A method for the co-treatment of coking desulfurization waste liquid, activated carbon acidic wastewater and cold rolling acidic waste liquid.

Abstract

The application discloses a method for synergistically disposing coking desulfurization waste liquid, activated carbon acidic waste water and cold-rolled acidic waste liquid. According to the characteristics of the coking desulfurization waste liquid, the activated carbon acidic waste water and the cold-rolled acidic waste liquid, the activated carbon acidic waste water and the cold-rolled acidic waste liquid are selectively mixed and treated in the coking desulfurization waste liquid treatment process, so that the synergism between the waste waters is generated, the pollutants are collectively treated, the high-purity single crystalline salt is obtained without salt separation treatment, the method has the advantages of simple process, easy operation, low disposal cost, no need of complicated salt separation treatment and the like, realizes the purpose of waste treatment by waste, has the characteristics of convenient popularization and application, and provides a new technical route for the development goal of synergistically disposing the waste water of the whole steel plant.

Description

Technical Field

[0001] This invention relates to wastewater treatment, specifically to a method for the synergistic treatment of coking desulfurization waste liquid, activated carbon acidic wastewater, and cold rolling acidic waste liquid, belonging to the field of multi-source wastewater synergistic treatment technology. Background Technology

[0002] The wet oxidation process for desulfurization and decyanation of coke oven gas generates a large amount of desulfurization wastewater. This wastewater has a high salt content, and returning it to production would cause severe corrosion and sulfur accumulation. Current methods for treating desulfurization wastewater mainly include salt separation crystallization, dissolution crystallization, and roasting acid production. Crystallization has lower investment and operating costs than roasting acid production and is currently the mainstream process. However, since the salts in the desulfurization wastewater are mainly ammonium sulfate, ammonium thiosulfate, and ammonium thiocyanate, their three-phase separation is difficult. Therefore, salt separation crystallization and dissolution crystallization methods primarily involve oxidizing ammonium thiosulfate before salt separation. For example, Chinese patent CN102161541A reports a method of obtaining ammonium thiocyanate and mixed salts through decolorization, concentration, and crystallization, followed by redissolution, oxidation, and evaporation to obtain ammonium sulfate. Chinese patent CN110921953A reports a method of directly oxidizing ammonium thiocyanate and ammonium thiosulfate to ammonium sulfate using catalytic oxidation, followed by evaporation crystallization to obtain ammonium sulfate crystalline salt. The main problems with the above methods are high operating costs and cumbersome processes, which have prevented their industrial application. Furthermore, they only consider the treatment of desulfurization wastewater itself, failing to address the issue from the perspective of co-treatment of wastewater from the entire steel plant, resulting in high investment costs in the steelmaking process. Therefore, they cannot meet the current development requirements for the co-treatment of wastewater from the entire steel plant. Summary of the Invention

[0003] To address the problems of difficulty in salt separation, high treatment costs, and lack of co-treatment with other steel plant wastewater in existing technologies, this invention provides a method for the co-treatment of co-processing ...

[0004] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is specifically as follows:

[0005] A method for the co-treatment of coking desulfurization wastewater, activated carbon acidic wastewater, and cold rolling acidic wastewater, the method comprising:

[0006] 1) After decolorizing the coking desulfurization waste liquid, it is mixed with activated carbon acidic wastewater and reacted. After solid-liquid separation, a primary filtrate is obtained.

[0007] 2) Add an iron source to the cold-rolled acidic waste liquid to react. After the reaction is complete, mix it with the first filtrate to obtain a mixed waste liquid.

[0008] 3) First, add an oxidant to the mixed waste liquid obtained in step 2) to carry out an oxidation reaction, and then add ammonia water to carry out a precipitation reaction. After solid-liquid separation, a secondary filtrate is obtained.

[0009] 4) The secondary filtrate is subjected to ultrafiltration and nanofiltration in sequence to obtain permeate and concentrate. The permeate is recycled into the mixed waste liquid obtained in step 2) or used in the sintering process. The concentrate is evaporated, crystallized and purified to obtain ammonium sulfate.

[0010] Preferably, the coking desulfurization waste liquid is the waste liquid generated during the coking gas desulfurization process.

[0011] Preferably, the activated carbon acidic wastewater is acid production wastewater from sintering flue gas activated carbon process.

[0012] Preferably, the cold-rolled acidic waste liquid is the waste liquid generated during the cold-rolled pickling process.

