High proportion hematite concentrate pellet and method for preparing the same

Abstract

The application discloses high-proportion hematite concentrate pellets and a preparation method thereof, and belongs to the technical field of iron ore pellets. The pellets comprise an inner layer and an outer layer, the inner layer comprises hematite, and the outer layer comprises magnetite, wherein the radius of the pellets is R, the spherical radius of the inner layer is r B , and r B / R<80%. The preparation method comprises the following steps: preparing green pellets by sequentially performing water dripping and water mist growing on the inner layer material comprising hematite powder through a disc pelletizer or a drum pelletizer; preparing composite green pellets by sequentially performing water mist growing on the green pellets and the outer layer material comprising magnetite powder through the disc pelletizer or the drum pelletizer; and preparing finished pellets by sequentially performing drying, preheating and roasting on the composite green pellets. The application can prepare high-proportion hematite concentrate pellets, can reduce the consumption of bentonite and can improve the strength of the hematite concentrate pellets. Further, the application further provides a preparation method of the high-proportion hematite concentrate pellets, and the production energy consumption of the pellets is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of iron ore pellets, and more particularly relates to a high-proportion hematite concentrate pellet and a preparation method thereof. BACKGROUND

[0002] Oxidized pellets are one of the important components of blast furnace burden structure, and the preparation method is as follows: iron concentrate and binders such as bentonite are rolled into balls under the action of a disc balling machine or a drum balling machine, and then are subjected to high-temperature oxidation roasting at 1200-1300 DEG C to form qualified pellets with a strength meeting the requirements of blast furnace production. The best raw material for the oxidized pellets is magnetite concentrate. In recent years, due to the continuous growth of pellet production in China, the resource of magnetite concentrate is increasingly scarce. The use of hematite concentrate for the oxidized pellets can reduce the production cost. However, due to the different solidification mechanisms, the hematite pellets often need a higher roasting temperature, which increases the load of the pellet production equipment and causes the energy consumption to increase. Therefore, it is of great practical significance and economic benefits to develop a preparation method of high-proportion hematite concentrate pellets.

[0003] A large number of researches have been carried out on the preparation of green pellets and the high-temperature solidification mechanism of high-proportion hematite concentrate pellets at home and abroad. The research results show that the oxidation exothermic of magnetite concentrate in the roasting process is beneficial to the high-temperature recrystallization of nascent Fe2O3, the crystal form is changed from cubic system to hexagonal system, and the volume of the pellets shrinks; the hematite concentrate does not undergo oxidation reaction and crystal lattice transformation in the roasting process, and the original Fe2O3 needs to be subjected to high-temperature recrystallization at a higher temperature, and the volume of the pellets basically does not change. At present, the application of large-proportion hematite concentrate in the pellets is mainly realized by the modification of production equipment and the optimization of process parameters, but the problems of the influence of high roasting temperature on the production equipment and high energy consumption have not been fundamentally solved by using the ordinary pellet preparation method.

[0004] After retrieval, the patent application file with the Chinese patent publication No. CN107739820A and the application publication date of February 27, 2018 discloses a magnetite powder pellet and a production method thereof. The method comprises: (1) batching: batching according to 8-20 parts by weight of hematite powder, 78-90 parts by weight of magnetite powder and 1-2 parts by weight of bentonite; (2) mixing and balling: after the raw materials of step (1) are mixed uniformly by a mixer, water is added to a disc balling machine to supplement the moisture, and green pellets are prepared by balling; (3) roasting: the green pellets prepared in step (2) are distributed and roasted on a chain grate-rotary kiln to obtain finished pellets. However, the purpose of the method is to improve and optimize the batching to improve the quality of the ultra-fine particle magnetite powder pellet, and the hematite only plays a role in preventing the ultra-fine particle magnetite powder from being oxidized too fast, and the problems of high consumption of bentonite for the green pellets of high-proportion hematite concentrate and high roasting temperature are still not solved.

[0005] Therefore, it is urgent to develop a high proportion of hematite concentrate pellet and a preparation method thereof. SUMMARY

[0006] 1. Problem to be solved

[0007] In view of the low utilization proportion of hematite concentrate in the existing pellet, the application provides a high proportion of hematite concentrate pellet, which can reduce the consumption of bentonite and improve the strength of hematite concentrate pellet. Further, the application provides a preparation method of the high proportion of hematite concentrate pellet, which reduces the production energy consumption of the pellet.

[0008] 2. Technical scheme

[0009] To solve the above problems, the application adopts the following technical scheme.

[0010] A high proportion of hematite concentrate pellet, comprising an inner layer and an outer layer, the inner layer comprising hematite, and the outer layer comprising magnetite, wherein the radius of the pellet is R, and the spherical radius of the inner layer is r B , r B The size is related to the proportion of hematite, and r B / R < 80%, preferably r B / R < 66%.

[0011] Further, 0 < r B ≤ 10 mm, and 10 < R ≤ 16 mm.

