Process for synergic utilization of sodium sulfate and ammonium-containing waste salt

Abstract

The application belongs to the technical field of chemical industry and secondary resource utilization, and specifically discloses a process for synergistically utilizing sodium sulfate and ammonium-containing waste salt. The application provides a high-value utilization method of sodium sulfate, which comprises the following steps: mixing sodium sulfate, organic ammonium salt and sulfuric acid, and adding water to configure a mixed solution; using an extractant to extract the mixed solution, and separating an aqueous phase and an organic phase; adding a pH adjuster into the aqueous phase to adjust the pH to weak alkalinity, passing in carbon dioxide gas to fully react, cooling and crystallizing, and filtering to obtain a filtrate and sodium bicarbonate precipitate; heating the filtrate to evaporate and crystallize, and obtaining ammonium sulfate; and recovering organic acid in the organic phase. The application provides a revolutionary solution for sodium sulfate byproduct accumulation and ammonium-containing wastewater treatment, has dual values of resource recycling and carbon emission reduction, has a full-process closed-loop design in the process, has wide applicability, has high product purity, and has high economic efficiency.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering and secondary resource utilization technology, and in particular to a process for the synergistic utilization of sodium sulfate and ammonium-containing waste salt. Background Technology

[0002] Sodium sulfate is a common inorganic salt, known as Glauber's salt in its anhydrous form and as sodium sulfate in its decahydrate form. As a basic chemical raw material, sodium sulfate has wide applications in traditional industries such as detergents, glass manufacturing, pulp and paper, and textile printing and dyeing. However, with the rapid development of modern industry, the source structure of sodium sulfate has undergone profound changes. In addition to natural minerals and salt lake extraction, more and more sodium sulfate is being separated as a byproduct from various industrial processes. For example, tens of millions of tons of sodium sulfate are generated annually as a byproduct in viscose fiber production, sodium dichromate manufacturing, lithium battery wet recycling, flue gas wet desulfurization (FGD), and certain organic synthesis processes.

[0003] This imbalance between supply and demand leads to low market prices for sodium sulfate, a byproduct. Large-scale accumulation not only occupies land resources but also risks polluting groundwater and soil through leaching, posing a potential threat to the ecological environment. Therefore, how to comprehensively utilize these bulk industrial byproducts in a high-value and resource-oriented manner has become a key link in achieving green chemical engineering and a circular economy. This challenge is common to resource utilization issues in many other industrial sectors, such as the comprehensive utilization of waste lithium-ion batteries and agricultural waste. The core of these studies is to transform low-value "waste" into useful resources, thereby improving the economic efficiency and environmental sustainability of the entire industrial chain.

[0004] In recent years, numerous innovative studies have emerged regarding the comprehensive utilization of sodium sulfate. Researchers are no longer limited to using it as a filler or low-end raw material, but are actively exploring technological pathways to transform it into high-value-added chemicals, functional materials, and key industrial additives. Among these, the process of converting sodium sulfate into sodium carbonate or sodium bicarbonate has become a research hotspot because it simultaneously consumes the greenhouse gas carbon dioxide. To this end, this invention proposes a novel co-utilization process of sodium sulfate and ammonium-containing waste salt to achieve high-value utilization of low-value waste salt. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention provides a process for the synergistic utilization of sodium sulfate and ammonium-containing waste salt. The synergistic utilization process of this invention proposes for the first time a three-stage design of waste salt synergistic reaction - extraction and impurity removal - carbonization and crystallization, realizing the simultaneous high-value conversion of sodium sulfate and ammonium-containing waste salt. Organic acid is recovered through the first metathesis reaction, and relatively pure NaHCO3 and (NH4)2SO4 are obtained through the second metathesis reaction and evaporation crystallization. Through process coupling, CO2 fixation, organic acid recovery and inorganic salt purification are integrated into a single system, realizing the overall high-value utilization.

[0006] This invention provides a method for the high-value utilization of sodium sulfate, comprising the following steps:

[0007] S1. Mix sodium sulfate, organic ammonium salt and sulfuric acid, and add water to prepare a mixed solution;

[0008] S2. Extract the mixed solution using an extractant to separate the aqueous phase and the organic phase;

[0009] S3. Add a pH adjuster to the aqueous phase to adjust the pH to weakly alkaline, introduce carbon dioxide gas to react fully, cool to crystallize, and filter to obtain filtrate and sodium bicarbonate precipitate.

[0010] S4. Heat the filtrate to evaporate and crystallize, to obtain ammonium sulfate;

[0011] S5. Recover the organic acids in the organic phase.

