Method, system and application of industrial waste salt sodium sulfate for producing alkali and co-producing ammonium sulfate

Abstract

This invention provides a method, system, and application for the co-production of ammonium sulfate from industrial waste sodium sulfate, belonging to the technical field of industrial waste salt resource utilization. The method includes: dissolving solid waste sodium sulfate in water to form a waste sodium sulfate solution; adding an additive for pretreatment; and obtaining a sodium sulfate mother liquor after solid-liquid separation; performing a metathesis reaction between the sodium sulfate mother liquor and solid ammonium bicarbonate; obtaining sodium bicarbonate and a first mother liquor after solid-liquid separation; heating and evaporating the first mother liquor to recover the generated ammonia and carbon dioxide, which are then used to prepare ammonium bicarbonate; cooling and crystallizing the evaporated first mother liquor; recovering solid sodium sulfate after solid-liquid separation; and evaporating and crystallizing the remaining portion to obtain ammonium sulfate; reusing the recovered ammonium bicarbonate in the metathesis reaction; and recycling the solid sodium sulfate. This invention constructs a closed-loop process for the high-value and resource-based utilization of industrial waste sodium sulfate.

Description

Technical Field

[0001] This invention relates to the technical field of industrial waste salt resource utilization, and in particular to a method, system and application for producing alkali and co-producing ammonium sulfate from industrial waste salt sodium sulfate. Background Technology

[0003] To realize the resource utilization of waste salt, various processes have emerged to convert sodium sulfate into sodium carbonate / sodium bicarbonate and produce ammonium sulfate in conjunction, but existing methods still have technical defects.

[0004] For example, methods using conversion media such as ammonium formate require high-purity chemical reagents, which are costly; methods using sodium sulfate and ammonium bicarbonate metathesis reaction do not take into account the serious impact of impurities in industrial waste salts on reaction efficiency and product quality.

[0005] Furthermore, most existing mixed waste salt treatment processes are complex and lengthy, with difficult reaction control and a lack of engineering feasibility. Additionally, the impurities in industrial waste salt are not effectively pretreated, making them difficult to directly apply to actual waste salt resource recovery production.

[0006] In view of this, a novel method, system, and application for the co-production of ammonium sulfate from industrial waste sodium sulfate are proposed to solve all or part of the above problems. Summary of the Invention

[0007] To address at least one of the aforementioned problems and deficiencies in the existing technology, embodiments of the present invention provide a method, system, and application for the co-production of ammonium sulfate from industrial waste sodium sulfate. The method involves efficient pretreatment of industrial waste sodium sulfate using activated carbon and / or polyaluminum chloride to specifically remove impurities such as organic matter and heavy metals, providing pure raw materials for subsequent reactions. The core metathesis reaction is carried out under optimized temperature, ratio, and time conditions, and combined with evaporation recovery and cooling crystallization steps to construct a closed-loop recycling system for ammonia, carbon dioxide, and unreacted sodium sulfate. This method successfully converts low-value waste salt into high-purity sodium carbonate (total alkali content > 98.5%) and ammonium sulfate (nitrogen content > 19.7%). The products exhibit good stability and meet quality standards, simultaneously achieving waste salt resource utilization, raw material recycling, production cost reduction, and clean production, demonstrating significant environmental and economic benefits. The technical solution is as follows:

[0008] According to one aspect of the present invention, a method for producing alkali and co-producing ammonium sulfate from industrial waste sodium sulfate is provided, the method comprising the following steps:

[0009] Step S110: Dissolve solid waste sodium sulfate in water to form a waste sodium sulfate solution, add additives for pretreatment, and obtain sodium sulfate mother liquor after solid-liquid separation;

[0010] Step S120: The sodium sulfate mother liquor is subjected to a double decomposition reaction with solid ammonium bicarbonate, and sodium bicarbonate and the first mother liquor are obtained after solid-liquid separation;

[0011] Step S130: The first mother liquor is heated and evaporated to recover the generated ammonia and carbon dioxide, which are then used to prepare ammonium bicarbonate;

[0012] Step S140: Cool the first mother liquor after heating and evaporation to crystallize, recover the sodium sulfate solid after solid-liquid separation, and obtain ammonium sulfate by evaporation and crystallization of the remaining part;

[0013] The ammonium bicarbonate obtained in step S130 is recycled for the metathesis reaction in step S120, and the sodium sulfate solid recovered in step S140 is recycled for step S110 or step S120.

