A device and method for treating chromium-containing wastewater

Abstract

A device and method for treating chromium-containing wastewater, in which a homogenizing tank is connected to a reduction reaction tank, a reduction reaction tank is connected to a chromium precipitation reaction tank, a chromium precipitation reaction tank is connected to a filter press, a discharge port of the filter press is connected to a dechromium water storage tank, the dechromium water storage tank is connected to a feed port at the bottom of a heater through a pump and a preheater in sequence, a discharge port at the top of the heater is connected to a feed port in the middle of an evaporator, a steam outlet at the top of the evaporator is connected to a steam inlet at the top of the heater through a compressor, a concentrated liquid discharge port at the bottom of the evaporator is connected to a centrifuge, a discharge port of the centrifuge is connected to a concentrated liquid intermediate tank, and a concentrated liquid intermediate tank is connected to a feed port of a homogenizing tank. The invention also discloses a method for treating chromium-containing wastewater. The device of the invention has a simple structure, a simple and stable process, and a low cost. It can treat high-concentration chromium-containing wastewater, recycle chromium resources, achieve zero discharge, and is suitable for industrial production.

Description

Technical Field

[0001] The invention relates to a wastewater treatment device and method, and in particular to a wastewater treatment device and method containing chromium. Background Art

[0002] Since the chrome-plated layer has the characteristics of high hardness, good wear resistance, good heat resistance, and high chemical stability, chrome plating is widely used. In the electroplating solution used in the chrome plating process, chromium mainly exists in the form of hexavalent chromium. Therefore, chrome plating wastewater is mainly hexavalent chromium. However, hexavalent chromium is the most toxic of chromium, which is 100 times more toxic than trivalent chromium. Hexavalent chromium is a swallowed poison and an extremely toxic inhaled substance. Contact with it can cause dermatitis and is an allergenic element. It can cause cancer when inhaled, and ingestion of excessive doses of chromium can cause kidney and liver damage, nausea, gastrointestinal irritation, gastric ulcers, cramps and even death. Therefore, chrome plating wastewater must be treated scientifically and reasonably to ensure personal and environmental safety.

[0003] In the existing technology, the main technologies for treating chromium-containing wastewater include chemical precipitation, adsorption, electrolysis, membrane separation, biodegradation, solvent extraction, etc. However, it is difficult to achieve the purpose of solving the problem of chromium-containing wastewater by simply using these technologies. In addition, the existing chromium-containing wastewater treatment equipment and processes have large sludge (solid waste) production and high energy consumption, making it difficult to achieve zero discharge of chromium-containing wastewater and the recycling of chromium and water resources.

[0004] CN110563177A discloses an online circulation treatment device and method for chromium-containing wastewater, wherein the treatment device comprises a slag removal device, a filtering device and an adsorption device connected in sequence through pipelines, wherein the slag removal device is used to remove precipitation and suspended matter in the chromium-containing wastewater; the filtering device is used to remove particulate matter in the chromium-containing wastewater; and the adsorption device is used to adsorb chromium metal ions. A method for online circulation treatment of chromium-containing wastewater using the device is also disclosed. Although the device and method can achieve separation and purification of chromium metal ions, it can also basically achieve zero discharge of wastewater and recovery and recycling of metal resources. However, the shortcomings of the device and method are: 1) the treatment device and method are not suitable for or even unable to treat high-concentration chromium-containing wastewater with a chromium content of 10g / L or even up to 100g / L; 2) its desorption process uses a certain concentration of hydrochloric acid to desorb trivalent chromium and hexavalent chromium, but many production systems do not accept hydrochloric acid as a medium. At the same time, the trivalent chromium or hexavalent chromium at this concentration contains other impurities in addition to hydrochloric acid and is not suitable for returning to the production system. Therefore, the return of the resulting desorption solution to the production system is restricted, and this part of the solution becomes a new waste liquid, increasing the difficulty of emission reduction; 3) a variety of new hazardous wastes will also be generated during the treatment process, which require further treatment.

[0005] CN105236639A discloses a chromium-containing wastewater treatment process, comprising the following steps: 1) preliminarily filtering chromium-containing wastewater with a concentration of 10 to 50 mg / L through a grid well; 2) sending the filtered chromium-containing wastewater to a homogenization adjustment tank for homogenization treatment; 3) sending the chromium-containing wastewater after homogenization adjustment treatment to a pH value adjustment tank, adding dilute sulfuric acid to the tank to adjust the pH value to 2 to 3; 4) sending the chromium-containing wastewater after pH adjustment to a reduction tank, adding a reducing agent to the reduction tank to reduce the Cr in the chromium-containing wastewater 6+ Reduction to Cr 3+ ; 5) Add NaOH to the reduction tank and adjust the pH value to 8-9 to reduce the Cr in the chromium-containing wastewater. 3+ Converted into Cr(OH)3 precipitate, reaction time 30-40min; 6) Wastewater storage and collection, precipitate filtered by filter press and then stored in a centralized manner. However, the technical defects are: 1) This process is more suitable for treating chromium-containing wastewater with a chromium content of less than 1g / L; 2) The chromium hydroxide produced cannot be a useful downstream raw material, and the chromium-containing compounds obtained can only be treated as hazardous waste; 3) After the chromium-free wastewater treated by this process only has chromium content that meets the emission standards, and other items are still unqualified and need further treatment, that is, the wastewater needs deep treatment to meet the emission standards.

[0006] Therefore, it is of great significance to find a stable, reliable, low-cost, simple and easy process and device for recovering chromium in wastewater to treat chromium-containing wastewater and reduce pollution to the environment and damage to the ecology. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a chromium-containing wastewater treatment device which has a simple structure, low cost, can treat high-concentration chromium-containing wastewater, recover chromium as a resource, achieve zero wastewater discharge, zero waste residue discharge, and meet gas emission standards, and is suitable for industrial production.

[0008] The technical problem further to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for treating chromium-containing wastewater which is simple, stable, has low treatment cost, can treat high-concentration chromium-containing wastewater, and recover chromium as a resource, thereby achieving zero discharge of wastewater, zero discharge of waste residue, and standard emission of gases, is green and environmentally friendly, and is suitable for industrial production.

