High-valued recycling method of rare earth oxalic acid precipitation wastewater

Abstract

The invention provides a high-valued recycling method of rare earth oxalic acid precipitation wastewater, which comprises the following steps: (1) mixing the rare earth oxalic acid precipitation wastewater and alkaline calcium salt under an external field strengthening condition, and carrying out neutralization reaction to obtain calcium oxalate precipitation and a calcium salt solution; (2) mixing rare earth chloride and the calcium oxalate precipitate under an external field strengthening condition, and carrying out a replacement reaction to obtain a rare earth oxalate precipitate and a calcium chloride solution; and (3) mixing the rare earth sulfate, the calcium salt solution and the calcium chloride solution, and carrying out precipitation reaction to obtain calcium sulfate precipitate and a rare earth chloride solution. The method provided by the invention not only realizes harmless treatment of the rare earth oxalic acid precipitation wastewater, but also realizes high-value recycling of oxalic acid resources in the wastewater, meanwhile, the building material calcium sulfate with high added value is prepared, waste is turned into wealth, the cost is reduced, the effect is improved, no salt-containing wastewater is discharged, and the method is environment-friendly. The method is a novel green and low-cost rare earth oxalic acid precipitation wastewater resource recycling technology, and green and sustainable development of the rare earth industry is promoted.

Description

Technical Field

[0001] The invention belongs to the field of resource recovery and utilization of rare earth oxalic acid wastewater, relates to a high-value recovery and utilization method of rare earth oxalic acid precipitation wastewater, and specifically relates to a high-value recovery and utilization method of rare earth oxalic acid precipitation wastewater calcium salt precipitation-rare earth transformation. Background Art

[0002] High-purity rare earth oxides are irreplaceable key raw materials for high-tech industries such as national defense, military industry, and intelligent manufacturing. They are mainly prepared by highly selective precipitation of rare earth ions by oxalic acid molecules, and at the same time produce highly acidic rare earth oxalic acid precipitation wastewater. The preparation of rare earths by selective precipitation of oxalic acid will produce toxic and harmful rare earth oxalic acid precipitation wastewater, which hinders the high-value development and utilization of rare earth resources. Therefore, it is urgent to treat and discharge the rare earth oxalic acid precipitation wastewater harmlessly or recycle it as a resource.

[0003] According to the characteristics of rare earth oxalic acid precipitation wastewater, domestic and foreign scholars have conducted a lot of research on its harmless disposal and recycling, and developed a series of technologies such as neutralization, extraction, concentration and distillation, oxidation, and direct reuse. However, there is currently no industrial technology that can achieve high-efficiency recycling of oxalic acid resources in wastewater, and most of them are mainly aimed at wastewater reduction and harmless discharge.

[0004] Among the various treatment methods currently available, the concentration distillation method and the electrolysis method (e.g., CN 112645413A) have the disadvantage of high treatment costs; the neutralization method (e.g., CN 1524841A) and the extraction method (e.g., CN 109252058A) will produce a large amount of additional saline wastewater; and the direct reuse method cannot be continuously and massively promoted. Therefore, there is still a lack of an effective method for recycling oxalic acid in wastewater with low cost, zero discharge, and high value.

[0005] In the context of ecological civilization construction, the rare earth industry urgently needs to develop new green and low-cost technologies for the resource recycling of rare earth grass sedimentation wastewater. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a high-value recycling method for rare earth oxalic acid precipitation wastewater. The method provided by the present invention not only realizes the harmless disposal of rare earth oxalic acid precipitation wastewater, but also realizes the high-value recycling of oxalic acid resources in the wastewater, and at the same time prepares high-value-added building material calcium sulfate, turning waste into treasure, reducing costs and increasing efficiency, and does not discharge salt-containing wastewater. It is a green and low-cost new technology for the resource recycling of rare earth oxalic acid precipitation wastewater, which promotes the green and sustainable development of the rare earth industry.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater, and the high-value recycling method comprises the following steps:

[0009] (1) Under external field enhanced conditions, rare earth oxalate precipitation wastewater and alkaline calcium salt are mixed, and calcium oxalate precipitation and calcium salt solution are obtained after neutralization reaction;

[0010] (2) under external field strengthening conditions, mixing rare earth chloride and the calcium oxalate precipitate obtained in step (1), and obtaining rare earth oxalate precipitate and calcium chloride solution after replacement reaction;

[0011] (3) mixing rare earth sulfate, the calcium salt solution obtained in step (1) and the calcium chloride solution obtained in step (2), and performing a precipitation reaction to obtain calcium sulfate precipitate and rare earth chloride solution.