[0014] According to another aspect of the present invention, a system for producing alkali and co-producing ammonium sulfate from industrial waste sodium sulfate is provided. This system uses the method for producing alkali and co-producing ammonium sulfate from industrial waste sodium sulfate as described above. The system comprises:

[0015] The pretreatment unit is used to dissolve solid waste sodium sulfate in water to form a waste sodium sulfate solution, add additives for purification, and obtain sodium sulfate mother liquor after solid-liquid separation;

[0016] The reaction unit is used to carry out a metathesis reaction between the purified sodium sulfate mother liquor and solid ammonium bicarbonate, and after solid-liquid separation, sodium bicarbonate and the first mother liquor are obtained.

[0017] The gas recovery and regeneration unit is used to heat and evaporate the first mother liquor, recover the generated ammonia and carbon dioxide, and use them to prepare ammonium bicarbonate.

[0018] The crystallization and recycling unit is used to cool and crystallize the first mother liquor after heating and evaporation, recover sodium sulfate solid after solid-liquid separation, and obtain ammonium sulfate by evaporation and crystallization of the remaining part.

[0019] The system forms a closed loop, with ammonium bicarbonate from the gas recovery and regeneration unit returning to the reaction unit, and sodium sulfate solid from the crystallization and circulation unit returning to the pretreatment unit or the reaction unit.

[0020] According to another aspect of the present invention, there is provided an application of industrial waste sodium sulfate in the co-production of ammonium sulfate from alkali production. The industrial waste sodium sulfate is industrial by-product sodium sulfate from the coking, printing and dyeing, metallurgy or pesticide industries, and is processed using the method for co-producing ammonium sulfate from industrial waste sodium sulfate described above to obtain sodium carbonate and ammonium sulfate.

[0021] The method, system, and application for producing ammonium sulfate from industrial waste sodium sulfate provided in the embodiments of the present invention have at least one or a portion of the following advantages:

[0022] (1) This invention provides a closed-loop process for the resource utilization of waste salt sodium sulfate. Through the process of "pretreatment-decomposition-recovery-crystallization", low-value industrial waste salt is converted into high-purity sodium carbonate / sodium bicarbonate and ammonium sulfate products. At the same time, the recycling of ammonia, carbon dioxide and unreacted sodium sulfate is realized, which significantly reduces the consumption of raw materials and the discharge of waste, and has both environmental and economic benefits.

[0023] (2) By selecting activated carbon and / or polyaluminum chloride as additives, organic matter, heavy metals and suspended matter and colloids can be adsorbed in a targeted manner and flocculated to remove them, significantly improving the purity of the raw material liquid, providing qualified raw materials for subsequent reactions and ensuring the quality of the final product.

[0024] (3) By controlling the dissolution temperature, time and solid-liquid ratio, the dissolution and pretreatment efficiency of waste salt was optimized, providing a basis for the stable progress of subsequent reactions;

[0025] (4) By optimizing the reactant mass ratio, reaction temperature and time of the metathesis reaction, the reaction conversion rate and product yield were significantly improved. The obtained sodium bicarbonate can be used directly or calcined to produce high-quality soda ash.

[0026] (5) By controlling the evaporation temperature of the first mother liquor and the concentration endpoint, unreacted ammonia and carbon dioxide are efficiently recovered, and ammonium bicarbonate is regenerated and reused in the system, so that the total utilization rate of ammonium bicarbonate is not less than 95%, which greatly reduces the production cost.

[0027] (6) By controlling the conditions of cooling crystallization and evaporation crystallization, sodium sulfate solid is efficiently separated and recovered (the recovery rate is not less than 78% based on sodium ions), and qualified ammonium sulfate products are obtained, thus maximizing the utilization of materials;

[0028] (7) By using a filter membrane with a specific pore size for filtration, efficient and stable solid-liquid separation was achieved in each process step, ensuring the continuity of the process and the purity of the final product.

