Method for recovering ferrous iron from mine acid wastewater and synthesizing ferroferric oxide

Abstract

The invention relates to the field of wastewater treatment and recycling, and discloses a method for recovering ferrous iron from mine acid wastewater and synthesizing ferroferric oxide. The method comprises the following steps: adding the mine acid wastewater into a cathode chamber and an anode chamber of a reactor for electrolytic reaction, and collecting an electrolytic product nano ferroferric oxide in the cathode chamber; the conditions of the electrolytic reaction at least meet the conditions that the electrolyte concentration is 15-30 g / L, the current intensity is 60-120 mA, the temperature is 25-35 DEG C, the pH is 2.5-4.5, and the stirring speed is 280-330 r / min. According to the method, no chemical additive needs to be added, the treatment efficiency is high, the cost is low, the treated main product is ferroferric oxide, the purity is 99%, the particle size is 297 + / -1.6 nm, the saturation magnetization is 54.2 emu / g, the application value is high, and the ferroferric oxide can be magnetically separated and recycled; in the presence of other ions, the main composition of the product is not affected.

Description

Technical Field

[0001] The invention relates to the field of wastewater treatment and resource utilization, and in particular to a method for recovering divalent iron from acid mine wastewater and synthesizing ferrosoferric oxide. Background Art

[0002] Acid mine drainage mainly comes from the oxidation of sulfur-containing minerals, with a pH of usually 2.5-4.5, and contains high concentrations of metal ions such as iron and manganese.

[0003] The current mainstream technology for treating acid mine wastewater is the high-density mud method, which has a higher treatment efficiency than the traditional limestone neutralization method, but the cost is quite high, about 5-12 yuan / ton; the high-density mud method produces a large amount of mud in the process of treating wastewater and belongs to Class I industrial solid waste, which occupies a large area and has high and complex subsequent treatment costs; and the treatment efficiency of various metal pollutants such as iron and manganese is low and difficult to remove simultaneously. Therefore, it is necessary to develop more efficient mine wastewater treatment processes, improve resource recovery rates and reduce energy consumption, so as to provide more options and possibilities for the treatment of acid mine wastewater.

[0004] With the rapid development of electrochemical wastewater treatment technology, the electro-Fenton method has gradually replaced the electrodialysis method with high effluent salt concentration and the electro-flocculation method with short electrode life and high operating cost. The electro-Fenton method can effectively treat acid mine wastewater at a lower cost. However, after the electro-Fenton method treats the wastewater, the synthesized Schmidtite is difficult to recover and has low utilization value.

[0005] In the prior art, the iron precipitation reaction is used to recover the divalent iron ions in acidic mine wastewater. The divalent iron ions need to be oxidized into trivalent iron ions first, and then the pH of the wastewater is adjusted by adding alkaline reagents or phosphates to remove the trivalent iron precipitation. During the precipitation process, coagulants are also added to promote precipitation. While removing the divalent iron ions, this method will introduce other chemical reagents, causing secondary pollution. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems of low metal pollutant treatment efficiency, great recovery difficulty and secondary pollution caused by adding chemical additives in the prior art, and to provide a method for recovering divalent iron from mine acidic wastewater and synthesizing ferroferric oxide. The method does not require the addition of chemical additives, has high treatment efficiency and low cost, and the main product after treatment is ferroferric oxide, which is easy to recover, and will not affect the removal effect of pollutants in the presence of other ions.

[0007] In order to achieve the above object, the present invention provides a method for recovering divalent iron from acid mine wastewater and synthesizing ferrosoferric oxide, the method comprising:

[0008] Acidic mine wastewater is added to the cathode chamber and anode chamber of a reactor for electrolysis reaction, and the electrolysis product nano-ferroferric oxide is collected in the cathode chamber; the conditions of the electrolysis reaction at least meet the following requirements: electrolyte concentration of 15-30 g / L, current intensity of 60-120 mA, temperature of 25-35° C., pH of 2.5-4.5, and stirring speed of 280-330 r / min.

[0009] Preferably, the reactor comprises an electrolytic cell and a diaphragm arranged in the electrolytic cell, wherein the diaphragm can separate the electrolytic cell into a cathode chamber and an anode chamber, and a magnetic stirrer is built in the cathode chamber.

[0010] Preferably, the reactor further comprises a cathode electrode and an anode electrode, the cathode electrode is a plate-like structure, and the anode electrode is a mesh-like structure.

[0011] Preferably, the cathode electrode is a platinum metal plate, a titanium metal plate or a nickel metal plate, and the anode electrode is an iridium-plated titanium mesh, a platinum-plated titanium mesh or an iridium-tantalum-titanium mesh.

[0012] Further preferably, the cathode electrode is a platinum metal plate, and the anode electrode is an iridium-plated titanium mesh.

[0013] Preferably, the membrane is a proton exchange membrane or an anion exchange membrane.

[0014] Further preferably, the membrane is a proton exchange membrane.

[0015] Preferably, the rotation speed of the magnetic stirrer is 280-330 r / min.

[0016] Preferably, the electrolyte is sodium sulfate, and the mass concentration of the electrolyte is 15-30 g / L.

[0017] Further preferably, the mass concentration of divalent iron ions in the acid mine wastewater is 200-800 mg / L.

[0018] Preferably, the acid mine wastewater may also contain interfering ions.

[0019] Further preferably, the interfering ions are selected from at least one of pentavalent arsenic ions, trivalent chromium ions, divalent manganese ions, divalent copper ions and divalent zinc ions.

[0020] Further preferably, the mass concentration of the interfering ions is no higher than 50 mg / L.

[0021] Preferably, the electrolysis time of the electrolysis reaction is 100-280 min, and the mass concentration of each ion is lower than 0.3 mg / L when the electrolysis is stopped.

