CN113955893B - Desulfurization wastewater treatment method and treatment system - Google Patents
Desulfurization wastewater treatment method and treatment system Download PDFInfo
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- CN113955893B CN113955893B CN202111406729.5A CN202111406729A CN113955893B CN 113955893 B CN113955893 B CN 113955893B CN 202111406729 A CN202111406729 A CN 202111406729A CN 113955893 B CN113955893 B CN 113955893B
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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- C01F5/00—Compounds of magnesium
- C01F5/14—Magnesium hydroxide
- C01F5/22—Magnesium hydroxide from magnesium compounds with alkali hydroxides or alkaline- earth oxides or hydroxides
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- C02F1/00—Treatment of water, waste water, or sewage
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- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
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- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
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Abstract
The application provides a desulfurization wastewater treatment method and a desulfurization wastewater treatment system, relates to the technical field of wastewater treatment, and solves the technical problem that the purity of magnesium hydroxide recovered at present is low. The method comprises the following steps: pretreatment: mixing the desulfurization wastewater with the first solution, reacting to obtain calcium sulfate, and separating out the calcium sulfate to obtain a second solution; magnesium hydroxide synthesis stage: and mixing the second solution with calcium hydroxide, reacting to obtain magnesium hydroxide precipitate, separating the magnesium hydroxide precipitate to obtain a third solution, and mixing at least part of the third solution serving as the first solution with the desulfurization wastewater in the pretreatment stage.
Description
Technical Field
The application relates to the technical field of wastewater treatment, in particular to a desulfurization wastewater treatment method and a desulfurization wastewater treatment system.
Background
The desulfurization waste water of the coal-fired power plant is high-salt and high-hardness waste water, wherein Mg 2+ The content is higher. Because of higher magnesium value, the magnesium in the desulfurization wastewater is usually treated by 2+ And (5) recycling.
At present, the calcium method is generally adopted for Mg 2+ And (3) recycling, namely directly putting slaked lime serving as a precipitator into the desulfurization wastewater to generate magnesium hydroxide precipitate and calcium sulfate precipitate. Although this approach is economical, the magnesium hydroxide precipitate and the calcium sulfate precipitate are difficult to separate, resulting in lower purity of the recovered magnesium hydroxide.
Disclosure of Invention
The application provides a desulfurization wastewater treatment method and a desulfurization wastewater treatment system, which can be used for solving the technical problem that the purity of magnesium hydroxide recovered at present is low.
In a first aspect, an embodiment of the present application provides a desulfurization wastewater treatment method, including:
pretreatment: mixing the desulfurization wastewater with the first solution, reacting to obtain calcium sulfate, and separating out the calcium sulfate to obtain a second solution;
magnesium hydroxide synthesis stage: and mixing the second solution with calcium hydroxide, reacting to obtain magnesium hydroxide precipitate, separating the magnesium hydroxide precipitate to obtain a third solution, and mixing at least part of the third solution serving as the first solution with the desulfurization wastewater in the pretreatment stage.
Optionally, in one embodiment, the mixing at least a portion of the third solution as the first solution with the desulfurization wastewater prior to the pretreatment stage, the treatment method further comprises:
the pH of the third solution is adjusted to 6-8.
Optionally, in one embodiment, after the magnesium hydroxide synthesis stage, the treatment method further comprises a washing stage:
the cleaning stage comprises: and washing the magnesium hydroxide precipitate by using a washing solution to obtain a magnesium hydroxide product and a cleaning solution.
Optionally, in one embodiment, a portion of the third solution is mixed as the first solution with the desulfurization wastewater in the pretreatment stage, and after the magnesium hydroxide synthesis stage, the treatment method further comprises a crystallization stage:
the crystallization stage comprises: mixing the rest of the third solution, the cleaning solution and the target solution, reacting to obtain calcium sulfate, and separating out the calcium sulfate to obtain a fourth solution; wherein the target solution contains sulfate ions.
Optionally, in one embodiment, after the crystallization stage, the treatment method further comprises a nanofiltration treatment stage:
the nanofiltration treatment stage comprises: treating the fourth solution by utilizing a nanofiltration process to obtain a first nanofiltration solution and a second nanofiltration solution; wherein the sulfate ion content in the first nanofiltration solution is greater than the sulfate ion content in the second nanofiltration solution;
at least part of the first nanofiltration solution is mixed as the target solution with the washing liquid and the remaining third solution in the crystallization stage.
Optionally, in one embodiment, the treatment method further comprises a filtration stage prior to the nanofiltration treatment stage,
The filtering stage comprises: and filtering the fourth solution to remove suspended matters and colloid.
Optionally, in one embodiment, after the nanofiltration treatment stage, the treatment process further comprises a concentration stage,
the concentration stage comprises: and treating the second nanofiltration solution by using a concentration process.
Optionally, in one embodiment, before the concentrating stage, the processing method further comprises:
washing the magnesium hydroxide precipitate in the washing stage with a portion of the second nanofiltration solution as the washing solution;
the processing of the second nanofiltration solution using a concentration process comprises:
and (3) treating the rest second nanofiltration solution by using a concentration process.
In a second aspect, an embodiment of the present application provides a treatment system used in the desulfurization wastewater treatment method provided in the first aspect of the embodiment of the present application, where the treatment system includes a pretreatment device, a magnesium hydroxide synthesis device, and a first return line;
wherein the pretreatment device is provided with a first outlet and a first inlet, and the magnesium hydroxide synthesis device is provided with a first inlet and a first outlet;
the first outlet of the pretreatment device is communicated with the first inlet of the magnesium hydroxide synthesis device, the first outlet of the magnesium hydroxide synthesis device is communicated with the inlet of the first return pipeline, and the outlet of the first return pipeline is communicated with the first inlet of the pretreatment device;
The first return line is for returning at least part of the third solution to the pretreatment device.
Optionally, in one embodiment, the magnesium hydroxide synthesis device comprises a pH adjustment tank,
the pH adjusting tank is used for adjusting the pH of the third solution to 6-8 before the at least part of the third solution is refluxed to the pretreatment device.
