Chromium-containing wastewater treatment system for recycling carnallite

Abstract

The utility model discloses a chromium-containing wastewater treatment system capable of recycling carnallite, which comprises a concentrated chromium waste liquid treatment unit, and the concentrated chromium waste liquid treatment unit comprises a concentrated chromium waste liquid regulating tank, a reduction tank, a neutralization sedimentation tank and a sedimentation tank; an inlet of the concentrated chromium waste liquid adjusting tank is communicated with a concentrated chromium waste liquid outlet of the unit line through a concentrated chromium waste liquid pipeline; an outlet of the concentrated chromium waste liquid adjusting tank, the reduction tank, the neutralization and sedimentation tank and the sedimentation tank are sequentially communicated through pipelines; and a liquid outlet of the settling tank is communicated with the unit line through a pipeline. The device disclosed by the utility model has the beneficial effects that the supernate in the settling tank is introduced into the unit line, the carnallite in the supernate enters the unit line to be recycled, no extra carnallite is generated, no new pollution ions are introduced, no discharged wastewater is generated, the environmental pollution is effectively prevented, the addition of related chemicals in the unit line is reduced, and the resource waste is reduced.

Description

TECHNICAL FIELD

[0001] The utility model relates to wastewater treatment technology, concretely relates to a kind of chromium-containing wastewater treatment systems of miscellaneous salt recycling. BACKGROUND

[0002] Cold rolling is an important link in the steel industry, and the sodium sulfate electrolysis process in the production process of cold rolled stainless steel can dissolve the iron oxide scale generated on the surface of the steel plate. The main purpose is to remove chromium oxide in the iron oxide scale, so the electrolyte has a high salt content, and a large amount of Cr 6+ Six-valent chromium compounds can cause great pollution to water bodies, and their toxicity is 100 times that of Cr 3+ , and they are easily absorbed by the human body and accumulated in the body. Related policies have set requirements for the discharge limits of Cr 6+ and total chromium for new enterprises, and many environmentally sensitive areas currently require that chromium-containing wastewater must achieve zero discharge.

[0003] Generally, the cold rolling mill line produces dilute chromium wastewater with a total chromium concentration of 13-50 mg / L and concentrated chromium wastewater with a total chromium concentration of 150-550 mg / L. The chromium-containing wastewater treatment process in the prior art is shown in Figure 1 , the dilute chromium wastewater and concentrated chromium wastewater produced by the mill line are mixed and then enter the adjustment tank, the water in the adjustment tank enters the first and second reduction tanks to add H2SO4 and NaHSO3 to reduce Cr 6+ to Cr 3+ , and then enters the first and second neutralization tanks to add NaOH for neutralization, and then enters the flocculation and sedimentation tank to remove the generated Cr(OH)3 precipitate, and then passes through a multi-media filter to further reduce suspended solids and turbidity, and then passes through ultrafiltration and reverse osmosis to reduce the salt content of the chromium-containing wastewater. At this time, the produced water is reused. The concentrated water from reverse osmosis has too high a salt content and cannot be reused to the mill line or discharged, and needs to be further treated by evaporation crystallization process. When the COD (chemical oxygen demand) content in the wastewater is high, it will affect the quality of the salt produced by evaporation crystallization, so the COD of the incoming water must be reduced first. First, the COD in the incoming water is reduced by ozone oxidation, and then the water enters the biological aerated filter to further reduce the COD of the incoming water, and finally passes through the Ca 2+ , Mg 2+ removal resin to remove Ca 2+ , Mg 2+ , and the produced water enters the evaporation crystallization treatment to obtain miscellaneous salt Na2SO4, which is transported out for disposal.

[0004] However, the existing chromium-containing wastewater treatment process produces a large amount of miscellaneous salt that cannot be recycled, causing resource waste, and the wastewater containing miscellaneous salt is discharged, causing some pollution to the environment. SUMMARY

[0005] The utility model aims at the deficiencies of the prior art, and provides a chromium-containing wastewater treatment system for recycling miscellaneous salt, to reduce environmental pollution.