[0012] According to some embodiments of the present invention, the molar ratio of sodium sulfate and sulfuric acid in step S1 is (0.5~1.5):(1~2), and the molar ratio of ammonium ions in the organic ammonium salt to hydrogen in the sulfuric acid is 1:(0.8~1.2).

[0013] According to some embodiments of the present invention, the mass concentration of the solute in the mixed solution in step S1 is 25 wt.% to 50 wt.%.

[0014] According to some embodiments of the present invention, the extractant in step S2 includes at least one of ether extractants, ester extractants, ketone extractants, halohydrocarbon extractants, phosphoric acid extractants, alcohol extractants, alkane extractants, amine extractants, or ionic liquid extractants.

[0015] According to some embodiments of the present invention, the extractant further includes a stabilizer, the stabilizer including kerosene or sulfonated kerosene.

[0016] According to some embodiments of the present invention, the oil-to-water volume ratio during the extraction process is (0.5~3):1.

[0017] As an alternative, extraction in step S2 can be replaced by cooling crystallization, and no restrictions are placed on the crystallization conditions here.

[0018] According to some embodiments of the present invention, step S3, adjusting the pH to a slightly alkaline state, means adjusting the pH to 8-10.

[0019] According to some embodiments of the present invention, the pH adjuster is selected from at least one of ammonia, NaOH, and Na2CO3.

[0020] According to some embodiments of the present invention, in step S3, when carbon dioxide gas is introduced to carry out the carbonation reaction, the solution is heated to 40°C to 70°C; the amount of carbon dioxide introduced needs to be adjusted according to the reaction situation, and a pressurized reaction can be carried out if necessary.

[0021] According to some embodiments of the present invention, during the cooling crystallization in step S3, the solution is cooled to 0°C to 12°C.

[0022] According to some embodiments of the present invention, in step S3, the sodium bicarbonate precipitate obtained by crystallization is further subjected to washing and drying treatment; the water used for washing should be distilled water with a water temperature of 0℃~10℃; in order to prevent the decomposition of NaHCO3 crystals, the drying temperature should not be too high, and the optimal temperature should be 30℃~70℃.

[0023] According to some embodiments of the present invention, the evaporation and crystallization temperature in step S4 is 50°C to 70°C.

[0024] According to some embodiments of the present invention, step S5 involves recovery processing based on the specific type of organic acid in the organic phase, and the recovery processing method includes, but is not limited to, at least one of the following methods 1) to 4):

[0025] 1) Evaporation-crystallization method;

[0026] 2) Evaporation-condensation method

[0027] 3) Column chromatography;

[0028] 4) Membrane electrolysis method.

[0029] According to some embodiments of the present invention, the evaporation crystallization method further includes back-extraction of the organic phase. The back-extraction agent can be an alkaline solution such as ammonia, NaOH, or Na2CO3, and the amount used must be specifically selected according to the extraction conditions. Preferably, the organic acid is recovered by adjusting the pH of the back-extraction solution to acidic and then using the evaporation crystallization method.

[0030] According to some embodiments of the present invention, the stripping agent may be selected from sulfuric acid, hydrochloric acid, nitric acid or other inorganic acids, with a pH of 0.5 to 3.

[0031] The beneficial effects of this invention are:

[0032] The process described in this invention is the first to propose a three-stage design of waste salt synergistic reaction - extraction and impurity removal - carbonization and crystallization, realizing the simultaneous high-value conversion of sodium sulfate and ammonium-containing waste salt. Organic acid is recovered through the first metathesis reaction, and relatively pure NaHCO3 and (NH4)2SO4 are obtained through the second metathesis reaction and evaporation crystallization. Through process coupling, CO2 fixation, organic acid recovery and inorganic salt purification are integrated into a single system, realizing the overall high-value utilization.

[0033] The solution described in this invention provides a revolutionary solution for the treatment of sodium sulfate byproduct accumulation and ammonium-containing wastewater. It has the dual value of resource recycling and carbon emission reduction, avoids high-temperature treatment, effectively reduces production energy consumption, and features a closed-loop design throughout the process. It can realize the recycling of extractants, supports multiple extractants, has wide applicability, and produces high-purity final products. It can simultaneously produce three commercial products (NaHCO3, (NH4)2SO4, and organic acids), which is highly economical and especially suitable for integrated waste salt treatment centers in chemical industrial parks.

