Process method for producing zinc oxide by recovering zinc from waste galvanized steel sheet

Abstract

The invention discloses a process method for producing zinc oxide by recovering zinc from waste galvanized steel sheets. The process method comprises the following steps: step 01, carrying out corrosion reaction on galvanized steel sheet wastes and acid liquor; 02, reacting the liquid with a hydrogen peroxide solution; step 03, injecting a sodium hydroxide solution into the liquid; step 04, filtering the liquid to obtain a ferric hydroxide flocculate precipitate; and step 05, filtering impurities in selective chelating adsorption resin to obtain a zinc-containing solution. Step 06, adding a sodium hydroxide solution into the zinc-containing solution to obtain a sodium metazincate solution; step 07, filtering the sodium metazincate solution, and introducing carbon dioxide gas into the obtained filtrate to obtain a sodium bicarbonate solution; and step 08, carrying out centrifugal separation on the solution, and calcining the obtained solid to obtain zinc oxide. According to the method, the zinc is effectively extracted by adopting the waste galvanized steel as the raw material, and the economic benefit of treating the waste galvanized steel is improved.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization technology of solid waste materials, and in particular to a process for recovering zinc from waste galvanized steel sheets to produce zinc oxide. Background Technology

[0002] Large quantities of galvanized steel sheets are used and processed into various equipment, generating galvanized steel scrap, offcuts, defective products, and galvanized steel waste from the processing of scrap equipment. These scrap galvanized steel materials typically require recycling to achieve resource reuse. Previously, a furnace remelting method was used to process scrap galvanized steel sheets. However, this method involves directly remelting the galvanized steel sheets in a scrap electric arc furnace. Because the temperature in the furnace exceeds 1000℃, surpassing the boiling point of zinc (906℃), a large amount of zinc enters the furnace ash. The zinc extraction process from the furnace ash is lengthy, energy-intensive, and inefficient. To achieve effective zinc recovery, current methods for recovering zinc during the processing of scrap galvanized steel include: alkaline dissolution, mechanical removal and reprocessing, vacuum baking, and acid dissolution.

[0003] The alkaline dissolution method involves directly immersing zinc from galvanized steel sheets in sodium hydroxide solution, but the alkaline dissolution process is slow and inefficient.

[0004] Mechanical removal and reprocessing methods typically employ shot peening, where zinc is removed by baking and shot peening at temperatures ranging from 495℃ to 550℃. The removed zinc is then sent to a recycled zinc plant for smelting. This process is complex, involves a poor working environment, and requires a large workload. Although it achieves a certain degree of zinc recovery, it results in significant loss of the substrate, low zinc recovery rate, and secondary pollution.

[0005] The vacuum baking method involves placing hot-dip galvanized scrap steel sheets in a vacuum furnace, raising the furnace temperature to over 900°C, and maintaining a vacuum level of <13Pa inside the furnace. Although this method can achieve high-purity zinc recovery, the recovery rate is low and the cost is difficult to control.

[0006] The acid dissolution method involves directly immersing galvanized steel sheets in an inorganic acid solution, causing the zinc to dissolve in the acid. While this method is highly efficient, its biggest problem is the presence of acid in the wastewater, resulting in large discharge volumes and heavy pollution, thus reducing the yield of zinc. Furthermore, the low yield is primarily due to the difficulty in separating iron from zinc.

[0007] Although there are currently jaundice alum process, goethite process and hematite process for removing iron after zinc leaching, these methods are not suitable for producing high-purity zinc oxide because they are applicable to iron concentrations exceeding 1 g / L after iron removal and require a large amount of chemical reagents or high energy consumption. Extraction methods can extract zinc or iron into the organic phase, which has a certain separation effect, but the extraction efficiency is low and the iron entrainment rate after extraction is high.

[0008] The ammonia process for producing high-purity zinc oxide can be referenced, which uses ammonia water to react with zinc sulfate to precipitate zinc. However, this method uses ammonia water as a raw material, which results in the volatilization of ammonia waste gas during the production process and the need to treat ammonia-containing wastewater, leading to increased environmental governance costs.