[0012] In the present invention, low-cost alkaline calcium salt is firstly used as a neutralizing precipitant, and then rare earth oxalate precipitate and calcium chloride solution are obtained through rare earth chloride replacement transformation. The obtained rare earth oxalate precipitate can be used to prepare high-purity rare earth oxides, and the obtained calcium chloride solution reacts with rare earth sulfate to prepare high-value-added building materials calcium sulfate and rare earth chloride solution. The obtained rare earth chloride can be reused for replacement transformation with calcium oxalate precipitate to prepare rare earth oxalate.

[0013] The present invention efficiently recycles oxalic acid in wastewater through the method of "calcium salt precipitation-replacement transformation-replacement precipitation", completes the additional utilization of introduced calcium ions, not only achieves the purpose of harmless disposal of wastewater, but also realizes the high-value recovery and utilization of oxalic acid resources in wastewater, and simultaneously prepares calcium sulfate as a building material, turning waste into treasure, reducing costs and increasing efficiency, and does not discharge salt-containing wastewater, thereby promoting the green and sustainable development of the rare earth industry.

[0014] As a preferred technical solution of the present invention, the external field strengthening conditions in step (1) and step (2) include any one of ultrasonic strengthening, microwave strengthening or magnetic field strengthening, preferably ultrasonic strengthening.

[0015] Preferably, the power of the ultrasonic enhancement is 300-1000W, for example, 300W, 400W, 500W, 600W, 700W, 800W, 900W or 1000W, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] Preferably, the frequency of the ultrasonic enhancement is 25 to 60 kHz, for example, 25 kHz, 30 kHz, 40 kHz, 50 kHz or 60 kHz, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0017] In the process of generating solid by liquid-solid reaction, the precipitate generated by the reaction is easily adsorbed and wrapped on the surface of the solid reactant, thereby hindering the contact between the liquid reactant and the solid reactant, resulting in a low degree of reaction and reduced efficiency. Therefore, the present invention drives the solution components to vibrate or diffuse by strengthening, so that the generated tiny solid particles are difficult to adsorb on the surface of the reaction solid particles, and at the same time, cracks are generated in some dense solid reaction particles, which promotes the reaction liquid to penetrate into the interior, promotes the reaction, and improves efficiency.

[0018] In the present invention, the power of ultrasonic enhancement in the external field enhancement condition is 300-1000W, and the frequency is 25-60kHz; if the intensity of the external field enhancement is too high, the growth of the crystal nuclei of the generated solid particles will be restricted, thereby causing difficulties in subsequent solid-liquid separation and affecting the production process. Therefore, the selection of a reasonable external field enhancement intensity is also one of the important factors affecting the reaction.

[0019] As a preferred technical solution of the present invention, the components of the rare earth oxalic acid precipitation wastewater in step (1) include hydrochloric acid, oxalic acid, nitric acid and sulfuric acid.

[0020] Preferably, the oxalic acid content in the rare earth oxalic acid precipitation wastewater is 0.133-0.167 mol·L -1 , for example, it can be 0.133 mol·L -1 , 0.14 mol·L -1 , 0.15mol·L -1 , 0.16mol·L -1 or 0.167 mol·L -1 , but not limited to the listed values, other values ​​not listed in the numerical range are also applicable;

[0021] Preferably, the hydrochloric acid content in the rare earth oxalic acid precipitation wastewater is 1.5 to 2.0 mol·L -1 , for example, it can be 1.5 mol·L -1 , 1.6 mol·L -1 , 1.7 mol·L -1 , 1.8 mol·L -1 , 1.9 mol·L -1 or 2.0 mol·L -1 , but not limited to the listed values, other values ​​not listed in the numerical range are also applicable;

[0022] Preferably, the nitric acid content in the rare earth oxalic acid precipitation wastewater is 0 to 0.167 mol·L -1 , for example, it can be 0 mol·L -1 , 0.05mol·L -1 , 0.1 mol·L -1, 0.15mol·L -1 or 0.167 mol·L -1 , but not limited to the listed values, other values ​​not listed within the numerical range are also applicable;

[0023] Preferably, the sulfuric acid content in the rare earth oxalic acid precipitation wastewater is 0 to 0.167 mol·L -1 , for example, it can be 0mo·L -1 , 0.05mol·L -1 , 0.1 mol·L -1 , 0.15mol·L -1 or 0.167 mol·L -1 , but not limited to the listed values, other values ​​not listed in the numerical range are also applicable.