[0034] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0036] Figure 1 This is a process flow diagram of the sodium sulfate-organic ammonium salt co-processing in Example 1 of the present invention. Detailed Implementation

[0037] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0038] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0039] Example 1

[0040] This embodiment provides a method for preparing sodium bicarbonate and ammonium sulfate products using sodium sulfate and organic ammonium salts in synergistic processes, as shown in the process flow diagram below. Figure 1 As shown, the specific steps are as follows:

[0041] 1) Mix Na2SO4, CH3COONH4, and H2SO4 in a molar ratio of 1:1:0.55 to prepare a solution with a mass concentration of 40 wt.% for reaction;

[0042] 2) Extraction was performed using a mixed extractant with a mass ratio of tributyl phosphate (TBP):kerosene:octanol of 6.5:2.5:1 and an oil-water ratio of 1.2:1, separating the aqueous phase and the organic phase.

[0043] 3) Adjust the pH of the aqueous phase to 9 with NaOH solution, raise the temperature to 50℃, and then introduce CO2. After the reaction is complete, immerse the reactor in 10℃ circulating cold water, stir and ensure the reactor is as airtight as possible. After sedimentation for about 30 minutes, filter to obtain filter cake and filtrate.

[0044] 4) Wash the filter cake twice with ice water and dry it at 40°C to obtain NaHCO3 with a purity of 96.31% and a Na utilization rate of 78.94%; evaporate and crystallize the filtrate at 50°C to obtain (NH4)2SO4 with a purity of 98.57% and an NH4 utilization rate of 80.36%.

[0045] 5) The organic phase was washed with hot water at 80°C until the pH was >6, and CH3COOH was recovered by evaporating the washing liquid. The total recovery rate was 90.44%.

[0046] Example 2

[0047] This embodiment provides a method for preparing sodium bicarbonate and ammonium sulfate products using sodium sulfate and organic ammonium salts in synergistic processes. The specific steps are as follows:

[0048] 1) Mix Na2SO4, (NH4)2C2O4 and H2SO4 in a molar ratio of 1:1:1.1 to prepare a solution with a mass concentration of 38 wt.%;

[0049] 2) Extraction was performed using a mixed extractant with a mass ratio of TBP:kerosene:octanol of 6:3:1 and an oil-water ratio of 1.2:1, resulting in the separation of the aqueous phase and the organic phase.

[0050] 3) Adjust the pH of the aqueous phase to 9 with NaOH solution, raise the temperature to 50℃, and then introduce CO2. After the reaction is complete, immerse the reactor in 10℃ circulating cold water, stir and ensure CO2 atmosphere. After precipitation for about 30 minutes, filter to obtain filter cake and filtrate.

[0051] 4) Wash the filter cake twice with ice water and dry it at 40°C to obtain NaHCO3 with a purity of 97.64% and a Na utilization rate of 83.76%; evaporate and crystallize the filtrate at 50°C to obtain (NH4)2SO4 with a purity of 97.93% and an NH4 utilization rate of 82.85%.

[0052] 5) After desorption of the organic phase with NaOH and acidification with H2SO4, part of the liquid was evaporated and cooled to 0℃. The resulting H2C2O4·2H2O crystals were obtained by filtration, with a total recovery rate of 87.91%.

[0053] Example 3

[0054] This embodiment provides a method for preparing sodium bicarbonate and ammonium sulfate products using sodium sulfate and organic ammonium salts in synergistic processes. The specific steps are as follows:

[0055] 1) Mix Na2SO4, CH3CH(OH)COONH4, and H2SO4 in a molar ratio of 1:1:0.55 to prepare a solution with a mass concentration of 40 wt.%.

[0056] 2) Extraction was performed using a mixed extractant with a mass ratio of trioctylamine (TOA):kerosene:n-octanol of 5:3:2. The oil-water ratio during the extraction process was 1.2:1, and the aqueous phase and organic phase were separated.

[0057] 3) Adjust the pH of the aqueous phase to 9 with ammonia, raise the temperature to 60°C, and then introduce CO2. After the reaction is complete, immerse the reactor in 10°C circulating cold water, stir and ensure CO2 atmosphere. After precipitation for about 30 minutes, filter to obtain filter cake and filtrate.

[0058] 4) Wash the filter cake twice with ice water and dry it at 40°C to obtain NaHCO3 with a purity of 98.92% and a Na utilization rate of 88.91%; evaporate and crystallize the filtrate at 60°C to obtain (NH4)2SO4 with a purity of 98.95% and an NH4 utilization rate of 76.89%.

[0059] 5) After desorption of the organic phase with NaOH and acidification with H2SO4, Na2SO4 was separated by evaporation and crystallization at 60℃. The temperature was then lowered to 0℃ for cooling crystallization to obtain CH3CH(OH)COOH crystals. The total recovery rate was 83.66%.

