Co-extraction system and extraction method for extracting light rare earths from industrial wastewater

Abstract

The present invention relates to a co - extraction system and an extraction method for extracting light rare earths from industrial wastewater. The co - extraction system of the present invention includes a mixed extraction system and a stripping agent. The mixed extraction system includes an extractant, an ionic liquid, and a diluent. The extractant includes one or more of bis(2 - ethylhexyl) phosphate and 2 - ethylhexyl 2 - ethylhexyl phosphate. The ionic liquid includes one or more of methyltrioctylammonium laurate and 1 - octyl - 3 - methylimidazolium tetrafluoroborate. The stripping agent includes hydrochloric acid. By selecting and using a specific co - extraction system to extract and strip industrial wastewater, the present invention can effectively extract and separate light rare earths from industrial wastewater.

Description

Technical Field

[0001] The present invention relates to the field of rare earth extraction, and particularly to a co-extraction system and an extraction method for extracting light rare earths from industrial wastewater. Background Art

[0002] Rare earth elements are the general name of 17 elements including the lanthanide elements in Group IIIB of the periodic table with atomic numbers from 57 to 71, as well as yttrium and scandium. Due to their unique physical and chemical properties, rare earths are widely used in fields such as metallurgical engineering, aerospace, electronic information, petrochemical industry, and environmental protection, and are key materials indispensable in modern high-tech industries and national defense advanced weapons and other fields. In addition to existing in the forms of bastnaesite, monazite, ion-adsorption rare earth ore, phosphorite, etc. in nature, rare earths are also dispersed in minerals such as coal and oil shale. With the growth of rare earth consumption and the development of rare earth resources, the enrichment and recovery of trace rare earths from the ash residues of relevant mineral resources have become a research hotspot.

[0003] Previous research results showed that the content of valuable elements in the inorganic components of the coal in the Jungar mining area is relatively high, containing abundant national economic important resources such as aluminum, gallium, lithium, and rare earths, and the value far exceeds that of the coal itself. The main mineral components in the medium coal of the Jungar mining area are kaolinite and boehmite, and the main chemical components are Al 2 O 3 、SiO 2 ,also containing a small amount of Fe 2 O 3 、TiO 2 、CaO, MgO, P 2 O 5 、K 2 O and Na 2 O, etc., among which the content of Al 2 O 3 is 50 - 60%, the content of SiO 2 is 30 - 38%, the ignition loss is 3 - 5%, the total rare earth content is 0.09 - 0.12%, and the light rare earths account for 90% of the total rare earths. In the process of producing alumina from fly ash by the acid method, these valuable elements are enriched in the aluminum extraction wastewater. The wastewater from the production of alumina from fly ash contains various chlorides, mainly calcium chloride, and also contains one or more of aluminum chloride, magnesium chloride, potassium chloride, sodium chloride, and lithium chloride, and at the same time contains a certain amount of rare earth chlorides.

[0004] If the rare earth elements in the industrial wastewater from the production of alumina from fly ash can be enriched and recovered, it will not only be a beneficial supplement to rare earth resources but also enable the high-value utilization of fly ash. Since the chemical composition and phase composition of the fly ash produced in the Jungar mining area are different from those of existing rare earth ore deposits, the existing rare earth element extraction methods are not applicable to the fly ash in this mining area. So far, there have been few research reports on the extraction of rare earth elements from the industrial wastewater of alumina production from fly ash.

[0005] The utility model patent "Automated production system for extracting rare earth elements from fly ash" with the application number 201520750525 discloses an automated production system for extracting rare earth elements from fly ash, which involves the connection of a raw material pretreatment unit, an intermediate treatment unit, a post-treatment unit, and a system control unit to achieve the automated control of the entire process. It mainly focuses on process control and does not mention the extraction technology of rare earth elements.

[0006] Liu Huidong et al. published an experimental process for the combined extraction of rare metals such as Ga from the circulating fluidized bed fly ash of Chongqing Anwen Power Plant using the alkali sintering-step leaching method, but it is not applicable to the process of extracting alumina from fly ash by acid method and recovering rare earth elements.

[0007] The patent number CN109628769A discloses a method for extracting light rare earth elements from acidic solutions using ionic liquid microemulsion extraction. The rare earth elements are transferred from the acidic solution to the ionic liquid through liquid-liquid extraction, and the extraction of rare earth from the aqueous solution is achieved through centrifugal separation. The raw material used is a solution prepared with lanthanum chloride, with a relatively single composition and relatively less extraction difficulty.

[0008] For the extraction of light rare earth from wastewater raw materials with a complex composition mainly containing calcium chloride and one or more other chloride salts, the existing methods of the prior art are not applicable. Therefore, there is a need to provide an extraction system and extraction method for extracting light rare earth from industrial wastewater with a complex composition containing multiple chlorides to solve the defect that the existing technical methods are not applicable. Summary of the Invention

[0009] The object of the present invention is to provide a synergistic extraction system and extraction method for extracting light rare earth from industrial wastewater with a complex composition containing multiple chlorides to solve the technical problem that the prior art cannot extract light rare earth from such industrial wastewater, especially the industrial wastewater from the production of alumina from fly ash.

