CN113333770B - Preparation method of powder metallurgy iron powder - Google Patents
Preparation method of powder metallurgy iron powder Download PDFInfo
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- CN113333770B CN113333770B CN202110603546.6A CN202110603546A CN113333770B CN 113333770 B CN113333770 B CN 113333770B CN 202110603546 A CN202110603546 A CN 202110603546A CN 113333770 B CN113333770 B CN 113333770B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
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- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
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- C—CHEMISTRY; METALLURGY
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- C—CHEMISTRY; METALLURGY
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- C21B—MANUFACTURE OF IRON OR STEEL
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- C21B13/08—Making spongy iron or liquid steel, by direct processes in rotary furnaces
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22B1/02—Roasting processes
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- C22B1/14—Agglomerating; Briquetting; Binding; Granulating
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Abstract
The invention discloses a preparation method of powder metallurgy iron powder, which comprises the following steps: pelletizing in the step (1); step (2): preheating and roasting; step (3): pre-reduction; step (4): crushing and grinding; step (5): and (5) hydrogen reduction. Aiming at the defects of low yield, high energy consumption, serious pollution and low automation degree of the traditional tunnel kiln method in the production of the direct reduced iron powder, the invention provides the rotary kiln direct reduction method, wherein iron concentrate pellets are used for replacing the iron concentrate in the traditional tunnel kiln method, so that metallized pellets with pure texture can be obtained due to easy separation of primary reduction products, the influence on the quality of subsequent products caused by the coal ash and carbon residue can be prevented, and meanwhile, the rotary kiln has the advantages of high yield, stable operation temperature, good controllability and pure product quality. Aiming at the difficult problem of easy pulverization in the high-purity magnetite concentrate ball reduction process, the invention provides a new idea of sectional reduction and sectional coal feeding, regulates and controls the reduction speed, reduces the structural stress generated by converting hematite reduction into magnetite lattice transformation, promotes the slow release of the stress, improves the strength of the pre-reduced pellets, and inhibits reduction pulverization.
Description
Technical Field
The invention belongs to the technical field of powder metallurgy, and particularly relates to a preparation method of powder metallurgy iron powder.
Background
The demand of the iron powder in China is rapidly increased, which benefits from the development of the powder metallurgy mechanical parts, and meanwhile, the powder metallurgy mechanical parts are indistinguishable from the automobile manufacturing industry, the application source of the powder metallurgy mechanical parts is 42%, and the powder metallurgy mechanical parts are increased to about 55%. The chemical components of steel rolling iron scale for producing iron powder have large fluctuation and high price, so the short process of producing iron powder by using ultrapure iron concentrate as raw material is one of the main processes for producing iron powder in future in China. Meanwhile, the method also accords with the trend of developing short flow in the iron and steel industry, the hydrogen reduction is energy-saving and environment-friendly, meets the time requirement of low carbon emission, has rich coal resources in China, and has resource conditions suitable for developing the process.
Chinese patent (application No. 201010613426.6) discloses a method for directly preparing reduced iron powder for powder metallurgy from iron concentrate powder. The method comprises the steps of refining ultrapure iron powder, manufacturing sponge iron, manufacturing primary iron powder and manufacturing reduced iron powder, and the powder metallurgy iron powder product obtained by the method has the properties of high purity, low carbon content and good compressibility, but has the problems of long reduction time and low production efficiency.
Chinese patent (application number 201310253233.8) discloses a preparation method of reduced iron powder for powder metallurgy, which uses the reduced iron purchased in the market as a raw material, reduces the raw material in a tunnel kiln, and then carries out crushing and magnetic separation; then, secondary reduction was performed in a mixed gas of 25% nitrogen and 75% hydrogen. Chinese patent (application number 201711340876.0) proposes a method for preparing superfine iron powder by low-temperature hydrocarbon duplex reduction, wherein iron concentrate powder, carbon powder and a catalyst with certain purity are respectively ball-milled; then uniformly mixing the materials subjected to ball milling in the first step according to a certain proportion; then, placing the uniformly mixed materials in a protective atmosphere for heating reduction, cooling to obtain primary reduced iron, and performing ball milling; the primary reduced iron after ball milling is placed in hydrogen atmosphere for final reduction, cooled and discharged from the furnace; ball milling the reduced iron powder after hydrogen reduction to obtain superfine iron powder. The additive added in the process is potassium carbonate, sodium carbonate or a mixture of the two, and the proportion of the additive is about 1%, so that the cost is increased, the iron grade of the reduced iron powder is easily reduced, and the quality of the reduced iron powder is influenced.