[0024] According to the different components in the rare earth oxalic acid precipitation wastewater, the calcium salt solution in step (1) includes calcium chloride solution, calcium sulfate solution and calcium nitrate solution.

[0025] Preferably, the alkaline calcium salt in step (1) comprises any one of calcium carbonate, calcium bicarbonate, calcium oxide or calcium hydroxide, or a combination of at least two thereof. Typical but non-limiting combinations include: a combination of calcium carbonate and calcium bicarbonate, a combination of calcium oxide and calcium hydroxide, or a combination of calcium carbonate, calcium bicarbonate, calcium oxide and calcium hydroxide.

[0026] It is worth noting that the alkaline calcium salt described in the present invention can be a solid calcium salt or a calcium salt solution.

[0027] Preferably, the molar ratio of the solute to the alkaline calcium salt in the rare earth oxalate precipitation wastewater in step (1) is 1:0.9 to 1.7, for example, it can be 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6 or 1:1.7, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] Furthermore, the solute in the rare earth oxalic acid precipitation wastewater in step (1) of the present invention refers to the acid solution in the rare earth oxalic acid precipitation wastewater.

[0029] As a preferred technical solution of the present invention, the temperature of the neutralization reaction in step (1) is 25-40°C, for example, it can be 25°C, 30°C, 35°C or 40°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the neutralization reaction time in step (1) is ≥ 4 h, for example, it can be 4 h, 4.2 h, 4.4 h, 4.6 h, 4.8 h or 5 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the stirring speed in the neutralization reaction in step (1) is 300 to 900 r / min, for example, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min or 900 r / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] Preferably, the reaction endpoint of the neutralization reaction in step (1) is: the acidity of the reaction solution is 0.063-0.1 mol / L, for example, it can be 0.063 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L or 0.1 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] In the present invention, when the neutralization reaction in step (1) is completed, the acidity of the reaction system is 0.063-0.1 mol / L (i.e., pH=1-2). If the pH value of the reaction system is too high at the end of the reaction, the solution will be alkaline, so that the rare earth oxalate precipitate obtained in step (2) contains rare earth hydroxide, impurities are introduced, and the difficulty of filtering is increased; if the pH value is too low, the oxalic acid reaction will be incomplete, and the oxalic acid will remain in the wastewater, causing environmental pollution.

[0034] As a preferred technical solution of the present invention, the rare earth chloride in step (2) includes any one of lanthanum chloride, yttrium chloride or neodymium trichloride, or a combination of at least two of them, for example, it can be a combination of lanthanum chloride and yttrium chloride, a combination of lanthanum chloride and neodymium trichloride, a combination of yttrium chloride and neodymium trichloride, or a combination of lanthanum chloride, yttrium chloride and neodymium trichloride.

[0035] It is worth noting that the rare earth chloride described in the present invention can be solid rare earth chloride or rare earth chloride solution.

[0036] Preferably, the molar ratio of the calcium oxalate precipitate and the rare earth chloride in step (2) is 1:1 to 1.3, for example, it can be 1:1, 1:1.4, 1:1.9, 1:2.3, 1:2.7 or 1:3, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] As a preferred technical solution of the present invention, the temperature of the replacement reaction in step (2) is 70-90°C, for example, it can be 70°C, 74°C, 78°C, 82°C, 86°C or 90°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] Preferably, the replacement reaction time in step (2) is 2 to 4 h, for example, 2 h, 2.4 h, 2.8 h, 3.2 h, 3.6 h or 4 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] Preferably, the stirring speed in the replacement reaction in step (2) is 300-900 r / min, for example, it can be 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min or 900 r / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] Preferably, the reaction endpoint of the replacement reaction in step (2) is: the pH value of the reaction solution is 1 to 3, for example, it can be 1, 1.4, 1.8, 2.2, 2.6 or 3, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] As a preferred technical solution of the present invention, the rare earth sulfate in step (3) includes any one of lanthanum sulfate, yttrium sulfate or neodymium sulfate, or a combination of at least two of them. Typical but non-limiting combinations include: a combination of lanthanum sulfate and yttrium sulfate, a combination of lanthanum sulfate and neodymium sulfate, a combination of yttrium sulfate and neodymium sulfate, or a combination of lanthanum sulfate, yttrium sulfate and neodymium sulfate.

