CN110317949B

CN110317949B - Preparation method of zinc-containing dust pellets

Info

Publication number: CN110317949B
Application number: CN201910718475.7A
Authority: CN
Inventors: 朱德庆; 郭正启; 潘建; 李启厚; 王定政; 杨聪聪; 李紫云
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2019-08-05
Filing date: 2019-08-05
Publication date: 2021-06-08
Anticipated expiration: 2039-08-05
Also published as: CN110317949A

Abstract

The invention provides a preparation method of zinc-containing dust pellets, which comprises the following steps: s1, batching: mixing zinc-containing dust such as blast furnace cloth bag ash, steelmaking ladle furnace ash, steelmaking converter smoke dust and the like with the carbon-containing fine powder to obtain a mixture; s2, preprocessing: adding water into the mixture obtained in the step S1 for wetting, stacking after wetting, and curing; s3, adding a composite binder into the cured mixture, and uniformly mixing to obtain a uniform mixture; s4, pelletizing the uniformly mixed material prepared in the step S3 to obtain green pellets; s5, drying the green pellets in the step S4 to obtain the zinc-containing dust dry pellets. The dry pellet has high compression strength, good reducibility, high metallization rate in the direct reduction process and good dezincification effect, and solves the technical problems of easy cracking and pulverization of the existing zinc-containing dust pellets in the reduction process.

Description

Preparation method of zinc-containing dust pellets

Technical Field

The invention relates to the field of ferrous metallurgy, in particular to a preparation method of zinc-containing dust pellets.

Background

The dust amount generated in the steel production process generally accounts for 8-15% of the steel yield, is rich in iron, zinc, carbon and other elements, and is a secondary resource with a high utilization value. However, zinc-containing dust is a hazardous solid waste. Therefore, the proper process is developed to recycle the dust, which is not only beneficial to improving the resource utilization rate, but also can solve the problem of environmental pollution caused by the dust of iron and steel enterprises.

The main processes for removing zinc from zinc-containing dust by pyrogenic process include rotary kiln reduction process and rotary hearth furnace reduction process, and the important process is preparation of zinc-containing dust pellets. The quality of the pellets directly influences the dezincification process effect and the product quality. The patent with publication number CN 102776309A discloses a method for processing zinc-containing dust in an iron and steel plant, which comprises the steps of uniformly mixing the zinc-containing dust in the iron and steel plant, coal powder and a binder in proportion to manufacture green pellets, then distributing the green pellets into a rotary hearth furnace for high-temperature reduction, introducing gas fuel and combustion air into the rotary hearth furnace, and collecting a slag iron mixture and flue gas of the rotary hearth furnace after the reduction is finished; crushing and screening the collected slag-iron mixture to obtain sponge iron and slag; introducing the collected flue gas into a wet dust collector, simultaneously spraying dilute sulfuric acid with the mass fraction of 2% -5%, reacting zinc contained in the flue gas of the rotary hearth furnace into a zinc sulfate solution, electrolyzing the zinc sulfate solution to obtain zinc and the dilute sulfuric acid, and discharging the flue gas after dust removal. In order to improve the pellet strength, the additive dosage in the pelletizing process is up to 4-8%, so that the process has high energy consumption and high cost. Patent publication No. CN 106399700A discloses a method and system for processing zinc-containing dust, mixing zinc-containing dust, reducing agent and binder, wet-grinding, pelletizing and drying to process pellets; the dried pellets are distributed on a furnace bed through a feeding port of the annular roasting furnace and are finally discharged through a discharging port of the cooling furnace chamber; then grinding and magnetically separating the roasted product to obtain metal iron powder and magnetically separated tailings; and the generated high-temperature flue gas finally enters a zinc recovery system to be collected to obtain volatilized valuable metal dust. The binder used in the patent is bentonite or starch solution, the addition amount of the binder is 1% -5%, and in order to further improve the pellet strength, wet grinding is adopted to pre-treat dust. Therefore, the use amount of the binder is large, the cost is high, the addition and the use are difficult due to the adoption of the liquid binder, and the grinding pretreatment is required, so that the process cost of grinding is further increased. In addition, because the zinc-containing dust is originally fine in particle size, the fineness can be further increased through the wet grinding pretreatment, the green pellet bursting temperature is reduced, the thermal stability of the green pellets is damaged, and the strength of the green pellets in the subsequent treatment process is seriously influenced. The patent with the publication number of CN 101386913B discloses a method for treating zinc-containing dust and recovering zinc oxide by a rotary hearth furnace, wherein 10-30% of coal, 70-90% of zinc-containing dust and 1-5% of additive are mixed according to the proportion; uniformly mixing the prepared raw materials and pressing into green balls; and (3) distributing the green balls into a heat accumulating type rotary hearth furnace, heating to 1100-1350 ℃, and keeping for 10-30 minutes for reduction to obtain zinc-containing dust and a metallized iron material. The additive amount of the fluxing agent and the single organic adhesive used in the pelletizing process is 1-5 percent.