The embodiment of the application has the following beneficial effects:
the desulfurization wastewater treatment method provided by the embodiment of the application comprises the following steps: pretreatment: mixing the desulfurization wastewater with the first solution, reacting to obtain calcium sulfate, and separating out the calcium sulfate to obtain a second solution; magnesium hydroxide synthesis stage: mixing the second solution with calcium hydroxide, reacting to obtain magnesium hydroxide precipitate, separating the magnesium hydroxide precipitate to obtain a third solution, and mixing at least part of the third solution serving as the first solution with the desulfurization wastewater in the pretreatment stage; at least part of the third solution rich in calcium ions, which is obtained after the magnesium hydroxide precipitation is separated in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage as the first solution, sulfate ions in the desulfurization wastewater are removed in advance by generating calcium sulfate, so that a large amount of calcium sulfate is prevented from being generated in the magnesium hydroxide synthesis stage, namely sulfate radicals are precipitated in the pretreatment stage first, and magnesium is precipitated in the magnesium hydroxide synthesis stage, calcium sulfate and magnesium hydroxide can be precipitated step by step, a large amount of calcium sulfate precipitation and magnesium hydroxide precipitation are prevented from being mixed, and the purity of the recovered magnesium hydroxide is further improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art. In the drawings:
FIG. 1 is a schematic flow chart of a desulfurization wastewater treatment method according to an embodiment of the present application;
FIG. 2 is a schematic flow chart of another desulfurization wastewater treatment method according to an embodiment of the present application;
FIG. 3 is a schematic flow chart of another method for treating desulfurization wastewater according to an embodiment of the present application;
FIG. 4 is a schematic structural diagram of a desulfurization wastewater treatment system according to an embodiment of the present application;
FIG. 5 is a schematic diagram of another desulfurization wastewater treatment system according to an embodiment of the present application.
Reference numerals:
30-a desulfurization wastewater treatment system; 301-a pretreatment device; 3011-a first reaction tank; 3012-a clarifier; 302-a magnesium hydroxide synthesis device; 3021-a second reaction tank; 3022-a sedimentation tank; 3023-pH adjusting tank; 303-a first return line; 304-a cleaning device; 305-crystallization device; 306-a filtering device; 307-nanofiltration device; 308-a second return line; 309-a third return line; 310-concentrating device; 311-evaporative crystallization apparatus.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the technical solutions of the present application will be clearly and completely described below with reference to specific embodiments of the present application and corresponding drawings. It will be apparent that the described embodiments are only some, but not all, embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
The features of the application "first", "second" and the like in the description and in the claims may be used for the explicit or implicit inclusion of one or more such features. In the description of the present application, unless otherwise indicated, the meaning of "a plurality" is two or more. Furthermore, in the description and claims, "and/or" means at least one of the connected objects, and the character "/", generally means that the associated object is an "or" relationship.
In the description of the present application, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present application will be understood in specific cases by those of ordinary skill in the art.
As described in the background of the application, the desulfurization waste water of coal-fired power plants is high-salt, high-hardness waste water, and generally has the following characteristics: 1) Weakly acidic, pH is between 4.5 and 7.0; 2) The content of Suspended Substances (SS) is high and is generally 2-20 g/L; 3) The salt content is high, and the Total Dissolved Solids (TDS) is as high as 20-50 g/L; 4) The hardness is high, and the content of Ca element and Mg element is 1-15 g/L; 5) The chlorine content is high, generally 5-20 g/L, and a large amount of sulfate ions are contained. Because of higher magnesium value, the Mg in the desulfurization wastewater is usually 2+ Is converted into magnesium hydroxide for recovery. At present, the calcium method is generally adopted for Mg 2+ And (3) recycling, namely adding slaked lime serving as a precipitator into the desulfurization wastewater to generate magnesium hydroxide precipitate so as to recycle the magnesium hydroxide. Although this approach is economical, calcium sulfate precipitation is generated at the same time, and the magnesium hydroxide precipitation and the calcium sulfate precipitation are difficult to separate, resulting in lower purity of the recovered magnesium hydroxide.
Aiming at the problem, the embodiment of the application provides a desulfurization wastewater treatment method which can be used for solving the technical problem that the purity of the magnesium hydroxide recovered at present is low. As shown in fig. 1, the processing method may include the steps of:
Step 101, pretreatment: mixing the desulfurization wastewater with the first solution, reacting to obtain calcium sulfate, and separating out the calcium sulfate to obtain a second solution.
Wherein the desulfurization wastewater contains a large amount of Mg 2+ 、Ca 2+ 、Cl - 、Na + 、SO 4 2- Etc
The first solution is a solution rich in calcium ions, the first solution rich in calcium ions is mixed with desulfurization wastewater, sulfate ions in the first solution can be removed in advance by generating calcium sulfate, and the calcium sulfate is further separated out, so that a large amount of calcium sulfate precipitation doped in magnesium hydroxide precipitation in the subsequent magnesium hydroxide synthesis stage can be avoided.
The second solution is a solution obtained by mixing the first solution with desulfurization wastewater to generate calcium sulfate and further removing the calcium sulfate through solid-liquid separation, wherein the solution contains a large amount of magnesium ions.
Step 102, magnesium hydroxide synthesis stage: and mixing the second solution with calcium hydroxide, reacting to obtain magnesium hydroxide precipitate, separating the magnesium hydroxide precipitate to obtain a third solution, and mixing at least part of the third solution serving as the first solution with the desulfurization wastewater in the pretreatment stage.
And after the second solution is led into the device corresponding to the magnesium hydroxide synthesis stage from the device corresponding to the pretreatment stage, calcium hydroxide is added into the second solution rich in magnesium ions, and magnesium hydroxide precipitation is generated through reaction. The magnesium hydroxide precipitate can be separated out for recovery by solid-liquid separation. The molar ratio of the adding amount of the calcium hydroxide to the magnesium ions in the second solution is 1-1.2:1, and the reaction time is 0.5-1h.
The third solution is a solution obtained by removing magnesium hydroxide precipitate through solid-liquid separation, and contains a large amount of calcium ions. The third solution rich in calcium ions may be refluxed to the pretreatment stage of step 101 as the first solution to remove sulfate ions in the desulfurization wastewater.
