Method for resource utilization of nitric acid-hydrofluoric acid type stainless steel pickling waste liquid

Abstract

The invention discloses a nitric acid-hydrofluoric acid type stainless steel pickling waste liquid resource utilization method, and belongs to the technical field of waste water resource utilization. The method comprises the steps of precipitation reaction, manganese sand filtration, electrodialysis, reverse osmosis and evaporative crystallization. Firstly, mixed precipitates are obtained through precipitation reaction; concentrating the obtained filtrate by adopting an electrodialysis technology, and recovering by adopting an evaporative crystallization mode to obtain a sodium nitrate product; and the produced water can meet the requirement of make-up water (GB / T 19923-2024) of a circulating cooling water system through a reverse osmosis technology. According to the method, the technologies of chemical precipitation, membrane separation, evaporative crystallization and the like are comprehensively adopted to extract and recover iron ions, fluorine ions, nitrate ions and the like in the stainless steel pickling waste liquid in the form of inorganic matters, and meanwhile, produced water in the recovery process reaches the standard of circulating cooling water. According to the method, the stainless steel pickling waste liquid can be recycled, meanwhile, produced water is recycled, and pollution to the environment is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater resource utilization, in particular to a method for resource utilization of nitric acid-hydrofluoric acid type stainless steel pickling waste liquid. Background Art

[0002] In stainless steel manufacturing, in order to remove the scale on the surface of steel after annealing, a mixed acid composed of nitric acid and hydrofluoric acid is generally used for surface cleaning and passivation. This process is called pickling or acid leaching. This cleaning dissolves iron, chromium, and manganese from the scale on the surface of steel or steel, thereby producing pickling waste liquid containing acid and heavy metal ions. The high acidity in the pickling waste liquid will corrode wastewater pipes and reinforced concrete, etc., and infiltration into the soil will cause soil calcification and crop yield reduction; heavy metal ions will pollute water bodies, poison organisms, and endanger human health. They must be treated to meet standards before they can be discharged. In view of factors such as convenient operation and maintenance and cost control, stainless steel companies currently use a precipitation treatment process with excessive addition of lime milk, which results in mixed sludge with complex composition, huge output, and high difficulty in utilization. According to the national hazardous waste list, this type of sludge is identified as hazardous waste and needs to be entrusted to qualified companies for further disposal, which not only requires more economic investment, but also causes waste of resources. Therefore, it has become an urgent need in the industry to develop a method that can not only recycle chemical resources in wastewater but also realize resource utilization of pickling waste liquid without pollutant discharge. Summary of the invention

[0003] The purpose of the present invention is to provide a method for resource utilization of nitric acid-hydrofluoric acid type stainless steel pickling waste liquid to solve the problems existing in the above-mentioned prior art. The method of the present invention is based on the combined operation of chemical precipitation, membrane separation and evaporation crystallization to achieve graded extraction and utilization of chemical resources in stainless steel pickling waste liquid, and finally obtain mixed precipitate and sodium nitrate products, and the produced water meets the requirements of circulating cooling water system make-up water (GB / T 19923-2024), thereby realizing the recycling of chemical resources in stainless steel pickling waste liquid.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention: a method for resource utilization of stainless steel pickling waste liquid, comprising the following steps:

[0006] Sodium hydroxide is added to the stainless steel pickling waste liquid to adjust the pH to 4-6, and the mixture is stirred to perform a precipitation reaction. After the precipitation reaction is completed, solid-liquid separation is performed to obtain a mixed precipitate and a filtrate 1;

[0007] Adding sodium hydroxide to the filtrate 1 to adjust the pH to 7-9, and then filtering through a manganese sand filter to obtain a filtrate 2;

[0008] Performing electrodialysis on the filtrate 2 to obtain a desalted solution and a concentrated solution;

[0009] The desalted liquid is subjected to reverse osmosis to obtain product water and concentrated water; the concentrated water is returned to the electrodialysis step for recycling; the product water is used as circulating cooling water;

[0010] The concentrated solution is evaporated and crystallized to obtain sodium nitrate, and the evaporated water (i.e., condensed water) is collected as circulating cooling water.

