Method for Separating Cerium from Fly Ash Industrial Wastewater and Method for Preparing High-Purity Cerium Oxide

Abstract

The present invention provides a method for separating cerium from fly ash industrial wastewater and a method for preparing high-purity cerium oxide. The method for separating cerium comprises the following steps: extracting fly ash industrial wastewater with a diluted extractant to obtain a rare earth organic phase, back-extracting with a back-extraction agent to obtain a rare earth back-extraction solution, adjusting the pH of the rare earth back-extraction solution to 0.5-1.5, and then oxidizing with an oxidizing agent to obtain a cerium-containing precipitate. The present invention first proposes a method for separating cerium from the industrial wastewater of acid leaching of fly ash and preparing high-purity cerium oxide, which can effectively reduce the extraction burden of other rare earths in the subsequent process and reduce the production cost while separating the cerium-containing material; the method is simple and easy to operate, the recovery rate of cerium can reach more than 95%, which is convenient for subsequent utilization, and the separated cerium can be used to prepare high-purity cerium oxide with a purity greater than 99.9%, which is more suitable for industrial mass production and provides a new way for the high-value utilization of fly ash.

Description

Technical Field

[0001] The present invention relates to the technical field of trace rare earth recovery, and in particular, to a method for separating cerium from fly ash industrial wastewater and a method for preparing high-purity cerium oxide. Background Art

[0002] The content of valuable elements in the inorganic components of coal in the Jungar mining area is relatively high, containing abundant aluminum, gallium, lithium and rare earths, all of which are important resources for the national economy. Among them, the content of Al 2 O 3 is 50-60%, the total rare earth content is 0.09-0.12%, and the light rare earths in the rare earths account for more than 90%, among which cerium accounts for 70% of the total rare earth content. During the process of acid method for producing alumina, these valuable elements will be enriched in the aluminum extraction wastewater. Usually, cerium can be removed by chemical process method before rare earth separation, thereby simplifying the separation of other rare earth resources. This can reduce the resource consumption of the factory feed by 50%, thus reducing the investment cost and operation cost of the factory. The separated cerium oxide product can be used in the industry to produce glass polishing materials.

[0003] However, since the chemical composition and phase composition of fly ash produced in the Jungar mining area are different from those of existing rare earth deposits, the existing rare earth element extraction methods are not applicable to the extraction of rare earths from fly ash in this mining area. So far, there are few research reports on the extraction of rare earth elements from fly ash, and there are even fewer literature on the separation of cerium element. Moreover, the raw materials used in the test process are mostly solutions prepared in the laboratory, and the elements in the slurry are relatively single, and the recovery difficulty is small, which cannot be applied to industrial large-scale production for the separation of cerium and the preparation of high-purity cerium oxide. In addition, the composition of the industrial wastewater from the acid method for producing alumina from fly ash is more complex than the raw materials used in other existing technologies. Therefore, it is necessary to study a new method for separating and enriching rare earth elements, especially cerium, in the industrial wastewater from the acid method for producing alumina from fly ash, and to prepare high-purity cerium oxide. Summary of the Invention

[0004] The main object of the present invention is to provide a method for separating cerium from fly ash industrial wastewater and a method for preparing high-purity cerium oxide, so as to solve the problems in the prior art that it is difficult to separate cerium from the industrial wastewater of acid method for extracting aluminum from fly ash, and the purity of the prepared cerium oxide is relatively low.

[0005] To achieve the above object, according to one aspect of the present invention, a method for separating cerium from fly ash industrial wastewater is provided. The method includes the following steps: Step S1, using a diluted extractant to extract the fly ash industrial wastewater to obtain a rare earth organic phase; Step S2, using a stripping agent to strip the rare earth organic phase to obtain a rare earth stripping solution; Step S3, adjusting the pH of the rare earth stripping solution to 0.5 - 1.5, and then using an oxidant for oxidation to obtain a cerium-containing precipitate; wherein, the solutes in the fly ash industrial wastewater include aluminum chloride, calcium chloride, magnesium chloride, potassium chloride, sodium chloride, lithium chloride, and rare earth chlorides, and the rare earth chlorides at least include cerium chloride; the oxidant is one or more of ozone, hydrogen peroxide, and sodium hypochlorite.

[0006] Further, in Step S3, the molar ratio of the oxidant to cerium in the fly ash industrial wastewater is (1.0 - 1.5):1; preferably, during the oxidation process, the oxidation temperature is controlled at 40 - 60°C, and the oxidation time is 0.5 - 2 h.

[0007] Further, in Step S1, in the diluted extractant, the extractant is one or more of P204, P507, P350, TBP, N1923, and N263, and the diluent is one or more of isooctanol, kerosene, and n-hexane; preferably, the volume ratio of the extractant to the diluent is 1:1 - 1:5; more preferably, the extractant is N1923 and / or TBP; in Step S2, the stripping agent is one or more of ammonium chloride, sulfuric acid, nitric acid, and hydrochloric acid, preferably, the concentration of the stripping agent is 1 - 5 mol / L, more preferably 2 - 4 mol / L.

