CN116891315A - Method for chromium plating wastewater hazardous waste reduction and chromium mud recycling - Google Patents

Abstract

The application relates to a sewageThe method for recycling chromium plating waste water and waste reduction and chromium mud mainly comprises COD degradation, separation and purification of chromium and product recovery, does not need adding of a catalyst ferrous sulfate in the degradation process of organic pollutants in the waste water, has no newly added sludge amount or newly added sludge type in the UV/Fenton treatment process, has no toxic and harmful gas generation, improves the purity of products obtained by recycling the subsequent chromium, and removes Ni from various heavy metal pollutants in the waste water after chromium recovery ²⁺ The external content can meet the requirements of the water pollutant emission limit value specified in the electroplating pollutant emission standard (GB 21900-2008) Table 2, and the recycling recovery of the heavy metal pollutant chromium is achieved, so that the solid dangerous waste amount in the wastewater treatment process is greatly reduced.

Description

A method for reducing hazardous waste in chrome plating wastewater and recycling chrome mud

Technical field

The invention relates to the fields of sewage treatment and resource recovery, specifically a method for reducing hazardous waste in chrome plating wastewater and recycling chrome mud.

Background technique

The chromium plating process is widely used. Its main function is decoration and anti-corrosion. For example, the main function of chromium plating on car door handles, logos and grilles, or chromium plating on plastics and hardware, is decoration or anti-corrosion. Chromium plating on the surface of mechanical parts is to improve Wear resistance, chromium plating on gun bores, etc. is mainly to improve wear resistance and ablation resistance. The chromium plating process will produce electroplating chromium wastewater. The main heavy metal pollutants in electroplating chromium wastewater vary depending on the plated parts, except for Cr ⁶⁺ In addition to Cr ³⁺ , there are also Fe ³⁺ , Cu ²⁺ , Ni ²⁺ and Zn ²⁺ . Cr ⁶⁺ is the strongest carcinogen among metal ions. The COD (chemical oxygen demand) value of wastewater is usually not high, but the organic pollutants in wastewater are difficult to degrade due to their resistance to oxidation.

The usual method of removing chromium from chromium plating wastewater is to use a reducing agent to reduce Cr ⁶⁺ in the wastewater to Cr ³⁺ and then adjust the pH value of the wastewater to alkaline precipitation. Due to the electroplating additives in the chromium plating process, it is difficult to directly reduce the Cr ³⁺ and other heavy metal ions Cu ²⁺ and even Fe ³⁺ in the wastewater to meet the "Electroplating Pollutant Emission Standards (GB21900-2008)" by adjusting the pH value. 》Maximum emission limit requirements for the above heavy metal ions. After the reduction and re-precipitation treatment process, a large amount of chromium-containing sludge will be formed. As a hazardous waste that is difficult to treat, chromium-containing sludge has high treatment costs and companies with hazardous waste treatment qualifications are usually unwilling to dispose of it.

Another method of treating Cr ⁶⁺ containing wastewater is recycling. The most direct way to recover Cr ⁶⁺ is to exchange it with anion exchange resin and then reuse the recovered product in electroplating. After years of research, it has been proven that ion exchange resin is scrapped due to rapid oxidation of Cr ⁶⁺ , which makes the ion exchange method to recover Cr ⁶⁺ a dead end; another recovery method is to first form PbCrO ₄ or BaCrO ₄ precipitation and then use sulfuric acid to treat it to obtain H ₂ Cr ₂ O ₇ or CrO ₃ is re-added into the electroplating tank. The products recovered by this method are reused in electroplating, which will seriously affect the quality of electroplated products, and therefore cannot be accepted by chromium plating manufacturers. Other methods for recycling chromium-containing wastewater are not practical due to high costs or low purity of the recovered products. Based on this, this application proposes a method for reducing hazardous waste in chromium plating wastewater and recycling chromium mud. Solve the above problems.

Contents of the invention

(1) Technical problems solved

In view of the shortcomings of the existing technology, the present invention provides a method for reducing hazardous waste in chrome plating wastewater and recycling chromium mud. The degradation process of organic pollutants does not require the addition of catalyst ferrous sulfate. During the UV/Fenton treatment process, there is neither new sludge amount nor new sludge type, and no toxic and harmful gases are generated. The subsequent chromium resource recovery proceeds The purity of the product has been improved. The content of various heavy metal pollutants in the wastewater after chromium recovery, except Ni ²⁺ , can meet the water pollutant discharge limits specified in Table 2 of the "Electroplating Pollutant Discharge Standard (GB 21900-2008)" Due to the resource recovery of heavy metal pollutant chromium, the amount of solid hazardous waste in the wastewater treatment process is greatly reduced.