It can be seen from the review that in the existing pelletizing process of zinc-containing dust, the binder dosage is large, the binder is single, the raw materials have no pretreatment process or the pretreatment process is not appropriate, the strength of the prepared pellets is poor, the pellets are easy to crack and pulverize in the reduction process after entering a kiln, the obtained iron-containing product is mainly powdery or has poor strength, cannot be directly smelted in a blast furnace, and only can return to the blast furnace for iron making after sintering and agglomeration, thereby seriously affecting the stable operation of the dezincification process, the dezincification rate and the direction of the reduction product. The preparation of the reinforced zinc-containing dust pellets has important significance for improving the yield of the subsequent process, improving the product quality and optimizing the direction of reduction products.

Disclosure of Invention

The invention provides a preparation method of zinc-containing dust pellets, and aims to improve the strength of the zinc-containing dust pellets, avoid the zinc-containing dust pellets from cracking and powdering in the rotary kiln dezincification process, and eliminate the ring formation phenomenon of the rotary kiln, thereby improving the yield of the rotary kiln and improving the quality of reduced products.

In order to achieve the above object, an embodiment of the present invention provides a method for preparing zinc-containing dust pellets, comprising the steps of:

s1, batching: preparing a zinc-containing dust material, wherein the carbon-iron ratio of the material is 0.10-0.25;

s2, preprocessing: adding water into the zinc dust-containing material in the step S1 for wetting, stacking and aging after wetting;

s3, adding 0.6-1.0 wt% of composite binder into the cured material to obtain a uniform mixture, wherein the composite binder comprises bentonite and polyacrylamide, and the weight ratio of the bentonite to the polyacrylamide is 70-90: 30-10 parts of;

s4, pelletizing the uniformly mixed material prepared in the step S3 to obtain green pellets;

s5, drying the green pellets in the step S4 to obtain the zinc-containing dust dry pellets.

Wherein the zinc-containing dust material in the step S1 comprises one or more of blast furnace cloth bag ash, steelmaking ladle ash and steelmaking converter smoke dust.

Wherein the step S1 further includes: and adding carbon-containing fine powder into the zinc-containing dust material, and mixing to obtain a mixture, wherein the mass ratio of carbon to iron of the mixture is 0.10-0.25.

Wherein, the step S2 specifically includes: and (3) adding 10-13% of water into the zinc-containing dust material or the mixture in the step S1 for wetting, wherein the wetting time is 10-20 min, the stacking and covering materials are aged for 20-40 min, and the temperature of the materials is increased by 15-35 ℃.

Wherein, the step S4 specifically includes: adding the mixture into a disc pelletizer to pelletize, wherein the pelletizing time is 15-25 min, the water content of the green pellets is 14-15%, and the granularity of the green pellets is 10-20 mm.

Specifically, in the step S5, the green pellets are dried on a belt dryer, and the height of the material layer is 80mm to 180 mm. And drying the material layer at 250-350 deg.c in the air speed of 0.8-1.2 m/s for 7-15 min and material layer height of 80-180 mm.

The scheme of the invention has the following beneficial effects:

(1) the invention provides a preparation method of zinc-containing dust pellets, wherein the zinc-containing dust is subjected to pretreatment such as water wetting, stacking, material covering and curing, and then is uniformly mixed by adding a composite binder to obtain a mixture, the composite additive comprises bentonite and high molecular substance polyacrylamide, and then pelletizing is carried out to obtain green pellets, the mixture overcomes the characteristic of weak pelletizing property of the zinc-containing dust, the binder consumption is lower than 1% (the conventional single binder bentonite or starch consumption is up to 1-8%), and the falling strength of the green pellets is greatly improved and is larger than 12 times/0.5 m (the falling strength of the green pellets is generally 4-5 times/0.5 m when the conventional binder and the wet grinding are carried out for pretreatment); particularly, the dry pellet obtained by drying the green pellet has the falling strength higher than 3 times/1 m (the falling strength of the conventional process is 0 time/1 m), and the compressive strength of the dry pellet is higher than 200N/more (the compressive strength of the dry pellet in the conventional process is generally 20-50N/more), so that the strength of the zinc-containing dust pellet is greatly improved. The invention fully utilizes the advantage of fine particle size of the zinc-containing dust, invents a stockpiling and material-covering curing pretreatment process according to the performance characteristics of the raw materials, and has the main functions of fully digesting calcium oxide in the zinc-containing dust, adsorbing sufficient moisture on the surface of particles and improving the hydrophilic performance of dust particles; during curing, a large amount of calcium hydroxide colloid formed in the zinc-containing dust mixture is a binder and has good cohesiveness, so that the balling property of the mixture is improved. In addition, a large amount of heat is released due to hydration reaction of calcium oxide and calcium silicate minerals in the curing process, so that the diffusion of water molecules is enhanced, the wetting capacity of the particle surface is improved, and the granulation is facilitated. Polyacrylamide is a macromolecular binder with large molecular weight and long molecular chain, and can form macromolecular bridges (bridging effect) among particles in the zinc-containing dust mixture to connect dispersed particles. In addition, the invention adopts the composite use of the organic binder and the inorganic binder, and fully combines the advantages of strong viscosity of the organic binder and good thermal stability of the inorganic binder, thereby ensuring that the effect of the composite binder is better than that of a single inorganic or organic binder. The wetting and curing pretreatment of the mixture and the favorable effect of the composite binder are superposed, so that the green ball strength, the thermal stability and the dry ball strength are greatly improved, the binder consumption is greatly reduced, and the production cost is reduced.

(2) The green ball prepared by the zinc-containing dust through the combined action of wetting and material-covering curing pretreatment and the composite binder is dried, the strength of the obtained dry ball reaches the index requirement of the rotary kiln reduction, and the dry ball is prevented from being damaged and pulverized in the reduction process, so that the ring forming hidden danger of the rotary kiln is eliminated. The obtained reduced pellet has high metallization rate and compressive strength, low zinc and alkali metal content and high zinc removal rate, can directly enter a blast furnace for ironmaking, does not need to return to sintering for agglomeration, and greatly improves the competitiveness of the process. Thus also proving that the zinc-containing dust pellets prepared by the invention have good quality.

Drawings

Fig. 1 is a flow chart of the preparation of zinc-containing dust pellets of the present invention.

Detailed Description

In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.

Comparative example 1

The zinc-containing dust pellet is prepared according to a conventional pelletizing process, and comprises the following steps:

(1) preparing materials: the blast furnace cloth bag ash, the steelmaking ladle furnace ash and the steelmaking converter smoke dust are mixed according to the weight ratio of 32.42%: 63.46%: 4.12 percent of the mixture is mixed to obtain mixed dust;

(2) adding carbon-containing dedusting ash from a coke oven into the mixed dust prepared in the step (1) to obtain a mixed material, wherein the mass ratio of carbon to iron of the mixed material is 0.35;

(3) adding 10% of water into the mixture prepared in the step (2) for wetting, wherein the wetting time is 10min, adding 1.5% of bentonite, and fully and uniformly mixing to obtain a mixed material;

(4) putting the uniformly mixed material into a disc pelletizer for pelletizing, wherein the pelletizing time is 20min, the moisture content of the green pellets is controlled to be about 14%, and the particle size of the green pellets is controlled to be 8-16 mm;

the falling strength of the prepared green pellets can reach 3.5 times/0.5 m, the compressive strength can reach 38N/green pellets, and the bursting temperature is 430 ℃.

(5) Drying the green pellets on a belt type roasting machine, wherein the drying temperature is 270-300 ℃, the drying air speed is 0.8-1.2 m/s, the material layer height is 80-120 mm, and the drying time is 10-15 min;

the obtained dry balls had falling strengths of 5.2 times/0.5 m and 2.3 times/1 m, and compressive strengths of 50 N.times^-1. The dry ball strength is lower than the direct reduction requirement of the rotary kiln.

(6) And (3) loading the dry pellets into a rotary kiln, introducing coal gas for combustion, reducing for 50min at the temperature of 1150-1250 ℃, and cooling under the protection of nitrogen to obtain reduced pellets.