[0009] In summary, all current processes for recovering zinc from scrap galvanized steel have certain shortcomings. Considering the high efficiency of acid dissolution for industrial applications, it is the current research direction. The main problems in this process are: waste acid pollution and difficulty in separating zinc from iron after acid etching. The recovery rate and purity of zinc oxide are not high, and the environmental governance pressure is great. Summary of the Invention

[0010] This invention provides a process for recovering zinc from waste galvanized steel sheets to produce zinc oxide, thereby overcoming the shortcomings of the prior art. This method achieves efficient zinc recovery from galvanized steel sheets, solves the pollution problem during the recovery process, improves the zinc recovery rate, and produces high-purity zinc oxide products.

[0011] In order to achieve the objectives of this invention, the following technologies are proposed: A process for recycling zinc from waste galvanized steel sheets to produce zinc oxide includes the following steps: Step 01: The galvanized steel scrap and acid solution undergo a dissolution reaction for 0.5 to 2 hours; Step 02: After filtering the liquid obtained after dissolution, inject hydrogen peroxide solution into the filtered liquid. The galvanized steel sheet scrap after erosion is cleaned with demineralized water, and the resulting galvanized steel sheet scrap is first pressed into blocks and then smelted in an electric furnace. Step 03: Sodium hydroxide solution is injected into the liquid in step 02 where hydrogen peroxide was injected, so that the pH value of the liquid is 3-4, and iron hydroxide colloids, which are reddish-brown flocculent precipitates, are produced. Step 04: Filter the liquid after step 03 to obtain ferric hydroxide flocculent gel precipitate, and transport it off-site for treatment of ferric hydroxide.

[0012] Step 05: The liquid obtained in step 04 is injected into a selective chelation adsorption resin for impurity filtration to obtain a zinc-containing solution.

[0013] Step 06: Add sodium hydroxide solution to the zinc-containing solution obtained in step 05 to make the pH value of the zinc-containing solution above 12, and obtain sodium zincate solution. Step 07: Filter the sodium zincate solution obtained in step 06, and pass carbon dioxide gas into the filtrate to react the carbon dioxide with the filtrate to obtain a sodium bicarbonate solution containing zinc hydroxide precipitate. Step 08: Centrifuge the sodium bicarbonate solution containing zinc hydroxide precipitate, and calcine the resulting solid to obtain zinc oxide; Add acid to the sodium bicarbonate solution obtained after centrifugation to obtain a sodium salt solution.

[0014] Furthermore, in step 01, the solid-liquid ratio of the galvanized steel scrap and the acid solution is 1:3 to 1:12.

[0015] Furthermore, the acid solution used in step 01 is one of sulfuric acid solution, hydrochloric acid solution, or nitric acid solution.

[0016] Furthermore, the concentration of the acid solution used in step 01 is 5% to 20%.

[0017] Furthermore, in step 01, during the etching reaction, an acid-resistant circulating pump is activated to circulate and stir the acid solution. During the etching reaction, the consumed acid solution is replenished, and the generated hydrogen gas is diluted and discharged. The circulation of the acid solution stirs the solution, facilitating full contact between the acid solution and the galvanized steel waste. Simultaneously, the replenishment of consumed acid solution during circulation maintains the etching reaction within a certain acidity range, promoting the reaction's progress.

[0018] Further, step 04 involves fractional filtration to separate the colloidal precipitate of ferric hydroxide; The colloidal precipitate of ferric hydroxide with a particle size greater than 20 μm in the liquid was separated by coarse filtration. Ferric hydroxide colloidal precipitate with a particle size greater than 100 nm was separated by microfiltration membrane; The colloidal precipitate of ferric hydroxide is separated using an ultrafiltration membrane with a hydrophilic coating. The hydrophilic coating reduces the surface tension of the ultrafiltration membrane, making it less likely for ferric hydroxide to be adsorbed onto the membrane. Cross-flow filtration in the ultrafiltration membrane reduces contamination, improves filtration efficiency, and extends its service life.

