A method for treating electroplating wastewater containing chromium

Abstract

The present application belongs to the technical field of wastewater treatment, and particularly relates to a treatment method of electroplating chromium-containing wastewater. The treatment method of electroplating chromium-containing wastewater provided by the present application comprises the following steps: after adjusting the pH value of the electroplating chromium-containing wastewater to 0-4, the electroplating chromium-containing wastewater is mixed with a first reducing substance to perform a first composite reduction reaction, so as to obtain primary chromium reduction wastewater; the mass ratio of the first reducing substance to the electroplating chromium-containing wastewater is 0.05-1:100, and the first composite reduction reaction comprises a first electrolytic reduction reaction and a first chemical reduction reaction; the primary chromium reduction wastewater is mixed with a second reducing substance to perform a second chemical reduction reaction, so as to obtain chromium reduction wastewater; the chromium reduction wastewater is mixed with an alkaline substance to perform flocculation and sedimentation, so as to obtain chromium-removed wastewater and chromium sludge, respectively. The combination of electrolytic reduction and redox can efficiently remove hexavalent chromium in the electroplating chromium-containing wastewater by using less reducing substance, and the generation of secondary pollution is avoided.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and specifically relates to a method for treating chromium-containing wastewater from electroplating. Background Technology

[0002] Chromium plating is a common surface treatment process that generates a large amount of wastewater. This wastewater mainly originates from the washing and rinsing of plated parts, waste liquid from the electroplating tank, and passivation processes. The wastewater may contain toxic and harmful chromium (Cr). 6+ Ions. Directly containing Cr 6+ Wastewater discharge containing Cr ions will pollute the environment. 6+ Remove or reduce Cr to a lower toxicity 3+ It is a key process for reducing pollution.

[0003] Currently removing Cr from wastewater 6+ Most methods for removing Cr involve chemical reduction precipitation, adsorption, ion exchange, membrane separation, biological treatment, and photocatalysis, with chemical reduction precipitation being the most widely used. Chemical reduction precipitation is used to remove Cr. 6+ The specific process is as follows: Under acidic conditions, Cr is reduced by adding reducing agents such as sodium metabisulfite. 6+ Reduced to Cr 3+ Then, under alkaline conditions, Cr 3+ The reagents are converted into Cr(OH)3 precipitate and precipitate out, thus removing them from the water. However, this method is complex, requires large dosages of reagents, and is prone to secondary pollution. Summary of the Invention

[0004] In view of this, the present invention provides a method for treating chromium-containing electroplating wastewater. The method provided by the present invention can efficiently remove hexavalent chromium from the wastewater using a small amount of reducing substances. The method is simple and easy to operate and does not produce secondary pollution.

[0005] To address the aforementioned technical problems, this invention provides a method for treating chromium-containing electroplating wastewater, comprising the following steps:

[0006] After adjusting the pH of the chromium-containing electroplating wastewater to 0-4, it is mixed with a first reducing agent to carry out a first complex reduction reaction, thereby obtaining primary chromium reduction wastewater; the mass ratio of the first reducing agent to the chromium-containing electroplating wastewater is 0.05-1:100, and the first complex reduction reaction includes a first electrolytic reduction reaction and a first chemical reduction reaction;

[0007] The primary chromium reduction wastewater and the second reducing substance are mixed to carry out a second chemical reduction reaction, resulting in chromium reduction wastewater.

[0008] The chromium reduction wastewater and alkaline substances were mixed and subjected to flocculation and sedimentation to obtain chromium-removed wastewater and chromium sludge, respectively.

[0009] Preferably, the first reducing substance and the second reducing substance independently include one or more of ferrous sulfate, sodium metabisulfite, sodium bisulfite, and sodium sulfite.

[0010] Preferably, the anode material for the first electrolytic reduction reaction includes titanium coated lead dioxide, titanium coated ruthenium iridium, titanium coated tantalum iridium, or graphite, and the cathode material for the first electrolytic reduction reaction is iron.

[0011] The current density used in the first electrolytic reduction reaction is 50–500 A / m. 2 ;

[0012] The first composite reduction reaction takes 0.5 to 4 hours.