[0008] Further, in Step S1, the extraction method is cross-flow extraction, and the volume ratio of the diluted extractant to the fly ash industrial wastewater is 1:1 - 1:20, the pH value of the extraction system is 1 - 7, the number of extraction stages is 1 - 6, and the extraction temperature is 25 - 60°C; preferably, the volume ratio of the diluted extractant to the fly ash industrial wastewater is 1:3 - 1:10, the pH value of the extraction system is 1.5 - 5, the number of extraction stages is 3 - 4, and the extraction temperature is 25 - 40°C; in Step S2, the stripping method is cross-flow stripping, and the volume ratio of the stripping agent to the rare earth organic phase is 1:1 - 1:10, the pH value of the stripping system is 0.5 - 7, the number of stripping stages is 1 - 4, and the stripping temperature is 25 - 60°C; preferably, the volume ratio of the stripping agent to the rare earth organic phase is 1:3 - 1:8, the pH value of the stripping system is 0.5 - 5, the number of stripping stages is 1 - 3, and the stripping temperature is 25 - 40°C.

[0009] Further, Step S3 also includes a step of washing the cerium-containing precipitate with water having a pH of 1 - 3 and a volume 2 - 8 times that of the precipitate, and the washing time is 10 - 40 min.

[0010] Furthermore, the component contents of the fly ash industrial wastewater are as follows: aluminum chloride 5 - 7 g / L, calcium chloride 22 - 26 g / L, magnesium chloride 2.0 - 2.4 g / L, potassium chloride 2.2 - 2.3 g / L, sodium chloride 2.8 - 3.2 g / L, lithium chloride 0.4 - 0.6 g / L, and rare earth chloride 1.5 - 2.1 g / L.

[0011] According to another aspect of the present invention, a method for preparing high-purity cerium oxide is provided, including the following steps: Step L1, performing a first calcination on the cerium-containing precipitate prepared by the preparation method of the present invention to obtain crude cerium oxide; then mixing the crude cerium oxide with an inorganic acid and heating for dissolution to obtain a cerium-containing solution; Step L2, adding oxalic acid to the cerium-containing solution to obtain cerium oxalate precipitate; Step L3, performing a second calcination on the cerium oxalate precipitate to obtain high-purity cerium oxide; wherein, the purity of the high-purity cerium oxide is greater than 99.9%.

[0012] Furthermore, in Step L1, the temperature of the first calcination is 600 - 1000 °C, preferably 800 - 950 °C; the time of the first calcination is 1 - 3 h, preferably 2 - 2.5 h; during the heating and dissolution process, the temperature is raised to 90 - 160 °C and dissolved for 2 - 5 h; preferably, the weight ratio of the crude cerium oxide to the inorganic acid is 1:(0.5 - 3).

[0013] Furthermore, in Step L2, the weight ratio of oxalic acid to cerium in the cerium-containing solution is (1.0 - 2.2):1.

[0014] Furthermore, in Step L3, first wash the cerium oxalate precipitate with softened water having a volume 2 - 5 times that of the precipitate, and then perform the second calcination; preferably, the temperature of the second calcination is 600 - 1000 °C, preferably 800 - 950 °C; the time of the second calcination is 1 - 3 h, preferably 2 - 2.5 h.

[0015] Applying the method for separating cerium from the industrial wastewater of acid leaching aluminum from fly ash and preparing high-purity cerium oxide first proposed by the present invention, oxidizing the cerium element in the fly ash industrial wastewater with a complex composition under acidic conditions using a suitable oxidant can oxidize trivalent cerium ions to tetravalent. Utilizing the chemical property differences between tetravalent cerium and trivalent rare earth elements, the cerium element can preferentially precipitate in the form of cerium hydroxide. Thus, while obtaining the cerium-containing material, the extraction burden of other rare earths in the subsequent process can be effectively reduced, and the production cost can be lowered. This method is simple and easy to operate, the recovery rate of cerium can reach more than 95%, which is convenient for subsequent utilization. Moreover, the separated cerium can be used to prepare high-purity cerium oxide with a purity greater than 99.9%, which is more suitable for industrial mass production and provides a new way for the high-value utilization of fly ash. Specific Embodiments

[0016] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0017] As described in the background art of the present invention, it is difficult to separate cerium from the industrial wastewater of acid leaching aluminum from fly ash and the purity of the prepared cerium oxide is relatively low. To solve the above problems, in a typical embodiment of the present invention, a method for separating cerium from fly ash industrial wastewater is provided, including the following steps: Step S1, using a diluted extractant to extract the fly ash industrial wastewater to obtain a rare earth organic phase; Step S2, using a stripping agent to strip the rare earth organic phase to obtain a rare earth stripping solution; Step S3, adjusting the pH of the rare earth stripping solution to 0.5-1.5, and then using an oxidant for oxidation to obtain a cerium-containing precipitate; wherein, the solutes in the fly ash industrial wastewater include aluminum chloride, calcium chloride, magnesium chloride, potassium chloride, sodium chloride, lithium chloride and rare earth chlorides, and the rare earth chlorides include at least cerium chloride; the oxidant is one or more of ozone, hydrogen peroxide and sodium hypochlorite.

