Salt-containing wastewater carbon fixation alkali system

Abstract

The application relates to the technical field of wastewater treatment, and provides a salt-containing wastewater carbon fixation and alkali preparation system. The system comprises a pretreatment unit, an output end of the pretreatment unit being connected with an evaporation and concentration unit, which is used for removing silicon, fluorine, COD and impurities in the salt-containing wastewater; the evaporation and concentration unit is used for evaporating and concentrating the pretreated salt-containing wastewater, and outputs saturated salt solution; a carbonization unit is used for carbonization reaction treatment of the saturated salt solution, and outputs sodium bicarbonate precipitate; a calcination unit is used for filtering and calcining the sodium bicarbonate precipitate, and obtains filtered mother liquor and alkali products; a crystallization unit is used for evaporating and concentrating the filtered mother liquor output by the calcination unit, so as to separate out ammonium chloride and ammonium sulfate by step crystallization. The salt-containing wastewater is used for carbon fixation, high-value-added soda ash is prepared, zero discharge of the salt-containing wastewater, carbon fixation environmental protection and resource utilization are organically combined, and great environmental protection benefits and economic benefits are realized.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology, specifically to a system for carbon sequestration and alkali production from saline wastewater. Background Technology

[0002] With increasing global emphasis on environmental protection and sustainable development, countries worldwide have introduced stringent environmental policies, imposing strict restrictions on the discharge of industrial wastewater. Saline wastewater, a common type of industrial wastewater, can cause severe pollution to water bodies and soil if discharged directly without effective treatment, disrupting the ecological balance. Currently, zero-discharge requirements have been set for saline wastewater from coal chemical industries. Furthermore, traditional alkali production processes often involve high carbon emissions, while carbon sequestration technology can effectively utilize the carbon resources in saline wastewater, achieving carbon fixation and emission reduction, thus meeting the global "dual carbon" goals.

[0003] Saline wastewater typically contains valuable resources such as sodium and chlorine. Through green, low-carbon saline wastewater carbon sequestration and alkali production technology, these resources can be recycled and reused to produce important chemical products such as soda ash. This not only achieves carbon sequestration and reduction, reducing dependence on natural resources, but also lowers production costs for enterprises, improves resource utilization efficiency, and realizes resource recycling.

[0004] Traditional soda ash manufacturing processes, such as the ammonia-soda process and the combined alkali process, still have some shortcomings. For example, the ammonia-soda process generates a large amount of calcium chloride waste residue, which is difficult to treat and easily causes environmental pollution; although the combined alkali process improves the utilization rate of raw materials to a certain extent, it still has problems such as high carbon emissions and severe equipment corrosion. Summary of the Invention

[0005] In view of this, the present application provides a saline wastewater carbon fixation and alkali production system to solve the problems of the ammonia-soda process generating a large amount of calcium chloride waste residue, which is difficult to treat and easily causes environmental pollution, and the combined alkali process having problems of large carbon emissions and equipment corrosion.

[0006] The first aspect of this application provides a system for carbon sequestration and alkali production from saline wastewater, comprising: The pretreatment unit has an input end for receiving saline wastewater and an output end connected to an evaporation and concentration unit for removing silicon, fluorine, COD and impurities from the saline wastewater. The evaporation and concentration unit has its input end connected to the output end of the pretreatment unit and the crystallization unit, and its output end connected to the carbonization unit. It is used to evaporate and concentrate the pretreated saline wastewater and output a saturated salt solution. The carbonization unit, with its output end connected to the calcination unit, is used to perform a carbonization reaction on the saturated salt solution and output sodium bicarbonate precipitate. The calcination unit, with its output end connected to the crystallization unit, is used to filter and calcine the sodium bicarbonate precipitate to obtain the mother liquor and alkali product. The CO2 generated by the calcination unit is output to the carbonation unit. The crystallization unit evaporates and concentrates the mother liquor output from the roasting unit to separate ammonium chloride and ammonium sulfate in steps, and outputs the mother liquor after separating ammonium chloride and ammonium sulfate to the evaporation and concentration unit.