(2) Technical solutions

In order to achieve the above object, the present invention provides the following technical solution: a method for reducing hazardous waste in chromium plating wastewater, which is characterized in that it includes the steps:

1) Collect chromium-containing wastewater and analyze its COD value, and calculate the required amount of hydrogen peroxide V ₁ (unit is L/m ³ or L/ton) based on the measured COD value (unit is g/L);

2) The COD value of the collected chromium-containing wastewater is measured and then discharged into the UV/Fenton treatment system. The pH ₄ value of the wastewater in the UV/Fenton treatment system is adjusted to between 3-10 and collected according to V ₁ and the UV/Fenton treatment system. Calculate the amount of hydrogen peroxide V (unit is L) from the volume or weight of the wastewater obtained, turn on the UV lamp of the UV/Fenton treatment system, and add hydrogen peroxide to the wastewater in the UV/Fenton treatment system. The amount of addition is V;

3) After the UV lamp is turned on for a certain period of time, add alkali into the UV/Fenton treatment system until the pH value of the wastewater in the system is between ₅ and 4-13. After the alkali addition is completed, add enough alkali into the UV/Fenton treatment system. amount of NaClO, and then continue to turn on the UV lamp for a certain period of time. The total time the UV lamp is turned on is 0.5-10h;

4) After the UV lamp is turned off, discharge the wastewater in the UV/Fenton treatment system to the filtration system 1. The wastewater filtered by the filtration system 1 is reduced by adding a certain reducing agent SP. The pH value of the reduced wastewater is adjusted to ₆ Between 5 and 13, the sludge filtered out by the filtration system 1 is processed separately;

5) After the pH ₆ adjustment is completed, discharge the wastewater to the filtration system 2. The concentrated sludge in the filtration system 2 is washed with clean water 1-10 times. The clean water filtered out by the filtration system 2 is processed separately. The cleaned sludge in the filtration system 2 is processed separately. The sludge is discharged into the sludge filter press system and filtered through the sludge filter press system to form dry sludge.

Preferably, the preferred value of the pH ₆ value range is between 6 and 9, and the preferred value of the pH ₅ value range is between 8 and 10.

Preferably, the preferred value for the number of times the concentrated sludge is cleaned in the filtration system 2 is 2-4, and the sludge filter press system is a high-pressure diaphragm plate and frame filter press.

Preferably, the COD value analysis method is as follows:

1) First take an appropriate amount of chromium-containing wastewater and measure the pH ₁ value and Cr ⁶⁺ content a (unit is g/L) of the wastewater, and determine the total chromium content b (unit is g/L) and the content of other heavy metal ions in the chromium-containing wastewater ;

2) After measuring the Cr ⁶⁺ content in the wastewater, add a sufficient amount of reducing agent GV according to the proportion;

3) After the GV is added, stir the above wastewater until the GV is completely dissolved. After the GV is completely dissolved, add an appropriate amount of acid or alkali to the wastewater to adjust the pH ₂ value of the wastewater to a suitable value. After the pH ₂ value is adjusted, the wastewater is allowed to stand still. Set for 10-500min;

4) After the standing time is over, add an appropriate amount of alkali to the wastewater to adjust the pH ₃ value of the wastewater to between 9 and 14. After the pH ₃ adjustment is completed, filter the wastewater;

5) After the wastewater is filtered, analyze and determine the COD value of the wastewater.

Preferably, the GV is ferrous sulfate (FeSO ₄ ·7H ₂ O), and the dosage of the ferrous sulfate is calculated according to the following formula:

m ≥ 5.4 × a (1)

In formula (1), m is the amount of FeSO ₄ ·7H ₂ O that needs to be added per liter of water. The unit is: g/L. V ₁ is calculated according to the following formula:

V ₁ = p × COD (2)

The value range of p is between 0.5-9.

Preferably, the preferred value of the p value range is between 2.8 and 5.6.

Preferably, the mass percentage content of the sodium hypochlorite is 10%, and the NaClO dosage is calculated according to the following formula:

V ₂ = q × (b – a) (3)

The units of b and a in formula (3) are both g/L, and the unit of V ₂ is L/m ³ , which is the volume of sodium hypochlorite that needs to be added per cubic meter or per ton of water;

In formula (3), q is the coefficient, and the value range of q is between 9 and 11.

Preferably, the preferred value of the q value range is between 9.3 and 10.2.