[0018] The industrial wastewater of acid leaching aluminum from fly ash has a complex composition, and its solutes include various impurities such as aluminum chloride, calcium chloride, magnesium chloride, potassium chloride, sodium chloride, lithium chloride and rare earth chlorides. The rare earth chlorides include at least cerium chloride. The conventional extraction method is easily affected by many impurities, resulting in difficult separation of cerium. In view of the above situation, the present invention first uses a diluted extractant to extract the fly ash industrial wastewater, so that each rare earth element enters the loaded organic phase to obtain a rare earth organic phase; then uses a stripping agent to strip the rare earth organic phase, so that each trivalent rare earth ion enters the stripping aqueous phase to obtain a rare earth stripping solution; finally, adjusts the pH of the rare earth stripping solution to 0.5-1.5, and selectively oxidizes it with an oxidant such as ozone, hydrogen peroxide or sodium hypochlorite under acidic conditions to oxidize trivalent cerium ions to tetravalent, and then utilizes the chemical property difference between tetravalent cerium and other trivalent rare earth elements, so that the cerium element preferentially precipitates in the form of cerium hydroxide to obtain a cerium-containing precipitate, realizing the separation and enrichment of cerium and other rare earth elements. Thus, while separating the cerium-containing material, the extraction pressure of other rare earths in the subsequent process can be effectively reduced, and the production cost can be reduced. This method is simple and easy to operate, and the recovery rate of cerium can reach more than 95%. It is convenient to prepare high-purity cerium oxide using the separated cerium subsequently, and it is more suitable for industrial mass production, providing a new way for the high-value utilization of fly ash.

[0019] In order to completely oxidize trivalent cerium to tetravalent cerium, in a preferred embodiment, in step S3, the molar ratio of the oxidant to cerium in the fly ash industrial wastewater is (1.0 - 1.5):1, so as to better control the oxidation degree of the rare earth stripping solution. While oxidizing trivalent cerium, the oxidation of other impurity ions can be reduced; at the same time, while further increasing the oxidation rate, the waste of the oxidant can be avoided. Specifically, during the preferred oxidation process, the oxidation temperature is controlled at 40 - 60 °C, and the oxidation time is 0.5 - 2 h, which can better control the oxidation process.

[0020] As mentioned above, the industrial wastewater from the acid leaching of fly ash for aluminum extraction is complex, and the content of impurities other than rare earths is relatively high. Therefore, in a preferred embodiment, in step S1, in the diluted extractant, the extractant is one or more of P204, P507, P350, TBP, N1923, and N263, and the diluent is one or more of isooctanol, kerosene, and n - hexane; preferably, the volume ratio of the extractant to the diluent is 1:1 - 1:5; more preferably, the extractant is N1923 and / or TBP; in step S2, the stripping agent is one or more of ammonium chloride, sulfuric acid, nitric acid, and hydrochloric acid. Preferably, the concentration of the stripping agent is 1 - 5 mol / L, and more preferably 2 - 4 mol / L. The above extraction system and stripping system can more specifically extract and strip the industrial wastewater from the acid leaching of fly ash for aluminum extraction. The extraction efficiency of the system is less affected by the high - content impurity ions in the industrial wastewater, and the separation efficiency of rare earth cerium can be further improved.

[0021] In the specific extraction process, preferably in step S1, the extraction method is cross - flow extraction, and the volume ratio of the diluted extractant to the fly ash industrial wastewater is 1:1 - 1:20, the pH value of the extraction system is 1 - 7, the number of extraction stages is 1 - 6, and the extraction temperature is 25 - 60 °C; preferably, the volume ratio of the diluted extractant to the fly ash industrial wastewater is 1:3 - 1:10, the pH value of the extraction system is 1.5 - 5, the number of extraction stages is 3 - 4, and the extraction temperature is 25 - 40 °C, so that the rare earth elements can enter the loaded organic phase more fully and be separated from other impurities. Preferably in step S2, the stripping method is cross - flow extraction, and the volume ratio of the stripping agent to the rare earth organic phase is 1:1 - 1:10, the pH value of the stripping system is 0.5 - 7, the number of extraction stages is 1 - 4, and the extraction temperature is 25 - 60 °C; preferably, the volume ratio of the stripping agent to the rare earth organic phase is 1:3 - 1:8, the pH value of the stripping system is 0.5 - 5, the number of extraction stages is 1 - 3, and the extraction temperature is 25 - 40 °C, so that the rare earth elements can enter the stripping aqueous phase more fully and exist in the form of ions, facilitating the subsequent oxidation step.

[0022] In order to further improve the separation effect of rare earth cerium, in a preferred embodiment, step S3 further includes a step of washing the cerium-containing precipitate with water having a pH of 1 to 3 and a volume 2 to 8 times that of the precipitate for 10 to 40 minutes, so as to more fully remove some water-soluble impurities.