[0022] Through the above technical scheme, the method provided by the present invention can recover ferrous iron from acid mine wastewater by electrolysis and synthesize ferroferric oxide. The method for recovering ferrous iron from acid mine wastewater and synthesizing ferroferric oxide provided by the present invention does not need to add chemical additives when removing iron ions in wastewater, and the treatment efficiency of Fe is as high as 100%, the cost is low, and the main product after treatment is ferroferric oxide, with a purity of 99%, a particle size of 297 ± 1.6nm, and a saturation magnetization of 54.2emu / g. It has high application value and can be recovered by magnetic separation; in the presence of other ions, the main composition of the product is not affected. At the same time, the method can achieve a removal rate of 100% for pollutants such as arsenic (V), chromium (III), manganese (II), copper (II) and zinc (II). BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of a specific embodiment of the reactor of the present invention;

[0024] Figure 2 This is a graph showing the change in removal rate of divalent iron ions during electrolysis of acid mine wastewater in Example 1 of the present invention;

[0025] Figure 3 This is an XRD diagram of an electrolysis product obtained by electrolyzing acidic mine wastewater in Example 1 of the present invention;

[0026] Figure 4 This is a magnetization curve diagram of the electrolysis product obtained by electrolyzing acid mine wastewater in Example 1 of the present invention;

[0027] Figure 5 This is a particle size distribution diagram of the electrolysis product obtained by electrolyzing acid mine wastewater in Example 1 of the present invention;

[0028] Figure 6 This is a graph showing the change in removal rate of divalent iron ions during electrolysis of acid mine wastewater in Example 2 of the present invention;

[0029] Figure 7 This is the product XRD diagram of divalent iron ions in the process of electrolysis of acid mine wastewater in Example 2 of the present invention;

[0030] Figure 8 This is a graph showing the change in removal rate of divalent iron ions during electrolysis of acid mine wastewater in Example 3 of the present invention;

[0031] Fig. 9 This is the XRD diagram of the product of divalent iron ions in the process of electrolysis of acid mine wastewater in Example 3 of the present invention;

[0032] Fig.10 This is a comparison chart of the treatment time for electrolyzing acid mine wastewater containing divalent iron ions and other interfering ions until the removal rate of each pollutant reaches 100% in Example 4 of the present invention;

[0033] Fig.11 This is the XRD diagram of the product of electrolysis of acid mine wastewater containing divalent iron ions and trivalent iron ions (divalent manganese ions / trivalent chromium ions) in Example 4 of the present invention;

[0034] Fig.12 This is the XRD diagram of the product of electrolysis of acid mine wastewater containing divalent iron ions and divalent copper ions (divalent zinc ions / pentavalent arsenic ions) in Example 4 of the present invention;

[0035] Fig.13 This is a graph showing the change in removal rate of iron and manganese ions in the acid mine wastewater from a mine in Loudi City by electrolysis in Example 5 of the present invention;

[0036] Fig.14 This is the XRD diagram of the product of electrolysis of acid mine wastewater from a mine in Loudi City in Example 5 of the present invention;

[0037] Fig.15 This is a graph showing the change in removal rate of iron and manganese ions in the acid mine wastewater from a mine in Zhuzhou City by electrolysis in Example 6 of the present invention;

[0038] Fig.16 This is the XRD diagram of the product of electrolysis of acid mine wastewater from a mine in Zhuzhou City in Example 6 of the present invention;

[0039] Fig.17 This is a graph showing the change in removal rate of iron and manganese ions in the acid mine wastewater from a mine in Dexing City by electrolysis in Example 7 of the present invention;

[0040] Fig.18 This is the XRD diagram of the product of electrolysis of acid mine wastewater from a mine in Dexing City in Example 7 of the present invention;

[0041] Fig.19 is a graph showing the change in removal rate of divalent iron ions during electrolysis of acid mine wastewater using different cathode materials in Example 8 of the present invention;

[0042] Fig. 20 is a graph showing the change in removal rate of divalent iron ions during electrolysis of acid mine wastewater using different anode materials in Example 9 of the present invention;

[0043] Fig.21 is a graph showing the change in removal rate of divalent iron ions during electrolysis of acid mine wastewater using different membrane materials in Example 10 of the present invention;

[0044] Fig. 22 is a graph showing the change in removal rate of divalent iron ions during electrolysis of acid mine wastewater using different current intensities in Example 11 of the present invention;

[0045] Fig.23 This is the XRD diagram of the product of electrolyzing acid mine wastewater using different current intensities in Example 11 of the present invention;

[0046] Fig.24 This is the XRD diagram of the product of electrolysis of acid mine wastewater containing only trivalent iron in Comparative Example 1 of the present invention;

[0047] Fig.25 This is a graph showing the change in removal rate of divalent iron ions during electrolysis of acid mine wastewater at low electrolyte concentration in Comparative Example 2 of the present invention.

[0048] Description of Reference Numerals

[0049] 1. Electrolytic cell; 2. Power supply; 3. Anode chamber; 4. Anode electrode; 5. Diaphragm; 6. Cathode electrode; 7. Cathode chamber; 8. Magnetic stirrer. DETAILED DESCRIPTION

[0050] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0051] The present invention provides a method for recovering divalent iron from acid mine wastewater and synthesizing ferrosoferric oxide, the method comprising:

[0052] Acidic mine wastewater is added to the cathode chamber and anode chamber of a reactor for electrolysis reaction, and the electrolysis product nano-iron tetroxide is collected in the cathode chamber; the conditions of the electrolysis reaction at least meet the following requirements: the current intensity is 60-120mA, specifically 60mA, 80mA, 100mA, 120mA, or any value between the above two values; the temperature is 25-35°C, specifically 25°C, 30°C, 35°C, or any value between the above two values; the pH is 2.5-4.5, specifically 2.5, 3, 3.5, 4, 4.5, or any value between the above two values; the stirring speed is 280-330r / min, specifically 280r / min, 300r / min, 320r / min, 330r / min, or any value between the above two values.

[0053] The inventor of the present invention unexpectedly discovered during the research process that the electrolysis reaction of acid mine wastewater and electrolyte as cathode electrolyte can remove iron ions in acid mine wastewater under the conditions of current intensity of 60-120mA, temperature of 25-35°C, pH of 2.5-4.5, and stirring speed of 280-330r / min, and solid ferroferric oxide electrolysis products can be generated without adding chemical additives other than electrolytes during the electrolysis process; other pollutants in the wastewater can also be removed while removing iron, and the iron removal rate is close to 100%, with high treatment efficiency and low cost. The main product after treatment is ferroferric oxide, which is easy to recycle, and in the presence of other ions, it will not affect the removal effect of pollutants. The iron ions in acid mine wastewater can be ferrous iron or mixed wastewater of ferrous iron and ferric iron.

[0054] The method for recovering ferrous iron from acid mine wastewater and synthesizing ferroferric oxide provided by the present invention has a removal rate of iron close to 100% when removing iron ions in wastewater, high processing efficiency and low cost. The main product after processing is ferroferric oxide with a purity of 99%, a particle size of 297±1.6nm, a saturation magnetization of 54.2emu / g, high application value, and can be recovered by magnetic separation; in the presence of other ions, the main composition of the product is not affected. Moreover, the method can achieve a removal rate of 100% for pollutants such as arsenic (V), chromium (III), manganese (II), copper (II) and zinc (II).