[0013] Preferably, the alkaline substance includes one or more of sodium hydroxide, calcium hydroxide, potassium hydroxide, and sodium carbonate;

[0014] The pH value of the mixed system obtained by mixing the chromium reduction wastewater and the alkaline substance is 6 to 10.

[0015] Preferably, before mixing the chromium reduction wastewater and the alkaline substance, the method further includes: mixing the chromium reduction wastewater and the phosphorus removal agent and then filtering to obtain phosphorus-removed chromium reduction wastewater.

[0016] Preferably, the phosphorus removal agent includes one or more of ferrous sulfate, ferrous chloride, ferric chloride, lime, and calcium chloride.

[0017] Preferably, after obtaining the chromium mud, the process further includes: washing the chromium mud and then sintering it to obtain chromite.

[0018] Preferably, the cleaning solution includes one or more of sodium bicarbonate solution, potassium bicarbonate solution, sodium carbonate solution, and potassium carbonate solution;

[0019] The mass concentration of the washing solution is 1-20%;

[0020] The sintering temperature is 1300–1600℃.

[0021] Preferably, after obtaining the chromium removal wastewater, the process further includes: using a membrane system to post-treat the chromium removal wastewater to obtain recycled water.

[0022] Preferably, the mass concentration of hexavalent chromium ions in the electroplating chromium-containing wastewater is 900–1100 mg / L.

[0023] This invention provides a method for treating chromium-containing electroplating wastewater, comprising the following steps: adjusting the pH of the chromium-containing electroplating wastewater to 0-4 and mixing it with a first reducing agent to conduct a first composite reduction reaction, obtaining primary chromium-reduced wastewater; the mass ratio of the first reducing agent to the chromium-containing electroplating wastewater is 0.05-1:100, and the first composite reduction reaction includes a first electrolytic reduction reaction and a first chemical reduction reaction; mixing the primary chromium-reduced wastewater with a second reducing agent to conduct a second chemical reduction, obtaining chromium-reduced wastewater; mixing the chromium-reduced wastewater with an alkaline substance for flocculation and sedimentation, respectively obtaining chromium-removed wastewater and chromium sludge. This invention combines electrolytic reduction and redox, using less reducing agent to efficiently remove hexavalent chromium from chromium-containing electroplating wastewater, avoiding secondary pollution; the treatment method provided by this invention is simple, easy to operate, and conducive to industrialization. Detailed Implementation

[0024] This invention provides a method for treating chromium-containing wastewater from electroplating, comprising the following steps:

[0025] After adjusting the pH of the chromium-containing electroplating wastewater to 0-4, it is mixed with a first reducing agent to carry out a first complex reduction reaction, thereby obtaining primary chromium reduction wastewater; the mass ratio of the first reducing agent to the chromium-containing electroplating wastewater is 0.05-1:100, and the first complex reduction reaction includes a first electrolytic reduction reaction and a first chemical reduction reaction;

[0026] The primary chromium reduction wastewater and the second reducing substance are mixed to carry out a second chemical reduction reaction, resulting in chromium reduction wastewater.

[0027] The chromium reduction wastewater and alkaline substances were mixed and subjected to flocculation and sedimentation to obtain chromium-removed wastewater and chromium sludge, respectively.

[0028] In this invention, unless otherwise specified, all raw materials are commercially available products.

[0029] This invention adjusts the pH of chromium-containing electroplating wastewater to 0-4 and then mixes it with a first reducing agent to conduct a first composite reduction reaction, obtaining primary chromium reduction wastewater. In this invention, the mass concentration of hexavalent chromium ions in the chromium-containing electroplating wastewater is preferably 900-1100 mg / L, more preferably 1000 mg / L. In this invention, the first reducing agent preferably includes one or more of ferrous sulfate, sodium metabisulfite, sodium bisulfite, and sodium sulfite, more preferably one of ferrous sulfate, sodium metabisulfite, sodium bisulfite, and sodium sulfite, and even more preferably ferrous sulfate. In this invention, the mass ratio of the first reducing agent to the chromium-containing electroplating wastewater is 0.05-1:100, preferably 0.1-0.8:100. In this invention, the first reducing agent can undergo a redox reaction with hexavalent chromium ions, reducing them to trivalent chromium ions.