[0023] As described above, the composition of fly ash industrial wastewater is complex. To enhance the practicability of the present invention, in a preferred embodiment, the content of each component in the fly ash industrial wastewater is as follows: aluminum chloride 5 - 7 g / L, calcium chloride 22 - 26 g / L, magnesium chloride 2.0 - 2.4 g / L, potassium chloride 2.2 - 2.3 g / L, sodium chloride 2.8 - 3.2 g / L, lithium chloride 0.4 - 0.6 g / L, rare earth chloride 1.5 - 2.1 g / L, which is more suitable for using the method of the present invention to separate rare earth cerium.

[0024] In another typical embodiment of the present invention, a method for preparing high-purity cerium oxide is further provided, including the following steps: Step L1, first roasting the cerium-containing precipitate obtained by using the separation method of the present invention to obtain crude cerium oxide; then mixing the crude cerium oxide with an inorganic acid and raising the temperature for dissolution to obtain a cerium-containing solution; Step L2, adding oxalic acid to the cerium-containing solution to obtain cerium oxalate precipitate; Step L3, second roasting the cerium oxalate precipitate to obtain high-purity cerium oxide; wherein, the purity of the high-purity cerium oxide is greater than 99.9%.

[0025] In the cerium-containing precipitate obtained by using the method of the present invention to extract rare earth cerium, there are fewer impurities. Therefore, the above method can be used to prepare high-purity cerium oxide. At this time, first roast the cerium-containing precipitate to obtain crude cerium oxide, then add an inorganic acid for high-temperature dissolution, so that tetravalent cerium can be dissolved into the solution to obtain a cerium-containing solution; subsequently, add oxalic acid to the cerium-containing solution to precipitate tetravalent cerium to obtain cerium oxalate precipitate; finally, roast the cerium oxalate precipitate to obtain high-purity cerium oxide with a purity greater than 99.9%. This preparation method is more simple and feasible, there are fewer impurities in the oxalic acid precipitate, and the cerium oxide obtained by two-step roasting has a higher purity.

[0026] Specifically, in a preferred embodiment, in step L1, the first roasting temperature is 600 - 1000 °C, preferably 800 - 950 °C, and the first roasting time is 1 - 3 h, preferably 2 - 2.5 h; during the temperature-raising dissolution process, raise the temperature to 90 - 160 °C and dissolve for 2 - 5 h; preferably, the weight ratio of crude cerium oxide to the inorganic acid is 1:(0.5 - 3), and the inorganic acid can be hydrochloric acid or sulfuric acid. The above reaction parameters can more fully dissolve the tetravalent cerium in the previously obtained cerium-containing precipitate and perform preliminary purification. To further simplify the operation steps and reduce costs, the cerium-containing solution can also be obtained by adding an inorganic acid to the cerium-containing precipitate and dissolving at 50 - 80 °C for 0.5 - 2 h.

[0027] To further accelerate the precipitation rate of cerium(IV) hydroxide, in a preferred embodiment, in step L2, the weight ratio of oxalic acid to cerium in the cerium-containing solution is (1.0-2.2):1.

[0028] In a preferred embodiment, in step L3, the cerium oxalate precipitate is first washed with softened water with a volume 2-5 times that of the precipitate, and then subjected to a second calcination to further remove residual soluble impurity ions; preferably, the second calcination temperature is 600-1000°C, more preferably 800-950°C; the second calcination time is 1-3 h, more preferably 2-2.5 h. The above calcination process can better cooperate with the first calcination process and the precipitation process to further improve the purity of the prepared cerium oxide.

[0029] The following further describes the present application in detail with reference to specific embodiments, which should not be construed as limiting the scope claimed in the present application.

[0030] Unless otherwise specified, the raw material fly ash industrial wastewater used in the following examples and comparative examples 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.

[0031] Example 1

[0032] (1) Separation and enrichment of cerium:

[0033] In step S1, the fly ash industrial wastewater is extracted using a diluted extractant. The diluted extractant is P507:kerosene 1:3 (v / v). The volume ratio of the diluted extractant to the fly ash industrial wastewater is 1:5. The pH value of the extraction system is 5. The extraction method is cross-flow extraction. The extraction temperature is 45°C. The number of extraction stages is 6. A rare earth organic phase is obtained, and the raffinate enters the next extraction stage.

[0034] In step S2, the rare earth organic phase is back-extracted using hydrochloric acid (1 mol / L). The volume ratio of hydrochloric acid to the rare earth organic phase is 1:5. The pH value of the back-extraction system is 0.5. The back-extraction method is cross-flow back-extraction. The back-extraction temperature is 45°C. The number of back-extraction stages is 3. A pure rare earth chloride solution is obtained;

[0035] In step S3, the pH of the rare earth chloride solution is adjusted to 0.5, and then ozone is used for oxidation. The molar ratio of the ozone addition amount to the theoretical value of cerium in the rare earth chloride solution is 1.2:1. The oxidation temperature is 50°C. The oxidation time is 0.5 h. After filtration, the precipitate is stirred and washed with water with a volume 2 times that of the precipitate and a pH of 1. The stirring speed is 200 r / min. The washing time is 20 min. A cerium-containing precipitate is obtained. The element extraction rate of rare earth cerium is 96%.

