Method for preparing high-quality ammonium sulfate from sodium-ammonium-containing sulfate solid waste

Abstract

The invention relates to a method for preparing high-quality ammonium sulfate by using sodium-ammonium-containing sulfate solid waste, which comprises the following steps: partially dissolving the sodium-ammonium-containing sulfate solid waste and carrying out solid-liquid separation to obtain a first dissolved solution and a first solid phase; the first dissolving solution is subjected to first evaporative crystallization and solid-liquid separation, and an ammonium sulfate product and a first mother solution are obtained; wherein the temperature of partial dissolution is 5-10 DEG C; efficient separation and recovery of ammonium sulfate and sodium sulfate resources in sulfate solid waste containing sodium and ammonium are achieved, the purity of an ammonium sulfate product obtained after first evaporative crystallization is preferably as high as 98.6% or above, the appearance color is white, the water content is preferably as low as 1.3% or below, and the recovery rate is high. The recovery rate is preferably up to 98.00% or above, the purity of the sodium sulfate product is up to 98.5% or above, the amount of sodium hydroxide required to be consumed is as low as 0.93% or below, and the method is simple in technological process, mild in condition and easy to industrialize.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste treatment and resource recycling, and in particular to a method for preparing high-quality ammonium sulfate by utilizing sulfate solid waste containing sodium ammonium. Background Art

[0002] Solid waste sulfate containing sodium ammonium comes from the semiconductor industry, mainly including mixed salts of sodium sulfate and ammonium sulfate, and contains a small amount of organic and metal impurities. It cannot be directly disposed as a product and can only be treated as waste for subsequent treatment, resulting in a waste of ammonium sulfate and sodium sulfate resources. At present, the main method is to completely dissolve the sulfate containing sodium ammonium into a mixed solution of ammonium sulfate and sodium sulfate, and then separate the ammonium sulfate and sodium sulfate. There are problems such as harsh separation conditions and low separation efficiency leading to poor product quality. However, when the sodium ammonium sulfate is directly calcined by pyrolysis for separation, the equipment requirements are high, the operation risk is high, and the energy consumption is high.

[0003] For example, CN115947473A discloses a low-cost treatment method for ammonia-sulfate-containing, high-salt, and high-organic wastewater. The method uses lime and sulfate to crystallize at room temperature to generate dihydrate gypsum, and deammonifies the wastewater to convert it into ammonia gas, thereby separating ammonium sulfate from sodium sulfate. However, the method still inevitably requires the use of a large amount of alkali to convert and blow off the ammonia nitrogen, and the reagent cost is high.

[0004] CN111547918A discloses a method for resource processing of sodium sulfate and ammonium sulfate wastewater. The method mainly comprises the following steps: first evaporating and concentrating raw water containing sodium sulfate and ammonium sulfate and performing solid-liquid separation to obtain sodium sulfate and centrifugal mother liquor; then freezing and crystallizing the centrifugal mother liquor and performing solid-liquid separation to obtain mixed salt and frozen mother liquor; and then evaporating and concentrating the frozen mother liquor to obtain ammonium sulfate crystalline salt. Since the method still processes a mixed solution of sodium sulfate and ammonium sulfate, the process parameters are strictly required, the product quality is relatively difficult to control, and the single recovery rate is low.

[0005] CN110015799A discloses a wastewater treatment method, which separates sodium ions from ammonium ions by dissolving and crystallizing wastewater containing ammonium ions, sodium ions and sulfate ions. The dissolving agent used in the dissolving and crystallizing method is an organic solvent, which is very harmful and will greatly affect the use and destination of the product.

[0006] CN107867708A discloses a method for treating a mixture of sodium sulfate and ammonium sulfate with sodium chloride. The method is to directly heat and roast the sodium chloride and mixed waste to remove ammonium ions in the mixture. This method has high disposal risks and is difficult to dispose of, has high equipment requirements and consumes a lot of energy.

[0007] Therefore, how to provide a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium, so as to efficiently separate and recover ammonium sulfate and ammonium sulfate in the sulfate solid waste containing sodium ammonium, and realize the resource utilization of sulfate solid waste containing sodium ammonium, has become a problem that needs to be solved urgently. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a method for preparing high-quality ammonium sulfate by using sulfate solid waste containing sodium ammonium. The method can realize efficient separation and recovery of ammonium sulfate and sodium sulfate in sulfate solid waste containing sodium ammonium, and the recovery rate and quality of the obtained ammonium sulfate and sodium sulfate products are high. The process flow is simple and the conditions are mild, thereby realizing full utilization of resources in sulfate solid waste containing sodium ammonium.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for preparing high-quality ammonium sulfate by using sulfate solid waste containing sodium ammonium, the method comprising the following steps:

[0011] (1) partially dissolving the sodium ammonium sulfate solid waste and performing solid-liquid separation to obtain a first dissolved liquid and a first solid phase;

[0012] (2) The first dissolved solution in step (1) is subjected to a first evaporation crystallization and solid-liquid separation to obtain an ammonium sulfate product and a first mother liquor;

[0013] The partial dissolution temperature in step (1) is 5-10°C, for example, 5°C, 6°C, 7°C, 8°C, 9°C or 10°C.

[0014] The present invention makes full use of the solubility difference between ammonium sulfate and sodium sulfate at low temperature, controls the temperature of partial dissolution within the range of 5-10°C, so that the ammonium sulfate in the sodium-ammonium sulfate solid waste is fully dissolved, while the sodium sulfate is only partially dissolved, and a large amount of undissolved sodium sulfate and a small amount of ammonium sulfate enter the first solid phase through solid-liquid separation, that is, the preliminary separation of ammonium sulfate and sodium sulfate in the sodium-ammonium sulfate solid waste is achieved in the partial dissolution step, the mass ratio of ammonium sulfate to sodium sulfate in the first dissolving liquid is increased, which is beneficial to the subsequent first evaporation crystallization step, and a high-quality ammonium sulfate product can be obtained, and the amount of liquid alkali required in the subsequent sodium sulfate product preparation process is greatly reduced, thereby reducing the production cost.