[0009] The technical solution adopted by the present invention to solve the technical problem is as follows: a device for treating chromium-containing wastewater, wherein a discharge port of a homogenizing tank is connected to a feed port of a reduction reaction tank through a pump, the discharge port of the reduction reaction tank is connected to a feed port of a chromium precipitation reaction tank through a pump, the discharge port of the chromium precipitation reaction tank is connected to a feed port of a filter press through a pump, the discharge port of the filter press is connected to a feed port of a dechromium water storage tank, the discharge port of the dechromium water storage tank is connected to a feed port at the bottom of a heater through a pump and a preheater in sequence, the discharge port at the top of the heater is connected to a feed port in the middle of an evaporator, the steam outlet at the top of the evaporator is connected to a steam inlet at the top of the heater through a compressor, the concentrated liquid discharge port at the bottom of the evaporator is connected to a feed port of a centrifuge, the discharge port of the centrifuge is connected to a feed port of a concentrated liquid intermediate tank, and the discharge port of the concentrated liquid intermediate tank is connected to the feed port of the homogenizing tank through a pump.

[0010] The working process of the device of the present invention is as follows: chromium-containing wastewater is injected into the homogenizing tank through the feed port of the homogenizing tank, the homogenized chromium-containing wastewater after homogenization treatment is injected into the reduction reaction tank through the feed port of the reduction reaction tank through a delivery pump, and a reducing agent is added to perform a reduction reaction at the same time, and the trivalent chromium wastewater after reduction is injected into the chromium precipitation reaction tank through the feed port of the chromium precipitation reaction tank through a delivery pump to perform a chromium precipitation reaction, and then the trivalent chromium wastewater is pumped into the diaphragm filter press through the feed port of the diaphragm filter press for pressure filtration, and the dechromized wastewater is discharged from the discharge port of the diaphragm filter press, and enters the dechromized water storage tank through the feed port of the dechromized water storage tank, and the dechromized wastewater enters the preheater through the delivery pump for preheating, and then enters the heater for heating through the feed port at the bottom of the heater, and then enters the MVR evaporator through the discharge port at the top of the heater through the feed port in the middle of the MVR evaporator for evaporation. The discharged steam is compressed and heated by the compressor through the steam outlet at the top of the MVR evaporator, and then enters the heater through the steam inlet at the upper part of the heater. The condensed water of the MVR evaporator is discharged through the condensed water drain outlet provided at the upper part of the MVR evaporator. The concentrated liquid obtained after evaporation by the MVR evaporator enters the centrifuge through the concentrated liquid discharge port at the bottom of the MVR evaporator and the feed port of the centrifuge. After the chromium-containing concentrated liquid is discharged from the discharge port of the centrifuge, it enters the concentrated liquid intermediate tank through the feed port of the concentrated liquid intermediate tank for storage. The chromium-containing concentrated liquid is sent from the discharge port of the concentrated liquid intermediate tank through the feed port of the homogenizing tank through the delivery pump to the homogenizing tank for circulation treatment. The waste gas generated in the reduction reaction tank and the chromium precipitation reaction tank is sent to the water foam absorption tower device through the exhaust port of the reduction reaction tank and the exhaust port of the chromium precipitation reaction tank for absorption treatment.

[0011] Preferably, the homogenization tank, reduction reaction tank and chromium precipitation reaction tank are equipped with a stirrer.

[0012] Preferably, the homogenizing tank, the reduction reaction tank and the chromium precipitation reaction tank are made of plastic or corrosion-resistant steel.

[0013] Preferably, the exhaust port of the reduction reaction tank and the exhaust port of the chromium precipitation reaction tank are both connected to the exhaust gas absorption system.

[0014] Preferably, the filter press is a centrifugal filter, a chamber filter press or a membrane filter press. More preferably, the filter press is a membrane filter press.

[0015] Preferably, the pump is a delivery pump or a filter press pump. The pump before entering the filter press is a filter press pump.

[0016] Preferably, a condensate drain port is provided on the upper portion of the evaporator.

[0017] Preferably, the evaporator is an MVR evaporator. The use of an MVR evaporation and concentration device can ensure that no new water is added during the process; although the commonly used multi-effect steam evaporation equipment is technically feasible, the addition of steam will cause new condensed water to be generated in the middle, thereby causing water expansion, which is unacceptable in the present invention.

[0018] Preferably, the waste gas absorption system is a water foam absorption tower device.

[0019] The present invention further solves the technical problem by adopting the following technical solution: a method for treating chromium-containing wastewater, comprising the following steps:

[0020] (1) Homogenization: Mix chromium-containing wastewater of different concentrations and perform homogenization treatment on it, and adjust the pH value at the same time to obtain homogenized chromium-containing wastewater;

[0021] (2) Reduction: adding a reducing agent to the homogenized chromium-containing wastewater obtained in step (1) under stirring, and stirring for reduction reaction to obtain trivalent chromium wastewater;

[0022] (3) precipitation: stirring and precipitating the trivalent chromium wastewater obtained in step (2), filtering, and obtaining chromium-containing compounds and dechromized wastewater;

[0023] (4) Evaporation and concentration: The chromium-removing wastewater obtained in step (3) is evaporated and concentrated, and the obtained concentrated solution is centrifuged to obtain a chromium-containing concentrated solution and crude salt, and the chromium-containing concentrated solution is returned to step (1) for circulation treatment.

[0024] Preferably, in step (1), the mass concentration of Cr in the chromium-containing wastewater of different concentrations is 1 to 200 g / L. Preferably, the pH value of the chromium-containing wastewater of different concentrations is 0.5 to 6.0.

[0025] Preferably, in step (1), the mass concentration of Cr in the mixed chromium-containing wastewater is 10-32 g / L, and the pH value is 0.5-6.0. When the chromium content of the chromium-containing wastewater is lower than 10 g / L, the particles of the chromium hydroxide obtained after treatment are fine, and the solid-liquid separation is slow. At the same time, the chromium hydroxide carries a lot of impurities, which reduces the chromium content in the chromium hydroxide, thereby affecting the use of the chromium hydroxide; when the chromium content in the chromium-containing wastewater is less than 1 g / L, the particles of the chromium hydroxide obtained are extremely fine, and the solid-liquid separation is difficult. At the same time, the ability to separate impurities is very weak, and the content of the chromium hydroxide obtained is very low, and it cannot be directly used by downstream enterprises; and when the chromium content in the chromium-containing wastewater is higher than 32 g / L, in the process of reducing and precipitating chromium hydroxide, the pH value rises quickly, making it difficult to control, and when the pH value rises above a certain value, the reduction reaction rate slows down. If the pH value is lowered by acid, the chromium hydroxide will be dissolved locally, resulting in a poor subsequent precipitation effect, and the particles of the generated chromium hydroxide become finer, and there are also undesirable phenomena such as difficulty in solid-liquid separation and high impurity content.