[0019] Furthermore, in step 05, the selective chelating adsorption resin is a resin that selectively adsorbs iron ions. The selective chelating adsorption resin can be selected from either an iminodiacetic acid type resin or a nuclear-grade sulfonic acid type resin. The iminodiacetic acid type resin can be either DIAION CR11 or Lewatit TP260, and the nuclear-grade sulfonic acid type resin can be Tulsimer T-62MP.

[0020] Furthermore, in step 07, when carbon dioxide gas reacts with the filtrate, the clarified liquid after separating the hydroxide precipitate is pressurized and then sent into the reaction cylinder of the micro-interface reaction system. Carbon dioxide enters the reaction cylinder after passing through the microporous membrane bubble generator of the micro-interface reaction system and reacts with the zinc solution to produce a white precipitate. The slurry containing the white precipitate flows out from the bottom of the reaction cylinder.

[0021] The micro-interface reaction system is a technology that enhances mass transfer and reaction. This technology introduces carbon dioxide gas into the cylinder of the micro-interface reaction system after passing it through a microporous membrane bubble generator. There, it reacts with pressurized zinc solution injected through a nozzle within the reaction cylinder, forming micron-sized bubbles through eddies and shear forces. This overcomes the liquid film resistance of carbon dioxide entering the liquid, significantly increasing the gas-liquid interface area and thus enhancing mass transfer and reaction rates. More specifically, the microporous membrane bubble generator injects pressurized carbon dioxide gas into the reaction cylinder at high speed and a small flow rate through pressure-resistant micropores. The high-speed gas cuts and shears the zinc solution, forming tiny droplets, ensuring sufficient contact between the gas and liquid. Through this interaction, uniform micron-sized bubbles are formed.

[0022] Further, in step 09, the obtained sodium salt solution is passed through a bipolar membrane electrodialysis device to obtain sodium hydroxide solution and the corresponding acid solution, respectively. Step 10: Concentrate the sodium hydroxide solution and the corresponding acid solution obtained in Step 09; The resulting concentrated sodium hydroxide solution is added to the liquid containing hydrogen peroxide in step 03 and / or added to the zinc-containing solution in step 06. The resulting concentrated acid solution is added to step 01 for a dissolution reaction, thus achieving the reuse of acid and alkali and reducing reagent spillage and wastewater discharge.

[0023] Furthermore, the concentration of the concentrated sodium hydroxide solution in step 10 is 20%; The concentration of the acid solution after concentration in step 10 is 20%.

[0024] The advantages of the above technical solution are: Firstly, this invention uses scrap galvanized steel as raw material to effectively extract zinc, thereby improving the economic benefits of processing scrap galvanized steel.

[0025] Secondly, this invention reduces product impurities and improves product purity. This invention enables the effective separation of ferric hydroxide flocculent colloids. Addressing the difficulty in filtering ferric hydroxide flocculent colloids and precipitates, this invention employs a three-stage filtration process—coarse filtration, microfiltration, and ultrafiltration—to effectively filter ferric hydroxide in different forms; simultaneously, selective chelating resins are used to further treat trace amounts of metallic impurities.

[0026] Thirdly, this invention can improve the filtration efficiency and extend the service life of ultrafiltration membranes. The ultrafiltration membrane of this invention has a hydrophilic coating, which not only reduces surface tension during filtration, causing ferric hydroxide colloids to be carried away by the water flow instead of adsorbing onto the ultrafiltration membrane; the cross-flow ultrafiltration structure in the ultrafiltration membrane allows the liquid to wash over the membrane surface, preventing the formation of a filter cake and avoiding concentration polarization; it is also less prone to fouling when filtering ferric hydroxide colloidal substances, enabling continuous and effective separation.

