An apparatus and process for removing hexavalent chromium ions from water

Abstract

This invention discloses an apparatus and process for removing hexavalent chromium ions from water, comprising: a positive electrode reaction chamber, a negative electrode reaction chamber, an electrocoagulation reaction chamber, and a sedimentation tank. The positive electrode reaction chamber contains graphite plates A and B, and is filled with brine. The negative electrode reaction chamber contains porous carbon material, with a sponge-structured graphite plate connected to the negative electrode of a DC power supply. Graphite plate C is laid flat at the bottom of the negative electrode reaction chamber and connected to graphite plate B. A buffer zone is connected to the electrocoagulation reaction chamber, which contains an array of iron electrodes. The iron electrodes at the two edges of the array are connected to the positive and negative electrodes of a second DC power supply. The bottom of the electrocoagulation reaction chamber is connected to the sedimentation tank. This invention requires only electricity and a small amount of iron to remove hexavalent chromium ions from water, significantly reducing the use of reducing agents, chemicals, acids, and alkalis in traditional hexavalent chromium treatment processes, and producing effluent with a salt content far lower than that of traditional treatment processes.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to an apparatus and process for removing hexavalent chromium ions from water. Background Technology

[0002] With the rapid development of modern industry, environmental problems have gradually affected people's normal lives and development. Among them, heavy metal pollution is one of the most concerning industrial pollutants. Hexavalent chromium ions are a common toxic heavy metal in wastewater, while cadmium-contaminated wastewater commonly originates from industries such as electroplating, metallurgy, and battery manufacturing. Developing an economical, environmentally friendly adsorbent with excellent adsorption performance is one of the key factors in the adsorption treatment of wastewater containing hexavalent chromium ions.

[0003] Existing hexavalent chromium ion removal processes use reducing agents, such as sodium bisulfate, which requires acidic or alkaline environments, necessitates large amounts of acid and alkali reagents, and results in high salinity in the effluent.

[0004] Therefore, we propose an apparatus and process for removing hexavalent chromium ions from water in order to solve the problems mentioned above. Summary of the Invention

[0005] The purpose of this invention is to provide an apparatus and process for removing hexavalent chromium ions from water, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an apparatus for removing hexavalent chromium ions from water, comprising: a positive electrode reaction chamber, a negative electrode reaction chamber, an electrocoagulation reaction chamber, and a sedimentation tank, wherein the positive and negative electrode reaction chambers and the negative electrode reaction chamber are both connected to a DC power supply one, and the electrocoagulation reaction chamber is connected to a DC power supply two.

[0007] The positive electrode reaction box is equipped with graphite plate A and graphite plate B, and there are several graphite plates A and B. Graphite plates A and B are in zero contact. Graphite plate A is connected to the positive terminal of DC power supply A. Salt water is injected into the positive electrode reaction box, and the salt water submerges graphite plates A and B. The positive electrode reaction box is equipped with an exhaust valve, a pressure gauge, a water inlet, and a drain outlet A.

[0008] The negative electrode reaction box is equipped with porous carbon material, and the sponge structure graphite is connected to the negative electrode of DC power supply one. Graphite plate C is laid flat at the bottom of the negative electrode reaction box. Graphite plate C is connected to graphite plate B and is connected to the negative electrode of DC power supply one.

[0009] The negative electrode reaction box is equipped with an exhaust valve and a water inlet at the bottom. The negative electrode reaction box is equipped with a water outlet B, which is connected to a buffer zone. The bottom of the buffer zone is equipped with a water outlet C, which is connected to an electrocoagulation reaction box.

[0010] The electrocoagulation reaction chamber is equipped with an iron electrode plate array. The iron electrode plates on both edges of the iron electrode plate array are respectively connected to the positive and negative terminals of DC power supply two. The bottom of the electrocoagulation reaction chamber is equipped with an outlet D, which is connected to a 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 iron electrode array plates is not less than three, and the spacing between the iron electrode plates is within 5-15mm.

[0013] Preferably, the buffer zone and the top of the flocculation reaction chamber are porous and breathable covers.

[0014] The process for removing hexavalent chromium ions from water involves the following steps:

[0015] S1: The positive electrode reaction chamber is filled with brine. Graphite plate A and graphite plate B are completely immersed in the brine and do not come into contact with each other. Graphite plate A in the positive electrode reaction chamber is connected to the positive terminal of an external DC power supply through a cable.