[0060] Example 4

[0061] This embodiment provides a method for preparing sodium bicarbonate and ammonium sulfate products using sodium sulfate and organic ammonium salts in synergistic processes. The specific steps are as follows:

[0062] 1) Take Na2SO4 and mixed ammonium salt (CH3COONH4:CH3CH(OH)COONH4:HCOONH4=1:1:1, with NH4 + Mix H2SO4 and H2SO4 in a molar ratio of 1:1:0.55 to prepare a solution with a mass concentration of 40 wt.%.

[0063] 2) Extraction was performed using a mixed extractant with a TBP:kerosene:octanol mass ratio of 6.5:2.5:1 and an oil-water ratio of 1.2:1, separating the aqueous phase and the organic phase.

[0064] 3) Adjust the pH of the aqueous phase to 9 with NaOH solution, raise the temperature to 50℃, and then introduce CO2. After the reaction is complete, immerse the reactor in 10℃ circulating cold water, stir and ensure the reactor is as airtight as possible. After sedimentation for about 30 minutes, filter to obtain filter cake and filtrate.

[0065] 4) Wash the filter cake twice with ice water and dry it at 40°C to obtain NaHCO3 with a purity of 98.55% and a Na utilization rate of 81.31%; evaporate and crystallize the filtrate at 50°C to obtain (NH4)2SO4 with a purity of 96.73% and an NH4 utilization rate of 85.68%.

[0066] 5) Organic acids in the organic phase were recovered by column chromatography, with recoveries of 75.19%, 83.16% and 77.76%, respectively.

[0067] Comparative Example 1

[0068] This comparative example provides a method for the co-preparation of sodium bicarbonate and ammonium sulfate products using sodium sulfate and organic ammonium salts. The specific steps are as follows:

[0069] 1) Mix Na2SO4 and CH3COONH4 in a 1:1 molar ratio to prepare a solution with a mass concentration of 35 wt.%;

[0070] 2) Extraction was performed using a mixed extractant with a mass ratio of tributyl phosphate (TBP):kerosene:octanol of 6.5:2.5:1 and an oil-water ratio of 1.2:1, separating the aqueous phase and the organic phase.

[0071] 3) Adjust the pH of the aqueous phase to 9 with NaOH solution, raise the temperature to 50℃, and then introduce CO2. After the reaction is complete, immerse the reactor in 10℃ circulating cold water, stir and ensure the reactor is as airtight as possible. After sedimentation for about 30 minutes, filter to obtain filter cake and filtrate.

[0072] 4) The filter cake was washed twice with ice water and dried at 40°C to obtain NaHCO3 with a purity of 97.55% and a Na utilization rate of 80.95%; the filtrate was evaporated and crystallized at 50°C to obtain (NH4)2SO4 with a purity of 87.16% and an NH4 utilization rate of 85.68%; the crystals precipitated at 50°C were found to contain certain amounts of CH3COONa and CH3COONH4.

[0073] In this comparative example, organic acids could not be obtained by back-extracting the organic phase.

[0074] Comparative Example 2

[0075] This comparative example provides a method for the synergistic preparation of sodium bicarbonate and ammonium sulfate products using sodium sulfate and inorganic ammonium salts. The specific steps are as follows:

[0076] 1) Mix Na2SO4, NH4Cl and H2SO4 in a molar ratio of 1:1:0.55 to prepare a solution with a mass concentration of 40 wt.%;

[0077] 2) Extraction was performed using a mixed extractant with a mass ratio of tributyl phosphate (TBP):kerosene:octanol of 6.5:2.5:1 and an oil-water ratio of 1.2:1, separating the aqueous phase and the organic phase.

[0078] 3) Adjust the pH of the aqueous phase to 9 with NaOH solution, raise the temperature to 50℃, and then introduce CO2. After the reaction is complete, immerse the reactor in 10℃ circulating cold water, stir and ensure the reactor is as airtight as possible. After sedimentation for about 30 minutes, filter to obtain filter cake and filtrate.

[0079] 4) The filter cake was washed twice with ice water and dried at 40°C to obtain NaHCO3 with a purity of 97.85% and a Na utilization rate of 83.31%, which contained some NaCl. The filtrate was evaporated and crystallized at 50°C to obtain (NH4)2SO4 with a purity of 65.46% and an NH4 utilization rate of 92.68%. Detection revealed that the precipitated (NH4)2SO4 contained a large amount of NH4Cl.