[0026] Preferably, in step (1), the temperature of the mixing and homogenizing treatment is room temperature, the rotation speed is 60-100 rpm, and the time is 60-120 min. The homogenizing treatment can make the main chemical components of chromium-containing wastewaters of different concentrations consistent, so as to facilitate the subsequent normal and uniform reduction. At the speed and time, sufficient stirring can be ensured, and chromium-containing wastewaters with different chromium contents can be fully mixed, but production efficiency and energy consumption need to be considered at the same time.

[0027] Preferably, in step (1), the pH value is adjusted to 0.50-1.00. The purpose of adjusting the pH value is to ensure the normal progress of the subsequent reduction reaction. If the pH value is too high, the pH value will rise too fast during the reduction reaction, reducing the reduction rate. By adjusting the initial pH value of the reduction, it is more conducive to ensuring that the pH value of the chromium-containing wastewater with a concentration of 10-30 g / L is controlled at 1.00-6.00 during the reduction process, and the end point pH value is controlled at 5.00-6.00.

[0028] Preferably, in step (2), the stirring speed when adding the reducing agent is 60 to 100 rpm.

[0029] Preferably, in step (2), the molar ratio of the reducing agent to the chromium in the homogenized chromium-containing wastewater is 1.0 to 1.1:1. A slightly excessive amount of reducing agent is more conducive to fully reducing the hexavalent chromium in the wastewater; hexavalent chromium is always in a solution state in the wastewater regardless of the pH value, and only trivalent chromium can be precipitated and separated from water after controlling a certain pH value. Excessive use of reducing agent will cause waste of reagents.

[0030] Preferably, in step (2), the reducing agent is one or more of sodium sulfide, sodium hydrosulfide, hydrazine hydrate or sodium sulfite. The reaction equation is as follows:

[0031] 3S 2- +2CrO4 2- +16H + →3S↓+2Cr 3+ +8H2O;

[0032] 3N2H4+4CrO4 2- +20H + →3N2↑+4Cr 3+ +16H2O;

[0033] 3SO3 2- +2CrO4 2- +10H + →3SO4 2- +2Cr 3+ +5H2O.

[0034] Preferably, in step (2), the temperature of the stirring reduction reaction is 15 to 80°C (more preferably 20 to 50°C), the stirring speed is 60 to 100 rpm, the time is 120 to 240 min, and the pH value of the stirring reduction reaction process is controlled to be 1.00 to 6.00, and the end point pH value is controlled to be 5.00 to 6.00. The purpose of the reduction reaction is to reduce the highly toxic hexavalent chromium in the chromium-containing wastewater to low-toxic trivalent chromium. If the reaction temperature is too low, the reaction speed is slow. As the reaction temperature increases, it is more conducive to the reduction reaction and the reaction speed gradually increases. However, when the temperature is too high, it not only increases energy consumption but also deteriorates the operating environment. During the reduction process, since the reducing agent itself is alkaline, the pH value continues to rise, and the reduction of hexavalent chromium under acidic conditions will consume a certain amount of acid. By fine-tuning, the pH value in the system can be maintained at a more suitable 1.00-6.00. At this time, the reduction speed is fast, and a small amount of coarse chromium hydroxide particles are produced, which is conducive to subsequent precipitation and solid-liquid separation. The content of the obtained chromium hydroxide is high, which meets the quality requirements of downstream enterprises for chromium hydroxide. If the pH value is higher than 6.00, the reduction rate of hexavalent chromium slows down rapidly. Under the stirring speed and reaction time, the reduction reaction is more sufficient. If the stirring speed is too fast, although the reduction speed can be accelerated, it will also break up the coarse chromium hydroxide particles that have been gathered, which is not conducive to the formation of subsequent large particle precipitation, thereby affecting the solid-liquid separation effect.

[0035] Preferably, in step (3), the temperature of the stirring precipitation reaction is room temperature, the stirring speed is 60-100 rpm, the time is 120-240 min, and the pH value during the stirring precipitation reaction is controlled to be 8.50-10.00. The purpose of the stirring precipitation reaction is to precipitate the trivalent chromium in the wastewater in the form of hydroxide by controlling the pH in the wastewater. The chromium-containing compound can be used as a raw material for ferrochrome or black ceramic pigments. The purpose of controlling the stirring speed and reaction time is to allow the chromium hydroxide to fully precipitate; during the precipitation process of chromium hydroxide, it is necessary to allow its particles to grow and to have an aging time. If the aging time is too short, the particles are small, and it is not easy to dehydrate during solid-liquid separation, and it is also not easy to separate impurities, so that more impurities remain in the chromium hydroxide, reducing the content and quality of chromium hydroxide, and making the obtained chromium hydroxide lose its proper use. Controlling the pH value is to allow the chromium hydroxide to fully precipitate and reduce the chromium content remaining in the wastewater as much as possible.

[0036] Preferably, in steps (2) and (3), the acid mist generated enters an absorption tower and is absorbed by an aqueous solution of sodium hydroxide or sodium carbonate with a pH value of ≥ 9.00. The alkaline aqueous solution at the pH value can ensure that the acid mist is fully absorbed.

[0037] Preferably, in step (4), the parameters of the evaporation and concentration are controlled as follows: the outlet temperature of the compressor is 105-110°C, the outlet temperature of the heater is 90-100°C, the evaporation temperature is 90-100°C, the internal pressure is 0.070-0.071MPa, and the mass concentration of Cr after evaporation and concentration is 20-1000mg / L. The condensed water produced by the evaporation and concentration can be returned to the system for use. Under the parameter conditions, it is more conducive to evaporating the water in the wastewater, improving the condensation water rate, and then the condensed water can be returned to the production system for reuse. After the reduction and precipitation of chromium hydroxide in the previous process, the wastewater still contains a certain amount of sodium sulfate and a trace amount of chromium. By using MVR evaporation, the water can be evaporated and condensed again without increasing the amount of new wastewater. At the same time, without adding reagents, the salt in the wastewater can also be crystallized, and the COD, suspended matter, and conductivity can also meet the standards, reducing the subsequent complex treatment process.