[0042] It is worth noting that the rare earth sulfate described in the present invention can be solid rare earth sulfate or a rare earth sulfate solution.

[0043] Preferably, the molar ratio of calcium ions to rare earth sulfate in the calcium salt solution and the calcium chloride solution is 1:1 to 1.3, for example, 1:1, 1:1.04, 1:1.08, 1:1.12, 1:1.16, 1:1.2, 1:1.24, 1:1.28 or 1:1.3, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] As a preferred technical solution of the present invention, the temperature of the precipitation reaction in step (3) is 20-50°C, for example, it can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] In the present invention, the temperature of the precipitation reaction in step (3) is 20-50° C. If the temperature is higher than 50° C., the nucleation rate increases rapidly, there is not enough solute and time to ensure the growth of calcium sulfate crystal particles, the calcium sulfate precipitate particle size is too small, it is difficult to filter, and solid-liquid separation is difficult; if the temperature is too low, the precipitation reaction time will be too long, which will reduce production efficiency and increase costs; the appropriate temperature (20-50° C.) can not only increase the reaction rate and appropriately shorten the precipitation reaction time, but also ensure that the grains have enough time to grow, which is beneficial to solid-liquid separation and production efficiency.

[0046] Preferably, the precipitation reaction time in step (3) is 2 to 8 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] Preferably, the stirring speed in the precipitation reaction in step (3) is 300 to 900 r / min, for example, it can be 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min or 900 r / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0048] Preferably, the reaction endpoint of the precipitation reaction in step (3) is: the pH value of the reaction solution is 1 to 4, for example, it can be 1, 1.5, 2, 2.5, 3, 3.5 or 4, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] As a preferred technical solution of the present invention, the method further comprises drying the rare earth oxalate precipitate in step (1).

[0050] As a preferred technical solution of the present invention, the method for high-value recycling of rare earth oxalic acid precipitation wastewater provided by the present invention comprises the following steps:

[0051] (1) Under external field enhanced conditions, rare earth oxalate precipitation wastewater and alkaline calcium salt are mixed, and calcium oxalate precipitation and calcium salt solution are obtained after neutralization reaction;

[0052] The molar ratio of the solute to the alkaline calcium salt in the rare earth oxalic acid precipitation wastewater is 1:0.9-1.7;

[0053] The neutralization reaction temperature is 25-40°C, the time is ≥4h, and the stirring speed is 300-900r / min; the reaction endpoint is: the acidity of the reaction solution is 0.063-0.1mol / L;

[0054] (2) under external field strengthening conditions, mixing rare earth chloride and the calcium oxalate precipitate obtained in step (1), and obtaining rare earth oxalate precipitate and calcium chloride solution after replacement reaction;

[0055] The molar ratio of the calcium oxalate precipitate to the rare earth chloride is 1:1 to 1.3;

[0056] The temperature of the replacement reaction is 70-90°C, the time is 2-4h, and the stirring speed is 300-900r / min; the reaction end point is: the pH value of the reaction solution is 1-3;

[0057] (3) mixing rare earth sulfate, the calcium salt solution obtained in step (1), and the calcium chloride solution obtained in step (2), and performing a precipitation reaction to obtain a calcium sulfate precipitate and a rare earth chloride solution;

[0058] The molar ratio of calcium ions to rare earth sulfate in the calcium salt solution and the calcium chloride solution is 1:1 to 1.3;

[0059] The precipitation reaction temperature is 20-50° C., the time is 2-8 hours, and the stirring speed is 300-900 r / min. The reaction end point is: the pH value of the reaction solution is 1-4.