[0011] More preferably, sodium hydroxide is added to the stainless steel pickling waste liquid to adjust the pH to 5-6, and the mixture is stirred to carry out a precipitation reaction.

[0012] Under the condition of pH 4-6, iron ions, fluoride ions, manganese ions and chromium ions in the stainless steel pickling waste liquid can undergo precipitation reaction to obtain mixed precipitates; the pH is further preferably 5-6, and under the condition of pH 5-6, a large amount of iron ions and fluoride ions can be removed.

[0013] Furthermore, the precipitation reaction time is 2 hours.

[0014] Furthermore, the filter material in the manganese sand filter is manganese sand with a particle size of 0.5-2 mm, and the content of manganese dioxide in the manganese sand is 35-45wt%.

[0015] The principle of manganese sand filter to remove iron and manganese includes oxidation reaction, catalysis and filtration adsorption. The relevant reaction equation is iron oxidation: 4Fe 2+ +3O2+6H2O=4Fe(OH)3↓; Oxidation of manganese: Mn 2+ +O2=MnO2↓. First, manganese sand has good physical adsorption properties. The pores and intergranular gaps on its surface can adsorb suspended particulate matter in the water, including heavy metal impurities. Secondly, the main component of manganese sand is manganese dioxide, which acts as a catalyst when in contact with iron-manganese-containing water. In this process, the divalent iron and divalent manganese in the raw water will be catalytically oxidized into insoluble trivalent iron and tetravalent manganese compounds. These compounds will be further precipitated and removed from the water under the adsorption and filtration of the manganese sand filter. In addition, manganese sand also has a strong adsorption effect on fluoride ions, chromium ions, etc.

[0016] Furthermore, the working pressure of the manganese sand filter is ≤0.6MPa.

[0017] Furthermore, the initial current of the electrodialysis is 3A, the initial voltage is 11V, and the reaction time is 4-6h.

[0018] The electrodialysis step is mainly based on the selective permeability of ion exchange membranes and the directional migration of ions under the action of electric fields to achieve wastewater treatment. Under the action of the electric field, the ions in the solution begin to migrate in a directional manner, with anions moving toward the anode and cations moving toward the cathode. Due to the selective migration of ions and the blocking effect of the membrane, the ion concentration in the concentrated water chamber gradually increases, while the ions in the desalinated water chamber are effectively removed, thereby achieving the concentration and desalination of the solution.

[0019] Furthermore, the reverse osmosis is specifically a two-stage reverse osmosis, and the nitrate concentration is further reduced by the two-stage reverse osmosis.

[0020] Furthermore, the membrane element models of the two-stage reverse osmosis are PROC10 (primary) and CPA3-LD (secondary).

[0021] Furthermore, the water inlet pressure of the secondary reverse osmosis is 1.5-2.0MP.

[0022] Furthermore, the purity of the sodium nitrate is greater than 96%.

[0023] Furthermore, the stainless steel pickling waste liquid is a nitric acid-hydrofluoric acid type pickling waste liquid.

[0024] Furthermore, the components of the nitric acid-hydrofluoric acid type stainless steel pickling waste liquid include: 10-100g / L NO3 - , 10-20g / L F-, 5-40g / L iron ion (total iron), 0.1-1g / L manganese ion (total manganese), 0.1-3g / L chromium ion (total chromium).

[0025] Furthermore, the components of the nitric acid-hydrofluoric acid type stainless steel pickling waste liquid also include: 0-0.1 g / L Na + , 0.01-0.1 g / L Ca 2+ , 0.01-0.1g / L Mg 2+ .

[0026] Furthermore, the total nitrogen (in terms of N) content in the nitric acid-hydrofluoric acid type stainless steel pickling wastewater is 6-8 g / L.

[0027] Furthermore, the specific operation of the evaporative crystallization is: heating the concentrated solution at 115-125° C., evaporating 80-90 vol% of the water, filtering, and drying to obtain sodium nitrate.

[0028] Furthermore, the produced water obtained in the reverse osmosis step and the evaporated water collected in the evaporation and crystallization step meet the requirements of make-up water for circulating cooling water system (GB / T 19923-2024).

