Method for treating arsenic in waste acid by electrochemically strengthening dissolution of iron ions

Abstract

The invention discloses a method for treating arsenic in waste acid through electrochemically-enhanced iron ion dissolution. The method comprises the steps of electrochemically-enhanced dissolution, generation of scorodite through a precipitation reaction and separation of precipitates. According to the method disclosed by the invention, the problems of low dissolution rate of iron ions, long reaction period and high operation cost in the traditional arsenic removal of contaminated acid are solved through a synergistic process of electrochemical enhanced iron ion release and scorodite directional crystallization; according to the electrochemical dissolution, iron oxide or iron-containing waste residues are adopted as an anode material, and the synergistic effect of a catalytic cathode and a direct-current electric field is combined, so that dissolution of iron ions is remarkably accelerated, efficient oxidation fixation of arsenic is synchronously promoted, and the reaction time is greatly shortened; the generated scorodite crystal structure is stable, and the fixation of arsenic can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial wastewater treatment, and particularly relates to a method for electrochemically enhancing the dissolution of iron ions for arsenic removal from contaminated acid. Background Art

[0002] In industrial processes such as non-ferrous metal smelting, chemical industry, and mining, a large amount of acidic wastewater (contaminated acid) containing high concentrations of arsenic is generated, and the main form of arsenic present is arsenate ions. Arsenic is a highly toxic element and poses a serious threat to the environment and human health. Therefore, effective treatment of arsenic-containing contaminated acid is necessary. Traditional arsenic removal technologies for contaminated acid (such as lime neutralization method, sulfide precipitation method, scorodite precipitation method) have problems such as large sludge production, poor arsenic stability, and long reaction time.

[0003] The scorodite (FeAsO4·2H2O) precipitation method has gradually attracted attention due to its small amount of slag and high stability, but its core relies on the rapid reaction of iron ions (Fe 3+ ) with arsenate (AsO4 3- ). To reduce the cost of iron salts, researchers mostly use iron oxides (Fe3O4, Fe2O3, Fe(OH)3) or iron-containing waste residues (such as red mud, copper slag) to replace commercial iron salts. However, the natural dissolution rate of iron oxides under acidic conditions is extremely low, resulting in a reaction cycle as long as 12 hours, which is difficult to meet the requirements of industrial continuous treatment. Existing technologies mostly accelerate the dissolution by high-temperature heating (>80°C), resulting in high energy consumption of the treatment technology and aggravated equipment corrosion. Therefore, how to accelerate the rapid dissolution of iron ions has become a limiting factor for arsenic removal by the scorodite method.

[0004] Based on this, the present invention proposes a method for electrochemically enhancing the dissolution of iron ions for arsenic removal from contaminated acid. Summary of the Invention

[0005] To solve the above technical problems, the purpose of the present invention is to provide a method for electrochemically enhancing the dissolution of iron ions for arsenic removal from contaminated acid, which electrochemically enhances the dissolution of iron / iron oxide to release iron ions, significantly improves the release rate of iron ions, shortens the reaction time, and realizes efficient arsenic removal from contaminated acid.

[0006] The purpose of the present invention is achieved as follows, including the following steps: (1) Add the contaminated acid to an electrochemical reactor, use pure iron, iron oxide or iron-containing waste residue as the anode, use an inert material as the cathode, apply direct current electricity to accelerate the dissolution of the anode and release iron ions; (2) Pass a gas into the reactor liquid or add H2O2 to form a scorodite FeAsO4·2H2O precipitate by reacting Fe 3+ with arsenate; (3) Separate the precipitate.

[0007] Preferably, the contaminated acid is arsenic-containing acidic wastewater generated during the washing process of sulfide ore roasting flue gas.

[0008] Preferably, the iron oxide is one or more of Fe3O4, Fe2O3, Fe(OH)3, and the iron-containing waste residue is one or more of copper slag, red mud, and steel slag.

[0009] Preferably, the material of the cathode is titanium plate, titanium mesh, titanium-coated iridium dioxide, titanium-coated ruthenium dioxide, or carbon material.

[0010] Preferably, the distance between the anode and the cathode is 5 cm to 20 cm.

[0011] Preferably, the current density of the direct current is 10 mA / cm² to 1000 mA / cm².

[0012] Preferably, the gas in step (2) is air, oxygen, ozone, and the addition amount of the gas or H2O2 is 1 to 1.5 times the sum of the molar concentrations of As 3+ and Fe 2+ in terms of molar concentration.