[0060] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] (1) The method provided by the present invention not only achieves the purpose of harmless disposal of rare earth oxalic acid wastewater, but also realizes the high-value recycling of oxalic acid resources in the wastewater, and at the same time prepares calcium sulfate as a building material, turning waste into treasure, reducing costs and increasing efficiency, and does not discharge salt-containing wastewater, which is green and pollution-free, and promotes the ecological sustainable development of the rare earth separation industry;

[0063] (2) The present invention avoids the encapsulation of alkaline calcium salt solid particles by calcium oxalate through external field strengthening, thereby improving the utilization rate of alkaline calcium salt;

[0064] (3) The present invention blocks the encapsulation of calcium oxalate by the newly generated rare earth oxalate precipitate through external field enhancement, so that the calcium oxalate is fully reacted with the rare earth chloride, thereby improving the utilization rate of oxalic acid;

[0065] (4) The method provided by the present invention does not produce high-salt wastewater and has the characteristic of zero emission. It can not only prepare calcium sulfate as a building material, but also obtain oxalic acid rare earth precipitate which can be used to prepare high-purity rare earth oxides. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 This is a process flow chart of the method for high-value recycling of rare earth oxalic acid precipitation wastewater provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0067] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0068] Example 1

[0069] This embodiment provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater, such as Figure 1 As shown, the high-value recycling method comprises the following steps:

[0070] (1) Under the conditions of 600W and 45kHz ultrasonic enhancement, rare earth oxalate precipitation wastewater and calcium oxide are mixed, and calcium oxalate precipitation and calcium salt solution are obtained after neutralization reaction;

[0071] The molar ratio of solute to calcium oxide in the rare earth oxalic acid precipitation wastewater is 1:1.4; the concentration of hydrochloric acid in the rare earth oxalic acid precipitation wastewater is 55 g / L, and the concentration of oxalic acid is 13 g / L;

[0072] The neutralization reaction temperature is 30°C, the time is 5h, and the stirring speed is 600r / min; the reaction endpoint is: the pH value of the reaction solution is 1.1;

[0073] (2) under 500W, 50kHz ultrasonic enhanced conditions, mixing 394.2g / L lanthanum chloride solution and the calcium oxalate precipitate obtained in step (1), and obtaining rare earth oxalate precipitate and calcium chloride solution after replacement reaction;

[0074] The molar ratio of the calcium oxalate precipitate to the rare earth chloride is 1:1.2;

[0075] The temperature of the replacement reaction is 80°C, the time is 3h, and the stirring speed is 300r / min; the reaction end point is: the pH value of the reaction solution is 2;

[0076] (3) mixing a lanthanum sulfate solution having a concentration of 16.1 g / L, the calcium salt solution obtained in step (1), and the calcium chloride solution obtained in step (2), and obtaining a calcium sulfate precipitate and a rare earth chloride solution after precipitation reaction;

[0077] The molar ratio of calcium ions to rare earth sulfate in the calcium salt solution and the calcium chloride solution is 1:1.2;

[0078] The precipitation reaction temperature is 30° C., the time is 5 h, and the stirring speed is 500 r / min; the reaction endpoint is: the pH value of the reaction solution is 2.

[0079] Example 2

[0080] This embodiment provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater, and the high-value recycling method comprises the following steps:

[0081] (1) Under magnetic field enhancement conditions, rare earth oxalate precipitation wastewater and calcium carbonate are mixed, and calcium oxalate precipitation and calcium salt solution are obtained after neutralization reaction;

[0082] The molar ratio of solute to calcium carbonate in the rare earth oxalate precipitation wastewater is 1:0.9;

[0083] The neutralization reaction temperature is 25°C, the time is 8h, and the stirring speed is 300r / min; the reaction end point is: the pH value of the reaction solution is 1;

[0084] (2) mixing the yttrium chloride solution and the calcium oxalate precipitate obtained in step (1) under 300W, 60kHz ultrasonic strengthening conditions to obtain rare earth oxalate precipitate and calcium chloride solution after replacement reaction;

[0085] The molar ratio of the calcium oxalate precipitate to the rare earth chloride is 1:1;

[0086] The temperature of the replacement reaction is 70° C., the time is 4 hours, and the stirring speed is 400 r / min; the reaction end point is: the pH value of the reaction solution is 1;

[0087] (3) mixing the yttrium sulfate solution, the calcium salt solution obtained in step (1), and the calcium chloride solution obtained in step (2), and obtaining calcium sulfate precipitate and rare earth chloride solution after precipitation reaction;

[0088] The molar ratio of calcium ions to rare earth sulfate in the calcium salt solution and the calcium chloride solution is 1:1;

[0089] The precipitation reaction was carried out at a temperature of 20° C., for 8 hours, with a stirring speed of 300 r / min; the reaction endpoint was: the pH value of the reaction solution was 1.