[0036] (2) Preparation of cerium oxide:

[0037] Step L1: Roast the obtained cerium-containing precipitate at 800 °C for 1 h to obtain crude cerium oxide with a purity of 96.2%. Add hydrochloric acid (30 wt%) with a weight twice that of the precipitate and dissolve it at 150 °C for 3 h. Filter to obtain a cerium chloride solution.

[0038] Step L2: Add oxalic acid to the cerium chloride solution. The weight ratio of the added oxalic acid to the theoretical value of cerium in the cerium-containing solution is 1.0:1. Perform vacuum filtration to obtain cerium oxalate precipitate.

[0039] Step L3: Wash the cerium oxalate precipitate with softened water with a volume twice that of the precipitate. After filtration, roast the filter residue precipitate at 800 °C for 2 h to obtain high-purity cerium oxide with a purity of 99.92%.

[0040] Example 2

[0041] (1) Separation and enrichment of cerium:

[0042] Step S1: Use a diluted extractant to extract fly ash industrial wastewater. The diluted extractant is P507:kerosene 1:3 (v / v). The volume ratio of the diluted extractant to the fly ash industrial wastewater is 1:5. The pH value of the extraction system is 3.5. The extraction method is cross-flow extraction. The extraction temperature is 30 °C. The number of extraction stages is 4. Obtain a rare earth organic phase. The raffinate enters the next extraction stage.

[0043] Step S2: Use hydrochloric acid (3 mol / L) to strip the rare earth organic phase. The volume ratio of hydrochloric acid to the rare earth organic phase is 1:5. The pH value of the stripping system is 2.5. The stripping method is cross-flow stripping. The stripping temperature is 35 °C. The number of stripping stages is 2. Obtain a pure rare earth chloride solution.

[0044] Step S3: Adjust the pH of the rare earth chloride solution to 1, and then use ozone for oxidation. The molar ratio of the added ozone to the theoretical value of cerium in the rare earth chloride solution is 1.2:1. The oxidation temperature is 50 °C. The oxidation time is 1 h. Filter. Stir and wash the precipitate with water with a volume five times that of the precipitate and a pH of 2. The stirring speed is 200 r / min. The washing time is 25 min. Obtain a cerium-containing precipitate.

[0045] (2) Preparation of cerium oxide:

[0046] Step L1: Roast the obtained cerium-containing precipitate at 900 °C for 2.5 h to obtain crude cerium oxide. Add hydrochloric acid (30 wt%) with a weight twice that of the precipitate and dissolve it at 150 °C for 3 h. Filter to obtain a cerium chloride solution.

[0047] Step L2: Add oxalic acid to the cerium chloride solution. The weight ratio of the added oxalic acid to the theoretical value of cerium in the cerium-containing solution is 1.5:1. Perform vacuum filtration to obtain cerium oxalate precipitate.

[0048] Step L3: Wash the cerium oxalate precipitate with softened water at 3 times the volume, filter, and calcine the residue precipitate at 900 °C for 2.5 h to obtain high-purity cerium oxide.

[0049] Example 3

[0050] (1) Separation and enrichment of cerium:

[0051] Step S1: Extract the fly ash industrial wastewater with a diluted extractant. The diluted extractant is P204: isooctanol 1:1 (v / v). The volume ratio of the diluted extractant to the fly ash industrial wastewater is 1:20, the pH value is 1, the extraction method is cross-flow extraction, the extraction temperature is 25 °C, and the extraction stage is 6 stages to obtain a rare earth organic phase. The raffinate enters the next extraction stage.

[0052] Step S2: Back-extract the rare earth organic phase with hydrochloric acid (1 mol / L). The volume ratio of hydrochloric acid to the rare earth organic phase is 1:1, the pH value is 0.5, the extraction method is cross-flow extraction, the extraction temperature is 25 °C, and the extraction stage is 4 stages to obtain a pure rare earth chloride solution;

[0053] Step S3: Adjust the pH of the rare earth chloride solution to 0.5, then oxidize it with ozone. The molar ratio of the ozone addition amount to the theoretical value of cerium in the rare earth chloride solution is 1.0:1. The oxidation temperature is 40 °C, the oxidation time is 2 h, filter, and stir and wash the precipitate with water at 2 times the volume with a pH of 1. The stirring speed is 200 r / min, and the washing time is 20 min to obtain a cerium-containing precipitate.

[0054] (2) Preparation of cerium oxide:

[0055] Step L1: Calcine the obtained cerium-containing precipitate at 600 °C for 3 h to obtain crude cerium oxide, add hydrochloric acid (36.5%) at 0.5 times the weight, dissolve it at 90 °C for 5 h, and filter to obtain a cerium chloride solution;

[0056] Step L2: Add oxalic acid to the cerium chloride solution. The weight ratio of the oxalic acid addition amount to the theoretical value of cerium in the cerium-containing solution is 1.0:1, and vacuum filter to obtain a cerium oxalate precipitate;

[0057] Step L3: Wash the cerium oxalate precipitate with softened water at 2 times the volume, filter, and calcine the residue precipitate at 600 °C for 3 h to obtain high-purity cerium oxide.

