CN115367924A - Method for treating chromium-containing wastewater by using thiourea dioxide - Google Patents

Abstract

The invention belongs to a method for treating chromium-containing wastewater, and in particular relates to a method for treating chromium-containing wastewater by using thiourea dioxide. The method includes: adjusting the pH value of the chromium-containing wastewater to be alkaline, optionally adding a reducing agent A, and then adding a reducing agent B under a constant temperature condition of 40-100°C to carry out the reaction, and the reducing agent A is an alcohol amine compound , the reducing agent B contains thiourea dioxide, the obtained reaction product is subjected to solid-liquid separation for the first time, and the liquid phase part obtained by the first solid-liquid separation is subjected to the second solid-liquid separation to obtain treated wastewater, chromium-containing wastewater The molar ratio of Cr(VI) to thiourea dioxide is 1:2~10. The chromium-containing wastewater treated by the method of the invention can quickly and efficiently meet the industrial wastewater discharge standard, and the reaction product has no pollution to the environment.

Description

A method for treating chromium-containing wastewater by using thiourea dioxide

technical field

The invention belongs to the technical field of chromium-containing wastewater treatment technology, and in particular relates to a method for treating chromium-containing wastewater by using thiourea dioxide.

Background technique

Chromium-containing wastewater discharged from tanning, electroplating, metallurgy, chrome chemical industry, printing and dyeing industries is mainly composed of highly toxic Cr(VI), which will flow into the human body or animals and plants through different channels and accumulate continuously, so as to induce various disease and even death.

Therefore, the treatment of industrial chromium-containing wastewater is becoming more and more important. At present, there are various treatment methods for chromium-containing wastewater, but more than 90% of enterprises use the chemical reduction method for the treatment of chromium-containing wastewater. The first step of this method is to discharge The pH of the wastewater is adjusted to be acidic, and then a reducing agent is added to convert Cr(VI) into Cr(III). In the second step, the pH of the wastewater is adjusted to weak alkaline to precipitate Cr(III).

The chemical reduction method has the advantages of less investment, large treatment capacity, and easy management, but consumes a lot of acid and alkali during the operation, and the concentration of Cr(VI) and total chromium in the treated wastewater fluctuates greatly with pH changes, resulting in an increase in actual costs and operation becomes complicated. At the same time, common reducing agents in this method include hydrosulfite, FeSO ₄ , iron powder, etc. Although these reducing agents can quickly and effectively reduce Cr(VI) to Cr(III), there are other Disadvantages in aspects, such as hydrosulfite will release a large amount of heat and produce acidic and toxic gas SO ₂ during the decomposition process, and the generated products will increase the COD content in the water, which not only has potential safety hazards, but also causes secondary pollution of water bodies, such as FeSO _4. A large amount of iron powder is required to effectively treat chromium-containing wastewater, and the amount of sludge produced is very large, which increases the cost of treatment.

Contents of the invention

The purpose of the present invention is to address the deficiencies in the prior art, thereby providing a kind of method utilizing thiourea dioxide to process chromium-containing wastewater, the method is in the process of processing chromium-containing wastewater, by one-time adjustment of chromium-containing wastewater to be alkaline, Then add thiourea dioxide alone or use thiourea dioxide in conjunction with a reducing agent of a specific component, and control the ratio of Cr(VI) to thiourea dioxide in the chromium-containing wastewater, and react under constant temperature conditions at a specific temperature, which can quickly and effectively Reduce the content of Cr(VI) and total Cr in chromium-containing wastewater, so that the treated wastewater can reach the discharge standard of Cr(VI) for industrial wastewater, and the amount of thiourea dioxide used is less, and the amount of reducing agent sludge produced is also less Very little, saving costs.

