Device and process for removing hexavalent chromium ions in water

Abstract

The device comprises a positive electrode reaction box, a negative electrode reaction box, an electric flocculation reaction box and a sedimentation tank, a graphite plate A and a graphite plate B are arranged in the positive electrode reaction box, saline water is injected into the positive electrode reaction box, a porous carbon material is arranged in the negative electrode reaction box, and the electric flocculation reaction box and the sedimentation tank are connected through a pipeline. A graphite plate C is laid at the bottom of the negative electrode reaction box and connected with a graphite plate B. The buffer area is connected with an electric flocculation reaction box, an iron pole plate array is arranged in the electric flocculation reaction box, iron pole pieces on the two edges of the iron pole plate array are connected with the positive electrode and the negative electrode of a second direct-current power source respectively, and the bottom of the electric flocculation reaction box is connected with a sedimentation tank. According to the method, hexavalent chromium ions in water can be removed only through electricity and a small amount of iron element, reducing agent chemicals and acid and alkali agents used for treating hexavalent chromium in a traditional process are greatly reduced, and the salt content of effluent is far lower than that of the traditional treatment process.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, in particular to a device and a process for removing hexavalent chromium ions from water. Background Art

[0002] With the rapid development of modern industry, environmental problems have gradually affected the normal life and development of human beings. Among them, heavy metal pollution is one of the most important pollutions in the industry. Among heavy metal pollutants, hexavalent chromium ions are common toxic heavy metals in wastewater, and common sources of cadmium-contaminated wastewater are electroplating, metallurgy, battery manufacturing and other industries. How to achieve economical, environmentally friendly and excellent adsorbents is one of the key factors in the adsorption treatment of wastewater containing hexavalent chromium ions.

[0003] The existing hexavalent chromium ion removal process uses a reducing agent, such as sodium bisulfate, for reduction. However, sodium bisulfate requires an acidic or alkaline environment, requires a large amount of acidic or alkaline reagents, and the salt content of the effluent is relatively high.

[0004] Therefore, we propose a device and process for removing hexavalent chromium ions in water in order to solve the above problems. Summary of the invention

[0005] The object of the present invention is to provide a device and process for removing hexavalent chromium ions in water, so as to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a device for removing hexavalent chromium ions from water, comprising: a positive electrode reaction box, a negative electrode reaction box, an electric flocculation reaction box and a sedimentation tank, wherein the positive and negative electrode reaction boxes and the negative electrode reaction box are all connected to a DC power supply 1, and the electric flocculation reaction box is connected to a DC power supply 2;

[0007] The positive electrode reaction box is provided with a graphite plate A and a graphite plate B, and a plurality of graphite plates A and B are provided, and the graphite plates A and B are zero-contact, the graphite plate A is connected to the positive electrode of a DC power supply, and salt water is injected into the positive electrode reaction box, and the salt water immerses the graphite plates A and B, and the positive electrode reaction box is provided with an exhaust valve, a pressure gauge, a water supply port and a drain port A;

[0008] The negative electrode reaction box is provided with a porous carbon material, the sponge structure graphite is connected to the negative electrode of the DC power supply, the bottom of the negative electrode reaction box is paved with a graphite plate C, the graphite plate C is connected to the graphite plate B, and the graphite plate C is connected to the negative electrode of the DC power supply;

[0009] The negative electrode reaction box is provided with an exhaust valve, a water inlet is provided at the bottom, the negative electrode reaction box is provided with a water outlet B, the water outlet B is connected to the buffer zone, the bottom of the buffer zone is provided with a water outlet C, and the water outlet C is connected to the electric flocculation reaction box;

[0010] An iron plate array is arranged in the electro-flocculation reaction box, and the iron plates at the two edges of the iron plate array are respectively connected to the positive and negative electrodes of the second DC power supply. A water outlet D is arranged at the bottom of the electro-flocculation reaction box, and the water outlet D is connected to the sedimentation tank.

[0011] Preferably, the porous carbon material comprises graphite sponge, graphene sponge, graphite felt, and carbon material particle filler.

