A method for dechlorination and salt extraction of zinc powder from a rotary hearth furnace, sintering machine head ash and blast furnace bag dust

Abstract

This invention proposes a method for improving the grade of zinc powder from a rotary hearth furnace and for combined dechlorination and salt extraction from sintering machine head ash and blast furnace baghouse ash, belonging to the technical field of dust removal and resource comprehensive utilization in the metallurgical industry. The method comprises six core steps: zinc powder washing and grade improvement from the rotary hearth furnace, dechlorination from blast furnace baghouse ash washing, pretreatment of baghouse ash filtrate, dechlorination from sintering machine head ash washing, impurity removal from blast furnace head ash filtrate, and salt separation by evaporation. By optimizing the solid-liquid ratio, recycling the feed solution, and precisely controlling process parameters, the zinc content of the rotary hearth furnace zinc powder is increased by 15%-25%, and the blast furnace baghouse ash and sintering machine head ash are efficiently dechlorinated. Simultaneously, potassium chloride and sodium chloride are extracted from the wastewater. This invention features a simple and versatile process flow, recyclable water and reagents, zero emissions, reduced costs for metallurgical dust removal, and meets industry requirements for preventing solid waste from leaving the plant. It is both environmentally friendly and economical, and suitable for large-scale promotion in the iron and steel metallurgical industry.

Description

Technical Field

[0001] This invention belongs to the technical field of dust removal and comprehensive resource utilization in the metallurgical industry, specifically involving a method for improving the grade of zinc powder from a rotary hearth furnace and for dechlorination and salt extraction of sintering machine head ash and blast furnace bag filter ash. Background Technology

[0002] The iron and steel metallurgical industry generates a large amount of sintering machine head ash and blast furnace baghouse dust during production. Sintering machine head ash is produced from the flue gas generated during iron ore sintering and collected through an electric field dust collector. The dust collected from the first and second electric fields contains relatively few harmful components and is generally returned to the sintering batch. However, the dust collected from the third and fourth electric fields contains large amounts of potassium, sodium, lead, and zinc elements that are harmful to steelmaking and ironmaking, and cannot be returned to the sintering batch. Currently, some steel plants have begun water washing treatment for sintering machine head ash. Blast furnace baghouse dust is the dust collected from the flue gas generated during blast furnace ironmaking after passing through a baghouse dust collector. Currently, most steel plants send it to a rotary hearth furnace or rotary kiln for pyrometallurgical enrichment and zinc extraction. However, the chlorine present in it can corrode the equipment and adversely affect the grade of the produced zinc oxide.

[0003] In 2021, it was clearly proposed to "innovate the comprehensive utilization model of bulk solid waste, promote the 'solid waste not leaving the factory' approach in the iron and steel metallurgical industry, and strengthen the full-scale utilization." As a result, steel mills have successively started to develop water washing technology for metallurgical dust removal, but the existing water washing technology is not mature enough and is difficult to adapt to the impact of changes in metallurgical dust removal. Summary of the Invention

