Desulfurization wastewater resource treatment method

Abstract

The application belongs to the technical field of wastewater treatment and recycling, and particularly relates to a desulfurization wastewater resource treatment method. The application can remove calcium ions to the maximum extent without reducing the concentration of magnesium ions in the first-stage calcium removal process by selecting a composite calcium removal agent with a specific composition, that is, effectively separating calcium ions and magnesium ions without introducing impurity ions, the concentration of calcium ions can be reduced to below 60 mg / L, and the removal rate of magnesium ions is below 10%; then the concentration of calcium ions is further reduced to below 10 mg / L through secondary calcium removal treatment; finally, through steps such as nanofiltration salt separation and concentration crystallization, sodium chloride with a purity of above 98% and magnesium sulfate heptahydrate with a purity of above 98.5% are obtained.

Description

Technical Field

[0001] This application belongs to the field of wastewater treatment and recycling technology, specifically relating to a method for the resource-based treatment of desulfurization wastewater. Background Technology

[0002] Limestone-gypsum wet desulfurization technology is the most commonly used, reliable, and efficient desulfurization process, and it is widely used in desulfurization treatment. In this process, limestone-gypsum wet flue gas desulfurization uses limestone slurry to absorb SO2 in the flue gas, generating CaSO3 and CaSO4, etc. Simultaneously, small amounts of hydrogen chloride gas and Cl- in the desulfurizing agent are also absorbed. - It will also be transferred to the desulfurization slurry. As the desulfurization process continues, Mg 2+ Cl - As the concentration accumulates, it can cause equipment corrosion and foaming when it reaches a certain level, affecting desulfurization efficiency and gypsum quality. Therefore, during operation, the desulfurization system needs to promptly discharge a portion of the desulfurization slurry to maintain the magnesium content. 2+ Cl - The concentration is within a certain level.

[0003] The discharged desulfurization slurry is called desulfurization wastewater. Its composition is complex and easily affected by factors such as coal quality, limestone composition, makeup water quality, and operating mode. Therefore, the discharge of desulfurization wastewater is discontinuous, and its water quality and quantity are unstable. Generally speaking, desulfurization wastewater contains a large amount of suspended solids, inorganic salts, organic matter, and heavy metal ions, and has high hardness. Since most of the substances are Class I pollutants, it causes serious and severe environmental pollution. Therefore, desulfurization wastewater must be effectively treated before it can be discharged.

[0004] Although the ion concentrations in the water of different power plants vary, they are all rich in NaCl and MgSO4. Recycling and utilizing these substances will generate certain economic benefits and social value. However, other substances will affect the quality of sodium chloride and magnesium sulfate products, so these other substances need to be removed.

[0005] Existing technologies disclose several methods for treating desulfurization wastewater from power plants. These methods first use a calcium removal agent to remove calcium, then employ nanofiltration to separate NaCl and MgSO4. However, the calcium removal agents used in these technologies fall into two categories: one uses calcium hydroxide / sodium sulfate, but during this process, some magnesium ions are also removed, resulting in magnesium hydroxide and calcium sulfate that cannot be effectively separated, becoming solid waste. Furthermore, in actual production, the small particle size of Mg(OH)2 easily clogs the ultrafiltration membrane, increasing operating costs. The other category uses oxalic acid / oxalate as a calcium removal agent. While this type of agent can avoid magnesium removal, calcium ion removal is incomplete. At this point, oxalate and calcium ions in the wastewater are in a precipitation equilibrium. Subsequent evaporation, concentration, or other treatments will lead to precipitation of calcium ions and oxalate, causing scaling on equipment and pipes, affecting normal equipment operation, and resulting in lower purity magnesium sulfate recovered later, failing to meet the national standard for industrial magnesium sulfate. Summary of the Invention

[0006] Therefore, the technical problem to be solved by this application is to overcome the above-mentioned defects in the existing power plant desulfurization wastewater recycling and treatment process, thereby providing a desulfurization wastewater resource utilization treatment method.

[0007] Therefore, this application provides the following technical solution:

[0008] This application provides a method for the resource-based treatment of desulfurization wastewater, including the following steps:

[0009] S1, a compound calcium removal agent is added to the wastewater to be treated to carry out a precipitation reaction and separation, and primary calcium removal wastewater is obtained;

[0010] The composite calcium removal agent includes a calcium removal reactant and a precipitant. The calcium removal reactant includes oxalic acid, and the molar ratio of oxalate to calcium ions in the calcium removal reactant is 0.8–1.8:1. The mass ratio of the precipitant to the calcium removal reactant is 3–5:1.