[0015] It is worth noting that, compared with the dissolution of pure ammonium sulfate and pure sodium sulfate, the dissolution of ammonium sulfate and sodium sulfate in the sodium ammonium sulfate solid waste of the present invention affects each other, and the solubility is lower than that of pure salt. This is because when pure salt is dissolved, when the sulfate and cation reach a certain value, the solution is saturated; and when the mixed salt of ammonium sulfate and sodium sulfate is dissolved, the sulfate is greater than the pure salt, so the corresponding solubility of ammonium sulfate and sodium sulfate is reduced.

[0016] Preferably, the sodium ammonium sulfate solid waste in step (1) comprises 40-75wt% ammonium sulfate, 20-50wt% sodium sulfate, 2-15wt% water, and the rest are metal impurities and organic impurities.

[0017] Among them, 40-75wt% ammonium sulfate can be, for example, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt% or 75wt%; 20-50wt% sodium sulfate can be, for example, 20wt%, 30wt%, 40wt% or 50wt%; 2-15wt% water can be, for example, 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt% or 15wt% or the like.

[0018] Preferably, the metal impurities include any one of Cu, Ni or Zn or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of Cu and Ni, a combination of Cu and Zn, or a combination of Ni and Zn.

[0019] Preferably, the partially dissolved solvent in step (1) comprises water.

[0020] Preferably, the mass volume ratio of the sodium ammonium sulfate solid waste to the solvent in step (1) is 1:(0.56-1.05), for example, it can be 1:0.56, 1:0.60, 1:0.80, 1:0.95, 1:1 or 1:1.05, etc.

[0021] Preferably, the molar ratio of ammonium to sodium in the first dissolving solution in step (1) is (5.8-7.2):1, for example, it can be 5.8:1, 6.0:1, 6.2:1, 6.4:1, 6.6:1, 6.8:1, 7.0:1 or 7.2:1, etc.

[0022] Preferably, in step (1), the molar ratio of ammonium to sodium in the first solid phase is 1:(10-50), for example, it can be 1:10, 1:20, 1:30, 1:40 or 1:50, etc.

[0023] In the present invention, it is further preferred that the mass volume ratio of the sodium ammonium sulfate solid waste to the solvent in step (1) is 1:(0.56-1.05), so that the ammonium sulfate in the sodium ammonium sulfate solid waste can be fully dissolved to saturation, which is beneficial to improving the recovery efficiency of ammonium sulfate and the product purity.

[0024] It is worth noting that the metal impurities and organic impurities in the sodium ammonium sulfate solid waste of the present invention are all soluble, and almost all enter the first dissolving solution after being dissolved, and no residue remains in the first solid phase.

[0025] Preferably, the temperature of the first evaporation crystallization in step (2) is 95-105°C, for example, 95°C, 100°C or 105°C.

[0026] Preferably, the endpoint of the first evaporative crystallization in step (2) is the Na + The content is less than 40000ppm, for example, it can be 39000ppm, 37000ppm, 35000ppm, 32000ppm or 30000ppm.

[0027] Preferably, the molar ratio of ammonium to sodium in the first mother liquor in step (2) is greater than or equal to 3:1, for example, it can be 3:1, 3.5:1, 4:1 or 4.5:1.

[0028] The present invention further preferably ends with the Na in the first mother liquor. + The content of <40000ppm ensures that the mass of ammonium sulfate and sodium sulfate in the first mother liquor is relatively large, thereby ensuring that the nitrogen content of the ammonium sulfate product is >20.5%, meeting the quality standard of the ammonium sulfate product for sale; if the first mother liquor contains Na + The content is too high, the sodium content in the ammonium sulfate product is too high, and the quality of the ammonium sulfate product is poor.

[0029] Preferably, before the first evaporation crystallization in step (2), the first dissolved solution is first subjected to a decontamination treatment.

[0030] Preferably, the impurity removal treatment comprises a precipitation treatment and an oxidation treatment performed sequentially.

[0031] Preferably, the precipitant used in the precipitation treatment includes any one of sodium sulfide, ammonium sulfide or hydrogen sulfide, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of sodium sulfate and ammonium sulfate, a combination of sodium sulfate and hydrogen sulfide, or ammonium sulfide or hydrogen sulfide, etc.

[0032] Preferably, the precipitate obtained by the precipitation treatment is metal mud, which includes copper sulfide, nickel sulfide or zinc sulfide, etc., and can be sold as a product after further treatment.

[0033] Preferably, the mass ratio of the precipitant to the metal impurities in the sodium ammonium sulfate solid waste is (0.5-2):1, for example, it can be 0.5:1, 0.8:1, 1:1, 1.5:1, 1.8:1 or 2:1, etc.

[0034] Preferably, the oxidant used in the oxidation treatment includes any one of hydrogen peroxide, sodium persulfate or ammonium persulfate, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of hydrogen peroxide and sodium persulfate, a combination of hydrogen peroxide and ammonium persulfate, or a combination of sodium persulfate and ammonium persulfate, etc.

[0035] Preferably, the ratio of the amount of the oxidant to the COD value (chemical oxygen demand) of organic impurities in the sodium ammonium sulfate solid waste is (2.2-12):1, for example, it can be 2.2:1, 2.5:1, 3:1, 5:1, 8:1, 10:1 or 12:1, etc.

[0036] The present invention further preferably performs precipitation treatment and oxidation treatment in sequence before the first evaporation crystallization in step (2), so as to remove metal impurities and organic impurities in the first dissolving solution in sequence, so as to ensure that the ammonium sulfate product obtained by the subsequent first evaporation crystallization has a high quality. Otherwise, the appearance color of the ammonium sulfate product will be bluish-green, the water content will be high, and it will be sticky, etc., which will affect the product quality.

[0037] That is, the method of the present invention aims to prepare high-quality ammonium sulfate products, which not only have high purity, but also have white appearance, are not prone to forming sticky blocks, and have a moisture content as low as below 1.3%.

[0038] Preferably, based on step (1) and step (2), the method further comprises the following steps:

[0039] (3) Step (2) The first mother liquor is cooled, crystallized and solid-liquid separated to obtain a second mother liquor and a second solid phase.