[0013] Preferably, in step 1), the decolorization treatment involves adding activated carbon to the coking desulfurization wastewater for adsorption decolorization. Preferably, the adsorption decolorization treatment time is not less than 10 minutes, and more preferably 30-60 minutes.

[0014] Preferably, in step 1), the mixing volume ratio of the decolorized coking desulfurization waste liquid to the activated carbon acidic wastewater is 1:1 to 1:3, so that the pH of the mixed system is 2 to 5, preferably 3 to 4.

[0015] Preferably, in step 2), the iron source is iron powder and / or a soluble ferrous salt, with iron powder being the most preferred. The reaction time is not less than 5 minutes, and preferably 20 to 60 minutes.

[0016] Preferably, in step 2), the amount of iron source added is such that the content of ferrous ions in the mixed waste liquid is 1.15 to 1.3 times the concentration of thiocyanate ions (for example, one of 1.15 times, 1.16 times, 1.17 times, 1.18 times, 1.19 times, 1.20 times, 1.22 times, 1.25 times, 1.27 times, 1.28 times, 1.29 times, or 1.30 times).

[0017] Preferably, in step 2), the mixing volume ratio of the reacted cold-rolled acidic waste liquid to the primary filtrate is 1:1 to 1:2.5, so that the pH of the mixed waste liquid is 2 to 4, preferably 2.5 to 3.5.

[0018] Preferably, in step 3), the oxidant is one or more of hydrogen peroxide, permanganate, hypochlorite, oxygen, ozone, and chlorine, with hydrogen peroxide being the most preferred.

[0019] Preferably, in step 3), the amount of oxidant added is 200-300 g / L (here, the amount added means that the content of the oxidant in the mixed system after addition needs to reach 200-300 g / L). The oxidation reaction time is not less than 10 min, preferably 15-60 min.

[0020] Preferably, in step 3), the concentration of the ammonia water is 5-25%, more preferably 10-20%. The amount of ammonia water added is 0.01-0.5 times the total amount of coking desulfurization waste liquid, more preferably 0.1-0.3 times. The precipitation reaction time is not less than 10 minutes, more preferably 20-60 minutes.

[0021] Preferably, in step 4), the ultrafiltration is submerged ultrafiltration. Preferably, an oxidizing gas is used for aeration during the ultrafiltration process. Preferably, the oxidizing gas is one or more of compressed air, oxygen, and ozone.

[0022] Preferably, in step 4), the nanofiltration is performed using a nanofiltration membrane for separation and filtration. Preferably, the thiocyanate ion content in the nanofiltration product water is not higher than 2 g / L.

[0023] Preferably, in step 4), the product water is recycled into the mixed waste liquid obtained in step 2) for disposal or used in the sintering process. Specifically, the chloride content in the product water is monitored in real time. When the chloride content in the product water is higher than 50 g / L (preferably higher than 45 g / L), it is recycled into the mixed waste liquid obtained in step 2). Otherwise, it is used in the sintering process for disposal.

[0024] Preferably, in step 4), the evaporation, crystallization, and purification specifically involve: first, concentrating and crystallizing the concentrated salt using an MVR evaporator to obtain a mixed salt; then, washing the mixed salt with a saturated ammonium sulfate solution to obtain ammonium sulfate salt. Preferably, the purity of the ammonium sulfate salt is not less than 99%.

[0025] Preferably, in step 4), the waste liquid generated when washing the mixed salt with a saturated ammonium sulfate solution is combined with the waste liquid after ultrafiltration and then subjected to nanofiltration.

[0026] In this invention, the coking desulfurization wastewater mainly consists of organic matter, ammonium thiosulfate, ammonium thiocyanate, and ammonium sulfate, which are difficult to separate directly by crystallization and involve complex phase separation. Based on the concept of co-treatment of wastewater from the entire steel plant, and considering the characteristics of activated carbon acidic wastewater and cold rolling acidic wastewater from steel plants, this invention rationally designs a wastewater treatment process to co-treat the coking desulfurization wastewater. Specifically, through co-acidification, mixing, neutralization, precipitation, multi-stage oxidation homogenization, nanofiltration separation, evaporation crystallization, and chloride washing, the organic matter, ammonium thiosulfate, and ammonium thiocyanate in the coking desulfurization wastewater are removed stepwise and efficiently. Finally, while obtaining a high-purity ammonium sulfate product with a single composition, other wastewater from the steel plant is also simultaneously disposed of. This method features low treatment costs, a short process, and eliminates the need for complex salt separation, achieving the goal of treating waste with waste.