[0011] S2, the obtained primary calcium removal wastewater is subjected to secondary calcium removal treatment to obtain secondary calcium removal wastewater;

[0012] S3, the obtained secondary calcium removal wastewater is subjected to nanofiltration for salt separation to obtain permeate and intercepted liquid;

[0013] S4. The obtained permeate and intercepted liquid are crystallized to obtain sodium chloride and magnesium sulfate, respectively.

[0014] In some embodiments, in step S1, the molar ratio of oxalate to calcium ions in the calcium removal agent is 1 to 1.3:1.

[0015] In some embodiments, in step S1, the mass ratio of the precipitant to the calcium removal agent is 4 to 5:1.

[0016] In this application, the more precipitant used, the better the calcium ion removal effect. Since the precipitant can be reused, the precipitant is always in excess. In order to avoid unnecessary waste, the mass ratio of the precipitant to the calcium removal reaction agent is limited to 3 to 5:1.

[0017] In some embodiments, in step S1, the composite calcium removal agent further includes a flocculant; optionally, the amount of the flocculant is 0.1 mg / L to 20 mg / L based on the volume of the wastewater to be treated.

[0018] And / or, the flocculant includes at least one of polyaluminum chloride (PAC), polyacrylamide (PAM), polyaluminum sulfate (PAS), polyferric chloride (PFC), and polyferric sulfate (PFS).

[0019] In some embodiments, the flocculant is a composite flocculant composed of polyaluminum chloride, polyacrylamide, and polyferric sulfate;

[0020] And / or, the precipitant includes calcium oxalate and / or calcium sulfate.

[0021] In some embodiments, in step S2, the secondary calcium removal process is carried out by using ion exchange resin or concentration.

[0022] In some embodiments, the ion exchange resin is a strong acid type ion exchange resin;

[0023] And / or, the operating parameters for secondary calcium removal using ion exchange resin include: space velocity control of 0.2-2 h⁻¹. -1 The temperature is controlled between 10℃ and 40℃.

[0024] In some embodiments, in step S4, the crystallization temperature of the permeate is 15°C to 45°C.

[0025] And / or, the crystallization treatment temperature of the intercepted liquid is 20℃~50℃;

[0026] And / or, the permeate may further include a concentration step before crystallization treatment; optionally, the concentration may be performed using a reverse osmosis device.

[0027] In some embodiments, in step S1, the calcium ion concentration in the primary calcium removal wastewater is controlled to be below 60 mg / L; optionally, it is controlled to be between 20.0 mg / L and 60.0 mg / L.

[0028] And / or, in step S2, the calcium ion concentration in the secondary calcium removal wastewater is controlled to be below 10 mg / L;

[0029] And / or, in step S3, the mass ratio of sodium chloride to other salts in the permeate is controlled to be 10-60:1 in the nanofiltration salt separation step; and the mass ratio of magnesium sulfate to other salts in the retrieval solution is 5-20:1.

[0030] And / or, in step S4, the total salt concentration in the concentrated permeate is controlled to be 60 g / L to 200 g / L.

[0031] In some embodiments, in step S1, the concentration of magnesium ions in the wastewater to be treated is 2000 mg / L-15000 mg / L, the concentration of sulfate ions is 6000 mg / L-50000 mg / L, and the concentration of calcium ions is 400 mg / L-1200 mg / L.

[0032] The technical solution of this application has the following advantages:

[0033] The desulfurization wastewater resource utilization treatment method provided in this application includes the following steps: S1, adding a composite calcium removal agent to the wastewater to be treated for precipitation reaction and separation to obtain primary calcium removal wastewater; wherein, the composite calcium removal agent includes a calcium removal reactant and a precipitant, the calcium removal reactant includes oxalic acid and / or sodium oxalate, the molar ratio of oxalate ions to calcium ions in the calcium removal reactant is 0.8-1.8:1; the mass ratio of the precipitant to the calcium removal reactant is 3-5:1; S2, subjecting the obtained primary calcium removal wastewater to secondary calcium removal treatment to obtain secondary calcium removal wastewater; S3, subjecting the obtained secondary calcium removal wastewater to nanofiltration for salt separation to obtain permeate and intercepted liquid; S4, subjecting the obtained permeate and intercepted liquid to crystallization treatment to obtain sodium chloride and magnesium sulfate respectively. This application utilizes a composite calcium removal agent with a specific composition selected during the primary calcium removal process. This allows for the maximum removal of calcium ions without significantly reducing the magnesium ion concentration, achieving effective separation of calcium and magnesium ions without introducing impurity ions. The calcium ion concentration can be reduced to below 60 mg / L, and the magnesium ion removal rate is below 10%. A secondary calcium removal process further reduces the calcium ion concentration to below 10 mg / L. Finally, through nanofiltration, salt separation, concentration, and crystallization, sodium chloride with a purity of over 98.0% and magnesium sulfate heptahydrate with a purity of over 98.5% are obtained.

[0034] The desulfurization wastewater resource utilization method provided in this application, in step S1, wherein the mass ratio of the precipitant to the calcium removal agent is 4-5:1. By limiting the mass ratio of the precipitant to the calcium removal agent, this application can further improve the calcium ion removal rate in the primary calcium removal step while maintaining a low magnesium ion removal rate.

[0035] The desulfurization wastewater resource utilization treatment method provided in this application, in step S1, the molar ratio of oxalate ions in the calcium removal reagent to calcium ions in the wastewater to be treated is 1 to 1.3:1. By limiting the molar ratio of oxalate ions in the calcium removal reagent to calcium ions in the wastewater to be treated, this application can further improve the calcium ion removal rate in the primary calcium removal step without significantly increasing the magnesium ion removal rate.

[0036] The desulfurization wastewater resource utilization method provided in this application uses flocculants to improve the purity of the recovered sodium chloride.

[0037] The desulfurization wastewater resource utilization treatment method provided in this application uses a composite flocculant composed of polyaluminum chloride, polyacrylamide, and polyferric sulfate. Compared with other flocculants, the composite flocculant with a specific composition used in this application can further improve the calcium ion removal rate in the primary calcium removal step.

[0038] The desulfurization wastewater resource utilization treatment method provided in this application uses ion exchange resin for secondary calcium removal. On the one hand, the calcium ion removal effect is better, which can effectively save reagents; on the other hand, since the calcium ion concentration is significantly reduced, it can also avoid pipe scaling in subsequent nanofiltration and crystallization steps, thus extending the service life of the equipment.

[0039] The desulfurization wastewater resource utilization method provided in this application uses a reverse osmosis device to concentrate the permeate to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to a reclaimed water tank, thus realizing water recycling. The entire project achieves resource utilization, generates no waste liquid, and can be recycled. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0041] Figure 1 This is a process flow diagram of the desulfurization wastewater resource utilization treatment method in Embodiment 1 of this application. Detailed Implementation

[0042] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0043] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0044] To facilitate data comparison, the source and parameter information of some raw materials are as follows:

[0045] PAC: Zhengzhou Shuangying Chemical, Model 1000, 26% content;

[0046] PAM: Average molecular weight 10 million;

[0047] PFS: Henan Zhongbang Environmental Protection Technology Co., Ltd., model ZB.

[0048] Example 1

[0049] This embodiment provides a method for the resource-based treatment of desulfurization wastewater, the process flow of which is as follows: Figure 1 As shown, the specific steps and operating parameters are as follows:

[0050] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 2000 mg / L, the sulfate ion concentration is 6000 mg / L, and the calcium ion content is 800 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is oxalic acid, and the molar ratio of oxalate ions to calcium ions is 1.3:1. The precipitant is calcium oxalate, and the mass ratio of precipitant to calcium removal agent is 4:1. The flocculant is 10 mg / L PAC+PAM+PFS, and the mass ratio of PAC, PAM, and PFS is 10:1:10. After precipitation reaction and clarification, primary calcium removal wastewater is obtained. The calcium ion concentration in the primary calcium removal wastewater is 28.8 mg / L, and the magnesium ion concentration remains basically unchanged.

[0051] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 0.5 h⁻¹. -1 The temperature is controlled at 10℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 5.1 mg / L.

[0052] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device, and the mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is controlled to be 60:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 5:1.