In order to achieve the above object, the invention provides a method utilizing thiourea dioxide to process chromium-containing wastewater, the method may further comprise the steps:

(1) Adjust the pH value of the chromium-containing wastewater to be alkaline, optionally add a reducing agent A, and then add a reducing agent B under a constant temperature of 40-100°C to carry out the reaction, wherein the reducing agent A is an alcohol amine Compound, reducing agent B contains thiourea dioxide;

(2) performing solid-liquid separation on the reaction product obtained in step (1) for the first time to obtain a first solid phase part and a first liquid phase part;

(3) performing solid-liquid separation on the first liquid phase obtained in step (2) for the second time to obtain treated waste water;

In step (1), the molar ratio of hexavalent Cr in the chromium-containing wastewater to the thiourea dioxide is 1:2-10.

Preferably, when the reducing agent A is not added, the step (1) includes: adjusting the pH value of the chromium-containing wastewater to 11-14, and then adding the reducing agent B at a constant temperature of 40-100°C to carry out the reaction . More preferably, the molar ratio of hexavalent Cr in the chromium-containing wastewater to the thiourea dioxide is 1:3-9.

Preferably, when the reducing agent A is added, the step (1) includes: adjusting the pH value of the chromium-containing wastewater to 7.5-12, adding the reducing agent A, and then adding the reducing agent at a constant temperature of 40-100°C B, to react. More preferably, the molar ratio of hexavalent Cr in the chromium-containing wastewater to the reducing agent A is 1:1-4, and the molar ratio of hexavalent Cr in the chromium-containing wastewater to the thiourea dioxide is 1 : 2-6. Further preferably, the molar ratio of hexavalent Cr in the chromium-containing wastewater to the reducing agent A is 1:2-3.

Preferably, in step (1), the reducing agent A is ethanolamine and/or diethanolamine. More preferably, the reducing agent A is ethanolamine.

Preferably, in step (1), the temperature of the constant temperature condition is 40-80°C, more preferably 40-50°C.

Preferably, in step (1), the reaction time is 5-60 minutes. More preferably, in step (1), the reaction time is 15-30min.

Preferably, in step (1), the pH value of the chromium-containing wastewater is adjusted by alkaline substances. More preferably, the alkaline substance is selected from one or more of sodium hydroxide, calcium hydroxide, potassium hydroxide, ammonia water, sodium carbonate and sodium bicarbonate. Further preferably, in step (1), the alkaline substance is sodium hydroxide and/or calcium hydroxide.

Preferably, in step (2), the method of the first solid-liquid separation is gravity sedimentation. More preferably, in step (2), the method of the first solid-liquid separation is static precipitation. Further preferably, the static precipitation time is 20-40 minutes.

Preferably, in step (3), the second solid-liquid separation is performed by filtration. More preferably, in step (3), the second solid-liquid separation is performed in a multimedia filter. Further preferably, the filter medium of the multimedia filter is anthracite, activated carbon, quartz sand and ceramics.

Through the above-mentioned technical scheme, a kind of method utilizing thiourea dioxide to process chromium-containing wastewater provided by the invention has at least the following beneficial effects:

(1) In the present invention, when Cr(VI) is rapidly reduced to Cr(III), the pH value of the solution is also reduced to the pH value of chromium hydroxide precipitation, thereby realizing one-step rapid treatment of industrial chromium-containing wastewater;

(2) In the present invention, there is no need to consume a large amount of acid and alkali, and the elimination of Cr(VI) can only be carried out by adjusting the pH value of the waste water to alkaline at one time;

(3) In the present invention, thiourea dioxide or the reductant A used in conjunction are all dissolved in water, and the sludge without reductant will not produce _SO2 Toxic gases such as, and no secondary pollution;

(4) In the present invention, the thiourea dioxide or reducing agent A used are chemically stable, will not explode and spontaneously ignite due to impact or contact with water to generate high temperatures, and are relatively mild when reacting in water.

Detailed ways

Specific embodiments of the present invention will be described in detail below. It should be understood that the specific embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

Neither the endpoints nor any values of the ranges disclosed herein are limited to such precise ranges or values, and these ranges or values are understood to include values approaching these ranges or values. For numerical ranges, between the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, these values Ranges should be considered as specifically disclosed herein.

