Method for recovering iron-containing waste acid through synergistic electrochemical method and contact catalysis method

Abstract

The invention provides a method for recovering iron-containing waste acid through a synergistic electrochemical method and a contact catalysis method, and relates to the technical field of waste acid treatment and resource recovery. The method comprises the following steps: S1, filtering the iron-containing waste acid solution to remove suspended solids and solid residues; s2, measuring the content of H < + > and iron ions with different valence states in the iron-containing waste acid solution, carrying out electrolysis under the condition of ultrasonic catalytic treatment, and oxidizing ferrous ions into ferric ions through generated redox pairs; s3, after the electrolytic reaction is finished, alkali is added into the iron-containing waste acid solution in the step S2, the PH value is adjusted to be alkaline, and then the reaction is conducted; and S4, adding water for dilution, filtering to obtain iron oxide, and concentrating filtrate to obtain inorganic salt. The problems of large equipment investment, easy secondary pollution to the environment, long reaction time, low purity of the recovered product and the like existing in iron-containing waste hydrochloric acid recovery in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of waste acid treatment and resource recovery, and particularly to a method for recovering iron-containing waste acid by synergistic electrochemical method and contact catalysis method. Background Art

[0002] When producing steel in industrial production, a large amount of hydrochloric acid is consumed for pickling before surface treatments such as hot-dip galvanizing, electroplating, powder spraying, and electrophoresis to remove rust on the surface. For steel surface treatment enterprises, hundreds of tons of waste acid are discharged every day. The general composition of hydrochloric acid pickling wastewater is that the free acid content is 1-10%, and the ferrous chloride content is 5-30%. At the same time, some heavy metals and other impurities are accompanied. If these acid waste liquids are discharged without treatment, it will not only pollute the environment but also waste precious resources. Therefore, preparing industrial products with market value has long-term social significance. At present, most domestic factories use the neutralization method to treat waste acid liquid. This method is simple to operate and convenient to use. Although the one-time investment is small, the operating cost is relatively high. Its fatal disadvantage is that it produces a large amount of sludge and a large amount of wastewater, and it is not easy for the COD and heavy metal values of the wastewater to meet the national discharge standards, resulting in secondary pollution. Other methods for treating iron-containing hydrochloric acid wastewater include extraction method, spray roasting method, fluidized bed roasting method, evaporation crystallization roasting method, and chlorine oxidation method. The Chinese patent application with the application number 201910645685.8 proposes to carry out the first oxidation by catalytic oxidation with compressed air or oxygen, and then select hydrogen peroxide or sodium chlorate for secondary oxidation. Although this method does not introduce new impurities, does not waste resources, and completely recycles the waste, the first catalytic oxidation time is 3-7 h, and the second oxidation time is 1-2 h. The oxidation rate is slow, and the cost of the oxidant is relatively high, which is not conducive to large-scale waste acid recovery; the Chinese patent application with the application number CN202111339620.4 proposes to use nitric acid as a catalyst to catalyze the oxidation of oxygen, and then distill under reduced pressure to separate dilute hydrochloric acid and iron phosphate solution. However, during the oxidation process, as the temperature changes, nitric acid may decompose into toxic gas nitrogen dioxide, and distillation under reduced pressure requires a vacuum system, which has high requirements for containers and high energy consumption; in addition, common methods also include neutralization precipitation method, high-temperature roasting method, solvent extraction method, etc. The disadvantage is that a lot of sludge will be generated during the treatment process, causing secondary pollution; the salt concentrate and iron oxide are likely to cause blockage and scaling in the equipment during the roasting process; and generally, highly efficient extractants are toxic organic solvents, and a large amount of extractants are required during the treatment process, with high costs.