[0053] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 100 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 15℃. Centrifugation is used to obtain sodium chloride with a purity of 99.2%. The effluent is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 20℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 99.1%.

[0054] Example 2

[0055] This embodiment provides a method for the resource-based treatment of desulfurization wastewater, the process flow of which is as follows: Figure 1 As shown, the specific steps and operating parameters are as follows:

[0056] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 5000 mg / L, the sulfate ion concentration is 18000 mg / L, and the calcium ion content is 400 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is oxalic acid, and the molar ratio of oxalate ions to calcium ions is 1.3:1. The precipitant is calcium oxalate, and the mass ratio of precipitant to calcium removal agent is 4:1. The flocculant is 10 mg / L PAC+PAM+PFS, and the mass ratio of PAC, PAM, and PFS is 10:1:10. After precipitation reaction and clarification, primary calcium removal wastewater is obtained, in which the calcium ion concentration in the primary calcium removal wastewater is 60.0 mg / L, and the magnesium ion concentration remains basically unchanged.

[0057] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 0.2 h⁻¹. -1 The temperature is controlled at 20℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 2.0 mg / L.

[0058] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device. The mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is 40:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 8:1.

[0059] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 150 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 30℃. Centrifugation is used to obtain sodium chloride with a purity of 99.1%. The effluent is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 40℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 99.2%.

[0060] Example 3

[0061] This embodiment provides a method for the resource-based treatment of desulfurization wastewater, the process flow of which is as follows: Figure 1 As shown, the specific steps and operating parameters are as follows:

[0062] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 8000 mg / L, the sulfate ion concentration is 23000 mg / L, and the calcium ion content is 1200 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is oxalic acid, and the molar ratio of oxalate ions to calcium ions is 1.3:1. The precipitant is calcium oxalate, and the mass ratio of precipitant to calcium removal agent is 4:1. The flocculant is 10 mg / L PAC+PAM+PFS, and the mass ratio of PAC, PAM, and PFS is 10:1:10. After precipitation reaction and clarification, primary calcium removal wastewater is obtained, in which the calcium ion concentration in the primary calcium removal wastewater is 20.0 mg / L, and the magnesium ion concentration remains basically unchanged.

[0063] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the operating space velocity of the resin unit is controlled at 2 h⁻¹. -1 The temperature is controlled at 30℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 9.2 mg / L.

[0064] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device. The mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is 30:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 10:1.

[0065] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 200 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 45℃. Centrifugation is used to obtain sodium chloride with a purity of 99.0%. The effluent is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 50℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 99.3%.

[0066] Example 4

[0067] This embodiment provides a method for the resource-based treatment of desulfurization wastewater, the process flow of which is as follows: Figure 1 As shown, the specific steps and operating parameters are as follows:

[0068] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 10000 mg / L, the sulfate ion concentration is 32000 mg / L, and the calcium ion content is 600 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is oxalic acid, and the molar ratio of oxalate ions to calcium ions is 1.3:1. The precipitant is calcium oxalate, and the mass ratio of precipitant to calcium removal agent is 4:1. The flocculant is 10 mg / L PAC+PAM+PFS, and the mass ratio of PAC, PAM, and PFS is 10:1:10. After precipitation reaction and clarification, primary calcium removal wastewater is obtained. The calcium ion concentration in the primary calcium removal wastewater is 52 mg / L, and the magnesium ion concentration remains basically unchanged.

[0069] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 0.8 h⁻¹. -1 The temperature is controlled at 20℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 4.5 mg / L.

[0070] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device. The mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is 20:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 15:1.

[0071] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 80 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 20℃. Centrifugation is used to obtain sodium chloride with a purity of 98.9%. The effluent is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 30℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 99.4%.

[0072] Example 5

[0073] This embodiment provides a method for the resource-based treatment of desulfurization wastewater, the process flow of which is as follows: Figure 1 As shown, the specific steps and operating parameters are as follows:

[0074] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 15000 mg / L, the sulfate ion concentration is 50000 mg / L, and the calcium ion content is 1000 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is oxalic acid, and the molar ratio of oxalate ions to calcium ions is 1.3:1. The precipitant is calcium oxalate, and the mass ratio of precipitant to calcium removal agent is 4:1. The flocculant is 10 mg / L PAC+PAM+PFS, and the mass ratio of PAC, PAM, and PFS is 10:1:10. After precipitation reaction and clarification, primary calcium removal wastewater is obtained. The calcium ion concentration in the primary calcium removal wastewater is 32.6 mg / L, and the magnesium ion concentration remains basically unchanged.