[0006] The utility model discloses a technical scheme for: a kind of miscellaneous salt recycling chromium-containing wastewater treatment system, including thick chromium waste liquid processing unit, the thick chromium waste liquid processing unit includes thick chromium waste liquid regulating pool, reduction pool, neutralization sedimentation tank and sedimentation tank;The inlet of the thick chromium waste liquid regulating pool is communicated with the thick chromium waste liquid outlet of unit line by thick chromium waste liquid pipeline, and the outlet of thick chromium waste liquid regulating pool, reduction pool, neutralization sedimentation tank and sedimentation tank are sequentially communicated by pipeline;The liquid outlet of sedimentation tank is communicated with the back liquid port of unit line by pipeline.

[0007] According to the above scheme, the thick chromium waste liquid processing unit further includes a filter press device, and the sludge outlet of the sedimentation tank is communicated with the inlet of the filter press device.

[0008] According to the above scheme, the thick chromium waste liquid processing unit further includes a filter press device, and the sludge outlet of the sedimentation tank is communicated with the inlet of the filter press device.

[0009] According to the above scheme, the thick chromium waste liquid processing unit further includes a filter press device, and the sludge outlet of the sedimentation tank is communicated with the inlet of the filter press device.

[0010] According to the above scheme, the thick chromium waste liquid processing unit further includes a filter press device, and the sludge outlet of the sedimentation tank is communicated with the inlet of the filter press device.

[0011] According to the above scheme, the thick chromium waste liquid processing unit further includes a filter press device, and the sludge outlet of the sedimentation tank is communicated with the inlet of the filter press device.

[0012] According to the above scheme, the thick chromium waste liquid processing unit further includes a filter press device, and the sludge outlet of the sedimentation tank is communicated with the inlet of the filter press device.

[0013] According to the above scheme, the thick chromium waste liquid processing unit further includes a filter press device, and the sludge outlet of the sedimentation tank is communicated with the inlet of the filter press device.

[0014] According to the above scheme, the thick chromium waste liquid processing unit further includes a filter press device, and the sludge outlet of the sedimentation tank is communicated with the inlet of the filter press device.

[0015] According to the above scheme, the thick chromium waste liquid processing unit further includes a filter press device, and the sludge outlet of the sedimentation tank is communicated with the inlet of the filter press device.

[0016] The utility model discloses the beneficial effect that:

[0017] 1. The concentrated chromium waste liquid treatment unit designed in the utility model, the supernatant in the precipitation tank is introduced into the unit line, the impurities (such as sodium sulfate generated in the treatment process) in the supernatant are introduced into the unit line for reuse, no additional impurities are generated, no new pollution ions are introduced, no external waste water is generated, environmental pollution is effectively prevented, the addition of the related reagents of the unit line is reduced, and resource waste is reduced.

[0018] 2. The concentrated chromium waste liquid treatment unit designed in the utility model adopts a filter pressing device to filter press the sludge generated by the precipitation tank, generates mud cake convenient for external transportation, and the filter pressing liquid is introduced into the unit line, and the impurities in the filter pressing liquid are introduced into the unit for reuse, so that no additional impurities are generated and the addition of the reagents of the unit line is reduced.

[0019] 3. The dilute chromium wastewater treatment unit designed in the utility model, the dilute chromium wastewater treatment unit is used for pretreating the dilute chromium wastewater of the unit, the concentrated water generated in the treatment is introduced into the concentrated chromium waste liquid treatment unit together with the concentrated chromium waste liquid from the unit line, compared with the prior art, the quality treatment mode can reduce the addition of the reagents, improve the utilization rate of the reagents, reduce the treatment cost, and is green and economical.

[0020] 4. The filter liquid generated by the filter pressing device of the dilute chromium wastewater treatment unit in the utility model is introduced into the concentrated chromium treatment unit through a filter and then introduced into the unit for reuse, and no impurities are generated. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a flow chart of the existing chromium-containing wastewater treatment technology.

[0022] Figure 2 It is a flow chart of the utility model.

[0023] Figure 3 It is a flow chart of the utility model.