[0038] Preferably, in step (4), the centrifugal speed is 1000-1500 rpm. The crude salt obtained by centrifugation can be used for purification as a product.

[0039] In the present invention, when the pH value is high, sulfuric acid is used for adjustment, and the sulfuric acid is preferably industrial grade concentrated sulfuric acid; when the pH value is low, sodium hydroxide or sodium carbonate is used for adjustment.

[0040] The beneficial effects of the present invention are as follows:

[0041] (1) The device of the present invention has a simple structure, a simple and stable process, and a low cost. It can treat high-concentration chromium-containing wastewater with a Cr content of up to 200.00 g / L, and recover chromium as a by-product for sale. The recovery rate of chromium in the wastewater is ≥99.97%. The obtained chromium-containing compounds can be used as raw materials for ferrochrome alloys or black ceramic pigments. The obtained by-product crude salt can also be purified and sold, achieving zero discharge of waste residues.

[0042] (2) The condensed water produced by the present invention can be returned to the production system for use, thereby achieving zero wastewater discharge. The very small amount of acid mist waste gas produced can also be absorbed by alkaline solution to achieve gas emission standards, which is green and environmentally friendly and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the structure of a treatment device for chromium-containing wastewater according to Examples 1 to 5 of the present invention. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with the embodiments and drawings.

[0045] The chromium-plating wastewater used in the embodiment of the present invention is derived from wastewater produced by multiple factories in a certain electroplating park: chromium-plating wastewater 1 (the mass concentration of Cr is 200.00 g / L and the pH value is 0.50), chromium-plating wastewater 2 (the mass concentration of Cr is 178.26 g / L and the pH value is 0.59), chromium-plating wastewater 3 (the mass concentration of Cr is 1.00 g / L and the pH value is 5.69), chromium-plating wastewater 4 (the mass concentration of Cr is 45.59 g / L and the pH value is 2.56), and chromium-plating wastewater 5 (the mass concentration of Cr is 15.90 g / L and the pH value is 6.00); the mass fraction of concentrated sulfuric acid used in the embodiment of the present invention is 95%; the raw materials or chemical reagents used in the embodiment of the present invention, unless otherwise specified, are obtained through conventional commercial channels.

[0046] In the embodiment of the present invention, when the pH value is high, concentrated sulfuric acid is used for adjustment; when the pH value is low, sodium hydroxide or sodium carbonate is used for adjustment.

[0047] A device for treating chromium-containing wastewater Examples 1 to 5

[0048] like Figure 1As shown, in the treatment device for chromium-containing wastewater, the discharge port 1-2 of the homogenizing tank 1 is connected to the feed port 3-1 of the reduction reaction tank 3 through the delivery pump 2, the discharge port 3-2 of the reduction reaction tank 3 is connected to the feed port 4-1 of the chromium precipitation reaction tank 4 through the delivery pump 2, the discharge port 4-2 of the chromium precipitation reaction tank 4 is connected to the feed port 5-1 of the diaphragm filter press 5 through the filter press pump 2, the discharge port 5-2 of the diaphragm filter press 5 is connected to the feed port 6-1 of the dechromium water storage tank 6, the discharge port 6-2 of the dechromium water storage tank 6 is connected to the feed port 8-1 at the bottom of the heater 8 through the delivery pump 2 and the preheater 7 in sequence, the discharge port 8-2 at the top of the heater 8 is connected to the feed port 9-1 in the middle of the MVR evaporator 9, and the steam outlet 9-2 at the top of the MVR evaporator 9 is connected to the steam outlet 9-2 at the top of the MVR evaporator 9 through the compressor 1 0 is connected to the steam inlet 8-3 at the top of the heater 8, the concentrated liquid discharge port 9-3 at the bottom of the MVR evaporator 9 is connected to the feed port 11-1 of the centrifuge 11, the discharge port 11-2 of the centrifuge 11 is connected to the feed port 12-1 of the concentrated liquid intermediate tank 12, and the discharge port 12-2 of the concentrated liquid intermediate tank 12 is connected to the feed port 1-1 of the homogenizing tank 1 through the delivery pump 2; the homogenizing tank 1, the reduction reaction tank 3 and the chromium precipitation reaction tank 4 are equipped with a stirrer; the material of the homogenizing tank 1 is corrosion-resistant steel, and the material of the reduction reaction tank 3 and the chromium precipitation reaction tank 4 is plastic; the exhaust port 3-3 of the reduction reaction tank 3 and the exhaust port 4-3 of the chromium precipitation reaction tank 4 are both connected to the water foam absorption tower device 13; the upper part of the MVR evaporator 9 is provided with a condensed water drain port 9-4.