[0013] Preferably, the molar ratio of Fe to As in the precipitation reaction in step (2) is 1.0 to 2.0.

[0014] Preferably, in step (3), the precipitate is separated by a plate-and-frame filter press or a centrifuge for solid-liquid separation. The pore size of the filter cloth of the plate-and-frame filter press is ≤5 μm, and the rotation speed of the centrifuge is controlled at 3000 rpm to 5000 rpm.

[0015] Preferably, the electrochemical reactor includes a cathode 1, an air diffuser pipe 2, a water inlet pipe 3, a water outlet pipe 4, an anode 5, a housing 6, a sludge hopper 7, and a sludge discharge pipe 8. A sludge hopper 7 is provided at the bottom of the housing 6, and a sludge discharge pipe 8 is provided at the bottom of the sludge hopper 7. The cathode 1 and the anode 5 are both plate-shaped, and the cathode 1 and the anode 5 are alternately arranged longitudinally and spaced from one side to the other side in the upper part of the housing 6. The number of the cathode 1 and the anode 5 is equal. The cathode 1 is electrically connected to the negative electrode of the DC power supply, and the anode is electrically connected to the positive electrode of the DC power supply. An air diffuser pipe 2 is provided in the lower part of the housing 6. The water inlet pipe 3 is provided at the lower part of the housing 6, and the water outlet pipe 4 is provided at the upper part of the housing 6. The electrochemical reactor combines electrochemical action with physical precipitation to achieve efficient removal of pollutants.

[0016] Advantages of the present invention: 1. The present invention solves the problems of low iron ion dissolution rate, long reaction period, and high operation cost in traditional arsenic removal from contaminated acid through a synergistic process of electrochemically enhancing iron ion release and oriented crystallization of scorodite. The electrochemical dissolution uses iron oxide or iron-containing waste residue as the anode material, combined with the synergistic effect of a catalytic cathode and a DC electric field, significantly accelerating iron ion dissolution and simultaneously promoting the efficient oxidation and fixation of arsenic, greatly shortening the reaction time. The generated scorodite has a stable crystal structure, enabling long-term and safe sequestration of arsenic. 2. The present invention uses metallurgical waste residue to replace traditional high-cost iron salt raw materials, significantly reducing the treatment cost. 3. The electrochemical reactor is flexible in operation and adaptable to complex wastewater environments, providing an efficient, economical, and sustainable solution for the treatment of high-arsenic pollution. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of the electrochemical reactor; In the figure: 1 - cathode, 2 - aeration pipe, 3 - water inlet pipe, 4 - water outlet pipe, 5 - anode, 6 - housing, 7 - sludge hopper, 8 - sludge discharge pipe. Detailed Embodiments

[0018] The present invention will be further described below in conjunction with the embodiments and the drawings, but it is not limited to the present invention in any way. Any transformation or replacement based on the teachings of the present invention falls within the protection scope of the present invention.

[0019] Example 1 The method for electrochemically enhancing iron ion dissolution for arsenic removal from contaminated acid in this example includes the following steps: (1) Add the contaminated acid to the electrochemical reactor, use Fe3O4 as the anode (please specify a certain iron oxide), use titanium-coated iridium dioxide as the cathode (please specify), apply a DC voltage of 1.5V, the electrolysis time is 40 minutes, and the current density is 200 mA / cm 2 , and electrochemical corrosion accelerates the dissolution of the anode to release Fe 2+ (Fe → Fe 2+ + 2e - ); (2) Introduce air into the reactor liquid to make the molar amount of oxygen 1.2 times the sum of the molar concentrations of As 3+ and Fe 2+ , control the molar ratio of Fe to As to be 1.5, and the oxygen in the air oxidizes Fe 2+ to Fe 3+ (4Fe 2+ + O2 + 4H + → 4Fe 3+ + 2H2O), and simultaneously oxidize As 3+ to As 5+ (As 3+ + O2 → As5+ ), react for 0.5 h to allow Fe 3+ and As 5+ to form scorodite (FeAsO4·2H2O) precipitate; (3) filter-press to separate the precipitate, and the resulting scorodite has a crystallinity of 99.95%.