It can be appreciated that in the pretreatment stage of step 101, sulfate is precipitated, and calcium sulfate is removed to obtain a second solution, and in the magnesium hydroxide synthesis stage of step 102, when magnesium ions in the second solution are precipitated, a large amount of calcium sulfate precipitation is avoided, so that a large amount of calcium sulfate precipitation doped in the magnesium hydroxide precipitation is avoided.
In practical applications, part or all of the third solution may be refluxed to the pretreatment stage of step 101 as the first solution. The volume ratio of the reflux quantity of the third solution to the pretreatment stage of the step 101 to the desulfurization wastewater is 1-2:1.
it can be understood that by adopting the desulfurization wastewater treatment method provided by the embodiment of the application, at least part of the third solution rich in calcium ions, which is obtained after the magnesium hydroxide precipitation is separated in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage as the first solution, sulfate ions in desulfurization wastewater are removed in advance by generating calcium sulfate, so that a large amount of calcium sulfate is prevented from being generated in the magnesium hydroxide synthesis stage, namely, sulfate is precipitated in the pretreatment stage first, magnesium is precipitated in the magnesium hydroxide synthesis stage, calcium sulfate and magnesium hydroxide can be precipitated step by step, mixing of a large amount of calcium sulfate precipitation and magnesium hydroxide precipitation is avoided, and further, the purity of the recovered magnesium hydroxide is improved. On the other hand, at least part of the third solution rich in calcium ions, which is obtained after the magnesium hydroxide precipitation is separated by adopting the magnesium hydroxide synthesis stage, flows back to the pretreatment stage as the first solution to provide a calcium source for precipitating sulfate radicals, so that other calcium medicaments are not needed to be added in the pretreatment stage, and the treatment cost of desulfurization wastewater is greatly reduced.
In the actual operation process, when the third solution is not available at first and at least part of the third solution cannot be refluxed to the pretreatment stage to serve as the first solution, the pretreatment stage can be skipped, the first batch of desulfurization wastewater directly enters the magnesium hydroxide synthesis stage, calcium hydroxide is added into the first batch of desulfurization wastewater, the third solution is obtained after precipitation is separated, and at least part of the third solution is refluxed to the next batch of desulfurization wastewater to perform the corresponding treatment steps of the pretreatment stage, so that the third solution in the steps 101 and 102 is recycled.
In the step 102 magnesium hydroxide synthesis stage, calcium hydroxide is added to precipitate magnesium ions, so that the third solution obtained after separating out magnesium hydroxide precipitate has higher hydroxide ion content and higher pH, and the pH is generally about 11. If the third solution is directly refluxed to the pretreatment stage as the first solution to precipitate sulfate radical in the desulfurization wastewater, a large amount of magnesium hydroxide precipitate can be generated while calcium sulfate precipitate is generated, so that calcium sulfate and magnesium hydroxide cannot be precipitated step by step, and a large amount of magnesium hydroxide precipitate exists in the pretreatment stage. If the solid-liquid separation is continued in the pretreatment stage to remove the precipitate, the magnesium hydroxide recovered in the magnesium hydroxide synthesis stage may be reduced, and if the solid-liquid separation is not performed, the magnesium hydroxide recovered in the magnesium hydroxide synthesis stage may be reduced in purity.
Thus, in one embodiment, the desulfurization wastewater treatment method provided by the embodiment of the present application further includes, before mixing at least a part of the third solution as the first solution with the desulfurization wastewater in the pretreatment stage: the pH of the third solution is adjusted to 6-8.
The pH of the third solution may be adjusted by adding hydrochloric acid to the third solution.
It is understood that by adjusting the pH of the third solution to 6-8 and then refluxing at least a portion of the third solution to the pretreatment stage as the first solution, a large amount of magnesium hydroxide precipitate can be prevented from being generated in the pretreatment stage, and thus the product amount and purity of the recovered magnesium hydroxide can be improved.
The magnesium hydroxide precipitate directly separated in the step 102 magnesium hydroxide synthesis stage is generally high in water content, exists in the form of slurry, and can be further subjected to filter pressing treatment to reduce the water content therein, so as to obtain magnesium hydroxide solid precipitate.
Considering that it is difficult to completely remove sulfate radical in the desulfurization wastewater in the pretreatment stage of step 101, the residual sulfate radical in the second solution reacts with the added calcium hydroxide to produce calcium sulfate in the magnesium hydroxide synthesis stage of step 102, so that a small amount of calcium sulfate is contained in the magnesium hydroxide precipitate. In order to further increase the purity of the recovered magnesium hydroxide, in one embodiment, after the magnesium hydroxide synthesis stage of step 102, the desulfurization wastewater treatment method provided in the embodiment of the present application further includes step 103, a cleaning stage: the magnesium hydroxide precipitate was washed with a washing solution as shown in fig. 2.
Wherein the washing solution is a solution containing no sulfate radical or less sulfate radical. The washing solution is used for washing the magnesium hydroxide precipitate containing a small amount of calcium sulfate, and the solubility difference of the calcium sulfate and the magnesium hydroxide in water can be used for dissolving the calcium sulfate, so that the calcium sulfate in the magnesium hydroxide precipitate is removed. The washed magnesium hydroxide precipitate may be specifically a magnesium hydroxide solid precipitate obtained by press filtration treatment, which contains a small amount of calcium sulfate solid precipitate. And washing the magnesium hydroxide precipitate by the washing solution, and after solid-liquid separation, obtaining a magnesium hydroxide product with higher purity, and further drying the magnesium hydroxide product to obtain a final product. After solid-liquid separation, the cleaning liquid which is remained after separating magnesium hydroxide can be obtained, and the cleaning liquid contains dissolved calcium ions, sulfate ions and the like.
In practical applications, refluxing a portion of the third solution to the pretreatment stage as the first solution may already provide a sufficient source of calcium for the pretreatment stage, and in order to avoid wasting resources, in one embodiment, in the step 102 magnesium hydroxide synthesis stage, at least a portion of the third solution is mixed as the first solution with the desulfurization wastewater in the pretreatment stage, specifically, a portion of the third solution is mixed as the first solution with the desulfurization wastewater in the pretreatment stage. Further, after the magnesium hydroxide synthesis stage, the desulfurization wastewater treatment method provided by the embodiment of the application further includes step 104, a crystallization stage: mixing the rest of the third solution, the cleaning solution and the target solution, reacting to obtain calcium sulfate, and separating out the calcium sulfate to obtain a fourth solution; wherein the target solution contains sulfate ions.