[0010] To achieve the above object, according to one aspect of the present invention, the present invention provides a co-extraction system for extracting light rare earths from industrial wastewater. The co-extraction system includes a mixed extraction system and a stripping agent. The mixed extraction system includes an extractant, an ionic liquid, and a diluent. The extractant includes one or more of bis(2-ethylhexyl) phosphate and 2-ethylhexyl 2-ethylhexyl phosphate. The ionic liquid includes one or more of methyltrioctylammonium laurate and 1-octyl-3-methylimidazolium tetrafluoroborate. The stripping agent includes hydrochloric acid.

[0011] Preferably, the diluent includes one or more selected from isooctanol, cyclohexane, and kerosene.

[0012] Preferably, the volume ratio of the ionic liquid: the extractant: the diluent is 50-70%: 20-30%: 10-20%.

[0013] According to another aspect of the present invention, the present invention provides a method for extracting light rare earths from industrial wastewater. The method uses the co-extraction system described in the above aspect of the present invention to extract light rare earths from the industrial wastewater. The industrial wastewater contains 20-30 g / L of calcium chloride and 1-4 g / L of rare earth chloride, as well as one or more of aluminum chloride, magnesium chloride, potassium chloride, sodium chloride, and lithium chloride. Preferably, the pH value of the industrial wastewater is 4-6, and more preferably, the industrial wastewater is the industrial wastewater for producing alumina from fly ash.

[0014] Preferably, the method includes the following steps:

[0015] S1: Using the mixed extraction system, centrifugally extract the industrial wastewater to obtain an organic phase containing light rare earth elements and a raffinate;

[0016] S2: Wash the organic phase with a detergent. Preferably, the detergent includes an ammonium salt, and more preferably, includes one or more of ammonium sulfate and ammonium chloride;

[0017] S3: Use the stripping agent to perform back-extraction on the washed organic phase to obtain an aqueous phase containing light rare earth elements.

[0018] Preferably, in step S1, the centrifugal extraction is carried out under the following conditions:

[0019] Centrifugal speed: 1000-2000 r / min;

[0020] Centrifugal time: 5-10 min;

[0021] Organic phase ratio O / A: 1:1-1:20, preferably 1:3-1:10;

[0022] pH value: 1-7, preferably 1.5-5;

[0023] Extraction temperature: 25 - 60°C, preferably 25 - 40°C;

[0024] Number of extraction stages: 1 - 6 stages, preferably 3 - 4 stages.

[0025] Preferably, in step S2, the washing is carried out under the following conditions:

[0026] Concentration of detergent: 1 - 10%, preferably 2 - 4%;

[0027] pH value: 1 - 7, preferably 1.5 - 5;

[0028] Washing time: 5 - 35 min, preferably 10 - 20 min;

[0029] Washing ratio O / A: 1:1 - 1:20, preferably 1:3 - 1:10;

[0030] Number of washing times: 1 - 4 times, preferably 1 - 3 times.

[0031] Preferably, in step S3, the back - extraction is carried out under the following conditions:

[0032] Number of extraction stages: 1 - 4 stages, preferably 1 - 3 stages;

[0033] Organic phase ratio O / A: 1:1 - 1:10, preferably 1:3 - 1:8;

[0034] pH value: 0.5 - 7, preferably 0.5 - 5;

[0035] Extraction temperature: 25 - 60°C, preferably 25 - 40°C;

[0036] Number of extraction stages: 1 - 6 stages, preferably 3 - 4 stages;

[0037] Concentration of stripping agent: 1 - 5 mol / L, preferably 2 - 4 mol / L.

[0038] Preferably, step S1 includes:

[0039] S1 - 1: Heat - treat the industrial wastewater until calcium chloride in the industrial wastewater crystallizes out to obtain a heat - treated product containing calcium chloride crystals;

[0040] S1 - 2: Filter the heat - treated product to obtain calcium chloride crystals and a wastewater filtrate; Wash the calcium chloride crystals with a detergent, preferably deionized water, to obtain a washing solution; Combine the washing solution and the wastewater filtrate into a mixture;

[0041] S1-3: Using the said mixed extraction system to perform the centrifugal extraction on the said mixture to obtain the said organic phase containing light rare earth elements and the said raffinate.

[0042] Preferably, the said method further includes:

[0043] S4: Adding a precipitant to the said aqueous phase containing light rare earth elements to generate light rare earth precipitates, and separating the light rare earth precipitates from the said aqueous phase. The said precipitant preferably includes oxalic acid or oxalate;

[0044] S5: Using a detergent, preferably softened water, to wash the said light rare earth precipitates, then filtering, and finally performing a calcination treatment to obtain light rare earth oxides. The temperature of the said calcination treatment is preferably 600 - 1000 °C, more preferably 800 - 950 °C, and the time of the said calcination treatment is preferably 1 - 3 h, more preferably 2 - 2.5 h.