[0040] The method of the present invention is based on step (1) and step (2), and further preferably cools and crystallizes the first mother liquor in step (2) and separates the solid from the liquid, so as to further remove the sodium sulfate in the first mother liquor and increase the mass ratio of ammonium sulfate to ammonium sulfate in the second mother liquor, which is beneficial to the subsequent recycling to the first evaporation and crystallization step to further recover the ammonium sulfate product, thereby improving the recovery rate of the ammonium sulfate product from the sodium ammonium sulfate solid waste; and, compared with the conventional method of directly recycling the first mother liquor to the first evaporation and crystallization step, the method of the present invention of additionally performing cooling and crystallization recycling further improves the quality of the ammonium sulfate product, and reduces the number of cycles required to achieve the same ammonium sulfate recovery rate, thereby reducing energy consumption and cost.

[0041] Preferably, the temperature of the cooling crystallization in step (3) is 5-10°C, for example, 5°C, 6°C, 7°C, 8°C, 9°C or 10°C.

[0042] Preferably, the end point of the cooling crystallization in step (3) is the Na + The content is less than 24000ppm, for example, it can be 23000ppm, 22000ppm, 20000ppm, 18000ppm or 15000ppm.

[0043] The present invention further preferably comprises step (3) wherein the temperature of the cooling crystallization is 5 to 10°C, and the end point is when the Na + The content is less than 24000ppm, which is beneficial to improve the purity of the ammonium sulfate product.

[0044] Preferably, in step (3), the second mother liquor is circulated to step (2) to continue evaporation and crystallization.

[0045] Preferably, in terms of mass percentage, the second solid phase in step (3) comprises a composite salt containing sodium sulfate and ammonium sulfate, that is, the molar ratio of sodium to ammonium in the second solid phase is about 1:1.

[0046] Preferably, the composite salt containing sodium sulfate and ammonium sulfate includes Na2SO4·(NH4)2SO4·4H2O.

[0047] In the process of cooling and crystallizing the first mother liquor of the present invention, ammonium sulfate and sodium sulfate are precipitated simultaneously, namely, Na2SO4·(NH4)2SO4·4H2O. If the content of components in the first mother liquor fluctuates, for example, if there is too much sodium sulfate, then mirabilite (Na2SO4·10H2O) may be produced, which is highly polluting. If there is too much ammonium sulfate, then ammonium sulfate may be produced, but its purity is poor and affects the yield of ammonium sulfate. Therefore, the control of the first evaporation crystallization endpoint of the present invention ensures the high quality of the ammonium sulfate product while avoiding the subsequent generation of harmful by-products.

[0048] Preferably, in step (3), the second solid phase is dried and then circulated to step (1) to continue partial dissolution.

[0049] Preferably, the drying temperature is 100-180°C, for example, 100°C, 120°C, 150°C or 180°C.

[0050] After the second solid phase of the present invention is dried at 100-180°C, the crystal structure of Na2SO4·(NH4)2SO4·4H2O is destroyed, thereby losing crystal water to obtain a mixed salt of ammonium sulfate and sodium sulfate, which can be returned to step (1) for continued dissolution, thereby realizing the recycling of raw materials and further improving the full utilization of resources in sodium ammonium sulfate solid waste; if the second solid phase is not dried, it will dissolve according to the ratio of ammonium sulfate and sodium sulfate in the composite salt, resulting in no further dissolution after saturation, resulting in the inability to fully reuse resources, resulting in waste.

[0051] Preferably, the method further comprises: step (1) dissolving the first solid phase to obtain a second dissolved liquid; then the second dissolved liquid is sequentially subjected to a first pH adjustment and aeration to obtain an aerated liquid and ammonia.

[0052] Preferably, the dissolving temperature is 40-80°C, for example, 40°C, 50°C, 60°C, 70°C or 80°C.

[0053] Preferably, the endpoint of the first pH adjustment is pH>11, for example, it may be 11.2, 11.5, 11.7 or 12.

[0054] The present invention further preferably has the endpoint of the first pH adjustment as pH>11, so that all ammonia nitrogen in the second dissolved solution is converted into ammonia gas and removed from the solution, thereby improving the purity of the subsequently obtained sodium sulfate product.

[0055] Preferably, the method further comprises sequentially subjecting the aerated liquid to a second pH adjustment and a second evaporation crystallization to obtain a sodium sulfate product.

[0056] Preferably, the second pH adjustment is performed using sulfuric acid.

[0057] Preferably, the endpoint of the second pH adjustment is pH 5-6, for example, 5, 5.2, 5.5, 5.8 or 6.

[0058] Preferably, the ammonia gas is absorbed by an absorption liquid to obtain an ammonium sulfate product.

[0059] The present invention has no special limitation on the solid-liquid separation in the above process. Any device and method for solid-liquid separation known to those skilled in the art can be used, and can also be adjusted according to the actual process, such as filtration, centrifugation or sedimentation separation, or a combination of different methods.

[0060] As a further preferred technical solution of the present invention, the method comprises the following steps:

[0061] (1) partially dissolving sodium ammonium sulfate solid waste at 5-10° C. and performing solid-liquid separation to obtain a first dissolved solution and a first solid phase; the mass volume ratio of the sodium ammonium sulfate solid waste to the solvent is 1:(0.56-1.05); the molar ratio of ammonium to sodium in the first dissolved solution is (5.8-7.2):1; the molar ratio of ammonium to sodium in the first solid phase is 1:(10-50);

[0062] (2) Step (1) The first dissolved liquid is first subjected to precipitation treatment with a precipitant, wherein the mass ratio of the precipitant to the metal impurities in the sodium ammonium sulfate solid waste is (0.5-2):1, to obtain a precipitation treatment liquid; then the precipitation treatment liquid is subjected to oxidation treatment with an oxidant, wherein the ratio of the amount of the oxidant to the COD value of the organic impurities in the sodium ammonium sulfate solid waste is (2.2-12):1, to obtain an oxidation treatment liquid;

[0063] The oxidation treatment liquid is subjected to a first evaporation crystallization and solid-liquid separation to obtain an ammonium sulfate product and a first mother liquor; the end point of the first evaporation crystallization is the Na + The content is less than 40000ppm;

[0064] (3) Step (2) The first mother liquor is cooled and crystallized at 5-10°C and solid-liquid separated to obtain a second mother liquor and a second solid phase; the second solid phase comprises a composite salt containing sodium sulfate and ammonium sulfate; the end point of the cooling crystallization is the Na + The content is less than 24000ppm;

[0065] The second mother liquor is circulated to step (2) to continue the first evaporation crystallization;

[0066] The second solid phase is dried at 100-180° C. and then circulated to step (1) to continue partial dissolution;

[0067] The method also includes: step (1) dissolving the first solid phase at 40-80° C. to obtain a second dissolved liquid, then adjusting the second dissolved liquid to a pH value greater than 11 through a first pH adjustment, and then aerating to obtain an aerated liquid and ammonia; adjusting the aerated liquid to a pH value of 5-6 through a second pH adjustment, and then performing a second evaporation crystallization to obtain a sodium sulfate product; and absorbing the ammonia through an absorption liquid to obtain an ammonium sulfate product.