The dry sludge produced by the above method can be processed into chromium mud resources. Specifically, the dry sludge filtered out by the sludge filter press system can be finally made into different finished products according to different treatment processes.

(3) Beneficial effects

Compared with the existing technology, the present invention provides a method for reducing hazardous waste in chrome plating wastewater and recycling chromium mud, which has the following beneficial effects:

1. Use the original Fe ³⁺ in the wastewater as the catalyst for the UV/Fenton treatment process. There is no need to add an external catalyst and no new sludge amount during the UV/Fenton treatment process. Because the original Fe ³⁺ content in the wastewater is high, the UV/Fenton The reaction speed is fast and can be completed within 30 minutes, so the equipment investment is low;

2. After UV/NaClO treatment, the Cr ³⁺ present in the wastewater is oxidized into Cr ⁶⁺ , which can avoid the loss of chromium during subsequent treatment. For cyanogen that may be mixed in the chromium plating wastewater, UV/NaClO can achieve Efficient and rapid cyanide removal. After two-stage oxidation of UV/Fenton → UV/NaClO, most of the organic pollutants in the wastewater and the cyanide that may be mixed are removed, which is beneficial to the subsequent precipitation and removal of Cu ²⁺ and Ni ²⁺ in the wastewater. and other heavy metal pollutants, to achieve the separation of impurity ions and chromium, thus effectively improving the purity of the final chromium-containing compound;

3. The resource recovery of heavy metal pollutant chromium in wastewater reduces the solid hazardous waste generated in electroplating chromium wastewater treatment by more than 99% and reduces the cost of sludge disposal;

4. In the treated wastewater, various pollutant indicators have been effectively reduced, which is conducive to subsequent treatment or discharge.

Description of the drawings

Figure 1 is a schematic flow diagram of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Please refer to Figure 1. The present invention provides a method for reducing hazardous waste in chromium plating wastewater, which is designed to treat chromium plating wastewater and reduce various heavy metal pollutants in chromium plating wastewater, mainly including COD degradation and separation and purification of chromium. In specific implementation In the process, you first need to collect chromium-containing wastewater and analyze its COD value. Calculate the required amount of hydrogen peroxide V ₁ (unit is L/m ³ or L/ton) based on the measured COD value (unit is g/L). The COD value of the collected chromium-containing wastewater is measured and then discharged into the UV/Fenton treatment system. The pH ₄ value of the wastewater in the UV/Fenton treatment system is adjusted to between 3-10. According to V ₁ and the UV/Fenton treatment system, the collected The volume or weight of wastewater is used to calculate the amount of hydrogen peroxide required V (unit is L).

Among them, the COD value analysis method is as follows:

1) First take an appropriate amount of chromium-containing wastewater and measure the pH ₁ value and Cr ⁶⁺ content a (unit is g/L) of the wastewater, and determine the total chromium content b (unit is g/L) and the content of other heavy metal ions in the chromium-containing wastewater ;

2) After measuring the Cr ⁶⁺ content in the wastewater, add a sufficient amount of reducing agent GV according to the proportion. GV is a type of substance that will not or is not easy to interfere with the measurement of COD value;

3) After the GV is added, stir the above wastewater until the GV is completely dissolved. After the GV is completely dissolved, add an appropriate amount of acid or alkali to the wastewater to adjust the pH ₂ value of the wastewater to a suitable value. After the pH ₂ value is adjusted, the wastewater is allowed to stand still. Set for 10-500min;

4) After the standing time is over, add an appropriate amount of alkali to the wastewater to adjust the pH ₃ value of the wastewater to between 9 and 14. After the pH ₃ adjustment is completed, filter the wastewater;

5) After the wastewater is filtered, analyze and determine the COD value of the wastewater.

GV is ferrous sulfate (FeSO ₄ ·7H ₂ O), and the dosage of ferrous sulfate is calculated according to the following formula:

m ≥ 5.4 × a (1)

In formula (1), m is the amount of FeSO ₄ ·7H ₂ O that needs to be added per liter of water. The unit is: g/L. V ₁ is calculated according to the following formula:

V ₁ = p × COD (2)

The value range of p is between 0.5-9, and the preferred value of p value range is between 2.8-5.6.

After the UV/Fenton treatment system calculates the required amount of hydrogen peroxide V, it turns on the UV lamp of the UV/Fenton treatment system and adds hydrogen peroxide to the wastewater in the UV/Fenton treatment system. The amount of hydrogen peroxide added is V.