[0007] In one embodiment, the pretreatment unit includes a desiliconization device, a defluorination device, and a COD removal device; The desilication device is an electrocoagulation device or a chemical precipitation device; The defluorination device is any one of a chemical precipitation device, an ion exchange device, a membrane separation device, and an adsorption device; The COD removal device is at least one of the following: a fenton oxidation device, an LDO wet hydrogen peroxide oxidation device, a WAO wet catalytic oxidation device, an electrocatalytic oxidation device, and a multi-element synergistic high-efficiency catalytic oxidation device.

[0008] In one embodiment, the pretreatment unit further includes a sludge removal device, which is an ultra-high pressure elastic press or a plate and frame filter press.

[0009] In one embodiment, the evaporation and concentration unit is a mechanical vapor recompression evaporator and / or a multi-effect evaporator.

[0010] In one embodiment, the carbonization unit includes a high-efficiency carbonization tower.

[0011] In one embodiment, the calcination unit includes a filtration device, a drying device, and a calcination device connected in sequence. The filtration device is used to filter the sodium bicarbonate precipitate output from the carbonation unit to separate sodium bicarbonate and the mother liquor. The drying device is used to dry the sodium bicarbonate. The calcination device is used to calcine the dried sodium bicarbonate to obtain sodium carbonate, CO2, and H2O. The sodium carbonate is used as an alkali product for output.

[0012] In one embodiment, the crystallization unit includes a mechanical vapor recompression evaporator and / or a multi-effect evaporator for evaporation and concentration, and a filtration separation device and / or a centrifugal separation device for solid-liquid separation.

[0013] The saline wastewater carbon fixation and alkali production system provided in this application embodiment improves raw material utilization by mixing and concentrating pretreated wastewater with crystallization mother liquor. Furthermore, the system fixes sodium ions in the wastewater into sodium bicarbonate through a carbonization reaction, thereby converting it into high-purity alkali product. Simultaneously, the system recycles the carbon dioxide generated during roasting into the carbonization unit and the crystallization mother liquor into the evaporation unit, fundamentally reducing external material input and waste discharge, achieving the dual goals of zero discharge and resource utilization of saline wastewater. This system utilizes saline wastewater for carbon fixation to produce high-value-added soda ash, organically combining zero discharge, carbon fixation environmental protection, and resource utilization of saline wastewater, achieving significant environmental and economic benefits. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the alkali production process of a saline wastewater carbon fixation and alkali production system provided in one embodiment of this application. Detailed Implementation

[0016] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0017] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0018] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0019] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0020] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0021] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0022] like Figure 1 As shown in the embodiment of this application, a system for carbon sequestration and alkali production from saline wastewater includes: Pretreatment unit 1 has an input end for receiving saline wastewater and an output end connected to evaporation and concentration unit 2 for removing silicon, fluorine, COD and impurities from saline wastewater. Evaporation and concentration unit 2 has its input end connected to the output end of pretreatment unit 1 and crystallization unit 5, and its output end connected to carbonization unit 3. It is used to evaporate and concentrate the pretreated saline wastewater and output a saturated salt solution. Carbonization unit 3, with its output end connected to calcination unit 4, is used to perform carbonization reaction treatment on the saturated salt solution and output sodium bicarbonate precipitate. The roasting unit 4 is connected to the crystallization unit 5 at its output end. It is used to filter and roast the sodium bicarbonate precipitate to obtain the mother liquor and alkali product. The CO2 generated by the roasting unit 4 is output to the carbonization unit 3. Crystallization unit 5 evaporates and concentrates the filtered mother liquor output from calcination unit 4 to separate ammonium chloride and ammonium sulfate by step crystallization, and outputs the mother liquor after separating ammonium chloride and ammonium sulfate to evaporation and concentration unit 2.

