Process for zinc extraction from zinc suboxide

Abstract

The application discloses a zinc extraction process from secondary zinc oxide, and belongs to the technical field of zinc oxide preparation. In the rotary kiln roasting, composite porous flaky reducing carbon with waste paper, rice husk and wooden chips as main raw materials is used as a reducing agent. Compared with the commercially available anthracite, the composite porous flaky reducing carbon has low cost, realizes resource recycling, and has a large specific surface area and porous properties. A multi-level structure of flaky layers and pores is constructed, so that the contact sites of the composite porous flaky reducing carbon and the secondary zinc oxide are increased. The porous structure can avoid the caking of the material layer caused by the stacking and agglomeration of the flaky layers, and avoid the obstruction of gas flow, so that the pain points of the traditional reducing agent, such as local agglomeration and insufficient contact, are solved. The surface of the composite porous flaky reducing carbon is deposited with calcium oxide. The presence of the calcium oxide can react with a small amount of sulfur elements generated in the rotary kiln roasting process of the composite porous flaky reducing carbon, so as to generate calcium sulfate and reduce the content of sulfur dioxide.

Description

Technical Field

[0001] This invention belongs to the field of zinc oxide preparation technology, specifically a zinc extraction process using secondary zinc oxide. Background Technology

[0002] Currently, zinc oxide production methods include the direct method, the indirect method, and the rotary kiln reduction oxidation method. Existing technology CN110015681A discloses a secondary zinc oxide production process, which uses a mixture of zinc-containing waste slag and anthracite in a certain proportion as raw material in a rotary kiln. It mainly uses carbon monoxide generated from anthracite as a reducing agent for the reaction. This existing technology uses anthracite as a raw material, which increases production costs and wastes coal resources. Furthermore, the use of anthracite in production has strict requirements on the amount of anthracite added and the sulfur content in the anthracite, which limits the development of secondary zinc oxide production processes.

[0003] The primary production method for zinc secondary oxide is the rotary kiln calcination and volatilization method. This method is specifically designed for steel mill flue dust. Flue dust is mixed with coke powder and fed into a rotary kiln. After high-temperature fumigation, the zinc grade in the steel mill flue dust can be increased from ten points to fifty or even sixty points. However, existing zinc secondary oxide production methods have low production efficiency and produce zinc secondary oxide with low purity. Therefore, improving the production efficiency and quality of zinc secondary oxide has become an urgent technical problem to be solved.

[0004] Chinese Patent Announcement No. CN110451556B discloses a production process for zinc oxide, zinc sulfate, and nano zinc oxide. This invention uses household waste to replace anthracite for the production of zinc oxide, which not only saves coal resources and reduces production costs, but also enables the recycling of household waste, thereby achieving the effect of environmental remediation. However, the carbon structure formed by the household waste in this invention is simple and prone to local agglomeration, resulting in insufficient contact sites. Summary of the Invention

[0005] The purpose of this invention is to provide a zinc extraction process using secondary zinc oxide. By adding composite porous sheet-like reducing carbon, mainly composed of waste paper, rice husks, and wood chips, as a reducing agent during rotary kiln roasting, the cost is lower than that of commercially available anthracite, achieving resource recovery. Furthermore, by utilizing the large specific surface area and porous properties of the composite porous sheet-like reducing carbon, a multi-level structure of sheets and pores is constructed, increasing the contact sites between the composite porous sheet-like reducing carbon and secondary zinc oxide. The porous structure can avoid the material layer caking caused by the stacking and agglomeration of sheets, which would obstruct gas flow and completely solve the pain points of local agglomeration and insufficient contact of traditional reducing agents.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A zinc extraction process using zinc oxide secondary oxidation includes the following steps:

[0008] Step 1: Mix waste paper, rice husks and wood chips, grind, crush and calcine to obtain reduced carbon; after hydrothermal pre-exfoliation, use hexadecyltrimethylammonium bromide for intercalation exfoliation to obtain modified flake reduced carbon.

[0009] Step 2: Calcium oxide is deposited on the surface of porous sheet-like reduced carbon using physical adsorption to obtain composite porous sheet-like reduced carbon.