Wherein the remaining third solution may refer to the third solution remaining after refluxing a portion of the third solution to the pretreatment stage, being enriched in calcium ions. The target solution may in particular be a sulfate-rich solution.
The third solution rich in calcium ions, the cleaning solution containing calcium ions and sulfate ions and the target solution rich in sulfate radicals are mixed, so that the calcium ions in the third solution and the cleaning solution can be precipitated to obtain calcium sulfate precipitate, further, the recovery of calcium sulfate can be realized, and the resource recovery utilization rate is improved. In particular, calcium sulfate may be recovered in a normal temperature crystallizer in a spontaneous crystallization process driven by supersaturation at normal temperature.
The calcium sulfate (also referred to as recovered gypsum crystals) can be recovered by solid-liquid separation, and a fourth solution can be obtained after separation of the calcium sulfate, which still contains more sulfate ions and chloride ions. In one embodiment, after the crystallization stage of step 104, the desulfurization wastewater treatment method provided in the embodiment of the present application further includes step 105, a nanofiltration treatment stage: treating the fourth solution by utilizing a nanofiltration process to obtain a first nanofiltration solution and a second nanofiltration solution; wherein the sulfate ion content in the first nanofiltration solution is greater than the sulfate ion content in the second nanofiltration solution; at least part of the first nanofiltration solution is mixed as the target solution with the washing liquid and the remaining third solution in the crystallization stage.
The fourth solution containing acid radical ions and chloride ions is treated by a nanofiltration process, so that a first nanofiltration solution rich in sulfate radical and a second nanofiltration solution rich in chloride ions can be respectively obtained. The nano-filtration technology is adopted to selectively separate sulfate ions and chloride ions, so that the purity of sodium chloride products obtained by subsequent evaporation and crystallization can be ensured.
In order to avoid the scaling of calcium sulfate precipitation in the nanofiltration process, a calcium sulfate scale inhibitor can be added into nanofiltration water to prevent the scaling of calcium sulfate and realize long-period stable operation. The separation pressure of the nanofiltration process is 0.5MPa-2MPa, and the volume flow ratio of the first nanofiltration solution to the second nanofiltration solution is 1:1-3. The removal rate of sulfate ions in the second nanofiltration solution is more than 98 percent.
And mixing at least part of the first nanofiltration solution rich in sulfate radical as the target solution with the cleaning solution and the rest of the third solution in the crystallization stage to precipitate and obtain calcium sulfate, so that other sulfate radical medicaments are not needed to be added in the crystallization stage, and the treatment cost of desulfurization wastewater is further reduced. In practice, in order to recover as much calcium sulfate as possible in the crystallization stage, all of the first nanofiltration solution may be mixed as the target solution with the washing liquid and the rest of the third solution in the crystallization stage. Considering that the first nanofiltration solution is refluxed to the crystallization stage, the added calcium sulfate scale inhibitor may be refluxed to the crystallization stage together, thereby inhibiting the formation of calcium sulfate. Therefore, in the crystallization stage, a scale inhibitor can be further added to destroy the scale inhibition effect of the calcium sulfate scale inhibitor. The addition amount of the scale inhibitor can be specifically 10ppm to 30ppm.
In order to avoid suspended matters, colloids and the like remained in the fourth solution, the nanofiltration treatment device is blocked in the nanofiltration treatment stage, so that the nanofiltration treatment effect on the fourth solution is not ideal, and in one implementation manner, before the nanofiltration treatment stage in step 105, the desulfurization wastewater treatment method provided by the embodiment of the application further comprises a filtration stage: and filtering the fourth solution to remove suspended matters and colloid.
And filtering the fourth solution, wherein a sand filtration-ultrafiltration treatment process can be adopted.
In order to further save the cost, in one embodiment, the desulfurization wastewater treatment method provided in the embodiment of the present application further includes using the second nanofiltration solution as the washing solution, and washing the magnesium hydroxide precipitate in the washing stage of step 103.
The second nanofiltration solution obtained by the nanofiltration process is just a solution with less sulfate radical content, and the removal rate of sulfate radical ions in the solution is over 98 percent through experiments, so that the requirement of the washing solution in the washing stage of the step 103 is met. The second nanofiltration solution is used as a washing solution to wash the magnesium hydroxide precipitate in the step 103 washing stage, so that other washing solutions are not needed to be added in the step 103 washing stage, and the treatment cost of the desulfurization wastewater is further reduced. In practical applications, a small amount of washing solution can meet the washing requirement of the magnesium hydroxide precipitate, so that only part of the second nanofiltration solution can be used as the washing solution, and the magnesium hydroxide precipitate is washed in the washing stage of step 103. The mass ratio of the washed magnesium hydroxide solid precipitate to the mass of the second nanofiltration solution was 1: 5-1:20.
In order to further realize resource recycling on the desulfurization wastewater, in one embodiment, after the nanofiltration treatment stage in step 105, the desulfurization wastewater treatment method provided in the embodiment of the present application further includes step 106, a concentration stage: and treating the second nanofiltration solution by using a concentration process.
The second nanofiltration solution treated by the concentration process may be all the second nanofiltration solution, or may be partially refluxed to the washing stage as the second nanofiltration solution remaining after the washing. The second nanofiltration solution is rich in not only chloride ions but also sodium ions.
The concentration process may specifically include any one or a combination of high pressure reverse osmosis, disc Tubular Reverse Osmosis (DTRO) and electrodialysis.
After the concentration process treatment, concentrated solution of sodium chloride can be obtained, wherein the mass fraction of the sodium chloride is 10% -15%. For further recovery, storage and reuse of the sodium chloride product, the sodium chloride concentrate may be treated with an evaporative crystallization process to yield a final sodium chloride product with the water removed. The evaporation crystallization process can specifically adopt a multi-effect evaporation or steam mechanical recompression evaporation technology. The high-pressure reverse osmosis and the DTRO or the electrodialysis are adopted for combined concentration in the concentration stage, so that the subsequent evaporation and crystallization treatment capacity can be greatly reduced, and the investment and the operation cost of an evaporation and crystallization device are reduced.