[0023] In application, the principle of carbon sequestration in saline wastewater is as follows: mNa2SO4 + nNaCl + (2m+n)NH3 + (2m+n)CO2 + (2m+n)H2O → (2m+n)NaHCO3↓ +m(NH4)2SO4 + nNH4Cl, where m and n ≥ 0, and m and n are not simultaneously 0; 2NaHCO3 → Na2CO3 + CO2↑ + H2O↑ The saline wastewater carbon fixation and alkali production system provided in this application embodiment improves raw material utilization by mixing and concentrating pretreated wastewater with crystallization mother liquor. Furthermore, the carbonization reaction fixes sodium ions in the wastewater into sodium bicarbonate, thereby converting it into a high-purity alkali product. Simultaneously, the system recycles the carbon dioxide generated during roasting into carbonization unit 3 and the crystallization mother liquor into the evaporation unit, fundamentally reducing external material input and waste discharge, achieving the dual goals of zero discharge and resource utilization of saline wastewater.

[0024] This application uses saline wastewater as a raw material to prepare soda ash. Compared with the traditional combined alkali process and ammonia-soda process, it can make reasonable use of saline wastewater generated in the production process of enterprises, which not only reduces the raw material cost of soda ash, but also solves the problem of waste salt disposal and realizes the recycling of water resources.

[0025] The embodiments of this application employ a mother liquor recycling process, with a theoretical recovery rate of over 99.5% for each element, which is far higher than the recovery rate of existing fractional crystallization processes.

[0026] The embodiments of this application achieve a CO2 and NH3 utilization rate of more than 99% through CO2 recycling during the roasting process and ammonia absorption recycling in the tail gas, which is far higher than the traditional ammonium bicarbonate alkali production process.

[0027] In one embodiment, the pretreatment unit 1 includes a desiliconization device, a defluorination device, and a COD removal device; The desilication device is an electrocoagulation device or a chemical precipitation device; The defluorination device is any one of a chemical precipitation device, an ion exchange device, a membrane separation device, and an adsorption device; The COD removal device is at least one of the following: a fenton oxidation device, an LDO wet hydrogen peroxide oxidation device, a WAO wet catalytic oxidation device, an electrocatalytic oxidation device, and a multi-element synergistic high-efficiency catalytic oxidation device.

[0028] This application provides modular and combined solutions for different impurity components. Electrocoagulation and chemical precipitation target silicon, various physicochemical methods target fluorine, and advanced oxidation technologies target recalcitrant COD. This integrated design of multiple technology paths ensures that the system can efficiently and flexibly treat industrial saline wastewater with complex and variable compositions, providing crucial raw material support for the stable operation of subsequent units.

[0029] In one embodiment, the pretreatment unit 1 further includes a sludge removal device, which is an ultra-high pressure elastic press or a plate and frame filter press.

[0030] This application embodiment adds a sludge treatment device, completing the final disposal stage of solid waste from pretreatment unit 1. The ultra-high pressure elastic press or plate and frame filter press can efficiently dewater and dry the sludge generated during impurity removal, significantly reducing its volume and weight, thereby lowering sludge transportation and disposal costs, avoiding secondary pollution, and forming a complete, environmentally friendly treatment chain throughout the pretreatment process.

[0031] In one embodiment, the evaporation and concentration unit 2 is a mechanical vapor recompression evaporator and / or a multi-effect evaporator.

[0032] This application's embodiments employ highly efficient and energy-saving equipment such as mechanical vapor recompression or multi-effect evaporation. By cleverly utilizing the latent heat of secondary steam, the large amount of heat energy required to concentrate the solution to saturation is significantly reduced, thereby fundamentally lowering the overall system operating cost and embodying the green and low-carbon technological concept.

[0033] In one embodiment, the carbonization unit 3 includes a high-efficiency carbonization tower.

[0034] The high-efficiency carbonation tower of this application provides a foundation for gas-liquid-solid three-phase reactions. The carbonation tower achieves sufficient contact and efficient mass transfer between carbon dioxide gas and saturated salt solution, ensuring the carbonation reaction proceeds rapidly and completely, maximizing the precipitation efficiency of sodium ions into sodium bicarbonate, and guaranteeing the yield and quality of soda ash products.

[0035] In one embodiment, the calcination unit 4 includes a filtration device, a drying device, and a calcination device connected in sequence. The filtration device is used to filter the sodium bicarbonate precipitate output from the carbonation unit 3 to separate sodium bicarbonate and the mother liquor. The drying device is used to dry the sodium bicarbonate. The calcination device is used to calcine the dried sodium bicarbonate to obtain sodium carbonate, CO2, and H2O. The sodium carbonate is used as an alkali product for output.