[0010] Step 3: Mix composite porous sheet-like reducing carbon and zinc-containing solid material at a mass ratio of 1:1 to prepare a mixture. Set the rotary kiln to tilt and place the mixture in the rotary kiln for roasting to obtain mixed slag. Then, the mixture moves towards the kiln head and is discharged to form a continuous feeding and slag discharge. The waste heat boiler is used for cooling and the bag filter is used for recovery to complete the secondary zinc oxide zinc extraction process.

[0011] Furthermore, the specific steps for preparing reduced carbon are as follows:

[0012] Waste paper, rice husks, and wood chips are mixed, ground, and pulverized to prepare a reduced carbon precursor with a particle size of 2-4 mm. The precursor is then placed in a muffle furnace and calcined at 700-750℃ for 2-4 hours under nitrogen protection to obtain reduced carbon.

[0013] Furthermore, the specific preparation steps for modified sheet-like reduced carbon are as follows:

[0014] Hydrothermal reduced carbon, hexadecyltrimethylammonium bromide, and methanol were added to a polytetrafluoroethylene hydrothermal reactor at a ratio of 3-3.2 kg: 100-120 g: 9-10 L. The mixture was stirred at 100-110 °C and 500-600 r / min for 24-26 h. After naturally cooling to room temperature, the mixture was centrifuged at 10000-12000 r / min for 3-4 min, filtered, and the filter cake was washed 2-4 times with methanol and deionized water. The cake was then vacuum dried at 60-80 °C for 1-2 h to obtain modified flaky reduced carbon.

[0015] Furthermore, the specific steps for preparing hydrothermally reduced carbon are as follows:

[0016] Reduced carbon and methanol are added to a polytetrafluoroethylene hydrothermal reactor at a ratio of 4-5 kg: 9-10 L. The reactor is hydrothermally reacted at 100-110 °C and 500-600 r / min for 24-26 h. The mixture is filtered, and the filter cake is washed 2-4 times with anhydrous ethanol and deionized water. It is then vacuum dried at 60-80 °C for 1-2 h to obtain hydrothermally reduced carbon.

[0017] Furthermore, the specific preparation steps for porous sheet-like reduced carbon are as follows:

[0018] Urea and deionized water are added to a reaction vessel and stirred for 30-40 minutes at 20-25℃ and 400-500 rpm. Then, modified flaky reduced carbon and sodium dodecyl sulfate are added to the reaction vessel and vacuum impregnated for 2-3 hours at 50-65℃ and 400-500 rpm. The mixture is then filtered, and the filter cake is washed 2-3 times with deionized water and anhydrous ethanol to remove residual urea solution from the surface. The cake is then vacuum dried at 60-80℃ for 1-2 hours, ground, and passed through a 100-120 mesh sieve. It is then transferred to a muffle furnace and kept at 800-900℃ for 4-6 hours under nitrogen protection. After natural cooling, porous flaky reduced carbon is obtained.

[0019] Furthermore, the ratio of urea, deionized water, modified flake reducing carbon, and sodium dodecyl sulfate is 700-800g: 10-12L: 2.5-2.7kg: 100-120g.

[0020] Furthermore, the specific preparation steps for composite porous sheet-like reduced carbon are as follows:

[0021] Porous sheet-like reduced carbon and deionized water are added to a reaction vessel and stirred for 40-50 min at 20-25℃ and 500-600 r / min. Then, calcium oxide powder is added and stirring is continued for 2-3 h. The mixture is then vacuum dried at 60-70℃ for 1-2 h. The product is transferred to a muffle furnace and heated to 700-750℃ at a heating rate of 5-6℃ / min to obtain composite porous sheet-like reduced carbon.

[0022] Furthermore, the ratio of porous sheet-like reduced carbon, deionized water, and calcium oxide powder is 2-2.2 kg: 5-6 L: 480-500 g.

[0023] Furthermore, the specific preparation steps for the mixed slag are as follows:

[0024] Composite porous flaky reducing carbon and zinc-containing solid material are mixed evenly at a mass ratio of 1:1 to prepare a mixture. The rotary kiln is tilted so that the kiln tail is higher than the kiln head, and the length of the rotary kiln is 42m. Then the rotary kiln is started and heated. When the temperature of the kiln tail reaches 480-490℃, the induced draft fan and Roots blower are started. At the same time, the mixture is fed into the rotary kiln tail through a disc feeder and belt conveyor. As the rotary kiln rotates, the mixture tumbles and moves towards the kiln head with the inclination of the rotary kiln and is fed into the rotary kiln for calcination. The temperature inside the rotary kiln is controlled at 1100-1150℃. The mixture is dehydrated and spontaneously combusted in the high-temperature environment to obtain mixed slag.