Therefore, by adopting the desulfurization wastewater treatment method provided by the embodiment of the application, the purity of the recovered magnesium hydroxide is improved, and other resources including calcium sulfate, sodium chloride and the like can be recovered; in addition, the second nanofiltration solution obtained in the nanofiltration treatment stage of the step 105 is adopted as a washing solution in the washing stage of the step 103, and the first nanofiltration solution obtained in the nanofiltration treatment stage of the step 105 is adopted as a target solution in the crystallization stage of the step 104, so that resources are saved, and meanwhile, the emission of desulfurization wastewater is greatly reduced.
Based on the desulfurization wastewater treatment method provided in the foregoing embodiments of the present application, the embodiments of the present application further provide a more specific desulfurization wastewater treatment method, and it should be understood that the desulfurization wastewater treatment method is only a specific example and is not meant to limit the technical solution of the present application.
As shown in the process flow chart in fig. 3, the desulfurization wastewater treatment method includes:
pretreatment: mixing the desulfurization wastewater with the first solution, reacting to obtain calcium sulfate (gypsum), and separating out the calcium sulfate to obtain a second solution;
magnesium hydroxide synthesis stage: mixing the second solution with calcium hydroxide, reacting to obtain magnesium hydroxide precipitate, separating the magnesium hydroxide precipitate to obtain a third solution, and refluxing part of the third solution to the pretreatment stage to be used as the first solution to be mixed with the desulfurization wastewater;
And (3) a filter pressing stage: carrying out filter pressing on the magnesium hydroxide precipitate separated in the magnesium hydroxide synthesis stage to obtain a magnesium hydroxide solid precipitate;
and (3) cleaning: washing the magnesium hydroxide solid precipitate by using a washing solution;
and (3) a drying stage: drying the magnesium hydroxide precipitate separated after washing in the washing stage to obtain a final magnesium hydroxide product;
crystallization stage: mixing the cleaning solution obtained after the magnesium hydroxide precipitate is washed and separated in the cleaning stage with the target solution, reacting to obtain calcium sulfate, and separating out the calcium sulfate to obtain a fourth solution;
and (3) a filtering stage: filtering the fourth solution to remove suspended matters and colloid in the fourth solution;
nanofiltration treatment stage: treating the fourth solution by utilizing a nanofiltration process to obtain a first nanofiltration solution rich in sulfate ions and a second nanofiltration solution rich in chloride ions; reflux the first nanofiltration solution to the crystallization stage, and mixing the first nanofiltration solution serving as the target solution with the residual third solution and a cleaning solution obtained after washing and separating magnesium hydroxide precipitate in a cleaning stage; refluxing a part of the second nanofiltration solution to the washing stage as the washing solution to wash the magnesium hydroxide precipitate;
Concentration stage: treating the remaining second nanofiltration solution by using a concentration process to obtain sodium chloride concentrate;
and (3) an evaporation crystallization stage: and (3) treating the sodium chloride concentrated solution by utilizing an evaporation crystallization process to obtain a final sodium chloride product with water removed.
It can be understood that by adopting the desulfurization wastewater treatment method provided by the embodiment of the application, part of the third solution rich in calcium ions obtained after separating magnesium hydroxide precipitation in the magnesium hydroxide synthesis stage is refluxed to the pretreatment stage as the first solution, sulfate ions in desulfurization wastewater are removed in advance by generating calcium sulfate, so that a large amount of calcium sulfate is prevented from being generated in the magnesium hydroxide synthesis stage, namely sulfate is precipitated in the pretreatment stage first, magnesium is precipitated in the magnesium hydroxide synthesis stage, calcium sulfate and magnesium hydroxide can be precipitated step by step, mixing of a large amount of calcium sulfate precipitation and magnesium hydroxide precipitation is avoided, and further the purity of the recovered magnesium hydroxide is improved. On the other hand, part of the third solution rich in calcium ions, which is obtained after separating magnesium hydroxide precipitation in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage as the first solution to provide a calcium source; the second nanofiltration solution obtained in the nanofiltration treatment stage is used as a washing solution in the cleaning stage to provide a sulfate source; and the first nanofiltration solution obtained in the nanofiltration treatment stage is used as a target solution in the crystallization stage, and no additional calcium medicament, sulfate radical medicament and washing solution are needed, so that the desulfurization wastewater treatment cost is greatly reduced, and the discharge of desulfurization wastewater is reduced.
Based on the desulfurization wastewater treatment method provided in the above embodiment of the present application, the embodiment of the present application further provides a desulfurization wastewater treatment system 30 corresponding to the desulfurization wastewater treatment method, as shown in fig. 4, the system 30 includes a pretreatment device 301, a magnesium hydroxide synthesis device 302, and a first return line 303; the pretreatment device 301 has a first outlet and a first inlet, and the magnesium hydroxide synthesis device 302 has a first inlet and a first outlet; the first outlet of the pretreatment device 301 is communicated with the first inlet of the magnesium hydroxide synthesis device 302, the first outlet of the magnesium hydroxide synthesis device 302 is communicated with the inlet of the first return line 303, and the outlet of the first return line 303 is communicated with the first inlet of the pretreatment device 301; the first return line 303 is used to return at least part of the third solution to the pretreatment device 301.
Wherein the preprocessing device 301 corresponds to the preprocessing stage. The pretreatment device 301 may specifically include a first reaction tank 3011 and a clarifier 3012 connected, as shown in FIG. 5. The first reaction tank 3011 may be used to mix the desulfurization wastewater and the first solution, where the mixed solution enters the clarification tank 3012, and sedimentation and stratification are performed in the clarification tank 3012; the clarifier 3012 may have a solution outlet (which may be considered the first outlet of the pretreatment device 301) from which the second solution flows out and into the magnesium hydroxide synthesis device 302, and a calcium sulfate outlet from which the calcium sulfate precipitate flows out for recovery.