[0055] According to the present invention, preferably, the reactor includes an electrolytic cell 1 and a diaphragm 5 arranged in the electrolytic cell 1, the diaphragm 5 can separate the electrolytic cell 1 into a cathode chamber 7 and an anode chamber 3, and a magnetic stirrer 8 is built in the cathode chamber 7. The inventor found that when acid mine wastewater is added to the cathode chamber 7 as an electrolyte, after electrolysis, the iron in the wastewater will be converted into ferroferric oxide and removed. Exemplarily, the electrolytic cell 1 can be an H-shaped spliced ​​cathode chamber 7 and anode chamber 3, the diaphragm 5 is fixed to the position where the cathode chamber 7 and the anode chamber 3 are connected in the middle, and after adding the electrolyte, the magnetic stirrer 8 is used to stir the cathode electrolyte, and the electrolytic cell 1 is sealed and electrolysis is started. After the electrolysis is completed, the electrolysis products in the cathode chamber 7 are separated, and the iron ions in the wastewater in the cathode chamber 7 can be removed.

[0056] According to the present invention, the reactor further comprises a cathode electrode 6 and an anode electrode 4, and the cathode electrode 6 and the anode electrode 4 can be independently designed into a plate-like, columnar, filamentous, mesh-like, spring-like, etc. structure. Preferably, the cathode electrode 6 is a plate-like structure, and the anode electrode 4 is a mesh-like structure. The inventors have found that when the cathode electrode 6 is a plate-like structure, the contact area between the electrode and the wastewater is large, which can speed up the electrolysis process and increase the electrolysis speed; the anode electrode 4 is a mesh-like structure, which can increase the effective contact area of ​​the electrode, increase the speed of electron exchange, promote the electrolysis process, and accelerate the generation of ferroferric oxide.

[0057] Specifically, the cathode electrode 6 of the plate structure and the anode electrode 4 of the mesh structure are respectively connected to the regulated DC power supply through electrode rods, and the cathode electrode 6 and the anode electrode 4 are connected to the DC regulated power supply through electrode rods and wires. One end of the electrode rod of the cathode electrode 6 is connected in series with the plate structure, and the other end is connected to the negative electrode of the regulated DC power supply through a wire; one end of the electrode rod of the anode electrode 4 is connected in series with the mesh structure, and the other end is connected to the positive electrode of the regulated DC power supply through a wire. Exemplarily, the electrode rod can be a gold-plated copper terminal and polytetrafluoroethylene wrapped around the outer periphery of the gold-plated copper terminal; the wire is a copper wire wire.

[0058] According to the present invention, preferably, the cathode electrode 6 is a platinum metal plate, a titanium metal plate or a nickel metal plate, and the anode electrode 4 is an iridium-plated titanium mesh, a platinum-plated titanium mesh or an iridium-tantalum-titanium mesh. The inventors have found that when the cathode electrode and the anode electrode adopt the above-mentioned electrodes, the wastewater treatment speed is faster. Further preferably, when the cathode electrode 6 is a platinum metal plate and the anode electrode 4 is an iridium-plated titanium mesh, the cathode of the platinum metal plate is coupled with the anode of the iridium-plated titanium mesh, which can further increase the speed of electrolysis. The cathode uses precious metal platinum as a catalyst. This material has high current efficiency and the d electron orbital is not filled. It can catalyze the production of a large number of active oxidizing groups ·OH during the electrolysis process, promoting Fe 2+ Oxidized to Fe 3+ , forming the initial trivalent iron species of ferroferric oxide.

[0059] According to the present invention, preferably, when the diaphragm 5 is a proton exchange membrane or an anion exchange membrane, the treatment effect of acid mine wastewater is better. Further preferably, when the diaphragm 5 is a proton exchange membrane, the removal effect of iron ions in the wastewater is best. Exemplarily, the proton exchange membrane is an N117 proton exchange membrane. The proton exchange membrane can block the transfer of oxygen in the anode chamber 3, retaining the divalent iron species in the cathode chamber 7; at the same time, the hydrogen produced by the cathode electrolysis wastewater and the proton exchange membrane can isolate the external oxygen from entering the cathode chamber, retaining the divalent iron species required for ferroferric oxide, and the cathode alkaline oxygen-deficient conditions created by the electrolysis reaction are conducive to the formation of ferroferric oxide in the later stage.

[0060] According to the present invention, it is further preferred that the diaphragm 5 is a proton exchange membrane, the cathode electrode 6 is a plate-shaped platinum electrode, and the anode electrode 4 is an iridium-plated titanium mesh. The reactor corresponding to the above technical solution has the best iron removal effect and the highest removal efficiency when treating acid mine wastewater. The main product after treatment is ferroferric oxide, which is easy to recover, and in the presence of other ions, it will not affect the removal effect of pollutants.

[0061] According to the present invention, preferably, when the rotation speed of the magnetic stirrer 8 is 280-330r / min, specifically 280r / min, 300r / min, 320r / min, 330r / min, or any value between the above two values, the inventors found that when the above preferred embodiment is adopted, the treatment effect of iron wastewater is better.

[0062] A relatively preferred embodiment of the above reactor is as follows Figure 1 As shown, it includes an electrolytic cell 1 and a N117 proton exchange membrane arranged in the electrolytic cell 1, and the N117 proton exchange membrane divides the electrolytic cell 1 into a cathode chamber 7 and an anode chamber 3; the reactor also includes a cathode electrode 6 and an anode electrode 4, the cathode electrode 6 is a platinum electrode with a plate structure, and the anode electrode 4 is an iridium-plated titanium electrode with a mesh structure; the cathode electrode 6 and the anode electrode 4 are respectively placed in the center of the cathode chamber 7 and the anode chamber 3, and the two electrodes are arranged opposite to each other, and a magnetic stirrer 8 is built in the cathode chamber 7. The longitudinal sections of the cathode chamber 7 and the anode chamber 3 of the electrolytic cell 1 form an H-like shape, and the N117 proton exchange membrane is fixed at the connection between the cathode chamber 7 and the anode chamber 3. Two silicone gaskets fix the proton exchange membrane in the middle to ensure the sealing of the device. The cathode chamber 7 and the anode chamber 3 also have corresponding covers, which are covered during electrolysis to protect the electrolyte and improve the safety of the device.

[0063] According to the present invention, preferably, the electrolyte is sodium sulfate. Preferably, in the cathode electrolyte and the anode electrolyte, the mass concentration of the electrolyte is 15-30 g / L, specifically 15 g / L, 20 g / L, 25 g / L, 30 g / L, or any value between the above two values. The inventors found that when sodium sulfate is used as the electrolyte and the mass concentration is within the above range, the iron removal effect in the wastewater is better.