[0029] (8) The system constructed based on the method of the present invention integrates pretreatment, reaction, recovery and crystallization units, forming a highly efficient closed-loop production system that is easy to scale up industrially and operate stably;

[0030] (9) The method of the present invention can be directly applied to sodium sulfate, an industrial by-product waste salt generated in multiple industries such as coking, printing and dyeing, metallurgy, and pesticides, providing a practical and feasible technical path for its high-value utilization. Attached Figure Description

[0031] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which:

[0032] Figure 1 This is a schematic diagram of the process steps of a method for producing alkali and co-producing ammonium sulfate from industrial waste sodium sulfate according to an embodiment of the present invention.

[0033] Figure 2 According to Figure 1 The diagram shows a process flow chart for the co-production of ammonium sulfate from industrial waste sodium sulfate.

[0034] Figure 3 This is a schematic diagram of the principle structure of a system for producing alkali and ammonium sulfate from industrial waste sodium sulfate according to an embodiment of the present invention. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. In this specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation thereof.

[0036] This invention provides a method for producing ammonium sulfate from industrial waste sodium sulfate using alkali production. The method involves efficient pretreatment of the industrial waste sodium sulfate with activated carbon and / or polyaluminum chloride to specifically remove impurities such as organic matter and heavy metals, providing pure raw materials for subsequent reactions. The core metathesis reaction is carried out under optimized temperature, ratio, and time conditions, and combined with evaporation recovery and cooling crystallization steps to construct a closed-loop circulation system for ammonia, carbon dioxide, and unreacted sodium sulfate.

[0037] This method successfully converts low-value waste salt into high-purity sodium carbonate (total alkali content > 98.5%) and ammonium sulfate (nitrogen content > 19.7%). The products have good stability and meet the requirements of quality standards (e.g., GB / T 1606-2008, GB / T 210-2022, GB / T535-2020). It simultaneously realizes the resource utilization of waste salt, the recycling of raw materials, the reduction of production costs, and clean production, and has significant environmental and economic benefits.

[0038] See Figure 1 The present invention illustrates the process flow of a method for producing alkali and co-producing ammonium sulfate from industrial waste sodium sulfate. The specific steps of this method and the core and key processing methods within those steps are described below:

[0039] Step S110: Dissolve solid waste sodium sulfate in water to form a waste sodium sulfate solution, add additives for pretreatment, and obtain sodium sulfate mother liquor after solid-liquid separation.

[0040] In one example, the additive is one of activated carbon and polyaluminum chloride, or a mixture of activated carbon and polyaluminum chloride. Preferably, the mass of the additive added is 0.31%-1.56% of the mass of the waste sodium sulfate solution.

[0041] In one example, activated carbon is used to remove organic pollutants and heavy metal ions from waste sodium sulfate solution; polyaluminum chloride is used for flocculation to remove suspended solids and colloidal particles from the waste sodium sulfate solution.

[0042] In one example, the mass ratio of waste sodium sulfate solid to water was 0.214-0.364, the dissolution temperature was 33-39℃, the dissolution time was 25-35 minutes, and the pretreatment time was 25-35 minutes.

[0043] Step S110 aims to pretreat and purify the waste salt, a crucial step in ensuring raw material purity and addressing the challenges of high impurity levels and direct utilization of industrial waste salt. Specifically, solid sodium sulfate waste (typically containing 60%-85% Na2SO4 and organic matter, heavy metals, and suspended solids) from industries such as coking plants is added to a reaction vessel (e.g., a dissolving tank equipped with stirring and heating devices). Under stirring conditions, it is dissolved in warm water at 33-39°C (e.g., 35°C, 37°C, 39°C, etc.), with a preferred dissolution time of 30 minutes. The mass ratio of sodium sulfate waste to water is controlled between 0.214-0.364 (e.g., preferably 3:14, approximately 0.214; 7:25, approximately 0.28). Subsequently, an additive is added to pretreat the solution. By adjusting and optimizing the temperature and ratio, dissolution efficiency can be effectively improved, while maintaining relatively low process energy consumption.