Chinese patent (application number 201510303028.7) discloses a preparation method of reduced iron powder for powder metallurgy, which comprises the steps of sequentially carrying out wet grinding and low-intensity magnetic separation on raw materials containing metal iron after crushing to obtain primary impurity-removed iron powder, carrying out decarburization roasting on the primary impurity-removed iron powder, and carrying out ore dressing impurity removal, acid washing, filtration, drying and batch mixing on a decarburization roasting product to obtain the reduced iron powder for powder metallurgy. The method expands the source of the raw materials of the powder metallurgy iron powder, opens up a new way for preparing the reduced iron powder for powder metallurgy, but also has the defects of long process flow, high treatment difficulty of acid washing wastewater and the like.
At present, the conventional tunnel kiln process for producing reduced iron powder has the defects of low yield, high energy consumption, serious pollution and low automation degree. Under the big tide of energy-saving, environment-friendly and industrial automation development, the tunnel kiln process obviously does not accord with the trend of future development. The iron concentrate pellets are used for replacing the iron concentrate powder in the traditional tunnel kiln method, so that the primary reduction products are easy to separate, the metallized pellets with pure texture can be obtained, and the influence on the quality of subsequent products due to the fact that coal ash and carbon residues are prevented from being brought in.
Disclosure of Invention
The invention aims to provide a preparation method of powder metallurgy iron powder with simple process and good product quality.
The preparation method of the powder metallurgy iron powder comprises the following steps:
(1) Pelletizing:
carrying out high-pressure roller grinding treatment on the high-purity magnetite concentrate, uniformly mixing the roller-ground mineral powder with an organic binder, and pelletizing to obtain green pellets;
step (2): preheating and roasting:
drying, preheating and roasting the green pellets prepared in the step (1) in a grate-rotary kiln to obtain roasted pellets with higher strength;
step (3): pre-reduction
The roasting pellets prepared in the step (2) are distributed with a reducing agent for a plurality of times, and then reduction reaction is carried out at a gradient temperature to obtain pre-reduced pellets;
step (4): crushing and grinding
Crushing the pre-reduced pellets prepared in the step (3), and grinding to obtain primary reduced iron powder;
step (5): hydrogen reduction
And (3) carrying out hydrogen reduction on the primary reduced iron powder obtained in the step (4) to obtain powder metallurgy iron powder.
In the step (1), the mineral powder is milled by a high-pressure roller until the specific surface area is not less than 1500cm 2 The granularity of the mineral powder is less than 0.074mm and accounts for about 80 percent; the organic binder is one or more of polyacrylamide, sodium carboxymethyl cellulose and humic acid; the addition amount of the organic binder is 0.1-0.2% of the mass of the mineral powder; pelletizing by a disc pelletizer, wherein pelletizing moisture is 7-9 wt%, pelletizing time is 9-15 min, and granularity of the green pellets is 8-16 mm.
In the step (2), the specific steps are as follows: drying the green pellets in a chain grate, heating to a preheating temperature after drying, carrying out preheating treatment to obtain high-temperature preheated pellets, and directly sending the high-temperature preheated pellets into a rotary kiln for roasting until the pellets are roasted.
Preferably, the height of the green pellets on the material layer of the grate is 60-80 mm; the drying temperature is 350-400 ℃ and the drying time is 4-6 min; the preheating temperature is 800-900 ℃ and the preheating time is 8-12 min; the roasting temperature is 1200-1250 ℃ and the roasting time is 16-20 min.
Further preferably, the compressive strength of the preheated pellets is more than 600N/piece, and the strength of the roasted pellets is more than 2600N/piece.
The compression strength of the preheated pellets can be more than 600N/number through the cooperation of parameters in each working procedure of the step (2). The preheated pellets with good strength are directly hot-packed into a rotary kiln for roasting at the temperature of more than 800 ℃. In the roasting process, the roasting temperature is too low, the development of hematite grains is insufficient, the pores in the pellets are large, the densification degree is low, and the pellet strength is low; with the increase of the roasting temperature, the energy obtained by particles is increased, the power enhancement of surrounding bond force constraint is overcome, the diffusion capacity is improved, and Fe is accelerated 2 O 3 The migration, aggregation and growth of crystal grains strengthen the recrystallization, eliminate lattice defects, increase the contact area of particles and improve the density of pellets, thereby obviously improving the compressive strength of finished pellets. When the roasting temperature exceeds 1250 ℃, the roasting temperature is too high, so that the liquid phase quantity is increased, and the pellet strength is reduced. When the roasting time is less than 16min, fe 2 O 3 The growth of crystal grains is insufficient, the crystal-connecting effect is not obvious, the consolidation of pellets is insufficient, the density of pellets is low, and the strength of pellets is not good; however, when the firing time is too long, the production efficiency is low.The strength of the baked balls can be increased to more than 2600N/by the cooperation of the parameters in each step (2).