[0025] Furthermore, the zinc-containing solid material is a mixture composed of flue dust from steel plant flue gas treatment, leaching slag from zinc smelting, water quenching slag from lead smelting, flue dust from copper smelting, and floating slag from recycled scrap copper in a mass ratio of 2:1:1.2:1.1:1.3.

[0026] Furthermore, the specific preparation steps of the zinc extraction process using zinc oxide are as follows:

[0027] The mixed slag moves towards the kiln head and is discharged. The feed rate is 1.5 times the weight of the rotary kiln volume, forming a continuous feeding and slag discharge. The zinc-containing flue gas generated in the rotary kiln moves towards the kiln tail under the action of the induced draft fan and is cooled by the waste heat boiler set at the kiln tail. The temperature of the zinc-containing flue gas at the kiln tail reaches 600-620℃. The waste heat boiler absorbs the heat of the zinc-containing flue gas and generates steam. The zinc-containing flue gas is cooled to 150-160℃ by the waste heat boiler. The secondary zinc oxide in the zinc-containing flue gas is recovered by the bag filter, completing the zinc extraction process of secondary zinc oxide.

[0028] The beneficial effects of this invention are:

[0029] 1. The zinc extraction process for secondary zinc oxide provided by this invention uses composite porous sheet-like reducing carbon, mainly composed of waste paper, rice husks, and wood chips, as a reducing agent during rotary kiln roasting. Compared with commercially available anthracite, this process is lower in cost and achieves resource recovery. Furthermore, by leveraging the large specific surface area and porous properties of the composite porous sheet-like reducing carbon, a multi-level structure of sheets and pores is constructed, increasing the contact sites between the composite porous sheet-like reducing carbon and secondary zinc oxide. The porous structure can prevent the material layer from caking and obstructing gas flow caused by the stacking and agglomeration of sheets, thus completely solving the pain points of local agglomeration and insufficient contact of traditional reducing agents.

[0030] 2. The composite porous sheet-like reduced carbon of the present invention is obtained by depositing calcium oxide on the surface of porous sheet-like reduced carbon. The porous sheet-like reduced carbon is obtained by grinding, crushing and calcining waste paper, rice husks and wood chips to obtain reduced carbon. After hydrothermal pre-exfoliation, it is further exfoliated by hexadecyltrimethylammonium bromide intercalation to obtain modified sheet-like reduced carbon. At this time, the structure of the reduced carbon is mostly stacked sheets. The sheet structure can greatly increase the specific surface area and superimpose urea volatilization to form pores, thereby obtaining porous sheet-like reduced carbon and maximizing the reduction efficiency.

[0031] 3. In this invention, calcium oxide is deposited on the surface of the composite porous sheet-like reduced carbon. The presence of calcium oxide allows it to react with the small amount of sulfur produced during the rotary kiln roasting process of the composite porous sheet-like reduced carbon, thereby generating calcium sulfate and reducing the sulfur dioxide content. The main function of the composite porous sheet-like reduced carbon in extracting zinc oxide is to generate carbon monoxide to reduce zinc-containing solids. However, traditional processes easily lead to excessive or residual carbon monoxide. Carbon monoxide is a highly toxic gas and a toxic flammable pollutant; direct emission would pollute the atmosphere and fail to meet environmental emission standards. However, calcium oxide reacts with the generated calcium sulfate deposited on the surface of the composite porous sheet-like reduced carbon. In the presence of oxygen, through static... The electro-effect and the synergistic adsorption effect of the large specific surface area and porosity of the composite porous sheet-like reduced carbon allow carbon monoxide molecules to adsorb onto the top of calcium atoms on the surface of calcium sulfate. The carbon atoms of carbon monoxide attract each other with the oxygen atoms on the surface of calcium sulfate, thereby pulling the adjacent oxygen atoms away from the surface. Carbon dioxide is then adsorbed onto the calcium atoms on the surface in an inclined manner, so that excess or residual carbon monoxide is converted into non-toxic carbon dioxide for emission, making the overall production process comply with environmental emission standards. Furthermore, the calcium oxide and calcium sulfate deposited by this invention have high melting points and do not volatilize or migrate with the flue gas during the rotary kiln roasting process. Instead, they move along the inclined slope of the kiln body towards the kiln head with the mixed slag and are eventually discharged with the slag. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1: A zinc extraction process using zinc oxide, comprising the following steps:

[0034] S1: Waste paper, rice husks, and wood chips were mixed, ground, and pulverized to prepare a reduced carbon precursor with a particle size of 2 mm. The precursor was placed in a muffle furnace and calcined at 700 °C for 2 h under nitrogen protection to obtain reduced carbon. 4 kg of reduced carbon and 9 L of methanol were added to a polytetrafluoroethylene hydrothermal reactor and hydrothermally reacted at 100 °C and 500 r / min for 24 h. The mixture was filtered, and the filter cake was washed twice with anhydrous ethanol and deionized water, and then vacuum dried at 60 °C for 1 h to obtain hydrothermal reduced carbon. 3 kg of hydrothermal reduced carbon, 100 g of hexadecyltrimethylammonium bromide, and 9 L of methanol were added to a polytetrafluoroethylene hydrothermal reactor and stirred at 100 °C and 500 r / min for 24 h. The mixture was naturally cooled to room temperature, centrifuged at 10000 r / min for 3 min, filtered, and the filter cake was washed twice with methanol and deionized water, and then vacuum dried at 60 °C for 1 h to obtain modified flake-shaped reduced carbon.

[0035] S2: Add 700g of urea and 10L of deionized water to a reactor and stir for 30min at 20℃ and 400r / min. Then add 2.5kg of modified flake reduced carbon and 100g of sodium dodecyl sulfate to the reactor and vacuum impregnate for 2h at 50℃ and 400r / min. Filter the mixture and wash the filter cake twice with deionized water and anhydrous ethanol to remove residual urea solution. Dry the mixture under vacuum at 60℃ for 1h, grind it, pass it through a 100-mesh sieve, transfer it to a muffle furnace, and heat it at 800℃ for 4h under nitrogen protection. Allow it to cool naturally to obtain porous flake reduced carbon.

[0036] S3: Add 2 kg of porous sheet-like reduced carbon and 5 L of deionized water to a reactor and stir for 40 min at 20 °C and 500 r / min. Then add 480 g of calcium oxide powder and continue stirring for 2 h. Dry under vacuum at 60 °C for 1 h. Transfer the product to a muffle furnace and heat to 700 °C at a heating rate of 5 °C / min to obtain composite porous sheet-like reduced carbon.

[0037] S4: The composite porous sheet-like reducing carbon and zinc-containing solid material are mixed evenly at a mass ratio of 1:1 to prepare a mixture. The rotary kiln is tilted so that the kiln tail is higher than the kiln head, and the length of the rotary kiln is 42m. Then the rotary kiln is started and heated. When the temperature of the kiln tail reaches 480℃, the induced draft fan and Roots blower are started. At the same time, the mixture is fed into the rotary kiln tail through a disc feeder and belt conveyor. As the rotary kiln rotates, the mixture rolls towards the kiln head with the tilt of the rotary kiln and is fed into the rotary kiln for roasting. The temperature inside the rotary kiln is controlled at 1100℃. The mixture is dehydrated and spontaneously combusted in the high-temperature environment to obtain mixed slag.

[0038] S5: The mixed slag moves towards the kiln head and is discharged. The feed rate is 1.5 times the weight of the rotary kiln volume to form a continuous feed and slag discharge. The zinc-containing flue gas generated in the rotary kiln moves towards the kiln tail under the action of the induced draft fan and is cooled by the waste heat boiler set at the kiln tail. The temperature of the zinc-containing flue gas at the kiln tail reaches 600℃. The waste heat boiler absorbs the heat of the zinc-containing flue gas and generates steam. The zinc-containing flue gas is cooled to 150℃ by the waste heat boiler. The secondary zinc oxide in the zinc-containing flue gas is recovered by the bag filter dust collector to complete the zinc extraction process of secondary zinc oxide.