[0036] This application embodiment breaks down the processing of sodium bicarbonate into three steps: filtration, drying, and calcination. This not only ensures the purity of the sodium carbonate product but also enables the separate collection and high-purity reuse of the byproduct carbon dioxide, creating a closed-loop carbon cycle within the system. This significantly improves raw material utilization, reduces carbon emissions, and enhances environmental friendliness.

[0037] In one embodiment, the crystallization unit 5 includes a mechanical vapor recompression evaporator and / or a multi-effect evaporator for evaporation and concentration, and a filtration separation device and / or a centrifugal separation device for solid-liquid separation.

[0038] The crystallization unit 5 in this embodiment combines a high-efficiency evaporator with a variety of solid-liquid separation devices. This combination enables precise control of the temperature and concentration during the crystallization process, thereby successfully achieving stepwise and sequential crystallization and separation of ammonium chloride and ammonium sulfate, ultimately yielding two high-purity by-product fertilizers, greatly enhancing the resource utilization output and value of the entire process.

[0039] The alkali production method of the above-mentioned saline wastewater carbon fixation and alkali production system includes: Pretreatment unit 1 is used to remove silicon, fluorine, COD and impurities from saline wastewater; The pretreated saline wastewater is mixed with the mother liquor from which ammonium chloride and ammonium sulfate have been separated, and then concentrated by evaporation and concentration unit 2 to obtain a saturated salt solution. A saturated salt solution is reacted with carbon dioxide in carbonization unit 3 to produce sodium bicarbonate precipitate. The sodium bicarbonate precipitate was filtered to obtain the mother liquor and sodium bicarbonate. The separated sodium bicarbonate was dried and roasted using roasting unit 4 to obtain the alkali product. The mother liquor was evaporated and concentrated, and ammonium chloride and ammonium sulfate were separated by stepwise crystallization. The mother liquor after separating ammonium chloride and ammonium sulfate is output to the evaporation and concentration unit 2 and mixed with the pretreated saline wastewater.

[0040] In the application, pretreatment unit 1 uses electrocoagulation or chemical precipitation technology to remove silicon from saline wastewater; it uses one of the following methods to remove fluoride from wastewater: chemical precipitation, ion exchange, membrane separation or adsorption fluoride removal technology; it uses one or more of the following coupled methods to remove COD from wastewater: Fenton oxidation, LDO wet hydrogen peroxide oxidation, WAO wet catalytic oxidation, electrocatalytic oxidation, and multi-element synergistic high-efficiency catalytic oxidation; the sludge formed by silicon removal, fluoride removal and COD removal in pretreatment unit 1 is removed by an ultra-high pressure elastic press or a plate and frame filter press.

[0041] In applications, the evaporation and concentration unit 2 employs one or more of the following: MVR, multi-effect evaporation, or MVR coupled with multi-effect evaporation.

[0042] In application, the carbonization unit 3 carbon fixation reaction fully absorbs and fixes CO2 until the saline wastewater becomes acidic (pH<7), and sodium ions are converted into NaHCO3↓.

[0043] In one embodiment, the carbon dioxide generated by the roasting unit 4 is output to the carbonization unit 3 for the carbonization reaction.

[0044] In one embodiment, the step of evaporating and concentrating the filtrate mother liquor, and then separating ammonium chloride and ammonium sulfate by stepwise crystallization, includes: The filtrate mother liquor was subjected to ammonia absorption treatment to adjust the pH of the solution to alkaline, thereby obtaining an ammonia mother liquor; The ammonia mother liquor was evaporated until it was saturated with ammonium chloride, and then the ammonium chloride precipitate was separated by freezing crystallization. The mother liquor after separating the ammonium chloride precipitate is evaporated until the ammonium sulfate solution is saturated; Ammonium sulfate solution was subjected to freeze crystallization to separate ammonium sulfate crystals; When evaporating the ammonia mother liquor and the mother liquor after separating the ammonium chloride precipitate, the endpoint temperature is controlled between -5℃ and 60℃, and the evaporation and crystallization time is 30 to 180 minutes.