[0045] Aiming at the technical problem that the prior art cannot extract light rare earths from industrial wastewater with complex components containing various chlorides, especially the industrial wastewater from the production of alumina from fly ash, the present invention proposes to select and use a specific co - extraction system to perform extraction and back - extraction on industrial wastewater, thereby being able to effectively extract and separate light rare earths from industrial wastewater. Specific Embodiments

[0046] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0047] In order to extract light rare earths from industrial wastewater with complex components containing various chlorides, according to one aspect of the present invention, a co - extraction system is provided. The co - extraction system includes a mixed extraction system and a back - extractant. The mixed extraction system includes an extractant, an ionic liquid, and a diluent. The extractant includes one or more of bis(2 - ethylhexyl) phosphate and 2 - ethylhexyl 2 - ethylhexyl phosphate. The ionic liquid includes one or more of methyltrioctylammonium laurate and 1 - octyl - 3 - methylimidazolium tetrafluoroborate. The back - extractant includes hydrochloric acid. By selecting specific extractants and ionic liquids as the extraction system and simultaneously matching a specific back - extractant, the present invention can achieve the efficient extraction and separation of light rare earths.

[0048] The co - extraction system of the present invention is particularly suitable for extracting light rare earths from industrial wastewater with complex components containing various chlorides. For example, when the industrial wastewater contains 20 - 30 g / L calcium chloride and 1 - 4 g / L rare earth chloride, and contains one or more of aluminum chloride, magnesium chloride, potassium chloride, sodium chloride, lithium chloride, and the pH value of the industrial wastewater is 4 - 6, the co - extraction system of the present invention is suitable for effectively extracting light rare earth elements from such industrial wastewater. Moreover, when the industrial wastewater is the industrial wastewater from the production of alumina from fly ash, the method of the present invention is particularly applicable.

[0049] Specifically, in the industrial wastewater from the production of alumina from fly ash, in addition to containing chlorides such as calcium chloride, there is also a certain amount of rare earth chloride; moreover, these rare earth chlorides involve not only light rare earth elements but also a small amount of heavy rare earth elements. The co - extraction system of the present invention selects bis(2 - ethylhexyl) phosphate and / or 2 - ethylhexyl 2 - ethylhexyl phosphate as extractants, selects methyltrioctylammonium laurate and / or 1 - octyl - 3 - methylimidazolium tetrafluoroborate as ionic liquids, forms a mixed extraction system with the two, and simultaneously selects hydrochloric acid as the stripping agent. By combining the specific mixed extraction system with the specific stripping agent, the industrial wastewater mentioned above is co - extracted, which can separate light rare earths from other chlorides and heavy rare earth elements in the industrial wastewater, and finally achieve the efficient extraction and recovery of light rare earth elements.

[0050] The light rare earth elements in the present invention refer to lanthanum, cerium, praseodymium, neodymium, promethium, samarium, and europium elements.

[0051] For the extraction of light rare earth elements, diluents commonly used in the art can be selected. For example, the diluent can be selected from one or more of alkanes or aromatics. Preferably, the alkanes are selected from one or more of heptane, octane, hexadecane, aviation kerosene, and 260# solvent kerosene, and the aromatics are selected from one or more of benzene, toluene, and xylene. Particularly preferably, for the specific extractants and ionic liquids used in the present invention, the mixed extraction system can preferably adopt one or more of isooctanol, cyclohexane, and kerosene. The addition of these diluents can reduce the specific gravity and viscosity of the extractants and ionic liquids, which is beneficial to the flow and separation of the two phases and promotes the extraction of light rare earth elements in industrial wastewater.

[0052] Preferably, in the above - mentioned mixed extraction system of the present invention, the volume ratio of ionic liquid: extractant: diluent is 50 - 70%: 20 - 30%: 10 - 20%. Within the above - mentioned ratio range, the extraction efficiency of light rare earths can be significantly increased.

[0053] According to another aspect of the present invention, there is provided a method for extracting light rare earths from industrial wastewater. This method uses the co - extraction system of the above - mentioned aspect of the present invention to extract light rare earths from industrial wastewater. The industrial wastewater contains 20 - 30 g / L of calcium chloride and 1 - 4 g / L of rare earth chlorides, as well as one or more of aluminum chloride, magnesium chloride, potassium chloride, sodium chloride, and lithium chloride. Preferably, the pH value of the industrial wastewater is 4 - 6, and more preferably, the industrial wastewater is the industrial wastewater from the production of alumina from fly ash. More preferably, the industrial wastewater is the industrial wastewater from the production of alumina from fly ash with the following elemental contents: 3 - 6 g / L of aluminum chloride, 24 - 30 g / L of calcium chloride, 1.2 - 2.2 g / L of magnesium chloride, 1.25 - 2.25 g / L of potassium chloride, 2 - 3 g / L of sodium chloride, 0.5 - 0.8 g / L of lithium chloride, 1.8 - 3.2 g / L of rare earth chlorides, and a pH value of 5 - 6. For example, the industrial wastewater is the industrial wastewater from the production of alumina from fly ash with the following elemental contents: 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, 1.8 g / L of rare earth chlorides, and a pH value of 5. Another example, the industrial wastewater is the industrial wastewater from the production of alumina from fly ash with the following elemental contents: 30 g / L of calcium chloride, 3 g / L of aluminum chloride, 1.2 g / L of magnesium chloride, 1.25 g / L of potassium chloride, 2 g / L of sodium chloride, 0.8 g / L of lithium chloride, 3.2 g / L of rare earth chlorides, and a pH value of 6.