[0044] After dissolution, an additive is added to the solution for further purification. The additive is one or a mixture of activated carbon, polyaluminum chloride (PAC), at a concentration of 0.31%-1.56% (e.g., preferably 1.25%) of the total solution mass. Activated carbon primarily adsorbs organic pollutants (such as phenols and benzene compounds), odor substances, and some heavy metal ions from the solution; polyaluminum chloride acts as a flocculant, using charge neutralization and adsorption bridging to aggregate fine suspended solids and colloidal particles into larger flocs.

[0045] Analysis of experimental data shows that activated carbon alone can achieve a TOC removal rate of up to 59.54%, while polyaluminum chloride alone can achieve a TOC removal rate of up to 5.64%. The combination of the two can achieve complementary purification effects.

[0046] Preferably, after pretreatment for 30 minutes, filtration is performed using an inorganic membrane with a pore size of 0.35-0.55 μm (more preferably 0.45 μm) to achieve solid-liquid separation, which can thoroughly retain activated carbon particles, flocs, and impurities adsorbed by them. The solid obtained by filtration is salt mud containing impurities, which can be further transferred to a specialized process treatment plant (hazardous waste treatment facility); the filtrate is the purified sodium sulfate mother liquor with a clear color and significantly reduced impurity content. Its TOC (total organic carbon) removal rate is significant, and its purity meets the requirements of subsequent high-quality chemical reactions, providing pure raw materials for subsequent reactions.

[0047] Step S120: The sodium sulfate mother liquor is subjected to a double decomposition reaction with solid ammonium bicarbonate, and sodium bicarbonate and the first mother liquor are obtained after solid-liquid separation.

[0048] In one example, the conditions for the metathesis reaction include: a mass ratio of ammonium bicarbonate to waste sodium sulfate of 1.2-1.3, a reaction temperature of 33-39℃, and a reaction time of 1-2 hours; after the metathesis reaction is completed, the sodium bicarbonate obtained by solid-liquid separation is calcined to obtain sodium carbonate.

[0049] Step S120 aims to produce alkali through a metathesis reaction, which is the core conversion process. Specifically, the sodium sulfate mother liquor is transferred to a metathesis reactor (e.g., a three-necked flask with a stirrer or an industrial reactor), and solid ammonium bicarbonate is added. The mass ratio of ammonium bicarbonate to waste sodium sulfate (based on the initial dry basis) is controlled at 1.2-1.3 (e.g., preferably 1.26, 1.28), and the reaction is carried out at a constant temperature of 33-39°C (e.g., preferably 37°C, 39°C) for 1-2 hours (preferably 1.5-2 hours). The reaction equation is: Na2SO4 + 2NH4HCO3 → 2NaHCO3↓ + (NH4)2SO4. This excess ratio is to promote the metathesis reaction to proceed as continuously and rapidly as possible to the right, thereby increasing the conversion rate of sodium sulfate.

[0050] After the reaction is complete, solid-liquid separation is immediately performed using vacuum filtration (preferably with an inorganic membrane with a pore size of 0.45 μm). The solid is sodium bicarbonate, which, after drying, yields the finished sodium bicarbonate product. Further, the solid sodium bicarbonate product can be placed in a calcining furnace and calcined at a suitable temperature (reaction equation: 2NaHCO3→Na2CO3+CO2↑+H2O), typically set at 250-300℃, to decompose and obtain sodium carbonate (soda ash) product. The filtered liquid is the first mother liquor, containing dissolved unreacted ammonium bicarbonate and a small amount of sodium sulfate.

[0051] Step S130: The first mother liquor is heated and evaporated to recover the generated ammonia and carbon dioxide, which are then used to prepare ammonium bicarbonate.

[0052] In one example, the heating temperature range for evaporating the first mother liquor is 60-80°C, and the concentration of the first mother liquor is concentrated to 24%-40% after heating and evaporation, with a total utilization rate of recovered ammonium bicarbonate of not less than 95%.

[0053] Specifically, the first mother liquor is pumped into an evaporation and concentration device (e.g., a single-effect or multi-effect evaporator), heated and evaporated at 60-80°C (preferably 70-80°C), and concentrated to a concentration of 24%-40% (e.g., preferably 32%, 36%, or 40%).