[0003] In recent years, the electrochemical method has been applied to a certain extent in the field of recovering iron-containing waste hydrochloric acid. The electrochemical method realizes the separation and migration of ions through the action of an electric field, and can recover hydrochloric acid and iron resources. The Chinese invention patent application with the application number 202411469355.5 discloses a method for electrochemically recovering iron-containing waste hydrochloric acid to prepare iron oxide and calcium chloride, belonging to the technical field of waste acid treatment. The method includes: S1. Place a cathode and an anode at both ends of the electrolytic cell respectively, separate the cathode and anode with a diaphragm, filter the iron-containing waste hydrochloric acid, remove suspended substances and solid residues, and then introduce it into the electrolytic cell; S2. Measure the iron element content and free acid content in the iron-containing waste hydrochloric acid, and add a neutralizing agent to neutralize the excess free acid; S3. Apply a voltage between the cathode and the anode according to the iron element content, carry out an electrolytic reaction to generate an oxidation intermediate, and use the oxidation intermediate to oxidize the iron element, thus obtaining a precipitate of iron oxide and a calcium chloride solution; S4. Add an appropriate amount of water to the reaction solution for dilution, filter to obtain iron oxide, and concentrate the filtrate to obtain calcium chloride. The Japanese invention patent application with the application number 2011500014 discloses an electrochemical method for simultaneously recovering iron-containing metals and chlorine from an iron-rich metal chloride solution. The method includes a cathode electrolytic cell having a hydrogen overvoltage about 2 or lower than that of iron, including a cathode chamber containing a cathode electrolyte with a pH of 1, an anode chamber containing an anode feldspar, and a partition allowing anions to pass through; the electrolysis process includes circulating an iron-rich metal chloride solution in the non-anode chamber of the electrolytic cell, thereby electroplating iron on the cathode, generating chlorine at the anode, removing it, and at least part of the solution is discharged; recovering in the iron-rich metal chloride solution; the iron-rich metal chloride solution is derived from carbon chloride waste, waste acid leaching solution or acid cleaning solution. However, the simple electrochemical method has problems such as low recovery efficiency and high energy consumption. Summary of the Invention

[0004] The main purpose of the present invention is to provide a method for recovering iron-containing waste acid by synergistically combining the electrochemical method and the contact catalytic method, so as to solve the problems existing in the recovery of iron-containing waste acid in the prior art, such as large equipment investment, easy secondary pollution to the environment, long reaction time and low purity of the recovered products.

[0005] The present invention uses a method of synergistically combining the electrochemical method and the contact catalytic method. First, a redox pair with strong oxidizing properties is prepared in the waste liquid as a clean oxidant, and the redox pair is used to selectively oxidize ferrous ions in the waste acid, doubling the yield of intermediate products at least, and forming a gradient oxidation system. No additional oxidants need to be added, no new impurities are generated during the oxidation process, the recovery time is shortened by half, the products are controllable, and the product purity is increased to more than 97%, having significant economic and social benefits.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is a method for recovering iron-containing waste acid by combining an electrochemical method and a contact catalysis method, comprising the following steps: S1. Filter the iron-containing waste acid solution to remove suspended solids and solid residues; S2. Measure the content of free acid and the content of iron ions in different valence states in the iron-containing waste acid solution, and perform electrolysis under the condition of ultrasonic catalytic treatment. The generated redox pair oxidizes ferrous ions to ferric ions; S3. After the electrolysis reaction ends, add alkali to the iron-containing waste acid solution in step S2, adjust the pH value to alkaline, and then carry out the reaction; S4. Dilute with water and then filter to obtain iron oxides, and concentrate the filtrate to obtain inorganic salts.

[0007] Principle of the ultrasonic-assisted electrolysis process: 1) Electrolysis can oxidize chloride ions and sulfate ions in the solution to hypochlorite ions, persulfate ions, etc. Ultrasonic oscillation further generates hydrogen peroxide, and the formed redox system has strong oxidizing properties; 2) The formed redox system can form chlorine oxide radicals, hydroxyl radicals, persulfate radicals, etc. under the catalysis of iron ions in the iron-containing waste liquid, further enhancing the oxidizing property and the concentration of oxidizing substances in the solution; 3) Ultrasonic oscillation can also promote the mixing of substances in the solution, catalyze the reaction and the subsequent reaction of iron ion oxidation. From the perspective of electrochemical principle, the greater the concentration of hydrogen ions and the lower the pH value, the stronger the oxidizing property of the redox pair generated by ultrasonic and electrolysis, and the easier it is for ferrous ions to be oxidized to ferric ions. The higher the ultrasonic frequency and the higher the voltage, the more redox pairs are generated. However, too high voltage will cause side reactions such as electrolysis of water, reducing the energy conversion efficiency.