[0027] Fourth, this invention increases the yield of zinc oxide products. This invention employs micro-interface reaction technology, which causes carbon dioxide to form tiny bubbles in the solution, promoting an increase in the interfacial transfer rate between carbon dioxide and sodium zincate solution, thus significantly enhancing the reaction rate and conversion rate; it not only reduces the amount of carbon dioxide used but also reduces the reactor volume.

[0028] Fifth, this invention can significantly reduce the cost of purchased chemical reagents, reduce waste acid emissions, and decrease environmental pollution. This invention uses bipolar membrane electrodialysis technology to produce the required acid-base solution from the generated sodium salt, which can then be reused in the zinc extraction process. Attached Figure Description

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings.

[0030] Appendix Figure 1 This is a process flow diagram of the recycling of zinc from waste galvanized steel sheets to produce zinc oxide, as described in this invention.

[0031] Appendix Figure 2 This is a schematic diagram of the micro-interface reaction system described in this invention. In the diagram, 1 represents the micro-interface reactor cylinder, 2 represents the microporous membrane bubble generator, 3 represents the liquid nozzle, 4 represents the reaction zone, 5 represents the gas-liquid separation zone, 6 represents the demister, 7 represents the gas outlet, 8 represents the slurry outlet, 9 represents the gas nozzle, and 10 represents the overflow port. Detailed Implementation

[0032] Example 1 After being crushed into steel sheets, galvanized steel sheets are placed in an acid dissolution reactor and soaked with 10% sulfuric acid at a solid-liquid ratio of 1:10. To enhance the reaction, a sulfuric acid circulation pump is turned on to circulate and agitate the sulfuric acid in the acid dissolution reactor; simultaneously, the consumed acid solution is replenished intermittently. After 0.5 hours of sulfuric acid etching, the zinc in the galvanized steel sheets dissolves in the acid solution, while the iron also reacts with the sulfuric acid. The iron-containing zinc sulfate solution enters the oxidation reactor from the bottom of the acid dissolution reactor through a filter. In the oxidation reactor, hydrogen peroxide is added according to the iron ion content to oxidize ferrous iron to ferric iron; then it enters the pH adjustment tank, where the pH is adjusted to 3-4 with concentrated sodium hydroxide solution. Ferric hydroxide forms a reddish-brown flocculent precipitate. After the zinc sulfate solution is discharged from the acid dissolution reactor, the dezincified steel sheets are unloaded into a washing device, where residual acid on the steel sheets is washed with demineralized water. The dezincified steel sheets are then sent to a briquetting machine, briquetting them before being sent to an electric furnace for remelting.

[0033] A zinc solution containing reddish-brown flocculent ferric hydroxide in a colloidal state was first passed through a coarse filter to remove ferric hydroxide precipitate particles larger than 20 μm. The ferric hydroxide was then pressurized to approximately 0.2 MPa and passed through a microfiltration membrane to remove ferric hydroxide flocculants and suspended solids with a particle size larger than 100 nm. The filtrate was then pressurized to approximately 0.3 MPa and passed through an ultrafiltration membrane to remove ferric hydroxide colloids in the 1 nm to 100 nm range. The separated ferric hydroxide was then transported for further processing.

[0034] A zinc solution containing most of the ferric hydroxide, after being removed, enters a selective adsorption resin to adsorb trace amounts of iron and some metal ions. The pH of the zinc solution after iron removal is adjusted to above 12 using a concentrated sodium hydroxide solution, completely converting it into a sodium zincate solution. Trace amounts of manganese in the zinc solution precipitate as Mn(OH)₂. After centrifugation, this precipitate enters the micro-interface reaction system. Pressurized carbon dioxide, after passing through a microporous membrane bubble generator, is stably injected into the reactor cylinder as a high-speed, fine gas stream. This gas comes into contact with the pressurized sodium zincate solution, which is then sprayed from a nozzle. The high-speed carbon dioxide gas continuously cuts through the sodium zincate solution, causing collisions and diffusion. Through eddies and shear forces, bubbles with a particle size of 10μm to 50μm are formed. These carbon dioxide bubbles continuously react with the sodium zincate to produce zinc hydroxide precipitate and sodium bicarbonate. The carbon dioxide gas is discharged after passing through a demister at the top of the micro-interface reactor, while the zinc hydroxide slurry is discharged from the bottom of the reactor. After centrifugation and calcination, zinc oxide is obtained. Sodium bicarbonate solution is neutralized with acid solution and then subjected to bipolar membrane electrodialysis to obtain sodium hydroxide solution and corresponding acid solution. The sodium hydroxide solution and acid solution are then concentrated to 20% concentration. The concentrated alkaline and acid solutions are returned to the intended use of the system, achieving recycling and reducing waste acid emissions.