The magnesium hydroxide synthesizing means 302 corresponds to the magnesium hydroxide synthesizing stage. The magnesium hydroxide synthesizing apparatus 302 may specifically include a second reaction tank 3021 and a precipitation tank 3022 connected as shown in fig. 5. The second reaction tank 3021 is used for mixing the second solution and the calcium hydroxide, the mixed solution enters the sedimentation tank 3022, and sedimentation delamination is performed in the sedimentation tank 3022; the solution outlet of the settling tank 3022 may be in communication with the inlet of the first return line 303, the outlet of the first return line 303 may be in communication with the first reaction tank 3011 (the inlet of the first reaction tank 3011 and the outlet of the first return line 303 may be regarded as the first inlet of the pretreatment device 301), and at least a portion of the third solution may be returned to the first reaction tank 3011.
It can be understood that, by adopting the desulfurization wastewater treatment system provided by the embodiment of the application, at least part of the third solution rich in calcium ions, which is obtained after the magnesium hydroxide precipitation is separated in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage as the first solution, sulfate ions in desulfurization wastewater are removed in advance by generating calcium sulfate, so that a large amount of calcium sulfate is prevented from being generated in the magnesium hydroxide synthesis stage, namely, sulfate is precipitated in the pretreatment stage first, magnesium is precipitated in the magnesium hydroxide synthesis stage, so that calcium sulfate and magnesium hydroxide can be precipitated step by step, a large amount of calcium sulfate precipitation and magnesium hydroxide precipitation are prevented from being mixed, and the purity of the recovered magnesium hydroxide is further improved. On the other hand, at least part of the third solution rich in calcium ions, which is obtained after the magnesium hydroxide precipitation is separated by adopting the magnesium hydroxide synthesis stage, flows back to the pretreatment stage as the first solution to provide a calcium source for precipitating sulfate radicals, so that other calcium medicaments are not needed to be added in the pretreatment stage, and the treatment cost of desulfurization wastewater is greatly reduced.
In one embodiment, the magnesium hydroxide synthesis apparatus 302 includes a pH adjustment tank 3023, the pH adjustment tank 3023 being configured to adjust the pH of the third solution to between 6 and 8 prior to the refluxing of at least a portion of the third solution to the pretreatment apparatus 301.
The magnesium hydroxide synthesizing apparatus 302 may further include a pH adjusting tank 3023 connected to the precipitation tank 3022 in addition to the second reaction tank 3021 and the precipitation tank 3022 connected thereto, as shown in fig. 5. The third solution flowing out from the solution outlet of the sedimentation tank 3022 enters the pH adjusting tank 3023, the outlet of the pH adjusting tank 3023 (which may be regarded as the first outlet of the magnesium hydroxide synthesis apparatus 302) is communicated with the inlet of the first return line 303, and after the third solution is pH-adjusted, the third solution may flow back to the first reaction tank 3011 through the first return line 303.
It will be appreciated that by adjusting the pH of the third solution and then refluxing at least a portion of the third solution to the pretreatment device 301 as the first solution, a large amount of magnesium hydroxide precipitate generated during the pretreatment stage can be avoided, and thus the product amount and purity of the recovered magnesium hydroxide can be improved.
In one embodiment, the desulfurization wastewater treatment system 30 provided in the embodiment of the present application further includes a cleaning device 304, where the cleaning device 304 is connected to the magnesium hydroxide synthesis device 302; the cleaning device 304 is used for introducing a cleaning solution to clean the magnesium hydroxide precipitate obtained by the magnesium hydroxide synthesizing device 302. The cleaning device 304 may be specifically connected to a sedimentation tank 3022 in the magnesium hydroxide synthesizing device 302.
After washing the magnesium hydroxide precipitate, solid-liquid separation is performed to obtain a cleaning solution from which the magnesium hydroxide precipitate is removed.
In one embodiment, the desulfurization wastewater treatment system provided in the embodiment of the present application further includes a crystallization device 305, where the crystallization device 305 is connected to the magnesium hydroxide synthesis device 302; the crystallization device 305 is configured to mix the remaining third solution, the cleaning solution, and the target solution after refluxing a part of the third solution to the pretreatment device 301, and react the mixture to obtain calcium sulfate. The fourth solution can be obtained after separation of the calcium sulfate. The crystallization device can be a normal temperature crystallizer.
In one embodiment, the desulfurization wastewater treatment system provided in the embodiment of the present application further includes a filtering device 306, where the filtering device 306 is connected to the crystallization device 305; the filtering device 306 is used for filtering the fourth solution to remove suspended matters and colloid.
In one embodiment, the desulfurization wastewater treatment system provided in the embodiment of the present application further includes a nanofiltration device 307, where the nanofiltration device 307 is connected to the filtration device 306; the nanofiltration device 307 is configured to process the fourth solution by using a nanofiltration process to obtain a first nanofiltration solution and a second nanofiltration solution; the sulfate ion content in the first nanofiltration solution is larger than that in the second nanofiltration solution, and the second nanofiltration solution is rich in chloride ions.
In one embodiment, the desulfurization wastewater treatment system provided in the embodiment of the present application further includes a second return line 308, and the nanofiltration device 307 is connected to the crystallization device 305 through the second return line 308; the second return line 308 is used to return at least a portion of the first nanofiltration solution to the crystallization apparatus 305.
In one embodiment, the desulfurization wastewater treatment system provided in the embodiment of the present application further includes a third return line 309, and the nanofiltration device 307 is connected to the cleaning device 304 through the third return line 309; the third return line 309 is configured to return a portion of the second nanofiltration solution to the cleaning device 304.
In one embodiment, the desulfurization wastewater treatment system provided by the embodiment of the application further comprises a concentration device 310 and an evaporation crystallization device 311 which are connected, wherein the concentration device 310 is connected with the nanofiltration device 307; the concentrating device 310 is configured to process the remaining second nanofiltration solution by using a concentrating process to obtain a sodium chloride concentrate; the evaporation crystallization device 311 is used for treating the sodium chloride concentrated solution by utilizing an evaporation crystallization process to obtain a sodium chloride product.
The desulfurization wastewater treatment method and treatment system provided in the embodiments of the present application will be described below with reference to specific application examples, and it should be understood that the following examples are only a few specific embodiments, and are not meant to limit the present application.