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

[0017] S3: 70% to 90% of the hexavalent chromium in the water passing through the carbon negative electrode of the sponge is reduced to trivalent chromium. It enters the electrocoagulation reaction box through the bottom outlet C in the buffer zone and rises upward through the iron electrode array in the electrocoagulation reaction box.

[0018] S4: The remaining hexavalent chromium in the water is completely reduced to trivalent chromium in the electrocoagulation reaction tank. All trivalent chromium becomes chromium hydroxide flocculent, which overflows from above the iron electrode array and enters the sedimentation tank through 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. The solid chromium hydroxide and iron hydroxide are discharged through mud and water.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] Only electricity and a small amount of iron are needed to remove hexavalent chromium ions from water, greatly reducing the use of reducing agents, chemicals, acids, and alkalis in traditional hexavalent chromium treatment processes, and the salinity of the effluent is far lower than that of traditional treatment processes. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the present invention;

[0022] Figure 2 This is a side sectional view of the positive electrode reaction chamber in this invention;

[0023] Figure 3 This is a top view of the positive electrode reaction chamber in this invention;

[0024] Figure 4 This is a side sectional view of the negative electrode reaction chamber in this invention;

[0025] Figure 5 This is a top view of the negative electrode reaction chamber in this invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Please see Figure 1-5 The present invention provides a technical solution: an apparatus and process for removing hexavalent chromium ions from water, comprising: a positive electrode reaction box, a negative electrode reaction box, an electrocoagulation reaction box and a sedimentation tank, wherein the positive and negative electrode reaction boxes and the negative electrode reaction box are both connected to a DC power supply one, and the electrocoagulation reaction box is connected to a DC power supply two.

[0028] The positive electrode reaction chamber contains graphite plates A and B, with several of each. Graphite plates A and B are in zero contact. Graphite plate A is connected to the positive terminal of DC power supply A. Salt water is injected into the positive electrode reaction chamber, submerging graphite plates A and B. The positive electrode reaction chamber is equipped with an exhaust valve, a pressure gauge, a water inlet, and a drain outlet A. An oxidation reaction occurs at the positive electrode, producing bubbles that are discharged from the exhaust valve.

[0029] The reaction on the surface of the graphite electrode inside the positive electrode reaction chamber is as follows:

[0030] 4H₂O - 4e - →O2+4OH -

[0031] The negative electrode reaction chamber is equipped with porous carbon material. In this embodiment, the porous carbon material is graphite sponge, and its specific surface area is not less than 3 square meters per gram. The sponge-structured graphite is connected to the negative electrode of DC power supply one. 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 at the bottom of the negative electrode reaction chamber. Graphite plate C is connected to graphite plate B. Graphite plate C is connected to the negative terminal of DC power supply one.

[0033] The negative electrode reaction box is equipped with an exhaust valve and a water inlet at the bottom. The water inlet is located below the sponge structure graphite. The negative electrode reaction box is equipped with an outlet B, which is connected to a buffer zone. The bottom of the buffer zone is equipped with an outlet C, which is connected to the electrocoagulation reaction box. The water after being reduced by the sponge structure graphite enters the electrocoagulation reaction box through the outlet C of the buffer zone and rises through the iron electrode plate array.

[0034] The reaction on the surface of the sponge-structured graphite electrode inside the negative electrode reaction chamber 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] The electrocoagulation reaction chamber is equipped with an iron electrode plate array, with no less than three iron electrode plates in the array. The iron electrode plates on both edges of the iron electrode plate array are respectively connected to the positive and negative terminals of DC power supply two. The bottom of the electrocoagulation reaction chamber is equipped with an outlet D, which is connected to a sedimentation tank.

[0042] The spacing 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 tank. All trivalent chromium becomes chromium hydroxide flocculent, which overflows from the top of the iron plate array and enters 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. The solid chromium hydroxide and iron hydroxide are discharged through mud and water.

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

[0044] Fe-2e - → Fe 2+

[0045] Cr 6+ + 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 at the negative electrode of the iron plate inside the electrocoagulation reactor 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 buffer zone and the top of the flocculation reaction chamber are covered with porous, breathable plates.

[0055] The process for removing hexavalent chromium ions using the above-mentioned apparatus comprises the following steps:

[0056] first step:

[0057] The positive electrode reaction chamber is filled with brine. Graphite plate A and graphite plate B are completely immersed in the brine and do not come into contact with each other. Graphite plate A in the positive electrode reaction chamber is connected to the positive terminal of an external DC power supply via a cable.