[0008] In the preferred embodiment, the content of free acid in the iron-containing waste acid solution described in step S1 is 1% - 20%, and the content of iron ions is 5% - 30%.

[0009] In the preferred embodiment, the acid in the iron-containing waste acid solution described in step S1 is one of hydrochloric acid, sulfuric acid or their mixed solution.

[0010] In the preferred embodiment, the cell body material of the electrolytic cell for the electrolysis reaction described in step S2 includes 316L stainless steel, polytetrafluoroethylene, polyethylene, fiberglass, cement or ceramic.

[0011] In the preferred embodiment, the anode electrode material for the electrolysis reaction described in step S2 is one or a composite of several elements among Pt, Ti, graphite, diamond, Pd, Au, B, Ni, Mn, Co or C3N4; the cathode electrode material is one or a composite of several elements among Pt, Ti, Ru, Ir, Sn, Pb, C, B, Ni, Mn or Co.

[0012] In the preferred embodiment, the addition amount of the iron-containing waste acid solution in the electrolysis reaction process described in step S2 is 10% to 80% of the volume of the electrolytic cell.

[0013] In the preferred embodiment, the ultrasonic frequency of the ultrasonic catalytic treatment described in step S2 is 2 to 150 KHz. If the frequency is too low, the reaction kinetics is insufficient and there are fewer redox pairs; if it is too high, the ultrasonic probe will overheat, affecting its lifespan.

[0014] In the preferred embodiment, the voltage of the electrolysis reaction described in step S2 is 1.2 to 12 V. If the voltage is too low, the rate of conversion of chloride ions and sulfate ions in the electrolytic oxidation solution to hypochlorite ions, persulfate ions, etc. is slow, or even no reaction occurs; if the voltage is too high, side reactions such as electrolysis of water will occur.

[0015] In the preferred embodiment, the redox pairs described in step S2 include hydroxyl radicals, persulfate radicals, hydrogen peroxide, hypochlorite ions, and persulfate ions.

[0016] In the preferred embodiment, the temperature of the reaction described in step S3 is 0.1 to 90 °C, the pH value is 8 to 13, and the time is 0.5 to 6 h. Temperature affects the rate of the redox reaction, especially the rate of generation of redox products by ultrasonic oscillation; ferrous ions are oxidized to ferric ions within such a pH value range, and corresponding oxides are formed; if the time is too short, the aging time is insufficient to completely form iron oxides, and if the time is too long, the iron oxides will grow too large.

[0017] In a further preferred embodiment, the pH value of the reaction described in step S3 is 10 to 11.

[0018] In the preferred embodiment, the alkali described in step S3 includes one or more of calcium hydroxide, calcium oxide, sodium hydroxide, or sodium oxide.

[0019] In the preferred embodiment, the inorganic salts described in step S4 include one or more of calcium chloride, calcium sulfate, sodium chloride, or sodium sulfate.

[0020] In the preferred embodiment, the iron oxide described in step S4 includes at least one of magnetite, hematite, or a mixture thereof.

[0021] In a further preferred embodiment, in step S2, when the molar ratio of ferrous ions to ferric ions after the electrolysis reaction is controlled to be 1:2, the iron oxide described in step S4 is magnetite.

[0022] In a further preferred embodiment, in step S2, when ferrous ions are completely oxidized to ferric ions after the electrolysis reaction, the iron oxide described in step S4 is hematite.

[0023] In the preferred solution, the dilution multiple described in step S4 is 0.5 to 100 times. Excessive dilution will increase the consumption of pure water in the recovery of iron oxides, and the salt solution concentration in the formed filtrate is low, which is not conducive to subsequent sales; a small dilution multiple will affect the recovery purity of iron oxides.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention synergistically combines the electrochemical method and the contact catalysis method to prepare a redox pair with strong oxidizing properties, without the need to additionally add an oxidant, which can reduce the cost of oxidant consumables.