[0075] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 1.5 h⁻¹. -1 The temperature is controlled at 40℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 6.5 mg / L.

[0076] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device. The mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is 10:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 20:1.

[0077] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 60 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 30℃. Centrifugation is used to obtain sodium chloride with a purity of 98.5%. The effluent is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 40℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 99.5%.

[0078] Example 6

[0079] This embodiment provides a method for the resource-based treatment of desulfurization wastewater. Compared with Embodiment 1, the only difference is that the molar ratio of oxalate to calcium ions in the calcium removal reagent is 1.6:1.

[0080] The calcium ion concentration in the primary calcium removal wastewater was 19.6 mg / L, and the magnesium ion concentration was 1800 mg / L, with a magnesium ion removal rate of 10%. The calcium ion concentration in the secondary calcium removal wastewater was controlled at 4.8 mg / L. Centrifugation yielded sodium chloride with a purity of 99.2% and magnesium sulfate heptahydrate with a purity of 99.2%, but the product quantity was reduced.

[0081] Example 7

[0082] This embodiment provides a method for the resource-based treatment of desulfurization wastewater, and the specific steps and operating parameters are as follows:

[0083] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 2000 mg / L, the sulfate ion concentration is 6000 mg / L, and the calcium ion content is 800 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is oxalic acid, and the molar ratio of oxalate ions to calcium ions is 1.3:1. The precipitant is calcium oxalate, and the mass ratio of precipitant to calcium removal agent is 10:1. The flocculant is 10 mg / L PAC+PAM+PFS. After precipitation reaction and clarification, primary calcium removal wastewater is obtained. The calcium ion concentration in the primary calcium removal wastewater is 19.6 mg / L, and the magnesium ion concentration remains basically unchanged.

[0084] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 0.5 h⁻¹. -1 The temperature is controlled at 10℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 4.6 mg / L.

[0085] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device, and the mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is controlled to be 60:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 5:1.

[0086] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 100 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 15℃. Centrifugation is used to obtain sodium chloride with a purity of 99.2%. The effluent is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 20℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 99.1%.

[0087] Example 8

[0088] This embodiment provides a method for the resource-based treatment of desulfurization wastewater, the process flow of which is as follows: Figure 1 As shown, the specific steps and operating parameters are as follows:

[0089] (1) The magnesium ion content in the desulfurization wastewater of a power plant was 8810 mg / L, the sulfate ion concentration was 23200 mg / L, and the calcium ion content was 750 mg / L. A composite calcium removal agent was added to the desulfurization wastewater for primary calcium removal. The calcium removal reactant was oxalic acid, with a molar ratio of oxalate ions to calcium ions of 1.3:1. The precipitant was calcium oxalate, with a mass ratio of precipitant to calcium removal reactant of 4:1. The specific dosage and composition of the flocculant are shown in the table below. After precipitation and clarification, primary calcium-removed wastewater was obtained. The calcium and magnesium ion removal rates in the primary calcium-removed wastewater are shown in the table below. The data in the table show that the PAC+PAM+PFS composite flocculant has the best effect on calcium ion removal.

[0090] (2) The parameters in steps (2) to (4) are controlled in the same way as in Example 5. The final purity of sodium chloride and magnesium sulfate heptahydrate is shown in the table below.

[0091] Table 1

[0092]

[0093] Example 9

[0094] This embodiment provides a method for the resource-based treatment of desulfurization wastewater, and the specific steps and operating parameters are as follows:

[0095] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 2000 mg / L, the sulfate ion concentration is 6000 mg / L, and the calcium ion content is 800 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is oxalic acid, and the molar ratio of oxalate ions to calcium ions is 1.3:1. The precipitant is calcium oxalate, and the mass ratio of precipitant to calcium removal agent is 4:1. After precipitation reaction and clarification, primary calcium removal wastewater is obtained. The calcium ion concentration in the primary calcium removal wastewater is 47.8 mg / L, and the magnesium ion concentration remains basically unchanged.

[0096] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 0.5 h⁻¹. -1 The temperature is controlled at 10℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 9.1 mg / L.