[0029] The present invention discloses the following technical effects:

[0030] The present invention provides a method for resource utilization of stainless steel pickling waste liquid (nitric acid-hydrofluoric acid type), including precipitation reaction, manganese sand filtration, electrodialysis, reverse osmosis and evaporation crystallization steps. First, a mixed precipitate is obtained by precipitation reaction; the obtained filtrate is concentrated by electrodialysis technology, and then recovered by evaporation crystallization to obtain a sodium nitrate product; reverse osmosis technology is used to make the produced water meet the requirements of circulating cooling water system make-up water (GB / T19923-2024). This method comprehensively adopts chemical precipitation, membrane separation, controlled crystallization and other technologies to extract and recover iron ions, fluoride ions, nitrate ions and the like in the stainless steel pickling waste liquid in the form of inorganic substances, and at the same time, the produced water in the recovery process meets the circulating cooling water standard. The present invention can realize the resource utilization of stainless steel pickling waste liquid, while producing water for reuse, reducing pollution to the environment.

[0031] In the whole treatment process of this method, only sodium hydroxide is added to the stainless steel pickling waste liquid, and less external chemical reagents are added, which reduces the cost of chemical reagents, avoids the introduction of new impurities, and is conducive to obtaining high-purity products. At the same time, the produced water is reused, and no secondary waste is generated in the whole treatment process. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 The present invention is a flow chart of the method for resource utilization of stainless steel pickling waste liquid. DETAILED DESCRIPTION

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0036] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0037] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0038] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0039] The present invention discloses a method for resource utilization of stainless steel pickling waste liquid (nitric acid-hydrofluoric acid type), and the specific steps are as follows (flow chart as shown in Figure 1 shown):

[0040] Precipitation reaction: sodium hydroxide is added to the stainless steel pickling waste liquid to adjust the pH to 4-6, and the precipitation reaction is carried out by stirring. After the precipitation reaction for 2 hours, the solid-liquid separation is carried out by filtering to obtain a mixed precipitation solid phase and a filtrate 1; after the precipitation reaction, a large amount of iron ions, chromium ions, manganese ions, and fluoride ions in the stainless steel pickling waste liquid are precipitated in the form of precipitation; after the precipitation reaction is completed, the content of each ion in the filtrate 1 is determined;

[0041] Manganese sand filtration: sodium hydroxide is added to the filtrate 1 to adjust the pH to 7-9, and then filtered through a manganese sand filter (the filter material in the manganese sand filter is manganese sand with a particle size of 0.5-2 mm, the content of manganese dioxide in the manganese sand is 35-45wt%, and the working pressure of the manganese sand filter is ≤0.6MPa) to obtain filtrate 2; the manganese sand filtration step can further remove trace amounts of iron and manganese in the filtrate 1, and fluoride ions and chromium ions will also be further reduced; after manganese sand filtration, the content of each ion in the filtrate 2 is determined, and the main components of the filtrate 2 are nitrate ions and sodium ions;

[0042] Electrodialysis: Perform an electrodialysis experiment on the filtrate 2 to obtain a desalted solution and a concentrated solution; the initial current of the electrodialysis is 3A, the initial voltage is 11V, and the reaction time is 4-6h; after the electrodialysis is completed, the content of each ion in the concentrated solution is determined;

[0043] Reverse osmosis: The desalted liquid is subjected to secondary reverse osmosis with an inlet pressure of 1.5-2.0MP to obtain produced water and concentrated water; the concentrated water is returned to the electrodialysis step for recycling; the pH value, chromaticity, turbidity, and the content of each ion and total nitrogen content in the produced water are measured to meet the requirements of the circulating cooling water system make-up water (GB / T 19923-2024) (specific requirements: pH 6.0-9.0, chromaticity ≤20, turbidity ≤5, total nitrogen (in terms of N) ≤15mg / L, iron ion ≤0.3mg / L, manganese ion ≤0.1mg / L; the components of nitric acid-hydrofluoric acid type stainless steel pickling waste liquid are mainly acid and heavy metal ions, and basically do not contain organic matter, microorganisms, surfactants, petroleum, silica, etc., so when judging whether the produced water meets the requirements of the circulating cooling water system make-up water, the control items related to these substances do not need to be tested) and used as circulating cooling water;

[0044] Evaporation crystallization: Heat the concentrated solution at 115-125°C, evaporate 80-90 vol% of the water, filter and dry to obtain sodium nitrate, and collect the evaporated water (i.e. condensed water) as circulating cooling water.