[0027] In this invention, the coking desulfurization wastewater contains a large amount of ammonium thiocyanate. This invention achieves deep purification of ammonium thiocyanate through a two-stage oxidation and a one-stage separation process. The first stage of oxidation is Fenton oxidation, which mainly utilizes ferrous iron in the cold-rolling acidic wastewater and added hydrogen peroxide to oxidize thiocyanate ions into nitrogen, carbon dioxide, and sulfate ions. The second stage of oxidation is air oxidation via ultrafiltration. The ultrafiltration membrane uses submerged ultrafiltration, which filters suspended solids while also oxidizing residual thiocyanate ions in the solution. The first-stage separation refers to separation using a nanofiltration membrane. This utilizes the characteristic that thiocyanate ions can permeate through the nanofiltration membrane while sulfate ions cannot, thus separating thiocyanate and sulfate ions and further ensuring the subsequent acquisition of high-purity ammonium sulfate salt.

[0028] In this invention, the coking desulfurization wastewater also contains a large amount of ammonium thiosulfate. This invention achieves deep purification of ammonium thiosulfate through wastewater-coordinated acidification, precipitation, and two-stage oxidation. The wastewater-coordinated acidification utilizes the strong acidity of activated carbon in the acidic wastewater to acidify the thiosulfate ions in the coking desulfurization wastewater into elemental sulfur and sulfite ions. Precipitation occurs when the generated sulfite ions further react with ferrous iron in the cold-rolling acidic wastewater and ammonium ions in the solution to form ferrous ammonium sulfite, achieving deep purification of residual thiosulfate and sulfite ions. The first stage of oxidation is Fenton oxidation, utilizing ferrous iron in the solution and added hydrogen peroxide to oxidize the residual thiosulfate and sulfite ions into sulfate ions. The second stage of oxidation is air oxidation in the ultrafiltration process. The ultrafiltration membrane uses submerged ultrafiltration, which filters suspended solids while simultaneously oxidizing residual thiosulfate and sulfite ions in the solution.

[0029] In this invention, the acidic wastewater from the activated carbon process contains a large amount of suspended activated carbon powder and is a mixed solution composed of dilute sulfuric acid, sulfurous acid, dilute hydrochloric acid, and ammonia nitrogen, with a pH generally <1. In this invention, it is primarily used to adjust the pH of the coking desulfurization wastewater. Furthermore, the sulfite ions in the solution can react with the ammonia nitrogen in the desulfurization wastewater and the ferrous iron in the cold-rolling acidic wastewater to form ferrous ammonium sulfite, achieving synergistic removal. In addition, the activated carbon powder in the wastewater can be used to adsorb sulfur produced by the acidolysis of thiosulfate ions, improving filtration efficiency.

[0030] In this invention, the acidic wastewater from cold rolling is mainly a mixed solution composed of ferrous chloride, ferric chloride, and dilute hydrochloric acid, with a pH generally <1. Ferrous chloride is primarily used in this invention to participate in the Fenton reaction to oxidize thiosulfate, sulfite, and thiocyanate, and to precipitate sulfite to form ferrous ammonium sulfite precipitate. Its acidity can be used to adjust the pH of the solution to acidic. Ferric iron (Fe3+) enhances the flocculation effect of sludge neutralization and precipitation; without the addition of ferric iron, the precipitate formed is smaller and finer, making filtration difficult.

[0031] In this invention, it should be noted that since the coking desulfurization wastewater contains both thiocyanate and thiosulfate ions, the presence of these two ions uniformly affects the purity of the subsequent ammonium sulfate salt. Therefore, a three-phase separation of ammonium sulfate, ammonium thiosulfate, and ammonium thiocyanate is required to obtain high-purity ammonium sulfate salt. Thus, this invention necessitates the deep removal of thiocyanate and thiosulfate ions. As mentioned earlier, the removal of thiosulfate ions requires the addition of activated carbon to acidic wastewater, utilizing its strong acidity to acidify the thiosulfate ions into elemental sulfur and sulfite. Although the cold-rolling acidic wastewater also has a strong acidity, it contains a certain amount of iron ions (Fe...). 2+ / Fe 3+ Ferrous ions combine with elemental sulfur to form toxic ferric sulfide substances. Simultaneously, ferrous ions are prematurely consumed by precipitating sulfite and ammonia in the wastewater, thus affecting the subsequent Fenton reaction and hindering the removal of thiocyanate and residual thiosulfate ions. Therefore, in this invention, coking desulfurization wastewater, activated carbon acidic wastewater, and cold rolling acidic wastewater cannot be mixed simultaneously during co-treatment. Instead, they must be added selectively and sequentially to achieve deep removal of pollutants from the three types of wastewater. Otherwise, incomplete or even ineffective removal of pollutants may occur.