In the step (3), the reducing agent is bituminous coal, and the granularity of the reducing agent is 5-25 mm. The granularity of the reducing coal is too fine and too coarse, which affects the uneven distribution of the coal in the reducing kiln, so that the reducing atmosphere is insufficient and the reducing effect is poor;
the ratio of the total amount of the reducing agent to the mass of the pellets is 5:1-7:1; the total reduction time is 20-24 h, and the gradient temperature is 900-1100 ℃.
The reducing agent is added for 3 to 4 times, and the gradient temperature has 3 gradients; the mass of the reducing agent added for the first time is 2-3 times of the pellet mass, the corresponding reducing temperature is 900 ℃, and the reducing time is 1-1.5 h; the mass of the secondary mixed reducing agent is 1-2 times of the mass of the pellets, the corresponding reducing temperature is 1000 ℃, and the reducing time is 1-2 hours; the mass of the reducing agent added for the third time is 1-2 times of the mass of the pellets, and the corresponding reduction temperature is 1100 ℃; then maintaining 1100 ℃, if the reducing agent is not added, adding the rest of the reducing agent completely, then reducing for 16-21 h, and if the reducing agent is added completely, maintaining the temperature and continuing reducing for 16-21 h.
The invention provides a unique reduction method, namely sectional reduction and sectional coal feeding, which can effectively avoid the problems that the high-temperature reduction speed of oxidized pellets is too high, the stress generated by lattice transformation is too large, thereby leading the pellets to be self-pulverized, being unfavorable for subsequent separation and leading the iron grade of iron powder to be low. By adopting the method for sectional reduction and sectional coal addition, the reduction rate can be reduced, on one hand, the structural stress generated by the change of crystal lattices generated by changing hematite into magnetite in the reduction process is reduced, and on the other hand, the reduction time is prolonged, and the slow release of the structural stress is also facilitated, so that the pulverization of pellets is avoided.
In addition, the total reduction time of the preferred reduction is 20-24 hours, the reduction time is too short, the growth and development of iron grains are imperfect, the size of the iron grains is smaller, the internal porosity of the direct reduced iron is larger, the compactness degree is low, the apparent density of the powder metallurgy iron powder is small, the fluidity is poor, the reduction time is prolonged to 20-24 hours, the iron grains are sufficiently long and are mutually connected, the porosity of the ball direct reduced iron is reduced, the compactness degree is improved, the apparent density of the powder metallurgy iron powder is improved, and the product quality is numbered. However, the reduction time is too long, resulting in reduced efficiency.
In the step (4), a twin-roll crusher is adopted for crushing, and the pellets are crushed to-1 mm; grinding the ore by vacuum ball milling, and crushing the ore to 0.15mm below zero; in the vacuum ball milling process, adding a composite organic additive accounting for 0.1 to 0.3 percent of the mass of the materials for strengthening ball milling; preferably, the composite organic additive is formed by combining polysiloxane and sodium sunflower-base sulfonate, and the ratio of the composite organic additive to the sodium sunflower-base sulfonate is 2-6:6-8.
The composite additive can improve the surface property of iron powder, improve the mechanical and chemical processes of the grinding process, overcome the attractive force among the iron powder, reduce the grinding resistance, improve the fluidity of the grinding powder, simultaneously generate selective adsorption and electric neutralization on the surface of the material, eliminate the static effect, reduce the capability and probability of fine and particle aggregation, and improve the dispersity of the fine powder material, thereby improving the grinding efficiency and reducing the particle size of the particles.
In the step (5), H 2 The flow is 0.3-0.5L/min, the hydrogen reduction temperature is 800-850 ℃, and the reduction time is 90-120 min.
The powder metallurgy iron powder is prepared according to the method, wherein the powder metallurgy iron powder comprises the following components: the iron grade exceeds 98.5%, the apparent density is 2.45-2.60 g/cm 3 The fluidity is 35s/50 g-39 s/50g, the compressibility is 6.40-6.65 g/cm 3 Meets the requirements of the first grade product of the powder metallurgy iron powder.
The invention has the beneficial effects that:
(1) Aiming at the defects of low yield, high energy consumption, serious pollution and low automation degree of the traditional tunnel kiln method in the production of the direct reduced iron powder, the invention provides the rotary kiln direct reduction method, wherein iron concentrate pellets are used for replacing the iron concentrate in the traditional tunnel kiln method, so that metallized pellets with pure texture can be obtained due to easy separation of primary reduction products, the influence on the quality of subsequent products caused by the coal ash and carbon residue can be prevented, and meanwhile, the rotary kiln has the advantages of high yield, stable operation temperature, good controllability and pure product quality.
(2) Aiming at the difficult problem of easy pulverization in the high-purity magnetite concentrate ball reduction process, the invention provides a new idea of sectional reduction and sectional coal feeding, regulates and controls the reduction speed, reduces the structural stress generated by converting hematite reduction into magnetite lattice transformation, promotes the slow release of the stress, improves the strength of the pre-reduced pellets, and inhibits reduction pulverization.