[0025] 2. The present invention introduces ultrasonic waves to generate redox intermediates, which can not only promote the reaction rate of chemical reactions, accelerate the recovery rate, and improve the recovery efficiency. The reaction time of the simple electrochemical method is about 30 minutes, and the reaction time of the present invention is about 10 minutes; moreover, it improves the recovery rate of iron elements, and the recovery rate of iron in the present invention is not less than 96%; at the same time, it can also improve the quality and stability of the product. The purity of iron oxides is as high as 98.1%, and the purity of inorganic salts is as high as 98.3%.

[0026] 3. The present invention is green and clean, and will not cause secondary pollution to the environment during the recovery process like the neutralization method or the roasting method.

[0027] 4. The products of the present invention are diverse. The reaction efficiency can be affected by adjusting the pH value and temperature, and the amount of iron in different valence states in the waste acid can be affected by the parameters of electrolysis and ultrasonic oscillation, so as to control the generated products. Specific Embodiments

[0028] The technical solution of the present invention will be further described and illustrated below through examples. The raw materials used in the examples can be purchased commercially or prepared by conventional methods.

[0029] Example 1 A method for recovering iron-containing waste hydrochloric acid by synergistically combining the electrochemical method and the contact catalysis method, comprising the following steps: S1. Filter the iron-containing waste hydrochloric acid solution to remove suspended substances and solid residues; S2. Measure that the free acid content of the iron-containing waste hydrochloric acid solution is 1%, and the mass fraction of iron ions in different valence states is 8.3%. Electrolyze under the condition of ultrasonic catalytic treatment. The addition amount of the iron-containing waste hydrochloric acid solution is 50% of the volume of the electrolytic cell. Select an electrolytic cell made of polytetrafluoroethylene. The anode electrode material is graphite, and the cathode electrode material is cobalt. Apply a voltage of 12V between the cathode and the anode, and control the ultrasonic frequency at 15 KHz. Use the redox pair hydroxyl radical generated during electrolysis and catalysis to oxidize ferrous ions to ferric ions; S3. After the electrolysis reaction ends, add sodium hydroxide to the iron-containing waste hydrochloric acid solution in step S2 to adjust the pH value to 9, and then react at 70 °C for 1 h; S4. Dilute with water by 1 times and then filter to obtain iron oxides, and concentrate the filtrate to obtain inorganic salt sodium chloride.

[0030] After ICP testing, the purity of the obtained magnetite is 97.5%, and the purity of sodium chloride is 96.8%.

[0031] After calculation, the recovery rate of iron element is 96.2%.

[0032] Example 2 A method for recovering iron-containing waste hydrochloric acid by combining electrochemistry and contact catalysis, comprising the following steps: S1. Filter the iron-containing waste hydrochloric acid solution to remove suspended substances and solid residues; S2. Measure that the free acid content of the iron-containing waste hydrochloric acid solution is 1.8%, and the mass fraction of iron ions in different valence states is 10.4%. Under the condition of ultrasonic catalytic treatment, perform electrolysis. The addition amount of the iron-containing waste hydrochloric acid solution is 80% of the volume of the electrolytic cell. Select an electrolytic cell made of polyethylene. The anode electrode material is Pt, the cathode electrode material is C. Apply a voltage of 1.2 V between the cathode and the anode, control the frequency of the ultrasonic wave at 150 KHz, and use the redox pair hydrogen peroxide generated during electrolysis and catalysis to oxidize ferrous ions to ferric ions; S3. After the electrolysis reaction ends, add sodium hydroxide to the iron-containing waste hydrochloric acid solution in step S2 to adjust the pH value to 12.4, and then react at 10 °C for 6 h; S4. Dilute with water by 100 times and then filter to obtain magnetite, and concentrate the filtrate to obtain inorganic salt sodium chloride.