[0035] The concentration of zinc leached was 5 g / L, the concentration of iron was 1.2 g / L, and the concentration of manganese was 0.0015 g / L. No clogging of the microfiltration and ultrafiltration membranes occurred during the iron separation process, and the yield of zinc oxide was 90%, with a purity greater than 99.7%.

[0036] Example 2 After being crushed into steel sheets, galvanized steel sheets are placed in an acid dissolution reactor and soaked with 20% sulfuric acid at a solid-liquid ratio of 1:8. To enhance the reaction, a sulfuric acid circulation pump is turned on to circulate and agitate the sulfuric acid in the acid dissolution reactor; the consumed acid solution is replenished every 20 minutes. After 1 hour of sulfuric acid etching, the zinc in the galvanized steel sheets dissolves in the acid solution, while the iron also reacts with the sulfuric acid. The iron-containing zinc sulfate solution enters the oxidation reactor from the bottom of the acid dissolution reactor through a filter. In the oxidation reactor, hydrogen peroxide is added according to the iron ion content to oxidize ferrous iron to ferric iron; then it enters the pH adjustment tank, where the pH is adjusted to 3-4 with concentrated sodium hydroxide solution. Ferric hydroxide forms a reddish-brown flocculent precipitate. After the zinc sulfate solution is discharged from the acid dissolution reactor, the dezincified steel sheets are unloaded into a washing device, where residual acid on the steel sheets is washed with demineralized water. The dezincified steel sheets are then sent to a briquetting machine, briquetting them before being sent to an electric furnace for remelting.

[0037] A zinc solution containing reddish-brown flocculent ferric hydroxide in a colloidal state was first passed through a coarse filter to remove ferric hydroxide precipitate particles larger than 20 μm. The ferric hydroxide was then pressurized to approximately 0.2 MPa and passed through a microfiltration membrane to remove ferric hydroxide flocculants and suspended solids with a particle size larger than 100 nm. The filtrate was then pressurized to approximately 0.3 MPa and passed through an ultrafiltration membrane to remove ferric hydroxide colloids in the 1 nm to 100 nm range. The separated ferric hydroxide was then transported for further processing.

[0038] The zinc-containing solution, after most of the ferric hydroxide has been removed, enters a selective adsorption resin to adsorb trace amounts of iron and some metal ions. The pH of the zinc solution after iron removal is adjusted to above 12 using a concentrated sodium hydroxide solution, completely converting the zinc solution into a sodium zincate solution. Trace amounts of manganese in the zinc solution precipitate as Mn(OH)₂. After centrifugation, this precipitate enters the micro-interface reaction system. Pressurized carbon dioxide, after passing through a microporous membrane bubble generator, is stably injected into the reactor cylinder as a high-speed, fine gas stream. This carbon dioxide comes into contact with the pressurized sodium zincate solution, which is sprayed from a nozzle. The high-speed carbon dioxide gas continuously cuts through the sodium zincate solution, causing collisions and diffusion. Through eddies and shear forces, bubbles with a particle size of 10μm to 50μm are formed. These carbon dioxide bubbles continuously react with the sodium zincate to produce zinc hydroxide precipitate and sodium bicarbonate. The carbon dioxide gas is discharged after passing through a demister at the top of the micro-interface reactor, while the zinc hydroxide slurry is discharged from the bottom of the reactor. After centrifugation and calcination, zinc oxide is obtained. Sodium bicarbonate solution is neutralized with acid solution and then subjected to bipolar membrane electrodialysis to obtain sodium hydroxide solution and corresponding acid solution. The sodium hydroxide solution and acid solution are then concentrated to 20% concentration. The concentrated alkaline and acid solutions are returned to the intended use of the system, achieving recycling and reducing waste acid emissions.