Among them, the calculation method of hydrogen peroxide dosage is as follows:

v ₀ = 13.241 × COD × n (4)

In formula (4), the unit of COD is g/L, n is the coefficient, the value range of n is between 0.06-0.4, and the unit of v ₀ in formula (4) is L/m ³ or L/t;

Calculate the dosage of hydrogen peroxide based on the effective volume in the UV/Fenton treatment system:

V = U × v ₀ (5)

The result V calculated by calculation formula (5) is the volume of hydrogen peroxide that needs to be added in the oxidation tank, and the unit is: L.

After the UV lamp is turned on for a certain period of time, add alkali into the UV/Fenton treatment system until the pH value of the wastewater in the system is between ₅ and 4-13. After the alkali addition is completed, add a sufficient amount of alkali into the UV/Fenton treatment system. NaClO, and then continue to turn on the UV lamp for a certain period of time. The total time the UV lamp is turned on is 0.5-10h.

Among them, the mass percentage content of sodium hypochlorite is 10%, and the dosage of NaClO is calculated according to the following formula:

V ₂ = q × (b – a) (3)

The units of b and a in formula (3) are both g/L, and the unit of V ₂ is L/m ³ , which is the volume of sodium hypochlorite that needs to be added per cubic meter or per ton of water;

In formula (3), q is a coefficient, the value range of q is between 9 and 11, and the preferred value of the value range of q is between 9.3 and 10.2.

After the UV lamp is turned off, discharge the wastewater in the UV/Fenton treatment system to filtration system 1. The filtered wastewater in filtration system 1 is reduced by adding a certain reducing agent SP. After the reduction, the pH value of the wastewater is adjusted from ₆ to 5. -13, the sludge filtered out by the filtration system 1 is processed separately.

After the pH ₆ adjustment is completed, the wastewater is discharged to the filtration system 2. The concentrated sludge in the filtration system 2 is washed with clean water 1-10 times. The clean water filtered out by the filtration system 2 is processed separately. The cleaned sludge in the filtration system 2 It is discharged into the sludge filter press system and filtered to form dry sludge. The preferred number of cleaning times for the concentrated sludge in the filtration system 2 is 2-4. The sludge filter press system is a high-pressure membrane type. Plate and frame filter press.

In the above treatment process, the optimal range of pH ₅ was determined through experiments. An experiment was conducted on a certain wastewater. The experimental process was as follows: after the UV lamp was turned on for a certain period of time, a certain volume of wastewater in the UV/Fenton treatment system was taken. The obtained UV/Fenton The wastewater in the system is divided into several groups; alkali is added to the wastewater in several groups to adjust the pH ₅ value of the wastewater; after the pH adjustment of the wastewater in several groups is completed, the wastewater in several groups is left to stand for 10-100 minutes; after the standing time of the wastewater in several groups is over, Filter several groups of wastewater; after filtering several groups of wastewater, measure the heavy metal ion content of several groups of wastewater respectively. The heavy metal ion content of several groups of wastewater is shown in Table 1 below. Determine the optimal value range of pH ₅ based on the data in the table below.

Table 1 Relationship between heavy metal ion content and pH ₇

Note: N/A means below the instrument detection limit (1μg/L)

The preferred value range of pH ₅ is the pH ₆ value range with the lowest content of heavy metal ions except total chromium. Comparing the data in Table 1 above, it can be seen that the preferred value range of pH ₅ is between 8-10.

The dry sludge produced by the above method can be processed into chromium mud resources to achieve low-cost recovery of pure chromium-containing compounds while achieving the purpose of resource utilization of chromium mud. Specifically, the chromium mud filtered out by the sludge filter press system Dry sludge can eventually be made into different finished products according to different treatment processes. One of the following treatment processes can be selected:

The dry sludge is dissolved with hydrochloric acid, and the solution obtained by dissolving the dry sludge is evaporated and crystallized to obtain the industrial product chromium chloride (CrCl ₃ ·6H ₂ O);

The dry sludge is dissolved with nitric acid, and the solution obtained by dissolving the dry sludge is evaporated and crystallized to obtain the industrial product chromium nitrate (Cr(NO ₃ ) ₃ ·9H ₂ O);

The dry sludge is calcined at high temperature to obtain chromium trioxide solid, and the chromium trioxide solid is ball milled to obtain chromium oxide green pigment;

After drying the dry sludge, anhydrous chromium sludge is sold directly as a product;

The dry sludge is dissolved in concentrated sulfuric acid and then sufficient oxidant is added to obtain A. Depending on the purpose, A can be processed to produce products containing Cr ⁶⁺ for direct sale or as raw material for electroplating hard chromium for reuse.