[0020] Example 2 The method for treating arsenic in waste acid by electrochemically enhanced iron ion dissolution in this example includes the following steps: (1) Add waste acid to an electrochemical reactor, use red mud as the anode and ruthenium dioxide-coated titanium as the cathode, apply a direct current of 2.0 V, with an electrolysis time of 30 min and a current density of 300 mA / cm 2 , and electrochemical corrosion accelerates the anodic dissolution to release Fe 2+ (Fe → Fe 2+ + 2e - ); (2) Add 0.1% H2O2 to the reactor liquid. The molar amount of H2O2 is 1.3 times the sum of the molar concentrations of As 3+ and Fe 2+ . Control the molar ratio of Fe to As to be 1.2. H2O2 and Fe 2+ undergo the Fenton reaction (Fe 2+ +H2O2 → Fe 3+ +·OH + OH - ), generating hydroxyl radicals (·OH) that efficiently oxidize As 3+ (As 3+ +·OH → As 5+ ), react for 1 h to allow Fe 3+ and As 5+ to form scorodite (FeAsO4·2H2O) precipitate; (3) Centrifuge to separate the precipitate, and the resulting scorodite has a crystallinity of 99.98%.

[0021] Example 3 The method for treating arsenic in waste acid by electrochemically enhanced iron ion dissolution in this example includes the following steps: (1) Add arsenic-containing acidic wastewater generated during the washing process of sulfide ore roasting flue gas to an electrochemical reactor, use copper slag as the anode and graphite plate as the cathode, apply a direct current of 2.5 V, with an electrolysis time of 50 min and a current density of 150 mA / cm 2 , and electrochemical corrosion accelerates the anodic dissolution to release Fe 2+ (Fe → Fe 2+ + 2e - ); (2) Add 0.1% ozone to the reactor liquid. The molar amount of ozone is 1.1 times the sum of the molar concentrations of As 3+ and Fe 2+ . Control the molar ratio of Fe to As to be 1.8. Ozone directly oxidizes Fe 2+ and As3+ to Fe 3+ and As 5+ React for 0.5 h to allow Fe 3+ to react with As 5+ to form scorodite (FeAsO4·2H2O) precipitate; (3) Centrifuge to separate the precipitate, and the resulting scorodite has a crystallinity of 99.98%.

[0022] Example 4 The method for electrochemically enhancing the dissolution of iron ions for arsenic removal from waste acid in this example includes the following steps: (1) Add the arsenic-containing acidic wastewater generated during the washing process of sulfide ore roasting flue gas to an electrochemical reactor. Use a pure iron plate as the anode and a titanium mesh platinum-plated electrode as the cathode. Apply a direct current of 2.2 V for an electrolysis time of 60 min and a current density of 250 mA / cm 2 , Electrochemical corrosion accelerates the dissolution of the anode to release Fe 2+ (Fe → Fe 2+ + 2e - );(2) Add 0.1% ozone to the reactor liquid. The molar amount of ozone is 1.4 times the sum of the molar concentrations of As 3+ and Fe 2+ . Control the molar ratio of Fe to As to be 1.6. Ozone directly oxidizes Fe 2+ and As 3+ to Fe 3+ and As 5+ , React for 0.5 h to allow Fe 3+ to react with As 5+ to form scorodite (FeAsO4·2H2O) precipitate; (3) Centrifuge to separate the precipitate, and the resulting scorodite has a crystallinity of 99.98%.

[0023] Example 5 As shown in the appendix Figure 1As shown in the figure, the method for treating arsenic in waste acid by electrochemically enhanced iron ion dissolution in this embodiment is based on Embodiment 1. The difference from Embodiment 1 is that the electrochemical reactor includes a cathode 1, an air supply pipe 2, a water inlet pipe 3, a water outlet pipe 4, an anode 5, a housing 6, a sludge hopper 7, and a sludge discharge pipe 8. The sludge hopper 7 is provided at the bottom of the housing 6, and the sludge discharge pipe 8 is provided at the bottom of the sludge hopper 7. Both the cathode 1 and the anode 5 are plate-shaped. The cathode 1 and the anode 5 are alternately arranged longitudinally and spaced 10 cm from one side to the other side in the upper part of the housing 6. The number of the cathode 1 and the anode 5 is equal. The cathode 1 is electrically connected to the negative electrode of the DC power supply, and the anode is electrically connected to the positive electrode of the DC power supply. The air supply pipe 2 is provided in the lower part of the housing 6. The water inlet pipe 3 is provided at the lower part of the housing 6, and the water outlet pipe 4 is provided at the upper part of the housing 6. When the reactor operates, the waste acid is continuously injected into the housing 6 through the water inlet pipe 3. The DC power supply applies a voltage to the alternately arranged cathode 1 and anode 5 to drive an electrochemical reaction in the solution environment. The air supply pipe 2 is used to supply air to the solution to promote the redox reaction through gas-liquid mixing. Under the synergistic effect of the electric field and aeration, pollutants such as heavy metals undergo electrochemical dissolution and oxidative degradation. Part of the suspended matter settles and accumulates in the sludge hopper 7 under the action of gravity and is finally discharged through the bottom sludge discharge pipe 8. The treated water body is discharged through the water outlet pipe 4 to complete the continuous treatment process from inlet water to outlet water. The whole process realizes the efficient removal of pollutants through the combination of electrochemical action and physical precipitation.