[0039] Example 2: A zinc extraction process using zinc oxide, comprising the following steps:

[0040] S1: Waste paper, rice husks, and wood chips were mixed, ground, and pulverized to prepare a reduced carbon precursor with a particle size of 3 mm. The precursor was placed in a muffle furnace and calcined at 725 °C for 3 h under nitrogen protection to obtain reduced carbon. 4.5 kg of reduced carbon and 9.5 L of methanol were added to a polytetrafluoroethylene hydrothermal reactor and hydrothermally reacted at 105 °C and 550 r / min for 25 h. The mixture was filtered, and the filter cake was washed three times with anhydrous ethanol and deionized water. It was then vacuum dried at 70 °C for 1.5 h to obtain hydrothermal reduced carbon. 3.1 kg of hydrothermal reduced carbon, 110 g of hexadecyltrimethylammonium bromide, and 9.5 L of methanol were added to a polytetrafluoroethylene hydrothermal reactor and stirred at 105 °C and 550 r / min for 25 h. The mixture was naturally cooled to room temperature, centrifuged at 11000 r / min for 3.5 min, filtered, and the filter cake was washed three times with methanol and deionized water. It was then vacuum dried at 70 °C for 1.5 h to obtain modified flake-shaped reduced carbon.

[0041] S2: Add 750g of urea and 11L of deionized water to a reactor and stir for 35min at 22.5℃ and 450r / min. Then add 2.6kg of modified flake reduced carbon and 110g of sodium dodecyl sulfate to the reactor and vacuum impregnate for 2.5h at 57.5℃ and 450r / min. Filter the mixture and wash the filter cake 2.5 times with deionized water and anhydrous ethanol to remove residual urea solution. Vacuum dry at 70℃ for 1.5h, grind the mixture, pass it through a 110-mesh sieve, transfer it to a muffle furnace, and heat it at 850℃ for 5h under nitrogen protection. After natural cooling, porous flake reduced carbon is obtained.

[0042] S3: Add 2.1 kg of porous sheet-like reduced carbon and 5.5 L of deionized water to a reactor and stir for 45 min at 22.5 °C and 550 r / min. Then add 490 g of calcium oxide powder and continue stirring for 2.5 h. Dry under vacuum at 65 °C for 1.5 h. Transfer the product to a muffle furnace and heat to 725 °C at a heating rate of 5.5 °C / min to obtain composite porous sheet-like reduced carbon.

[0043] S4: The composite porous sheet-like reducing carbon and zinc-containing solid material are mixed evenly at a mass ratio of 1:1 to prepare a mixture. The rotary kiln is tilted so that the kiln tail is higher than the kiln head, and the length of the rotary kiln is 42m. Then the rotary kiln is started and heated. When the temperature of the kiln tail reaches 485℃, the induced draft fan and Roots blower are started. At the same time, the mixture is fed into the rotary kiln tail through a disc feeder and belt conveyor. As the rotary kiln rotates, the mixture rolls towards the kiln head with the tilt of the rotary kiln and is fed into the rotary kiln for roasting. The temperature inside the rotary kiln is controlled at 1125℃. The mixture is dehydrated and spontaneously combusted in the high-temperature environment to obtain mixed slag.

[0044] S5: The mixed slag moves towards the kiln head and is discharged. The feed rate is 1.5 times the weight of the rotary kiln volume to form a continuous feed and discharge. The zinc-containing flue gas generated in the rotary kiln moves towards the kiln tail under the action of the induced draft fan and is cooled by the waste heat boiler set at the kiln tail. The temperature of the zinc-containing flue gas at the kiln tail reaches 610℃. The waste heat boiler absorbs the heat of the zinc-containing flue gas and generates steam. The zinc-containing flue gas is cooled to 155℃ by the waste heat boiler. The secondary zinc oxide in the zinc-containing flue gas is recovered by the bag filter, completing the zinc extraction process of secondary zinc oxide.

[0045] Example 3: A zinc extraction process using zinc oxide, comprising the following steps:

[0046] S1: Waste paper, rice husks, and wood chips were mixed, ground, and pulverized to prepare a reduced carbon precursor with a particle size of 4 mm. The precursor was placed in a muffle furnace and calcined at 750 °C for 4 h under nitrogen protection to obtain reduced carbon. 5 kg of reduced carbon and 10 L of methanol were added to a polytetrafluoroethylene hydrothermal reactor and hydrothermally reacted at 110 °C and 600 r / min for 26 h. The mixture was filtered, and the filter cake was washed four times with anhydrous ethanol and deionized water. It was then vacuum dried at 80 °C for 2 h to obtain hydrothermal reduced carbon. 3.2 kg of hydrothermal reduced carbon, 120 g of hexadecyltrimethylammonium bromide, and 10 L of methanol were added to a polytetrafluoroethylene hydrothermal reactor and stirred at 110 °C and 600 r / min for 26 h. The mixture was naturally cooled to room temperature, centrifuged at 12000 r / min for 4 min, filtered, and the filter cake was washed four times with methanol and deionized water. It was then vacuum dried at 80 °C for 2 h to obtain modified flake-shaped reduced carbon.