[0045] In applications, the solid-liquid separation process of ammonium sulfate and ammonium chloride is any one or a combination of several of the following: hydrocyclone separation, centrifugal separation, sedimentation separation, or filtration separation.

[0046] This application's embodiments achieve efficient separation of ammonium salts through precise pH adjustment and staged temperature control. Ammonia absorption creates optimal conditions for crystallization, while the evaporation and cooling crystallization steps, tailored to the solubility characteristics of different ammonium salts, ensure that ammonium chloride and ammonium sulfate can be crystallized separately with high recovery rates and purity, contributing to high-quality products and resource utilization.

[0047] Example 1 The following is a specific embodiment to illustrate this system and its alkali production method: Pretreatment Unit 1: Pretreatment Unit 1 uses sodium aluminate desilication + high-efficiency aluminum salt coupled defluorination + advanced oxidation to remove COD + sludge thickening and drying to purify and remove impurities from saline wastewater.

[0048] Flow rate 100m 3 At a temperature of 40℃ and a flow rate of [h], saline wastewater was treated using sodium metachlorite as a chemical agent. Sodium aluminate underwent a hydrolysis reaction in the water, forming a uniformly dispersed system and dissociating positively charged Al atoms. 3+ It can adsorb negatively charged SiO3 in wastewater 2- And it destroys colloidal silicon {[SiO2]mSiO3} 2-·2(nx)H +}·2xH + The stability of the active and inactive silicon causes them to gradually aggregate and flocculate into larger particles, thus removing SiO2 from the saline wastewater.

[0049] A novel high-efficiency composite aluminum salt is used to remove fluoride from saline wastewater. After the novel high-efficiency composite aluminum salt is added to the water, Al... 3+ With F - The complexation of aluminum salts and the intermediate products of aluminum salt hydrolysis and the final product Al(OH)3(am), Al 13 O4(OH) 24 7+ Polyhydroxy cations and the amorphous Al(OH)3 (am) formed after hydrolysis form positively charged colloidal particles in water. These particles exchange ligands with fluoride ions in the wastewater, undergo physical adsorption and sweeping to form strong chemical bonds of polydentate ligands. The colloidal particles then aggregate into larger flocculent precipitates through inter-particle complexation.

[0050] Employing a multi-component synergistic high-efficiency catalytic oxidation technology, the oxidant is efficiently converted into high-density hydroxyl radicals through the dual catalytic action of homogeneous and heterogeneous salt-resistant catalysts. These radicals then undergo a rapid oxidation reaction with the functional groups of pollutants, thereby removing COD from saline wastewater.

[0051] The sludge thickening and drying process consists of four steps: (1) sludge thickening, which initially reduces the volume of the sludge; (2) sludge digestion, which decomposes the organic matter in the sludge and stabilizes the properties of the sludge; (3) sludge dewatering and drying using a plate and frame filter press; and (4) the pretreated wastewater is sent to the evaporation and thickening unit 2.

[0052] Evaporation and concentration unit 2: After pretreatment to remove impurities such as fluorine, silicon, and heavy metals from the wastewater, it is mixed with mother liquor IV and then concentrated to 40% using MVR coupling double effect. After secondary ammonia absorption, the 40% saline wastewater forms ammonia mother liquor II, which enters carbonization unit 3.

[0053] Carbonization Unit 3: Mother liquor II reacts with NH3 and CO2 in a carbonization tower. The two react countercurrently in the tower to generate sodium bicarbonate slurry. The heat released by the reaction is removed by circulating water. The reaction product—the extract containing heavy alkali—is sent to a plate and frame filter to separate the sodium bicarbonate. The mother liquor is sent to crystallization unit 5. The carbonization tail gas is vented after being washed and qualified.