[0012] Preferably, the number of the iron electrode array plates is not less than three, and the distance between the iron electrode plates is within 5-15 mm.

[0013] Preferably, the buffer zone and the top of the flocculation reaction box are porous breathable cover plates.

[0014] The process of removing hexavalent chromium ions from water is as follows:

[0015] S1: The cathode reaction box is filled with salt water, graphite plate A and graphite plate B are completely immersed in the salt water and are not in contact with each other, and graphite plate A in the cathode reaction box is connected to the positive electrode of an external DC power supply through a cable;

[0016] S2: Raw water containing hexavalent chromium enters the negative electrode reaction box through the water inlet between the sponge carbon negative electrode and the bottom graphite plate positive electrode, and rises upward through the sponge carbon negative electrode and overflows into the buffer zone through the water outlet B;

[0017] S3: 70% to 90% of the hexavalent chromium in the water passing through the sponge carbon negative electrode is reduced to trivalent chromium, and enters the electro-flocculation reaction box through the bottom outlet C in the buffer zone, and rises upward and passes through the iron plate array in the electro-flocculation reaction box;

[0018] S4: The remaining hexavalent chromium in the water is completely reduced to trivalent chromium in the electrocoagulation reaction box. All trivalent chromium turns into chromium hydroxide floccules, which overflow from the top of the iron plate array and enter the sedimentation tank through the outlet D. The solid-liquid separation is completed in the sedimentation tank. The total chromium content of the discharged clear liquid is <0.5mg / L, and the hexavalent chromium content is <0.1mg / L. The chromium hydroxide and ferric hydroxide solids are discharged through the muddy water.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] Only electricity and a small amount of iron are needed to remove hexavalent chromium ions from water, which greatly reduces the reducing chemicals, acid and alkali agents used in traditional processes to treat hexavalent chromium, and the salt content of the effluent is much lower than that of traditional treatment processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the present invention;

[0022] Figure 2 It is a side sectional view of the positive electrode reaction box in the present invention;

[0023] Figure 3 A top view of the positive electrode reaction box of the present invention;

[0024] Figure 4 It is a side sectional view of the negative electrode reaction box in the present invention;

[0025] Figure 5 It is a top view of the negative electrode reaction box in the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] See also Figure 1-5 , the present invention provides a technical solution: a device and process for removing hexavalent chromium ions from water, comprising: a positive electrode reaction box, a negative electrode reaction box, an electric flocculation reaction box and a sedimentation tank, wherein the positive and negative electrode reaction boxes and the negative electrode reaction box are all connected to a DC power supply 1, and the electric flocculation reaction box is connected to a DC power supply 2;

[0028] A graphite plate A and a graphite plate B are provided in the positive electrode reaction box. There are several graphite plates A and B, and the graphite plates A and B have zero contact. The graphite plate A is connected to the positive electrode of a DC power supply. Salt water is injected into the positive electrode reaction box, and the salt water immerses the graphite plates A and B. The positive electrode reaction box is provided with an exhaust valve, a pressure gauge, a water supply port and a drain port A. The positive electrode will react with oxidation water to generate bubbles, which are discharged from the exhaust valve.

[0029] The surface reaction of the graphite electrode in the positive electrode reaction box is as follows:

[0030] 4H2O-4e - →O2+4OH -

[0031] A porous carbon material is provided in the negative electrode reaction box. In this embodiment, the porous carbon material is a graphite sponge, and its specific surface area cannot be less than 3 square meters per gram. The sponge-structured graphite is connected to the negative electrode of a DC power supply, and 70% to 90% of the hexavalent chromium in the water passing through the sponge carbon negative electrode is reduced to trivalent chromium;

[0032] A graphite plate C is laid flat on the bottom of the negative electrode reaction box, the graphite plate C is connected to the graphite plate B, and the graphite plate C is connected to the negative electrode of a DC power supply;