The inventors have found through research that thiourea dioxide shows strong reducibility under the common conditions of alkalinity and heating, E ₀ [CrO ₄ ^2- /Cr(OH) ₃ ]=-0.13V in alkaline medium, and The electrode potential of thiourea dioxide under alkaline conditions is far lower than that of Cr(VI) being reduced to Cr(III), indicating that the reaction can be carried out; by constantly consuming OH in the solution ^- to promote the formation of high reduction potential, While rapidly reducing Cr(VI) to Cr(III), the pH value of the solution is also reduced to the pH value of chromium hydroxide precipitation, thereby achieving one-step rapid treatment of industrial chromium-containing wastewater. Based on this principle, the inventors have accomplished the present invention.

The invention provides a method for utilizing thiourea dioxide to treat chromium-containing wastewater, the method comprising the following steps:

(1) Add alkaline substances to the chromium-containing wastewater, adjust the pH value to be alkaline, optionally add reducing agent A, and then add reducing agent B at a constant temperature of 40-100°C for reaction, wherein Agent A is an alcohol amine compound, and reducing agent B contains thiourea dioxide;

(2) performing solid-liquid separation on the reaction product obtained in step (1) for the first time to obtain a first solid phase part and a first liquid phase part;

(3) performing a second solid-liquid separation on the first liquid phase obtained in step (2) to obtain treated wastewater.

The method of the present invention uses a specific reducing agent to reduce Cr(VI) to Cr(III) under alkaline and heating conditions, and at the same time Cr(III) forms a chromium hydroxide precipitate, and then performs the first solid-liquid separation to remove Chromium hydroxide precipitation, followed by a second solid-liquid separation to filter out macromolecules, precipitate impurities, and clarify the wastewater solution, so that the treated wastewater meets the industrial wastewater discharge standards.

In the method of the present invention, in a specific embodiment, the total concentration in the chromium-containing wastewater is 1-200 mg/L, and the concentration of Cr(VI) is 1-150 mg/L. In a preferred embodiment, the total concentration in the chromium-containing wastewater is 10-120 mg/L, and the concentration of Cr(VI) is 10-100 mg/L. In a more preferred embodiment, the total concentration in the chromium-containing wastewater is 30-80 mg/L, and the concentration of Cr(VI) is 30-70 mg/L.

In the method of the present invention, in a specific embodiment, the method of the present invention can be directly used to treat the chromium-containing wastewater, or the chromium-containing wastewater can be discharged into the wastewater collection tank with a submersible mixer , and uniformly mixed, and then processed by the method of the present invention.

In the method of the present invention, in a specific embodiment, in step (1), the molar ratio of the hexavalent Cr in the chromium-containing wastewater to the thiourea dioxide is 1:2-10, for example, it can be 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10.

In the method of the present invention, in a specific embodiment, when the reducing agent A is not added, the step (1) includes: adjusting the pH value of the chromium-containing wastewater to 11-14, for example, the pH value can be 11 , 12, 13 or 14, and then at a constant temperature of 40 to 100°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C, adding reducing agent B to carry out the reaction. In a preferred embodiment, the molar ratio of the hexavalent Cr in the chromium-containing wastewater to the thiourea dioxide is 1:3-9, for example, it can be 1:3, 1:4, 1:5, 1:6, 1:7, 1:8 or 1:9.

In the method of the present invention, in a specific embodiment, when adding the reducing agent A, the step (1) includes: adjusting the pH value of the chromium-containing wastewater to 7.5-12, for example, the pH value can be 7.5, 8, 9, 10, 11 or 12, adding reducing agent A, and then under constant temperature conditions of 40-100°C, such as 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C, Add reducing agent B to carry out the reaction. In a preferred embodiment, the molar ratio of the hexavalent Cr in the chromium-containing wastewater to the reducing agent A is 1:1-4, for example, it can be 1:1, 1:2, 1:3 or 1:4 , The molar ratio of the hexavalent Cr in the chromium-containing wastewater to the thiourea dioxide is 1:2-6, for example, it can be 1:2, 1:3, 1:4, 1:5, 1:6. In a more preferred embodiment, the molar ratio of hexavalent Cr in the chromium-containing wastewater to the reducing agent A is 1:2-3.