[0012] Further, the inner layer and the outer layer further comprise a binder, wherein the mass fraction of the binder in the inner layer is 1.5% to 2.0%, and the mass fraction of the binder in the outer layer is 1.2% to 1.7%.

[0013] Further, the binder is bentonite.

[0014] Further, the content of montmorillonite in the bentonite is ≥ 55%.

[0015] Further, the compressive strength of the pellet is ≥ 2300 N / pellet. It should be noted that the strength here is point strength, which is generally represented by the average value of 10 pellets.

[0016] A preparation method of the above high proportion of hematite concentrate pellet, comprising the following steps: preparing green pellets by successively dripping water into balls and growing by mist water through a disc pelletizer or a drum pelletizer for the inner layer material comprising hematite powder; preparing composite green pellets by growing by mist water through a disc pelletizer or a drum pelletizer for the green pellets and the outer layer material comprising magnetite powder; and preparing finished pellets by successively drying, preheating and roasting the composite green pellets.

[0017] Further, the application provides a preparation method of high-proportion hematite concentrate pellets, which uses hematite concentrate and bentonite as the inner layer of the pellets, and uses magnetite concentrate and bentonite as the outer layer of the pellets, wherein the water content of the hematite concentrate and bentonite mixture is 7%-9%, and the water content of the magnetite concentrate and bentonite mixture is 6.5%-8.5%.

[0018] Further, in the hematite concentrate, the proportion of particles with a particle size less than 74 μm is ≥90%, and the specific surface area is ≥1400 cm 2 / g; in the magnetite concentrate, the proportion of particles with a particle size less than 74 μm is ≥85%, and the specific surface area is ≥1200 cm 2 / g.

[0019] Further, the water absorption rate of the green pellets and the composite green pellets is ≥400 % after 2h.

[0020] Further, the water content of the green pellets is 8%-10%, and the water content of the outer layer of the composite green pellets is 8%-10%.

[0021] Further, in the drying, preheating and roasting steps: the drying temperature is 300-450℃, the preheating temperature is 900-1000℃, and the roasting temperature is 1230℃-1260℃.

[0022] 3. Beneficial effects

[0023] Compared with the prior art, the application has the following beneficial effects:

[0024] (1) The application uses the different solidification mechanisms of hematite and magnetite re-pellet roasting, uses the hematite concentrate with substantially unchanged volume after roasting as the inner layer of the pellets, and uses the magnetite concentrate which releases heat and shrinks in volume after roasting as the outer layer, so as to achieve the effect of the outer layer wrapping the inner layer and making the pellets self-tight, thereby reducing the consumption of bentonite, improving the strength of the hematite concentrate pellets, and reducing the energy consumption of pellet production.

[0025] (2) The application uses the characteristics of the shrinkage and heat release of the magnetite concentrate in the roasting and solidification process, and uses the layered pelletizing method of the inner layer being hematite concentrate and the outer layer being magnetite concentrate, so as to use the heat released by the magnetite concentrate for high-temperature recrystallization of the hematite, thereby improving the strength of the finished pellets. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a cross-sectional schematic diagram of the layered pellets of the application. DETAILED DESCRIPTION

[0027] The application will be further described below in combination with specific embodiments and drawings.

[0028] EMBODIMENT

[0029] This embodiment uses different proportions of hematite through the layered preparation method of the application and the traditional preparation method respectively, records the falling strength of the composite green ball and the compressive strength of the finished pellet, and compares the beneficial effects of the method provided by the application.

[0030] The magnet concentrate A, the hematite concentrate B and the bentonite F used by a typical domestic steel enterprise are used to prepare pellets:

[0031] In the traditional preparation method, the A concentrate and the B concentrate are mixed uniformly for pellet preparation, and the proportion of the B concentrate is controlled in sequence as 11.1%~59.3% and corresponds to the eight traditional preparation schemes in Table 1 in sequence, that is, in the traditional preparation method of serial number 1, the proportion of the B concentrate is controlled as 11.1%; in the traditional preparation method of serial number 2, the proportion of the B concentrate is controlled as 21.6%, and so on, wherein the bentonite F addition amount in the four traditional preparation schemes of serial numbers 1~4 in Table 1 is fixed as 1.8%.

[0032] In the layered preparation method, the inner layer is the B concentrate, the bentonite addition amount is 2.0%, and the inner layer diameter is 6.0 mm~10.5 mm in sequence; the outer layer is the A concentrate, the bentonite addition amount is 1.6%, and the green ball diameter is controlled as 12.5 mm, and the green ball moisture is controlled between 8.0~9.0%. Among them, in the layered preparation method, the bentonite consumption is calculated according to the following method: m A ×1.6%+ m B ×2.0%) / ( m A + m B ) ×100%, wherein m A is the weight of the outer layer, m B is the weight of the inner layer.