[0039] The concentration of zinc leached was 85 g / L, the concentration of iron was 35 g / L, and the concentration of manganese was 0.03 g / L. During the iron separation process, a large amount of ferric hydroxide was generated, the ultrafiltration membrane operating pressure reached 0.6 MPa, and the yield of zinc oxide reached 98%, with a purity greater than 99.7%.

[0040] Example 3 After being crushed into steel sheets, galvanized steel sheets are placed in an acid dissolution reactor and soaked with 5% sulfuric acid at a solid-liquid ratio of 1:10. To enhance the reaction, a sulfuric acid circulation pump is turned on, circulating and agitating the sulfuric acid within the reactor. After 1 hour of sulfuric acid immersion, the zinc in the steel sheets dissolves in the acid, while the iron also reacts with the sulfuric acid. The iron-containing zinc sulfate solution flows from the bottom of the acid dissolution reactor through a filter into an oxidation reactor. In the oxidation reactor, hydrogen peroxide is added according to the iron ion content to oxidize ferrous iron to ferric iron; then, the solution enters a pH adjustment tank, where a concentrated sodium hydroxide solution is used to adjust the pH to 3-4. Ferric hydroxide forms a reddish-brown flocculent precipitate. After the zinc sulfate solution is drained from the acid dissolution reactor, the dezincified steel sheets are unloaded into a washing device, where residual acid is washed off with demineralized water. The dezincified steel sheets are then fed into a briquetting machine, briquetting them before being sent to an electric furnace for remelting.

[0041] A zinc solution containing reddish-brown flocculent ferric hydroxide in a colloidal state was first passed through a coarse filter to remove ferric hydroxide precipitate particles larger than 20 μm. The ferric hydroxide was then pressurized to approximately 0.2 MPa and passed through a microfiltration membrane to remove ferric hydroxide flocculants and suspended solids with a particle size larger than 100 nm. The filtrate was then pressurized to approximately 0.3 MPa and passed through an ultrafiltration membrane to remove ferric hydroxide colloids in the 1 nm to 100 nm range. The separated ferric hydroxide was then transported for further processing.

[0042] The zinc-containing solution, after most of the ferric hydroxide has been removed, enters a selective adsorption resin to adsorb trace amounts of iron and some metal ions. The pH of the zinc solution after iron removal is adjusted to above 12 using a concentrated sodium hydroxide solution, completely converting the zinc solution into a sodium zincate solution. Trace amounts of manganese in the zinc solution precipitate as Mn(OH)₂. After centrifugation, this precipitate enters the micro-interface reaction system. Pressurized carbon dioxide, after passing through a microporous membrane bubble generator, is stably injected into the reactor cylinder as a high-speed, fine gas stream. This carbon dioxide comes into contact with the pressurized sodium zincate solution, which is sprayed from a nozzle. The high-speed carbon dioxide gas continuously cuts through the sodium zincate solution, causing collisions and diffusion. Through eddies and shear forces, bubbles with a particle size of 10μm to 50μm are formed. These carbon dioxide bubbles continuously react with the sodium zincate to produce zinc hydroxide precipitate and sodium bicarbonate. The carbon dioxide gas is discharged after passing through a demister at the top of the micro-interface reactor, while the zinc hydroxide slurry is discharged from the bottom of the reactor. After centrifugation and calcination, zinc oxide is obtained. Sodium bicarbonate solution is neutralized with acid solution and then subjected to bipolar membrane electrodialysis to obtain sodium hydroxide solution and corresponding acid solution. The sodium hydroxide solution and acid solution are then concentrated to 20% concentration. The concentrated alkaline and acid solutions are returned to the intended use of the system, achieving recycling and reducing waste acid emissions.