(3) Aiming at the problems that the energy consumption is high in the primary reduced iron powder fine grinding process, the fine-grinding iron powder is easy to aggregate to form clusters, the fluidity of products is poor, the loose packing density is low, the composite additive is developed, the attractive force between iron powder is overcome, the grinding resistance is reduced, the fluidity of the powder is improved, meanwhile, the selective adsorption and the electric neutralization are generated on the surface of the material, the static effect is eliminated, the primary reduced iron powder grinding efficiency is improved, and the product quality is improved.
Drawings
FIG. 1 is a schematic diagram of the process flow of the preparation method of the invention.
Detailed Description
The following description of the technical solutions in the embodiments of the present invention will be clear and complete, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which are derived by a person skilled in the art based on the embodiments of the invention, fall within the scope of protection of the invention.
The following examples and comparative examples, unless otherwise specified, used magnetite concentrates were from Gansu corporation and had the following chemical composition: TFe71.52%, feO27.36%, caO0.079%, siO 2 0.57％,Al 2 O 3 0.39%, mgO 0.06%, S0.011%, P0.0016%; the reducing coal has a carbon content up to 52%, volatile matter content 30.41%, ash content less than 5%, sulfur content 0.34%, deformation temperature 1332 ℃, softening temperature 1376 ℃, hemispherical temperature 1450 ℃ and flowing temperature 1469 ℃.
The preparation flow of the embodiment of the invention is shown in fig. 1, and specific process parameters can be seen in the embodiment.
Comparative example 1
Performing high-pressure roller grinding treatment on the magnetite concentrate to make the specific surface area of the magnetite concentrate be 1530cm 2 /g; magnetite concentrateMixing with PAM, wherein the proportion of PAM is 0.1%, pelletizing the mixture by a disc pelletizer, controlling the pelletizing moisture to 7.5%, and the pelletizing time to 12min, wherein the falling strength of the obtained green pellets is 4.4 times/0.5 m, the compression strength of the green pellets is 10.9N/each, and the burst temperature of the green pellets is 410 ℃; the prepared green pellets are subjected to blast drying at 350 ℃ for 3min and air draft drying at 350 ℃ for 2min on a chain grate (the height of a green pellet layer is 70 mm), and then are preheated at 800 ℃ for 10min, and the compressive strength of the preheated pellets is 635N/number; directly feeding the hot preheated pellets into a rotary kiln for roasting, wherein the roasting temperature is 1250 ℃, the roasting time is 18min, and the strength of the obtained roasted pellets is 2757N/pellet; directly reducing the obtained roasting balls in a rotary kiln at 1100 ℃ for 22 hours, wherein the mass ratio of the coal mine is 6:1, and the obtained metallized balls are basically powder and have no complete balls; crushing the powder to-1 mm, adding 0.1% of compound organic additive (polysiloxane and sodium sunflower-base sulfonate with the ratio of 3:7), performing vacuum ball milling to-0.15 mm, and performing secondary hydrogen reduction on the obtained metal iron powder to obtain H 2 The flow is 0.4L/min, the hydrogen reduction temperature is 850 ℃, the reduction time is 100min, and the finally obtained powder metallurgy iron powder is 97.35 percent of iron grade and 2.45g/cm of apparent density 3 Fluidity of 37s/50g and compressibility of 6.48/cm 3 。
As can be seen from the quality of the obtained iron powder, the method of sectional reduction and sectional coal feeding is not adopted in the comparative example 1, so that the powder is seriously pulverized in the pellet reduction process, the separation from the coal ash is incomplete, and finally, the iron grade of the metallurgical iron powder product is lower, namely, only 97.35%, and the 98% standard of the metallurgical iron powder cannot be met.