[0049] The working process of the device of the present invention is as follows: chromium-containing wastewater is injected into the homogenizing tank 1 through the feed port 1-1 of the homogenizing tank 1, the homogenized chromium-containing wastewater after homogenization is injected into the reduction reaction tank 3 through the feed port 3-1 of the reduction reaction tank 3 through the delivery pump 2, and a reducing agent is added to perform a reduction reaction, and the trivalent chromium wastewater after reduction is injected into the chromium precipitation reaction tank 4 through the feed port 4-1 of the chromium precipitation reaction tank 4 through the delivery pump 2 for chromium precipitation reaction, and then the trivalent chromium wastewater is injected into the chromium precipitation reaction tank 4 through the feed port 5-1 of the diaphragm filter press 5 through the filter press pump 2 for chromium precipitation reaction. 1 is driven into the membrane filter press 5 for filtration, and the chromium-removing wastewater is discharged from the discharge port 5-2 of the membrane filter press 5, and enters the chromium-removing water storage tank 6 from the feed port 6-1 of the chromium-removing water storage tank 6. The chromium-removing wastewater then enters the preheater 7 through the delivery pump 2 for preheating, and then enters the heater 8 through the feed port 8-1 at the bottom of the heater 8 for heating, and then enters the MVR evaporator 9 through the discharge port 8-2 at the top of the heater 8 through the feed port 9-1 in the middle of the MVR evaporator 9 for evaporation, and the discharged steam is discharged by the MV The steam outlet 9-2 at the top of the R evaporator 9 is compressed and heated by the compressor 10, and then enters the heater 8 through the steam inlet 8-3 at the upper part of the heater 8. The condensed water of the MVR evaporator 9 is discharged through the condensed water drain port 9-4 provided at the upper part of the MVR evaporator 9. The concentrated liquid obtained after evaporation in the MVR evaporator 9 enters the centrifuge 11 through the concentrated liquid discharge port 9-3 at the bottom of the MVR evaporator 9 and the feed port 11-1 of the centrifuge 11. The chromium-containing concentrated liquid is discharged from the centrifuge 11. After being discharged from the outlet 11-2, the concentrated solution enters the concentrated solution intermediate tank 12 through the feed port 12-1 of the concentrated solution intermediate tank 12 for storage, and the chromium-containing concentrated solution is sent from the discharge port 12-2 of the concentrated solution intermediate tank 12 through the delivery pump 2 and the feed port 1-1 of the homogenizing tank 1 to the homogenizing tank 1 for circulation treatment; the waste gas generated in the reduction reaction tank 3 and the chromium precipitation reaction tank 4 is sent to the water foam absorption tower device 13 through the exhaust port 3-3 of the reduction reaction tank 3 and the exhaust port 4-3 of the chromium precipitation reaction tank 4 for absorption treatment.

[0050] A method for treating chromium-containing wastewater Example 1

[0051] (1) Homogenization: Mix 1 to 5 chromium plating wastewaters with 10m 3 Chromium plating wastewater (Cr mass concentration of 30.77g / L (containing Cr5.92kmol), pH value of 4.73) was mixed and homogenized for 60min at room temperature and a rotation speed of 60rpm, and the pH value was adjusted to 0.50 with concentrated sulfuric acid to obtain 10m 3 Homogenization of chromium-containing wastewater;

[0052] (2) Reduction: In step (1), the 10m 3After adding 693.04 kg (8.88 kmol) of sodium sulfide to the homogenized chromium-containing wastewater at a stirring speed of 60 rpm, the reduction reaction was stirred for 120 min at 20 ° C and a speed of 60 rpm. The pH value of the stirring reduction reaction process was controlled to be 1.00-5.00, and the end point pH value was controlled to be 5.00, and 9.8 m 3 Trivalent chromium wastewater;

[0053] (3) Precipitation: The 9.8 m 3 The trivalent chromium wastewater was stirred and precipitated for 120 minutes at room temperature and a rotation speed of 60 rpm, and the pH value of the stirring precipitation reaction process was controlled to be 8.50. After filtration, 806.2 kg (dry basis, Cr mass content of 38.15%) of chromium-containing compounds and 9.1 m 3 Dechromized wastewater (Cr mass concentration is 10 mg / L);

[0054] (4) Evaporation and concentration: 9.1 m 3 The chromium-removed wastewater is evaporated and concentrated until the mass concentration of Cr in the concentrated liquid is 25.45 mg / L. The parameters of the evaporation and concentration are controlled as follows: the outlet temperature of the compressor is 105°C, the outlet temperature of the heater is 90°C, the evaporation temperature is 90°C, and the internal pressure is 0.070 MPa. The obtained concentrated liquid is centrifuged at 1500 rpm to obtain 182 L of chromium-containing concentrated liquid (the mass concentration of Cr is 44.54 mg / L) and 1232.0 kg of crude sodium sulfate (dry basis, the mass content of sodium sulfate is 96.80%). The chromium-containing concentrated liquid is returned to step (1) for circulation treatment.

[0055] In steps (2) and (3), the acid mist generated is sent to an absorption tower and absorbed by a sodium hydroxide aqueous solution with a pH value of 9.5.

[0056] After testing and calculation, after being treated by the embodiment of the present invention, the recovery rate of chromium in the chromium plating wastewater is 99.97%; the obtained chromium-containing compound can be used as a raw material for ferrochrome alloy or black ceramic pigment; the evaporation and concentration obtains 5.52m condensed water 3 The condensed water production rate is 55.25%, and the condensed water produced can be returned to the system for use; the obtained crude sodium sulfate can be used to purify sodium sulfate products.

[0057] A method for treating chromium-containing wastewater Example 2

[0058] (1) Homogenization: Mix 1 to 5 chromium plating wastewaters with 10m 3Chromium plating wastewater (Cr mass concentration of 25.36g / L (containing Cr4.88kmol), pH value of 4.95) was mixed and homogenized for 70min at room temperature and a rotation speed of 70rpm, and the pH value was adjusted to 0.60 with concentrated sulfuric acid to obtain 10m 3 Homogenization of chromium-containing wastewater;

[0059] (2) Reduction: In step (1), the 10m 3 After adding 430.54 kg (7.68 kmol) of sodium hydrosulfide to the homogenized chromium-containing wastewater at a stirring speed of 80 rpm, the reduction reaction was stirred for 130 min at 30 ° C and a rotation speed of 80 rpm. The pH value of the stirring reduction reaction process was controlled to be 1.00-5.16, and the end point pH value was controlled to be 5.16, and 9.7 m 3 Trivalent chromium wastewater;

[0060] (3) Precipitation: The 9.7 m 3 The trivalent chromium wastewater was stirred and precipitated for 160 minutes at room temperature and a rotation speed of 70 rpm, and the pH value of the stirring precipitation reaction process was controlled to be 9.01. After filtration, 642.0 kg (dry basis, Cr mass content of 39.48%) of chromium compounds and 9.0 m 3 Dechromized wastewater (Cr mass concentration is 9 mg / L);

[0061] (4) Evaporation and concentration: The 9.0 m 3 The chromium-removed wastewater is evaporated and concentrated until the mass concentration of Cr in the concentrated liquid is 43.81 mg / L. The parameters of the evaporation and concentration are controlled as follows: the outlet temperature of the compressor is 106°C, the outlet temperature of the heater is 95°C, the evaporation temperature is 95°C, and the internal pressure is 0.0705 MPa. The obtained concentrated liquid is centrifuged at 1400 rpm to obtain 81 L of chromium-containing concentrated liquid (the mass concentration of Cr is 79.73 mg / L) and 833.1 kg of crude sodium sulfate (dry basis, the mass content of sodium sulfate is 95.50%). The chromium-containing concentrated liquid is returned to step (1) for circulation treatment.