The above method is used to degrade organic pollutants in wastewater. The addition of catalyst ferrous sulfate is not required during the degradation process. There is neither new sludge amount nor new sludge type during the UV/Fenton treatment process. Toxic and harmful gases are produced and the COD value is degraded in advance, which is beneficial to the subsequent precipitation and removal of various heavy metal impurity ions. It is beneficial to the purification of wastewater pollutants. The purity of the products obtained from subsequent chromium resource recovery is improved.

The content of various heavy metal pollutants in the wastewater after chromium recovery, except Ni ²⁺ , can meet the water pollutant emission limits specified in Table 2 of the "Electroplating Pollutant Discharge Standard (GB 21900-2008)". The COD value and The reduction in the content of heavy metal pollutants is more conducive to the subsequent treatment of wastewater. After treatment, the purity of the chromium compound finally recovered can meet the purity requirements of general chemical raw materials or electroplating raw materials. Since the resource recovery of heavy metal pollutant chromium is achieved, It greatly reduces the amount of solid hazardous waste in the wastewater treatment process.

Experimental example 1:

An electroplating wastewater treatment company in Longfu Town collects 960m ³ of chromium-containing electroplating wastewater every day. The effective volume of the wastewater collection tank is 393.9m ³ . The original treatment process adopts the traditional treatment process: wastewater collection → acid-base adjustment → reduction → acid-base adjustment → flocculation. Precipitation. The Cr ³⁺ -containing sludge after flocculation and precipitation is treated as hazardous waste after filtering and other steps. The clean water after flocculation and precipitation then undergoes a series of treatments to remove heavy metal ions that cannot be removed by precipitation through conventional processes. It is then mixed with other electroplating wastewater and enters the biochemical system for treatment.

The method of the present invention is used to carry out system transformation, mainly adding two sets of ultrafiltration systems, one set of UV/Fenton treatment system (processing capacity ^80m3 ), one set of sludge filter press system, several other pH meters, etc., and sludge reduction And the chromium-containing sludge obtained after resource utilization is dried and sold directly as a product.

The specific processing process is as follows:

(1) Collect chromium-containing wastewater and analyze its COD value. The COD value analysis method is as follows:

A. First take an appropriate amount of chromium-containing wastewater and measure the pH ₁ and Cr ⁶⁺ content a of the wastewater, and measure the total chromium content b and the content of other heavy metal ions in the chromium-containing wastewater;

B. After the wastewater is filtered, analyze and measure the COD value of the wastewater according to the method described in the present invention. Calculate the required amount of hydrogen peroxide V ₁ =0.53L/m3 based on the measured COD value and b;

(2) The COD value of the collected chromium-containing wastewater is measured and then discharged into the UV/Fenton treatment system. After the wastewater UV/Fenton treatment system collects enough ^80m3 of wastewater, the pH ₄ value of the wastewater in the UV/Fenton treatment system is adjusted to 3- between 5;

(3) Calculate the amount of hydrogen peroxide required V according to V ₁ and the volume of wastewater collected by the UV/Fenton treatment system;

(4) After adjusting the pH value of the wastewater in the UV/Fenton treatment system, turn on the UV lamp of the UV/Fenton treatment system. After the UV lamp is turned on, add hydrogen peroxide to the wastewater in the UV/Fenton treatment system. The dosage of hydrogen peroxide is 28L;

(5) 30 minutes after the addition of hydrogen peroxide is completed, add alkali in the UV/Fenton treatment system until the pH value of the wastewater in the system reaches between ₅ and 8-10;

(6) After the pH ₅ adjustment is completed, add sodium hypochlorite to the wastewater. The dosage of sodium hypochlorite is 510L;

(7) After adding sodium hypochlorite, continue to turn on the UV lamp for 30 minutes; after the UV lamp on time is over, turn off the UV lamp;

(8) After the UV lamp is turned off, discharge the wastewater in the UV/Fenton treatment system to the filtration system 1;

(9) For the wastewater filtered by the filtration system 1, add a certain amount of metabisulfite (Na ₂ S ₂ O ₅ ) for reduction. After the reduction, adjust the pH ₆ value of the reduced wastewater to between 8-9 and filter it with the filtration system 1. The sewage sludge will be processed separately;

(10) After the pH ₆ adjustment is completed, discharge the wastewater to the filtration system 2. The concentrated sludge in the filtration system 2 is washed three times with clean water. The cleaned sludge in the filtration system 2 is discharged into the sludge filter press system. The clean water filtered by the filtration system is mixed with other electroplating wastewater and then enters the original biochemical system;

(11) After drying the dry sludge, analyze and test the content of various components in the sludge.