[0054] During the evaporation process, the unreacted ammonium bicarbonate in the mother liquor decomposes upon heating (reaction equation: NH4HCO3→NH3↑+CO2↑+H2O), and the resulting ammonia and carbon dioxide are collected and transported to the supporting ammonium production process.

[0055] In the ammonium production process, ammonia and carbon dioxide are introduced into water and react again to generate ammonium bicarbonate solution. After crystallization and drying, solid ammonium bicarbonate is obtained. This recovered ammonium bicarbonate can be reused as a raw material in the metathesis reaction of step S120. Through this recycling cycle, the overall utilization rate of ammonium bicarbonate in the process is no less than 95%.

[0056] Unreacted raw materials are recovered in step S130, significantly reducing production costs and ammonia emissions, achieving closed-loop circulation and cost control. The resulting ammonia and carbon dioxide mixture is extracted by a negative pressure collection system. Ammonia is readily soluble in water and can be absorbed by water in an absorption tower to produce ammonia water; carbon dioxide can be used for carbonization.

[0057] A more preferred approach is to directly transport the mixed gas to the supporting ammonium production workshop. Under specific pressure and with the aid of a catalyst, ammonia and carbon dioxide react with water to regenerate ammonium bicarbonate solution. After concentration, cooling crystallization, centrifugation, and drying, solid ammonium bicarbonate product is obtained. This regenerated ammonium bicarbonate is used as a raw material and is entirely recycled for the metathesis reaction in step S120, forming an internal material loop. According to experimental data, the total utilization rate of ammonium bicarbonate through this recovery process can reach over 95.67%, significantly reducing dependence on purchased raw materials and resulting in outstanding economic benefits.

[0058] Step S140: Cool the first mother liquor after heating and evaporation to crystallize, recover the sodium sulfate solid after solid-liquid separation, and obtain ammonium sulfate by evaporation and crystallization of the remaining part.

[0059] In one example, the cooling temperature range for the first mother liquor after heating and evaporation to crystallize is 5-15°C, and the cooling time is 2.5-3.5 hours; the heating temperature range for the remaining part to evaporate and crystallize is 75-85°C; the recovery rate of sodium sulfate solid, calculated as sodium ions, is not less than 78%.

[0060] The purpose of step S140 is to crystallize ammonium sulfate and recover sodium sulfate, achieving product separation and maximizing resources. Specifically, the concentrated mother liquor from step S130 is transferred to a crystallization vessel and cooled for crystallization at 5-15°C (preferably 5°C or 10°C) for 2.5-3.5 hours (preferably 3 hours). Under these low-temperature conditions, the solubility of ammonium sulfate decreases sharply, resulting in a large amount of precipitation in crystalline form. Simultaneously, residual sodium sulfate in the solution may also partially precipitate due to supersaturation.

[0061] After cooling, the cooled slurry is filtered again (preferably using an inorganic membrane with a pore size of 0.45 μm) to separate the solids. The filtered solids are a mixture of sodium sulfate and ammonium sulfate or mainly sodium sulfate (depending on concentration and temperature conditions). Since sodium sulfate is the initial feedstock of this process, this portion of solids is defined as recovered sodium sulfate solids, in terms of sodium ions (Na+). + Based on the above calculation, the recovery rate is not less than 78%. The solid can be returned to step S110 for re-dissolution and purification, or directly returned to the reaction system of step S120 after simple washing, thus realizing the recycling of sodium.

[0062] After filtration, ammonium sulfate becomes the main component in the remaining filtrate at a high concentration. This filtrate is pumped into an evaporator crystallizer and evaporated to dryness at 75-85℃ (preferably 75℃, 80℃, or 85℃). The resulting crystals are then dried and sieved to obtain high-purity ammonium sulfate. This entire process transforms waste sodium sulfate into two high-value products and achieves efficient recycling of ammonia, carbon, and sodium elements.