[0068] Compared with the prior art, the present invention has at least the following beneficial effects:

[0069] (1) The present invention provides a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium. The method makes full use of the solubility difference between ammonium sulfate and sodium sulfate under low temperature conditions, and controls the temperature of partial dissolution within the range of 5-10°C so that ammonium sulfate is fully dissolved in the first dissolving solution, while sodium sulfate mainly enters the first solid phase for subsequent production of high-purity sodium sulfate products; the preliminary separation of ammonium sulfate and sodium sulfate in the sulfate solid waste containing sodium ammonium is achieved; the mass ratio of ammonium sulfate to sodium sulfate in the first dissolving solution is relatively large, and a high-purity ammonium sulfate product is obtained through the subsequent first evaporation and crystallization, thereby achieving full utilization of resources in the sulfate solid waste containing sodium ammonium.

[0070] (2) The method for resource utilization of sodium ammonium sulfate solid waste provided by the present invention further improves the quality and recovery rate of the ammonium sulfate product obtained by the first evaporation and crystallization by further preferably performing precipitation treatment and oxidation treatment on the first dissolving solution in sequence before the first evaporation and crystallization to remove metal impurities and organic impurities, and further preferably performing cooling crystallization on the first mother liquor to remove sodium, and selecting the end points of the first evaporation and crystallization and cooling crystallization, etc. The purity of the ammonium sulfate product is preferably as high as 98.6% or more, the appearance color is white, the water content is preferably as low as 1.3% or less, and the recovery rate is preferably as high as 98.00% or more; the recovery rate of sodium in the first solid phase is preferably as high as 99.25% or more, and the amount of sodium hydroxide required to achieve a purity of the sodium sulfate product of 98.5% or more is as low as 0.93% or less, and the recovery rate is as high as 99.25% or more. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 The present invention provides a flow chart of a method for preparing high-quality ammonium sulfate by using sulfate solid waste containing sodium ammonium. DETAILED DESCRIPTION

[0072] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0073] As a specific embodiment of the present invention, a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium is provided, such as Figure 1 As shown, the method comprises the following steps:

[0074] (1) partially dissolving sodium ammonium sulfate solid waste at 5-10° C. and performing solid-liquid separation to obtain a first dissolved solution and a first solid phase; the mass volume ratio of the sodium ammonium sulfate solid waste to the solvent is 1:(0.56-1.05); the molar ratio of ammonium to sodium in the first dissolved solution is (5.8-7.2):1; the molar ratio of ammonium to sodium in the first solid phase is 1:(10-50);

[0075] (2) Step (1) The first dissolved liquid is first subjected to precipitation treatment with a precipitant and solid-liquid separation, wherein the mass ratio of the precipitant to the metal impurities in the sodium ammonium sulfate solid waste is (0.5-2):1, to obtain a precipitation treatment liquid and a metal mud; then the precipitation treatment liquid is subjected to oxidation treatment with an oxidant, wherein the ratio of the COD value of the oxidant to the organic impurities in the sodium ammonium sulfate solid waste is (2.2-12):1, to obtain an oxidation treatment liquid;

[0076] The oxidation treatment liquid is subjected to a first evaporation crystallization at 95-105°C and solid-liquid separation to obtain an ammonium sulfate product and a first mother liquor; the end point of the first evaporation crystallization is the Na + The content is less than 40000ppm;

[0077] Step (1) the first solid phase is dissolved at 40-80° C. to obtain a second solution, and then the second solution is adjusted to a pH>11 by a first pH adjustment, and aerated to obtain an aerated liquid and ammonia; then the aerated liquid is first adjusted to a pH of 5-6 by sulfuric acid, and then subjected to a second evaporation crystallization to obtain a sodium sulfate product;

[0078] The ammonia gas is absorbed by sulfuric acid to obtain an ammonium sulfate solution, which is then subjected to a third evaporation crystallization to obtain an ammonium sulfate product;

[0079] (3) Step (2) The first mother liquor is cooled and crystallized at 5-10°C and solid-liquid separated to obtain a second mother liquor and a second solid phase; the second solid phase comprises a composite salt containing sodium sulfate and ammonium sulfate; the end point of the cooling crystallization is the Na + The content is less than 24000ppm;

[0080] The second mother liquor is circulated to step (2) to continue the first evaporation crystallization;

[0081] The second solid phase is dried at 100-180°C and then circulated to step (1) to continue partial dissolution.

[0082] It should be understood that, in the description of the present invention, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0083] 1. Implementation

[0084] Example 1

[0085] This embodiment provides a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium, the method comprising the following steps:

[0086] (1) partially dissolving sodium ammonium sulfate solid waste in water at 8° C. and filtering to obtain a first dissolved solution and a first solid phase; the mass volume ratio of the sodium ammonium sulfate solid waste to water is 1:0.84; the molar ratio of ammonium to sodium in the first dissolved solution is 6.8:1; and the molar ratio of ammonium to sodium in the first solid phase is 1:41.4;

[0087] (2) Step (1) The first dissolved liquid is first subjected to precipitation treatment with ammonium sulfide and filtered, wherein the mass ratio of the ammonium sulfide to the metal impurities in the sodium ammonium sulfate solid waste is 1:1, to obtain a precipitation treatment liquid and a metal mud, wherein the metal mud includes copper sulfide and nickel sulfide; then the precipitation treatment liquid is subjected to oxidation treatment with hydrogen peroxide, wherein the ratio of the amount of hydrogen peroxide to the COD value of the organic impurities in the sodium ammonium sulfate solid waste is 8:1, to obtain an oxidation treatment liquid;

[0088] The oxidation treatment liquid is subjected to a first evaporation crystallization at 100°C and filtered to obtain an ammonium sulfate product and a first mother liquor; the endpoint of the first evaporation crystallization is the Na + The content is 35000ppm;

