of magnesium chloride, 2.25 g / L of potassium chloride, 3 g / L of sodium chloride, 0.5 g / L of lithium chloride, and 1.8 g / L of rare earth chloride; preferably, the pH of the industrial wastewater is 4-5, and more preferably, the pH of the industrial wastewater is 5.

3. The method according to claim 1 or 2, characterized in that: In the step S1, the extraction uses an extractant and a diluent, preferably the extractant includes an ester compound and / or an amine compound, preferably the extractant includes one or more of di(2-ethylhexylphosphoric acid), 2-ethylhexylphosphoric acid-2-ethylhexyl ester, tributyl phosphate, diisooctyl phosphate, secondary carbon primary amine, methyltrialkylammonium chloride, more preferably one or more of secondary carbon primary amine and / or tributyl phosphate; Preferably, the diluent is isooctyl alcohol and / or kerosene.

4. The method according to any one of claims 1 to 3, characterized in that In step S1, the extraction method is cross-current extraction or countercurrent extraction, and the number of extraction stages is preferably 1 to 6, more preferably 3 to 4; the volume ratio of the extraction phase (O / A) in the extraction is preferably 1:1 to 1:20, more preferably 1:3 to 1:10; the extraction temperature is preferably 25 to 60°C, more preferably 25 to 40°C; the pH value of the organic phase is preferably 1 to 7, more preferably 1.5 to 5.

5. The method according to any one of claims 1 to 3, characterized in that In the step S2, the washing adopts a detergent, preferably the detergent is an ammonium salt, more preferably the ammonium salt is ammonium sulfate and / or ammonium chloride; preferably the mass concentration of the detergent is 1-10%, more preferably 2-4%; preferably during the washing process, the pH of the organic phase is maintained at 1-7, more preferably 1.5-5; preferably the washing time is 5-35 min, more preferably 10-20 min; preferably the washing volume ratio (O / A) of the washing is 1:1-1:20, more preferably 1:3-1:10; preferably the number of washing times is 1-4 times, more preferably 1-3 times.

6. The method according to any one of claims 1 to 3, characterized in that In the step S3, the stripping agent is used for the stripping, and the stripping agent preferably includes an acid solution, and more preferably includes one or more of sulfuric acid, nitric acid or hydrochloric acid; more preferably, the concentration of the stripping agent is 1 to 5 mol / L, and preferably 2 to 4 mol / L; preferably, the extraction ratio (O / A) of the stripping is 1:1 to 1:10, and more preferably 1:3 to 1:8; preferably, the stripping method is cross-current extraction or countercurrent extraction, and preferably, the extraction level of the stripping is 1 to 6, and preferably 3 to 4; preferably, the stripping temperature is 25 to 60°C, and preferably 25 to 40°C.

7. The method according to any one of claims 1 to 3, characterized in that In step S4, the precipitation reaction uses a precipitant, and preferably the precipitant is one or more of oxalic acid, potassium oxalate, sodium oxalate and calcium oxalate.

8. The method according to any one of claims 1 to 3, characterized in that In the step S5, before the calcination, the rare earth compound precipitate is first washed with softened water. The calcination temperature is preferably 600-1000°C, preferably 800-950°C, and the calcination time is preferably 1-3 hours, more preferably 2-2.5 hours.

9. The method according to claim 1, characterized in that: The recovery rate of the rare earth oxide is above 80%, and preferably the purity of the rare earth oxide is greater than 90%.

10. A rare earth oxide, characterized in that: The rare earth oxides are extracted according to the method according to any one of claims 1 to 9.