[0090] Example 3

[0091] This embodiment provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater, and the high-value recycling method comprises the following steps:

[0092] (1) Under the conditions of 1000W and 25kHz ultrasonic enhancement, rare earth oxalic acid precipitation wastewater and calcium hydroxide are mixed, and calcium oxalate precipitation and calcium salt solution are obtained after neutralization reaction;

[0093] The molar ratio of solute to calcium hydroxide in the rare earth oxalic acid precipitation wastewater is 1:1.7;

[0094] The neutralization reaction temperature is 40°C, the time is 4h, and the stirring speed is 900r / min; the reaction end point is: the pH value of the reaction solution is 2;

[0095] (2) under microwave-enhanced conditions, mixing neodymium trichloride and the calcium oxalate precipitate obtained in step (1), and obtaining rare earth oxalate precipitate and calcium chloride solution after replacement reaction;

[0096] The molar ratio of the calcium oxalate precipitate to the rare earth chloride is 1:1.3;

[0097] The temperature of the replacement reaction is 90° C., the time is 2 h, and the stirring speed is 900 r / min; the reaction end point is: the pH value of the reaction solution is 3;

[0098] (3) mixing neodymium sulfate, the calcium salt solution obtained in step (1), and the calcium chloride solution obtained in step (2), and performing a precipitation reaction to obtain a calcium sulfate precipitate and a rare earth chloride solution;

[0099] The molar ratio of calcium ions to rare earth sulfate in the calcium salt solution and the calcium chloride solution is 1:1.3;

[0100] The precipitation reaction was carried out at a temperature of 50° C., a time of 2 h, and a stirring speed of 700 r / min. The reaction endpoint was: the pH value of the reaction solution was 4.

[0101] Example 4

[0102] This embodiment provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater. The difference between the high-value recycling method and embodiment 1 is that:

[0103] In this embodiment, the reaction endpoint of the neutralization reaction in step (1) is adjusted to a pH value of 3.5.

[0104] Example 5

[0105] This embodiment provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater. The difference between the high-value recycling method and embodiment 1 is that:

[0106] In this example, the temperature of the precipitation reaction in step (3) is adjusted to 60°C.

[0107] Example 6

[0108] This embodiment provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater. The difference between the high-value recycling method and embodiment 1 is that:

[0109] In this embodiment, the power of the ultrasonic enhancement in step (1) is adjusted to 1200 W and the frequency is adjusted to 20 kHz.

[0110] Example 7

[0111] This embodiment provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater. The difference between the high-value recycling method and embodiment 1 is that:

[0112] In this embodiment, the power of the ultrasonic enhancement in step (1) is adjusted to 200 W and the frequency is adjusted to 70 kHz.

[0113] Example 8

[0114] This embodiment provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater. The difference between the high-value recycling method and embodiment 1 is that:

[0115] In this embodiment, the power of the ultrasonic enhancement in step (2) is adjusted to 1200 W and the frequency is adjusted to 20 kHz.

[0116] Example 9

[0117] This embodiment provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater. The difference between the high-value recycling method and embodiment 1 is that:

[0118] In this embodiment, the power of the ultrasonic enhancement in step (2) is adjusted to 200 W and the frequency is adjusted to 70 kHz.

[0119] Example 10

[0120] This embodiment provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater. The difference between the high-value recycling method and embodiment 1 is that:

[0121] In this embodiment, the ultrasonic strengthening described in step (1) and step (2) is adjusted to microwave strengthening.

[0122] Embodiment 11

[0123] This embodiment provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater. The difference between the high-value recycling method and embodiment 1 is that:

[0124] In this embodiment, the ultrasonic enhancement described in step (1) and step (2) is adjusted to magnetic field enhancement.

[0125] Comparative Example 1

[0126] This comparative example provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater, which differs from Example 1 only in that:

[0127] In this comparative example, the ultrasonic strengthening described in step (1) was omitted.

[0128] Comparative Example 2

[0129] This comparative example provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater, which differs from Example 1 only in that:

[0130] In this comparative example, the ultrasonic strengthening described in step (2) was omitted.

[0131] Comparative Example 3

[0132] This comparative example provides a method for high-value recycling of rare earth oxalic acid precipitation wastewater, which differs from Example 1 only in that:

[0133] In this comparative example, the rare earth chloride in step (2) is adjusted to rare earth nitrate, specifically lanthanum nitrate solution.