[0097] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device, and the mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is controlled to be 60:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 5:1.

[0098] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 100 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 15℃. Centrifugation is used to obtain sodium chloride with a purity of 99.0%. The effluent is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 20℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 98.7%.

[0099] Compared with Example 1, the composite calcium removal agent in Example 9 does not include flocculants. The calcium ion concentration in the solution after the first-stage calcium removal is relatively high. If the calcium ion concentration is well controlled in step (2), the purity of the salt product is still high, which increases the difficulty of control.

[0100] Comparative Example 1

[0101] This comparative example provides a method for the resource-based treatment of desulfurization wastewater, with the specific steps and operating parameters as follows:

[0102] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 2000 mg / L, the sulfate ion concentration is 6000 mg / L, and the calcium ion content is 800 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is oxalic acid, the molar ratio of oxalate ions to calcium ions is 1.3:1, and the flocculant is 10 mg / L PAC+PAM+PFS. After precipitation reaction and clarification, primary calcium removal wastewater is obtained. The calcium ion concentration in the primary calcium removal wastewater is 235 mg / L, and the magnesium ion concentration remains basically unchanged.

[0103] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 0.5 h⁻¹. -1 The temperature is controlled at 10℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 162mg / L.

[0104] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device, and the mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is controlled to be 60:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 5:1.

[0105] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 100 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 15℃. Centrifugation is used to obtain sodium chloride with a purity of 85.6%. The effluent is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 20℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 74.8%.

[0106] Comparative Example 2

[0107] This comparative example provides a method for the resource-based treatment of desulfurization wastewater, with the specific steps and operating parameters as follows:

[0108] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 2000 mg / L, the sulfate ion concentration is 6000 mg / L, and the calcium ion content is 800 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is oxalic acid, and the molar ratio of oxalate ions to calcium ions is 0.5:1. The precipitant is calcium oxalate, and the mass ratio of precipitant to calcium removal agent is 4:1. The flocculant is 10 mg / L PAC+PAM+PFS. After precipitation reaction and clarification, primary calcium removal wastewater is obtained. The calcium ion concentration in the primary calcium removal wastewater is 372 mg / L, and the magnesium ion concentration remains basically unchanged.

[0109] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 0.5 h⁻¹. -1 The temperature is controlled at 10℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 226mg / L.

[0110] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device, and the mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is controlled to be 60:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 5:1.

[0111] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 100 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 15℃. Centrifugation is used to obtain sodium chloride with a purity of 80.7%. The effluent is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 20℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 71.6%.

[0112] Comparative Example 3

[0113] This comparative example provides a method for the resource-based treatment of desulfurization wastewater, with the specific steps and operating parameters as follows:

[0114] (1) The desulfurization wastewater of a power plant contains 2000 mg / L of magnesium ions, 6000 mg / L of sulfate ions, and 800 mg / L of calcium ions. A composite calcium removal agent is added to the desulfurization wastewater for primary calcium removal. The calcium removal agent is oxalic acid, with a molar ratio of oxalate ions to calcium ions of 2:1. The precipitant is calcium oxalate, with a mass ratio of precipitant to calcium removal agent of 4:1. The flocculant is 10 mg / L PAC+PAM+PFS. After precipitation reaction and clarification, primary calcium removal wastewater is obtained. The calcium ion concentration in the primary calcium removal wastewater is 16.5 mg / L, the magnesium ion concentration is 1650 mg / L, and the magnesium ion removal rate is 17.5%.

[0115] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 0.5 h⁻¹. -1 The temperature is controlled at 10℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 4.2 mg / L.

[0116] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device, and the mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is controlled to be 60:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 6.8:1.

[0117] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 100 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation, concentration, and crystallization temperature is controlled at 15℃. Centrifugation is used to obtain sodium chloride with a purity of 99.2%. The effluent is sent to the evaporator, and the evaporation, concentration, and crystallization temperature is controlled at 20℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 99.2%, but the product quantity is significantly reduced, and complete recycling cannot be achieved.

[0118] Comparative Example 4

[0119] This comparative example provides a method for the resource-based treatment of desulfurization wastewater. The only difference from Example 1 is that the mass ratio of the precipitant to the calcium removal agent is 2:1.