[0024] Figure 2 The reference numerals in the drawings are as follows: 1, unit line; 2, concentrated chromium waste liquid pipeline; 3, concentrated chromium waste liquid adjusting tank; 4, reduction tank; 5, neutralization and precipitation tank; 6, precipitation tank; 7, filter pressing device; 8, dilute chromium wastewater pipeline; 9, adjusting tank; 10, precipitation tank; 11, filter; 12, primary raw water tank; 13, primary electrochemical concentration device; 14, filter press; and 15, secondary electrochemical concentration device. DETAILED DESCRIPTION

[0025] In order to better understand the utility model, the utility model will be further described in detail in combination with the schematic drawing.

[0026] For example, Figure 2 and Figure 3The illustrated one kind of mixed salt recycling contains chromium wastewater treatment system, including thick chromium waste liquid processing unit;The thick chromium waste liquid processing unit includes thick chromium waste liquid conditioning pool 3, reduction pool 4, neutralization precipitation tank 5, precipitation tank 6 and filter press device 7;The inlet of the thick chromium waste liquid conditioning pool 3 is communicated with the chromium-containing waste liquid outlet of the unit line 1 by thick chromium waste liquid pipeline 2, and the outlet of the thick chromium waste liquid conditioning pool 3, the neutralization precipitation tank 5, the precipitation tank 6 are sequentially communicated by pipeline;The liquid outlet of the precipitation tank 6 is communicated with the liquid return port of the unit line 1 by pipeline, and the sludge outlet of the precipitation tank 6 is communicated with the inlet of the filter press device 7, the liquid outlet of the filter press device 7 is communicated with the liquid return port of the unit line 1 by pipeline, and the mud cake generated by the filter press device 7 is transported out.

[0027] In the utility model, the supernatant of the precipitation tank 6 and the filtrate of the filter press device 7 in the thick chromium waste liquid processing unit are introduced into the unit line 1 for recycling, so that the recycling of mixed salt is realized, and no mixed salt is generated.

[0028] Preferably, the reduction pool 4 is provided with an aeration stirring device, and the reduction pool 4 is aerated by using the aeration stirring device to improve the reduction efficiency.

[0029] In the utility model, sulfuric acid is added into the thick chromium waste liquid conditioning pool 3, the thick chromium waste liquid entering the thick chromium waste liquid conditioning pool 3 is adjusted to pH 2.0-3.0 by sulfuric acid, and then enters the reduction pool 4, and a reducing agent NaHSO3 solution is added into the reduction pool 4, so that Cr 6+ in the waste liquid is reduced to Cr 3+ , and water is generated and enters the neutralization precipitation tank 5 (specifically, a NaOH neutralization precipitation tank), and Cr 3+ forms Cr (OH) 3 in the neutralization precipitation tank 5, and then enters the precipitation tank 6 for precipitation, and the supernatant (including various mixed salts such as sodium sulfate) of the precipitation tank 6 after precipitation is introduced into the unit line 1 through the liquid outlet for recycling;The sludge generated by the precipitation tank 6 enters the filter press device 7 through the sludge outlet for filter pressing treatment, and the filtrate (including mixed salts such as sodium sulfate, and the unit line is cleaned by electrolytic sodium sulfate on the surface of the steel plate, so that a large amount of Cr 6+ is stripped from the surface of the steel plate) is recycled to the unit line 1 after the concentration of the supplemented sodium sulfate is adjusted, and the mud cake is transported out for next step treatment.

[0030] Preferably, the mixed salt recycling chromium-containing wastewater treatment system further comprises a dilute chromium wastewater treatment unit, and the dilute chromium wastewater outlet of the unit line 1 is communicated with the inlet of the dilute chromium wastewater treatment unit by a dilute chromium wastewater pipeline 8, and the concentrated water outlet of the dilute chromium wastewater treatment unit is communicated with the inlet of the thick chromium waste liquid processing unit by a pipeline (specifically, the inlet of the thick chromium waste liquid conditioning pool 3).