[0089] Step (1) the first solid phase is dissolved in water at 60° C. to obtain a second dissolved liquid, and then the second dissolved liquid is first adjusted to a pH of 12 by a sodium hydroxide solution, and aerated to obtain ammonia and an aerated liquid; then the aerated liquid is first adjusted to a pH of 5.5 by sulfuric acid, and then subjected to a second evaporation crystallization and filtered to obtain a sodium sulfate product;

[0090] The ammonia gas is absorbed by sulfuric acid to obtain an ammonium sulfate solution, which is then subjected to a third evaporation crystallization to obtain an ammonium sulfate product;

[0091] (3) Step (2) The first mother liquor is cooled and crystallized at 7°C and solid-liquid separated to obtain a second mother liquor and Na2SO4·(NH4)2SO4·4H2O; the end point of the cooling crystallization is Na + The content is 21457ppm;

[0092] The second mother liquor is circulated to step (2) to continue the first evaporation crystallization;

[0093] The Na2SO4·(NH4)2SO4·4H2O is dried at 150°C and then circulated to step (1) to continue partial dissolution.

[0094] The components and contents of the sodium ammonium sulfate solid waste in this embodiment are shown in Table 1;

[0095] Table 1

[0096]

[0097] Example 2

[0098] This embodiment provides a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium, the method comprising the following steps:

[0099] (1) partially dissolving sodium ammonium sulfate solid waste in water at 5° C. and filtering to obtain a first dissolved solution and a first solid phase; the mass volume ratio of the sodium ammonium sulfate solid waste to water is 1:0.56; the molar ratio of ammonium to sodium in the first dissolved solution is 7.2:1; and the molar ratio of ammonium to sodium in the first solid phase is 1:47.91;

[0100] (2) Step (1) The first dissolved liquid is first subjected to precipitation treatment with sodium sulfide and filtered, wherein the mass ratio of the sodium sulfide to the metal impurities in the sodium ammonium sulfate solid waste is 0.5:1, to obtain a precipitation treatment liquid and a metal mud, wherein the metal mud includes copper sulfide and nickel sulfide; then the precipitation treatment liquid is subjected to oxidation treatment with ammonium sulfate, wherein the ratio of the amount of ammonium persulfate to the COD value of organic impurities in the sodium ammonium sulfate solid waste is 2.2:1, to obtain an oxidation treatment liquid;

[0101] The oxidation treatment liquid is subjected to a first evaporation crystallization at 95°C and filtered to obtain an ammonium sulfate product and a first mother liquor; the end point of the evaporation crystallization is the Na + The content of the solid phase is 32000ppm; in step (1), the first solid phase is dissolved in water at 40°C to obtain a second solution, and then the second solution is first adjusted to a pH of 12.5 by a sodium hydroxide solution, and aerated to obtain ammonia and an aerated liquid; then the aerated liquid is first adjusted to a pH of 5 by sulfuric acid, and then subjected to a second evaporation crystallization and filtration to obtain a sodium sulfate product;

[0102] The ammonia gas is absorbed by sulfuric acid to obtain an ammonium sulfate solution, which is then subjected to a third evaporation crystallization to obtain an ammonium sulfate product;

[0103] (3) Step (2) The first mother liquor is cooled and crystallized at 5°C and solid-liquid separated to obtain a second mother liquor and Na2SO4·(NH4)2SO4·4H2O; the end point of the cooling crystallization is Na + The content is 20613ppm;

[0104] The second mother liquor is circulated to step (2) to continue the first evaporation crystallization;

[0105] The Na2SO4·(NH4)2SO4·4H2O is dried at 100°C and then circulated to step (1) to continue partial dissolution.

[0106] The components and contents of the sodium ammonium sulfate solid waste in this embodiment are shown in Table 2;

[0107] Table 2

[0108]

[0109] Example 3

[0110] This embodiment provides a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium, the method comprising the following steps:

[0111] (1) partially dissolving sodium ammonium sulfate solid waste in water at 10° C. and filtering to obtain a first dissolved solution and a first solid phase; the mass volume ratio of the sodium ammonium sulfate solid waste to water is 1:1; the molar ratio of ammonium to sodium in the first dissolved solution is 5.9:1; and the molar ratio of ammonium to sodium in the first solid phase is 1:10.53;

[0112] (2) Step (1) The first dissolving liquid is first subjected to precipitation treatment with hydrogen sulfide and filtered, wherein the mass ratio of the hydrogen sulfide to the metal impurities in the sodium ammonium sulfate solid waste is 2:1, to obtain a precipitation treatment liquid and a metal mud, wherein the metal mud includes copper sulfide and nickel sulfide; then the precipitation treatment liquid is subjected to oxidation treatment with sodium sulfate, wherein the ratio of the amount of sodium persulfate to the COD value of the organic impurities in the sodium ammonium sulfate solid waste is 12:1, to obtain an oxidation treatment liquid;

[0113] The oxidation treatment liquid is subjected to a first evaporation crystallization at 105°C and filtered to obtain an ammonium sulfate product and a first mother liquor; the end point of the evaporation crystallization is the Na + The content is 39000ppm;

[0114] Step (1) the first solid phase is dissolved in water at 80° C. to obtain a second dissolved liquid, and then the second dissolved liquid is first adjusted to a pH of 11.5 by a sodium hydroxide solution, and aerated to obtain ammonia and an aerated liquid; then the aerated liquid is first adjusted to a pH of 6 by sulfuric acid, and then subjected to a second evaporation crystallization and filtration to obtain a sodium sulfate product;

[0115] The ammonia gas is absorbed by sulfuric acid to obtain an ammonium sulfate solution, which is then subjected to a third evaporation crystallization to obtain an ammonium sulfate product;

[0116] (3) Step (2) The first mother liquor is cooled and crystallized at 10°C and solid-liquid separated to obtain a second mother liquor and Na2SO4·(NH4)2SO4·4H2O; the end point of the cooling crystallization is Na + The content is 23491ppm;

[0117] The second mother liquor is circulated to step (2) to continue the first evaporation crystallization;

[0118] The Na2SO4·(NH4)2SO4·4H2O is dried at 180°C and then circulated to step (1) to continue the first dissolution.