In the method of the present invention, in a specific embodiment, in step (1), the reducing agent A is ethanolamine and/or diethanolamine. In a preferred embodiment, the reducing agent A is ethanolamine.

In the method of the present invention, in a preferred embodiment, in step (1), the temperature of the constant temperature condition is 40-80°C, such as 40°C, 45°C, 50°C, 55°C, 60°C , 65°C, 70°C, 75°C, 80°C. In a more preferred embodiment, in step (1), the constant temperature condition is 40-50°C.

In the method of the present invention, in a specific embodiment, in step (1), the reaction time is 5 to 60 minutes, for example, it can be 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 40 minutes, 50 minutes or 60min. In a preferred embodiment, in step (1), the reaction time is 15-30 minutes.

In the method of the present invention, in a specific embodiment, in step (1), the alkaline substance is selected from sodium hydroxide, calcium hydroxide, potassium hydroxide, ammonia, sodium carbonate and sodium bicarbonate one or more of two. In a preferred embodiment, in step (1), the alkaline substance is sodium hydroxide and/or calcium hydroxide.

In the method of the present invention, in a specific embodiment, in step (2), the first solid-liquid separation method is gravity sedimentation. In a preferred embodiment, in step (2), the method of the first solid-liquid separation is static precipitation. In a more preferred embodiment, in step (2), the standing precipitation time is 20-40 minutes, such as 20 minutes, 25 minutes, 30 minutes, 35 minutes or 40 minutes.

In the method of the present invention, in a specific embodiment, in step (2), the solid phase part obtained by the first solid-liquid separation is chromium hydroxide precipitation or a mixed precipitation of chromium hydroxide and calcium sulfate .

In the method of the present invention, in a specific embodiment, in step (3), the second solid-liquid separation is performed by filtration. In a preferred embodiment, in step (3), the second solid-liquid separation is performed in a multimedia filter. In a more preferred embodiment, the filter medium of the multimedia filter is anthracite, activated carbon, quartz sand and ceramics.

In the method of the present invention, in a specific embodiment, in step (3), the pH value of the treated wastewater obtained from the second solid-liquid separation is 6-9, for example, it can be 6, 7, 8, or 9.

In the method of the present invention, in a specific embodiment, in step (2), the obtained first solid phase part needs to be further concentrated, and the conditions of the concentration are: the concentration is in the sludge concentration tank Carry out, the concentration temperature is 30-80°C, such as 30°C, 40°C, 50°C, 60°C, 70°C or 80°C, and the concentration time is 60-240min, such as 60min, 80min, 90min, 100min , 120min, 140min, 160min, 180min, 200min, 220min or 240min.

In the method of the present invention, in a specific embodiment, in step (2), the first solid phase part needs to be further filtered after being concentrated. In a preferred embodiment, the filtering conditions are: the device used for filtering is a filter press, and the filtering pressure is 0.3-0.8MPa, such as 0.3MPa, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa or 0.8 MPa. In a more preferred embodiment, part of the liquid phase obtained from the filtration treatment is reused for pretreatment for mixing with chromium-containing wastewater.

The present invention will be described in detail through examples below, but the protection scope of the present invention is not limited thereto.

In the examples and comparative examples of the present invention, all reagents used are commercially available unless otherwise specified.

The chromium-containing wastewater is derived from the chromium-containing wastewater produced by a steel plant in Wuhan, the concentration of Cr(VI) is 50.58mg/L, the concentration of total chromium is 52.72mg/L, pH=5.89;

Example 1

(1) Add sodium hydroxide to 1L of chromium-containing wastewater, and adjust the pH value of the wastewater to 11. At this time, the color of the solution changes from orange to yellow quickly, and then add 0.349g of chromium-containing wastewater at a constant temperature of 50°C. thiourea dioxide (the molar ratio of Cr(VI) in chromium-containing wastewater to thiourea dioxide is 1:5), then the color gradually changes from yellow to light green, and the reaction lasts for 30 minutes;