[0032] Furthermore, in this invention, the coking desulfurization waste liquid generally needs to be decolorized before being mixed with activated carbon acidic wastewater. Specifically, a certain amount of activated carbon is added to the coking desulfurization waste liquid for decolorization, and then a certain amount of activated carbon acidic wastewater is added. After the reaction is completed, the mixture is filtered to obtain saturated activated carbon and decolorized acidic coking desulfurization waste liquid (i.e., primary filtrate).

[0033] In this invention, after treatments such as co-current mixing, Fenton oxidation, neutralization precipitation, ultrafiltration, and nanofiltration, the thiocyanate and thiosulfate ions in the mixed wastewater solution are basically removed. The resulting solution mainly consists of high-concentration ammonium sulfate and a small amount of ammonium chloride. Then, after direct evaporation through MVR, a mixed salt of ammonium sulfate and ammonium chloride is obtained. Furthermore, the mixed salt is washed with a saturated ammonium sulfate solution to dissolve the ammonium chloride, thereby obtaining a high-purity ammonium sulfate crystalline salt.

[0034] In this invention, the chloride (ammonium chloride) mainly originates from activated carbon acidic wastewater and cold rolling acidic waste liquid. A portion of the chloride enters the freshwater side (i.e., the permeate) of the nanofiltration system during the treatment process, while the remainder crystallizes with the concentrated water and enters the ammonium sulfate crystals. The chlorine in the crystals is removed through washing and returned to the nanofiltration system, eventually also entering the freshwater side of the nanofiltration system. The freshwater solution, after multiple cycles, reaches a certain concentration and is then returned to the sintering process for co-processing.

[0035] In this invention, the process for the co-treatment of coking desulfurization wastewater, activated carbon acidic wastewater, and cold rolling acidic wastewater is generally as follows: 1) Add a certain amount of activated carbon to the coking desulfurization wastewater, then add a certain amount of activated carbon acidic wastewater, react for 30-60 minutes, and filter to obtain saturated activated carbon and decolorized acidic coking desulfurization wastewater; 2) Take cold rolling acidic wastewater, add iron powder for reduction treatment, react for 30-60 minutes, and mix with the solution obtained in step 1); 3) Pass the reaction liquid obtained in step 2) through hydrogen peroxide for oxidation treatment, and then add dilute ammonia water for further treatment. Neutralize the precipitate and remove suspended solids from the solution through submerged ultrafiltration before entering the nanofiltration system to obtain concentrated water and permeate; 4) The permeate obtained in step 3) is returned to the recycling process in step 2). When the salinity of the permeate reaches a certain concentration, it is returned to the sintering system for recycling and disposal. The concentrated water obtained in step 3) is added to the MVR evaporation system to obtain condensate and a mixed salt of ammonium sulfate and ammonium chloride; 5) The mixed salt obtained in step 3) is washed with a saturated ammonium sulfate solution. The wash water is returned to the nanofiltration section of step 3) for recycling. The solid phase is high-purity ammonium sulfate.

[0036] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0037] 1. This invention is based on the concept of co-treatment of wastewater from the entire steel plant. According to the characteristics of other activated carbon wastewater and cold rolling acidic wastewater in steel plants, the wastewater treatment process is rationally designed to co-treat coking desulfurization wastewater. This achieves the stepwise and efficient removal of organic matter, ammonium thiosulfate, and ammonium thiocyanate from the coking desulfurization wastewater. While obtaining a high-purity ammonium sulfate product with a single composition, it also co-treats other wastewater from the steel plant, achieving the goal of treating waste with waste.