The metallization rate of the reduced pellet is 74.45 percent, the content of residual zinc is 0.582 percent, the dezincification rate in the reduction process is 84.96 percent, and K is₂The removal rate of O is 35.6%, Na₂The O removal rate was 40.1%. In addition, the pulverization phenomenon of the pellets in the reduction process is serious, and the compressive strength of the reduced pellets is low. Therefore, the zinc content and the strength index of the reduced pellets cannot meet the furnace charging requirement.

In addition, the zinc hypoxide containing 43.2% of zinc is recovered from the smoke of the rotary kiln, and the recovery rate of zinc is 81.4%. Because the pellets are seriously pulverized and the dust amount is large, the iron ore powder is mixed into the smoke dust, so that the secondary zinc oxide is low in grade.

Comparative example 2

(1) preparing materials: the blast furnace cloth bag ash, the steelmaking ladle furnace ash and the steelmaking converter smoke dust are mixed according to the weight ratio of 32.42%: 63.46%: 4.12 percent of the mixture is mixed to obtain a mixture;

(2) adding the mixture prepared in the step (1) into carbon-containing dust from a coke oven, wherein the mass ratio of carbon to iron of the mixture is 0.25;

(4) putting the uniformly mixed material into a disc pelletizer for pelletizing to obtain green pellets, wherein the pelletizing time is 20min, the moisture content of the green pellets is controlled at 14.5%, and the particle size of the green pellets is controlled at 8-16 mm;

the falling strength of the prepared green pellets can reach 4.1 times/0.5 m, the compressive strength can reach 46N/green pellets, and the bursting temperature is 420 ℃.

the obtained dry balls had falling strengths of 5.2 times/0.5 m and 3.0 times/1 m, and compressive strengths of 70N · pieces^-1. The dry ball strength is lower than the direct reduction requirement of the rotary kiln.

The metallization rate of the reduced pellet is 80.46 percent, the content of residual zinc still remains 0.68 percent, the dezincification rate in the reduction process is only 79.36 percent, and the dezincification effect is poor. K₂The removal rate of O was 37.5%, Na₂The O removal rate was 39.2%. The pulverization phenomenon of the pellets in the reduction process is serious, and the reduced pellets basically have no strength. Therefore, the zinc content and strength index of the reduced pellets can not meet the requirements of the rotary kiln.

In addition, the zinc hypoxide containing 40.1% of zinc was recovered from the dust, and the recovery rate of zinc was 78.6%. Because the ball pulverization is serious and the dust amount is large, the grade of the secondary zinc oxide is low. Can not meet the requirement of entering the furnace.

Example 1

Aiming at the existing problems, the invention provides a preparation method of zinc-containing dust pellets, which comprises the following steps:

(2) adding carbon-containing fly ash from a coke oven into the mixed dust prepared in the step (1) to obtain a mixed material, wherein the mass ratio of carbon to iron of the mixed material is 0.25;

(3) pretreatment: adding water into the mixture prepared in the step (2) for wetting, wherein the addition amount of the water accounts for 10% of the total weight of the mixture, the wetting time is 10min, then stacking and curing the mixture for 20min, and raising the temperature of the mixture by about 15 ℃;

(4) adding 1% of composite binder into the mixture, and uniformly mixing to obtain a mixed material, wherein the composite binder comprises bentonite and polyacrylamide, and the weight ratio of the bentonite to the polyacryl is 80: 20;

(5) adding the uniformly mixed material into a disc pelletizer to pelletize to obtain green pellets, wherein the pelletizing time is 15min, the green pellet moisture is controlled to be about 14.5%, and the green pellet granularity is controlled to be 10-20 mm;

the falling strength of the prepared green ball can reach 15.5 times/0.5 m, and the compressive strength can reach 56 N.^-1The bursting temperature is 406 ℃;

(6) drying the green pellets on a belt type roasting machine at the drying temperature of 300 ℃, the drying air speed of 0.8m/s, the material layer height of 80mm and the drying time of 7.5 min;

the obtained dry balls have dropping strength of 12.4 times/0.5 m and 4.3 times/1 m, and compressive strength of 210 N.^-1. The dry ball strength meets the direct reduction requirement of the rotary kiln.