[0045] The method for resource utilization of stainless steel pickling waste liquid of the present invention is further described below in conjunction with specific embodiments.

[0046] The stainless steel pickling waste liquid treated in the following embodiments is a nitric acid-hydrofluoric acid type stainless steel pickling waste liquid taken from a stainless steel manufacturer. The pH value of the stainless steel pickling waste liquid is tested using a pH acidity meter; the chromaticity of the stainless steel pickling waste liquid is tested using a platinum-cobalt standard colorimetric method; the turbidity of the stainless steel pickling waste liquid is tested using a turbidimeter; the content of iron, manganese and chromium ions in the stainless steel pickling waste liquid is determined by an ICP analysis method; the content of nitrate and sodium ions in the stainless steel pickling waste liquid is determined by an ion chromatography method; the content of fluoride ions in the stainless steel pickling waste liquid is determined by an ion selective electrode method; the content of calcium and magnesium ions in the stainless steel pickling waste liquid is determined by a volumetric analysis method; the total nitrogen (in terms of N) content in the stainless steel pickling waste liquid is determined by an ultraviolet spectrophotometer (the method listed here is used to determine the ion content in the liquid after each treatment step); after measurement, the main components in the nitric acid-hydrofluoric acid type stainless steel pickling waste liquid are shown in Table 1:

[0047] Table 1 Composition of stainless steel pickling wastewater

[0048]

[0049]

[0050] Example 1

[0051] Sodium hydroxide was added to the stainless steel pickling waste liquid to adjust the pH to 4.5, and the solution was stirred for precipitation reaction. After 2 hours of precipitation reaction, the solution was filtered for solid-liquid separation to obtain a mixed precipitate and a filtrate 1. The contents of various ions in the filtrate 1 were determined, as shown in Table 2. In addition, the solid phase mixed precipitate was weighed and dried at 80°C, 0.363 g of the dried sample was weighed, and the volume was adjusted to 50 mL after being dissolved with HCl. The concentration of various ions in the sample solution was tested, and the content of various elements in the solid phase mixed precipitate was calculated, as shown in Table 3.

[0052] Sodium hydroxide was added to the filtrate 1 to adjust the pH to 7, and then filtered through a manganese sand filter (the filter material in the manganese sand filter was manganese sand with a particle size of 2 mm, the content of manganese dioxide in the manganese sand was 35 wt%, and the working pressure of the manganese sand filter was 0.6 MPa) to obtain a filtrate 2; the content of each ion in the filtrate 2 was determined, as shown in Table 2; iron ions, chromium ions, and manganese ions were not detected in the filtrate 2; fluoride ions were greatly reduced, and the main components of the filtrate 2 were nitrate ions and sodium ions;

[0053] The filtrate 2 was passed through an electrodialysis device (the electrodialysis device had 20 pairs of positive and negative ion exchange membranes) and reacted for 4 hours under the conditions of an initial current of 3A and an initial voltage of 11V to obtain a desalted solution and a concentrated solution; after the electrodialysis was completed, the contents of nitrate ions and sodium ions in the concentrated solution were determined, as shown in Table 2;

[0054] The desalted liquid was subjected to secondary reverse osmosis (the membrane element models of the secondary reverse osmosis were PROC10 (primary) and CPA3-LD (secondary), and the water inlet pressure was 1.5MP) to obtain produced water (after testing, the pH value was 6.2, the chroma was 4, and the turbidity was 0.2NTU) and concentrated water, and the production water recovery rate was 52.9%; the concentrated water was returned to the electrodialysis step for recycling; the content of each ion and the total nitrogen content in the produced water were tested, as shown in Table 2; the produced water met the requirements of the circulating cooling water system make-up water (GB / T 19923-2024) (specific requirements: total nitrogen (in terms of N) ≤15mg / L, iron ions ≤0.3mg / L, manganese ions ≤0.1mg / L), and was used as circulating cooling water;

[0055] The concentrated solution was heated at 120°C, 90 vol% of the water was evaporated, and then filtered and dried to obtain a sodium nitrate product (the purity was 98% after measurement), and the evaporated water (i.e., condensed water) was collected as circulating cooling water.