[0004] This invention addresses the problems of existing technologies by providing a method for improving the grade of zinc powder from a rotary hearth furnace and for dechlorinating and extracting salt from sintering machine head ash and blast furnace baghouse ash.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: A method for improving the grade of zinc powder from a rotary hearth furnace and for dechlorinating and extracting salt by combining sintering machine head ash and blast furnace bag filter ash, the specific steps of which are as follows: Step 1: Rotary hearth furnace zinc powder washing and grade improvement: Mix rotary hearth furnace zinc powder and water at a mass ratio of 1:5-10 and stir for 1.5 hours. After solid-liquid separation, dry the solid to obtain refined zinc powder and leaching solution. The leaching solution is recycled for use in subsequent leaching processes of rotary hearth furnace zinc powder until the chloride ion concentration in the leaching solution is ≥50g / L. Add soluble carbonate to the leaching solution to adjust the pH to 7.5. After solid-liquid separation, obtain zinc slag and zinc washing water. The main component of the rotary hearth furnace zinc powder is zinc oxide. Step 2: Blast Furnace Bag Ash Washing and Dechlorination: Blast furnace bag ash and zinc washing solution are mixed and stirred for 1 hour at a mass ratio of 1:2-2.5. Solid-liquid separation is then performed to obtain bag ash residue and bag ash filtrate. The bag ash residue is used for rotary hearth furnace feeding, and the bag ash filtrate is used for cyclic washing of the blast furnace bag ash until the chloride ion concentration in the filtrate reaches 80-90 g / L, resulting in a high-concentration bag ash filtrate. The first washing solution is then replaced with zinc washing solution. The first washing solution includes both bag ash filtrate and zinc washing solution. Specifically, the method for using the blast furnace bag ash washing solution is as follows: the first washing solution for the initial washing of blast furnace bag ash is zinc washing solution; the first washing solution for subsequent blast furnace bag ash washing is recycled bag ash filtrate; this is repeated until the chloride ion concentration in the bag ash filtrate reaches 80-90 g / L, resulting in a high-concentration bag ash filtrate, which is then used in Step 3. Finally, the first washing solution is replaced with zinc washing solution, and the above steps are repeated. Step 3: Pretreatment of high-concentration bag filter ash filtrate: Add strong alkali to the high-concentration bag filter ash filtrate, adjust the pH of the filtrate to 12, and after full reaction, separate the solid and liquid to obtain the pretreated liquid and zinc-containing slag. Step 4: Sintering Mill Head Ash Washing and Dechlorination: The sintering mill head ash and the pretreatment liquid obtained in Step 3 are mixed and stirred at a mass ratio of 1:4. Solid-liquid separation is performed to obtain iron-rich material and mill head ash filtrate. The iron-rich material is sent to the sintering process. The mill head ash filtrate is used to wash the sintering mill head ash of the subsequent process until the chloride ion concentration in the filtrate reaches 110-120 g / L, resulting in high-concentration mill head ash filtrate. Subsequently, the second washing liquid is used to replace the pretreatment liquid. The second washing liquid includes both the mill head ash filtrate and the pretreatment liquid. Specifically, the usage method of the sintering mill head ash washing liquid is as follows: the second washing liquid from the first washing of the sintering mill head ash is the pretreatment liquid; the second washing liquid from the subsequent washing of the blast furnace bag filter ash is the recycled mill head ash filtrate. This is repeated until the chloride ion concentration in the mill head ash filtrate reaches 110-120 g / L, resulting in high-concentration mill head ash filtrate, which is then used in Step 5. Finally, the second washing liquid is used to replace the pretreatment liquid, and the above steps are repeated. Step 5: Removal of impurities from high-concentration machine head ash filtrate: Add soda ash and sodium sulfide to the high-concentration machine head ash filtrate in stages, and separate the solid and liquid to obtain purified liquid and purified residue. Step 6: The purified liquid is passed into the evaporator, and the salts are separated by evaporation using the difference in solubility between potassium chloride and sodium chloride to obtain potassium chloride and sodium chloride products. The steam generated by the evaporator is cooled and returned to the circulating water tank. The water in the circulating water tank is used for the zinc powder washing in the rotary hearth furnace in the subsequent process, so as to realize the recycling of water.

[0006] Preferably, in step one, the soluble carbonate is sodium carbonate.

[0007] Preferably, in step three, the strong alkali is slaked lime. Slaked lime is preferred due to its lower cost; however, other strong alkalis can also be used in actual production; in addition, if equipment conditions permit, calcium oxide can also be used instead. Specifically, the main disadvantage of calcium oxide is that it releases a large amount of heat when dissolved in water, requiring it to be slurryed before being used in the process; it is essentially still slaked lime. Preferably, in step one, the zinc slag mainly consists of zinc carbonate and basic zinc carbonate.

[0008] As a preferred option, in step two, when the chloride ion content of the blast furnace bag ash is high or the requirement for a high chloride ion content in the slag after water washing is high, the dechlorination of the blast furnace bag ash by water washing can adopt a two-stage water washing process. Specifically, the blast furnace bag ash undergoes a first water washing, crushing, and a second water washing in sequence; new material liquid is added in the second water washing, and the resulting wash water enters the first water washing process to leach out the new blast furnace bag ash. Each stage of water washing is circulated separately, and after reaching the set chloride ion concentration, it enters the next stage process.

[0009] Preferably, in step one, more than 95% of the zinc in the feed solution is removed by soluble carbonate precipitation.

[0010] As a preferred option, in step two, the resulting bag filter ash has the following specifications: moisture 16-20%, chloride ion ≤1%.

[0011] As a preferred option, the iron-rich material obtained in step four has the following specifications: moisture ≤ 22%, chloride ions ≤ 2%, potassium oxide ≤ 2%, and sodium oxide ≤ 1%.