[0064] According to the present invention, preferably, the mass concentration of divalent iron ions in the acid mine wastewater is 200-800 mg / L, specifically 200 mg / L, 400 mg / L, 600 mg / L, 800 mg / L, or any value between the above two values. The inventors found that when the mass concentration of divalent iron ions in the acid mine wastewater is within the above range, the pollutant removal efficiency in the wastewater is higher, and the main components of the products are all ferroferric oxide.

[0065] According to the present invention, preferably, the acid mine wastewater may contain interfering ions. The inventors found that in the presence of other interfering ions, both iron and interfering ions in the wastewater can be removed together. Further preferably, the interfering ions are selected from one of arsenic (V), chromium (III), manganese (II), copper (II) and zinc (II); further preferably, when the concentration of the interfering ions is not higher than 50 mg / L, the removal efficiency is higher, and the product is mainly composed of ferroferric oxide.

[0066] According to the present invention, the acid mine wastewater is electrolyzed to remove pollutants using the above-mentioned treatment method for acid mine wastewater. In addition, the treatment of acid mine wastewater also includes the steps of precipitation, membrane treatment and neutralization treatment. The sedimentation treatment in the sedimentation tank can remove the sediment in the acid mine wastewater; the membrane treatment can remove the sulfate in the wastewater after electrolysis, and then the sulfate solid is obtained by evaporation and crystallization, which can be used as an electrolyte during the electrolysis treatment to reduce the cost of wastewater treatment; the wastewater treated by the membrane can be further treated by neutralization to reduce the alkalinity of the wastewater, so that the pH is reduced to 6-7, meeting the standard for wastewater discharge, and can also be recycled and reused.

[0067] According to the present invention, preferably, the electrolysis time of the electrolysis reaction is 100-280min, specifically 100min, 120min, 140min, 160min, 180min, 200min, 220min, 240min, 260min, 280min, or any value between the above two values; when the electrolysis is stopped, the ion concentration is less than 0.3mg / L, specifically 0mg / L, 0.1mg / L, 0.15mg / L, 0.2mg / L, 0.25mg / L, 0.29mg / L, or any value between the above two values, or any value between 0.29mg / L and 0.3mg / L. After the electrolysis treatment for the above time, the iron ion concentration in the acid mine wastewater can reach the discharge standard. The standards for wastewater discharge refer to the standard values ​​in Standard Table 2 of centralized drinking water surface water sources in the national standard GB3838-2002 "Surface Water Environmental Quality Standards", that is, the iron concentration is less than 0.3 mg / L and the manganese concentration is less than 0.1 mg / L.

[0068] The present invention will be described in detail below through examples.

[0069] In the following examples, the iron ion concentration was measured according to the standard HJ / T345-2007 "Determination of Iron in Water by O-phenanthroline Spectrophotometry (Trial)", and the minimum detection concentration of iron was 0.03 mg / L; the manganese ion concentration was measured according to the national standard GB11911-89 "Determination of Iron and Manganese in Water by Flame Atomic Absorption Spectrophotometry", and the minimum detection concentration of manganese was 0.01 mg / L; the arsenic ion was measured by ICP-AES method, and the specific method was determined according to the "Water and The content on page 308 of "Water Quality Monitoring and Analysis Methods (Fourth Edition)" was used for determination; the chromium ion was determined according to the standard HJ757-2015 "Water Quality - Determination of Chromium - Flame Atomic Absorption Spectrophotometry"; the copper ion was determined according to the national standard GB7475-1987 "Water Quality - Determination of Copper, Zinc, Lead and Cadmium - Atomic Absorption Spectrophotometry"; the zinc ion was determined according to the national standard GB7475-1987 "Water Quality - Determination of Copper, Zinc, Lead and Cadmium - Atomic Absorption Spectrophotometry".

[0070] Example 1

[0071] The reactor used in the electrolysis reaction is Figure 1 , including an electrolytic cell 1 and an N117 proton exchange membrane arranged in the electrolytic cell 1, the N117 proton exchange membrane divides the electrolytic cell 1 into a cathode chamber 7 and an anode chamber 3; the reactor also includes a cathode electrode 6 and an anode electrode 4, the cathode electrode 6 is a platinum electrode with a plate structure, and the anode electrode 4 is an iridium-plated titanium electrode with a mesh structure; the cathode electrode 6 and the anode electrode 4 are respectively placed in the center of the cathode chamber 7 and the anode chamber 3, and the two electrodes are arranged opposite to each other; the cathode electrode 6 and the anode electrode 4 are connected to a regulated DC power supply through an electrode rod and a wire; a magnetic stirrer 8 is built in the cathode chamber 7. One end of the cathode electrode rod is connected in series with the platinum electrode with a plate structure, and the other end is connected to the negative electrode of the power supply through a wire; one end of the anode electrode rod is connected in series with the iridium-plated titanium mesh electrode with a mesh structure, and the other end is connected to the positive electrode of the power supply through a wire.

[0072] The cathode chamber 7 and the anode chamber 3 are both made of organic glass, with a size of Φ60mm×80mm, a thickness of 2.5mm, and an effective volume of 200mL; the platinum electrode with a plate structure has a size of 10mm×10mm×0.2mm; the iridium-plated titanium electrode with a mesh structure has a size of 30mm×30mm, and the effective area of ​​the coating is about 6.3cm 2 ; The N117 proton exchange membrane separates the electrolytic cell, and its size is Φ30mm. Two concentric circle structured silica gel gaskets are sandwiched at the connection between the cathode chamber 7 and the anode chamber 3, and the size is Φ30mm in outer diameter, Φ15mm in inner diameter, and hollow inside; the N117 proton exchange membrane is sandwiched between the two silica gel gaskets. The built-in magnetic stirrer 8 in the cathode chamber 7 has a size of Φ5×30mm.