The content of pollutants in raw water is as follows in Table 2, the content of pollutants in clean water after filtering is as follows in Table 3, and the content of impurities in chrome mud is as follows in Table 4:

Table 2 Raw water pollutant content

in:

^1. Determination of water chemical oxygen demand by dichromate method (HJ 828-2017), measured according to the method described in the patent of the present invention;

² Determination of water quality hexavalent chromium flow injection-diphenylcarbazide photometric method (HJ 908-2017);

³ Calculated from the difference between total chromium content and hexavalent chromium;

^4. Determination of water quality copper, zinc, lead and cadmium by atomic absorption spectrophotometry (GB 7475-1987);

⁵ Determination of water quality nickel flame atomic absorption spectrophotometry (GB 11912-1989);

^6. Determination of water quality iron and manganese by flame atomic absorption spectrophotometry (GB 11911-1989).

Table 3 Contents of pollutants in clean water after filter press

in:

^* N/A means below the instrument detection limit (1μg/L);

⁷ Determination of water quality chromium by flame atomic absorption spectrophotometry (HJ 757-2015).

Table 4 Impurity content in chrome mud

in:

⁸ Gravimetric method for determination of moisture and dry matter content of solid waste (HJ 1222-2021);

⁹ Determination of nickel and copper in solid waste by flame atomic absorption spectrophotometry (HJ 751-2015);

¹⁰ Determination of lead, zinc and cadmium in solid waste by flame atomic absorption spectrophotometry (HJ 786-2016).

According to the above test data, all pollutants in the clean water after pressure filtration have been greatly reduced. Except for the Ni ²⁺ content, the other heavy metal ion contents meet the "Electroplating Pollutant Emission Standard (GB 21900-2008)" table According to the maximum emission limit specified in 3, the COD value of wastewater has also been reduced to a certain extent, which is beneficial to subsequent treatment. The content of various heavy metal pollutants in anhydrous chromium mud can meet the requirements of general enterprise resource acquisition. Can be sold directly as a product.

In the company's original sewage treatment process, chromium-containing wastewater produced approximately 200-300 tons of chromium-containing hazardous waste every year. After the transformation using the method described in the present invention, the amount of hazardous waste produced per year was close to 1 ton, and the hazardous waste was reduced by 99.5% before and after transformation. As mentioned above, no other new solid waste or hazardous waste is generated during the treatment process, achieving the reduction and resource utilization of hazardous solid waste.

Experimental example 2:

The electroplating wastewater station of an industrial company in Shajing collects 180m ³ of chromium-containing electroplating wastewater every day. The effective volume of the wastewater collection tank is 200m ³ . The original treatment process adopts the traditional treatment process: wastewater collection → acid-base adjustment → reduction → acid-base adjustment → flocculation and sedimentation. After flocculation and sedimentation, the Cr ³⁺ -containing sludge is filtered and finally treated as hazardous waste. The clean water after flocculation and sedimentation is then subjected to a series of treatments to remove heavy metal ions that cannot be removed through conventional processes and is then mixed with other The electroplating wastewater is mixed and then enters the biochemical system for treatment.

The method of the present invention is used to carry out system transformation, mainly adding two sets of ultrafiltration systems, one set of UV/Fenton treatment system (processing capacity is ^6m3 each time), one set of evaporation crystallization equipment, one set of sludge filter press system, and the remaining pH The chromium-containing sludge obtained after sludge reduction and resource utilization is processed and sold as chemical products.

The specific processing process is as follows:

(1) Collect chromium-containing wastewater and analyze its COD value. The COD value analysis method is as follows:

A. First take an appropriate amount of chromium-containing wastewater and measure the pH ₁ and Cr ⁶⁺ content a of the wastewater, and measure the total chromium content b and the content of other heavy metal ions in the chromium-containing wastewater;

B. After the wastewater is filtered, analyze and measure the COD value of the wastewater according to the method described in the present invention. Calculate the required amount of hydrogen peroxide V ₁ =1.456L/m3 based on the measured COD value and b;

(2) The COD value of the collected chromium-containing wastewater is measured and then discharged into the UV/Fenton treatment system. After the wastewater UV/Fenton treatment system collects enough ^5m3 of wastewater, the pH ₄ value of the wastewater in the UV/Fenton treatment system is adjusted to 3- between 5;

(3) Calculate the amount of hydrogen peroxide required V according to V ₁ and the volume of wastewater collected by the UV/Fenton treatment system;