[0120] The calcium ion concentration in the primary calcium removal wastewater was 65.5 mg / L, while the magnesium ion concentration remained essentially unchanged. The calcium ion concentration in the secondary calcium removal wastewater was controlled at 42.6 mg / L. Centrifugation yielded sodium chloride with a purity of 88.8% and magnesium sulfate heptahydrate with a purity of 85.6%.

[0121] Comparative Example 5

[0122] This comparative example provides a method for the resource-based treatment of desulfurization wastewater, with the specific steps and operating parameters as follows:

[0123] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 2000 mg / L, the sulfate ion concentration is 6000 mg / L, and the calcium ion content is 800 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is oxalic acid, and the molar ratio of oxalate ions to calcium ions is 1.3:1. The precipitant is calcium oxalate, and the mass ratio of precipitant to calcium removal agent is 0.5:1. The flocculant is 10 mg / L PAC+PAM+PFS. After precipitation reaction and clarification, primary calcium removal wastewater is obtained. The calcium ion concentration in the primary calcium removal wastewater is 160 mg / L, and the magnesium ion concentration remains basically unchanged.

[0124] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 0.5 h⁻¹. -1 The temperature is controlled at 10℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 42mg / L.

[0125] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device, and the mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is controlled to be 60:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 5:1.

[0126] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 100 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 15℃. Centrifugation is used to obtain sodium chloride with a purity of 88.9%. The effluent is sent to the evaporator, and the evaporation concentration and crystallization temperature is controlled at 20℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 85.2%.

[0127] Comparative Example 6

[0128] This comparative example provides a method for the resource-based treatment of desulfurization wastewater, with the specific steps and operating parameters as follows:

[0129] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 2000 mg / L, the sulfate ion concentration is 6000 mg / L, and the calcium ion content is 800 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is sodium oxalate, the molar ratio of oxalate ions to calcium ions is 1.3:1, the precipitant is calcium oxalate, the mass ratio of precipitant to calcium removal agent is 4:1, and the flocculant is 10 mg / L PAC+PAM+PFS. After precipitation reaction and clarification, primary calcium removal wastewater is obtained. The calcium ion concentration in the primary calcium removal wastewater is 29.1 mg / L, and the magnesium ion concentration remains basically unchanged.

[0130] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 0.5 h⁻¹. -1 The temperature is controlled at 10℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 5.2 mg / L.

[0131] (3) The secondary calcium removal wastewater is sent to the nanofiltration membrane separation device, and the mass ratio of sodium chloride to other salts in the permeate obtained by the nanofiltration membrane separation device is controlled to be 80:1, and the mass ratio of magnesium sulfate to other salts in the intercepted liquid obtained by the nanofiltration membrane separation device is 4.4:1.

[0132] (4) The permeate is fed into the reverse osmosis membrane unit to obtain reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate is sent to the reclaimed water tank, and the total salt concentration of the reverse osmosis concentrate is 100 g / L. The reverse osmosis concentrate is sent to the evaporator, and the evaporation, concentration, and crystallization temperature is controlled at 15℃. Centrifugation is used to obtain sodium chloride with a purity of 99.3%. The effluent is sent to the evaporator, and the evaporation, concentration, and crystallization temperature is controlled at 20℃. Centrifugation is used to obtain magnesium sulfate heptahydrate with a purity of 85.7%, which is too low.

[0133] Comparative Example 7

[0134] This comparative example provides a method for the resource-based treatment of desulfurization wastewater, with the specific steps and operating parameters as follows:

[0135] (1) The magnesium ion content in the desulfurization wastewater of a power plant is 2000 mg / L, the sulfate ion concentration is 6000 mg / L, and the calcium ion content is 800 mg / L. The desulfurization wastewater is treated with a compound calcium removal agent for primary calcium removal. The calcium removal agent is oxalic acid, and the molar ratio of oxalate ions to calcium ions is 1.3:1. The precipitant is calcium oxalate, and the mass ratio of precipitant to calcium removal agent is 4:1. The flocculant is 100 mg / L PAC+PAM+PFS. After precipitation reaction and clarification, primary calcium removal wastewater is obtained. The calcium ion concentration in the primary calcium removal wastewater is 24.5 mg / L, and the magnesium ion concentration remains basically unchanged.