[0033] After ICP testing, the purity of the obtained iron oxides is 97.4%, and the purity of sodium chloride is 96.8%.

[0034] After calculation, the recovery rate of iron element is 97.9%.

[0035] Example 3 A method for recovering iron-containing waste hydrochloric acid by combining electrochemistry and contact catalysis, comprising the following steps: S1. Filter the iron-containing waste hydrochloric acid solution to remove suspended substances and solid residues; S2. Measure that the free acid content of the iron-containing waste hydrochloric acid solution is 12%, and the mass fraction of iron ions in different valence states is 29%. Electrolyze under the condition of ultrasonic catalysis. The addition amount of the iron-containing waste hydrochloric acid solution is 10% of the volume of the electrolytic cell. Select an electrolytic cell made of cement. The anode electrode material is a Pt-Pd composite, and the cathode electrode material is a Pt-C composite. Apply a voltage of 10 V between the cathode and the anode, control the frequency of the ultrasonic wave at 30 KHz, and use the redox pair hydrogen peroxide generated during the electrolysis and catalysis process to oxidize ferrous ions to ferric ions; S3. After the electrolysis reaction ends, add calcium hydroxide to the iron-containing waste hydrochloric acid solution in step S2 to adjust the pH value to 13, and then react at 50 °C for 3 h; S4. Dilute with water by 50 times and then filter to obtain iron oxide, and concentrate the filtrate to obtain the inorganic salt calcium chloride.

[0036] After ICP testing, the purity of the obtained iron oxide is 98.1%, and the purity of calcium chloride is 97.2%.

[0037] After calculation, the recovery rate of iron elements is 98.2%.

[0038] Example 4 A method for recovering iron-containing waste hydrochloric acid by combining electrochemistry and contact catalysis, comprising the following steps: S1. Filter the iron-containing waste sulfuric acid solution to remove suspended matter and solid residues; S2. Measure that the free acid content of the iron-containing waste hydrochloric acid solution is 4.5%, and the mass fraction of iron ions in different valence states is 20%. Electrolyze under the condition of ultrasonic catalysis. The addition amount of the iron-containing waste sulfuric acid solution is 33% of the volume of the electrolytic cell. Select an electrolytic cell made of stainless steel. The anode electrode material is diamond, and the cathode electrode material is a Ni-Mn composite. Apply a voltage of 2.0 V between the cathode and the anode, control the frequency of the ultrasonic wave at 150 KHz, and use the redox pair persulfate generated during the electrolysis and catalysis process to oxidize ferrous ions to ferric ions; S3. After the electrolysis reaction ends, add calcium oxide to the iron-containing sulfuric acid solution in step S2 to adjust the pH value to 10, and then react at 30 °C for 1 h; S4. Dilute with water by 30 times and then filter to obtain magnetite, and concentrate the filtrate to obtain the inorganic salt.

[0039] After ICP testing, the purity of the obtained iron oxide is 98.1%, and the purity of calcium sulfate is 98.2%.

[0040] After calculation, the recovery rate of iron elements is 98.3%.

[0041] Example 5 A method for recycling iron-containing waste hydrochloric acid by a synergistic electrochemical method and a contact catalysis method, comprising the following steps: S1. Filter the iron-containing waste sulfuric acid solution to remove suspended matter and solid residues; S2. Measure that the free acid content of the iron-containing waste hydrochloric acid solution is 20%, and the mass fraction of iron ions in different valence states is 30%. Electrolyze under the condition of ultrasonic catalytic treatment. The addition amount of the iron-containing waste hydrochloric acid solution is 60% of the volume of the electrolytic cell. Select an electrolytic cell made of fiberglass. The anode electrode material is B, the cathode electrode material is Sn. Apply a voltage of 8.0 V between the cathode and the anode, control the frequency of the ultrasonic wave at 100 KHz, and use the redox pairs hydrogen peroxide and persulfate generated during the electrolysis and catalysis process to oxidize ferrous ions to ferric ions; S3. After the electrolysis reaction is completed, add sodium hydroxide to the iron-containing sulfuric acid solution in step S2 to adjust the pH value to 11.4, and then react at 60 °C for 3 h; S4. Dilute with water by 20 times and then filter to obtain iron oxide, and concentrate the filtrate to obtain inorganic salts.