[0062] In steps (2) and (3), the acid mist generated is sent to an absorption tower and absorbed by a sodium hydroxide aqueous solution with a pH value of 10.0.

[0063] After testing and calculation, after being treated by the embodiment of the present invention, the recovery rate of chromium in the chromium plating wastewater is 99.97%; the obtained chromium-containing compound can be used as a raw material for ferrochrome alloy or black ceramic pigment; the evaporation and concentration obtains 7.15m3 of condensed water 3 The condensed water production rate is 71.51%, and the condensed water produced can be returned to the system for use; the obtained crude sodium sulfate can be used to purify sodium sulfate products.

[0064] A method for treating chromium-containing wastewater Example 3

[0065] (1) Homogenization: Mix 1 to 5 chromium plating wastewaters with 10m 3 Chromium plating wastewater (Cr mass concentration of 10.05g / L (containing Cr1.93kmol), pH value of 5.50) was mixed and homogenized at room temperature and rotation speed of 90rpm for 90min, and the pH value was adjusted to 0.89 with concentrated sulfuric acid to obtain 10m 3 Homogenization of chromium-containing wastewater;

[0066] (2) Reduction: In step (1), the 10m 3 After adding 386.94 kg (3.07 kmol) of sodium sulfite to the homogenized chromium-containing wastewater at a stirring speed of 90 rpm, the reduction reaction was stirred at 40 ° C and a speed of 90 rpm for 170 minutes, and the pH value of the stirring reduction reaction process was controlled to be 1.00-5.96, and the end point pH value was controlled to be 5.96, and 9.5 m 3 Trivalent chromium wastewater;

[0067] (3) Precipitation: The 9.5 m 3 The trivalent chromium wastewater was stirred and precipitated for 180 minutes at room temperature and a rotation speed of 90 rpm, and the pH value of the stirring precipitation reaction process was controlled to be 10.00. After filtration, 250.2 kg (dry basis, Cr mass content of 40.16%) of chromium compounds and 9.2 m 3 Dechromized wastewater (Cr mass concentration is 6 mg / L);

[0068] (4) Evaporation and concentration: The 9.2 m 3 The chromium-removed wastewater is evaporated and concentrated until the mass concentration of Cr in the concentrated liquid is 31.49 mg / L. The parameters of the evaporation and concentration are controlled as follows: the outlet temperature of the compressor is 107° C., the outlet temperature of the heater is 100° C., the evaporation temperature is 100° C., and the internal pressure is 0.0710 MPa. The obtained concentrated liquid is centrifuged at 1300 rpm to obtain 61 L of chromium-containing concentrated liquid (the mass concentration of Cr is 53.79 mg / L) and 726.7 kg of crude sodium sulfate (dry basis, the mass content of sodium sulfate is 98.50%). The chromium-containing concentrated liquid is returned to step (1) for circulation treatment.

[0069] In steps (2) and (3), the generated acid mist is sent to an absorption tower and absorbed by a sodium carbonate aqueous solution with a pH value of 9.80.

[0070] After testing and calculation, after being treated by the embodiment of the present invention, the recovery rate of chromium in the chromium plating wastewater is 99.98%; the obtained chromium-containing compound can be used as a raw material for ferrochrome alloy or black ceramic pigment; the evaporation and concentration obtains 7.45m3 of condensed water 3 The condensed water production rate is 74.47%, and the condensed water produced can be returned to the system for use; the obtained crude sodium sulfate can be used to purify sodium sulfate products.

[0071] A method for treating chromium-containing wastewater Example 4

[0072] (1) Homogenization: Mix 1 to 5 chromium plating wastewaters with 10m 3 Chromium plating wastewater (Cr mass concentration of 18.02g / L (containing Cr3.47kmol), pH value of 5.26) was mixed and homogenized for 120min at room temperature and a rotation speed of 100rpm, and the pH value was adjusted to 1.00 with concentrated sulfuric acid to obtain 10m 3 Homogenization of chromium-containing wastewater;

[0073] (2) Reduction: In step (1), the 10m 3 In the homogenized chromium-containing wastewater, 136.66 kg (2.73 kmol) of hydrazine hydrate was added under stirring at a speed of 100 rpm, and the reduction reaction was stirred at 80 ° C and a speed of 100 rpm for 150 minutes. The pH value of the stirring reduction reaction process was controlled to be 1.00-6.00, and the end point pH value was controlled to be 6.00, and 9.3 m 3 Trivalent chromium wastewater;

[0074] (3) Precipitation: The 9.3 m 3 The trivalent chromium wastewater was stirred and precipitated for 240 minutes at room temperature and a rotation speed of 100 rpm, and the pH value of the stirring precipitation reaction process was controlled to be 9.57. After filtration, 375.3 kg of chromium-containing compounds (dry basis, Cr mass content of 48.00%) and 8.9 m 3 Dechromized wastewater (Cr mass concentration is 8 mg / L);

[0075] (4) Evaporation and concentration: 8.9 m 3 The chromium-removed wastewater is evaporated and concentrated until the mass concentration of Cr in the concentrated liquid is 621.55 mg / L. The parameters of the evaporation and concentration are controlled as follows: the outlet temperature of the compressor is 110° C., the outlet temperature of the heater is 98° C., the evaporation temperature is 98° C., and the internal pressure is 0.0708 MPa. The obtained concentrated liquid is centrifuged at 1000 rpm to obtain 35 L of chromium-containing concentrated liquid (the mass concentration of Cr is 911.47 mg / L) and 36.4 kg of crude sodium sulfate (dry basis, the mass content of sodium sulfate is 96.50%). The chromium-containing concentrated liquid is returned to step (1) for circulation treatment.

[0076] In steps (2) and (3), the acid mist generated is sent to an absorption tower and absorbed by a sodium carbonate aqueous solution with a pH value of 9.50.