[0119] The components and contents of the sodium ammonium sulfate solid waste in this embodiment are shown in Table 3;

[0120] Table 3

[0121]

[0122] Example 4

[0123] This embodiment provides a method for preparing high-quality ammonium sulfate using sodium ammonium sulfate solid waste. The method is the same as that of Example 1 except that the mass volume ratio of the sodium ammonium sulfate solid waste to water in step (1) is 1:0.5.

[0124] Example 5

[0125] This embodiment provides a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium. The method includes step (2) wherein the endpoint of the first evaporation crystallization is the Na in the first mother liquor. + Except that the content of is 42000ppm, the rest are the same as Example 1.

[0126] Example 6

[0127] This embodiment provides a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium. The method is the same as that of Embodiment 1 except that step (3) is not performed, but the first mother liquor is directly circulated to perform the first evaporation crystallization three times.

[0128] Example 7

[0129] This embodiment provides a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium. The method includes step (3) wherein the end point of the cooling crystallization is the Na in the second mother liquor. + Except that the content of is 28000ppm, the rest are the same as in Example 1.

[0130] The method described in this embodiment is due to the Na in the second mother liquor in step (3). + There is a lot of residue, resulting in a lower single ammonium sulfate yield in the subsequent first evaporation crystallization; for example: the sodium in the first mother liquor is removed from 40000ppn to 20000ppm, the sodium removal rate is 50%, and the sodium removal rate is 30% when it is removed to 28000ppm. Therefore, removing sodium to 20000ppm once is equivalent to removing sodium to 28000ppm twice), that is, it does not affect the quality of ammonium sulfate crystallization and process operation, but the operating cost is relatively high.

[0131] Example 8

[0132] This embodiment provides a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium. The method is the same as that of Example 1 except that the precipitation treatment described in step (2) is not performed.

[0133] The ammonium sulfate product obtained in this example has an abnormal appearance, being blue-green crystals.

[0134] Example 9

[0135] This embodiment provides a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium. The method is the same as that of Embodiment 1 except that the oxidation treatment described in step (2) is not performed.

[0136] The ammonium sulfate product obtained in this embodiment has a high moisture content, is sticky, and is easy to agglomerate.

[0137] Example 10

[0138] This embodiment provides a method for preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium. The method is the same as that of Embodiment 1 except that step (2) is preceded by oxidation treatment and then precipitation treatment.

[0139] The ammonium sulfate product obtained in this embodiment is doped with a trace amount of ammonium sulfide, which leads to a decrease in the purity of the ammonium sulfate product. In addition, the impurity ammonium sulfide will produce hydrogen sulfide poisonous gas under acidic conditions, which is relatively dangerous.

[0140] 2. Comparison

[0141] Comparative Example 1

[0142] This comparative example provides a method for preparing ammonium sulfate using sulfate solid waste containing sodium ammonium. The method is the same as Example 1 except that the temperature of the partial dissolution in step (1) is 4°C.

[0143] The method described in this comparative example has a relatively low temperature, which not only places high requirements on equipment, but also increases energy consumption costs.

[0144] Comparative Example 2

[0145] This comparative example provides a method for preparing ammonium sulfate using sulfate solid waste containing sodium ammonium. The method is the same as Example 1 except that the temperature of the partial dissolution in step (1) is 12°C.

[0146] The method described in this comparative example has a high sodium content in the first dissolving solution due to the high temperature, which increases the cost of subsequent sodium removal. Otherwise, the quality of the obtained ammonium sulfate product is low.

[0147] Comparative Example 3

[0148] This comparative example provides a method for preparing ammonium sulfate using sodium ammonium-containing sulfate solid waste, the method comprising first dissolving all of the sodium ammonium-containing sulfate solid waste in water at 40° C., and then directly cooling to 5° C. to crystallize and precipitate the product.

[0149] In this comparative example, since the sodium ammonium sulfate solid waste is completely dissolved in water, the product precipitated by cooling and crystallization is Na2SO4·(NH4)2SO4·4H2O instead of ammonium sulfate product.

[0150] Comparative Example 4

[0151] This comparative example provides a method for preparing ammonium sulfate using sulfate solid waste containing sodium ammonium. After obtaining the oxidation treatment liquid in Example 1, the method does not perform the first evaporation crystallization, but directly performs the cooling crystallization in step (3), and no longer reuses the evaporation crystallization. The rest is the same as Example 1.

[0152] After direct cooling and crystallization in the method described in this comparative example, the oxidation treatment liquid does not change. This is because the oxidation treatment liquid is a saturated solution at low temperature and an unsaturated solution at room temperature. If it is directly cooled from room temperature to low temperature again, no crystals will be precipitated, and the ammonium sulfate product cannot be obtained.

[0153] Comparative Example 5

[0154] The present comparative example provides a method for preparing ammonium sulfate by using sodium ammonium sulfate solid waste. The method adopts the scheme in Example 1 of CN107867708A, and specifically comprises: mixing sodium ammonium sulfate solid waste and an appropriate amount of sodium chloride and heating to 350°C, and keeping the temperature for 2 hours until the ammonium chloride generated by the reaction of ammonium sulfate and sodium chloride in the sodium ammonium sulfate solid waste is completely volatilized. At the same time, the volatilized ammonium chloride gas is cooled and collected again to obtain high-purity ammonium chloride solid. The tail gas is passed into water to obtain an ammonium chloride aqueous solution, and the non-volatilized gas is relatively high-purity sodium sulfate, wherein the N content is 0.0001%.

[0155] This comparative example converts ammonium sulfate into ammonium chloride for recovery, but does not achieve the recovery and utilization of ammonium sulfate. Moreover, it is carried out at a relatively high temperature, which places high requirements on equipment.

[0156] Comparative Example 6

[0157] The present comparative example provides a method for preparing ammonium sulfate by using sodium ammonium-containing sulfate solid waste. The method directly dissolves the sodium ammonium-containing sulfate in water at 60° C., then adjusts the pH value to 12 by a sodium hydroxide solution, and obtains ammonia and an aerated liquid by aeration; then, the aerated liquid is firstly adjusted to a pH value of 5.5 by a second pH adjustment by sulfuric acid, and then subjected to a second evaporation crystallization and filtration to obtain a sodium sulfate product; the ammonia is absorbed by sulfuric acid to obtain an ammonium sulfate solution, and then subjected to a third evaporation crystallization to obtain an ammonium sulfate product.