[0043] The concentration of leached zinc was 3.0 g / L, the concentration of iron was 0.25 g / L, and the concentration of manganese was 0.001 g / L. During the iron separation process, the amount of ferric hydroxide produced was small. No fouling of the microfiltration membrane and ultrafiltration membrane occurred during the iron separation process. The ultrafiltration membrane operating pressure reached 0.25 MPa. The yield of zinc oxide was 80%, and its purity was greater than 99.7%.

[0044] The micro-interface reaction system provided in the above embodiments includes a micro-interface reactor cylinder 1. The upper end of the micro-interface reactor cylinder 1 has a cylindrical structure, and the lower end has a conical structure. The diameter of the lower end of the micro-interface reactor cylinder 1 is smaller than that of the upper end. The upper end of the micro-interface reactor cylinder 1 has a gas-liquid separation zone 5. Air and sodium zincate solution splashed onto the gas-liquid separation zone 5 will flow upward due to carbon dioxide, while the sodium zincate solution will settle downward. The upper end of the micro-interface reactor cylinder 1 is provided with a demister 6. The sodium zincate solution is adsorbed or blocked by the filter membrane in the demister 6 to prevent it from being discharged. In addition, a microporous plate can also be provided inside it to prevent the eccentric sodium zincate solution from escaping upward. The upper end of the demister 6 is provided with a gas outlet 7. To ensure the space height for gas-liquid separation, an overflow port 10 is connected to the gas-liquid separation zone 5 of the micro-interface reactor cylinder 1. When the liquid level exceeds the upper limit, it will be discharged from the overflow port 10, thereby ensuring the normal operation of gas-liquid separation and preventing the space of the gas-liquid separation zone 5 from shrinking as the liquid level rises, which would cause the gas-liquid separation to fail.

[0045] Multiple liquid nozzles 3 are fixed to the upper end of the micro-interface reactor cylinder 1. Each liquid nozzle 3 has an inner column with multiple spiral grooves arranged in a spiral pattern on its outer periphery. The inner wall of the liquid nozzle 3 has outer spiral grooves that match the spiral grooves. Thus, when the sodium zincate solution passes through, it will rotate. Furthermore, the liquid nozzles 3 are located below the gas-liquid separation zone 5. More specifically, the axial direction of the liquid nozzles 3 is arranged along the tangent of the inner periphery of the micro-interface reactor cylinder 1. More preferably, the axial direction of the liquid nozzles 3 is slightly inclined downwards. With this arrangement, when the sodium zincate solution is sprayed into the micro-interface reactor cylinder 1, it will flow downwards in a spiral pattern along the inner wall of the micro-interface reactor cylinder 1.