[0038] 2. The method of the present invention has the advantages of simple process, easy operation, low treatment cost and no need for complicated salt separation treatment. It is easy to promote and apply, and provides a new technical route for the development goal of co-treatment of wastewater from the entire steel plant. Attached Figure Description

[0039] Figure 1 This is a flowchart illustrating the method described in this invention. Detailed Implementation

[0040] The technical solution of the present invention will be illustrated below with examples. The scope of protection sought by the present invention includes, but is not limited to, the following embodiments. Example 1

[0041] like Figure 1 As shown, a method for the co-treatment of coking desulfurization wastewater, activated carbon acidic wastewater, and cold rolling acidic wastewater is disclosed. The method includes:

[0042] 1) After decolorizing the coking desulfurization waste liquid, it is mixed with activated carbon acidic wastewater and reacted. After solid-liquid separation, a primary filtrate is obtained.

[0043] 2) Add an iron source to the cold-rolled acidic waste liquid to react. After the reaction is complete, mix it with the first filtrate to obtain a mixed waste liquid.

[0044] 3) First, add an oxidant to the mixed waste liquid obtained in step 2) to carry out an oxidation reaction, and then add ammonia water to carry out a precipitation reaction. After solid-liquid separation, a secondary filtrate is obtained.

[0045] 4) The secondary filtrate is subjected to ultrafiltration and nanofiltration in sequence to obtain permeate and concentrate. The permeate is recycled into the mixed waste liquid obtained in step 2) or used in the sintering process. The concentrate is evaporated, crystallized and purified to obtain ammonium sulfate.

[0046] The coking desulfurization waste liquid is the waste liquid generated during the coking gas desulfurization process. The activated carbon acidic wastewater is sintering acid production wastewater. The cold rolling acidic waste liquid is the waste liquid generated during the cold rolling pickling process. Example 2

[0047] Example 1 is repeated, except that in step 1), the decolorization treatment involves adding activated carbon to the coking desulfurization wastewater for adsorption decolorization. The adsorption decolorization treatment time is 40 minutes. Example 3

[0048] Repeat Example 2, except that in step 1), the mixing volume ratio of the decolorized coking desulfurization wastewater to the activated carbon acidic wastewater is 1:1.5, so that the pH of the mixed system is about 3. Example 4

[0049] Example 3 was repeated, except that in step 2), the iron source was iron powder. The reaction time was 35 minutes. The amount of iron source added was such that the ferrous ion content in the mixed waste liquid was 1.2 times the thiocyanate ion concentration. Example 5

[0050] Repeat Example 4, except that in step 2), the mixing volume ratio of the cold-rolled acidic waste liquid after reaction to the primary filtrate is 1:1.8, so that the pH of the mixed waste liquid is about 2.5. Example 6

[0051] Example 5 was repeated, except that in step 3), the oxidant was hydrogen peroxide. The amount of hydrogen peroxide added was 230 g / L. The oxidation reaction time was 40 min. Example 7

[0052] Repeat Example 6, except that in step 3), the concentration of the ammonia water is 20%. The amount of ammonia water added is 0.2 times the amount of coking desulfurization waste liquid. The precipitation reaction time is 30 minutes. Example 8

[0053] Example 7 is repeated, except that in step 4), the ultrafiltration is submerged ultrafiltration. An oxidizing gas, specifically compressed air, is used for aeration during the ultrafiltration process. Example 9

[0054] Example 8 is repeated, except that in step 4), the nanofiltration is performed using a nanofiltration membrane. The thiocyanate ion content in the nanofiltration product water is not higher than 1.8 g / L. Example 10

[0055] Repeat Example 9, except that in step 4), the chloride content in the product water is monitored in real time. When the chloride content in the product water is higher than 45 g / L, it is collected into the mixed waste liquid obtained in step 2) for recycling and treatment; otherwise, it is used for disposal in the sintering process. Example 11

[0056] Repeat Example 10, except that in step 4), the evaporation, crystallization, and purification are specifically performed as follows: first, the concentrated salt is concentrated and crystallized using an MVR evaporator to obtain a mixed salt; then, the mixed salt is washed with a saturated ammonium sulfate solution to obtain ammonium sulfate salt. The purity of the ammonium sulfate salt is not less than 99%. Example 12

[0057] Repeat Example 11, except that in step 4), the waste liquid generated when washing the mixed salt with a saturated ammonium sulfate solution is combined with the waste liquid after ultrafiltration and then subjected to nanofiltration.

[0058] Application Example 1

[0059] The method described in Example 12 was used for the synergistic treatment of coking desulfurization wastewater, activated carbon acidic wastewater, and cold rolling acidic wastewater.