[0056] Table 2

[0057] Content of each ion (mg / L) Filtrate 1 Filtrate 2 Concentrate Desalted liquid Water production Iron 455 - - - - Manganese ion 52.1 - - - - Chromium ion 560 - - - - <![CDATA[F - ]]> 952 31.5 65 11.7 0.002 <![CDATA[NO3 - ]]> 26480 28200 94700 10109 13 <![CDATA[Na + ]]> 9720 10300 34600 3773 4.8 <![CDATA[Ca 2+ ]]> 8.03 8 25 3.1 - <![CDATA[Mg 2+ ]]> 19.62 20.2 67 7.5 - Total Nitrogen 5980 6368 21384 2283 3.0

[0058] - stands for Not Detected

[0059] Table 3

[0060] Fe F Mn Cr Solid content 31.5wt% 17.87wt% 1.9wt% 3.41wt%

[0061] Example 2

[0062] Sodium hydroxide was added to the stainless steel pickling waste liquid to adjust the pH to 5, and the solution was stirred for precipitation reaction. After 2 hours of precipitation reaction, the solution was filtered for solid-liquid separation to obtain iron-fluoride coprecipitate and filtrate 1. The concentrations of various ions in filtrate 1 were determined, as shown in Table 4.

[0063] Sodium hydroxide was added to the filtrate 1 to adjust the pH to 7, and then filtered through a manganese sand filter (the filter material in the manganese sand filter was manganese sand with a particle size of 2 mm, the content of manganese dioxide in the manganese sand was 40wt%, and the working pressure of the manganese sand filter was 0.6MPa) to obtain a filtrate 2; the content of each ion in the filtrate 2 was determined, as shown in Table 4; iron ions, chromium ions, and manganese ions were not detected in the filtrate 2; fluoride ions were greatly reduced, and the main components of the filtrate 2 were nitrate ions and sodium ions;

[0064] The filtrate 2 was passed through an electrodialysis device (the electrodialysis device had 20 pairs of positive and negative ion exchange membranes) and reacted for 6 hours under the conditions of an initial current of 3A and an initial voltage of 11V to obtain a desalted solution and a concentrated solution; after the electrodialysis was completed, the contents of nitrate ions and sodium ions in the concentrated solution were determined, as shown in Table 4;

[0065] The desalted liquid was subjected to secondary reverse osmosis (the membrane element models of the secondary reverse osmosis were PROC10 (primary) and CPA3-LD (secondary), and the water inlet pressure was 1.5MP) to obtain produced water (after testing, the pH value was 6.3, the chromaticity was 3, and the turbidity was 0.2NTU) and concentrated water, and the production water recovery rate was 53.2%; the concentrated water was returned to the electrodialysis step for recycling; the content of each ion and the total nitrogen content in the produced water were tested, as shown in Table 4; the produced water met the requirements of the circulating cooling water system make-up water (GB / T 19923-2024) and was used as circulating cooling water;

[0066] The concentrated solution was heated at 120°C, 90 vol% of the water was evaporated, and then filtered and dried to obtain a sodium nitrate product (the purity was measured to be 97.8%). The evaporated water (i.e., condensed water) was collected as circulating cooling water.

[0067] Table 4

[0068] Concentration of each ion (mg / L) Filtrate 1 Filtrate 2 Concentrate Desalted liquid Water production Iron 202 - - - - Manganese ion 47.6 - - - - Chromium ion 296 - - - - F- 610 26.2 79 9.24 0.002 <![CDATA[NO3 - ]]> 25800 27500 114900 7930 11.98 <![CDATA[Na + ]]> 9650 10100 42000 2960 4.452 <![CDATA[Ca 2+ ]]> 7.06 7.2 29.3 2.3 - <![CDATA[Mg 2+ ]]> 18.79 19.5 81.2 5.82 - Total Nitrogen 5826 6210 25946 1791 2.72

[0069] Example 3

[0070] Sodium hydroxide was added to the stainless steel pickling waste liquid to adjust the pH to 6, and the solution was stirred for precipitation reaction. After 2 hours of precipitation reaction, the solution was filtered for solid-liquid separation to obtain iron-fluoride coprecipitate and filtrate 1. The contents of various ions in filtrate 1 were determined, as shown in Table 5.