[0073] Prepare 400 mL of an acid mine wastewater solution with a ferrous ion mass concentration of 800 mg / L and a pH of 2.5, wherein the iron source is ferrous sulfate heptahydrate ion. Add 22 g of sodium sulfate to prepare an electrolyte solution with a mass concentration of 15 g / L, then add 200 mL of acid mine wastewater and sodium sulfate as cathode electrolyte into the cathode chamber 7, and another 200 mL as anode electrolyte into the anode chamber 3, and the speed of the magnetic stirrer 8 is 300 r / min. The electrolysis reaction is carried out at a current intensity of 60 mA and a temperature of 30°C. Take 2 mL of water sample for testing at intervals. After the water quality test is qualified, stop the electrolysis reaction and collect the electrolysis product Fe3O4 in the cathode chamber by magnetic separation. The concentration change of the ferrous ion during the electrolysis process is as shown in the figure. Figure 2 As shown, from Figure 2It can be seen that after 250 minutes of electrolysis, the removal rate of divalent iron ions in the wastewater is close to 100%, and the electricity consumption is 10.8 kWh / ton. Referring to the "Electricity Price List for Commercial and Industrial Users of State Grid Jiangxi Electric Power Co., Ltd.", the price of electricity for large industrial electricity 1-10 kV is 0.6974125 yuan / kWh, and the average cost is about 7.5 yuan / ton.

[0074] XRD analysis was performed on the electrolysis products collected by magnetic separation (such as Figure 3 ). Figure 3 It can be seen that the diffraction peaks of the electrolysis products at 2θ values ​​of 30.1°, 35.5°, 43.2°, 53.4°, 56.9° and 62.5° correspond to the (220), (311), (400), (422), (511) and (440) crystal planes of ferroferric oxide with spinel structure. The results of XRD test show that the main component of the electrolysis product of acid mine wastewater is ferroferric oxide.

[0075] The electrolysis products collected by magnetic separation were analyzed for purity, VSM and DLS (such as Figure 4 and 5 The purity of the electrolysis product is 99%, the saturation magnetization is 54.2emu / g, and the particle size is 297±1.6nm.

[0076] Example 2

[0077] The same reactor and method as in Example 1 were used to electrolyze acid mine wastewater of different concentrations. 400 mL of an acid mine wastewater solution with a mass concentration of 200 mg / L of ferrous ions and a pH of 2.5 was prepared, wherein the iron source was ferrous sulfate heptahydrate ions. 30 g of sodium sulfate was added to prepare an electrolyte solution with a mass concentration of 20 g / L, and then 200 mL of acid mine wastewater and sodium sulfate were added to the cathode chamber 7 as cathode electrolyte, and another 200 mL was added to the anode chamber 3 as anode electrolyte, and the speed of the magnetic stirrer 8 was 330 r / min. The electrolysis reaction was carried out at a current intensity of 60 mA and a temperature of 35°C. 2 mL of water samples were taken for testing at intervals. After the water quality test was qualified, the electrolysis reaction was stopped, and the electrolysis product Fe3O4 in the cathode chamber was collected by magnetic separation. The concentration change of ferrous ions during the electrolysis process is as shown in the figure: Figure 6 As shown, from Figure 6 It can be seen that after 100 minutes of electrolysis, the removal rate of divalent iron ions in the wastewater is close to 100%, and the electricity consumption is 4.3 kWh / ton. Referring to the "Electricity Price List for Commercial and Industrial Users of State Grid Jiangxi Electric Power Co., Ltd.", the price of electricity for large industrial electricity 1-10 kV is 0.6974125 yuan / kWh, and the electricity cost is about 3.0 yuan / ton.

[0078] The above iron ion concentration wastewater is treated with limestone neutralization process with the same power consumption of 2.5 kWh / ton. According to the "Electricity Price List for Commercial and Industrial Users of State Grid Jiangxi Electric Power Co., Ltd.", the price of large industrial electricity 1-10 kV is 0.6974125 yuan / kWh, and the electricity cost is 1.8 yuan / ton, plus the cost of chemicals of 12 yuan / ton and the cost of sludge treatment of 4.9 yuan / ton, the average cost is about 18.7 yuan / ton.

[0079] The precipitate collected by magnetic separation was subjected to XRD analysis (e.g. Figure 7 ). Figure 7 It can be seen that the diffraction peaks of the electrolysis products at 2θ values ​​of 30.1°, 35.5°, 43.2°, 53.4°, 56.9° and 62.5° correspond to the (220), (311), (400), (422), (511) and (440) crystal planes of ferroferric oxide with spinel structure. The results of XRD test show that the main component of the electrolysis products of acid mine drainage with different divalent iron ion concentrations is ferroferric oxide.

[0080] Example 3

[0081] The same reactor and method as in Example 1 were used to electrolyze acid mine wastewater of different pH values. 400 mL of an acid mine wastewater solution with a mass concentration of 800 mg / L of ferrous ions and a pH of 4.5 was prepared, wherein the iron source was ferrous sulfate heptahydrate. 44 g of sodium sulfate was added to prepare an electrolyte solution with a mass concentration of 30 g / L, and then 200 mL of acid mine wastewater and sodium sulfate were added to the cathode chamber 7 as cathode electrolyte, and another 200 mL was added to the anode chamber 3 as anode electrolyte, and the speed of the magnetic stirrer 8 was 280 r / min. The electrolysis reaction was carried out at a current intensity of 60 mA and a temperature of 25°C. 3 mL of water sample was taken for testing at intervals. After the water quality test was qualified, the electrolysis reaction was stopped, and the electrolysis product Fe3O4 in the cathode chamber was collected by magnetic separation. The concentration change of ferrous ions during the electrolysis process is as shown in the figure: Figure 8 As shown, from Figure 5 It can be seen that after 150 minutes of electrolysis, the removal rate of divalent iron ions in the wastewater is close to 100%, and the electricity consumption is 6.5 kWh / ton. Referring to the "Electricity Price List for Commercial and Industrial Users of State Grid Jiangxi Electric Power Co., Ltd.", the price of electricity for large industrial electricity 1-10 kV is 0.6974125 yuan / kWh, and the electricity cost is about 4.5 yuan / ton.

[0082] The precipitate collected by magnetic separation was subjected to XRD analysis (e.g. Fig. 9 ). Fig. 9It can be seen that the diffraction peaks of the electrolysis products at 2θ values ​​of 30.1°, 35.5°, 43.2°, 53.4°, 56.9° and 62.5° correspond to the (220), (311), (400), (422), (511) and (440) crystal planes of ferroferric oxide with spinel structure. The results of XRD test show that the main component of the electrolysis products of acid mine drainage with different pH values ​​is ferroferric oxide.