[0031] The dilute chromium wastewater generated by the cold rolling unit line 1 firstly enters a dilute chromium wastewater treatment unit through a dilute chromium wastewater pipeline 8 for treatment, the concentrated chromium-containing wastewater generated by the dilute chromium wastewater treatment unit is merged into a concentrated chromium wastewater treatment unit, and is mixed with the concentrated chromium wastewater from the cold rolling unit line 1, and the solution generated after the treatment of the concentrated chromium wastewater treatment unit is reused in the cold rolling unit line 1; and the water generated by the dilute chromium wastewater treatment unit is introduced into other existing treatment systems for conventional recovery treatment.

[0032] In the utility model, the total chromium concentration in the dilute chromium wastewater generated by the cold rolling unit line 1 is 13-50 mg / L, and the total chromium concentration in the concentrated chromium wastewater is 150-550 mg / L. The total chromium concentration of the water generated after the treatment of the dilute chromium wastewater treatment unit is ≤5 mg / L, the total chromium concentration in the concentrated chromium-containing wastewater generated after the treatment of the dilute chromium wastewater treatment unit is 50-200 mg / L, and the total chromium concentration in the solution generated after the treatment of the concentrated chromium wastewater treatment unit is 0.1-0.5 mg / L.

[0033] Preferably, the dilute chromium wastewater treatment unit comprises an adjusting pool 9, a sedimentation pool 10, a primary raw water pool 12 and a primary electrochemical concentration device 13; the inlet of the adjusting pool 9 is communicated with the dilute chromium wastewater pipeline 8, the outlet of the adjusting pool 9, the inlet of the sedimentation pool 10, the liquid outlet of the sedimentation pool 10, the primary raw water pool 12 and the primary electrochemical concentration device 13 are sequentially communicated through pipelines, the concentrated water outlet of the primary electrochemical concentration device 13 is communicated with the inlet of the concentrated chromium wastewater treatment unit (specifically communicated with the inlet of the concentrated chromium wastewater adjusting pool 3), and the water outlet of the primary electrochemical concentration device 13 is communicated with other treatment systems for conventional recovery treatment.

[0034] Preferably, the dilute chromium wastewater treatment unit further comprises a secondary electrochemical concentration device 15; the inlet of the secondary electrochemical concentration device 15 is communicated with the water outlet of the primary electrochemical concentration device 13, and the concentrated water outlet of the secondary electrochemical concentration device 15 is communicated with the primary raw water pool 12; and the water outlet of the secondary electrochemical concentration device 15 is communicated with other treatment systems for conventional recovery treatment.

[0035] Preferably, the dilute chromium wastewater treatment unit further comprises a filter 11 arranged between the sedimentation pool 10 and the primary raw water pool 12, and the liquid outlet of the sedimentation pool 10, the filter 11 and the primary raw water pool 12 are sequentially communicated through pipelines. The filter 11 comprises a quartz sand filter and a security filter arranged in series.

[0036] Preferably, the dilute chromium wastewater treatment unit further comprises a filter press 14, the inlet of the filter press 14 is communicated with the sludge outlet of the sedimentation pool 10, the liquid outlet of the filter press 14 is communicated with the filter 11, and the sludge outlet of the filter press 14 is communicated with the outside.

[0037] The utility model discloses, the unit line 1 produces the water volume of dilute chromium waste water, after collecting, transport to the adjusting pool 9, and the waste water is treated in the homogenization in adjusting pool 9 9, then is transported to the sedimentation tank 10, and the flocculating agent is added in the sedimentation tank 10 for removing the suspended solids in dilute chromium waste water, and the sludge of sedimentation tank 10 deposits and sends into filter press 14, and the mud cake of filter press 14 produces and transports, and the filtrate (containing miscellaneous salt sodium sulfate) of filter press 14 is sent into filter 11 again;The supernatant (containing miscellaneous salt sodium sulfate) after the deposition of sedimentation tank 10 is further removed the suspended solids after filter 11, and then enters the storage and homogenization treatment in primary raw water pool 12, and the water in primary raw water pool 12 is treated by primary electrochemical concentration device 13 and removes 70% or so ions (Cr 6+ 、Cr 3+ 、Na + 、SO4 2— , and the concentrated water (that is, the salt-containing concentrated water) generated is entered into the concentrated chromium waste liquid adjusting pool 3, and the water produced (that is, the solution after removing ions) is entered into the secondary electrochemical concentration device 15 for further desalination treatment, and the concentrated water (that is, the salt-containing concentrated water, and the total chromium concentration is 13-50 mg / L) generated by the secondary electrochemical concentration device 15 is entered into the primary raw water pool 12 for treatment; and the water produced (the total chromium concentration is ≤5 mg / L) obtained by the secondary electrochemical concentration device 15 is entered into other treatment systems for conventional recovery treatment.