(2) The reaction product obtained in step (1) is left to stand for 30 minutes, waiting for the precipitation to sink to the bottom;

(3) the liquid phase part obtained in step (2) is filtered through the multimedia filter of gac, quartz sand and ceramics through the filter medium, and the water body obtained is evaluated, the pH value of the water body is 6.73, the evaluation of the water body The result is shown in Table 1;

(4) Concentrate the sludge containing chromium hydroxide precipitation that is obtained in step (1) in the sludge thickening tank, the temperature of concentration is 40 ℃, the time of concentration is 90min, at last, the throw out after concentration is in Filter in a 0.4MPa filter press to obtain the solid phase for sending out for processing, and the obtained liquid phase is used for pre-treatment for mixing with chromium-containing wastewater.

Example 2

(1) Add calcium hydroxide to 1L of chromium-containing wastewater, and adjust the pH value of the wastewater to be 8. At this time, the color of the solution changes rapidly from orange to yellow, and adds 0.077mL of ethanolamine (Cr(VI) in chromium-containing wastewater and The molar ratio of ethanolamine is 1:2), then add 0.279g of thiourea dioxide to the chromium-containing wastewater at a constant temperature of 40°C (the molar ratio of Cr(VI) to thiourea dioxide in the chromium-containing wastewater is 1:4) , react for 20min;

(2) The reaction product obtained in step (1) is left to stand for 40 minutes, waiting for the precipitation to sink to the bottom;

(3) The liquid phase part that obtains in step (2) is filtered by the multimedia filter of active carbon, quartz sand and pottery through filter medium, and the water body obtained is evaluated, the pH value of water body is 7.31, the evaluation of water body The result is shown in Table 1;

(4) Concentrate the sludge containing chromium hydroxide precipitation that is obtained in step (1) in the sludge thickening tank, the temperature of concentration is 50 DEG C, the time of concentration is 60min, at last, the throw out after concentration is in Filter in a 0.5MPa filter press to obtain the solid phase for sending out for processing, and the obtained liquid phase is used for pre-treatment for mixing with chromium-containing wastewater.

Example 3

(1) Add calcium hydroxide to 1L of chromium-containing wastewater, and adjust the pH of the wastewater to 13. At this time, the color of the solution changes from orange to yellow quickly, and then add 0.488g of chromium-containing wastewater at a constant temperature of 80°C. Thiourea dioxide (the molar ratio of Cr(VI) in the chromium-containing wastewater to thiourea dioxide is 1:7) was reacted for 50 minutes;

(2) The reaction product obtained in step (1) was left to stand for 20 minutes, waiting for the precipitation to sink to the bottom;

(3) The liquid phase part that obtains in step (2) is filtered through the multimedia filter that filter medium is activated carbon, quartz sand and pottery, and the water body that obtains is evaluated, and the pH value of water body is 8.15, and the evaluation of water body The result is shown in Table 1;

(4) Concentrate the sludge containing chromium hydroxide precipitation that is obtained in step (1) in the sludge thickening tank, the temperature of concentration is 50 DEG C, the time of concentration is 60min, at last, the throw out after concentration is in Filter in a 0.5MPa filter press to obtain the solid phase for sending out for processing, and the obtained liquid phase is used for pre-treatment for mixing with chromium-containing wastewater.

Example 4

(1) Add sodium hydroxide in the chromium-containing wastewater of 1L, adjust the pH value of the wastewater to be 10, at this moment, the color of the solution changes from orange to yellow rapidly, add 0.116ml of ethanolamine (Cr(VI) in the chromium-containing wastewater and The molar ratio of ethanolamine is 1:3), then add 0.349g of thiourea dioxide to the chromium-containing wastewater at a constant temperature of 80°C (the molar ratio of Cr(VI) to thiourea dioxide in the chromium-containing wastewater is 1:5) , and then the color gradually changed from yellow to light green, and the reaction lasted for 40 minutes;

(2) The reaction product obtained in step (1) is left to stand for 30 minutes, waiting for the precipitation to sink to the bottom;