[0083] Example 4

[0084] The same reactor and method as in Example 1 were used to electrolyze acid mine wastewater containing other different ions, the wastewater pH was 2.5, the mass concentration of Fe(II) was 800 mg / L, the other ions were Fe(III), Cu(II), Mn(II), Zn(II), As(V) and Cr(III), the mass concentration of the other ions in the electrolyte was 50 mg / L, and 22 g of sodium sulfate was added to prepare an electrolyte solution with a mass concentration of 15 g / L. 400 mL of electrolyte containing a binary system of Fe(II) and Fe(III), Fe(II) and Cu(II), Fe(II) and Mn(II), Fe(II) and Zn(II), Fe(II) and As(V), Fe(II) and Cr(III) were prepared respectively, wherein each ion source was hydrated ferric sulfate, copper sulfate pentahydrate, hydrated manganese sulfate, zinc sulfate heptahydrate, disodium hydrogen arsenate heptahydrate and anhydrous chromium sulfate. The above binary system of acid mine wastewater was electrolyzed at a current intensity of 60 mA and a temperature of 30°C. 2 mL of samples were taken at intervals to detect the removal of metal ions in the binary system. Finally, the results were compared with those of Example 1. Fig.10 As shown, Fig.10 The time corresponding to the vertical axis is the electrolysis time used when each pollutant is below 0.3 mg / L. Fig.10 It can be seen that when other ions are present, the removal time of divalent iron ions will change, but all pollutants can be removed. Among them, the presence of Fe(III), Cu(II) and Zn(II) will inhibit the removal of Fe, the presence of Mn(II) and Cr(III) will promote the removal of Fe, and the presence of As(V) has no effect on the removal of Fe. Fe(III), Cu(II), Zn(II), Mn(II) and Cr(III) are mainly removed by co-precipitation with Fe(II); As(V) is removed by adsorption.

[0085] The precipitate collected by magnetic separation was subjected to XRD analysis (e.g. Fig.11 and Fig.12 ). Fig.11 and 12It can be seen that the diffraction peaks of the electrolysis products at 2θ values ​​of 30.1°, 35.5°, 43.2°, 53.4°, 56.9° and 62.5° correspond to the (220), (311), (400), (422), (511) and (440) crystal planes of ferroferric oxide with spinel structure. The results of XRD test show that the main component of the electrolysis product of acid mine wastewater containing interfering ions is ferroferric oxide.

[0086] Example 5

[0087] The same reactor and method as in Example 1 were used to electrolyze a sample of acid mine wastewater obtained from a mine in Loudi City.

[0088] The acid mine wastewater is a water sample obtained from a mine in Loudi City, in which: the divalent iron ion concentration is about 706 mg / L, the total iron concentration is about 722 mg / L, the manganese concentration is about 10.6 mg / L, and the pH is 4.3. Take 400 mL of the above wastewater, add 22 g of sodium sulfate to prepare an electrolyte solution with a mass concentration of 15 g / L, and then add 200 mL of electrolyte as cathode electrolyte into the cathode chamber 7, and another 200 mL as anode electrolyte into the anode chamber 3, and the speed of the magnetic stirrer 8 is 300 r / min. The electrolysis reaction is carried out at a current intensity of 60 mA and a temperature of 35°C. At intervals, 2 mL of water sample is taken for testing. After the water quality test is qualified, the electrolysis reaction is stopped, and the electrolysis product Fe3O4 in the cathode chamber is collected by magnetic separation. The changes in ion concentration during the electrolysis process are as follows: Fig.13 As shown, from Fig.13 It can be seen that after 190 minutes of electrolysis, the removal rate of iron and manganese ions is close to 100%, which meets the iron and manganese ion emission standards in the national standard GB3838-2002 "Surface Water Environmental Quality Standard".

[0089] The precipitate collected by magnetic separation was subjected to XRD analysis (e.g. Fig.14 ). Fig.14 It can be seen that the diffraction peaks of the electrolysis products at 2θ values ​​of 30.1°, 35.5°, 43.2°, 53.4°, 56.9° and 62.5° correspond to the (220), (311), (400), (422), (511) and (440) crystal planes of ferroferric oxide with spinel structure. The results of XRD test show that the main component of the electrolysis products of the actual acid mine wastewater from Loudi is ferroferric oxide.

[0090] Example 6

[0091] The same reactor and method as in Example 1 were used to electrolyze a water sample of acid mine wastewater obtained from a mine in Zhuzhou City.

[0092] The acid mine wastewater is a water sample obtained from a mine in Zhuzhou City, in which: the divalent iron ion concentration is about 635 mg / L, the total iron concentration is 653 mg / L, the manganese concentration is about 9.6 mg / L, and the pH is 4.5. Take 400 mL of the above wastewater, add 22 g of sodium sulfate to prepare an electrolyte solution with a mass concentration of 15 g / L, and then add 200 mL of electrolyte as cathode electrolyte into the cathode chamber 7, and another 200 mL as anode electrolyte into the anode chamber 3, and the speed of the magnetic stirrer 8 is 300 r / min. The electrolysis reaction is carried out at a current intensity of 60 mA and a temperature of 25°C. At intervals, 2 mL of water sample is taken for testing. After the water quality test is qualified, the electrolysis reaction is stopped, and the electrolysis product Fe3O4 in the cathode chamber is collected by magnetic separation. The changes in ion concentration during the electrolysis process are as follows: Fig.15 As shown, from Fig.15 It can be seen that after 180 minutes of electrolysis, the removal rate of iron and manganese ions is close to 100%, which meets the iron and manganese ion emission standards in the national standard GB3838-2002 "Surface Water Environmental Quality Standard".

[0093] The precipitate collected by magnetic separation was subjected to XRD analysis (e.g. Fig.16 ). Fig.16 It can be seen that the diffraction peaks of the electrolysis products at 2θ values ​​of 30.1°, 35.5°, 43.2°, 53.4°, 56.9° and 62.5° correspond to the (220), (311), (400), (422), (511) and (440) crystal planes of ferroferric oxide with spinel structure. The results of XRD test show that the main component of the electrolysis product of the actual acid mine wastewater from Zhuzhou is ferroferric oxide.

[0094] Example 7

[0095] The same reactor and method as in Example 1 were used to electrolyze a sample of acid mine wastewater obtained from a mine in Dexing City.

[0096] The acid mine wastewater is a water sample obtained from a mine in Dexing City, in which: the divalent iron ion concentration is about 1050 mg / L, the total iron concentration is 1155 mg / L, the manganese concentration is about 242 mg / L, and the pH is 3.3. Take 400 mL of the above wastewater, add 22 g of sodium sulfate to prepare an electrolyte solution with a mass concentration of 15 g / L, and then add 200 mL of electrolyte as cathode electrolyte into the cathode chamber 7, and another 200 mL as anode electrolyte into the anode chamber 3, and the speed of the magnetic stirrer 8 is 300 r / min. The electrolysis reaction is carried out at a current intensity of 60 mA and a temperature of 30°C. At intervals, 2 mL of water sample is taken for testing. After the water quality test is qualified, the electrolysis reaction is stopped, and the electrolysis product Fe3O4 in the cathode chamber is collected by magnetic separation. The changes in ion concentration during the electrolysis process are as follows: Fig.17 As shown, from Fig.17 It can be seen that after 270 minutes of electrolysis, the removal rate of iron and manganese ions is close to 100%, which meets the iron and manganese ion emission standards in the national standard GB3838-2002 "Surface Water Environmental Quality Standard".