[0038] In the utility model, the pipes are connected between the devices.

[0039] Embodiment

[0040] The water volume of dilute chromium waste water generated by each unit line 1 of a certain steel plant is 30 m 3 / h, the water volume of concentrated chromium waste liquid is 5 m 3 / h, and the water quality indexes of the two are shown in Table 1.

[0041] Table 1: Water quality of dilute chromium waste water and concentrated chromium waste liquid

[0042] Detection item Unit Dilute chromium wastewater detection value Concentrated chromium wastewater detection value PH 7～8 7～8 Conductivity μs / cm 1500-8000 20000～120000 Turbidity NTU 500～700 7500～9000 Suspended solids mg / L 200～500 3000～5500 Total hardness mg / L 100～500 1200～5500 Cl - ]]> mg / L 1000～5000 10000～50000 Total iron mg / L 0.5～10 5～100 Hexavalent chromium mg / L 12～50 150～480 Total chromium mg / L 13～50 150～550 Chemical oxygen demand COD mg / L 30～100 300～1300 Total salt content mg / 750～5000 10000～60000

[0043] The dilute chromium waste water and the concentrated chromium waste liquid are treated by adopting the utility model, and the specific treatment process is as follows:

[0044] The dilute chromium waste water is collected and then entered into a dilute chromium waste water treatment unit, is treated in the homogenization in adjusting pool 9, and the effluent of adjusting pool 9 is added with flocculating agent to remove the precipitate in the incoming water, and the effluent after the precipitation is filtered by filter 11 (firstly filtered by a quartz sand filter to remove the suspended solids and turbidity in the incoming water, and the effluent of the quartz sand filter is further filtered by a security filter) and then entered into primary raw water pool 12; and the water in primary raw water pool 12 is treated by primary electrochemical concentration device 13 to remove 70% of the ions (Cr6+ , Cr 3+ , Na + , SO4 2— ), at this time the effluent conductivity is about 2000-3000 us / cm, the total chromium concentration is ≤15 mg / L, the effluent of the first electrochemical concentration device 13 enters the second electrochemical concentration device 15 for further capacitive desalination treatment, the effluent after the second desalination treatment has a conductivity of ≤1000 us / cm and a total chromium concentration of ≤5 mg / L, and the effluent enters other treatment systems for treatment and reuse.

[0045] The concentrated water of the first electrochemical concentration device 13 has a conductivity of about 40000-50000 us / cm, and a water volume of about 6 m 3 / h (adjustable), and the concentrated water enters the concentrated chromium waste liquid adjusting tank 3 and is treated at the same time as the concentrated chromium waste liquid generated by the unit line 1, at this time, the waste sulfuric acid added to the unit line 1 is used for acid pre-adjustment, and is lifted by a pump into the reduction tank 4 (the reduction tank 4 is provided with multiple-stage reduction tanks, and the number of stages can be adjusted according to reduction requirements and on-site water quality), NaHSO3 is added in a pH environment of 2.0-3.0 to reduce Cr 6+ to Cr 3+ , and then the wastewater enters the neutralization and precipitation tank 5, NaOH is added to adjust the pH to 7.0-9.0, so that the wastewater reaches the optimal pH value required for metal ion co-precipitation; the wastewater that has exited the neutralization and precipitation tank 5 has metal hydroxide Cr(OH)3 precipitated, the wastewater enters the precipitation tank 6 for precipitation, if the site space is sufficient, a coagulation and flocculation tank can also be added to add a flocculating agent to improve the precipitation effect; the supernatant after precipitation is reused to the unit line 1, the sludge produced by precipitation is sent to the filter press device 7, the filtered liquid is reused to the unit line 1, and the mud cake is transported out for treatment.