[0063] In one example, preferably, in steps S110, S120, and S140, solid-liquid separation is performed using vacuum filtration, with the filter medium being an inorganic membrane with a pore size of 0.35-0.55 μm. The ammonium bicarbonate obtained in step S130 is recycled to the metathesis reaction in step S120, and the sodium sulfate solid recovered in step S140 is recycled to either step S110 or step S120.

[0064] Using the methods described in the specific embodiments above, and adjusting specific parameters (such as reaction temperature, material ratio, concentration, cooling temperature, etc.) in multiple examples (see Examples 1-6), the resulting products all exhibited excellent quality. Table 1 below shows the specific process parameters for Examples 1-6 and Comparative Examples 1-2. Table 2 shows the test results for Examples 1-6.

[0065] Table 1. Specific process parameters for Examples 1-6 and Comparative Examples 1-2

[0066]

[0067] Table 2 Test results of Examples 1-6

[0068]

[0069] Examples 1-6 were conducted within the preferred parameter range. Although slight adjustments were made to the reaction ratio (1.26, 1.28), concentration (24%, 32%, 40%), cooling temperature (5℃, 10℃), and final evaporation and crystallization temperature (75℃, 80℃, 85℃), the total alkali content of the sodium carbonate product obtained in all examples remained consistently high at 98.73%-99.27%, and the nitrogen content of the ammonium sulfate product remained consistently between 19.78%-20.56%. This indicates that the process of the present invention has good robustness and product stability, and all product indicators meet or exceed national standards: sodium bicarbonate meets the requirements of GB / T 1606-2008 Class III, sodium carbonate meets the requirements of GB / T 210-2022 Class II qualified product, and ammonium sulfate meets the requirements of GB / T 535-2020 Fertilizer Grade II.

[0070] A comparison of Examples 1 and 2 shows that the reaction temperature, reaction time, and mass ratio of solid ammonium bicarbonate to waste sodium sulfate have a significant impact on the quality of sodium bicarbonate and sodium carbonate products. Suitable experimental conditions can improve product quality.

[0071] A comparison of Examples 2 and 6 shows that pretreatment of waste sodium sulfate improves the quality of raw materials, which not only improves the quality of sodium bicarbonate and sodium carbonate products, but also enhances the stability of the products.

[0072] The results of Comparative Example 1 (reaction temperature 33℃, ammonium bicarbonate / sodium sulfate mass ratio 1.2, reaction time 1h) and Comparative Example 2 (reaction temperature 33℃, ammonium bicarbonate / sodium sulfate mass ratio 1.28, reaction time 2h) further validate the importance of parameter adjustment.

[0073] Comparative Example 1 had a total alkali content of only 84.65% due to a low reaction temperature, insufficient reactant ratio, and short reaction time. Comparative Example 2 had the same ratio and reaction time as some examples, but the total alkali content was only 88.78% due to a lower reaction temperature of 33°C, both of which failed to meet the standard.

[0074] These two comparative examples demonstrate that controlling the metathesis reaction temperature at 33-39℃ (preferably at the medium-high temperature end), ensuring a reaction time of 1-2 hours, and using an excess of ammonium bicarbonate (mass ratio 1.2-1.3) are crucial for complete reaction and high product purity.

[0075] See Figure 2 The present invention illustrates the process cycle flow of the method for producing alkali and co-producing ammonium sulfate from industrial waste sodium sulfate.

[0076] See Figure 3 The present invention illustrates the principle structure of the system for producing ammonium sulfate from industrial waste sodium sulfate.

[0077] Combination Figure 2 and Figure 3 As shown, based on the method of the above embodiments, a system 200 for the co-production of ammonium sulfate from industrial waste sodium sulfate is constructed. The system 200 includes:

[0078] Pretreatment unit 210, exemplarily, includes a dissolving tank, a dosing device, and a solid-liquid separation device (such as a vacuum filter) for performing step S110.

[0079] The reaction unit 220, exemplarily, includes a metathesis reaction vessel and a solid-liquid separation device for performing step S120.

[0080] The gas recovery and regeneration unit 230, exemplarily, includes an evaporator, a gas collection and delivery pipeline, and an ammonium production reaction-crystallization device for performing step S130.