(7) And (3) putting the dry pellets into a rotary kiln, introducing coal gas for combustion to directly reduce the dry pellets at 1250 ℃, wherein the reduction time is 50min, and cooling the reduced and dezincified pellets in nitrogen after reduction to obtain the reduced and dezincified pellets.

The metallization rate of the reduction dezincification pellets is 84.56 percent, and the compressive strength is 1690N^-1The content of residual zinc in the reduced pellet is 0.086 percent, and the dezincification rate in the reduction process is as high as 94.1 percent. K₂The removal rate of O is 50.2%, Na₂The O removal rate was 52.3%. The reduced pellets were visually intact without pulverization and cracking. Therefore, the zinc content and the strength index of the reduced pellets meet the furnace charging requirement, and the reduced pellets can be directly used for blast furnace iron making. The zinc hypoxide with 60.1 percent of zinc is obtained by recovering from the smoke dust of the rotary kiln, and the recovery rate of the zinc is 92.3 percent.

Compared with comparative examples 1 and 2, the falling strength, the compressive strength and the dry pellet strength of the green pellets are obviously improved, particularly the dry pellet strength meets the direct reduction requirement of a rotary kiln, so that the zinc content and the strength index of the reduced pellets meet the charging requirement of a blast furnace, and the dezincification rate and the alkali metal removal rate are obviously improved.

Example 2

(1) preparing materials: the blast furnace cloth bag ash, the steelmaking ladle furnace ash and the steelmaking converter smoke dust are mixed according to the weight ratio of 32.42%: 63.46%: 4.12 percent of the zinc-containing dust is obtained by mixing;

(2) adding fine grinding bituminous coal into the zinc dust prepared in the step (1) to obtain a mixture, wherein the mass ratio of carbon to iron of the mixture is 0.25;

(3) pretreatment: adding water into the mixture prepared in the step (2) for wetting, wherein the addition amount of the water accounts for 12% of the total weight of the mixture, the wetting time is 20min, then stacking and curing the mixture for 30min, and raising the temperature of the mixture to about 20 ℃;

(4) adding 0.6% of composite binder into the cured mixture, and uniformly mixing to obtain a mixed material, wherein the composite binder comprises bentonite and polyacrylamide, and the weight ratio of the bentonite to the polyacrylamide is 70: 30, of a nitrogen-containing gas;

(5) adding the uniformly mixed material into a disc pelletizer to pelletize to obtain green pellets, wherein the pelletizing time is 20min, the green pellet moisture is controlled to be about 14.5%, and the green pellet granularity is controlled to be 10-20 mm;

the falling strength of the prepared green ball can reach 13.6 times/0.5 m, and the compressive strength reaches 54 N.^-1The bursting temperature was 395 ℃.

(6) Drying the green pellets on a belt type roasting machine at the drying temperature of 250 ℃, the drying air speed of 1.2m/s, the material layer height of 100mm and the drying time of 10 min;

the obtained dry balls have dropping strength of 16.3 times/0.5 m and 7.7 times/1 m, and compression strength of 235N^-1；

(7) And (3) putting the dry pellets into a rotary kiln, introducing coal gas for combustion and direct reduction, wherein the reduction temperature is 1250 ℃, the reduction time is 90min, and cooling in nitrogen after reduction to obtain the reduced and dezincified pellets.

The obtained reduction dezincification pellet has the metallization rate of 86.54 percent and the compressive strength of 1895N^-1The content of residual zinc in the reduced pellet is 0.060 percent, and the dezincification rate in the reduction process is 96.3 percent. K₂The removal rate of O was 51.9%, Na₂The O-removal rate was 53.0%. The reduced pellets were visually intact without pulverization and cracking. Therefore, the zinc content and the strength index of the reduced pellets meet the furnace charging requirement, and the reduced pellets can be directly used for blast furnace iron making. The zinc hypoxide containing 63.2% of zinc is recovered from the smoke dust of the rotary kiln, and the recovery rate of zinc is 93.5%.

Compared with comparative examples 1 and 2, the falling strength, the compressive strength and the dry pellet strength of the green pellets are obviously improved, particularly the dry pellet strength meets the direct reduction requirement of the rotary kiln, so that the zinc content and the strength index of the reduced pellets meet the furnace entering requirement, and the dezincification rate and the alkali metal removal rate are obviously improved.