[0030] This invention does not have special requirements for the pH adjuster used to adjust the pH value, as long as the desired pH value can be achieved. Under the aforementioned defined pH conditions, this invention can achieve the electrolytic reduction of hexavalent chromium ions.

[0031] In this invention, the first composite reduction reaction includes a first electrolytic reduction reaction and a first chemical reduction reaction. In this invention, the anode material for the first electrolytic reduction reaction preferably includes titanium coated with lead dioxide, titanium coated with ruthenium-iridium, titanium coated with tantalum-iridium, or graphite, more preferably graphite; the cathode material for the first electrolytic reduction reaction is preferably iron. In this invention, the current density for the first electrolytic reduction reaction is preferably 50–500 A / m. 2 More preferably, it is 150–300 A / m 2 In this invention, the duration of the first composite reduction reaction is preferably 0.5–4 hours, more preferably 1–3 hours. In this invention, the duration of the first electrolytic reduction reaction is preferably the same as the duration of the first composite reduction reaction. In this invention, the duration of the first electrolytic reduction reaction is preferably calculated according to Formula 1:

[0032] t = C²V² / k²I (Formula 1)

[0033] Where t is the time of the first electrolytic reduction reaction, h; C2 represents the concentration of hexavalent chromium ions in the chromium-containing electroplating wastewater, g / L; V2 represents the volume of the wastewater after pH adjustment, L; k2 represents the electrolytic constant of chromium ions, selected from 0.10 to 0.30 g / Ah; and I represents the current during electrolysis, A.

[0034] This invention combines electrolysis with a small amount of reducing substances. Through the combined action of electrolytic reduction and chemical reduction, most of the hexavalent chromium ions in chromium-containing electroplating wastewater can be reduced to trivalent chromium ions.

[0035] After obtaining the primary chromium reduction wastewater, this invention mixes the primary chromium reduction wastewater with a second reducing agent to perform a second chemical reduction, obtaining chromium reduction wastewater. Preferably, this invention detects the content of hexavalent chromium ions in the primary chromium reduction wastewater before mixing; the mass concentration of hexavalent chromium ions in the primary chromium reduction wastewater is preferably 15–80 mg / L, more preferably 30–40 mg / L. In this invention, the second reducing agent preferably includes one or more of ferrous sulfate, sodium metabisulfite, sodium bisulfite, and sodium sulfite, more preferably one of ferrous sulfate, sodium metabisulfite, sodium bisulfite, and sodium sulfite, and even more preferably ferrous sulfate. This invention preferably limits the amount of the second reducing agent according to the content of hexavalent chromium ions in the primary chromium reduction wastewater, facilitating the reduction of unreduced hexavalent chromium ions from the first composite reduction to trivalent chromium ions using a smaller amount of reducing agent.

[0036] In this invention, the time for the second chemical reduction reaction is preferably 10 to 60 minutes, more preferably 20 to 30 minutes.

[0037] In this invention, the mass concentration of hexavalent chromium ions in the chromium reduction wastewater is preferably below 0.01 mg / L.

[0038] After obtaining chromium reduction wastewater, this invention mixes the chromium reduction wastewater with an alkaline substance for flocculation and sedimentation, obtaining chromium-removed wastewater and chromium sludge respectively. In this invention, before mixing the chromium reduction wastewater with the alkaline substance, it preferably further includes: mixing the chromium reduction wastewater with a phosphorus removal agent and then filtering, to obtain phosphorus-removed chromium reduction wastewater. In this invention, the phosphorus removal agent preferably includes one or more of ferrous sulfate, ferrous chloride, ferric chloride, lime, and calcium chloride, more preferably ferric chloride, lime, or calcium chloride, and even more preferably calcium chloride. This invention preferably detects the total phosphorus (phosphate and hypophosphite) content in the chromium reduction wastewater and adds the phosphorus removal agent according to the phosphorus content. This invention utilizes the phosphorus removal agent to remove phosphorus from the chromium reduction wastewater, which is beneficial for subsequent reclaimed water, while reducing phosphorus residue in the chromium sludge, improving the purity of the chromium sludge, and facilitating the resource utilization of the chromium sludge. This invention does not have a special limitation on the mixing method, as long as it can be mixed evenly. In this invention, the mixing time is preferably 10-60 min, more preferably 20-30 min. The present invention does not have any special requirements for the filtration process; conventional methods in the field can be used.