Comparative example 2
Performing high-pressure roller grinding treatment on the magnetite concentrate to make the specific surface area of the magnetite concentrate be 1530cm 2 /g; mixing magnetite concentrate and PAM, wherein the proportion of the PAM is 0.1%, pelletizing the mixture by a disc pelletizer, controlling pelletizing moisture to be 7.5%, and pelletizing for 12min, wherein the falling strength of the obtained green pellets is 4.4 times/0.5 m, the compression strength of the green pellets is 10.9N/one, and the burst temperature of the green pellets is 410 ℃; the green pellets are dried by blowing at 350 ℃ for 3min and by exhausting at 350 ℃ for 2min on a grate (the height of the green pellet layer is 70 mm), and then preheated at 800 ℃ for 10min, and the compressive strength of the preheated pellets is635N/number; directly feeding the hot preheated pellets into a rotary kiln for roasting, wherein the roasting temperature is 1250 ℃, the roasting time is 18min, and the strength of the obtained roasted pellets is 2757N/pellet; the obtained roasting balls directly enter a rotary kiln for reduction, and the reduction procedure is as follows: the coal mine ratio in the first stage is 2:1, and the reduction temperature is 900 ℃ for 1h; the coal mine ratio in the second stage is 1:1, and the reduction temperature is 1000 ℃ for 1h; the coal mine ratio in the third stage is 1:1, and the reduction temperature is 1100 ℃ for 1.5h; the fourth stage has a coal mine ratio of 3:1, and a reduction temperature of 1100 ℃ and a reduction time of 20 hours; the obtained metallized pellets have complete appearance, the pellet strength is 635N/m, and the metallized pellets can be thoroughly separated from coal ash only by sieving. Crushing the metallized pellets to-1 mm, then performing vacuum ball milling to-0.15 mm (no composite additive is added), and performing secondary hydrogen reduction on the obtained metal iron powder to obtain H 2 The flow is 0.4L/min, the hydrogen reduction temperature is 850 ℃, the reduction time is 100min, and the finally obtained powder metallurgy iron powder is 98.34 percent of iron grade and 2.35g/cm of apparent density 3 Fluidity 40s/50g, compressibility 6.38/cm 3 。
As can be seen from the quality of the obtained iron powder, the method of sectional reduction and sectional coal addition is adopted in the comparative example 2, so that the obtained metallized pellets have complete morphology, good strength and capability of being effectively separated from coal ash, the iron grade of the prepared metallurgical powder is high and is 98.34%, the requirements of first-class products are met, but the ore grinding efficiency is lower due to the fact that no composite additive is adopted in the ore grinding process, the particle morphology is poor, and finally the prepared powder metallurgical iron powder has low apparent density, poor flowability and poor compression performance.
Comparative example 3
Performing high-pressure roller grinding treatment on the magnetite concentrate to make the specific surface area of the magnetite concentrate be 1530cm 2 /g; mixing magnetite concentrate and PAM, wherein the proportion of the PAM is 0.1%, pelletizing the mixture by a disc pelletizer, controlling pelletizing moisture to be 7.5%, and pelletizing for 12min, wherein the falling strength of the obtained green pellets is 4.4 times/0.5 m, the compression strength of the green pellets is 10.9N/one, and the burst temperature of the green pellets is 410 ℃; the green pellets prepared were air-dried at 350deg.C for 3min and air-dried at 350deg.C for 2min on a grate (green pellet layer height of 70 mm), and then preheated at 800deg.C for 10min, with the compression strength of 635N/minThe method comprises the steps of carrying out a first treatment on the surface of the Directly feeding the hot preheated pellets into a rotary kiln for roasting, wherein the roasting temperature is 1250 ℃, the roasting time is 18min, and the strength of the obtained roasted pellets is 2757N/pellet; the obtained roasting balls directly enter a rotary kiln for reduction, and the reduction procedure is as follows: the coal mine ratio in the first stage is 2:1, and the reduction temperature is 900 ℃ for 1h; the coal mine ratio in the second stage is 1:1, and the reduction temperature is 1000 ℃ for 1h; the coal mine ratio in the third stage is 1:1, and the reduction temperature is 1100 ℃ for 1.5h; the fourth stage has a coal mine ratio of 3:1, and a reduction temperature of 1100 ℃ and a reduction time of 15 hours; the obtained metallized pellets have complete appearance, the pellet strength is 635N/m, and the metallized pellets can be thoroughly separated from coal ash only by sieving. Crushing the metallized pellets to-1 mm, adding 0.1% of composite organic additive (polysiloxane and sodium sunflower-base sulfonate in a ratio of 3:7), performing vacuum ball milling to-0.15 mm, and performing secondary hydrogen reduction and H reduction on the obtained metal iron powder 2 The flow is 0.4L/min, the hydrogen reduction temperature is 850 ℃, the reduction time is 100min, and the finally obtained powder metallurgy iron powder is 98.21 percent of iron grade and 2.17g/cm of apparent density 3 Fluidity of 43s/50g and compressibility of 6.20/cm 3 。
From comparative example 3, it can be seen that when the total reduction time is only 18.5 hours, the obtained powder metallurgy iron powder has low bulk density, poor fluidity and poor compression performance, and can not meet the first grade product requirement far.