(4) After adjusting the pH value of the wastewater in the UV/Fenton treatment system, turn on the UV lamp of the UV/Fenton treatment system. After the UV lamp is turned on, add hydrogen peroxide to the wastewater in the UV/Fenton treatment system. The dosage of hydrogen peroxide is 7.28L;

(5) After the UV lamp is turned on for a certain period of time, add alkali into the UV/Fenton treatment system until the pH value of the wastewater in the system reaches between ₅ and 9-10;

(6) The total time the UV light is on is 40 minutes. After the UV light on time is over, turn off the UV light;

(7) After the UV lamp is turned off, discharge the wastewater in the UV/Fenton treatment system to the filtration system 1;

(8) For the wastewater filtered by the filtration system 1, add a certain amount of metabisulphite (Na ₂ S ₂ O ₅ ) for reduction. After the reduction, adjust the pH ₆ value of the reduced wastewater to between 8-9 and filter it with the filtration system 1. The sewage sludge will be processed separately;

(9) After the pH ₆ adjustment is completed, discharge the wastewater to the filtration system 2;

(10) The concentrated sludge in the filtration system 2 is washed three times with clean water. The cleaned sludge in the filtration system 2 is discharged into the sludge filter press system. The clean water filtered by the filtration system is mixed with other electroplating wastewater and then enters the original There are biochemical systems;

(11) After drying the dry sludge, analyze and test the content of various components in the sludge.

The content of pollutants in raw water is as follows in Table 5, the content of pollutants in clean water after filtering is as follows in Table 6, and the technical indicators of the product after evaporation and crystallization are as follows in Table 7:

Table 5 Raw water pollutant content

in:

^1. Determination of water chemical oxygen demand by dichromate method (HJ 828-2017). The determination method is carried out according to the method described in the patent of the present invention;

² Determination of water quality chromium flame atomic absorption spectrophotometry (HJ 757-2015);

^3. Determination of water quality copper, zinc, lead and cadmium by atomic absorption spectrophotometry (GB 7475-1987);

⁴ Determination of water quality nickel flame atomic absorption spectrophotometry (GB 11912-1989);

^5. Determination of water quality iron and manganese by flame atomic absorption spectrophotometry (GB 11911-1989).

Table 6 Pollutant content in clean water after filter press

Among them: ^* N/A means below the instrument detection limit (1μg/L).

Table 7 Technical indicators of products after evaporation and crystallization ⁶

Among them: ⁶ Industrial Chromium Chloride (HG/T 4311-2012). All technical indicators in the table are tested in accordance with the methods or methods described in the HG/T4311-2012 standard.

According to the above test data, all pollutants in the clean water after pressure filtration have been greatly reduced. Except for the Ni ²⁺ content, the other heavy metal ion contents meet the "Electroplating Pollutant Emission Standard (GB 21900-2008)" table 3, the COD value of wastewater has also been reduced to a certain extent, which is beneficial to subsequent treatment.

The chromium chloride product obtained after evaporation and crystallization meets the technical requirements of the first-class product in Table 1 of "Industrial Chromium Chloride (HG/T 4311-2012)" and can be sold directly as a chemical product.

In the company's original sewage treatment process, chromium-containing wastewater produced nearly 300 tons of chromium-containing hazardous waste every year (the moisture content is about 50%, after the sludge is dried). After being transformed by the method described in the present invention, the amount of hazardous waste produced every year Nearly 2 tons (moisture content is about 50%, after sludge drying), hazardous waste was reduced by more than 99.5% before and after the transformation, and no other solid waste or hazardous waste was added during the treatment process, achieving the reduction of hazardous solid waste. Quantity and resource utilization.

Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art will understand that various changes, modifications, and substitutions can be made to these embodiments without departing from the principles and spirit of the invention. and modifications, the scope of the invention is defined by the appended claims and their equivalents.

Claims (10)

1. The chromium plating waste water dangerous waste reduction method is characterized by comprising the following steps:

1) Collecting chromium-containing wastewater, analyzing the COD value of the wastewater, and calculating the required hydrogen peroxide amount V according to the measured COD value (g/L) ₁ (the unit is L/m ³ Or L/ton);

2) The collected chromium-containing wastewater is discharged into a UV/Fenton treatment system after the COD value is measured, and the pH value of the wastewater in the UV/Fenton treatment system is adjusted ₄ The value is adjusted to 3-10 according to V ₁ And calculating the volume or weight of the waste water collected by the UV/Fenton treatment system to obtain the required added hydrogen peroxide V (the unit is L), starting a UV lamp of the UV/Fenton treatment system, and adding hydrogen peroxide into the waste water in the UV/Fenton treatment system, wherein the added hydrogen peroxide is V;