[0058] Example 4

[0059] (1) Separation and enrichment of cerium:

[0060] Step S1: Extract the fly ash industrial wastewater using a diluted extractant. The diluted extractant is P204: isooctanol 1:5 (v / v). The volume ratio of the diluted extractant to the fly ash industrial wastewater is 1:1, the pH value is 7, the extraction method is cross-flow extraction, the extraction temperature is 60 °C, and the extraction stage is 1 stage. Obtain the rare earth organic phase, and the raffinate enters the next extraction stage.

[0061] Step S2: Back-extract the rare earth organic phase using hydrochloric acid (5 mol / L). The volume ratio of hydrochloric acid to the rare earth organic phase is 1:10, the pH value is 7, the extraction method is cross-flow extraction, the extraction temperature is 60 °C, and the extraction stage is 1 stage. Obtain a pure rare earth chloride solution;

[0062] Step S3: Adjust the pH of the rare earth chloride solution to 1.5, and then oxidize it using ozone. The molar ratio of the ozone addition amount to the theoretical value of cerium in the rare earth chloride solution is 1.5:1. The oxidation temperature is 60 °C, the oxidation time is 0.5 h. Filter, and wash the precipitate with water having a pH of 1 and a volume 2 times that of the precipitate at a stirring speed of 200 r / min for 20 min to obtain a cerium-containing precipitate.

[0063] (2) Preparation of cerium oxide:

[0064] Step L1: Calcinate the obtained cerium-containing precipitate at 1000 °C for 1 h to obtain crude cerium oxide. Add hydrochloric acid (25%) with a weight 3 times that of the crude cerium oxide and dissolve it at 160 °C for 2 h. Filter to obtain a cerium chloride solution;

[0065] Step L2: Add oxalic acid to the cerium chloride solution. The weight ratio of the oxalic acid addition amount to the theoretical value of cerium in the cerium-containing solution is 2.2:1. Perform vacuum filtration to obtain cerium oxalate precipitate;

[0066] Step L3: Wash the cerium oxalate precipitate with softened water having a volume 2 times that of the precipitate, and filter; calcinate the filter residue precipitate at 1000 °C for 1 h to obtain high-purity cerium oxide.

[0067] Example 5

[0068] (1) Separation and enrichment of cerium:

[0069] Step S1: Extract the fly ash industrial wastewater using a diluted extractant. The diluted extractant is P507: kerosene 1:3 (v / v). The volume ratio of the diluted extractant to the fly ash industrial wastewater is 1:5, the pH value of the extraction system is 1.5, the extraction method is cross-flow extraction, the extraction temperature is 25 °C, and the extraction stage is 4 stages. Obtain the rare earth organic phase, and the raffinate enters the next extraction stage.

[0070] Step S2: Use hydrochloric acid (2 mol / L) to strip the rare earth organic phase. The volume ratio of hydrochloric acid to the rare earth organic phase is 1:3. The pH value of the stripping system is 0.5. The stripping method is cross-flow stripping. The stripping temperature is 25 °C, and the number of stripping stages is 3 to obtain a pure rare earth chloride solution.

[0071] Step S3: Adjust the pH of the rare earth chloride solution to 1, and then use ozone for oxidation. The molar ratio of the ozone addition amount to the theoretical value of cerium in the rare earth chloride solution is 1.2:1. The oxidation temperature is 50 °C, and the oxidation time is 1 h. Filter, and wash the precipitate with water with a pH of 2 and a volume 5 times that of the precipitate. The stirring speed is 200 r / min, and the washing time is 25 min to obtain a cerium-containing precipitate.

[0072] (2) Preparation of cerium oxide:

[0073] Step L1: Calcinate the obtained cerium-containing precipitate at 800 °C for 2.5 h to obtain crude cerium oxide. Add hydrochloric acid (30 wt%) with a weight 2 times that of the crude cerium oxide and dissolve it at 150 °C for 3 h. Filter to obtain a cerium chloride solution.

[0074] Step L2: Add oxalic acid to the cerium chloride solution. The weight ratio of the oxalic acid addition amount to the theoretical value of cerium in the cerium-containing solution is 1.5:1. Perform vacuum filtration to obtain cerium oxalate precipitate.

[0075] Step L3: Wash the cerium oxalate precipitate with softened water with a volume 2 times that of the precipitate. After filtration, calcinate the filter residue precipitate at 800 °C for 2.5 h to obtain high-purity cerium oxide.

[0076] Example 6

[0077] (1) Separation and enrichment of cerium:

[0078] Step S1: Use a diluted extractant to extract fly ash industrial wastewater. The diluted extractant is P507:kerosene 1:3 (v / v). The volume ratio of the diluted extractant to fly ash industrial wastewater is 1:5. The pH value of the extraction system is 5. The extraction method is cross-flow extraction. The extraction temperature is 40 °C, and the number of extraction stages is 3 to obtain a rare earth organic phase. The raffinate enters the next extraction stage.