Example 1
Performing high-pressure roller grinding treatment on the magnetite concentrate to make the specific surface area of the magnetite concentrate be 1530cm 2 /g; mixing magnetite concentrate and PAM, wherein the proportion of the PAM is 0.1%, pelletizing the mixture by a disc pelletizer, controlling pelletizing moisture to be 7.5%, and pelletizing for 12min, wherein the falling strength of the obtained green pellets is 4.4 times/0.5 m, the compression strength of the green pellets is 10.9N/one, and the burst temperature of the green pellets is 410 ℃; the prepared green pellets are subjected to blast drying at 350 ℃ for 3min and air draft drying at 350 ℃ for 2min on a chain grate (the height of a green pellet layer is 70 mm), and then are preheated at 800 ℃ for 10min, and the compressive strength of the preheated pellets is 635N/number; directly feeding the hot preheated pellets into a rotary kiln for roasting, wherein the roasting temperature is 1250 ℃, the roasting time is 18min, and the strength of the obtained roasted pellets is 2757N/pellet; the obtained roasting balls directly enter a rotary kiln for reduction, and the reduction processThe method comprises the following steps: the coal mine ratio in the first stage is 2:1, and the reduction temperature is 900 ℃ for 1.5h; the coal mine ratio in the second stage is 1:1, and the reduction temperature is 1000 ℃ for 1h; the coal mine ratio in the third stage is 1:1, and the reduction temperature is 1100 ℃ for 1.5h; the fourth stage has a coal mine ratio of 3:1, and a reduction temperature of 1100 ℃ and a reduction time of 16 hours; the obtained metallized pellets have complete appearance, the pellet strength is 721N/pellet, and the metallized pellets can be thoroughly separated from coal ash only by sieving. Crushing the metallized pellet to-1 mm, adding 0.1% of compound organic additive (polysiloxane and sodium sunflower-base sulfonate (the ratio is 3:7)), vacuum ball milling to-0.15 mm, and reducing the obtained metal iron powder with secondary hydrogen to obtain H 2 The flow is 0.4L/min, the hydrogen reduction temperature is 850 ℃, the reduction time is 100min, and the finally obtained powder metallurgy iron powder is 98.47 percent of iron grade and the apparent density is 2.25g/cm 3 Fluidity of 38s/50g and compressibility of 6.42/cm 3 。
In example 1, the reduction time was prolonged to 20 hours, the apparent density of the powder metallurgical iron powder was increased, the fluidity was improved, and the compressibility was improved, as compared with comparative example 3.
Example 2
Performing high-pressure roller grinding treatment on the magnetite concentrate to make the specific surface area of the magnetite concentrate be 1530cm 2 /g; mixing magnetite concentrate and PAM, wherein the proportion of the PAM is 0.1%, pelletizing the mixture by a disc pelletizer, controlling pelletizing moisture to be 7.5%, and pelletizing for 12min, wherein the falling strength of the obtained green pellets is 4.4 times/0.5 m, the compression strength of the green pellets is 10.9N/one, and the burst temperature of the green pellets is 410 ℃; the prepared green pellets are subjected to blast drying at 350 ℃ for 3min and air draft drying at 350 ℃ for 2min on a chain grate (the height of a green pellet layer is 70 mm), and then are preheated at 800 ℃ for 10min, and the compressive strength of the preheated pellets is 635N/number; directly feeding the hot preheated pellets into a rotary kiln for roasting, wherein the roasting temperature is 1250 ℃, the roasting time is 18min, and the strength of the obtained roasted pellets is 2757N/pellet; the obtained roasting balls directly enter a rotary kiln for reduction, and the reduction procedure is as follows: the coal mine ratio in the first stage is 2:1, and the reduction temperature is 900 ℃ for 1.5h; the coal mine ratio in the second stage is 1:1, and the reduction temperature is 1000 ℃ for 1.5h; in the third stage, the coal mine ratio is 1:1, and the reduction temperature is 1100 ℃ for 2h; the fourth stage coal mine ratio is 3:1, and the reduction temperature is 1100 ℃ and the reduction time is17h; the obtained metallized pellets have complete appearance, the pellet strength is 732N/number, and the metallized pellets can be thoroughly separated from coal ash only by sieving. Crushing the metallized pellets to-1 mm, adding 0.1% of composite organic additive (polysiloxane and sodium sunflower-base sulfonate in a ratio of 3:7), performing vacuum ball milling to-0.15 mm, and performing secondary hydrogen reduction and H reduction on the obtained metal iron powder 2 The flow is 0.4L/min, the hydrogen reduction temperature is 850 ℃, the reduction time is 100min, and the finally obtained powder metallurgy iron powder is 98.52 percent of iron grade and the apparent density is 2.45g/cm 3 Fluidity of 37s/50g and compressibility of 6.49/cm 3 。
In example 2, compared with example 1 and comparative example 3, the reduction time was further prolonged to 22 hours, the apparent density of the powder metallurgy iron powder was further increased, the fluidity was further improved, and the compression performance was significantly improved.