[0054] The method of the present invention combines a specific mixed extraction system with a specific stripping agent. By using a mixed extraction system containing bis(2 - ethylhexyl) phosphate and / or 2 - ethylhexyl 2 - ethylhexyl phosphate as extractants, and methyltrioctylammonium laurate and / or 1 - octyl - 3 - methylimidazolium tetrafluoroborate as ionic liquids, and simultaneously using hydrochloric acid as the stripping agent, the method can carry out co - extraction on the above - mentioned industrial wastewater, separate light rare earths from other chlorides and heavy rare earth elements in the industrial wastewater, and finally achieve the efficient extraction and recovery of light rare earth elements.

[0055] According to a specific embodiment, the method of the present invention includes the following steps:

[0056] S1: Using the above - mentioned mixed extraction system, centrifugally extract the industrial wastewater to obtain an organic phase containing light rare earth elements and a raffinate.

[0057] S2: Wash the organic phase with a detergent. Preferably, the detergent includes ammonium salts, and more preferably, it includes one or more of ammonium sulfate and ammonium chloride.

[0058] S3: Strip the washed organic phase with a stripping agent to obtain an aqueous phase containing light rare earth elements.

[0059] In step S1, the industrial wastewater is extracted using a mixed extraction system, and the light rare earth elements can be enriched in the organic phase. The organic phase enriched with light rare earth elements is separated from the raffinate containing other components of the wastewater (other chlorides except light rare earth chlorides) by centrifugation.

[0060] Since the organic phase obtained in step S1 may contain a small amount of other chloride components in addition to the enriched light rare earth elements, in step S2, the organic phase is washed with an ammonium salt, especially ammonium sulfate or ammonium chloride, whereby these small amounts of other chloride components can be separated from the organic phase, improving the purity of the light rare earth elements in the organic phase.

[0061] In step S3, the washed organic phase is back-extracted to obtain a pure solution of light rare earths, such as a light rare earth chloride solution or a light rare earth sulfate solution.

[0062] In order to obtain an organic phase as enriched as possible with light rare earths by centrifugal extraction in S1, the operating parameters of centrifugal extraction can be appropriately adjusted. Preferably, the centrifugal extraction is carried out under the following conditions:

[0063] Centrifugal speed: 1000 - 2000 r / min;

[0064] Centrifugal time: 5 - 10 min;

[0065] Organic phase ratio O / A (i.e., volume of mixed extraction system / volume of industrial wastewater): 1:1 - 1:20, preferably 1:3 - 1:10;

[0066] pH value: 1 - 7, preferably 1.5 - 5;

[0067] Extraction temperature: 25 - 60 °C, preferably 25 - 40 °C;

[0068] Number of extraction stages: 1 - 6 stages, preferably 3 - 4 stages.

[0069] Preferably, the rotational speed of the oscillator used for extraction is 200 - 400 r / min; the extraction method is cross-flow extraction; and the raffinate enters the next stage of extraction.

[0070] During the extraction process, when the aqueous phase and the organic phase come into contact only once, a relatively complete separation is often not achieved. In actual production, several extractors are often connected in series to form cascade extraction, that is, multi-stage extraction, so that the two phases come into contact multiple times to improve the separation effect. According to the flow patterns of the aqueous phase and the organic phase, a cross-flow extraction method can be adopted. Specifically, a fresh extraction system is added to each stage. The wastewater feed liquid is added to the first stage, and then the raffinate enters the second-stage extraction (the second extractor), where it comes into contact with the fresh extraction system for extraction again. This process is carried out sequentially through several extractors until the last stage. Since a fresh extraction system is added to each stage, a better separation effect can be obtained with fewer stages.

[0071] Preferably, in step S2, the washing is carried out under the following conditions:

[0072] Detergent concentration: 1 - 10%, preferably 2 - 4%;

[0073] pH value: 1 - 7, preferably 1.5 - 5;

[0074] Washing time: 5 - 35 min, preferably 10 - 20 min;

[0075] Washing ratio O / A (i.e., organic phase volume / detergent volume): 1:1 - 1:20, preferably 1:3 - 1:10;

[0076] Number of washing times: 1 - 4 times, preferably 1 - 3 times.

[0077] Preferably, in step S3, the back-extraction is carried out under the following conditions:

[0078] Number of extraction stages: 1 - 4 stages, preferably 1 - 3 stages;

[0079] Organic phase ratio O / A (i.e., volume of washed organic phase / volume of back-extracting agent): 1:1 - 1:10, preferably 1:3 - 1:8;

[0080] pH value: 0.5 - 7, preferably 0.5 - 5;

[0081] Extraction temperature: 25 - 60 °C, preferably 25 - 40 °C;

[0082] Number of extraction stages: 1 - 6 stages, preferably 3 - 4 stages;

[0083] Concentration of back-extracting agent: 1 - 5 mol / L, preferably 2 - 4 mol / L.

[0084] In step S3, cross-flow extraction is also preferably adopted for back-extraction.