[0012] Compared with the prior art, the advantages and positive effects of the present invention are as follows: This application discloses a method for improving the grade of rotary hearth furnace zinc powder and for combined dechlorination and salt extraction of sintering machine head ash and blast furnace bag filter ash. This method can significantly improve the grade of zinc powder: the zinc content of rotary hearth furnace zinc powder increases by 15%-25% after treatment, and the zinc content in zinc slag can reach 45%, greatly increasing the added value of the product. Among them, the chloride ion content of blast furnace bag filter ash after dechlorination is ≤1% in the efficient dechlorination and solid waste recycling process, and it can be directly used for rotary hearth furnace feeding. After removing harmful elements such as potassium, sodium, and chloride from sintering machine head ash, the iron-rich material can be returned to sintering, realizing the full utilization of metallurgical solid waste. The leaching solution, zinc washing water, and filtrate in the process are all recycled, and the evaporator condensate is returned to the front-end process, realizing zero water discharge. The process flow of this application is simple, requires fewer equipment, and has low disposal costs. The reagents are mostly conventional chemicals such as sodium carbonate and quicklime, which are highly safe. It can adapt to the treatment needs of metallurgical dust removal ash with different chloride contents and different compositions, and meets the development requirements of the steel industry for solid waste not leaving the plant and low-carbon sintering. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 Flowchart of zinc powder washing process in converter; Figure 2 Flowchart for the washing of blast furnace bag filter ash and the pretreatment of high-concentration bag filter ash filtrate; Figure 3 This is a flowchart of the ash washing process for the sintering machine head. Detailed Implementation

[0015] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0016] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification.

[0017] Example 1, such as Figure 1 As shown, a method for improving the grade of zinc powder from a rotary hearth furnace and for dechlorinating and extracting salt by combining sintering machine head ash and blast furnace bag filter ash is described, with the following specific steps: Rotary hearth furnace zinc powder washing and grade improvement: Take 100 kg of low-zinc-content rotary hearth furnace zinc powder with an initial zinc content of approximately 31.5%. The main component is zinc oxide, and there is a certain proportion of soluble zinc salts. In addition, impurities account for about 68.5 kg, including 12 kg of soluble impurities such as chlorine, potassium, and sodium, and 56.5 kg of insoluble impurities. Mix the low-zinc-content rotary hearth furnace zinc powder with 500 kg of clean water and stir for 1.5 h. After solid-liquid separation, dry to obtain 88 kg of refined zinc powder (dry basis). The zinc content in the refined zinc powder is tested to be 39.36%. The leaching solution obtained from solid-liquid separation is circulated to leach the rotary hearth furnace zinc powder in the subsequent process until the chloride ion concentration reaches 50 g / L. Sodium carbonate is added to the leaching solution to adjust the pH to 7.5. Solid-liquid separation yields 7 kg of zinc slag with a zinc content of 45%. The zinc washing water is collected for later use.

[0018] Blast furnace bag filter ash dechlorination by washing: Take 200 kg of blast furnace bag filter ash and mix it with 400 kg of zinc washing water for 1 hour. After solid-liquid separation, 231 kg of bag filter ash residue (wet basis) is obtained. The moisture content of the bag filter ash residue is 18% and the chloride ion content is 0.8%. The bag filter ash filtrate is then used to wash the blast furnace bag filter ash in the process until the chloride ion concentration of the first filtrate reaches 75 g / L. About 600 kg of high-concentration bag filter ash filtrate is collected.

[0019] Pretreatment of bag filter ash filtrate: Add quicklime to high-concentration bag filter ash filtrate, adjust pH to 12, and separate solid and liquid to obtain pretreated liquid and 15 kg of zinc-containing slag.

[0020] Sintering machine head ash water washing and dechlorination: Take 150 kg of sintering machine head ash and mix it with 600 kg of pretreatment liquid for 1 hour. After solid-liquid separation, 149 kg of iron-rich material (wet basis) is obtained. The iron-rich material is tested to have a moisture content of 20%, chloride ion content of 1.5%, potassium oxide content of 1.8%, and sodium oxide content of 0.9%. The sintering machine head ash filtrate is then circulated and washed with water until the chloride ion concentration of the second filtrate reaches 105 g / L. The high-concentration sintering machine head ash filtrate is then collected.

[0021] Purification of the ash filtrate from the machine head: Add 24 kg of soda ash and 0.4 kg of sodium sulfide to the high-concentration ash filtrate in stages, and separate the solid and liquid to obtain 28 kg of purified liquid and purified residue (wet basis).