[0060] First, add sufficient activated carbon to the coking desulfurization waste liquid for adsorption and decolorization treatment. Then, add activated carbon and acidic wastewater for reaction. After the reaction is completed, filter to obtain saturated activated carbon and primary filtrate.

[0061] Iron powder is added to the cold-rolled acidic waste liquid for reduction treatment. After the reaction is completed, it is mixed and homogenized with the primary filtrate to obtain a mixed waste liquid. Then, hydrogen peroxide is passed into the obtained mixed waste liquid for oxidation treatment. After the oxidation reaction is completed, dilute ammonia is added for neutralization and precipitation. After precipitation is completed, the liquid is filtered to obtain a secondary filtrate.

[0062] The secondary filtrate is treated by submerged ultrafiltration to remove suspended solids. The ultrafiltration wastewater then enters a nanofiltration system, where concentrated water and permeate are obtained. Depending on the chloride content in the permeate, it is selectively recycled to the mixed wastewater or used for disposal in the sintering process. The obtained concentrated water is added to an MVR evaporation system to obtain condensate and a mixed salt of ammonium sulfate and ammonium chloride (ammonium sulfate content approximately 85%). The mixed salt is washed with a saturated ammonium sulfate solution, and the resulting solid phase is high-purity ammonium sulfate (purity detected to be approximately 99.99%). The wash water is sent to the nanofiltration section for recycling.

[0063] Comparative Example 1

[0064] First, add sufficient activated carbon to the coking desulfurization waste liquid for adsorption and decolorization treatment, and filter to obtain saturated activated carbon and decolorized coking desulfurization waste liquid; add iron powder to the cold rolling acidic waste liquid for reduction treatment to obtain reduced cold rolling acidic waste liquid.

[0065] The desulfurized coking wastewater to be decolorized, the acidic wastewater from cold rolling after reduction, and the acidic wastewater from activated carbon were mixed and homogenized to obtain a mixed wastewater (pH controlled in the same way as in Application Example 1). Hydrogen peroxide was then introduced into the mixed wastewater for oxidation treatment. After the oxidation reaction was complete, dilute ammonia was added for neutralization and precipitation. After precipitation, the solution was filtered to obtain filtrate. The filtrate was treated by submerged ultrafiltration to remove suspended solids. The ultrafiltration wastewater entered a nanofiltration system, where concentrated water and permeate were obtained. The concentrated water was added to an MVR evaporation system to obtain condensate and a mixed salt composed of ammonium sulfate, ammonium chloride, and organic matter (ammonium sulfate content approximately 81%). The mixed salt was washed with a saturated ammonium sulfate solution, and the solid phase obtained after washing was ammonium sulfate (purity detected to be approximately 95%).

[0066] Comparative Example 2

[0067] Repeat Example 1, except without the cold-rolling acidic waste liquid.

[0068] The mixed salt composition obtained by evaporating and crystallizing concentrated water consists of ammonium sulfate, ammonium chloride, ammonium sulfite, ammonium thiocyanate, etc. (ammonium sulfate content is about 62%). The yield of high-purity ammonium sulfate is about 32% lower than that of application example 1.

[0069] Comparative Example 3

[0070] Repeat Example 1, except without activated carbon in the acidic wastewater.

[0071] The mixed salt obtained by evaporating and crystallizing the concentrated water consists of ammonium sulfate, ammonium chloride, ammonium thiosulfate, ammonium thiocyanate, sulfur, etc. (ammonium sulfate content is about 55%), and the purity was detected to be about 96%. The yield of high-purity ammonium sulfate decreased by about 45% compared with Application Example 1.

Claims

1. A method for the co-treatment of coking desulfurization wastewater, activated carbon acidic wastewater, and cold rolling acidic wastewater, characterized in that: The method comprises: 1) mixing and reacting the coking desulfurization waste liquid with activated carbon acidic waste water after decoloring treatment, and then performing solid-liquid separation to obtain a first filtrate; the coking desulfurization waste liquid contains ammonium thiosulfate and ammonium thiocyanate; 2) adding an iron source to the cold-rolled acidic waste liquid to perform reaction, and then mixing the reacted cold-rolled acidic waste liquid with the first filtrate to obtain a mixed waste liquid; the iron source is iron powder and / or soluble ferrous salt; 3) adding an oxidizing agent to the mixed waste liquid obtained in step 2) to perform oxidation reaction, and then adding ammonia water to perform precipitation reaction, and then performing solid-liquid separation to obtain a second filtrate; 4) performing ultrafiltration and nanofiltration on the second filtrate in sequence to obtain product water and concentrated water, the product water is recycled into the mixed waste liquid obtained in step 2) for disposal or used in a sintering process, and the concentrated water is subjected to evaporation crystallization and purification to obtain ammonium sulfate salt.