[0039] In this invention, the alkaline substance preferably includes one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium carbonate, more preferably sodium hydroxide and / or calcium hydroxide. In this invention, the pH value of the mixed system obtained by mixing the chromium reduction wastewater and the alkaline substance is preferably 4-10, more preferably 6-10. This invention does not have special requirements on the amount of the alkaline substance used, as long as the desired pH value is achieved. In this invention, trivalent chromium ions in the chromium reduction wastewater combine with hydroxide ions in an alkaline environment to form a precipitate.

[0040] In this invention, the flocculation and sedimentation process preferably further includes: solid-liquid separation of the flocculated system, wherein the solid obtained from the solid-liquid separation is chromium sludge, and the liquid obtained from the solid-liquid separation is chromium removal wastewater. This invention has no special requirements for the solid-liquid separation, as long as the solid and liquid can be separated.

[0041] In this invention, after obtaining the chromium mud, the process preferably further includes: washing the chromium mud and then sintering it to obtain chromite. In this invention, the washing solution preferably includes one or more of sodium bicarbonate solution, potassium bicarbonate solution, sodium carbonate solution, and potassium carbonate solution, more preferably one of sodium bicarbonate solution, potassium bicarbonate solution, sodium carbonate solution, and potassium carbonate solution, and even more preferably sodium bicarbonate solution or sodium carbonate solution. In this invention, the mass concentration of the washing solution is preferably 1-20%, more preferably 5-20%. In this invention, the mass percentage content of impurities in the washed chromium mud is preferably S < 0.2%, P ≤ 0.05%, F ≤ 1%, and Na₂O + K₂O ≤ 0.25%.

[0042] In this invention, the sintering temperature is preferably 1300–1600°C, more preferably 1400–1500°C. In this invention, the chromite is preferably smelted to obtain stainless steel. In this invention, the smelting temperature is preferably 1300–1600°C, more preferably 1400–1500°C.

[0043] In this invention, after obtaining the chromium-removed wastewater, the process preferably further includes: post-treatment of the chromium-removed wastewater using a membrane system to obtain reclaimed water. In this invention, the mass percentage of impurities in the reclaimed water is preferably COD < 50 mg / L, total phosphorus < 0.5 mg / L, total chromium < 0.5 mg / L, and Cr(VI) < 0.1 mg / L. In this invention, the reclaimed water can be directly discharged or used as reclaimed water in a greywater reuse tank, achieving wastewater reuse. This invention does not have special requirements for the membrane system; conventional methods in the art can be used.

[0044] In this invention, a first reducing agent assists in reducing Cr(VI) in chromium-containing wastewater to Cr(III); electrolysis reduces most of the Cr(VI) in the chromium-containing wastewater to Cr(III); the addition of a second reducing agent completely reduces Cr(VI) in the primary chromium reduction wastewater to Cr(III); filtration with a phosphorus removal agent removes phosphorus impurities from the solution; flocculation and sedimentation completely precipitate the chromium sludge for recycling; washing the chromium sludge again allows for further sintering and ore making, followed by secondary sintering and smelting of stainless steel; and the chromium-removed wastewater after chromium sludge recovery is post-treated using a membrane system, achieving water resource reuse.

[0045] The wastewater treatment method provided by this invention combines electrolysis with traditional chemical reduction reactions, significantly reducing the consumption of chemical reducing agents and achieving chromium recovery and reuse to a certain extent, thus realizing waste resource utilization. Simultaneously, the recycled water obtained from this treatment can be used as greywater, with a water resource reuse rate as high as 95%. The treatment method provided by this invention does not generate waste liquid or solid waste after treating chromium-containing electroplating wastewater, avoiding secondary pollution.