Example 1:
the desulfurization wastewater treatment water quantity of a certain power plant is 10m 3 And/h, the water quality of the desulfurization wastewater and each process section is shown in table 1.
TABLE 1 Water quality index
(1) The desulfurization waste water firstly enters a pretreatment device, the pretreatment device comprises a first reaction tank and a clarification tank, and a third solution rich in calcium ions in the first reaction tank reacts with the desulfurization waste water to remove most sulfate ions in the waste water. The volume ratio of the reflux quantity of the third solution to the desulfurization wastewater is 1:1, gypsum is obtained through solid-liquid separation of a clarifier after the reaction, and supernatant fluid enters a magnesium hydroxide synthesizer.
(2) The magnesium hydroxide synthesizing device comprises a second reaction tank, a sedimentation tank and a pH regulating tank, wherein the second reaction tank is added with calcium hydroxide, magnesium hydroxide sediment is reacted with magnesium ions in the conveyed supernatant (namely second solution), magnesium hydroxide slurry is obtained through solid-liquid separation of sediment, and magnesium hydroxide solid is obtained through pressure filtration of the slurry. The molar ratio of the adding amount of the calcium hydroxide to magnesium ions in the supernatant is 1.2:1, the reaction time is 1h, and the pH value of the effluent (namely the third solution) of the sedimentation tank is regulated to 6-8.
(3) Because sulfate radical in the desulfurization wastewater is difficult to completely remove in the pretreatment stage, the magnesium hydroxide solid obtained in the step (2) contains a small amount of calcium sulfate, the magnesium hydroxide solid is washed by adopting a second nanofiltration solution with smaller sulfate radical content by utilizing the solubility difference of the calcium sulfate and the magnesium hydroxide in water, and the small amount of the calcium sulfate in the magnesium hydroxide solid is removed, wherein the mass ratio of the magnesium hydroxide solid to the second nanofiltration solution is 1:10. the magnesium hydroxide product is obtained after cleaning and separating and drying, the water content is less than 0.5 percent, the mass fraction of the magnesium hydroxide is more than 97.5 percent, and the magnesium hydroxide product can reach the I standard of the industrial magnesium hydroxide specification (HG/T3607-2007).
(4) And (3) the third solution obtained in the step (2) is rich in calcium ions, a part of the third solution flows back to the pretreatment device to precipitate sulfate ions in the desulfurization wastewater, the other part of the third solution enters the crystallization device and is mixed with the first nanofiltration solution rich in sulfate ions, the scale inhibitor and the inactivating agent are added for inactivating the calcium sulfate scale inhibitor, the calcium ions react with the sulfate radicals to form gypsum, and the gypsum product is obtained after separation.
(5) And (3) performing sand filtration-ultrafiltration treatment on the wastewater obtained after the treatment in the step (4) to remove suspended matters and colloid in the water.
(6) The water produced in the step (5) enters a nanofiltration treatment device to obtain a first nanofiltration solution rich in sulfate radical and a second nanofiltration solution rich in chloride ions, and the nanofiltration concentrated water flows back to a normal temperature crystallization unit to precipitate calcium ions in wastewater; adding 15ppm of calcium sulfate scale inhibitor into nanofiltration water, wherein the nanofiltration separation pressure is 1.2MPa, the volume flow ratio of the first nanofiltration solution to the second nanofiltration solution is 1:1, and the sulfate radical removal rate in the second nanofiltration solution is more than 98%.
(7) And (3) a part of the second nanofiltration solution enters a cleaning device to clean magnesium hydroxide precipitation, and the other part enters a concentrating device to concentrate the second nanofiltration solution by adopting a process combination of electrodialysis and high-pressure reverse osmosis, wherein NaCl in concentrated water is 13.4%.
(8) And (5) feeding the sodium chloride concentrated solution into an evaporation crystallization device to recycle sodium chloride products. The evaporation crystallization adopts a multi-effect evaporation technology.
Example 2:
the desulfurization wastewater treatment water quantity of a certain power plant is 5m 3 And/h, the desulfurization wastewater and the water quality of each process section are shown in Table 2,
TABLE 2 Water quality index
(1) The desulfurization waste water firstly enters a pretreatment device, the pretreatment device comprises a first reaction tank and a clarification tank, and a third solution rich in calcium ions in the first reaction tank reacts with the desulfurization waste water to remove most sulfate ions in the waste water. The volume ratio of the reflux quantity of the third solution to the desulfurization wastewater is 2:1, gypsum is obtained through solid-liquid separation of a clarifier after the reaction, and supernatant fluid enters a magnesium hydroxide synthesizer.
(2) The magnesium hydroxide synthesizing device comprises a second reaction tank, a sedimentation tank and a pH regulating tank, wherein the second reaction tank is added with calcium hydroxide, magnesium hydroxide sediment is reacted with magnesium ions in the conveyed supernatant (namely second solution), magnesium hydroxide slurry is obtained through solid-liquid separation of sediment, and magnesium hydroxide solid is obtained through pressure filtration of the slurry. The molar ratio of the adding amount of the calcium hydroxide to magnesium ions in the supernatant is 1.1:1, the reaction time is 0.5h, and the pH value of the effluent (namely the third solution) of the sedimentation tank is regulated to 6-8.
(3) Because sulfate radical in the desulfurization wastewater is difficult to completely remove in the pretreatment stage, the magnesium hydroxide solid obtained in the step (2) contains a small amount of calcium sulfate, the magnesium hydroxide solid is washed by adopting a second nanofiltration solution with smaller sulfate radical content by utilizing the solubility difference of the calcium sulfate and the magnesium hydroxide in water, and the small amount of the calcium sulfate in the magnesium hydroxide solid is removed, wherein the mass ratio of the magnesium hydroxide solid to the second nanofiltration solution is 1:20. the magnesium hydroxide product is obtained after cleaning and separating and drying, the water content is less than 0.5 percent, the mass fraction of the magnesium hydroxide is more than 97.5 percent, and the magnesium hydroxide product can reach the I standard of the industrial magnesium hydroxide specification (HG/T3607-2007).