[0046] In this embodiment, the specific functions of each device are as follows:

[0047] a. The adjusting tank 9: homogenizes the water from the unit line 1;

[0048] b. The precipitation tank 10: used for removing suspended solids in the water body;

[0049] c. The filter 11: reduces the turbidity of the incoming water to meet the water quality requirements of the electrochemical concentration device;

[0050] d. The primary electrochemical concentration device 13 and the secondary electrochemical concentration device 15: both are capacitive desalination devices based on capacitive desalination technology, the basic principle of which is to apply an external voltage to an electrode-solution interface to form a double-electron layer. Raw water flows into the electrode-solution interface from one end of the electro-adsorption water treatment module and flows out from the other end. When a positive voltage is applied to the module, the anions and cations in the raw water move towards the anode and cathode respectively, and are adsorbed on the porous carbon material on the positive and negative electrode surfaces, so that the concentration of salts (such as Cr 6+ , Cr 3+ , Na + , SO4 2— ), charged colloidal particles and other point substances in the solution is reduced, organic matter is decomposed, and thus desalination and purification of water are achieved. When adsorption saturation is reached, the ions adsorbed on the electrode plate are released into the regenerated solution by applying a reverse external voltage or reversing the power supply, and the electrode plate after desorption can be reused. The core electrode material of the electro-adsorption desalination technology is inert carbon material, which is resistant to strong acid and strong base. The desalination device adopts a channel type structure (the channel width is millimeter level), which is not easy to block. In the utility model, the primary electrochemical concentration device 13 and the secondary electrochemical concentration device 15 are mature devices in the industry, and the structure and function are the same as the existing ones, which will not be described here.

[0051] e. The concentrated chromium waste liquid adjusting tank 3: uses waste sulfuric acid generated in the factory to adjust the pH of the wastewater, saving cost;

[0052] f. The reduction tank 4: Cr 6+ is reduced to Cr 3+ by adding NaHSO3. An aeration stirring device can also be added in the reduction tank 4;

[0053] g. The neutralization and precipitation tank 5: NaOH is added to react with Cr 3+ to generate Cr(OH)3 precipitation;

[0054] h. The precipitation tank 6: a flocculating agent such as polyacrylamide is added to enhance the precipitation effect;

[0055] i. The filter press device 7: the mud cake generated by the filter press 14 is transported and disposed, and the filtered liquid is reused to the unit line 1.

[0056] Through cost analysis of different chromium-containing wastewater treatment processes for this steel plant, as described above, the dilute chromium wastewater 30m 3 / h and the concentrated chromium waste liquid 5m 3 / h are mixed and treated by the traditional process, and the total amount is 35m 3The initial investment cost per ton of water is 800,000 yuan, with a total investment cost of 28 million yuan and an operating cost of 20-30 yuan per ton. In contrast, the total investment cost using the technology described in this invention is 12 million yuan, with an operating cost of 10-15 yuan per ton. Comparing investment and operating costs, for the same treatment scale, this invention saves 16 million yuan in investment costs and 10-20 yuan per ton in operating costs. Compared to traditional processes, this invention has significant advantages in both investment and operating costs.

[0057] In this invention, the concentrated chromium waste liquid and dilute chromium wastewater generated by unit line 1 are treated by this process, and the resulting sodium sulfate, filtrate, and supernatant are recycled back to unit line 1, forming a complete recycling cycle. This achieves near-zero discharge of chromium-containing wastewater, with no external wastewater generated. The system produces no impurities; Cr is reduced by NaHSO3. 6+ The sodium sulfate and Cr produced in the process 3+ , for subsequent Cr 3+ Precipitation creates conditions, and the sodium sulfate generated during the reaction can be introduced into unit line 1 for reuse, recycling sodium sulfate in wastewater and reducing reagent usage; the concentrated water from the primary electrochemical concentration unit 13 is mixed with the concentrated chromium waste liquid from unit line 1 for further treatment, and the permeate from the primary electrochemical concentration unit 13 is then treated in the secondary electrochemical concentration unit 15, separating the concentrated and dilute water for green and economical treatment; highly toxic Cr 6+ Reduced to Cr by NaHSO3 3+ Then it enters the neutralization sedimentation tank 5, without the introduction of new polluting ions, thus reducing environmental pollution. The system has the advantages of low investment and operating costs, green economy, no introduction of polluting ions, recycling of sodium sulfate in wastewater, good concentration effect, and high sedimentation efficiency, which is of great significance for the resource utilization of chromium-containing wastewater.