[0047] S2: Add 800g of urea and 12L of deionized water to a reactor and stir for 40min at 25℃ and 500r / min. Then add 2.7kg of modified flake reduced carbon and 120g of sodium dodecyl sulfate to the reactor and vacuum impregnate for 3h at 65℃ and 500r / min. Filter the mixture and wash the filter cake three times with deionized water and anhydrous ethanol to remove residual urea solution. Dry the mixture under vacuum at 80℃ for 2h, grind it, pass it through a 120-mesh sieve, transfer it to a muffle furnace, and heat it at 900℃ for 6h under nitrogen protection. After natural cooling, porous flake reduced carbon is obtained.

[0048] S3: Add 2.2 kg of porous sheet-like reduced carbon and 6 L of deionized water to a reactor, stir for 50 min at 25 °C and 600 r / min, then add 500 g of calcium oxide powder, continue stirring for 3 h, vacuum dry at 70 °C for 2 h, transfer the product to a muffle furnace, heat to 750 °C at a heating rate of 6 °C / min to obtain composite porous sheet-like reduced carbon.

[0049] S4: The composite porous sheet-like reducing carbon and zinc-containing solid material are mixed evenly at a mass ratio of 1:1 to prepare a mixture. The rotary kiln is tilted so that the kiln tail is higher than the kiln head, and the length of the rotary kiln is 42m. Then the rotary kiln is started and heated. When the temperature of the kiln tail reaches 490℃, the induced draft fan and Roots blower are started. At the same time, the mixture is fed from the tail of the rotary kiln through a disc feeder and belt conveyor. As the rotary kiln rotates, the mixture rolls towards the kiln head with the tilt of the rotary kiln and is fed into the rotary kiln for roasting. The temperature inside the rotary kiln is controlled at 1150℃. The mixture is dehydrated and spontaneously combusted in the high-temperature environment to obtain mixed slag.

[0050] S5: The mixed slag moves towards the kiln head and is discharged. The feed rate is 1.5 times the weight of the rotary kiln volume to form a continuous feed and slag discharge. The zinc-containing flue gas generated in the rotary kiln moves towards the kiln tail under the action of the induced draft fan and is cooled by the waste heat boiler set at the kiln tail. The temperature of the zinc-containing flue gas at the kiln tail reaches 620℃. The waste heat boiler absorbs the heat of the zinc-containing flue gas and generates steam. The zinc-containing flue gas is cooled to 160℃ by the waste heat boiler. The secondary zinc oxide in the zinc-containing flue gas is recovered by the bag filter dust collector to complete the zinc extraction process of secondary zinc oxide.

[0051] The zinc-containing solid material in the embodiment is a mixture composed of flue gas ash from steel plant flue gas treatment, leaching residue from zinc smelting, water quenching residue from lead smelting, flue dust from copper smelting, and floating slag from recycled scrap copper in a mass ratio of 2:1:1.2:1.1:1.3.

[0052] Comparative Example 1: Based on Example 3, the composite porous sheet-like reduced carbon in step S4 was replaced with the reduced carbon in step S1.

[0053] Comparative Example 2: Based on Example 3, the composite porous sheet-like reduced carbon in step S4 was replaced with the porous sheet-like reduced carbon prepared in step S2.

[0054] Comparative Example 3: Based on Example 3, the porous sheet-like reduced carbon in step S3 was replaced with the modified sheet-like reduced carbon prepared in step S1.

[0055] Performance tests were conducted on Examples 1-3 and Comparative Examples 1-3. The content and extraction rate of zinc oxide were tested by atomic absorption spectrophotometry, and the results are shown in Table 1.