[0054] Crystallization Unit 5: After carbonization, the mother liquor from which sodium bicarbonate is separated is replenished with NH3 to adjust the pH of the solution to alkaline. The mother liquor is then evaporated until ammonium chloride is saturated. After freezing and crystallization, the ammonium chloride precipitate is separated by centrifugation. Subsequently, the mother liquor is heated and evaporated until the ammonium sulfate solution is saturated. After cooling and crystallization, the ammonium sulfate crystals are separated, and the mother liquor IV enters the evaporation and concentration unit 2.

[0055] Calcination Unit 4: After drying, sodium bicarbonate is fed into calcination unit 4, where it is calcined to produce sodium carbonate, CO2, and H2O. The CO2 is sent to carbonation unit 3 for reuse, and the H2O is recycled to the production unit.

[0056] In this embodiment, the annual operating time of the equipment is 8400 hours. The produced soda ash should meet the Class II qualified product requirements of (GB / T210-2022), the ammonium sulfate product should meet the Type I product requirements of (GB535-2020), and the ammonium chloride should meet the agricultural ammonium chloride requirements of GB / T 2946-2018.

[0057] The system produces 60,000 tons of carbon annually, along with 145,000 tons of ammonium sulfate, 118,000 tons of soda ash, and 42,000 tons of ammonium chloride. Annual sales are approximately 300 million yuan. This system addresses the environmental issue of zero-discharge of saline wastewater coupled with carbon sequestration, while simultaneously achieving significant economic and social benefits. Table 1 shows the composition of the pre-treatment saline wastewater, and Table 2 shows the quality of the product water. The product water from this system is used for makeup water for the circulating water system and other production water applications.

[0058] Table 1 Table 2 The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A system for carbon sequestration and alkali production from saline wastewater, characterized in that, include: The pretreatment unit has an input end for receiving saline wastewater and an output end connected to an evaporation and concentration unit for removing silicon, fluorine, COD and impurities from the saline wastewater. The evaporation and concentration unit has its input end connected to the output end of the pretreatment unit and the crystallization unit, and its output end connected to the carbonization unit. It is used to evaporate and concentrate the pretreated saline wastewater and output a saturated salt solution. The carbonization unit, with its output end connected to the calcination unit, is used to perform a carbonization reaction on the saturated salt solution and output sodium bicarbonate precipitate. The calcination unit, with its output end connected to the crystallization unit, is used to filter and calcine the sodium bicarbonate precipitate to obtain the mother liquor and alkali product. The CO2 generated by the calcination unit is output to the carbonation unit. The crystallization unit evaporates and concentrates the mother liquor output from the roasting unit to separate ammonium chloride and ammonium sulfate in steps, and outputs the mother liquor after separating ammonium chloride and ammonium sulfate to the evaporation and concentration unit.

2. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The pretreatment unit includes a desiliconization device, a defluorination device, and a COD removal device; The desilication device is an electrocoagulation device or a chemical precipitation device; The defluorination device is any one of a chemical precipitation device, an ion exchange device, a membrane separation device, and an adsorption device; The COD removal device is at least one of the following: a fenton oxidation device, an LDO wet hydrogen peroxide oxidation device, a WAO wet catalytic oxidation device, an electrocatalytic oxidation device, and a multi-element synergistic high-efficiency catalytic oxidation device.

3. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The pretreatment unit also includes a sludge removal device, which is an ultra-high pressure elastic press or a plate and frame filter press.

4. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The evaporation and concentration unit is a mechanical vapor recompression evaporator and / or a multi-effect evaporator.

5. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The carbonization unit includes a high-efficiency carbonization tower.

6. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The calcination unit includes a filtration device, a drying device, and a calcination device connected in sequence. The filtration device is used to filter the sodium bicarbonate precipitate output from the carbonation unit to separate sodium bicarbonate and the mother liquor. The drying device is used to dry the sodium bicarbonate. The calcination device is used to calcine the dried sodium bicarbonate to obtain sodium carbonate, CO2, and H2O. The sodium carbonate is used as an alkali product for output.

7. The saline wastewater carbon fixation and alkali production system as described in claim 1, characterized in that, The crystallization unit includes a mechanical vapor recompression evaporator and / or a multi-effect evaporator for evaporation and concentration, and a filtration separation device and / or a centrifugal separation device for solid-liquid separation.

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