[0085] Since industrial wastewater contains a relatively large amount of calcium chloride, for example, the content is 20 - 30 g / L. In order to further improve the extraction and recovery efficiency of light rare earths, the industrial wastewater can be heated before extraction to crystallize out calcium chloride. Therefore, according to a specific embodiment of the present invention, step S1 of the above method may include the following sub-steps: S1-1: Heat the industrial wastewater until calcium chloride in the industrial wastewater crystallizes out to obtain a heated product containing calcium chloride crystals; S1-2: Filter the heated product to obtain calcium chloride crystals and wastewater filtrate; Use a detergent, preferably deionized water, to wash the calcium chloride crystals to obtain a washing solution; Combine the washing solution and the wastewater filtrate into a mixture; S1-3: Use the mixed extraction system to perform centrifugal extraction on the mixture to obtain an organic phase containing light rare earth elements and a raffinate.

[0086] In the above method, since a small amount of light rare earth elements may be adsorbed on the calcium chloride crystals precipitated in step S1-1, the calcium chloride crystals can be washed with a detergent such as deionized water in step S1-2 to elute the light rare earth elements and other possible adsorbed wastewater components into the washing solution. The washing solution, together with the wastewater filtrate, is used for subsequent light rare earth extraction, thereby improving the recovery rate of light rare earth elements.

[0087] In the above step S1-1, the temperature of the heat treatment is preferably 60 - 120 °C. At this temperature, the industrial wastewater can be evaporated until calcium chloride precipitates, and the crystallization precipitation rate of calcium chloride is, for example, 20 - 50%. In the above step S1-2, the washing ratio of the crystals (calcium chloride crystals / deionized water) is preferably 1:0.5 - 1:5.

[0088] According to a specific embodiment of the present invention, after steps S1 - S3, the method further includes the following steps:

[0089] S4: Add a precipitant to the aqueous phase containing light rare earth elements to form light rare earth precipitates, and separate the light rare earth precipitates from the aqueous phase. The precipitant preferably includes oxalic acid or oxalate;

[0090] S5: Use a detergent, preferably softened water, to wash the light rare earth precipitates, then filter, and finally perform a calcination treatment to obtain light rare earth oxides. The temperature of the calcination treatment is preferably 600 - 1000 °C, more preferably 800 - 950 °C, and the time of the calcination treatment is preferably 1 - 3 h, more preferably 2 - 2.5 h.

[0091] In the above step S4, preferably, the addition amount of oxalic acid or oxalate as the precipitant is 1 - 1.5 times the theoretical value (measured value) of rare earth ions in terms of oxalate radical. In the above step S4, to separate the light rare earth precipitates from the aqueous phase, a filtration method is used, preferably vacuum filtration or centrifugal filtration.

[0092] The co - extraction system and light rare earth extraction method provided by the present invention are applicable to extracting and recovering light rare earths from industrial wastewater with complex components containing various chlorides with high recovery rates and high purity. The method of the present invention is simple to operate and is particularly applicable to enriching and recovering light rare earths from industrial wastewater produced in the production of alumina from fly ash, providing a new way for the high - value utilization of fly ash.

[0093] Specifically, the co - extraction system and light rare earth extraction method of the present invention have the following advantages and positive effects:

[0094] (1) The present invention first proposes a method for extracting light rare earth elements from industrial wastewater with complex compositions (containing various chlorides, more specifically, containing a relatively large amount (20 - 30 g / L) of calcium chloride and one or more chlorides selected from aluminum chloride, magnesium chloride, potassium chloride, sodium chloride, and lithium chloride).

[0095] (2) The present invention combines an extractant with an ionic liquid to form a mixed extraction system, realizing the efficient separation of light rare earths from heavy rare earths and impurity elements.

[0096] (3) The method for extracting light rare earth elements of the present invention is simple and easy to operate, greatly improving the recovery rate and purity of rare earths. The recovery rate preferably can reach more than 80%, even more than 90%, and the purity of the obtained rare earth oxide is preferably greater than 97%, even greater than 98%.

[0097] (4) The present invention provides a new way for the high - value utilization of fly ash and provides new technical support for the progress of the rare earth industry.

[0098] The beneficial effects of the present invention will be further illustrated below with reference to the examples.

[0099] Example 1

[0100] In Example 1, the raw materials used come from industrial wastewater produced in the acid - method production of alumina from fly ash. After testing, it contains 24 g / L of calcium chloride, 6 g / L of aluminum 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, 1.8 g / L of rare earth chloride, and the pH value is 5.

[0101] The light rare earths are extracted from the above - mentioned industrial wastewater through the following steps:

[0102] Wastewater concentration: The above - mentioned wastewater is heated and evaporated at 80 °C until calcium chloride precipitates. The crystallization precipitation rate of calcium chloride is 40%. The calcium chloride crystals are filtered and separated, and deionized water is used to wash the calcium chloride crystals. The washing liquid and the wastewater filtrate are combined for extracting light rare earths. The washing ratio of the crystals (crystals / water) is 1:5;

[0103] Extraction and enrichment of light rare earths: The light rare earths in the above-mentioned combined feed liquid are extracted and enriched using a mixed extraction system composed of an extractant + ionic liquid + diluent. After centrifugal separation, an organic phase loaded with light rare earths and a raffinate are obtained. The centrifugal speed is 1000 r / min and the centrifugal time is 10 min. The mixed extraction system is methyltrioctylammonium laurate ([N1888][LA]): P507 (2-ethylhexyl phosphoric acid 2-ethylhexyl ester): isooctanol at 70%:20%:10%. The organic phase ratio (O / A) is 1:5, the pH value is 4, the extraction temperature is 40 °C, the number of extraction stages is 3, the rotation speed of the oscillator is 200 r / min, and the extraction method is cross-flow extraction. The raffinate enters the next extraction stage.