[0056] Table 1

[0057]

[0058] As shown in Table 1, in Comparative Example 1, the composite porous sheet-like reduced carbon in step S4 was replaced with the reduced carbon in step S1. The reduced carbon was prepared by calcining a mixture of waste paper, rice husks, and wood chips without undergoing hydrothermal pre-stripping, hexadecyltrimethylammonium bromide intercalation stripping, or urea pore-forming treatment. Its structure was dense and blocky or severely agglomerated, with an extremely small specific surface area. The sheet structure was not formed, and there were no porous channels, resulting in very few contact sites with the zinc-containing solid material. The material layer was prone to caking, and gas flow was obstructed. The reduction reaction could only take place on the surface of the material. Without calcium oxide, it could not react with the sulfur produced during the roasting process, resulting in a high concentration of sulfur dioxide in the flue gas, which did not meet the environmental emission standards. It also could not catalyze the conversion of carbon monoxide to carbon dioxide through electrostatic adsorption and the synergistic effect of large specific surface area. The highly toxic carbon monoxide gas was directly emitted from the flue gas, polluting the atmosphere and posing a safety hazard.

[0059] In Comparative Example 2, the composite porous sheet-like reduced carbon in step S4 was replaced with the porous sheet-like reduced carbon prepared in step S2. After hydrothermal exfoliation, hexadecyltrimethylammonium bromide intercalation, and urea pore formation, a sheet-like and porous multi-level structure was formed. The specific surface area and contact sites were significantly better than those in Comparative Example 1, and the problem of material layer caking was alleviated. Therefore, the reduction reaction efficiency was improved, the zinc oxide extraction rate was increased, and the zinc oxide content was increased. However, due to the lack of calcium oxide to assist in dispersion, the sheet-like structure still showed slight stacking. The connectivity of the porous channels was slightly inferior to that of the example, resulting in the contact efficiency not reaching the optimal level. No calcium oxide was deposited, resulting in the lack of desulfurization capacity and carbon monoxide conversion function.

[0060] Comparative Example 3 replaced the composite porous sheet-like reduced carbon in step S4 with the modified sheet-like reduced carbon prepared in step S1. After hydrothermal pre-peeling and hexadecyltrimethylammonium bromide intercalation peeling, a sheet structure was formed with a higher specific surface area than Comparative Example 1. However, it lacked the urea pore-forming step and had no porous channels. The sheet structure was prone to recombination and agglomeration due to thermal motion during the roasting process, resulting in local caking of the material layer and obstruction of gas flow. The contact points with the zinc-containing solid material were only on the sheet surface, without internal contact with porous channels. The contact efficiency was between that of Comparative Example 1 and Comparative Example 2.

[0061] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A zinc extraction process using zinc oxide, characterized in that, Includes the following steps: Step 1: Mix waste paper, rice husks and wood chips, grind, crush and calcine to obtain reduced carbon; after hydrothermal pre-exfoliation, use hexadecyltrimethylammonium bromide for intercalation exfoliation to obtain modified flake reduced carbon; Step 2: Calcium oxide is deposited on the surface of porous sheet-like reduced carbon using physical adsorption to obtain composite porous sheet-like reduced carbon; Step 3: Mix composite porous sheet-like reducing carbon and zinc-containing solid material at a mass ratio of 1:1 to prepare a mixture. Set the rotary kiln to tilt and place the mixture in the rotary kiln for roasting to obtain mixed slag. Then, it moves towards the kiln head and is discharged to form a continuous feeding and slag discharge. The waste heat boiler is used for cooling and the bag filter is used for recovery to complete the secondary zinc oxide zinc extraction process. The specific preparation steps for the modified flaky reduced carbon are as follows: Hydrothermal reduced carbon, hexadecyltrimethylammonium bromide, and methanol were added to a polytetrafluoroethylene hydrothermal reactor at a ratio of 3-3.2 kg: 100-120 g: 9-10 L. The mixture was stirred at 100-110 °C and 500-600 r / min for 24-26 h. After naturally cooling to room temperature, the mixture was centrifuged at 10000-12000 r / min for 3-4 min, filtered, and the filter cake was washed 2-4 times with methanol and deionized water. The cake was then vacuum dried at 60-80 °C for 1-2 h to obtain modified flake-shaped reduced carbon. The specific preparation steps for the porous sheet-like reduced carbon are as follows: Urea and deionized water are added to a reaction vessel and stirred for 30-40 minutes at 20-25℃ and 400-500 r / min. Then, modified flaky reduced carbon and sodium dodecyl sulfate are added to the reaction vessel and vacuum impregnated for 2-3 hours at 50-65℃ and 400-500 r / min. The mixture is filtered, and the filter cake is washed 2-3 times with deionized water and anhydrous ethanol to remove residual urea solution from the surface. The cake is then vacuum dried at 60-80℃ for 1-2 hours, ground, passed through a 100-120 mesh sieve, transferred to a muffle furnace, and kept at 800-900℃ for 4-6 hours under nitrogen protection. After natural cooling, porous flaky reduced carbon is obtained. The specific preparation steps for the composite porous sheet-like reduced carbon are as follows: Porous sheet-like reduced carbon and deionized water are added to a reaction vessel and stirred for 40-50 min at 20-25℃ and 500-600 r / min. Then, calcium oxide powder is added and stirring is continued for 2-3 h. The mixture is then vacuum dried at 60-70℃ for 1-2 h. The product is transferred to a muffle furnace and heated to 700-750℃ at a heating rate of 5-6℃ / min to obtain composite porous sheet-like reduced carbon.