Example 3
Performing high-pressure roller grinding treatment on the magnetite concentrate to make the specific surface area of the magnetite concentrate be 1530cm 2 /g; mixing magnetite concentrate and PAM, wherein the proportion of the PAM is 0.1%, pelletizing the mixture by a disc pelletizer, controlling pelletizing moisture to be 7.5%, and pelletizing for 12min, wherein the falling strength of the obtained green pellets is 4.4 times/0.5 m, the compression strength of the green pellets is 10.9N/one, and the burst temperature of the green pellets is 410 ℃; the prepared green pellets are subjected to blast drying at 350 ℃ for 3min and air draft drying at 350 ℃ for 2min on a chain grate (the height of a green pellet layer is 70 mm), and then are preheated at 800 ℃ for 10min, and the compressive strength of the preheated pellets is 635N/number; directly feeding the hot preheated pellets into a rotary kiln for roasting, wherein the roasting temperature is 1250 ℃, the roasting time is 18min, and the strength of the obtained roasted pellets is 2757N/pellet; the obtained roasting balls directly enter a rotary kiln for reduction, and the reduction procedure is as follows: the coal mine ratio in the first stage is 2:1, and the reduction temperature is 900 ℃ for 1.5h; the coal mine ratio in the second stage is 1:1, and the reduction temperature is 1000 ℃ for 1.5h; in the third stage, the coal mine ratio is 1:1, and the reduction temperature is 1100 ℃ for 2h; the fourth stage has a coal mine ratio of 2:1, and the reduction time is 19 hours at the reduction temperature of 1100 ℃; the obtained metallized pellets have complete appearance, the pellet strength is 755N/min, and the metallized pellets can be thoroughly separated from coal ash by sieving. The metallized pellets are jaw-crushed to-1 mm, and then 0.1% of compound organic is addedVacuum ball milling the additive (polysiloxane and sodium sunflower sulfonate in the ratio of 3 to 7) to 0.15mm to obtain metal iron powder, and secondary hydrogen reduction to obtain H 2 The flow is 0.4L/min, the hydrogen reduction temperature is 850 ℃, the reduction time is 100min, and the finally obtained powder metallurgy iron powder is 98.54 percent of iron grade and the loose packed density is 2.49g/cm 3 Fluidity of 36s/50g and compressibility of 6.51/cm 3 。
In example 3, compared with example 1, example 2 and comparative example 3, the reduction time is further prolonged to 24 hours, the apparent density of the powder metallurgy iron powder is further improved, the fluidity is further improved, and the compression performance is remarkably improved.
Example 4
Performing high-pressure roller grinding treatment on the magnetite concentrate to make the specific surface area of the magnetite concentrate be 1530cm 2 /g; mixing magnetite concentrate and PAM, wherein the proportion of the PAM is 0.1%, pelletizing the mixture by a disc pelletizer, controlling pelletizing moisture to be 7.5%, and pelletizing for 12min, wherein the falling strength of the obtained green pellets is 4.4 times/0.5 m, the compression strength of the green pellets is 10.9N/one, and the burst temperature of the green pellets is 410 ℃; the prepared green pellets are subjected to blast drying at 350 ℃ for 3min and air draft drying at 350 ℃ for 2min on a chain grate (the height of a green pellet layer is 70 mm), and then are preheated at 800 ℃ for 10min, and the compressive strength of the preheated pellets is 635N/number; directly feeding the hot preheated pellets into a rotary kiln for roasting, wherein the roasting temperature is 1250 ℃, the roasting time is 18min, and the strength of the obtained roasted pellets is 2757N/pellet; the obtained roasting balls directly enter a rotary kiln for reduction, and the reduction procedure is as follows: the coal mine ratio in the first stage is 2:1, and the reduction temperature is 900 ℃ for 1.5h; the coal mine ratio in the second stage is 1:1, and the reduction temperature is 1000 ℃ for 1.5h; in the third stage, the coal mine ratio is 1:1, and the reduction temperature is 1100 ℃ for 2h; the fourth stage has a coal mine ratio of 2:1, and the reduction time is 19 hours at the reduction temperature of 1100 ℃; the obtained metallized pellets have complete appearance, the pellet strength is 755N/min, and the metallized pellets can be thoroughly separated from coal ash by sieving. Crushing the metallized pellets to-1 mm, adding 0.3% of composite organic additive (polysiloxane and sodium sunflower-base sulfonate in a ratio of 3:7), performing vacuum ball milling to-0.15 mm, and performing secondary hydrogen reduction and H reduction on the obtained metal iron powder 2 The flow rate is 0.4L/min, the hydrogen reduction temperature is 850 ℃, and the reduction is carried outThe time is 100min, and the finally obtained powder metallurgy iron powder is 98.54 percent of iron grade and 2.55g/cm of apparent density 3 Fluidity of 35s/50g and compressibility of 6.60/cm 3 。
Example 4 compared with example 3, the bulk density, flowability and compression performance of the powder metallurgy iron powder can be obviously improved by increasing the amount of the composite additive in the ore grinding process.