[0081] Crystallization and circulation unit 240, exemplarily, includes a cooling crystallizer, a solid-liquid separation device, an evaporation crystallizer, and a material conveying pipeline for performing step S140.

[0082] The above units are connected by material and gas pipelines, so that ammonium bicarbonate can be returned from gas recovery and regeneration unit 230 to reaction unit 220; and sodium sulfate solid can be returned from crystallization and recycling unit 240 to pretreatment unit 210 or reaction unit 220, thus forming a closed-loop production system.

[0083] The method of this invention is particularly suitable for treating sodium sulfate waste salt, an industrial byproduct from the coking, dyeing, metallurgy, or pesticide industries. This waste salt typically has a complex composition and high impurity content, making it difficult to directly utilize it for high-value purposes using existing traditional methods. Through the method, process flow, and system provided by this invention, waste salt from such specific sources can be effectively converted into high-value sodium carbonate and ammonium sulfate products, achieving targeted resource utilization from "waste" to "product."

[0084] The method, system, and application for producing ammonium sulfate from industrial waste sodium sulfate provided in the embodiments of the present invention have at least one or a portion of the following advantages:

[0085] (1) This invention provides a closed-loop process for the resource utilization of waste salt sodium sulfate. Through the process of "pretreatment-decomposition-recovery-crystallization", low-value industrial waste salt is converted into high-purity sodium carbonate / sodium bicarbonate and ammonium sulfate products. At the same time, the recycling of ammonia, carbon dioxide and unreacted sodium sulfate is realized, which significantly reduces the consumption of raw materials and the discharge of waste, and has both environmental and economic benefits.

[0086] (2) By selecting activated carbon and / or polyaluminum chloride as additives, organic matter, heavy metals and suspended matter and colloids can be adsorbed in a targeted manner and flocculated to remove them, significantly improving the purity of the raw material liquid, providing qualified raw materials for subsequent reactions and ensuring the quality of the final product.

[0087] (3) By controlling the dissolution temperature, time and solid-liquid ratio, the dissolution and pretreatment efficiency of waste salt was optimized, providing a basis for the stable progress of subsequent reactions;

[0088] (4) By optimizing the reactant mass ratio, reaction temperature and time of the metathesis reaction, the reaction conversion rate and product yield were significantly improved. The obtained sodium bicarbonate can be used directly or calcined to produce high-quality soda ash.

[0089] (5) By controlling the evaporation temperature of the first mother liquor and the concentration endpoint, unreacted ammonia and carbon dioxide are efficiently recovered, and ammonium bicarbonate is regenerated and reused in the system, so that the total utilization rate of ammonium bicarbonate is not less than 95%, which greatly reduces the production cost.

[0090] (6) By controlling the conditions of cooling crystallization and evaporation crystallization, sodium sulfate solid is efficiently separated and recovered (the recovery rate is not less than 78% based on sodium ions), and qualified ammonium sulfate products are obtained, thus maximizing the utilization of materials;

[0091] (7) By using a filter membrane with a specific pore size for filtration, efficient and stable solid-liquid separation was achieved in each process step, ensuring the continuity of the process and the purity of the final product.

[0092] (8) The system constructed based on the method of the present invention integrates pretreatment, reaction, recovery and crystallization units, forming a highly efficient closed-loop production system that is easy to scale up industrially and operate stably;

[0093] (9) The method of the present invention can be directly applied to sodium sulfate, an industrial by-product waste salt generated in multiple industries such as coking, printing and dyeing, metallurgy, and pesticides, providing a practical and feasible technical path for its high-value utilization.

[0094] While some embodiments of the present general inventive concept have been shown and described, those skilled in the art will understand that changes may be made to these embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for producing alkali and co-producing ammonium sulfate from industrial waste sodium sulfate, characterized in that, The method includes the following steps: Step S110: Dissolve solid waste sodium sulfate in water to form a waste sodium sulfate solution, add additives for pretreatment, and obtain sodium sulfate mother liquor after solid-liquid separation; Step S120: The sodium sulfate mother liquor is subjected to a metathesis reaction with solid ammonium bicarbonate, and sodium bicarbonate and the first mother liquor are obtained after solid-liquid separation; Step S130: The first mother liquor is heated and evaporated to recover the generated ammonia and carbon dioxide, which are then used to prepare ammonium bicarbonate; Step S140: The first mother liquor after heating and evaporation is cooled and crystallized. Sodium sulfate solid is recovered after solid-liquid separation, and the remaining portion is evaporated and crystallized to obtain ammonium sulfate; wherein... The ammonium bicarbonate obtained in step S130 is recycled for the metathesis reaction in step S120. The sodium sulfate solid recovered in step S140 is recycled back to step S110 or step S120.