[0071] Sodium hydroxide was added to the filtrate 1 to adjust the pH to 7, and then filtered through a manganese sand filter (the filter material in the manganese sand filter was manganese sand with a particle size of 2 mm, the content of manganese dioxide in the manganese sand was 45 wt%, and the working pressure of the manganese sand filter was 0.6 MPa) to obtain a filtrate 2; the content of each ion in the filtrate 2 was determined, as shown in Table 5; iron ions, chromium ions, and manganese ions were not detected in the filtrate 2; fluoride ions were greatly reduced, and the main components of the filtrate 2 were nitrate ions and sodium ions;

[0072] The filtrate 2 was passed through an electrodialysis device (the electrodialysis device had 20 pairs of positive and negative ion exchange membranes), and reacted for 5 hours under the conditions of an initial current of 3A and an initial voltage of 11V to obtain a desalted solution and a concentrated solution; after the electrodialysis was completed, the contents of nitrate ions and sodium ions in the concentrated solution were determined, as shown in Table 5;

[0073] The desalted liquid was subjected to secondary reverse osmosis (the membrane element models of the secondary reverse osmosis were PROC10 (primary) and CPA3-LD (secondary), and the water inlet pressure was 1.5MP) to obtain produced water (after testing, the pH value was 6.5, the chroma was 3, and the turbidity was 0.1NTU) and concentrated water, and the production water recovery rate was 52.6%; the concentrated water was returned to the electrodialysis step for recycling; the content of each ion and the total nitrogen content in the produced water were tested, as shown in Table 5; the produced water met the requirements of the circulating cooling water system make-up water (GB / T 19923-2024) and was used as circulating cooling water;

[0074] The concentrated solution was heated at 120°C, 90 vol% of the water was evaporated, and then filtered and dried to obtain a sodium nitrate product (the purity was measured to be 97.2%). The evaporated water (i.e., condensed water) was collected as circulating cooling water.

[0075] Table 5

[0076]

[0077]

[0078] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for resource utilization of stainless steel pickling waste liquid, characterized in that: The following steps are involved: Sodium hydroxide is added to the stainless steel pickling waste liquid to adjust the pH to 4-6, and the mixture is stirred to perform a precipitation reaction. After the precipitation reaction is completed, the solid and liquid are separated to obtain a mixed precipitate and a filtrate 1; Adding sodium hydroxide to the filtrate 1 to adjust the pH to 7-9, and then filtering through a manganese sand filter to obtain a filtrate 2; Performing electrodialysis on the filtrate 2 to obtain a desalted solution and a concentrated solution; Performing reverse osmosis on the desalted liquid to obtain product water and concentrated water; The concentrated water is returned to the electrodialysis step for recycling; the produced water is used as circulating cooling water; The concentrated solution is evaporated and crystallized to obtain sodium nitrate, and the evaporated water is collected as circulating cooling water.

2. The method for recycling stainless steel pickling waste liquid as claimed in claim 1, characterized in that: The filter material in the manganese sand filter is manganese sand with a particle size of 0.5-2 mm, and the content of manganese dioxide in the manganese sand is 35-45wt%.

3. The method for resource utilization of stainless steel pickling waste liquid as claimed in claim 1, characterized in that: The initial current of the electrodialysis was 3A, and the initial voltage was 11V.

4. The method for recycling stainless steel pickling waste liquid as claimed in claim 1, characterized in that: The reverse osmosis is specifically two-stage reverse osmosis.

5. The method for recycling stainless steel pickling waste liquid as claimed in claim 1, characterized in that: The purity of the sodium nitrate is greater than 96%.

6. The method for recycling stainless steel pickling waste liquid as claimed in claim 1, characterized in that: The stainless steel pickling waste liquid is a nitric acid-hydrofluoric acid type stainless steel pickling waste liquid.

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