[0134] The conversion rates of calcium oxalate precipitate, rare earth oxalate precipitate and calcium sulfate precipitate produced during the operation of the methods provided in the above embodiments and comparative examples were detected and calculated, and the results are shown in Table 1.

[0135] Table 1

[0136] Calcium oxalate conversion rate / % Rare earth oxalate conversion rate / % Calcium sulfate conversion rate / % Example 1 99.2 98.5 95.3 Example 2 98.8 97.8 94.2 Example 3 99.0 98.2 94.8 Example 4 95.6 97.2 93.5 Example 5 99.0 98.4 88.6 Example 6 92.3 96.6 90.5 Example 7 91.8 98.0 91.8 Example 8 98.4 92.7 92.6 Example 9 98.2 91.1 90.8 Example 10 92.0 92.3 89.0 Embodiment 11 91.8 91.5 88.5 Comparative Example 1 85.0 88.0 81.6 Comparative Example 2 95.1 84.5 82.5 Comparative Example 3 90.0 92.0 85.0

[0137] According to Table 1, we can know the following points:

[0138] (1) Comprehensive analysis of Examples 1-3 shows that the high-value recycling method provided by the present invention can be used to prepare calcium sulfate, a building material, and oxalic acid rare earth precipitate for preparing high-purity rare earth oxides. No high-salt wastewater is generated during the reaction process, thereby achieving high-value recycling of oxalic acid resources in wastewater. Moreover, the method provided by the present invention can further improve the recovery rate and utilization rate of oxalic acid.

[0139] (2) Comprehensive analysis of Example 1 and Examples 4-5 shows that the reaction conditions provided in steps (1)-(3) of the method provided by the present invention will affect the reaction process;

[0140] When the pH value at the reaction end point of the neutralization reaction in step (1) is too high, the solution will be alkaline, which will cause the rare earth oxalate obtained in step (2) to contain rare earth hydroxide, introduce impurities, and increase the difficulty of filtration;

[0141] When the temperature of the precipitation reaction in step (3) is too high, the calcium sulfate particles will be too fine, the filtration speed will be slow, and the energy consumption will increase;

[0142] (3) Comprehensive analysis of Example 1, Examples 6-9 and Comparative Examples 1-2 shows that external field enhancement is one of the important factors affecting the reaction process;

[0143] More specifically, when the external field enhancement intensity in step (1) is too low (or the external field enhancement is omitted), the vibration or convection degree will be insufficient, the coating shell cannot be broken, and the reaction efficiency cannot be improved; when the intensity is too high, the energy consumption will increase, and the production cost will increase;

[0144] When the external field enhancement intensity in step (2) is too low (or the external field enhancement is omitted), the vibration or convection degree will be insufficient, the coating shell cannot be broken, and the reaction efficiency cannot be improved; when the intensity is too high, energy consumption will increase, and production costs will increase.

[0145] In summary, the method provided by the present invention not only realizes the harmless disposal of rare earth oxalic acid precipitation wastewater, but also realizes the high-value recycling of oxalic acid resources in the wastewater, and simultaneously prepares high-value-added building material calcium sulfate, turning waste into treasure, reducing costs and increasing efficiency, and does not discharge salt-containing wastewater. It is a green and low-cost new technology for the resource recycling of rare earth oxalic acid precipitation wastewater, which promotes the green and sustainable development of the rare earth industry.

[0146] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for high-value recycling of rare earth oxalic acid precipitation wastewater, characterized in that: The high-value recycling method comprises the following steps: (1) Under external field enhanced conditions, rare earth oxalate precipitation wastewater and alkaline calcium salt are mixed, and calcium oxalate precipitation and calcium salt solution are obtained after neutralization reaction; (2) under external field strengthening conditions, mixing rare earth chloride and the calcium oxalate precipitate obtained in step (1), and obtaining rare earth oxalate precipitate and calcium chloride solution after replacement reaction; (3) mixing rare earth sulfate, the calcium salt solution obtained in step (1) and the calcium chloride solution obtained in step (2), and performing a precipitation reaction to obtain calcium sulfate precipitate and rare earth chloride solution.

2. The high-value recycling method according to claim 1, characterized in that: The external field strengthening conditions in step (1) and step (2) include any one of ultrasonic strengthening, microwave strengthening or magnetic field strengthening, preferably ultrasonic strengthening; Preferably, the power of the ultrasonic enhancement is 300-1000W; Preferably, the frequency of the ultrasonic enhancement is 25-60 kHz.