2. The method according to claim 1, characterized in that, In step S110, The additive is one of activated carbon and polyaluminum chloride, or The additive is a mixture of activated carbon and polyaluminum chloride; The mass of the additive is 0.31%-1.56% of the mass of the waste sodium sulfate solution.

3. The method according to claim 2, characterized in that, The activated carbon is used to remove organic pollutants and heavy metal ions from the waste sodium sulfate solution; The polyaluminum chloride is used to remove suspended solids and colloidal particles from the waste sodium sulfate solution via flocculation.

4. The method according to claim 1, characterized in that, In step S110, The mass ratio of the waste sodium sulfate solid to water is 0.214-0.

364. The dissolution temperature is 33-39℃, and the dissolution time is 25-35 minutes. Pre-processing time is 25-35 minutes.

5. The method according to claim 1, characterized in that, In step S120, The conditions for the metathesis reaction include: The mass ratio of ammonium bicarbonate to waste sodium sulfate is 1.2-1.

3. The reaction temperature is 33-39℃. The reaction time is 1-2 hours; After the metathesis reaction is completed, the sodium bicarbonate obtained by solid-liquid separation is calcined to obtain sodium carbonate.

6. The method according to claim 1, characterized in that, In step S130, The heating temperature range for evaporating the first mother liquor is 60-80℃. The mother liquor was concentrated by heating and evaporation to a concentration of 24%-40%. The total utilization rate of the recovered ammonium bicarbonate is no less than 95%.

7. The method according to claim 1, characterized in that, In step S140, The cooling temperature range for crystallizing the first mother liquor after heating and evaporation is 5-15℃, and the cooling time is 2.5-3.5 hours. The heating temperature range for the remaining part to evaporate and crystallize is 75-85℃; The recovery rate of the recovered sodium sulfate solid, calculated as sodium ions, is not less than 78%.

8. The method according to any one of claims 1-7, characterized in that, In steps S110, S120 and S140, solid-liquid separation is performed using vacuum filtration, with the filter medium being an inorganic membrane with a pore size of 0.35-0.55 μm.

9. A system for producing alkali and co-producing ammonium sulfate from industrial waste sodium sulfate, said system using the method according to any one of claims 1-8, characterized in that, The system includes: The pretreatment unit is used to dissolve solid waste sodium sulfate in water to form a waste sodium sulfate solution, add additives for purification, and obtain sodium sulfate mother liquor after solid-liquid separation; The reaction unit is used to carry out a metathesis reaction between the purified sodium sulfate mother liquor and solid ammonium bicarbonate, and after solid-liquid separation, sodium bicarbonate and the first mother liquor are obtained. The gas recovery and regeneration unit is used to heat and evaporate the first mother liquor, recover the generated ammonia and carbon dioxide, and use them to prepare ammonium bicarbonate. The crystallization and recycling unit is used to cool and crystallize the first mother liquor after heating and evaporation, recover sodium sulfate solid after solid-liquid separation, and obtain ammonium sulfate by evaporation and crystallization of the remaining part; wherein The system forms a closed loop, with the ammonium bicarbonate output from the gas recovery and regeneration unit returning to the reaction unit, and the sodium sulfate solid output from the crystallization and circulation unit returning to the pretreatment unit or the reaction unit.

10. An application of industrial waste sodium sulfate in the co-production of ammonium sulfate from alkali production, characterized in that, The industrial waste sodium sulfate is industrial by-product sodium sulfate from the coking, printing and dyeing, metallurgy or pesticide industries, and is treated using the method according to any one of claims 1-8 to obtain sodium carbonate and ammonium sulfate.

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