[0077] After testing and calculation, after being treated by the embodiment of the present invention, the recovery rate of chromium in the chromium plating wastewater is 99.99%; the obtained chromium-containing compound can be used as a raw material for ferrochrome alloy or black ceramic pigment; the evaporation and concentration obtains 8.79m condensed water 3 The condensed water production rate is 87.85%, and the condensed water produced can be returned to the system for use; the obtained crude sodium sulfate can be used to purify sodium sulfate products.

[0078] A method for treating chromium-containing wastewater Example 5

[0079] (1) Homogenization: Mix 1 to 5 chromium plating wastewaters with 10m 3 Chromium plating wastewater (Cr mass concentration of 20.01g / L (containing Cr3.85kmol), pH value of 5.21) was mixed and homogenized for 110min at room temperature and a rotation speed of 85rpm, and the pH value was adjusted to 0.58 with concentrated sulfuric acid to obtain 10m 3 Homogenization of chromium-containing wastewater;

[0080] (2) Reduction: In step (1), the 10m 3 After adding 177.71kg (3.17mol) of sodium hydrosulfide and 79.60kg (1.59mol) of hydrazine hydrate to the homogenized chromium-containing wastewater at a stirring speed of 85rpm, the reduction reaction was stirred at 45℃ and a speed of 85rpm for 240min, and the pH value of the stirring reduction reaction process was controlled to be 1.00-5.57, and the end point pH value was controlled to be 5.57, and 9.5m 3 Trivalent chromium wastewater;

[0081] (3) Precipitation: The 9.5 m 3 The trivalent chromium wastewater was stirred and precipitated for 200 minutes at room temperature and a rotation speed of 85 rpm, and the pH value of the stirring precipitation reaction process was controlled to be 9.77. After filtration, 442.8 kg of chromium-containing compounds (dry basis, Cr mass content of 45.18%) and 9.1 m 3 Dechromized wastewater (Cr mass concentration is 10 mg / L);

[0082] (4) Evaporation and concentration: 9.1 m 3The chromium-removed wastewater is evaporated and concentrated until the mass concentration of Cr in the concentrated liquid is 152.10 mg / L. The parameters of the evaporation and concentration are controlled as follows: the outlet temperature of the compressor is 108°C, the outlet temperature of the heater is 92°C, the evaporation temperature is 92°C, and the internal pressure is 0.0701 MPa. The obtained concentrated liquid is centrifuged at 1200 rpm to obtain 30 L of chromium-containing concentrated liquid (the mass concentration of Cr is 263.74 mg / L) and 253.3 kg of crude sodium sulfate (dry basis, the mass content of sodium sulfate is 96.55%). The chromium-containing concentrated liquid is returned to step (1) for circulation treatment.

[0083] In steps (2) and (3), the acid mist generated is sent to an absorption tower and absorbed by a sodium hydroxide aqueous solution with a pH value of 10.20.

[0084] After testing and calculation, after being treated by the embodiment of the present invention, the recovery rate of chromium in the chromium plating wastewater is 99.98%; the obtained chromium-containing compound can be used as a raw material for ferrochrome alloy or black ceramic pigment; the evaporation and concentration obtains 8.50m3 of condensed water 3 The condensed water production rate is 85.02%, and the condensed water produced can be returned to the system for use; the obtained crude sodium sulfate can be used to purify sodium sulfate products.

Claims

1. A method for treating chromium-containing wastewater, characterized in that: The following steps are involved: (1) Homogenization: Mix chromium-containing wastewater with different concentrations and chromium-containing wastewater with a pH value of 0.5 to 6.0, perform mixing and homogenization treatment, and adjust the pH value to 0.50 to 1.00 to obtain homogenized chromium-containing wastewater with a mass concentration of Cr of 10.05 to 32 g / L; (2) Reduction: adding a reducing agent to the homogenized chromium-containing wastewater obtained in step (1) under stirring, and performing a reduction reaction by stirring to obtain trivalent chromium wastewater; the temperature of the stirring reduction reaction is 15 to 80° C., the stirring speed is 60 to 100 rpm, the time is 120 to 240 min, and the pH value of the stirring reduction reaction process is controlled to be 1.00 to 6.00, and the end point pH value is controlled to be 5.00 to 6.00; (3) precipitation: subjecting the trivalent chromium wastewater obtained in step (2) to a stirring precipitation reaction, filtering, and obtaining chromium-containing compounds and dechromized wastewater; the stirring precipitation reaction is carried out at room temperature, at a stirring speed of 60 to 100 rpm, for a time of 120 to 240 min, and the pH value during the stirring precipitation reaction is controlled to be 8.50 to 10.00; (4) Evaporation and concentration: The chromium-removing wastewater obtained in step (3) is evaporated and concentrated, and the obtained concentrated solution is centrifuged to obtain a chromium-containing concentrated solution and crude salt, and the chromium-containing concentrated solution is returned to step (1) for circulation treatment.

2. The method for treating chromium-containing wastewater according to claim 1, characterized in that: In step (1), the mass concentration of Cr in the chromium-containing wastewater of different concentrations is 1 to 200 g / L; the temperature of the mixing and homogenizing treatment is room temperature, the rotation speed is 60 to 100 rpm, and the time is 60 to 120 min.

3. The method for treating chromium-containing wastewater according to claim 1 or 2, characterized in that: In step (2), the stirring speed when adding the reducing agent is 60-100 rpm; the molar ratio of the reducing agent to the chromium in the homogenized chromium-containing wastewater is 1.0-1.1:1; and the reducing agent is one or more of sodium sulfide, sodium hydrosulfide, hydrazine hydrate or sodium sulfite.

4. The method for treating chromium-containing wastewater according to claim 1 or 2, characterized in that: In steps (2) and (3), the acid mist generated enters an absorption tower and is absorbed by an aqueous solution of sodium hydroxide or sodium carbonate with a pH value of ≥9.

00.

5. The method for treating chromium-containing wastewater according to claim 3, characterized in that: In steps (2) and (3), the acid mist generated enters an absorption tower and is absorbed by an aqueous solution of sodium hydroxide or sodium carbonate with a pH value of ≥9.

00.