2. The zinc extraction process using secondary zinc oxide according to claim 1, characterized in that, The specific steps for preparing the reduced carbon are as follows: Waste paper, rice husks, and wood chips are mixed, ground, and pulverized to prepare a reduced carbon precursor with a particle size of 2-4 mm. The precursor is then placed in a muffle furnace and calcined at 700-750℃ for 2-4 hours under nitrogen protection to obtain reduced carbon.

3. The zinc extraction process using zinc oxide as described in claim 1, characterized in that, The specific steps for preparing the hydrothermal reduced carbon are as follows: Reduced carbon and methanol are added to a polytetrafluoroethylene hydrothermal reactor at a ratio of 4-5 kg: 9-10 L. The reactor is hydrothermally reacted at 100-110 °C and 500-600 r / min for 24-26 h. The mixture is filtered, and the filter cake is washed 2-4 times with anhydrous ethanol and deionized water. It is then vacuum dried at 60-80 °C for 1-2 h to obtain hydrothermally reduced carbon.

4. The zinc extraction process using zinc oxide as described in claim 1, characterized in that, The ratio of urea, deionized water, modified flaky reducing carbon, and sodium dodecyl sulfate is 700-800g: 10-12L: 2.5-2.7kg: 100-120g.

5. The zinc extraction process using secondary zinc oxide according to claim 1, characterized in that, The ratio of porous sheet-like reduced carbon, deionized water, and calcium oxide powder is 2-2.2 kg: 5-6 L: 480-500 g.

6. The zinc extraction process using zinc oxide as described in claim 1, characterized in that, The specific preparation steps for the mixed residue are as follows: Composite porous flaky reducing carbon and zinc-containing solid material are mixed evenly at a mass ratio of 1:1 to prepare a mixture. The rotary kiln is tilted so that the kiln tail is higher than the kiln head, and the length of the rotary kiln is 42m. Then the rotary kiln is started and heated. When the temperature of the kiln tail reaches 480-490℃, the induced draft fan and Roots blower are started. At the same time, the mixture is fed into the rotary kiln tail through a disc feeder and belt conveyor. As the rotary kiln rotates, the mixture tumbles and moves towards the kiln head with the inclination of the rotary kiln and is fed into the rotary kiln for calcination. The temperature inside the rotary kiln is controlled at 1100-1150℃. The mixture is dehydrated and spontaneously combusted in the high-temperature environment to obtain mixed slag.

7. The zinc extraction process using zinc oxide as described in claim 1, characterized in that, The specific preparation steps of the zinc extraction process using secondary zinc oxide are as follows: The mixed slag moves towards the kiln head and is discharged. The feed rate is 1.5 times the weight of the rotary kiln volume, forming a continuous feeding and slag discharge. The zinc-containing flue gas generated in the rotary kiln moves towards the kiln tail under the action of the induced draft fan and is cooled by the waste heat boiler set at the kiln tail. The temperature of the zinc-containing flue gas at the kiln tail reaches 600-620℃. The waste heat boiler absorbs the heat of the zinc-containing flue gas and generates steam. The zinc-containing flue gas is cooled to 150-160℃ by the waste heat boiler. The secondary zinc oxide in the zinc-containing flue gas is recovered by the bag filter, completing the zinc extraction process of secondary zinc oxide.

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