[0080] 5) There are no recyclable products in the organic phase.

[0081] As can be seen from Examples 1 to 4 of the present invention, the process provided by the present invention for preparing sodium bicarbonate and ammonium sulfate products by synergistic use of sodium sulfate and organic ammonium salts has a good separation effect on both single organic ammonium salts and mixed ammonium salts. It can be adapted to ammonium-containing waste salts from different sources and can prepare high-purity, high-value sodium bicarbonate, ammonium sulfate and organic acid products.

[0082] This invention uses sulfuric acid as a raw material for acidification, which can effectively promote the conversion of organic ammonium salts into organic acids that can be captured by the extractant, thereby purifying the reaction system and improving separation efficiency. However, using hydrochloric acid or nitric acid introduces impurity anions, leading to the formation of mixed salts during crystallization and affecting the final purity. In Comparative Example 1, the ammonium sulfate product prepared without sulfuric acid had low purity, contained mixed organic sodium salts, and could not yield organic acid products, resulting in low production efficiency. Comparative Example 2 used inorganic ammonium salts as raw materials, and the final ammonium sulfate product had even lower purity, with a significant amount of inorganic ammonium salt contamination. This indicates that the co-utilization process of sodium sulfate and ammonium-containing waste salts in this invention is not suitable for inorganic ammonium salts because inorganic acids are difficult to bind with the extractant, leading to the contamination of other inorganic ammonium salts during ammonium sulfate crystallization. Furthermore, the decreased sodium utilization rate reflects the adverse effect of the introduction of inorganic ions on system stability.

[0083] The technical solution described in this invention successfully transforms low-value sodium sulfate and ammonium-containing waste salt into three high-value products: high-purity sodium bicarbonate, ammonium sulfate, and organic acids through an innovative three-step process of "reaction-extraction-carbonization." It has significant environmental and economic advantages, achieving energy conservation and carbon reduction through low-temperature processes and CO2 fixation, and forming a green circular economy model for efficient resource recovery through extractant recycling and closed-loop design. This provides a highly efficient and widely adaptable comprehensive solution for the resource utilization of waste salt in chemical industrial parks.

[0084] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for the high-value utilization of sodium sulfate, characterized in that, Includes the following steps: S1. Mix sodium sulfate, organic ammonium salt and sulfuric acid, and add water to prepare a mixed solution; S2. Extract the mixed solution using an extractant to separate the aqueous phase and the organic phase; S3. Add a pH adjuster to the aqueous phase to adjust the pH to weakly alkaline, introduce carbon dioxide gas to react fully, cool to crystallize, and filter to obtain filtrate and sodium bicarbonate precipitate. S4. Heat the filtrate to evaporate and crystallize, to obtain ammonium sulfate; S5. Recover the organic acids in the organic phase.

2. The method according to claim 1, characterized in that, In step S1, the molar ratio of sodium sulfate to sulfuric acid is (0.5~1.5):(1~2), and the molar ratio of ammonium ions in the organic ammonium salt to hydrogen in the sulfuric acid is 1:(0.8~1.2).

3. The method according to claim 1, characterized in that, The mass concentration of the solute in the mixed solution in step S1 is 25 wt.%~50 wt.%.

4. The method according to claim 1, characterized in that, The extractant in step S2 includes at least one of the following: ether extractant, ester extractant, ketone extractant, halohydrocarbon extractant, phosphoric acid extractant, alcohol extractant, alkane extractant, amine extractant, or ionic liquid extractant.

5. The method according to claim 4, characterized in that, The extractant also includes a stabilizer, which includes kerosene or sulfonated kerosene.

6. The method according to claim 1, characterized in that, Step S3, adjusting the pH to a slightly alkaline state, means adjusting the pH to 8-10.

7. The method according to claim 1, characterized in that, In step S3, when carbon dioxide gas is introduced to carry out the carbonation reaction, the solution is heated to 40℃~70℃; when cooling to crystallize, the solution is cooled to 0℃~12℃.

8. The method according to claim 1, characterized in that, In step S3, the sodium bicarbonate precipitate obtained by crystallization is further washed and dried.

9. The method according to claim 1, characterized in that, The evaporation and crystallization temperature in step S4 is 60℃~100℃.

10. The method according to claim 1, characterized in that, Step S5 involves recovery processing based on the specific type of organic acid in the organic phase. The recovery processing method includes, but is not limited to, at least one of the following methods 1) to 4): 1) Evaporation-crystallization method; 2) Evaporation-condensation method 3) Column chromatography; 4) Membrane electrolysis method.

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