3. The high-value recycling method according to claim 1 or 2, characterized in that: The components of the rare earth oxalic acid precipitation wastewater in step (1) include hydrochloric acid, oxalic acid, nitric acid and sulfuric acid; Preferably, the alkaline calcium salt in step (1) comprises any one of calcium carbonate, calcium bicarbonate, calcium oxide or calcium hydroxide, or a combination of at least two thereof; Preferably, the molar ratio of the solute to the alkaline calcium salt in the rare earth oxalic acid precipitation wastewater in step (1) is 1:0.9-1.

7.

4. The high-value recycling method according to any one of claims 1 to 3, characterized in that: The temperature of the neutralization reaction in step (1) is 25-40° C.; Preferably, the neutralization reaction time in step (1) is ≥ 4 h; Preferably, the stirring speed in the neutralization reaction in step (1) is 300 to 900 r / min; Preferably, the reaction endpoint of the neutralization reaction in step (1) is: the acidity of the reaction solution is 0.063 to 0.1 mol / L.

5. The high-value recycling method according to any one of claims 1 to 4, characterized in that: The rare earth chloride in step (2) includes any one of lanthanum chloride, yttrium chloride or neodymium trichloride, or a combination of at least two thereof; Preferably, the molar ratio of the calcium oxalate precipitate to the rare earth chloride in step (2) is 1:1 to 1.

3.

6. The high-value recycling method according to any one of claims 1 to 5, characterized in that: The temperature of the replacement reaction in step (2) is 70-90° C. Preferably, the replacement reaction time in step (2) is 2 to 4 hours; Preferably, the stirring speed in the replacement reaction in step (2) is 300 to 900 r / min; Preferably, the reaction endpoint of the replacement reaction in step (2) is: the pH value of the reaction solution is 1-3.

7. The high-value recycling method according to any one of claims 1 to 6, characterized in that: The rare earth sulfate in step (3) includes any one of lanthanum sulfate, yttrium sulfate or neodymium sulfate, or a combination of at least two thereof; Preferably, the molar ratio of calcium ions to rare earth sulfate in the calcium salt solution and the calcium chloride solution is 1:1 to 1.

3.

8. The high-value recycling method according to any one of claims 1 to 7, characterized in that: The temperature of the precipitation reaction in step (3) is 20 to 50° C. Preferably, the precipitation reaction time in step (3) is 2 to 8 hours; Preferably, the stirring speed in the precipitation reaction in step (3) is 300 to 900 r / min; Preferably, the reaction endpoint of the precipitation reaction in step (3) is: the pH value of the reaction solution is 1-4.

9. The high-value recycling method according to any one of claims 1 to 8, characterized in that: The method further comprises drying the rare earth oxalate precipitate in step (1).

10. The high-value recycling method according to any one of claims 1 to 9, characterized in that: The high-value recycling method comprises the following steps: (1) Under external field enhanced conditions, rare earth oxalate precipitation wastewater and alkaline calcium salt are mixed, and calcium oxalate precipitation and calcium salt solution are obtained after neutralization reaction; The molar ratio of the solute to the alkaline calcium salt in the rare earth oxalic acid precipitation wastewater is 1:0.9-1.7; The neutralization reaction temperature is 25-40°C, the time is ≥4h, and the stirring speed is 300-900r / min; the reaction endpoint is: the acidity of the reaction solution is 0.063-0.1mol / L; (2) under external field strengthening conditions, mixing rare earth chloride and the calcium oxalate precipitate obtained in step (1), and obtaining rare earth oxalate precipitate and calcium chloride solution after replacement reaction; The molar ratio of the calcium oxalate precipitate to the rare earth chloride is 1:1 to 1.3; The temperature of the replacement reaction is 70-90°C, the time is 2-4h, and the stirring speed is 300-900r / min; the reaction end point is: the pH value of the reaction solution is 1-3; (3) mixing rare earth sulfate, the calcium salt solution obtained in step (1), and the calcium chloride solution obtained in step (2), and performing a precipitation reaction to obtain a calcium sulfate precipitate and a rare earth chloride solution; The molar ratio of calcium ions to rare earth sulfate in the calcium salt solution and the calcium chloride solution is 1:1 to 1.3; The precipitation reaction temperature is 20-50° C., the time is 2-8 hours, and the stirring speed is 300-900 r / min. The reaction end point is: the pH value of the reaction solution is 1-4.

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