[0033] An exhaust valve is provided on the negative electrode reaction box, and a water inlet is provided at the bottom, the water inlet is located below the sponge structure graphite, and a water outlet B is provided in the negative electrode reaction box, the water outlet B is connected to the buffer zone, and a water outlet C is provided at the bottom of the buffer zone, and the water outlet C is connected to the electric flocculation reaction box. The water reduced by the sponge structure graphite enters the electric flocculation reaction box through the water outlet C of the buffer zone, and rises through the iron plate array;

[0034] The surface reaction of the sponge-structured graphite electrode in the negative electrode reaction box is as follows:

[0035] Cr2O7 2- +14H + +6e - →2Cr 3+ +7H2O

[0036] HCrO 4- +4H + +3e - →Cr 3+ +4H2O

[0037] 2H2O+2e - →H2+2HO -

[0038] The above formula can be simplified to:

[0039] Cr 6+ +3e - →Cr 3+

[0040] 2H + +e - →H2

[0041] An iron plate array is provided in the electro-flocculation reaction box, the number of plates in the iron plate array is not less than three, the iron plates at the two edges of the iron plate array are respectively connected to the positive and negative poles of the DC power supply 2, and a water outlet D is provided at the bottom of the electro-flocculation reaction box, and the water outlet D is connected to the sedimentation tank.

[0042] The distance between the iron plates should be within 5-15mm. The remaining hexavalent chromium in the water is completely reduced to trivalent chromium in the electrocoagulation reaction box. All trivalent chromium turns into chromium hydroxide floccules, which overflow from the top of the iron plate array and enter the sedimentation tank through the outlet D. Solid-liquid separation is completed in the sedimentation tank. The total chromium content of the discharged clear liquid is <0.5mg / L, and the hexavalent chromium content is <0.1mg / L. Chromium hydroxide and iron hydroxide solids are discharged through muddy water.

[0043] The positive electrode reaction of the iron plate in the electrocoagulation reaction box is as follows:

[0044] Fe-2e - →Fe 2+

[0045] Cr6+ +3Fe 2+ →Cr 3+ +3Fe 3+

[0046] 2H2O+2e - →H2+2HO -

[0047] Cr 3+ +3OH - →Cr(OH)3

[0048] Fe 3+ +3OH - →Fe(OH)3

[0049] The reaction of the iron plate cathode in the electrocoagulation reaction box is as follows:

[0050] Cr 6+ +3e - →Cr 3+

[0051] 4H2O-4e - →O2+4OH -

[0052] Cr 3+ +3OH - →Cr(OH)3

[0053] Fe 3+ +3OH - →Fe(OH)3

[0054] The top of the buffer zone and the flocculation reaction box are porous breathable covers.

[0055] The process of removing hexavalent chromium ions using the above device is as follows:

[0056] first step:

[0057] The positive electrode reaction box is filled with salt water, and the graphite plate A and the graphite plate B are completely immersed in the salt water without contacting each other. The graphite plate A in the positive electrode reaction box is connected to the positive electrode of the external DC power supply through a cable;

[0058] Step 2:

[0059] The raw water containing hexavalent chromium enters the negative electrode reaction box through the water inlet between the sponge carbon negative electrode and the bottom graphite plate positive electrode, and rises upward through the sponge carbon negative electrode and overflows into the buffer zone through the water outlet B;

[0060] Step 3:

[0061] 70% to 90% of the hexavalent chromium in the water passing through the sponge carbon negative electrode is reduced to trivalent chromium, and enters the electro-flocculation reaction box through the bottom water outlet C in the buffer zone, and rises upward and passes through the iron plate array in the electro-flocculation reaction box;

[0062] Step 4:

[0063] The remaining hexavalent chromium in the water is completely reduced to trivalent chromium in the electrocoagulation reaction box. All trivalent chromium turns into chromium hydroxide floccules, which overflow from the top of the iron plate array and enter the sedimentation tank through the outlet D. The solid-liquid separation is completed in the sedimentation tank. The total chromium content of the discharged clear liquid is <0.5mg / L, and the hexavalent chromium content is <0.1mg / L. The chromium hydroxide and ferric hydroxide solids are discharged through the muddy water.