[0136] (2) The primary calcium removal wastewater is fed into a high-selectivity calcium removal cation exchange resin unit, and the space velocity of the resin unit is controlled at 0.5 h⁻¹. -1 The temperature is controlled at 10℃, and after calcium removal, secondary calcium removal wastewater is obtained, in which the calcium ion concentration is controlled at 5.0 mg / L.

[0137] (3) When the secondary calcium removal wastewater is sent into the nanofiltration membrane separation device, the high concentration of flocculant will increase the viscosity of the solution, making it impossible to complete the nanofiltration step.

[0138] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for resource-based treatment of desulfurization wastewater, characterized in that, Includes the following steps: S1, a compound calcium removal agent is added to the wastewater to be treated to carry out a precipitation reaction and separation, and primary calcium removal wastewater is obtained; The composite calcium removal agent includes a calcium removal reactant and a precipitant. The calcium removal reactant includes oxalic acid, and the molar ratio of oxalate ions to calcium ions in the wastewater to be treated is 0.8~1.8:

1. The mass ratio of the precipitant to the calcium removal reactant is 3~5:

1. The composite calcium removal agent also includes a flocculant. The dosage of the flocculant is 0.1 mg / L~20 mg / L based on the volume of the wastewater to be treated. The precipitant includes calcium oxalate and / or calcium sulfate; The flocculant includes at least one of polyaluminum chloride (PAC), polyacrylamide (PAM), polyaluminum sulfate (PAS), polyferric chloride (PFC), and polyferric sulfate (PFS); S2, the obtained primary calcium removal wastewater is subjected to secondary calcium removal treatment to obtain secondary calcium removal wastewater; the secondary calcium removal treatment method is to remove calcium using ion exchange resin; S3, the obtained secondary calcium removal wastewater is subjected to nanofiltration for salt separation to obtain permeate and intercepted liquid; S4. The obtained permeate and intercepted liquid are crystallized to obtain sodium chloride and magnesium sulfate, respectively.

2. The method for resource-based treatment of desulfurization wastewater according to claim 1, characterized in that, In step S1, the molar ratio of oxalate ions to calcium ions in the calcium removal agent is 1~1.3:

1.

3. The method for resource-based treatment of desulfurization wastewater according to claim 2, characterized in that, In step S1, the mass ratio of the precipitant to the calcium removal agent is 4~5:

1.

4. The method for resource-based treatment of desulfurization wastewater according to any one of claims 1-3, characterized in that, The flocculant is a composite flocculant composed of polyaluminum chloride, polyacrylamide, and polyferric sulfate.

5. The method for resource-based treatment of desulfurization wastewater according to any one of claims 1-3, characterized in that, The ion exchange resin is a strong acid type ion exchange resin; And / or, the operating parameters for secondary calcium removal using ion exchange resin include: space velocity control of 0.2-2 h⁻¹. -1 The temperature is controlled between 10℃ and 40℃.

6. The method for resource-based treatment of desulfurization wastewater according to any one of claims 1-3, characterized in that, In step S4, the crystallization temperature of the permeate is 15℃~45℃; And / or, the crystallization treatment temperature of the intercepted liquid is 20℃~50℃; And / or, the permeate may further include a concentration step before crystallization treatment.

7. The method for resource-based treatment of desulfurization wastewater according to claim 6, characterized in that, The concentration is carried out using a reverse osmosis device.

8. The method for resource-based treatment of desulfurization wastewater according to any one of claims 1-3, characterized in that, In step S1, the calcium ion concentration in the primary calcium removal wastewater is controlled to be below 60 mg / L; And / or, in step S2, the calcium ion concentration in the secondary calcium removal wastewater is controlled to be below 10 mg / L; And / or, in step S4, the total salt concentration in the concentrated permeate is controlled to be 60 g / L to 200 g / L.

9. The method for resource-based treatment of desulfurization wastewater according to claim 8, characterized in that, In step S1, the calcium ion concentration in the primary calcium removal wastewater is controlled between 20.0 mg / L and 60.0 mg / L.

10. The method for resource-based treatment of desulfurization wastewater according to any one of claims 1-3, characterized in that, In step S1, the concentration of magnesium ions in the wastewater to be treated is 2000 mg / L-15000 mg / L, the concentration of sulfate ions is 6000 mg / L-50000 mg / L, and the concentration of calcium ions is 400 mg / L-1200 mg / L.

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