(4) And (3) the third solution obtained in the step (2) is rich in calcium ions, a part of the third solution flows back to the pretreatment device to precipitate sulfate ions in the desulfurization wastewater, the other part of the third solution enters the crystallization device and is mixed with the first nanofiltration solution rich in sulfate ions, the scale inhibitor and the inactivating agent are added for inactivating the calcium sulfate scale inhibitor, the calcium ions react with the sulfate radicals to form gypsum, and the gypsum product is obtained after separation.
(5) And (3) performing sand filtration-ultrafiltration treatment on the wastewater obtained after the treatment in the step (4) to remove suspended matters and colloid in the water.
(6) The water produced in the step (5) enters a nanofiltration treatment device to obtain a first nanofiltration solution rich in sulfate radical and a second nanofiltration solution rich in chloride ions, and the nanofiltration concentrated water flows back to a normal temperature crystallization unit to precipitate calcium ions in wastewater; the calcium sulfate scale inhibitor is added into the nanofiltration water at 20ppm, the nanofiltration separation pressure is 1.6MPa, the volume flow ratio of the first nanofiltration solution to the second nanofiltration solution is 1:1, and the sulfate radical removal rate in the second nanofiltration solution is more than 98%.
(7) And (3) a part of the second nanofiltration solution enters a cleaning device to clean magnesium hydroxide precipitation, and the other part enters a concentrating device to concentrate the second nanofiltration solution by adopting a process combination of electrodialysis and high-pressure reverse osmosis, wherein NaCl in concentrated water is 13.6%.
(8) And (5) feeding the sodium chloride concentrated solution into an evaporation crystallization device to recycle sodium chloride products. The evaporation crystallization adopts a multi-effect evaporation technology.
It can be understood that by adopting the desulfurization wastewater treatment method and the treatment system provided by the embodiment of the application, part of the third solution rich in calcium ions, which is obtained after the magnesium hydroxide precipitation is separated in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage as the first solution, sulfate ions in desulfurization wastewater are removed in advance by generating calcium sulfate, so that a large amount of calcium sulfate is prevented from being generated in the magnesium hydroxide synthesis stage, namely sulfate radicals are precipitated in the pretreatment stage first, magnesium is precipitated in the magnesium hydroxide synthesis stage, calcium sulfate and magnesium hydroxide can be precipitated step by step, a large amount of calcium sulfate precipitates are prevented from being mixed with magnesium hydroxide precipitates, and the purity of the recovered magnesium hydroxide is further improved. On the other hand, part of the third solution rich in calcium ions, which is obtained after separating magnesium hydroxide precipitation in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage as the first solution to provide a calcium source; the second nanofiltration solution obtained in the nanofiltration treatment stage is used as a washing solution in the cleaning stage to provide a sulfate source; and the first nanofiltration solution obtained in the nanofiltration treatment stage is used as a target solution in the crystallization stage, and no additional calcium medicament, sulfate radical medicament and washing solution are needed, so that the desulfurization wastewater treatment cost is greatly reduced, and the discharge of desulfurization wastewater is reduced.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article or apparatus that comprises the element.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The foregoing is merely exemplary of the present application and is not intended to limit the present application. Various modifications and variations of the present application will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the application are to be included in the scope of the claims of the present application.
Claims (4)
1. A method for treating desulfurization wastewater, the method comprising: pretreatment: mixing the desulfurization wastewater with the first solution, reacting to obtain calcium sulfate, and separating out the calcium sulfate to obtain a second solution; magnesium hydroxide synthesis stage: mixing the second solution with calcium hydroxide, reacting to obtain magnesium hydroxide precipitate, separating the magnesium hydroxide precipitate to obtain a third solution, and mixing part of the third solution serving as the first solution with the desulfurization wastewater in the pretreatment stage; after the magnesium hydroxide synthesis stage, the treatment process further comprises a washing stage and a crystallization stage: the cleaning stage comprises: washing the magnesium hydroxide precipitate by using a washing solution to obtain a magnesium hydroxide product and a cleaning solution; the crystallization stage comprises: mixing the rest of the third solution, the cleaning solution and the target solution, reacting to obtain calcium sulfate, and separating out the calcium sulfate to obtain a fourth solution; wherein the target solution contains sulfate ions; after the crystallization stage, the treatment method further comprises a nanofiltration treatment stage: the nanofiltration treatment stage comprises: treating the fourth solution by utilizing a nanofiltration process to obtain a first nanofiltration solution and a second nanofiltration solution; wherein the sulfate ion content in the first nanofiltration solution is greater than the sulfate ion content in the second nanofiltration solution; mixing at least part of the first nanofiltration solution as the target solution with the washing liquid and the remaining third solution in the crystallization stage; washing the magnesium hydroxide precipitate in the washing stage with a portion of the second nanofiltration solution as the washing solution; said combining a portion of said third solution as said first solution with said desulfurization wastewater prior to said pretreatment stage, said treatment process further comprising: the pH of the third solution is adjusted to 6-8.
2. The desulfurization wastewater treatment process of claim 1, wherein prior to the nanofiltration treatment stage, the treatment process further comprises a filtration stage comprising: and filtering the fourth solution to remove suspended matters and colloid.
3. The desulfurization wastewater treatment process of claim 1, wherein after the nanofiltration treatment stage, the treatment process further comprises a concentration stage comprising: and (3) treating the rest second nanofiltration solution by using a concentration process.
4. A treatment system for use in the desulfurization wastewater treatment method according to any one of claims 1 to 3, characterized in that the treatment system comprises a pretreatment device, a magnesium hydroxide synthesis device, and a first return line; wherein the pretreatment device is provided with a first outlet and a first inlet, and the magnesium hydroxide synthesis device is provided with a first inlet and a first outlet; the first outlet of the pretreatment device is communicated with the first inlet of the magnesium hydroxide synthesis device, the first outlet of the magnesium hydroxide synthesis device is communicated with the inlet of the first return pipeline, and the outlet of the first return pipeline is communicated with the first inlet of the pretreatment device; the first return line is used for returning part of the third solution to the pretreatment device; the magnesium hydroxide synthesizing device comprises a pH adjusting tank, wherein the pH adjusting tank is used for adjusting the pH of the third solution to 6-8 before part of the third solution is refluxed to the pretreatment device.
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