(3) the liquid phase part obtained in step (2) is filtered through the multimedia filter of gac, quartz sand and ceramics through the filter medium, and the water body obtained is evaluated, the pH value of the water body is 6.53, the evaluation of the water body The result is shown in Table 1;

(4) Concentrate the sludge containing chromium hydroxide precipitation that is obtained in step (1) in the sludge thickening tank, the temperature of concentration is 40 ℃, the time of concentration is 90min, at last, the throw out after concentration is in Filter in a 0.4MPa filter press to obtain the solid phase for sending out for processing, and the obtained liquid phase is used for pre-treatment for mixing with chromium-containing wastewater.

Example 5

(1) Add sodium hydroxide to 1L of chromium-containing wastewater, and adjust the pH value of the wastewater to 12. At this time, the color of the solution changes from orange to yellow rapidly, and then add 0.349g of chromium-containing wastewater at a constant temperature of 50°C. thiourea dioxide (the molar ratio of Cr(VI) in chromium-containing wastewater to thiourea dioxide is 1:5), then the color gradually changes from yellow to light green, and the reaction lasts for 30 minutes;

(2) The reaction product obtained in step (1) is left to stand for 30 minutes, waiting for the precipitation to sink to the bottom;

(3) The liquid phase part obtained in the step (2) is filtered through a filter medium through a multimedia filter of activated carbon, quartz sand and pottery, and the obtained water body is evaluated. The pH value of the water body is 7.81, and the evaluation of the water body The result is shown in Table 1;

(4) Concentrate the sludge containing chromium hydroxide precipitation obtained in step (1) in the sludge thickening tank, the temperature of concentration is 60 ℃, the time of concentration is 90min, and finally, the precipitate after concentration is in Filter in a 0.4MPa filter press to obtain the solid phase for sending out for processing, and the obtained liquid phase is used for pre-treatment for mixing with chromium-containing wastewater.

Comparative example 1

Implement according to the method of Example 1, the difference is that in step (1), the temperature of the constant temperature condition is 30°C.

Comparative example 2

Implement according to the method of Example 2, the difference is that in step (1), the temperature of the constant temperature condition is 30°C.

Comparative example 3

Implementation according to the method of Example 1, the difference is that in step (1), the pH value of the chromium-containing wastewater is adjusted to 6.

Comparative example 4

Implement according to the method for embodiment 2, difference is, in step (1), does not add thiourea dioxide.

Comparative example 5

Implement according to the method for embodiment 1, difference is, in step (1), change thiourea dioxide into ferrous sulfate.

Comparative example 6

Implement according to the method of Example 1, the difference is that in step (1), 0.069g of thiourea dioxide is added, so that the molar ratio of Cr(VI) and thiourea dioxide in the chromium-containing wastewater is 1:1.

Comparative example 7

Implement according to the method of Example 1, the difference is that in step (1), 0.837g of thiourea dioxide is added, so that the molar ratio of Cr(VI) and thiourea dioxide in the chromium-containing wastewater is 1:12.

test case

The total chromium concentration, Cr(VI) concentration and pH value in the treated wastewater obtained in Examples 1-5 and Comparative Examples 1-7 were tested.

According to " the mensuration of total chromium in water quality " in " GB7466-1987 ", potassium permanganate oxidized diphenylcarbazide spectrophotometric method measures the total chromium in the waste water after the treatment of embodiment 1-5 and comparative example 1-7 obtains. Chromium concentration.

The concentration of Cr(VI) in the treated wastewater obtained in Examples 1-5 and Comparative Examples 1-7 was measured according to "GB7467-1987 Determination of Hexavalent Chromium in Water Quality Diphenylcarbazide Spectrophotometry".

The pH value in the treated wastewater obtained in Examples 1-5 and Comparative Examples 1-7 was measured according to the "Glass Electrode Method for Determination of Water Quality pH Value".

The test results are shown in Table 1.