[0079] Step S2: Use hydrochloric acid (4 mol / L) to strip the rare earth organic phase. The volume ratio of hydrochloric acid to the rare earth organic phase is 1:8. The pH value of the stripping system is 5. The stripping method is cross-flow stripping. The stripping temperature is 40 °C, and the number of stripping stages is 1 to obtain a pure rare earth chloride solution.

[0080] Step S3: Adjust the pH of the rare earth chloride solution to 1, then oxidize it with ozone. The molar ratio of the ozone addition amount to the theoretical value of cerium in the rare earth chloride solution is 1.2:1. The oxidation temperature is 50°C and the oxidation time is 1 h. Filter, and wash the precipitate with water having a pH of 2 and a volume 5 times that of the precipitate at a stirring speed of 200 r / min for 25 min to obtain a cerium-containing precipitate.

[0081] (2) Preparation of cerium oxide:

[0082] Step L1: Calcinate the obtained cerium-containing precipitate at 950°C for 2 h to obtain crude cerium oxide, add hydrochloric acid (30 wt%) with a weight 2 times that of the crude cerium oxide, dissolve it at 150°C for 3 h, and filter to obtain a cerium chloride solution;

[0083] Step L2: Add oxalic acid to the cerium chloride solution. The weight ratio of the oxalic acid addition amount to the theoretical value of cerium in the cerium-containing solution is 1.5:1, and perform vacuum filtration to obtain a cerium oxalate precipitate;

[0084] Step L3: Wash the cerium oxalate precipitate with softened water having a volume 2 times that of the precipitate, filter, and calcinate the filter residue precipitate at 950°C for 2 h to obtain high-purity cerium oxide.

[0085] Example 7

[0086] The difference between Example 7 and Example 2 lies in that during the separation and enrichment of cerium, in Step S1, the extraction pH is 5, the extraction stage number is 3, and the extraction temperature is 40°C; in Step S2, the stripping agent is hydrochloric acid (2 mol / L), and the volume ratio of hydrochloric acid to the rare earth organic phase is 1:3, the stripping pH is 5, the extraction stage number is 3, and the extraction temperature is 40°C.

[0087] During the preparation process of cerium oxide, in Step L1, calcinate at 800°C for 2.5 h to obtain crude cerium oxide, and in Step L3, calcinate at 800°C for 2.5 h to obtain high-purity cerium oxide.

[0088] Example 8

[0089] The difference between Example 8 and Example 2 lies in that during the separation and enrichment of cerium, in Step S2, the stripping agent is hydrochloric acid (4 mol / L), and the volume ratio of hydrochloric acid to the rare earth organic phase is 1:8.

[0090] During the preparation process of cerium oxide, in Step L1, calcinate at 950°C for 2 h to obtain crude cerium oxide, and in Step L3, calcinate at 950°C for 2 h.

[0091] Comparative Example 1

[0092] The difference between Comparative Example 1 and Example 1 lies in that during the separation and enrichment of cerium, in Step S3, adjust the pH of the rare earth chloride solution to 3, and then oxidize it with ozone.

[0093] Comparative Example 2

[0094] The difference between Comparative Example 2 and Example 1 is that during the separation and enrichment of cerium, in step S3, the pH of the rare earth chloride solution was adjusted to 9, and then ozone was used for oxidation.

[0095] In Examples 1 to 8 and Comparative Examples 1 to 2, the cerium recovery rate during the separation and enrichment of cerium, the purity of crude cerium oxide during the preparation of cerium oxide, and the purity of the finally prepared high-purity cerium oxide are shown in Table 1.

[0096] Table 1

[0097]

[0098]

[0099] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: The method for separating cerium and preparing high-purity cerium oxide from the industrial wastewater of acid leaching aluminum from fly ash proposed for the first time in the present invention oxidizes cerium elements in the complex fly ash industrial wastewater under acidic conditions using a suitable oxidant, oxidizes trivalent cerium ions to tetravalent, and utilizes the chemical property differences between tetravalent cerium and trivalent rare earth elements, so that cerium elements are preferentially precipitated in the form of cerium hydroxide, thereby effectively reducing the extraction pressure of other rare earths in the subsequent process while separating the cerium-containing material and reducing the production cost. This method is simple and easy to operate, the cerium recovery rate can reach more than 95%, which is convenient for the subsequent preparation of high-purity cerium oxide with a purity greater than 99.9% using the separated cerium, providing a new way for the high-value utilization of fly ash.