[0058] Step Two:

[0059] Raw water containing hexavalent chromium enters the negative electrode reaction tank through the inlet between the sponge carbon negative electrode and the bottom graphite plate, rises upward through the sponge carbon negative electrode, and overflows into the buffer zone through outlet B.

[0060] Step 3:

[0061] 70% to 90% of the hexavalent chromium in the water passing through the carbon negative electrode of the sponge is reduced to trivalent chromium. It enters the electrocoagulation reaction box through the bottom outlet C in the buffer zone and rises upward through the iron electrode array inside the electrocoagulation reaction box.

[0062] Step 4:

[0063] The remaining hexavalent chromium in the water is completely reduced to trivalent chromium in the electrocoagulation reaction tank. All the trivalent chromium becomes chromium hydroxide flocs, which overflow from above the iron electrode array and enter the sedimentation tank through 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. The solid chromium hydroxide and iron hydroxide are discharged through mud and water.

[0064] Using graphite sponges with a surface area of ​​3.1-3.7 m² / g, experiments were conducted to treat raw water from an electroplating plant, with voltages of 20-50V and currents of 1.5-2A applied. The data are shown in the table below:

[0065]

[0066] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

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

Claims

1. An apparatus for removing hexavalent chromium ions from water, characterized in that, include: The system includes a positive electrode reaction chamber, a negative electrode reaction chamber, an electrocoagulation reaction chamber, and a sedimentation tank. The positive electrode reaction chamber and the negative electrode reaction chamber are both connected to DC power supply one, and the electrocoagulation reaction chamber is connected to DC power supply two. The positive electrode reaction box is equipped with graphite plate A and graphite plate B, and there are several graphite plates A and B. Graphite plates A and B are in zero contact. Graphite plate A is connected to the positive terminal of DC power supply A. Salt water is injected into the positive electrode reaction box, and the salt water submerges graphite plates A and B. The positive electrode reaction box is equipped with an exhaust valve, a pressure gauge, a water inlet, and a drain outlet A. The negative electrode reaction box is equipped with porous carbon material, and the sponge structure graphite is connected to the negative electrode of DC power supply one. Graphite plate C is laid flat at the bottom of the negative electrode reaction box. Graphite plate C is connected to graphite plate B and is connected to the negative electrode of DC power supply one. The negative electrode reaction box is equipped with an exhaust valve and a water inlet at the bottom. The negative electrode reaction box is equipped with a water outlet B, which is connected to a buffer zone. The bottom of the buffer zone is equipped with a water outlet C, which is connected to an electrocoagulation reaction box. The electrocoagulation reaction chamber is equipped with an iron electrode plate array. The iron electrode plates on both edges of the iron electrode plate array are respectively connected to the positive and negative terminals of DC power supply two. The bottom of the electrocoagulation reaction chamber is equipped with an outlet D, which is connected to a sedimentation tank.

2. The apparatus for removing hexavalent chromium ions from water according to claim 1, characterized in that, The porous carbon material includes graphite sponge, graphene sponge, graphite felt, and carbon material particle filler.

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

4. The apparatus for removing hexavalent chromium ions from water according to claim 1, characterized in that, The buffer zone and the top of the electrocoagulation reaction chamber are covered with porous, breathable covers.

5. A process for removing hexavalent chromium ions from water using the apparatus according to claim 1, characterized in that, The process steps are as follows: S1: The positive electrode reaction chamber is filled with brine. Graphite plate A and graphite plate B are completely immersed in the brine and do not come into contact with each other. Graphite plate A in the positive electrode reaction chamber is connected to the positive terminal of an external DC power supply through a cable. S2: Raw water containing hexavalent chromium enters the negative electrode reaction tank through the inlet between the sponge carbon negative electrode and the bottom graphite plate, rises upward through the sponge carbon negative electrode, and overflows into the buffer zone through the outlet B. S3: 70% to 90% of the hexavalent chromium in the water passing through the carbon negative electrode of the sponge is reduced to trivalent chromium. It enters the electrocoagulation reaction box through the bottom outlet C in the buffer zone and rises upward through the iron electrode array in the electrocoagulation reaction box. S4: The remaining hexavalent chromium in the water is completely reduced to trivalent chromium in the electrocoagulation reaction tank. All trivalent chromium becomes chromium hydroxide flocculent, which overflows from above the iron electrode array and enters the sedimentation tank through 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. The solid chromium hydroxide and iron hydroxide are discharged through mud and water.

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