Claims (6)
1. The preparation method of the powder metallurgy iron powder comprises the following steps:
step (1): pelletizing
Carrying out high-pressure roller grinding treatment on the high-purity magnetite concentrate, uniformly mixing the roller-ground mineral powder with an organic binder, and pelletizing to obtain green pellets;
step (2): preheating and roasting
Drying, preheating and roasting the green pellets prepared in the step (1) in a grate-rotary kiln to obtain roasted pellets with higher strength; the compressive strength of the preheated pellets is more than 600N/number, and the strength of the baked pellets is more than 2600N/number;
step (3): pre-reduction
The roasting pellets prepared in the step (2) are distributed with a reducing agent for a plurality of times, and then reduction reaction is carried out at a gradient temperature to obtain pre-reduced pellets;
the reducing agent is bituminous coal, and the granularity of the reducing agent is 5-25 mm; the ratio of the total amount of the reducing agent to the mass of the pellets is 5:1-7:1; the total reduction time is 20-24 hours, and the gradient temperature is 900-1100 ℃;
the reducing agent is added for 3-4 times, and the gradient temperature has 3 gradients; the mass of the reducing agent is 2-3 times of the pellet mass, the corresponding reducing temperature is 900 ℃, and the reducing time is 1-1.5 h; the mass of the secondary mixed reducing agent is 1-2 times of the mass of the pellets, the corresponding reducing temperature is 1000 ℃, and the reducing time is 1-2 hours; the mass of the reducing agent added for the third time is 1-2 times of the mass of the pellets, and the corresponding reduction temperature is 1100 ℃; then maintaining 1100 ℃, if the reducing agent is not added, adding all the rest, then reducing for 16-21 hours, and if the reducing agent is added, maintaining the temperature and continuing to reduce for 16-21 hours;
step (4): crushing and grinding
Crushing the pre-reduced pellets prepared in the step (3), and grinding to obtain primary reduced iron powder;
grinding the ore by vacuum ball milling, and crushing the ore to 0.15mm below zero; in the vacuum ball milling process, adding a composite organic additive accounting for 0.1-0.3% of the mass of the materials for strengthening ball milling; the composite organic additive is formed by combining polysiloxane and sodium sunflower-based sulfonate, and the ratio of the composite organic additive to the sodium sunflower-based sulfonate is 2-6:6-8;
step (5): hydrogen reduction
And (3) carrying out hydrogen reduction on the primary reduced iron powder obtained in the step (4) to obtain powder metallurgy iron powder.
2. The method for producing powder metallurgical iron powder of claim 1, wherein in step (1), the powder is high-pressure roller milled to a specific surface area of not less than 1500cm 2 Per gram, the granularity of the mineral powder is less than 0.074mm and accounts for 80 percent; the organic binder is one or more of sodium carboxymethyl cellulose and humic acid, and the addition amount of the organic binder is 0.1-0.2% of the mass of the mineral powder; pelletizing by a disc pelletizer, wherein pelletizing moisture is 7-9 wt%, pelletizing time is 9-15 min, and granularity of the green pellets is 8-16 mm.
3. The method for preparing powder metallurgical iron powder according to claim 1, wherein in the step (2), the specific steps are as follows: drying the green pellets in a chain grate, heating to a preheating temperature after drying, carrying out preheating treatment to obtain high-temperature preheated pellets, and directly sending the high-temperature preheated pellets into a rotary kiln for roasting until the pellets are roasted.
4. The method for preparing powder metallurgy iron powder according to claim 3, wherein the height of the green pellets on a material layer of a grate is 60-80 mm; the drying temperature is 350-400 ℃, and the drying time is 4-6 min; the preheating temperature is 800-900 ℃, and the preheating time is 8-12 min; the roasting temperature is 1200-1250 ℃, and the roasting time is 16-20 min.
5. The method for producing powder metallurgical iron powder of claim 1, wherein in step (5), H 2 The flow rate is 0.3-0.5L/min, the hydrogen reduction temperature is 800-850 ℃, and the reduction time is 90-120 min.
6. The powder metallurgy iron powder prepared by the preparation method according to any one of claims 1 to 5, wherein the powder metallurgy iron powder is characterized in that: the iron grade exceeds 98.5%, and the apparent density is 2.45-2.60 g/cm 3 Fluidity is 35s/50 g-39 s/50g, compressibility is 6.40-6.65 g/cm 3 Meets the requirements of the first grade product of the powder metallurgy iron powder.
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| CN102242252A (en) * | 2011-06-29 | 2011-11-16 | 中南大学 | Method for preparing high-nickel concentrate from low-grade red soil nickel ore |
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| CN107254563B (en) * | 2017-06-20 | 2019-03-29 | 中南大学 | The compound additive of high magnesium types lateritic nickel ore direct-reduction and its application in reinforcing |
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| US3759693A (en) * | 1969-08-18 | 1973-09-18 | Kobe Steel Ltd | Method of producing reduced iron ore pellets |
| AU2008100427A4 (en) * | 2008-03-05 | 2008-07-03 | Central South Univeristy | Efficient separation method for low grade complex iron ore |
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