[0046] At least one microporous membrane bubble generator 2 is fixed on the micro-interface reactor cylinder 1. Multiple gas nozzles 9 are connected to the inner end of the microporous membrane bubble generator 2. Pressurized carbon dioxide is introduced into the microporous membrane bubble generator 2, and then the carbon dioxide is ejected through the gas nozzles 9. The micro-interface reactor cylinder 1 also has a reaction zone 4, located below the liquid nozzle 3 and in some areas where the gas nozzles 9 are located. In this way, when carbon dioxide is ejected, it will come into contact with and react with the sodium zincate solution, significantly improving the reaction efficiency between the sodium zincate solution and carbon dioxide. The resulting zinc hydroxide solution is discharged through the slurry outlet 8 located at the lower end of the micro-interface reactor cylinder 1.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A process for recovering zinc from waste galvanized steel sheets to produce zinc oxide, characterized in that, Including the following steps: Step 01: The galvanized steel scrap and acid solution undergo a dissolution reaction for 0.5 to 2 hours; Step 02: After filtering the liquid obtained after dissolution, inject hydrogen peroxide solution into the filtered liquid. The galvanized steel sheet scrap after erosion is cleaned with demineralized water, and the resulting galvanized steel sheet scrap is then smelted. Step 03: Inject sodium hydroxide solution into the liquid in which hydrogen peroxide was injected in Step 02 to make the pH value of the liquid 3-4; Step 04: Filter the liquid after step 03 to obtain ferric hydroxide flocculent gel precipitate, and transport the obtained ferric hydroxide flocculent gel precipitate for off-site processing. Step 05: The liquid obtained in step 04 is injected into a selective chelation adsorption resin for impurity filtration to obtain a zinc-containing solution. Step 06: Add sodium hydroxide solution to the zinc-containing solution obtained in step 05 to make the pH value of the zinc-containing solution above 12, and obtain sodium zincate solution. Step 07: Filter the sodium zincate solution obtained in step 06, and pass carbon dioxide gas into the filtrate to react the carbon dioxide with the filtrate to obtain a sodium bicarbonate solution containing zinc hydroxide precipitate. Step 08: Centrifuge the sodium bicarbonate solution containing zinc hydroxide precipitate, and calcine the resulting solid to obtain zinc oxide; Add acid to the sodium bicarbonate solution obtained after centrifugation to obtain a sodium salt solution.

2. The process for recovering zinc from waste galvanized steel sheets to produce zinc oxide according to claim 1, characterized in that, In step 01, the solid-liquid ratio of the galvanized steel scrap and the acid solution is 1:3 to 1:

12.

3. The process for recovering zinc from waste galvanized steel sheets to produce zinc oxide according to claim 1, characterized in that, The acid solution used in step 01 is one of sulfuric acid solution, hydrochloric acid solution, or nitric acid solution.

4. The process for recovering zinc from waste galvanized steel sheets to produce zinc oxide according to claim 1, characterized in that, The concentration of the acid solution used in step 01 is 5% to 20%.

5. The process for recovering zinc from waste galvanized steel sheets to produce zinc oxide according to claim 1, characterized in that, In step 01, the acid solution is in a circulating state during the dissolution reaction.

6. The process for recovering zinc from waste galvanized steel sheets to produce zinc oxide according to claim 1, characterized in that, Step 04 involves fractional filtration to separate the colloidal precipitate of ferric hydroxide. The colloidal precipitate of ferric hydroxide with a particle size greater than 20 μm in the liquid was separated by coarse filtration. Ferric hydroxide colloidal precipitate with a particle size greater than 100 nm was separated by microfiltration membrane; The colloidal precipitate of ferric hydroxide was separated using an ultrafiltration membrane with a hydrophilic coating.

7. The process for recovering zinc from waste galvanized steel sheets to produce zinc oxide according to claim 1, characterized in that, In step 05, the selective chelation adsorption resin is a resin that selectively adsorbs iron ions.

8. The process for recovering zinc from waste galvanized steel sheets to produce zinc oxide according to claim 1, characterized in that, In step 07, when carbon dioxide gas reacts with the filtrate, the resulting filtrate passes through a micro-interface reaction system, and carbon dioxide gas is injected into the micro-interface reaction system to allow the carbon dioxide to react with the filtrate.

9. The process for recovering zinc from waste galvanized steel sheets to produce zinc oxide according to claim 1, characterized in that, Step 09: The obtained sodium salt solution is passed through a bipolar membrane electrodialysis device to obtain sodium hydroxide solution and the corresponding acid solution, respectively. Step 10: Concentrate the sodium hydroxide solution and the corresponding acid solution obtained in Step 09; The resulting concentrated sodium hydroxide solution is added to the liquid containing hydrogen peroxide in step 03 and / or to the zinc-containing solution in step 06. The resulting concentrated acid solution is added to step 01 to carry out the dissolution reaction.

10. The process for recovering zinc from waste galvanized steel sheets to produce zinc oxide according to claim 9, characterized in that, The concentration of the concentrated sodium hydroxide solution in step 10 is 20%. The concentration of the acid solution after concentration in step 10 is 20%.

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