[0158] The method described in this comparative example needs to consume a large amount of alkali to convert the ammonium ions in the solution into NH3, which makes the production cost very high.

[0159] 3. Test and its results

[0160] In order to obtain sodium sulfate with a purity of 98.5% or more in step (1), the second dissolving solution needs to be adjusted to a pH value by using a sodium hydroxide solution, and the adjustment of the pH value depends on the concentration of ammonium ions in the original second dissolving solution. If the amount of sodium hydroxide used in this step is too large, the cost of the overall solid waste treatment will increase significantly. In the above embodiments and comparative examples, the purity of the final sodium sulfate is fixed at 98.5% or more, and the amount of sodium hydroxide required to be added is evaluated to evaluate the environmental protection and economy of the overall process.

[0161] The total recovery rate of ammonium sulfate and sodium sulfate obtained by the methods described in the above embodiments and comparative examples, the purity of the sodium sulfate product, and the purity, appearance color and moisture content of the ammonium sulfate product obtained after the first evaporation crystallization were tested and calculated, and the results are shown in Table 4;

[0162] Table 4

[0163]

[0164]

[0165] Note: “ / ” in Table 4 indicates no relevant data.

[0166] From Table 4 we can see that:

[0167] (1) It can be seen from Examples 1 to 3 that the method for preparing high-quality ammonium sulfate from sulfate solid waste containing sodium ammonium provided by the present invention can efficiently separate and recycle the ammonium sulfate and sodium sulfate resources in the sulfate solid waste containing sodium ammonium, and the recovery rate of the ammonium sulfate product obtained after the first evaporation and crystallization is preferably as high as 98.00% or more, the purity is as high as 98.6% or more, the color is white, and the water content is as low as 1.3% or less, the sodium recovery rate in the first solid phase is as high as 99.25% or more, and the purity of the sodium sulfate product is as high as 98.6% or more, and the amount of sodium hydroxide added required is as low as 0.93% or less.

[0168] (2) Combining Example 1 and Example 4, it can be seen that the mass volume ratio of the sodium ammonium sulfate solid waste and water in step (1) of Example 4 is too large, resulting in the recovery rate of the ammonium sulfate product after the first evaporation and crystallization being only 67.31%, and the amount of sodium hydroxide added required to prepare the qualified sodium sulfate product is increased to 14.4%; thus, it is further preferred that the mass volume ratio of the sodium ammonium sulfate solid waste and the solvent during the partial dissolution in step (1) of the present invention is 1: (0.56-1.05), which further improves the recovery rate of ammonium sulfate after the first evaporation and crystallization of the sodium ammonium sulfate solid waste and reduces the consumption of alkali.

[0169] (3) Combining Example 1 and Example 5, it can be seen that: in Example 5, step (2) at the end of the first evaporation crystallization, the Na content in the first mother liquor is + The content of Na in the first mother liquor is relatively high, resulting in the purity of the ammonium sulfate product after the first evaporation crystallization being only 96.2%. It can be seen that the present invention further prefers that the end point of the first evaporation crystallization is Na in the first mother liquor. + The content is less than 40000ppm, which further improves the quality of ammonium sulfate products.

[0170] (4) Combining Example 1 with Examples 6 to 7, it can be seen that: in Example 6, since step (3) is not performed, but the first mother liquor is directly circulated for three times of first evaporation crystallization, the recovery rate of ammonium sulfate is not affected. However, multiple evaporation crystallizations will increase the sodium content in the first mother liquor, thereby reducing the purity of ammonium sulfate. The purity of ammonium sulfate is only 90.1%, and the recovery rate of sodium in the first solid phase is also reduced to 85.41%. In Example 7, due to the Na content in the second mother liquor at the end of the cooling crystallization in step (3), the recovery rate of sodium in the first solid phase is reduced to 85.41%. + The content of is still high, resulting in a decrease in the yield of the single ammonium sulfate product; This shows that the present invention further preferably performs the cooling crystallization in step (3) to further remove the sodium in the first mother liquor, and further preferably the end point of the cooling crystallization in step (3) is Na in the second mother liquor. + The content is less than 24000ppm, so that a higher purity ammonium sulfate product can be obtained in one cycle, and the recovery rate is higher.

[0171] (5) Combining Example 1 with Examples 8 to 10, it can be seen that in Example 8, no precipitation treatment was performed, resulting in an abnormal appearance of ammonium sulfate crystals, which were bluish green and could not be sold normally. In Example 9, no oxidation treatment was performed, resulting in the ammonium sulfate product being sticky and easy to agglomerate, with a moisture content as high as 2.4%, thereby reducing its purity to 97.3%. In Example 10, oxidation treatment was performed first and then precipitation treatment was performed, resulting in S 2- The introduction of the first dissolving solution into the ammonium sulfate product subsequently leads to the introduction of ammonium sulfide impurities, which will produce hydrogen sulfide toxic gas under acidic conditions, posing a greater safety hazard; this shows that the present invention further preferably sequentially performs precipitation treatment and oxidation treatment on the first dissolving solution, thereby further improving the quality of the ammonium sulfate product.

[0172] (6) It can be seen from the comprehensive implementation of Example 1 and Comparative Examples 1 to Comparative Examples 6 that in Comparative Example 1, due to the low temperature of partial dissolution, the equipment requirements are high and the energy consumption cost increases; in Comparative Example 2, due to the high temperature of partial dissolution, the solubility difference between ammonium sulfate and sodium sulfate in the first dissolving solution is reduced, which increases the cost of subsequent sodium removal operations; in Comparative Example 3, since the sodium ammonium sulfate solid waste is completely dissolved in water, the product precipitated by cooling crystallization is Na2SO4·(NH4)2SO4·4H2O; in Comparative Example 4, since the oxidation treatment solution is directly cooled and crystallized, no crystal is precipitated, which has no practical significance and wastes equipment energy consumption costs; in Comparative Example 5, pyrocalcination is used for treatment, and the recovery rate of the obtained ammonium sulfate product is low, and the equipment requirements and energy consumption are high; in Comparative Example 6, the traditional method of preparing sodium sulfate and ammonium sulfate by complete dissolution and then denitrification is adopted, which requires the addition of 43.64% sodium hydroxide, consumes a large amount of alkali, has a very high production cost, and has poor economic benefits.