[0042] After ICP testing, the purity of the obtained iron oxide is 97.9%, and the purity of sodium sulfate is 98.3%.

[0043] After calculation, the recovery rate of iron elements is 98.1%.

[0044] It should be understood that the above embodiments are only used to illustrate the content of the present invention and are not used to limit the protection scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A method for recovering iron-containing waste acid by a synergistic electrochemical method and a contact catalysis method, characterized in that, It includes the following steps: S1. Filter the iron-containing waste acid solution to remove suspended solids and solid residues; S2. Measure the content of free acid and the content of iron ions in different valence states in the iron-containing waste acid solution, and perform electrolysis under the condition of ultrasonic catalytic treatment. The generated redox pair oxidizes ferrous ions to ferric ions; S3. After the electrolysis reaction ends, add alkali to the iron-containing waste acid solution in step S2, adjust the pH value to alkaline and then carry out the reaction; S4. Dilute with water and filter to obtain iron oxides, and concentrate the filtrate to obtain inorganic salts.

2. The method for recovering iron-containing waste acid by the collaborative electrochemical method and the contact catalysis method according to claim 1, wherein In step S1, the content of free acid in the iron-containing waste acid solution is 1% - 20%, and the content of iron ions is 5% - 30%; the acid in the iron-containing waste acid solution described in step S1 includes one of hydrochloric acid, sulfuric acid or their mixed solution.

3. The method for recovering iron-containing waste acid by synergistic electrochemical method and contact catalysis method according to claim 1, characterized in that: In step S2, the anode electrode material of the electrolysis reaction is one or a composite of several elements among Pt, Ti, graphite, diamond, Pd, Au, B, Ni, Mn, Co or C3N4; the cathode electrode material is one or a composite of several of the elements Pt, Ti, Ru, Ir, Sn, Pb, C, B, Ni, Mn or Co.

4. The method for recovering iron-containing waste acid by a synergistic electrochemical method and a contact catalysis method according to claim 1, wherein In step S2, the ultrasonic frequency of the ultrasonic catalytic treatment is 2 - 150 KHz; the voltage of the electrolysis reaction described in step S2 is 1.2 - 12 V; the redox pair described in step S2 includes hydroxyl radical, persulfate radical, hydrogen peroxide, hypochlorite ion, persulfate ion.

5. The method for recovering iron-containing waste acid by synergistic electrochemical method and contact catalytic method according to claim 1, characterized in that: In step S3, the temperature of the reaction is 0.1 - 90 °C, the pH value is 8 - 13, and the time is 0.5 - 6 h.

6. The method for recovering iron-containing waste acid by synergistic electrochemical method and contact catalysis method according to claim 5, characterized in that: In step S3, the pH value of the reaction is 10 - 11.

7. The method for recovering iron-containing waste acid by synergistic electrochemical method and contact catalysis method according to claim 1, characterized in that: The alkali described in step S3 includes one or several of calcium hydroxide, calcium oxide, sodium hydroxide or sodium oxide.

8. The method for recycling iron-containing waste acid by the collaborative electrochemical method and the contact catalysis method according to claim 1, characterized in that, The inorganic salts described in step S4 include one or several of calcium chloride, calcium sulfate, sodium chloride or sodium sulfate; the iron oxides described in step S4 include at least one of magnetite, ferric oxide or their mixture.

9. The method for recycling iron-containing waste acid by a collaborative electrochemical method and a contact catalysis method according to claim 8, characterized in that, In step S2, when the molar ratio of ferrous ions to ferric ions after the electrolysis reaction is controlled to be 1:2, the iron oxide described in step S4 is magnetite.

10. The method for recovering iron-containing waste acid by synergistic electrochemical method and contact catalytic method according to claim 8, characterized in that: In step S2, after the electrolysis reaction, ferrous ions are completely oxidized to ferric ions, and the iron oxide described in step S4 is ferric oxide.