[0033] The pellet preparation scheme is shown in Table 1:

[0034]

[0035] The green ball preparation is carried out in a disc balling machine with a diameter of 1000 mm, the rotating speed is 23 r / min, and the inclination angle is 47°. During the test, the green ball with the target thickness is prepared by using the mixed and uniform hematite concentrate B and bentonite F, and the green ball particle size is determined by a circular screen; then the balling raw material is switched to the mixed and uniform magnet concentrate A and bentonite F to prepare the green ball with a diameter of 12.5 mm. The pellet drying, preheating and roasting are carried out in a multi-stage horizontal tube furnace, the drying temperature is 300℃, the drying time is 10 min, the preheating temperature is 920℃, the preheating time is 15 min, the roasting temperature is 1250℃, and the roasting time is 18 min.

[0036] Experimental results and analysis

[0037] Pellet detection includes composite green ball drop strength, compressive strength and moisture and finished pellet compressive strength detection.

[0038] The drop strength determination method is that 10 12.5 mm composite green balls are taken, and are dropped freely from 0.5 m to a 10 mm thick steel plate, and are repeatedly performed until the green ball cracks. The drop strength of each green ball is the drop times minus 1, and the average of the drop strength of each green ball is the drop strength of the green ball under a certain process condition, and the unit is times / (0.5 m). Each group of experiments is detected in parallel for three times, and the average value is the drop strength of the green ball.

[0039] The compressive strength determination method is that a green ball compressive strength tester is used to determine the compressive strength of 10 12 mm green balls, and then the average value is taken, and the unit is N / P. Each group of experiments is detected in parallel for three times, and the average value is the green ball compressive strength. The experimental results are shown in Table 2.

[0040]

[0041] It can be found from Table 2 that the drop strength of the green ball prepared by the layered preparation method of the application is not much different, the green ball compressive strength and the finished pellet compressive strength are basically consistent, but the bentonite addition amount is lower than that of the traditional method; with the increase of the proportion of hematite concentrate B, the pellet compressive strength appears a large amplitude decline due to the increase of the proportion of hematite concentrate B, but the pellet strength prepared by the layered preparation method appears different degrees of rise, mainly due to the gradual approach of the bentonite addition amount to the traditional method. When the inner layer thickness is more than 10 mm, the proportion of hematite concentrate B reaches 51.2%, and the bentonite consumption is the same as that of the traditional method, and the advantage is not in place. Therefore, the radius of the inner layer should not be more than 10 mm, and the bentonite consumption can be reduced to 1.36% to 8.65% by using the method.

[0042] The examples described in the application only describe the preferred embodiments of the application, and do not limit the concept and scope of the application. Without departing from the design idea of the application, various deformations and improvements of the technical solutions of the application made by the engineering and technical personnel in the field shall fall within the protection scope of the application.

Claims

1. A high proportion haematite concentrate pellet characterised in that: The inner layer is composed of hematite and a binder, the mass percentage of the binder in the inner layer is 1.5%-2.0%, the outer layer is composed of magnetite and a binder, the mass percentage of the binder in the outer layer is 1.2%-1.7%, wherein the binder is bentonite, the radius of the pellet is R, 10 B ≤R≤16 mm, the radius of the inner layer is r B , 0 B ≤r≤10 mm, and r / R<80%.

2. A high proportion hematite concentrate pellet according to claim 1, characterized by: The content of montmorillonite in the bentonite is greater than or equal to 55%.

3. A high proportion hematite concentrate pellet according to any one of claims 1-2, characterized in that: The compressive strength of the pellet is greater than or equal to 2300 N / pellet.

4. A process for the preparation of high proportioned hematite concentrate pellets as claimed in claim 3, wherein the said process comprises the steps of: The steps are: the inner layer material including hematite powder is sequentially prepared into green pellets through water dripping and water mist growing by a disc pelletizer or a drum pelletizer; the green pellets and the outer layer material including magnetite powder are prepared into composite green pellets through water mist growing by a disc pelletizer or a drum pelletizer; and the composite green pellets are sequentially prepared into finished pellets through drying, preheating and roasting.

5. A process for the preparation of high proportioned hematite concentrate pellets as claimed in claim 4, wherein: The hematite powder has a particle size less than 74 μm accounting for ≥90%, and a specific surface area ≥1400 cm 2 ∙g -1 The magnetite powder has a particle size less than 74 μm accounting for ≥85%, and a specific surface area ≥1200 cm 2 ∙g -1 .

6. A process for the preparation of high proportion of hematite concentrate pellets as claimed in claim 4 wherein: The water content of the composite green pellets is 8% to 10%.

7. A process for the preparation of high proportion of hematite concentrate pellets as claimed in claim 4 wherein the said process is characterized by: In the drying, preheating and roasting steps: the drying temperature is 300 to 450 DEG C, the preheating temperature is 900 to 1000 DEG C, and the roasting temperature is 1230 DEG C to 1260 DEG C.

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