[0100] 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 modification, equivalent replacement, improvement, 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 preparing high-purity cerium oxide, characterized in that, the preparation method comprises the following steps: Step L1, subjecting the cerium-containing precipitate to a first calcination to obtain crude cerium oxide; then mixing the crude cerium oxide with an inorganic acid and carrying out temperature-rising dissolution to obtain a cerium-containing solution; Step L2, adding oxalic acid to the cerium-containing solution to obtain cerium oxalate precipitate; Step L3, subjecting the cerium oxalate precipitate to a second calcination to obtain the high-purity cerium oxide; wherein the purity of the high-purity cerium oxide is greater than 99.9%; wherein the cerium-containing precipitate is separated from fly ash industrial wastewater, and the separation method comprises the following steps: Step S1, extracting the fly ash industrial wastewater with a diluted extractant to obtain a rare earth organic phase; Step S2, stripping the rare earth organic phase with a stripping agent to obtain a rare earth stripping solution; Step S3, adjusting the pH of the rare earth stripping solution to 0.5 - 1.5, and then oxidizing with an oxidizing agent to obtain a cerium-containing precipitate; wherein the contents of each component in the fly ash industrial wastewater are as follows: aluminum chloride 5 - 7 g / L, calcium chloride 22 - 26 g / L, magnesium chloride 2.0 - 2.4 g / L, potassium chloride 2.2 - 2.3 g / L, sodium chloride 2.8 - 3.2 g / L, lithium chloride 0.4 - 0.6 g / L, rare earth chlorides 1.5 - 2.1 g / L, and the rare earth chlorides at least include cerium chloride; the oxidizing agent is one or more of ozone, hydrogen peroxide, and sodium hypochlorite; wherein the volume ratio of the diluted extractant to the fly ash industrial wastewater is 1:3 - 1:10; the stripping agent is one or more of ammonium chloride, sulfuric acid, nitric acid, and hydrochloric acid.

2. The method according to claim 1, characterized in that, in step S3, the molar ratio of the oxidizing agent to cerium in the fly ash industrial wastewater is (1.0 - 1.5):

1.

3. The method according to claim 1 or 2, characterized in that, in step S3, during the oxidation process, the oxidation temperature is controlled at 40 - 60 °C, and the oxidation time is 0.5 - 2 h.

4. The method according to claim 1 or 2, characterized in that, in step S1, in the diluted extractant, the extractant is one or more of P204, P507, P350, TBP, N1923, and N263, and the diluent is one or more of isooctanol, kerosene, and n-hexane.

5. The method according to claim 4, characterized in that, in step S1, the volume ratio of the extractant to the diluent is 1:1 - 1:

5.

6. The method according to claim 4, characterized in that, in step S1, the extractant is N1923 and / or TBP.

7. The method according to claim 1 or 2, characterized in that, in step S2, the concentration of the stripping agent is 1 - 5 mol / L.

8. The method according to claim 1 or 2, characterized in that, in step S2, the concentration of the stripping agent is 2 - 4 mol / L.

9. The method according to claim 1 or 2, characterized in that, In the step S1, the extraction method is cross-flow extraction, and the pH value of the extraction system is 1 to 7, the number of extraction stages is 1 to 6, and the extraction temperature is 25 to 60 °C.

10. According to the method described in claim 9, it is characterized in that in the step S1, the pH value of the extraction system is 1.5 to 5, the number of extraction stages is 3 to 4, and the extraction temperature is 25 to 40 °C.

11. According to the method described in claim 1 or 2, it is characterized in that in the step S2, the stripping method is cross-flow stripping, and the volume ratio of the stripping agent to the rare earth organic phase is 1:1 to 1:10, the pH value of the stripping system is 0.5 to 7, the number of stripping stages is 1 to 4, and the stripping temperature is 25 to 60 °C.

12. According to the method described in claim 11, it is characterized in that in the step S2, the volume ratio of the stripping agent to the rare earth organic phase is 1:3 to 1:8, the pH value of the stripping system is 0.5 to 5, the number of stripping stages is 1 to 3, and the stripping temperature is 25 to 40 °C.

13. According to the method described in claim 1 or 2, it is characterized in that in the step S3, it further includes the step of washing the cerium-containing precipitate with water having a pH of 1 to 3 and a volume 2 to 8 times that of the precipitate, and the washing time is 10 to 40 min.

14. According to the method described in claim 1 or 2, it is characterized in that in the step L1, the temperature of the first calcination is 600 to 1000 °C; the time of the first calcination is 1 to 3 h; during the heating and dissolution process, the temperature is raised to 90 to 160 °C and dissolved for 2 to 5 h.

15. According to the method described in claim 14, it is characterized in that in the step L1, the temperature of the first calcination is 800 to 950 °C; the time of the first calcination is 2 to 2.5 h.

16. According to the method described in claim 1 or 2, it is characterized in that in the step L1, the weight ratio of the crude cerium oxide to the inorganic acid is 1:(0.5 to 3).

17. According to the method described in claim 1 or 2, it is characterized in that in the step L2, the weight ratio of oxalic acid to cerium in the cerium-containing solution is (1.0 to 2.2):

1.

18. According to the method described in claim 1 or 2, it is characterized in that in the step L3, first wash the cerium oxalate precipitate with softened water having a volume 2 to 5 times that of the precipitate, and then perform the second calcination.

19. According to the method described in claim 1 or 2, it is characterized in that in the step L3, the temperature of the second calcination is 600 to 1000 °C; the time of the second calcination is 1 to 3 h.

20. According to the method described in claim 19, it is characterized in that in the step L3, the temperature of the second calcination is 800 to 950 °C; the time of the second calcination is 2 to 2.5 h.

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