[0064] A graphite sponge with a surface area of ​​3.1-3.7 square meters / gram was used to treat the raw water of a certain electroplating plant. The experiment was conducted by applying a voltage of 20-50V and a current of 1.5-2A. The data are shown in the following table:

[0065]

[0066] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0067] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A device for removing hexavalent chromium ions from water, characterized in that: include: A positive electrode reaction box, a negative electrode reaction box, an electric flocculation reaction box and a sedimentation tank, wherein the positive and negative electrode reaction boxes and the negative electrode reaction box are all connected to a DC power supply 1, and the electric flocculation reaction box is connected to a DC power supply 2; The positive electrode reaction box is provided with a graphite plate A and a graphite plate B, and a plurality of graphite plates A and B are provided, and the graphite plates A and B are zero-contact, the graphite plate A is connected to the positive electrode of a DC power supply, and salt water is injected into the positive electrode reaction box, and the salt water immerses the graphite plates A and B, and the positive electrode reaction box is provided with an exhaust valve, a pressure gauge, a water supply port and a drain port A; The negative electrode reaction box is provided with a porous carbon material, the sponge structure graphite is connected to the negative electrode of the DC power supply, the bottom of the negative electrode reaction box is paved with a graphite plate C, the graphite plate C is connected to the graphite plate B, and the graphite plate C is connected to the negative electrode of the DC power supply; The negative electrode reaction box is provided with an exhaust valve, a water inlet is provided at the bottom, the negative electrode reaction box is provided with a water outlet B, the water outlet B is connected to the buffer zone, the bottom of the buffer zone is provided with a water outlet C, and the water outlet C is connected to the electric flocculation reaction box; An iron plate array is arranged in the electro-flocculation reaction box, and the iron plates at the two edges of the iron plate array are respectively connected to the positive and negative electrodes of the second DC power supply. A water outlet D is arranged at the bottom of the electro-flocculation reaction box, and the water outlet D is connected to the sedimentation tank.

2. A device for removing hexavalent chromium ions from water according to claim 1, characterized in that: The porous carbon material comprises graphite sponge, graphene sponge, graphite felt, and carbon material particle fillers.

3. The device for removing hexavalent chromium ions from water according to claim 1, characterized in that: The number of the iron plate array plates is not less than three, and the distance between the iron plates is within 5-15 mm.

4. The device for removing hexavalent chromium ions from water according to claim 1, characterized in that: The buffer zone and the top of the flocculation reaction box are porous air-permeable cover plates.

5. A process for removing hexavalent chromium ions from water according to claim 1, characterized in that: The process steps are as follows: S1: The cathode reaction box is filled with salt water, graphite plate A and graphite plate B are completely immersed in the salt water and are not in contact with each other, and graphite plate A in the cathode reaction box is connected to the positive electrode of an external DC power supply through a cable; S2: Raw water containing hexavalent chromium enters the negative electrode reaction box through the water inlet between the sponge carbon negative electrode and the bottom graphite plate positive electrode, and rises upward through the sponge carbon negative electrode and overflows into the buffer zone through the water outlet B; S3: 70% to 90% of the hexavalent chromium in the water passing through the sponge carbon negative electrode is reduced to trivalent chromium, and enters the electro-flocculation reaction box through the bottom outlet C in the buffer zone, and rises upward and passes through the iron plate array in the electro-flocculation reaction box; S4: The remaining hexavalent chromium in the water is completely reduced to trivalent chromium in the electrocoagulation reaction box. All trivalent chromium turns into chromium hydroxide floccules, which overflow from the top of the iron plate array and enter the sedimentation tank through the outlet D. The solid-liquid separation is completed in the sedimentation tank. The total chromium content of the discharged clear liquid is <0.5mg / L, and the hexavalent chromium content is <0.1mg / L. The chromium hydroxide and ferric hydroxide solids are discharged through the muddy water.

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