[0097] The precipitate collected by magnetic separation was subjected to XRD analysis (e.g. Fig.18 ). Fig.18 It can be seen that the diffraction peaks of the electrolysis products at 2θ values ​​of 30.1°, 35.5°, 43.2°, 53.4°, 56.9° and 62.5° correspond to the (220), (311), (400), (422), (511) and (440) crystal planes of ferroferric oxide with spinel structure. The results of XRD test show that the main component of the electrolysis products of the actual acid mine wastewater from Dexing is ferroferric oxide.

[0098] Example 8

[0099] The same reactor as in Example 1 is used, except that the platinum electrode with a plate-like structure of the cathode electrode 6 is replaced by a titanium electrode and a nickel electrode with a plate-like structure of the cathode electrode 6 .

[0100] Prepare 400 mL of an acid mine wastewater solution with a ferrous ion mass concentration of 800 mg / L and a pH of 2.5, wherein the iron source is ferrous sulfate heptahydrate ion. Add 22 g of sodium sulfate to prepare an electrolyte solution with a mass concentration of 15 g / L, then add 200 mL of acid mine wastewater and sodium sulfate as cathode electrolyte into the cathode chamber 7, and another 200 mL as anode electrolyte into the anode chamber 3. Select titanium and nickel sheets to replace the platinum sheet as the cathode, and the speed of the magnetic stirrer 8 is 300 r / min. The electrolysis reaction is carried out at a current intensity of 60 mA and a temperature of 25°C. Take 3 mL of water sample for testing at intervals. After the water quality test is qualified, stop the electrolysis reaction, and collect the electrolysis product Fe3O4 in the cathode chamber by magnetic separation. The concentration change of the ferrous ion during the electrolysis process is as follows: Fig.19 As shown, from Fig.19 It can be seen that after 250 minutes of electrolysis, the removal rate of divalent iron ions in the wastewater is close to 100%.

[0101] Example 9

[0102] The same reactor as in Example 1 is used, except that the iridium-plated titanium electrode with a mesh structure of the anode electrode 4 is replaced by a platinum-titanium electrode and an iridium-tantalum-titanium electrode with a mesh structure of the anode electrode 4 .

[0103] Prepare 400 mL of an acid mine wastewater solution with a ferrous ion mass concentration of 800 mg / L and a pH of 2.5, wherein the iron source is ferrous sulfate heptahydrate ion. Add 22 g of sodium sulfate to prepare an electrolyte solution with a mass concentration of 15 g / L, then add 200 mL of acid mine wastewater and sodium sulfate as cathode electrolyte into the cathode chamber 7, and another 200 mL as anode electrolyte into the anode chamber 3. Select a platinum titanium mesh or an iridium tantalum titanium mesh to replace the iridium-plated titanium mesh as the anode, and the speed of the magnetic stirrer 8 is 300 r / min. Carry out the electrolysis reaction at a current intensity of 60 mA and a temperature of 25°C. Take 2 mL of water sample for testing at intervals. After the water quality test is qualified, stop the electrolysis reaction, and collect the electrolysis product Fe3O4 in the cathode chamber by magnetic separation. The concentration change of the ferrous ion during the electrolysis process is as follows: Fig. 20 As shown, from Fig. 20 It can be seen that after 260 minutes of electrolysis, the removal rate of divalent iron ions in the wastewater is close to 100%.

[0104] Example 10

[0105] The same reactor as in Example 1 was used, except that the 5-diaphragm N117 proton exchange membrane was replaced with a FAA-3-20 anion exchange membrane.

[0106] Prepare 400 mL of an acid mine wastewater solution with a ferrous ion mass concentration of 800 mg / L and a pH of 2.5, wherein the iron source is ferrous sulfate heptahydrate ion. Add 22 g of sodium sulfate to prepare an electrolyte solution with a mass concentration of 15 g / L, then add 200 mL of acid mine wastewater and sodium sulfate as cathode electrolyte into the cathode chamber 7, and another 200 mL as anode electrolyte into the anode chamber 3. Select FAA-3-20 anion exchange membrane as the diaphragm, and the speed of the magnetic stirrer 8 is 300 r / min. Carry out the electrolysis reaction at a current intensity of 60 mA and a temperature of 25°C. Take 2 mL of water sample for testing at intervals. After the water quality test is qualified, stop the electrolysis reaction, and collect the electrolysis product Fe3O4 in the cathode chamber by magnetic separation. The concentration change of the ferrous ion during the electrolysis process is as follows: Fig.21 As shown, from Fig.21 It can be seen that after 220 minutes of electrolysis, the removal rate of divalent iron ions in the wastewater is close to 100%.

[0107] Embodiment 11

[0108] The same reactor as in Example 1 was used to electrolyze acid mine wastewater at different current intensities. 400 mL of an acid mine wastewater solution with a mass concentration of 800 mg / L of ferrous ions and a pH of 2.5 was prepared, wherein the iron source was ferrous sulfate heptahydrate. 22 g of sodium sulfate was added to prepare an electrolyte solution with a mass concentration of 15 g / L, and then 200 mL of acid mine wastewater and sodium sulfate were added to the cathode chamber 7 as cathode electrolyte, and another 200 mL was added to the anode chamber 3 as anode electrolyte, and the speed of the magnetic stirrer 8 was 300 r / min. The electrolysis reaction was carried out at a current intensity of 120 mA and a temperature of 30°C. 2 mL of water sample was taken for testing at intervals. After the water quality test was qualified, the electrolysis reaction was stopped, and the electrolysis product Fe3O4 in the cathode chamber was collected by magnetic separation. The concentration change of ferrous ions during the electrolysis process is as shown in the figure: Fig. 22 As shown, from Fig. 22 It can be seen that after 140 minutes of electrolysis, the removal rate of divalent iron ions in the wastewater is close to 100%.

[0109] The precipitate collected by magnetic separation was subjected to XRD analysis (e.g. Fig.23 ). Fig.23 It can be seen that the diffraction peaks of the electrolysis products at 2θ values ​​of 30.1°, 35.5°, 43.2°, 53.4°, 56.9° and 62.5° correspond to the (220), (311), (400), (422), (511) and (440) crystal planes of ferroferric oxide with spinel structure. The results of XRD test show that the main component of the electrolysis products obtained by electrolyzing acid mine wastewater with different current intensities is ferroferric oxide.