[0022] Salt separation by evaporation: The purified liquid is fed into the evaporator to separate the salts, yielding 44 kg of potassium chloride and 74 kg of sodium chloride. The condensate from the evaporator is returned to the circulating water tank for use in the front-end water washing process.

[0023] Example 2: A method for improving the grade of zinc powder from a rotary hearth furnace and for dechlorinating and extracting salt by combining sintering machine head ash and blast furnace bag filter ash. The specific steps are as follows: Rotary hearth furnace zinc powder washing and grade improvement: 100 kg of high-zinc-content rotary hearth furnace zinc powder with an initial zinc content of 48% was taken. The main component was zinc oxide, and there was a certain proportion of soluble zinc salts. In addition, impurities accounted for about 52 kg, including 27 kg of soluble impurities such as chlorine, potassium, and sodium, and 25 kg of insoluble impurities. The high-zinc-content rotary hearth furnace zinc powder was mixed with 1000 kg of water and stirred for 1.5 h. After solid-liquid separation, it was dried to obtain 73 kg of upgraded zinc powder (dry basis). The zinc content of the upgraded zinc powder was tested to be 60.26%, which is 20% higher than that of the original high-zinc-content rotary hearth furnace zinc powder. The leaching solution obtained from solid-liquid separation was circulated to leach the rotary hearth furnace zinc powder in the subsequent process until the chloride ion concentration reached 50 g / L. Sodium carbonate was added to the leaching solution to adjust the pH to 7.5. Solid-liquid separation yielded 21.8 kg of zinc slag with a zinc content of 45%. The zinc washing water was collected for later use.

[0024] Dechlorination of blast furnace bag filter ash by washing: Take 200 kg of blast furnace bag filter ash with high chloride content, mix it with 400 kg of circulating wash water for 1 hour, and crush it after solid-liquid separation. Then mix it with 450 kg of zinc washing water for 1 hour. After solid-liquid separation, 222 kg of bag filter ash residue (wet basis) is obtained. The moisture content of the bag filter ash residue is 19% and the chloride ion content is 0.7%. The wash water obtained from the second washing enters the first washing process and is recycled until the chloride ion concentration reaches 88 g / L. Collect about 650 kg of high-concentration bag filter ash filtrate.

[0025] Pretreatment of bag filter ash filtrate: Add quicklime to high-concentration bag filter ash filtrate, adjust pH to 12, and separate solid and liquid to obtain pretreated liquid and 16 kg of zinc-containing slag.

[0026] Sintering machine head ash washing and dechlorination: Take 150 kg of sintering machine head ash and mix it with 600 kg of pretreatment liquid at a mass ratio of 1:4 for 1 hour. After solid-liquid separation, 151 kg of iron-rich material (wet basis) is obtained. The moisture content of the iron-rich material is 21%, chloride ion is 1.8%, potassium oxide is 1.7%, and sodium oxide is 0.8%. The filtrate of the machine head ash is used to wash the sintering machine head ash in the process until the chloride ion concentration of the second filtrate reaches 118 g / L. About 650 kg of high-concentration machine head ash filtrate is collected.

[0027] Purification of the ash filtrate from the machine head: Add 28 kg of soda ash and 0.55 kg of sodium sulfide to the high-concentration ash filtrate in stages, and separate the solid and liquid to obtain 33.2 kg of purified liquid and purified residue (wet basis).

[0028] Salt separation by evaporation: The purified liquid is passed into the evaporator and the salts are separated by evaporation to obtain 52 kg of potassium chloride and 81 kg of sodium chloride. The condensate from the evaporator is returned to the circulating water tank for reuse.

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for improving the grade of zinc powder from a rotary hearth furnace and for combined dechlorination treatment of sintering machine head ash and blast furnace bag filter ash to extract salt, characterized in that, The specific steps are as follows: Step 1: Rotary hearth furnace zinc powder washing and grade improvement: Mix rotary hearth furnace zinc powder and water at a mass ratio of 1:5-10 and stir for 1.5 hours. After solid-liquid separation, dry the solid to obtain refined zinc powder and leaching solution. The leaching solution is recycled for the rotary hearth furnace zinc powder in subsequent leaching processes until the chloride ion concentration in the leaching solution is ≥50g / L. Add soluble carbonate to the leaching solution to adjust the pH to 7.