Table 1

As can be seen from Table 1, according to the method described in the present invention, utilize thiourea dioxide to use alone or compound use of thiourea dioxide and alcohol amine reducing agent to directly process industrial chromium-containing wastewater under alkaline conditions, obviously and effectively avoid The traditional process needs to adjust the acidity and alkalinity of wastewater and the secondary pollution caused by reducing agents, which not only saves the actual treatment cost, but also improves the efficiency of chromium removal. Among them, the Cr(VI) in the wastewater treated in Examples 1-5 The concentration and total chromium concentration are far lower than the discharge requirements of Cr(VI) concentration and total chromium concentration in industrial wastewater, and the pH value of the wastewater is between 6 and 9, which also meets the national standard for sewage pH value discharge .

The above are only examples of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent transformations made using the content of the description of the present invention, or directly or indirectly used in other related technical fields, are equally included in the scope of the present invention. within the scope of patent protection.

Claims (10)

1. A method for treating chromium-containing wastewater by using thiourea dioxide comprises the following steps:

(1) Adjusting the pH value of the chromium-containing wastewater to be alkaline, optionally adding a reducing agent A, and then adding a reducing agent B under the constant temperature condition of 40-100 ℃ to react, wherein the reducing agent A is an alcohol amine compound, and the reducing agent B contains thiourea dioxide;

(2) Carrying out first solid-liquid separation on the reaction product obtained in the step (1) to obtain a first solid phase part and a first liquid phase part;

(3) Performing second solid-liquid separation on the first liquid phase part obtained in the step (2) to obtain treated wastewater;

in the step (1), the mol ratio of hexavalent Cr to thiourea dioxide in the chromium-containing wastewater is 1:2 to 10.

2. The method according to claim 1, wherein when reducing agent a is not added, step (1) comprises: adjusting the pH value of the chromium-containing wastewater to 11-14, and then adding a reducing agent B under the constant temperature condition of 40-100 ℃ for reaction;

preferably, the mol ratio of the hexavalent Cr to the thiourea dioxide in the chromium-containing wastewater is 1:3 to 9.

3. The method of claim 1, wherein when reducing agent a is added, step (1) comprises: regulating the pH value of the chromium-containing wastewater to 7.5-12, adding a reducing agent A, and then adding a reducing agent B under the constant temperature condition of 40-100 ℃ to react.

4. The method of claim 3 wherein the molar ratio of hexavalent Cr to reducing agent A in the chromium-containing wastewater is from 1: 1-4, wherein the molar ratio of hexavalent Cr to thiourea dioxide in the chromium-containing wastewater is 1:2 to 6;

preferably, the mol ratio of the hexavalent Cr in the chromium-containing wastewater to the reducing agent A is 1:2 to 3.

5. The method according to claim 1 or 2, wherein in step (1), the reducing agent A is ethanolamine and/or diethanolamine;

preferably, the reducing agent a is ethanolamine.

6. The method according to claim 1 or 2, wherein in the step (1), the temperature of the constant temperature condition is 40-80 ℃;

preferably, in the step (1), the temperature of the constant temperature condition is 40-50 ℃.

7. The method according to claim 1 or 2, wherein in the step (1), the reaction time is 5 to 60min;

preferably, in the step (1), the reaction time is 15-30 min.

8. The method according to claim 1 or 7, wherein in the step (1), the pH value of the chromium-containing wastewater is adjusted by alkaline substances;

preferably, the alkaline substance is selected from one or more of sodium hydroxide, calcium hydroxide, potassium hydroxide, ammonia water and sodium carbonate;

more preferably, in the step (1), the alkaline substance is sodium hydroxide and/or calcium hydroxide.

9. The method according to claim 1 or 7, wherein in the step (2), the first solid-liquid separation mode is gravity settling;

preferably, in the step (2), the first solid-liquid separation mode is standing precipitation;

more preferably, the standing and precipitating time is 20-40 min.

10. The method according to claim 1 or 7, wherein in the step (3), the second solid-liquid separation mode is filtration;

preferably, in step (3), the second solid-liquid separation is carried out in a multimedia filter; more preferably, the filter media of the multi-media filter are anthracite, activated carbon, quartz sand and ceramic.