6. The method for treating chromium-containing wastewater according to claim 1 or 2, characterized in that: In step (4), the parameters of the evaporation concentration are controlled as follows: the outlet temperature of the compressor is 105-110°C, the outlet temperature of the heater is 90-100°C, the evaporation temperature is 90-100°C, the internal pressure is 0.070-0.071 MPa, and the mass concentration of Cr by evaporation concentration is 20-1000 mg / L; the rotation speed of the centrifuge is 1000-1500 rpm.

7. The method for treating chromium-containing wastewater according to claim 3, characterized in that: In step (4), the parameters of the evaporation concentration are controlled as follows: the outlet temperature of the compressor is 105-110°C, the outlet temperature of the heater is 90-100°C, the evaporation temperature is 90-100°C, the internal pressure is 0.070-0.071 MPa, and the mass concentration of Cr by evaporation concentration is 20-1000 mg / L; the rotation speed of the centrifuge is 1000-1500 rpm.

8. The method for treating chromium-containing wastewater according to claim 4, characterized in that: In step (4), the parameters of the evaporation concentration are controlled as follows: the outlet temperature of the compressor is 105-110°C, the outlet temperature of the heater is 90-100°C, the evaporation temperature is 90-100°C, the internal pressure is 0.070-0.071 MPa, and the mass concentration of Cr by evaporation concentration is 20-1000 mg / L; the rotation speed of the centrifuge is 1000-1500 rpm.

9. The method for treating chromium-containing wastewater according to claim 1 or 2, characterized in that: In the chromium-containing wastewater treatment device used in the method, the discharge port of the homogenizing tank is connected to the feed port of the reduction reaction tank through a pump, the discharge port of the reduction reaction tank is connected to the feed port of the chromium precipitation reaction tank through a pump, the discharge port of the chromium precipitation reaction tank is connected to the feed port of the filter press through a pump, the discharge port of the filter press is connected to the feed port of the dechromium water storage tank, the discharge port of the dechromium water storage tank is connected to the feed port at the bottom of the heater through a pump and a preheater in sequence, the discharge port at the top of the heater is connected to the feed port in the middle of the evaporator, the steam outlet at the top of the evaporator is connected to the steam inlet at the top of the heater through a compressor, the concentrated liquid discharge port at the bottom of the evaporator is connected to the feed port of the centrifuge, the discharge port of the centrifuge is connected to the feed port of the concentrated liquid intermediate tank, and the discharge port of the concentrated liquid intermediate tank is connected to the feed port of the homogenizing tank through a pump.

10. The method for treating chromium-containing wastewater according to claim 3, characterized in that: In the chromium-containing wastewater treatment device used in the method, the discharge port of the homogenizing tank is connected to the feed port of the reduction reaction tank through a pump, the discharge port of the reduction reaction tank is connected to the feed port of the chromium precipitation reaction tank through a pump, the discharge port of the chromium precipitation reaction tank is connected to the feed port of the filter press through a pump, the discharge port of the filter press is connected to the feed port of the dechromium water storage tank, the discharge port of the dechromium water storage tank is connected to the feed port at the bottom of the heater through a pump and a preheater in sequence, the discharge port at the top of the heater is connected to the feed port in the middle of the evaporator, the steam outlet at the top of the evaporator is connected to the steam inlet at the top of the heater through a compressor, the concentrated liquid discharge port at the bottom of the evaporator is connected to the feed port of the centrifuge, the discharge port of the centrifuge is connected to the feed port of the concentrated liquid intermediate tank, and the discharge port of the concentrated liquid intermediate tank is connected to the feed port of the homogenizing tank through a pump.

11. The method for treating chromium-containing wastewater according to claim 4, characterized in that: In the chromium-containing wastewater treatment device used in the method, the discharge port of the homogenizing tank is connected to the feed port of the reduction reaction tank through a pump, the discharge port of the reduction reaction tank is connected to the feed port of the chromium precipitation reaction tank through a pump, the discharge port of the chromium precipitation reaction tank is connected to the feed port of the filter press through a pump, the discharge port of the filter press is connected to the feed port of the dechromium water storage tank, the discharge port of the dechromium water storage tank is connected to the feed port at the bottom of the heater through a pump and a preheater in sequence, the discharge port at the top of the heater is connected to the feed port in the middle of the evaporator, the steam outlet at the top of the evaporator is connected to the steam inlet at the top of the heater through a compressor, the concentrated liquid discharge port at the bottom of the evaporator is connected to the feed port of the centrifuge, the discharge port of the centrifuge is connected to the feed port of the concentrated liquid intermediate tank, and the discharge port of the concentrated liquid intermediate tank is connected to the feed port of the homogenizing tank through a pump.

12. The method for treating chromium-containing wastewater according to claim 6, characterized in that: In the chromium-containing wastewater treatment device used in the method, the discharge port of the homogenizing tank is connected to the feed port of the reduction reaction tank through a pump, the discharge port of the reduction reaction tank is connected to the feed port of the chromium precipitation reaction tank through a pump, the discharge port of the chromium precipitation reaction tank is connected to the feed port of the filter press through a pump, the discharge port of the filter press is connected to the feed port of the dechromium water storage tank, the discharge port of the dechromium water storage tank is connected to the feed port at the bottom of the heater through a pump and a preheater in sequence, the discharge port at the top of the heater is connected to the feed port in the middle of the evaporator, the steam outlet at the top of the evaporator is connected to the steam inlet at the top of the heater through a compressor, the concentrated liquid discharge port at the bottom of the evaporator is connected to the feed port of the centrifuge, the discharge port of the centrifuge is connected to the feed port of the concentrated liquid intermediate tank, and the discharge port of the concentrated liquid intermediate tank is connected to the feed port of the homogenizing tank through a pump.

13. The method for treating chromium-containing wastewater according to claim 9, characterized in that: The homogenizing tank, reduction reaction tank and chromium precipitation reaction tank are equipped with agitators; the materials of the homogenizing tank, reduction reaction tank and chromium precipitation reaction tank are plastic or corrosion-resistant steel; the exhaust port of the reduction reaction tank and the exhaust port of the chromium precipitation reaction tank are both connected to the exhaust gas absorption system; the filter press is a centrifugal filter, a chamber filter press or a diaphragm filter press; the pump is a delivery pump or a filter pressure pump; a condensate drain outlet is provided on the upper part of the evaporator; the evaporator is an MVR evaporator; the exhaust gas absorption system is a water foam absorption tower device.

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