[0104] Washing of the organic phase: The organic phase is washed with ammonium chloride. The ammonium chloride concentration is 4%, the pH value is 4, the washing time is 5 min, the washing ratio (O / A) is 1:5, and the number of washing times is 1.

[0105] Back-extraction of the organic phase: Hydrochloric acid is used as the back-extraction agent to back-extract the light rare earth organic phase to obtain a solution of pure light rare earth chlorides. The organic phase ratio (O / A) is 1:8, the pH value is 5, the extraction temperature is 45 °C, the number of extraction stages is 3, and the concentration of the back-extraction agent is 2 mol / L.

[0106] Precipitation of light rare earths: Oxalic acid is added to the solution containing pure light rare earth chlorides to form light rare earth oxalate precipitates. The amount of oxalate added is 1.0 times the theoretical value of the light rare earth ions.

[0107] Filtration of oxalate precipitates: The above-mentioned precipitates are filtered using a filtration device. Vacuum filtration is used for filtration.

[0108] Preparation of light rare earth oxides: The light rare earth precipitates obtained by the above filtration are washed with softened water, then filtered, and then calcined at 800 °C for 2 h to obtain rare earth oxides.

[0109] Example 2

[0110] In Example 2, the raw materials used are from the industrial wastewater of alumina production by the acid method from fly ash. After detection, it contains 30 g / L of calcium chloride, 3 g / L of aluminum chloride, 1.2 g / L of magnesium chloride, 1.25 g / L of potassium chloride, 2 g / L of sodium chloride, 0.8 g / L of lithium chloride, 3.2 g / L of rare earth chlorides, and the pH value is 6.

[0111] The light rare earths are extracted from the above industrial wastewater through the following steps:

[0112] Concentration of wastewater: The above wastewater is heated and evaporated at 80 °C until calcium chloride precipitates. The crystallization precipitation rate of calcium chloride is 30%. The calcium chloride crystals are filtered and separated, and the calcium chloride crystals are washed with deionized water. The washing liquid and the wastewater filtrate are combined for the extraction of light rare earths. The washing ratio of the crystals (crystals / water) is 1:5.

[0113] Extraction and enrichment of light rare earths: The light rare earths in the above-mentioned combined feed liquid are extracted and enriched using a mixed extraction system composed of an extractant + ionic liquid + diluent. After centrifugal separation, an organic phase loaded with light rare earths and a raffinate are obtained. The centrifugal speed is 2000 r / min, and the centrifugal time is 5 min. The mixed extraction system is methyltrioctylammonium laurate ([N1888][LA]): bis(2-ethylhexyl) phosphate (P204): cyclohexane at 60%:30%:10%. The organic-to-aqueous ratio (O / A) is 1:5, the pH value is 4, the extraction temperature is 40 °C, the number of extraction stages is 3, the rotation speed of the oscillator is 200 r / min, and the extraction method is cross-flow extraction. The raffinate enters the next extraction stage.

[0114] Washing of the organic phase: The organic phase is washed with ammonium chloride. The ammonium chloride concentration is 4%, the pH value is 4, the washing time is 5 min, the washing ratio (O / A) is 1:5, and the number of washing times is 1.

[0115] Back-extraction of the organic phase: Hydrochloric acid is used as the back-extraction agent to back-extract the light rare earth organic phase to obtain a solution of pure light rare earth chlorides. The organic-to-aqueous ratio (O / A) is 1:5, the pH value is 5, the extraction temperature is 25 °C, the number of extraction stages is 3, and the concentration of the back-extraction agent is 2 mol / L.

[0116] Precipitation of light rare earths: Oxalic acid is added to the solution containing pure light rare earth chlorides to form light rare earth oxalate precipitate. The amount of oxalate added is 1.2 times the theoretical value of the light rare earth ions.

[0117] Filtration of the oxalate precipitate: The above-mentioned precipitate is filtered using a filtration device. Centrifugal filtration is used for filtration.

[0118] Preparation of light rare earth oxides: The rare earth precipitate obtained by the above filtration is washed with softened water, then filtered, and then calcined at 800 °C for 2 h to obtain rare earth oxides.

[0119] Example 3

[0120] The industrial wastewater raw materials used are the same as those in Example 1.

[0121] The method for extracting light rare earths from industrial wastewater is basically the same as that in Example 1, except that:

[0122] In the extraction and enrichment of light rare earths, the mixed extraction system is 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIM]BF4): P507 (2-ethylhexyl 2-ethylhexyl phosphate): isooctanol, and the ratio is 70%:20%:10%.

[0123] Example 4

[0124] The industrial wastewater raw materials used are the same as those in Example 1.