[0046] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1

[0048] The treatment of chromium-containing electroplating wastewater with a hexavalent chromium ion concentration of 1000 mg / L and a total phosphorus content of 400 mg / L includes the following steps:

[0049] Step 1) Adjust the pH of 2L of chromium-containing electroplating wastewater to 0.5;

[0050] Step 2) Add 1% ferrous sulfate (by mass of the chromium-containing electroplating wastewater) to the chromium-containing electroplating wastewater after adjusting its pH in Step 1);

[0051] Step 3) Electrolyze the chromium-containing electroplating wastewater containing reducing agents added in Step 2) (the anode is graphite, the cathode is iron; the current density is 200 A / m). 2 Electrolytic reduction and chemical reduction were carried out for 2 hours to obtain primary chromium reduction wastewater;

[0052] Step 4) After detecting that the mass concentration of hexavalent chromium ions in the primary chromium reduction wastewater after the electrolytic reduction in step 3) is 50 mg / L, ferrous sulfate (0.5% of the mass of the system) is added to carry out oxidation-reduction to reduce the incompletely reduced hexavalent chromium ions, resulting in chromium reduction wastewater with a hexavalent chromium ion mass concentration of 0.01 mg / L.

[0053] Step 5) Add 0.1% calcium chloride (phosphorus removal agent) to the chromium reduction wastewater from Step 4), mix for 30 minutes, and then filter to remove phosphorus, obtaining phosphorus-removed chromium reduction wastewater;

[0054] Step 6) Mix the chromium reduction wastewater from step 5) with sodium hydroxide, adjust the pH of the mixture to 9, and then perform flocculation and sedimentation followed by solid-liquid separation to obtain chromium sludge and chromium removal wastewater, respectively.

[0055] Step 7) After cleaning the chromium mud recovered in Step 6 with a 10% sodium carbonate solution, sinter it at 1400℃ to obtain chromite. Then, smelt the chromite at 1400℃ to obtain stainless steel. The mass percentage of impurities in the cleaned chromium mud is as follows: S content is ND (not detected), total phosphorus content is ND, F content is 3 mg / L, and Na2O+K2O content is ND.

[0056] Step 8) Use a membrane system to post-treat the chromium removal wastewater from step 6) to obtain recycled water; the recycled water meets the wastewater discharge standards or is reused in a reclaimed water tank; the mass concentration of impurities in the recycled water is COD < 50 mg / L, total phosphorus content < 0.5 mg / L, total chromium < 0.1 mg / L, and Cr(VI) < 0.01 mg / L.

[0057] Example 2

[0058] The treatment of electroplating wastewater containing chromium, with a hexavalent chromium ion concentration of 900 mg / L and a total phosphorus content of 20 mg / L, includes the following steps:

[0059] Step 1) Adjust the pH of 3L of chromium-containing electroplating wastewater to 0.5;

[0060] Step 2) Add 0.5% ferrous sulfate (by mass of the chromium-containing electroplating wastewater) to the chromium-containing electroplating wastewater after adjusting its pH in Step 1);

[0061] Step 3) Electrolyze the chromium-containing electroplating wastewater containing reducing agents added in Step 2) (the anode is graphite, the cathode is iron; the current density is 200 A / m). 2 Electrolytic reduction and chemical reduction were carried out for 1 hour to obtain primary chromium reduction wastewater;

[0062] Step 4) After detecting that the mass concentration of hexavalent chromium ions in the primary chromium reduction wastewater after the electrolytic reduction in step 3) is 20 mg / L, ferrous sulfate (0.15% of the mass of the system) is added to carry out oxidation-reduction to reduce the incompletely reduced hexavalent chromium ions, resulting in chromium reduction wastewater with a hexavalent chromium ion mass concentration of 0.01 mg / L.

