Iron-carbon micro-electrolysis reactor (fixed bed) 1. Application range With the development of industry, the difficulty of sewage treatment is also increasing. Among the treatment technologies for refractory industrial wastewater, micro-electrolysis technology is receiving increasing attention and has been widely used in engineering practice. At present, it is widely used in chemical, pesticide, dye, pharmaceutical and other high-color, biodegradable wastewater, used to reduce organic pollution and high biodegradability of wastewater. 2. Technical principle The principle of iron internal electrolysis of wastewater is very simple. It is the use of potential difference between iron-carbon particles to form numerous fine primary batteries. These fine batteries are made of iron having a low potential as a cathode, and carbon having a high potential as an anode, and an electrochemical reaction occurs in an aqueous solution containing an acidic electrolyte. The result of the reaction is that the iron is corroded into divalent iron ions into the solution. Because of the coagulation effect of iron ions, it is absorbed by the particles with weak negative charge in the contaminants to form a relatively stable floc (also called iron mud) and removed. When the sewage passes through the filler containing iron and carbon, the iron becomes the anode, the carbon becomes the cathode, and the micro-current flows, forming thousands of tiny batteries, causing "internal electrolysis", causing corrosion, that is, redox reaction: Anodic reaction: Fe-2e-Fe2+ E0(Fe2+/Fe)=-0.44V Cathodic reaction: 2H++2e→H2↑ E0(H+/H2)=0.00V When there is oxygen: O2+4H++4e→2H2O E0(O2)=1.23V O2+2H2O+4e→40H-E0(O2/OH-)=0.40V The above reaction is most corrosive in the case of acidity and oxygenation, and has the following proven function: due to organic matter The reduction reaction of the pre-cathode changes the functional group, changes the original organic property, reduces the chromaticity, and improves the B/C value; some inorganic substances are also pre-reacted to form a precipitate, such as: Fe2++S2-→FeS↓ The colloidal particles and minutely dispersed contaminants of the wastewater are subjected to an electric field to generate an electrophoresis phenomenon, which moves toward the oppositely charged electrode and accumulates on the electrode to clarify the water; the new ecological Fe2+ formed by the anode is neutralized by lime (Fe) 3) has a strong adsorption capacity to clarify water; cathode generation Hydrogen, having a flotation effect. 2.1 Electrode Reaction Anode (Fe): Cathode (C): When there is O2: It can be seen from the standard electrode potential E0 of the above reaction that the E0 of the electrode reaction is the largest under acidic oxygenation conditions, and the electrode reaction proceeds most when O2 is present. Fast, the reaction continuously consumes H + in the wastewater to raise its pH. Therefore, when the pH is low and the acidity is large, the electrode potential of oxygen is increased, and the potential difference of the microbattery is increased to promote the progress of the electrode reaction. This theoretically explains the reason why the micro-electrolysis reaction of acid wastewater is better. 2.2 Redox reaction 2.2.1 Reduction of iron Iron is an active metal, which can reduce some heavy metal ions and organic matter to a reduced state under acidic conditions, for example: (1) reduction of mercury ions to elemental mercury: (2) The valence of chromium is reduced to trivalent chromium: (3) the chromophore of the azo dye is reduced: (4) the reduction of the nitro group to the amine group: the reduction of iron causes the heavy metal ions in the wastewater to be converted into simple substances or precipitates. Removal, some macromolecular dyes are degraded into small molecule colorless substances, which have decolorization effect and improve the biodegradability of wastewater. 2.2.2 Hydrogen redox The new ecological hydrogen obtained in the electrode reaction has greater activity. It can redox with many components in wastewater, destroy the structure of coloring and color-promoting groups, break the azo bond, decompose macromolecules into small molecules, and reduce the nitration to amine compounds to achieve decolorization. purpose. Generally, [H] is a combination of Fe2+ to interrupt the azo bond and reduce the nitro group to an amine group. 1.3 Electrochemical epitaxy When a small galvanic cell is formed between iron and iron carbide or other impurities, an electric field will be generated around it. In many wastewaters, there will be stable colloids such as printing and dyeing wastewater. When these colloids are under electric field, they will Produced by electrophoresis and attached. Under the action of the electric field, the electrophoretic velocity of the colloidal particles can be obtained by the following formula: where: V——electrophoretic velocity (cm/s) of colloidal particles—potential (V) D—dielectric constant E of the dispersion medium— —Electrical field strength (V/cm) ——Viscosity of dispersion medium (Pa•S) K——The coefficient is, for example, waste iron scrap and coke particles with a potential difference of 1.2V, immersed in a wastewater solution with a potential of 0.30 mV, The separation distance between the materials is 0.10cm, and the separation speed of 5?0-3cm/s can be obtained. The electrophoretic deposition process can be completed by theoretically calculating 20s. 2.3 Physical adsorption In the weakly acidic solution, the specific surface area rich in iron filings shows a high surface activity, can adsorb a variety of metal ions, can promote the removal of metal, and the adsorption of metal by the micro carbon particles in the iron filings is also Not to be ignored. Moreover, cast iron is a porous substance with a strong activity on the surface, which can adsorb organic pollutants in wastewater, purify wastewater, especially when adding materials such as flue ash, and its large specific surface area and crystallite surface. It contains a large number of unsaturated bonds and oxygen-containing reactive groups, and adsorbs dye molecules in a wide pH range. 2.4 Coagulation and precipitation of iron Under acidic conditions, when treated with iron filings, Fe2 and Fe3 are produced. Fe2 and Fe3 are good flocculants. When the pH of the solution is adjusted to be alkaline and O2 is present, a good flocculant of Fe(OH)2 and Fe(OH)3 is formed, and flocculation and precipitation occur. The reaction formula is as follows: The produced Fe(OH)3 is a colloidal flocculant, and its adsorption capacity is higher than that of Fe(OH)3 obtained by hydrolysis of a general agent. In this way, the intrinsic suspended matter in the wastewater, the insoluble matter generated by the reaction of the microbattery and the insoluble dye constituting the chromaticity can be adsorbed and aggregated. 2.5 Precipitation of iron ions In the products of the battery reaction, Fe2 and Fe3 will also react with some inorganic substances to form precipitates to remove these inorganic substances to reduce their toxicity to the subsequent biochemical section. For example, S2, CN-, etc. will precipitate FeS, Fe3[Fe(CN)6]2, Fe4[Fe(CN)6]3, etc. and will be removed.
[Reduction of iron]
Iron is an active metal that reduces some heavy metal ions and organics to a reduced state under acidic conditions, such as:
(1) Reduction of mercury ions to elemental mercury:
(2) Reduction of hexavalent chromium to trivalent chromium:
(3) Reduction of the chromophore of the azo dye:
(4) Reduction of the nitro group to an amine group:
The reduction of iron causes the heavy metal ions in the wastewater to be converted into simple substances or precipitates to be removed, which degrades some macromolecular dyes into small molecules and colorless substances, which has a decolorizing effect and at the same time improves the biodegradability of the wastewater.
[Redox effect of hydrogen]
The new ecological hydrogen obtained in the electrode reaction has greater activity. It can redox with many components in wastewater, destroy the structure of coloring and color-promoting groups, break the azo bond, decompose macromolecules into small molecules, and reduce the nitration to amine compounds to achieve decolorization. purpose. Generally, [H] is a combination of Fe2+ to interrupt the azo bond and reduce the nitro group to an amine group.
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