[0125] The method for extracting light rare earths from industrial wastewater is basically the same as that of Example 1, except that:

[0126] In the extraction and enrichment of light rare earths, the mixed extraction system is methyltrioctylammonium laurate ([N1888][LA]): P507 (2-ethylhexyl 2-ethylhexylphosphate): kerosene, and the ratio is 70%:20%:10%.

[0127] Example 5

[0128] The industrial wastewater raw material used is the same as that of Example 1.

[0129] The method for extracting light rare earths from industrial wastewater is basically the same as that of Example 1, except that:

[0130] In the extraction and enrichment of light rare earths, the mixed extraction system is methyltrioctylammonium laurate ([N1888][LA]): P507 (2-ethylhexyl 2-ethylhexylphosphate): isooctanol, and the ratio is 50%:30%:20%.

[0131] Example 6

[0132] The industrial wastewater raw material used is the same as that of Example 1.

[0133] The method for extracting light rare earths from industrial wastewater is basically the same as that of Example 1, except that:

[0134] In the extraction and enrichment of light rare earths, the mixed extraction system is methyltrioctylammonium laurate ([N1888][LA]): P507 (2-ethylhexyl 2-ethylhexylphosphate): isooctanol, and the ratio is 40%:10%:50%.

[0135] Example 7

[0136] The industrial wastewater raw material used is the same as that of Example 1.

[0137] The method for extracting light rare earths from industrial wastewater is basically the same as that of Example 1, except that the initial wastewater concentration step is omitted.

[0138] Example 8

[0139] The industrial wastewater raw material used is the same as that of Example 1.

[0140] The method for extracting light rare earths from industrial wastewater is basically the same as that of Example 1, except that in the step of extracting and enriching light rare earths, the organic phase ratio O / A is 1:1.

[0141] Example 9

[0142] The industrial wastewater raw material used is the same as that in Example 1.

[0143] The method for extracting light rare earths from industrial wastewater is basically the same as that in Example 1, except that: in the step of extracting and enriching light rare earths, the organic phase ratio O / A is 1:20.

[0144] Example 10

[0145] The industrial wastewater raw material used is the same as that in Example 1.

[0146] The method for extracting light rare earths from industrial wastewater is basically the same as that in Example 1, except that: in the step of extracting and enriching light rare earths, the organic phase ratio O / A is 1:25.

[0147] Example 11

[0148] The industrial wastewater raw material used is the same as that in Example 1.

[0149] The method for extracting light rare earths from industrial wastewater is basically the same as that in Example 1, except that: in the step of stripping the organic phase, the organic phase ratio O / A is 1:1.

[0150] Example 12

[0151] The industrial wastewater raw material used is the same as that in Example 1.

[0152] The method for extracting light rare earths from industrial wastewater is basically the same as that in Example 1, except that: in the step of stripping the organic phase, the organic phase ratio O / A is 1:10.

[0153] Example 13

[0154] The industrial wastewater raw material used is the same as that in Example 1.

[0155] The method for extracting light rare earths from industrial wastewater is basically the same as that in Example 1, except that: in the step of stripping the organic phase, the organic phase ratio O / A is 2:1.

[0156] Comparative Example 1

[0157] The industrial wastewater raw material used is the same as that in Example 1.

[0158] The method for extracting light rare earths from industrial wastewater is basically the same as that in Example 1, except that:

[0159] In the step of extracting and enriching light rare earths, methyltrioctylammonium nitrate and bis(2-ethylhexyl) 2-ethylhexylphosphonate combined with isooctanol (70%:20%:10%) are used as a mixed extraction system.

[0160] Comparative Example 2

[0161] The industrial wastewater raw materials used are the same as those in Example 1.

[0162] The method for extracting light rare earths from industrial wastewater is basically the same as that in Example 1, except that:

[0163] In the organic phase stripping step, NaOH is used as the stripping agent.

[0164] Results and Discussion

[0165] Using the ICP-OES determination method, the products obtained in the above Examples 1-13 and Comparative Examples 1-2 were measured and analyzed, and the extraction rate and purity results of light rare earth elements in industrial wastewater were calculated.

[0166] In Table 1 below, the extraction rate and purity results of light rare earth elements in the above Examples 1-13 and Comparative Examples 1-2 are listed.

[0167]

[0168]

[0169] By comparing the results of Examples 1-13 with those of Comparative Examples 1-2, it can be seen that the present invention significantly improves the extraction rate and recovery purity of light rare earth elements by co-extracting industrial wastewater raw materials with specific ionic liquids (methyltrioctylammonium laurate or 1-octyl-3-methylimidazolium tetrafluoroborate) and extractants (bis(2-ethylhexyl)phosphoric acid or 2-ethylhexyl 2-ethylhexyl phosphate) and combining with a specific stripping agent (hydrochloric acid), compared with other co-extraction systems.

[0170] By comparing Example 1, Example 5 and Example 6, it can be found that when the ratio range of the ionic liquid: extractant: diluent in the present invention is set at 50-70%: 20-30%: 10-20%, it can promote the extraction efficiency of the mixed extraction system in the present invention and further improve the extraction rate and recovery purity of light rare earth elements in industrial wastewater.