[0173] 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 preparing high-quality ammonium sulfate using sulfate solid waste containing sodium ammonium, characterized in that: The method comprises the following steps: (1) partially dissolving the sodium ammonium sulfate solid waste and performing solid-liquid separation to obtain a first dissolved liquid and a first solid phase; (2) The first dissolved solution in step (1) is subjected to a first evaporation crystallization and solid-liquid separation to obtain an ammonium sulfate product and a first mother liquor; Wherein, the temperature of partial dissolution in step (1) is 5-10°C.

2. The method according to claim 1, characterized in that: In terms of mass percentage, the sodium ammonium sulfate solid waste in step (1) comprises 40-75wt% ammonium sulfate, 20-50wt% sodium sulfate, 2-15wt% water, and the rest are metal impurities and organic impurities; Preferably, the metal impurities include any one of Cu, Ni or Zn, or a combination of at least two of them.

3. The method according to claim 1 or 2, characterized in that: The partially dissolved solvent in step (1) includes water; Preferably, the mass volume ratio of the sodium ammonium sulfate solid waste to the solvent in step (1) is 1:(0.56-1.05); Preferably, in step (1), the molar ratio of ammonium to sodium in the first dissolving solution is (5.8-7.2):1; Preferably, in step (1), the molar ratio of ammonium to sodium in the first solid phase is 1:(10-50).

4. The method according to any one of claims 1 to 3, characterized in that: Step (2) The endpoint of the first evaporation crystallization is the Na + The content is less than 40000ppm.

5. The method according to any one of claims 1 to 4, characterized in that: Step (2) Before the first evaporation crystallization, the first solution is first subjected to impurity removal treatment; Preferably, the impurity removal treatment comprises a precipitation treatment and an oxidation treatment performed sequentially; Preferably, the precipitant used in the precipitation treatment includes any one of sodium sulfide, ammonium sulfide or hydrogen sulfide, or a combination of at least two thereof; Preferably, the mass ratio of the precipitant to the metal impurities in the sodium ammonium sulfate solid waste is (0.5-2):1; Preferably, the oxidant used in the oxidation treatment includes any one of hydrogen peroxide, sodium persulfate or ammonium persulfate, or a combination of at least two thereof; Preferably, the ratio of the amount of the oxidant to the COD value of organic impurities in the sodium ammonium sulfate solid waste is (2.2-12):

1.

6. The method according to any one of claims 1 to 5, characterized in that: Based on step (1) and step (2), the method further comprises the following steps: (3) Step (2) The first mother liquor is cooled, crystallized and solid-liquid separated to obtain a second mother liquor and a second solid phase.

7. The method according to claim 6, characterized in that The temperature of the cooling crystallization in step (3) is 5-10°C; Preferably, the end point of the cooling crystallization in step (3) is the Na + The content is less than 24000ppm; Preferably, in step (3), the second mother liquor is circulated to step (2) to continue evaporation and crystallization.

8. The method according to claim 6 or 7, characterized in that: In terms of mass percentage, the second solid phase in step (3) comprises a composite salt containing sodium sulfate and ammonium sulfate; Preferably, the composite salt containing sodium sulfate and ammonium sulfate includes Na2SO4·(NH4)2SO4·4H2O; Preferably, in step (3), the second solid phase is dried and then circulated to step (1) to continue partial dissolution; Preferably, the drying temperature is 100-180°C.

9. The method according to any one of claims 6 to 8, characterized in that: The method further comprises: step (1) dissolving the first solid phase to obtain a second dissolved liquid; then sequentially adjusting the pH value of the second dissolved liquid and aerating the second dissolved liquid to obtain an aerated liquid and ammonia; Preferably, the dissolving temperature is 40-80°C; Preferably, the endpoint of the first pH adjustment is pH>11; Preferably, the method further comprises sequentially subjecting the aerated liquid to a second pH adjustment and a second evaporation crystallization to obtain a sodium sulfate product; Preferably, the endpoint of the second pH adjustment is pH 5-6; Preferably, the ammonia gas is absorbed by an absorption liquid to obtain an ammonium sulfate product.

10. The method according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: (1) partially dissolving sodium ammonium sulfate solid waste at 5-10° C. and performing solid-liquid separation to obtain a first dissolved solution and a first solid phase; the mass volume ratio of the sodium ammonium sulfate solid waste to the solvent is 1:(0.56-1.05); the molar ratio of ammonium to sodium in the first dissolved solution is (5.8-7.2):1; the molar ratio of ammonium to sodium in the first solid phase is 1:(10-50); (2) Step (1) The first dissolved liquid is first subjected to precipitation treatment with a precipitant, wherein the mass ratio of the precipitant to the metal impurities in the sodium ammonium sulfate solid waste is (0.5-2):1, to obtain a precipitation treatment liquid; then the precipitation treatment liquid is subjected to oxidation treatment with an oxidant, wherein the ratio of the amount of the oxidant to the COD value of the organic impurities in the sodium ammonium sulfate solid waste is (2.2-12):1, to obtain an oxidation treatment liquid; The oxidation treatment liquid is subjected to a first evaporation crystallization and solid-liquid separation to obtain an ammonium sulfate product and a first mother liquor; the end point of the first evaporation crystallization is the Na + The content is less than 40000ppm; (3) Step (2) The first mother liquor is cooled and crystallized at 5-10°C and solid-liquid separated to obtain a second mother liquor and a second solid phase; the second solid phase comprises a composite salt containing sodium sulfate and ammonium sulfate; the end point of the cooling crystallization is the Na + The content is less than 24000ppm; The second mother liquor is circulated to step (2) to continue the first evaporation crystallization; The second solid phase is dried at 100-180°C and then circulated to step (1) to continue partial dissolution; The method further comprises: step (1) dissolving the first solid phase at 40-80° C. to obtain a second dissolved liquid, then adjusting the second dissolved liquid to a pH>11 through a first pH adjustment, and then aerating the second dissolved liquid to obtain an aerated liquid and ammonia; The aeration liquid is subjected to a second pH adjustment to a pH of 5-6, and then subjected to a second evaporation crystallization to obtain a sodium sulfate product; The ammonia gas is absorbed by the absorption liquid to obtain an ammonium sulfate product.

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