3) After the UV lamp is started for a certain time, adding alkali into the UV/Fenton treatment system until the pH value of wastewater in the system is reached ₅ Adding a sufficient amount of NaClO into the UV/Fenton treatment system after the alkali addition is finished until the value is between 4 and 13, and then continuously starting the UV lamp for a certain time, wherein the total starting time of the UV lamp is 0.5 to 10 hours;

4) After the UV lamp is turned off, the wastewater in the UV/Fenton treatment system is discharged to the filtering system 1, the wastewater filtered by the filtering system 1 is added with a certain reducing agent SP for reduction, and the pH of the reduced wastewater is adjusted ₆ The value is adjusted to be between 5 and 13, and the sludge filtered by the filtering system 1 is additionally treated;

5)pH ₆ after the adjustment is finished, the wastewater is discharged to a filter system 2, the concentrated sludge in the filter system 2 is washed for 1-10 times by adopting clear water, clear water filtered by the filter system 2 is additionally treated, the cleaned sludge in the filter system 2 is discharged to a sludge press filtration system, and the sludge is press-filtered by the sludge press filtration system to form dry sludge.

2. The chromium plating wastewater hazardous waste reduction method according to claim 1, which comprisesCharacterized in that the pH is ₆ The preferred value of the value range is between 6 and 9, the pH value ₅ The preferred value of the value range is between 8 and 10.

3. The method for reducing the risk of waste chrome plating wastewater according to claim 1, wherein the optimal value of the number of times of concentrated sludge cleaning in the filtering system 2 is 2-4, and the sludge press filtration system is a high-pressure diaphragm type plate-and-frame filter press.

4. The chromium plating wastewater hazardous waste reduction method according to any one of claims 1 to 3, wherein the COD value analysis method is as follows:

1) Firstly taking a proper amount of chromium-containing wastewater and measuring the pH value of the wastewater ₁ Value and Cr ⁶⁺ The content a (g/L) is measured, and the total chromium content b (g/L) and the content of other heavy metal ions in the chromium-containing wastewater are measured;

2) Determination of Cr in wastewater ⁶⁺ Adding sufficient reducing agent GV according to the proportion after the content;

3) After GV is added, stirring the wastewater until GV is dissolved, and adding a proper amount of acid or alkali into the wastewater to adjust the pH of the wastewater after GV is dissolved ₂ Value, pH ₂ After the value adjustment is finished, standing the wastewater for 10-500min;

4) After the standing time is over, adding a proper amount of alkali into the wastewater to adjust the pH value of the wastewater ₃ A pH of between 9 and 14 ₃ After the adjustment is finished, filtering the wastewater;

5) After the wastewater is filtered, the COD value of the wastewater is analyzed and measured.

5. The method for reducing chromium plating wastewater risk according to claim 4, wherein said GV is ferrous sulfate (FeSO) ₄ ·7H ₂ O), the addition amount of the ferrous sulfate is calculated according to the following formula:

m ≥ 5.4 × a (1)

in the formula (1), m is FeSO which needs to be added in each liter of water ₄ ·7H ₂ The amount of O is given in units of: g/L, V ₁ The calculation is carried out according to the following formula:

V ₁ ＝ p × COD (2)

the value range of p is 0.5-9.

6. The method for reducing chromium plating wastewater risk and waste according to claim 5, wherein the preferable value of the p value range is 2.8-5.6.

7. The method for reducing the risk of chromium plating wastewater according to any one of claims 1 to 3, wherein the mass percentage content of the sodium hypochlorite is 10%, and the addition amount of the NaClO is calculated according to the following formula:

V ₂ ＝ q × (b – a) (3)

in the formula (3), the units of b and a are g/L and V ₂ Is L/m ³ I.e. the volume of sodium hypochlorite to be added per cubic meter or ton of water;

in the formula (3), q is a coefficient, and the value range of q is 9-11.

8. The method for reducing chromium plating wastewater risk and waste according to claim 7, wherein the q value range is preferably 9.3-10.2.

9. Use of dry sludge produced by the chromium plating wastewater hazardous waste reduction method according to any one of claims 1 to 8 in chromium sludge recycling.

10. The method for recycling chromium sludge by using the dry sludge obtained by the chromium plating wastewater hazardous waste reduction method according to any one of claims 1 to 8, which is characterized in that the dry sludge filtered by the sludge press filtration system can be finally manufactured into different finished products according to different treatment processes.