[0110] Comparative Example 1

[0111] The reactor and method of Example 1 are different, except that 400 mL of the acid mine wastewater solution prepared with a mass concentration of 800 mg / L of divalent iron ions and a pH of 2.5 is replaced with 400 mL of the acid mine wastewater solution prepared with a mass concentration of 800 mg / L of trivalent iron ions and a pH of 2.5. Then 200 mL of the acid mine wastewater is added to the cathode chamber 7 as the cathode electrolyte, and another 200 mL is added to the anode chamber 3 as the anode electrolyte. The speed of the magnetic stirrer 8 is 300 r / min. The electrolytic reaction is carried out at a current intensity of 60 mA and a temperature of 30°C. 2 mL of the water sample is taken for detection at intervals. After 180 minutes, the electrolytic reaction is stopped. The collected precipitate is subjected to XRD analysis (such as Fig.24 ). Fig.24 It can be seen that the diffraction peak of the electrolysis product corresponds to the standard card of Schroeder mineral. The results of XRD test show that the main component of the electrolysis product of electrolysis of acid mine wastewater is Schroeder mineral, not ferroferric oxide.

[0112] Comparative Example 2

[0113] The reactor and method of Example 1 are used, except that 7.4 g of sodium sulfate is added to prepare an electrolyte solution with a mass concentration of 5 g / L instead of adding 22 g of sodium sulfate to prepare an electrolyte solution with a mass concentration of 15 g / L. Then 200 mL of electrolyte is added to the cathode chamber 7 as the cathode electrolyte, and another 200 mL is added to the anode chamber 3 as the anode electrolyte. The speed of the magnetic stirrer 8 is 300 r / min. The electrolysis reaction is carried out at a current intensity of 60 mA and a temperature of 30°C. 2 mL of water sample is taken for detection at intervals. After 270 minutes, the electrolysis reaction is stopped. The change in ion concentration during the electrolysis process is shown in the following figure. Fig.25 As shown, from Fig.25 It can be seen that after 270 minutes of electrolysis, the iron ion removal rate is 61%, which does not meet the ion emission standard in the national standard GB3838-2002 "Surface Water Environmental Quality Standard".

[0114] From the effects of the electrolytic reactions of Examples 1-11 and Comparative Examples 1-2, it can be seen that Examples 1-11 using the reactor and method of the present invention have significantly better iron ion removal effects, and no other chemical additives need to be added to the electrolyte solution to generate solid ferroferric oxide electrolytic products. Other pollutants in wastewater can also be removed while removing iron, and the iron removal rate is close to 100%, with high treatment efficiency and low cost. The main product after treatment is ferroferric oxide, which is easy to recycle, and the removal effect of pollutants will not be affected in the presence of other ions.

[0115] The method provided by the present invention can recover ferrous iron from acid mine wastewater by electrolysis and synthesize ferroferric oxide. The method provided by the present invention recovers ferrous iron from acid mine wastewater and synthesizes ferroferric oxide. The method for treating acid mine wastewater does not require the addition of chemical additives when removing iron ions from wastewater. The treatment efficiency of Fe is as high as 100%, the cost is low, and the main product after treatment is ferroferric oxide with a purity of 99%, a particle size of 297±1.6nm, and a saturation magnetization of 54.2emu / g. It has high application value and can be recovered by magnetic separation; in the presence of other ions, the main composition of the product is not affected. At the same time, the method can achieve a removal rate of 100% for pollutants such as arsenic (V), chromium (III), manganese (II), copper (II) and zinc (II).

[0116] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for recovering ferrous iron from acid mine wastewater and synthesizing ferrosoferric oxide, characterized in that: The method includes: Acidic mine wastewater is added to the cathode chamber and anode chamber of a reactor for electrolysis reaction, and the electrolysis product nano-ferroferric oxide is collected in the cathode chamber; the conditions of the electrolysis reaction at least meet the following requirements: electrolyte concentration of 15-30 g / L, current intensity of 60-120 mA, temperature of 25-35° C., pH of 2.5-4.5, and stirring speed of 280-330 r / min.

2. The method according to claim 1, characterized in that The reactor comprises an electrolytic cell (1) and a diaphragm (5) arranged in the electrolytic cell (1), wherein the diaphragm (5) can separate the electrolytic cell (1) into a cathode chamber (7) and an anode chamber (3), and a magnetic stirrer (8) is built in the cathode chamber (7).

3. The method according to claim 2, characterized in that The reactor further comprises a cathode electrode (6) and an anode electrode (4); the cathode electrode (6) is a plate-like structure, and the anode electrode (4) is a mesh-like structure.

4. The method according to claim 3, characterized in that The cathode electrode (6) is a platinum metal plate, a titanium metal plate or a nickel metal plate, and the anode electrode (4) is an iridium-plated titanium mesh, a platinum-plated titanium mesh or an iridium-tantalum-titanium mesh; Preferably, the cathode electrode (6) is a platinum metal plate, and the anode electrode (4) is an iridium-plated titanium mesh.

5. The method according to claim 2, characterized in that: The diaphragm (5) is a proton exchange membrane or an anion exchange membrane; Preferably, the membrane (5) is a proton exchange membrane.

6. The method according to claim 2, characterized in that The rotation speed of the magnetic stirrer (8) is 280-330 r / min.

7. The method according to claim 1, characterized in that The electrolyte is sodium sulfate, and the mass concentration of the electrolyte is 15-30 g / L; Preferably, the mass concentration of divalent iron ions in the acid mine wastewater is 200-800 mg / L.

8. The method according to claim 7, characterized in that The acid mine wastewater may also contain interfering ions; Preferably, the interfering ions are selected from at least one of pentavalent arsenic ions, trivalent chromium ions, divalent manganese ions, divalent copper ions and divalent zinc ions; Preferably, the mass concentration of the interfering ions should be no higher than 50 mg / L.

9. The method according to claim 8, characterized in that The electrolysis time of the electrolysis reaction is 100-280 minutes, and the mass concentration of each ion is lower than 0.3 mg / L when the electrolysis is stopped.

10. The method according to claim 1, characterized in that The electrolysis product, nano-ferroferric oxide, is produced in the cathode chamber (7); Preferably, the purity of the nano-ferroferric oxide is 95-99%, the particle size is 295-300nm, and the saturation magnetization is 54-60emu / g; Preferably, the electrolysis product, nano-ferroferric oxide, can be recovered by magnetic separation.

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