[0171] By comparing Example 1 and Example 7, it can be found that by heating and concentrating the industrial wastewater before the step of extracting and enriching light rare earths in the present invention, specifically reducing the content of impurities such as calcium chloride rich in the industrial wastewater, it can help further improve the final extraction rate and recovery purity of light rare earth elements in the method of the present invention.

[0172] By comparing Example 1, Example 8, Example 9 and Example 10, it can be found that when the organic phase ratio in the step of extracting and enriching light rare earths in the present invention is set at 1:1-1:20, it can promote the extraction efficiency of the mixed extraction system in the present invention and further improve the extraction rate and recovery purity of light rare earth elements in industrial wastewater.

[0173] By comparing Example 1, Example 11, Example 12 and Example 13, it can be found that when the organic phase ratio in the organic back-extraction step of the present invention is set to 1:1 to 1:10, the back-extraction efficiency of the present invention can be promoted, and the extraction rate and recovery purity of light rare earth elements in industrial wastewater can be further improved.

[0174] From the result analysis of the examples and comparative examples, it can be seen that the co-extraction system and extraction method for extracting light rare earth elements from industrial wastewater with complex components of the present invention can extract and recover light rare earth elements more effectively compared with the existing co-extraction systems and extraction methods. The extraction recovery rate and purity of light rare earths are greatly improved. The extraction recovery rate reaches more than 80%, even more than 90%, and the purity of the obtained rare earth oxide can be greater than 97%, even greater than 98%.

[0175] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for extracting light rare earths from industrial wastewater, characterized in that, the method uses a co-extraction system to extract light rare earths from the industrial wastewater, the pH value of the industrial wastewater is 4-6, the industrial wastewater is the industrial wastewater from the production of alumina from fly ash, the industrial wastewater contains 20-30 g / L calcium chloride and 1-4 g / L rare earth chloride, and one or more of aluminum chloride, magnesium chloride, potassium chloride, sodium chloride, and lithium chloride. The co-extraction system includes a mixed extraction system and a stripping agent. The mixed extraction system includes an extractant, an ionic liquid, and a diluent. The extractant includes one or more of bis(2-ethylhexyl) phosphate and 2-ethylhexyl 2-ethylhexyl phosphate. The ionic liquid includes one or more of methyltrioctylammonium laurate and 1-octyl-3-methylimidazolium tetrafluoroborate. The stripping agent includes hydrochloric acid. The diluent includes one or more selected from isooctanol, cyclohexane, and kerosene. The volume ratio of the ionic liquid: the extractant: the diluent is 50-70%: 20-30%: 10-20%. The method includes the following steps: S1: Using the mixed extraction system, centrifugally extract the industrial wastewater to obtain an organic phase containing light rare earth elements and a raffinate; S2: Wash the organic phase with a detergent, and the detergent includes an ammonium salt; S3: Use the stripping agent to perform back-extraction on the washed organic phase to obtain an aqueous phase containing light rare earth elements. Step S1 includes: S1-1: Heat-treat the industrial wastewater until the calcium chloride in the industrial wastewater crystallizes out to obtain a heated product containing calcium chloride crystals; S1-2: Filter the heated product to obtain calcium chloride crystals and a wastewater filtrate; wash the calcium chloride crystals with a detergent to obtain a washing solution; combine the washing solution and the wastewater filtrate into a mixture; S1-3: Use the mixed extraction system to perform the centrifugal extraction on the mixture to obtain the organic phase containing light rare earth elements and the raffinate.

2. The method according to claim 1, characterized in that, the detergent in step S2 includes one or more of ammonium sulfate and ammonium chloride.

3. The method according to claim 1, characterized in that, in step S1, the centrifugal extraction is carried out under the following conditions: Centrifugal speed: 1000-2000 r / min; Centrifugal time: 5-10 min; Organic phase ratio O / A: 1:1-1:20; pH value: 1-7; Extraction temperature: 25-60 °C; Extraction stage: 1-6 stages.

4. The method according to claim 1, characterized in that, in step S2, the washing is carried out under the following conditions: Detergent concentration: 1-10%; pH value: 1-7; Washing time: 5-35 min; Washing ratio O / A: 1:1-1:20; Number of washing times: 1-4 times.

5. The method according to claim 1, characterized in that, in step S3, the back-extraction is carried out under the following conditions: Extraction stage: 1-4 stages; Organic phase ratio O / A: 1:1 to 1:10; pH value: 0.5 to 7; Extraction temperature: 25 to 60 °C; Number of extraction stages: 1 to 6 stages; Concentration of stripping agent: 1 to 5 mol / L.

6. The method according to claim 1, characterized in that, the detergent described in step S1-2 is deionized water.

7. The method according to claim 1, characterized in that, the method further includes: S4: adding a precipitating agent to the aqueous phase containing light rare earth elements to form a light rare earth precipitate, and separating the light rare earth precipitate from the aqueous phase; S5: washing the light rare earth precipitate with a detergent, then filtering, and finally performing a calcination treatment to obtain light rare earth oxide, the temperature of the calcination treatment is 600 to 1000 °C, and the time of the calcination treatment is 1 to 3 h.

8. The method according to claim 7, characterized in that, the precipitating agent described in step S4 includes oxalic acid or oxalate, and the detergent described in step S5 is softened water.

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