[0063] Step 5) Add 0.1% calcium chloride (phosphorus removal agent) to the chromium reduction wastewater from Step 4), mix for 30 minutes, and then filter to remove phosphorus, obtaining phosphorus-removed chromium reduction wastewater;

[0064] Step 6) Mix the chromium reduction wastewater from step 5) with potassium hydroxide, adjust the pH of the mixture to 9, and then perform flocculation and sedimentation followed by solid-liquid separation to obtain chromium sludge and chromium removal wastewater, respectively.

[0065] Step 7) After cleaning the chromium mud recovered in Step 6 with a 15% sodium bicarbonate solution, sinter it at 1400℃ to obtain chromite. Then, smelt the chromite at 1400℃ to obtain stainless steel. The mass percentage of impurities in the cleaned chromium mud is: S content is ND, total phosphorus content is ND, F content is 2mg / L, and Na2O+K2O content is ND.

[0066] Step 8) Use a membrane system to post-treat the chromium removal wastewater from step 6) to obtain recycled water; the recycled water meets the wastewater discharge standards or is reused in a reclaimed water tank; the mass concentration of impurities in the recycled water is COD < 50 mg / L, total phosphorus content < 0.5 mg / L, total chromium < 0.1 mg / L, and Cr(VI) < 0.01 mg / L.

[0067] Example 3

[0068] Treatment of electroplating wastewater containing chromium, with a hexavalent chromium ion concentration of 1100 mg / L and a total phosphorus content of 50 mg / L, includes the following steps:

[0069] Step 1) Adjust the pH of 5L of chromium-containing electroplating wastewater to 0.5;

[0070] Step 2) Add 1% ferrous sulfate (by mass of the chromium-containing electroplating wastewater) to the chromium-containing electroplating wastewater after adjusting its pH in Step 1);

[0071] Step 3) Electrolyze the chromium-containing electroplating wastewater containing a suitable amount of reducing agent added in Step 2) (the electrolytic anode is graphite, the cathode is iron; the current density is 200 A / m). 2 Electrolytic reduction and redox reactions were carried out for 2 hours to obtain primary chromium reduction wastewater;

[0072] Step 4) After detecting that the mass concentration of hexavalent chromium ions in the primary chromium reduction wastewater after the electrolytic reduction in step 3) is 50 mg / L, sodium metabisulfite (0.2% of the mass of the system) is added to carry out oxidation-reduction to reduce the incompletely reduced hexavalent chromium ions, resulting in chromium reduction wastewater with a hexavalent chromium ion mass concentration of 0.01 mg / L.

[0073] Step 5) Add 0.1% calcium chloride (phosphorus removal agent) to the chromium reduction wastewater from Step 4), mix for 30 minutes, and then filter to remove phosphorus, obtaining phosphorus-removed chromium reduction wastewater;

[0074] Step 6) Mix the chromium reduction wastewater from step 5) with calcium hydroxide, adjust the pH of the mixture to 9, and then perform flocculation and sedimentation followed by solid-liquid separation to obtain chromium sludge and chromium removal wastewater, respectively.

[0075] Step 7) After cleaning the chromium mud recovered in Step 6 with a 15% sodium bicarbonate solution, sinter it at 1400℃ to obtain chromite. Then, smelt the chromite at 1400℃ to obtain stainless steel. The mass percentage of impurities in the cleaned chromium mud is: S content is ND, total phosphorus content is ND, F content is 4 mg / L, and Na2O+K2O content is ND.

[0076] Step 8) Use a membrane system to post-treat the chromium removal wastewater from step 6) to obtain recycled water; the recycled water meets the wastewater discharge standards or is reused in a reclaimed water tank; the mass concentration of impurities in the recycled water is COD < 50 mg / L, total phosphorus content < 0.5 mg / L, total chromium < 0.1 mg / L, and Cr(VI) < 0.01 mg / L.