5. After solid-liquid separation, obtain zinc slag and zinc washing water. Step 2: Blast furnace bag filter ash washing and dechlorination: Blast furnace bag filter ash and zinc washing water are mixed and stirred for 1 hour at a mass ratio of 1:2-2.

5. Then, solid-liquid separation is performed to obtain bag filter ash residue and bag filter ash filtrate. The bag filter ash residue is used for rotary hearth furnace feeding. The bag filter ash filtrate is recycled to wash the blast furnace bag filter ash in the subsequent process until the chloride ion concentration in the filtrate reaches 80-90 g / L, resulting in high-concentration bag filter ash filtrate. Then, the first washing solution is replaced with zinc washing water. Step 3: Pretreatment of high-concentration bag filter ash filtrate: Add strong alkali to the high-concentration bag filter ash filtrate, adjust the pH of the filtrate to 12, and after full reaction, separate the solid and liquid to obtain the pretreated liquid and zinc-containing slag. Step 4: Sintering machine head ash water washing and dechlorination: The sintering machine head ash and the pretreatment liquid obtained in Step 3 are mixed and stirred at a mass ratio of 1:

4. Solid-liquid separation is performed to obtain iron-rich material and machine head ash filtrate. The iron-rich material is sent to the sintering process. The machine head ash filtrate is circulated and used to wash the sintering machine head ash of the subsequent process until the chloride ion concentration in the filtrate reaches 110-120 g / L, resulting in high-concentration machine head ash filtrate. Then, the second water washing liquid is used to replace the pretreatment liquid. Step 5: Removal of impurities from high-concentration machine head ash filtrate: Add soda ash and sodium sulfide to the high-concentration machine head ash filtrate in stages, and separate the solid and liquid to obtain purified liquid and purified residue. Step 6: Pass the purified liquid into the evaporator and use the solubility difference between potassium chloride and sodium chloride to evaporate and separate the salts, obtaining potassium chloride and sodium chloride products; the steam generated by the evaporator is cooled and returned to the circulating water tank, and the water in the circulating water tank is used for the subsequent washing of zinc powder in the rotary hearth furnace.

2. The method for improving the grade of zinc powder in a rotary hearth furnace and for dechlorinating and extracting salt from sintering machine head ash and blast furnace baghouse ash, as described in claim 1, is characterized in that... In step one, the soluble carbonate is sodium carbonate.

3. The method for improving the grade of zinc powder in a rotary hearth furnace and for combined dechlorination treatment of sintering machine head ash and blast furnace baghouse ash according to claim 1, characterized in that, In step three, the strong alkali is slaked lime.

4. The method for improving the grade of zinc powder in a rotary hearth furnace and for combined dechlorination treatment of sintering machine head ash and blast furnace baghouse ash according to claim 1, characterized in that, In step one, the zinc slag mainly consists of zinc carbonate and basic zinc carbonate.

5. The method for improving the grade of zinc powder from a rotary hearth furnace and for combined dechlorination treatment of sintering machine head ash and blast furnace baghouse ash according to claim 1, characterized in that, In step two, the blast furnace bag filter ash dechlorination process adopts a two-stage washing process, specifically: the blast furnace bag filter ash undergoes a first washing, crushing, and a second washing in sequence; new feed liquid is added in the second washing, and the resulting wash water enters the first washing process to leach out the new blast furnace bag filter ash. Each stage of the washing process is circulated separately, and after reaching the set chloride ion concentration, it enters the next stage process.

6. The method for improving the grade of zinc powder in a rotary hearth furnace and for combined dechlorination treatment of sintering machine head ash and blast furnace baghouse ash according to claim 1, characterized in that, In step one, more than 95% of the zinc in the feed solution is removed by soluble carbonate precipitation.

7. The method for improving the grade of zinc powder from a rotary hearth furnace and for combined dechlorination treatment of sintering machine head ash and blast furnace baghouse ash according to claim 1, characterized in that, In step two, the resulting bag filter ash residue has the following specifications: moisture 16-20%, chloride ions ≤1%.

8. The method for improving the grade of zinc powder from a rotary hearth furnace and for combined dechlorination treatment of sintering machine head ash and blast furnace baghouse ash according to claim 1, characterized in that, In step four, the resulting iron-rich material has the following specifications: moisture ≤ 22%, chloride ions ≤ 2%, potassium oxide ≤ 2%, and sodium oxide ≤ 1%.

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