In comparison with example 1, the binder ratio was decreased, and the green pellet falling strength and compressive strength were decreased, but the dry pellet strength was improved by optimizing the drying system. Along with the prolonging of the reduction time, the metallization rate, the dezincification rate and the alkali metal removal rate of the reduced pellets are improved. Especially, the compression resistance of the reduced pellets is obviously improved, the dry pellet strength is mainly improved, and the reduction time is prolonged.

Example 3

(2) adding carbon-containing fly ash from a coke oven into the zinc-containing dust prepared in the step (1)

Obtaining a mixture, wherein the mass ratio of carbon to iron of the mixture is 0.25;

(3) pretreatment: adding water into the mixture prepared in the step (2) for wetting, wherein the addition amount of the water accounts for 13% of the total weight of the mixture, the wetting time is 10min, and then stacking and curing the mixture for 30min to increase the temperature of the mixture by about 20 ℃;

(4) adding 0.8% of composite binder into the mixture, and uniformly mixing to obtain a mixed material, wherein the composite binder comprises bentonite and polyacrylamide, and the weight ratio of the bentonite to the polyacrylamide is 90: 10;

the falling strength of the prepared green ball can reach 9.4 times/0.5 m, and the compressive strength can reach 69 N.^-1The bursting temperature was 415 ℃.

(6) Drying the green pellets on a belt type roasting machine, wherein the drying temperature is 350 ℃, the drying air speed is 0.8m/s, the material layer height is 180mm, and the drying time is 15 min;

the obtained dry ball has a falling strength of 10.5 times/0.5 m and a compressive strength of 3.3 times/1 m of 220N^-1。

(7) And (3) putting the dry pellets into a rotary kiln, directly reducing at 1110 ℃ for 120min, and cooling in nitrogen after reduction to obtain the reduced dezincification pellets. And in the reduction period, adding lignite of 5-25mm into the kiln every 3-5 min, wherein the total carbon-iron ratio of the lignite is 0.55. And after reduction, introducing nitrogen for cooling, and performing dry magnetic separation to obtain metallized pellets and nonmagnetic substances.

The metallization rate of the obtained reduced pellet is 84.55 percent, and the compressive strength is 910N^-1The content of residual zinc in the reduced pellets is 0.092%, and the dezincification rate in the reduction process is higher than 92.5%. K₂The removal rate of O is 60.9%, Na₂The O removal rate was 58.3%. The reduced pellets were visually intact without pulverization and cracking. Therefore, the zinc content and the strength index of the reduced pellets meet the furnace charging requirement, and the reduced pellets can be directly used for blast furnace iron making. The zinc hypoxide containing 64.6% of zinc is recovered from the smoke dust of the rotary kiln, and the recovery rate of zinc is 91.4%.

Compared with the example 1, the binder ratio is reduced, the polymer binder ratio is also reduced, the green ball falling strength is reduced, but the compressive strength and the bursting temperature are increased, and the dry ball strength is also reduced. The green pellet and the dry pellet are both much stronger than the conventional iron ore pellets in general. As the reduction temperature is reduced, but the mass ratio of carbon to iron is improved, the metallization rate and the compressive strength of the reduced pellets are basically similar, and the dezincification rate and the alkali metal removal rate are improved.

Compared with the example 2, the binder proportion is increased, but the polymer binder proportion is obviously reduced, the falling strength of green pellets is reduced, the compressive strength and the bursting temperature are increased, and the dry pellet strength is also reduced. The green pellet and the dry pellet are both much stronger than the conventional iron ore pellets in general. As the reduction temperature is reduced, although the mass ratio of carbon to iron is improved, the metallization rate, the compressive strength and the dezincification rate of the reduced pellets are reduced, but the alkali metal removal rate is increased.

Example 4

(1) preparing materials: the blast furnace cloth bag ash, the steelmaking ladle furnace ash and the steelmaking converter smoke dust are mixed according to the weight ratio of 32.42%: 63.46%: 4.12 percent of the zinc-containing dust is mixed to obtain a mixture, no additional solid fuel is added, and the mass ratio of carbon to iron in the zinc-containing dust is 0.10;

(2) pretreatment: adding water into the mixture prepared in the step (1) for wetting, wherein the addition amount of the water accounts for 13% of the total weight of the mixture, the wetting time is 10min, then stacking and curing the mixture for 40min, and raising the temperature of the material by about 35 ℃;

(3) adding 0.8% of composite binder into the mixture obtained in the step (2), and uniformly mixing to obtain a mixed material, wherein the composite binder comprises bentonite and polyacrylamide, and the mass ratio of the bentonite to the polyacrylamide is 90: 10

(4) Adding the uniformly mixed material into a disc pelletizer to pelletize to obtain green pellets, wherein the pelletizing time is 25min, the green pellet moisture is controlled to be about 14.9%, and the green pellet granularity is controlled to be 10-20 mm;

the falling strength of the prepared green ball can reach 12.6 times/0.5 m, and the compressive strength can reach 68 N.^-1The bursting temperature was 390 ℃.