[0077] This invention employs electrolysis to reduce the large amount of Cr(VI) in chromium-containing electroplating wastewater. This method significantly reduces the consumption of chemical reagents, requiring only a very small amount to completely reduce the remaining Cr(VI) in the solution without introducing new impurities. This avoids secondary pollution from reagent impurities and the economic costs associated with using large quantities of chemical reagents. Simultaneously, it ensures the complete removal of Cr(VI) from the water body. The amount of reagent used is far lower than that of traditional chemical methods, and the Cr(VI) content in the water is lower than that of electrochemical methods with the same energy consumption. Furthermore, the treatment method provided by this invention enables the reuse of both chromium and water resources.

[0078] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for treating chromium-containing wastewater from electroplating, comprising the following steps: After adjusting the pH of the chromium-containing electroplating wastewater to 0-4, it is mixed with the first reducing agent to carry out the first complex reduction reaction, thus obtaining primary chromium reduction wastewater; The mass ratio of the first reducing agent to the chromium-containing electroplating wastewater is 0.05~1:100; the first composite reduction reaction includes a first electrolytic reduction reaction and a first chemical reduction reaction; the anode material for the first electrolytic reduction reaction includes titanium-coated lead dioxide, titanium-coated ruthenium-iridium, titanium-coated tantalum-iridium, or graphite; the cathode material for the first electrolytic reduction reaction is iron; the current density for the first electrolytic reduction reaction is 150~300 A / m. 2 The time for the first electrolytic reduction reaction is calculated according to Formula 1: t = C2V2 / k2I (Formula 1); where t is the time of the first electrolytic reduction reaction, h; C2 represents the concentration of hexavalent chromium ions in the electroplating chromium-containing wastewater, g / L; V2 represents the volume of the wastewater after pH adjustment, L; k2 represents the electrolytic constant of chromium ions, 0.10~0.30g / Ah; I represents the current during electrolysis, A; the time for the first composite reduction reaction is 0.5~4h; the mass concentration of hexavalent chromium ions in the electroplating chromium-containing wastewater is 900~1100mg / L, and the mass concentration of hexavalent chromium ions in the primary chromium reduction wastewater is 15~80mg / L. The primary chromium reduction wastewater and the second reducing substance are mixed to carry out a second chemical reduction reaction, resulting in chromium reduction wastewater. The mass concentration of hexavalent chromium ions in the chromium reduction wastewater is below 0.01 mg / L; The chromium reduction wastewater and alkaline substances are mixed and subjected to flocculation and sedimentation to obtain chromium-removed wastewater and chromium sludge, respectively; the alkaline substances include one or more of sodium hydroxide, calcium hydroxide, potassium hydroxide and sodium carbonate; the pH value of the mixed system obtained by mixing the chromium reduction wastewater and alkaline substances is 6~10.

2. The method for treating chromium-containing electroplating wastewater according to claim 1, characterized in that, The first reducing substance and the second reducing substance independently include one or more of ferrous sulfate, sodium metabisulfite, sodium bisulfite, and sodium sulfite.

3. The method for treating chromium-containing electroplating wastewater according to claim 1, characterized in that, Before mixing the chromium reduction wastewater with the alkaline substance, the process further includes: mixing the chromium reduction wastewater with the phosphorus removal agent and then filtering to obtain phosphorus-removed chromium reduction wastewater.

4. The method for treating chromium-containing electroplating wastewater according to claim 3, characterized in that, The phosphorus removal agent includes one or more of ferrous sulfate, ferrous chloride, ferric chloride, lime, and calcium chloride.

5. The method for treating chromium-containing electroplating wastewater according to claim 1, characterized in that, The process of obtaining chromium mud also includes: washing and sintering the chromium mud to obtain chromite.

6. The method for treating chromium-containing electroplating wastewater according to claim 5, characterized in that, The cleaning solution includes one or more of sodium bicarbonate solution, potassium bicarbonate solution, sodium carbonate solution, and potassium carbonate solution. The mass concentration of the washing solution is 1-20%; The sintering temperature is 1300~1600℃.

7. The method for treating chromium-containing electroplating wastewater according to claim 1, characterized in that, The process of obtaining chromium-removed wastewater also includes: post-treatment of the chromium-removed wastewater using a membrane system to obtain recycled water.