[0058] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0059] Finally, it should be noted that the above are merely preferred embodiments of the present utility model and are not intended to limit the present utility model. Although the present utility model has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A chromium-containing wastewater treatment system for the recovery of a hetero salt, characterized by, The concentrated chromium waste liquid treatment unit comprises a concentrated chromium waste liquid adjusting tank, a reduction tank, a neutralization and precipitation tank and a precipitation tank; the inlet of the concentrated chromium waste liquid adjusting tank is communicated with the concentrated chromium waste liquid outlet of the unit line through a concentrated chromium waste liquid pipeline, and the outlet of the concentrated chromium waste liquid adjusting tank, the reduction tank, the neutralization and precipitation tank and the precipitation tank are sequentially communicated through pipelines; the liquid outlet of the precipitation tank is communicated with the liquid return port of the unit line through a pipeline.

2. The chromium-containing wastewater treatment system for zwitterion recycling according to claim 1, characterized by, The concentrated chromium waste liquid treatment unit further comprises a filter pressing device, and the sludge outlet of the precipitation tank is communicated with the inlet of the filter pressing device, and the liquid outlet of the filter pressing device is communicated with the liquid return port of the unit line through a pipeline.

3. The chromium-containing wastewater treatment system for zwitterion recycling according to claim 2, characterized by, The dilute chromium waste water treatment unit is further provided, and the dilute chromium waste water outlet of the unit line is communicated with the inlet of the dilute chromium waste water treatment unit through a dilute chromium waste water pipeline, and the concentrated water outlet of the dilute chromium waste water treatment unit is communicated with the inlet of the concentrated chromium waste liquid adjusting tank through a pipeline.

4. The chromium-containing wastewater treatment system for zwitterion recycling according to claim 3, characterized by, The dilute chromium waste water treatment unit comprises an adjusting tank, a precipitation tank, a primary raw water tank and a primary electrochemical concentration device; the inlet of the adjusting tank is communicated with the dilute chromium waste water pipeline, the adjusting tank, the precipitation tank, the primary raw water tank and the primary electrochemical concentration device are sequentially communicated through pipelines, and the concentrated water outlet of the primary electrochemical concentration device is communicated with the inlet of the concentrated chromium waste liquid adjusting tank.

5. The chromium-containing wastewater treatment system for zwitterion recycling according to claim 4, characterized by, The dilute chromium waste water treatment unit further comprises a secondary electrochemical concentration device; the inlet of the secondary electrochemical concentration device is communicated with the water production outlet of the primary electrochemical concentration device, and the concentrated water outlet of the secondary electrochemical concentration device is communicated with the primary raw water tank.

6. The chromium-containing wastewater treatment system for zwitterion recycling according to claim 5, characterized by The dilute chromium waste water treatment unit further comprises a filter arranged between the precipitation tank and the primary raw water tank, and the liquid outlet of the precipitation tank, the filter and the primary raw water tank are sequentially communicated through pipelines.

7. The chromium-containing wastewater treatment system for zwitterion recycling according to claim 5, wherein The dilute chromium waste water treatment unit further comprises a filter pressing device, and the inlet of the filter pressing device is communicated with the sludge outlet of the precipitation tank.

8. The chromium-containing wastewater treatment system for zwitterion recycling according to claim 7, characterized by, The liquid outlet of the filter pressing device is communicated with the filter.

9. The chromium-containing wastewater treatment system for zwitterion recycling according to claim 1, wherein The reduction tank is provided with an aeration stirring device.

10. The chromium-containing wastewater treatment system for zwitterion recycling according to claim 6, characterized by, The filter comprises a quartz sand filter and a security filter arranged in series.

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