(5) Drying the green pellets on a belt type roasting machine, wherein the drying temperature is 350 ℃, the drying air speed is 0.8m/s, the material layer height is 180mm, and the drying time is 15 min;

the obtained dry ball has a dropping strength of 12.8 times/0.5 m and a compressive strength of 3.9 times/1 m of 230 Ntimes^-1。

(6) And (3) putting the dry pellets into a rotary kiln, directly reducing at 1100 ℃ for 120min, and cooling in nitrogen after reduction to obtain the reduced dezincification pellets. And (3) adding bituminous coal of 5-25mm into the kiln every 3-5 min during the reduction period, wherein the carbon-iron ratio of the bituminous coal is 0.45, and the total carbon-iron mass ratio is 0.55. And after reduction, introducing nitrogen for cooling, and performing dry magnetic separation to obtain metallized pellets and nonmagnetic substances.

The metallization rate of the metallized pellet is 97.02 percent, and the compressive strength is 880 N.^-1. The residual zinc content of the metallized pellet is 0.03 percent, and the dezincification rate is 99.0 percent. K₂The removal rate of O is 66.2%, Na₂The O removal rate was 65.5%. The reduced pellets were visually intact without pulverization and cracking. Therefore, the zinc content and the strength index of the reduced pellets meet the furnace charging requirement, and the reduced pellets can be directly used for blast furnace iron making. The zinc hypoxide with 68.5 percent of zinc is obtained by recovering from the smoke dust of the rotary kiln, and the recovery rate of the zinc is 96.5 percent.

Compared with the example 3, the binder has the same proportion, but because the carbon-containing fine powder is not added as a reducing agent, the falling strength of green pellets is obviously improved, the compressive strength and the bursting temperature are reduced, and the dry pellet strength is increased. The green pellet and the dry pellet are both much stronger than the conventional iron ore pellets in general. Although the reduction temperature, the reduction time and the mass ratio of carbon to iron are not changed, because no internal coal is added, the amount of external coal is increased in the reduction process, the reduction atmosphere is enhanced, the metallization rate and the compressive strength of the reduced pellets are increased, and the dezincification rate and the alkali metal removal rate are increased.

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. The preparation method of the zinc-containing dust pellets is characterized by comprising the following steps:

s1, batching: preparing a zinc-containing dust material, adding carbon-containing fine powder into the zinc-containing dust material, and mixing to obtain a mixture, wherein the mass ratio of carbon to iron of the mixture is 0.10-0.25;

s2, preprocessing: adding 10-13% of water into the zinc-containing dust mixture obtained in the step S1 for wetting, wherein the wetting time is 10-20 min, stacking and curing the mixture for 20-40 min, and the temperature of the material rises to 15-35 ℃;

s3, adding a composite binder with a weight percentage of 0.6% -1.0% into the cured mixture to obtain a uniform mixture, wherein the composite binder comprises bentonite and polyacrylamide, and the weight ratio of the bentonite to the polyacrylamide is 70-90: 30-10 parts of;

2. The method for preparing zinc-containing dust pellets in claim 1, wherein the zinc-containing dust material in the step S1 comprises one or more of blast furnace bag ash, steelmaking ladle ash and steelmaking converter dust.

3. The method for preparing zinc-containing dust pellets according to claim 1, wherein the step S4 is specifically: adding the mixture into a disc pelletizer to pelletize, wherein the pelletizing time is 15-25 min, the water content of the green pellets is 14-15%, and the granularity of the green pellets is 10-20 mm.

4. The preparation method of the zinc-containing dust pellets according to claim 3, wherein the step S5 is specifically to dry the green pellets on a belt dryer, wherein the height of the material layer is 80mm to 180mm, the drying temperature is 250 ℃ to 350 ℃, the drying wind speed is 0.8m/S to 1.2m/S, and the drying time is 7min to 15 min.