Claims

1. A method for electrochemically enhancing the dissolution of iron ions for arsenic removal from waste acid, characterized in that It includes the following steps: (1) Add the contaminated acid into an electrochemical reactor, use pure iron, iron oxide or iron-containing waste residue as the anode, use an inert material as the cathode, apply direct current, and accelerate the dissolution of the anode to release iron ions; (2) Introduce gas into the reactor liquid or add H2O2 to cause Fe 3+ to react with arsenate to form scorodite FeAsO4·2H2O precipitate; (3) Separate the precipitate.

2. The method for electrochemically enhancing iron ion dissolution for arsenic removal from waste acid according to claim 1, wherein The contaminated acid is arsenic-containing acidic wastewater generated during the washing process of sulfide ore roasting flue gas.

3. The method for electrochemically enhancing the dissolution of iron ions for arsenic removal from waste acid according to claim 1, wherein The iron oxide is one or more of Fe3O4, Fe2O3, Fe(OH)3, and the iron-containing waste residue is one or more of copper slag, red mud, and steel slag.

4. The method for arsenic removal from waste acid by electrochemically enhancing iron ion dissolution according to claim 1, characterized in that The material of the cathode is titanium plate, titanium mesh, titanium-plated iridium dioxide, titanium-plated ruthenium dioxide or carbon material.

5. The method for electrochemically enhancing iron ion dissolution for arsenic removal from waste acid according to claim 1, wherein The distance between the anode and the cathode is 5 cm to 20 cm.

6. The method for electrochemically enhancing the dissolution of ferric ions for arsenic removal from waste acid according to claim 1, wherein The current density of the direct current is 10 mA / cm² to 1000 mA / cm².

7. The method for electrochemically enhancing iron ion dissolution for arsenic removal from waste acid according to claim 1, characterized in that The gas described in step (2) is air, oxygen, ozone, or H2O2, and the addition amount of the gas or H2O2 is 1 to 1.5 times the sum of the molar concentrations of As 3+ and Fe 2+ times the sum of the molar concentrations.

8. The method for electrochemically enhancing the dissolution of iron ions for arsenic removal from contaminated acid according to claim 1, wherein In step (2), the molar ratio of Fe to As in the precipitation reaction is 1.0 to 2.

0.

9. The method for electrochemically enhancing the dissolution of iron ions for arsenic removal from contaminated acid according to claim 1, wherein In step (3), separating the precipitate is to perform solid-liquid separation using a plate and frame filter press or a centrifuge. The pore diameter of the filter cloth of the plate and frame filter press is ≤5 μm, and the rotation speed of the centrifuge is controlled at 3000 rpm to 5000 rpm.

10. The method for electrochemically enhancing the dissolution of iron ions for arsenic removal from waste acid according to claim 1, wherein The electrochemical reactor includes a cathode (1), an air pipe (2), a water inlet pipe (3), a water outlet pipe (4), an anode (5), a housing (6), a sludge hopper (7), and a sludge discharge pipe (8). A sludge hopper (7) is provided at the bottom of the housing (6), and a sludge discharge pipe (8) is provided at the bottom of the sludge hopper (7). The cathode (1) and the anode (5) are both plate-shaped. The cathode (1) and the anode (5) are alternately arranged longitudinally and at intervals from one side to the other side in the upper part of the housing (6). The number of the cathode (1) and the anode (5) is equal. The cathode (1) is electrically connected to the negative electrode of the direct current power supply, and the anode is electrically connected to the positive electrode of the direct current power supply. An air pipe (2) is provided in the lower part of the housing (6), the water inlet pipe (3) is provided in the lower part of the housing (6), and the water outlet pipe (4) is provided in the upper part of the housing (6).

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