2. The method of claim 1, wherein: The coking desulfurization waste liquid is a waste liquid generated in a coking gas desulfurization process; The activated carbon acidic waste water is sintering flue gas activated carbon method acid waste water; The cold-rolled acidic waste liquid is a waste liquid generated in a cold-rolled pickling process.

3. The method of claim 1, wherein: In step 1), the decoloring treatment is adsorption decoloring treatment by adding activated carbon to the coking desulfurization waste liquid.

4. The method of claim 3, wherein: The adsorption decoloring treatment time is not less than 10 minutes.

5. The method of claim 4, wherein: The adsorption decoloring treatment time is 30-60 minutes.

6. The method of claim 3, wherein: The mixed volume ratio of the coking desulfurization waste liquid after decoloring treatment to the activated carbon acidic waste water is 1:1-1:3, so that the pH of the mixed system is 2-5.

7. The method of claim 6, wherein: The pH of the mixed system after decoloring treatment is 3-4.

8. The method of claim 1, wherein: In step 2), the iron source is iron powder; the reaction time is not less than 5 minutes.

9. The method of claim 8, wherein: In step 2), the reaction time is 20-60 minutes.

10. The method of claim 1, wherein: In step 2), the amount of the iron source added is such that the content of ferrous ions in the mixed waste liquid is 1.15-1.3 times the concentration of thiocyanate ions; and / or The mixed volume ratio of the reacted cold-rolled acidic waste liquid to the first filtrate is 1:1-1:2.5, so that the pH of the mixed waste liquid is 2-4.

11. The method of claim 1, wherein: In step 3), the oxidizing agent is one or more of hydrogen peroxide, permanganate and hypochlorite.

12. The method of claim 1, wherein: In step 3), the oxidizing agent is hydrogen peroxide.

13. The method of claim 11, wherein: In step 3), the amount of the oxidizing agent added is 200-300 g / L; the oxidation reaction time is not less than 10 minutes.

14. The method of claim 13, wherein: In step 3), the oxidation reaction time is 15-60 minutes.

15. The method of claim 1, wherein: In step 3), the concentration of the ammonia water is 5-25%; the amount of the ammonia water added is 0.01-0.5 times the total amount of the coking desulfurization waste liquid; the precipitation reaction time is not less than 10 minutes.

16. The method of claim 15, wherein: In step 3), the concentration of the ammonia water is 10-20%; the amount of the ammonia water added is 0.1-0.3 times the total amount of the coking desulfurization waste liquid; the precipitation reaction time is 20-60 minutes.

17. The method of claim 1, wherein: In step 4), the ultrafiltration is submerged ultrafiltration.

18. The method of claim 17, wherein: An oxidizing gas is used for aeration during the ultrafiltration process.

19. The method of claim 18, wherein: The oxidizing gas is one or more of compressed air, oxygen and ozone.

20. The method of claim 1, wherein: In step 4), the nanofiltration is separation and filtration treatment by using a nanofiltration membrane.

21. The method of claim 20, wherein: The content of thiocyanate ions in the product water after nanofiltration is not higher than 2 g / L.

22. The method of claim 1, wherein: In step 4), the produced water is mixed into the mixed waste liquid obtained in step 2) for recycling treatment or used in the sintering process, specifically: the content of chlorides in the produced water is detected in real time, and when the content of chlorides in the produced water is higher than 50 g / L, the produced water is mixed into the mixed waste liquid obtained in step 2) for recycling treatment, otherwise, the produced water is used in the sintering process for consumption.

23. The method of claim 1, wherein: In step 4), the evaporation crystallization and purification are specifically as follows: the concentrated salt is first concentrated and crystallized by using an MVR evaporator to obtain mixed salt, and then the mixed salt is washed by using an ammonium sulfate saturated solution to obtain an ammonium sulfate salt.

24. The method of claim 23, wherein: The purity of the ammonium sulfate salt is not less than 99%.

25. The method of claim 23, wherein: The salt washing waste liquid generated when the mixed salt is washed by using the ammonium sulfate saturated solution is mixed with the waste liquid after ultrafiltration and then subjected to nanofiltration treatment.

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