Preparation method of high-silicon high-hematite limonite pellets

Abstract

The invention discloses a preparation method of high-silicon high-hematite limonite pellets, and belongs to the field of blast furnace burden, and the preparation method specifically comprises the following steps: step A, carrying out primary batching, drying and wet grinding on concentrate powder, Kara concentrate powder, Brazil concentrate powder, laterite-nickel ore, red mud iron powder and boron-magnesium concentrate powder in proportion; step B, proportionally adding bentonite into the wet-ground material in the step A, and carrying out secondary batching; step C, conveying the materials in the step B into a vertical mixer for strong mixing; step D, conveying the mixed material to a pelletizing chamber for pelletizing; and E, the green pellets are conveyed to a roasting cooling system to be prepared into finished pellets. According to the pellet prepared through the method, the adding amount of bentonite is reduced, the cost is reduced, the compressive strength of the finished pellet can reach 2500N / P or above, the green pellet drop strength, the compressive strength and the dry pellet compressive strength are far higher than those of on-site pellets, and the production requirement can be met.

Description

Technical Field

[0001] The invention belongs to the technical field of blast furnace charges, and in particular relates to a method for preparing high-silicon and high-hematite pellets. Background Art

[0002] Pellets are made by pelletizing fine-grained ore powder or other raw materials into balls of a certain strength and size. They are primarily used in blast furnaces or direct reduced iron (DRI) in steelmaking. They are used to improve the smelting properties (such as permeability and reducibility) of fine-grained ore, increase iron grade, and reduce impurity content.

[0003] The main raw materials include finely ground iron ore concentrates (typically <0.074mm) such as magnetite (Fe3O4) and hematite (Fe2O3). Binders and additives are also included. Binders primarily include bentonite (most commonly added at approximately 0.5% to 2%), limestone, and slaked lime, which are used to increase green ball strength. Additives such as coke powder and olivine may be added to adjust chemical composition or metallurgical properties, depending on process requirements.

[0004] However, traditional pellets have the following defects:

[0005] 1. Domestic high-quality iron ore concentrate resources are in short supply. Limited by the resource and price issues of magnetic concentrate, over-reliance on it leads to large cost fluctuations;

[0006] 2. The amount of bentonite added is generally more than 2%, resulting in a loss of pellet iron grade and an increase in binder costs;

[0007] 3. Low utilization rate of low-grade iron ore restricts production cost optimization;

[0008] 4. The domestic production of high-proportion hematite pellets is relatively rare. The roasting performance, energy consumption and process control of hematite pellets are more difficult than those of magnetite, and the compressive strength and metallurgical properties of the finished balls are also difficult to guarantee.

[0009] Due to the above-mentioned defects, how to achieve the stable application of high-proportion hematite raw materials in the pellet production process and ensure the quality of the finished balls is an important research topic. Summary of the Invention

[0010] The purpose of the present invention is to provide a method for preparing high-silicon and high-hematite pellets, which can reduce the amount of bentonite added without affecting the quality of the finished pellets, fully utilize the hematite pellets, and reduce costs and increase efficiency.

[0011] To achieve the above object, the technical solution adopted by the present invention is:

[0012] A method for preparing high-silicon high-hematite pellets comprises the following steps:

[0013] Step A, mixing, drying and grinding the concentrate powder, Carrara concentrate powder, Brazilian concentrate powder, laterite nickel ore, red mud iron powder and boron magnesium concentrate powder according to a certain proportion;

[0014] Step B, adding bentonite in proportion to the material ground in step A to form a secondary batch;

[0015] Step C, conveying the material in step B to a vertical mixer for strong mixing;

[0016] Step D, transporting the mixed material to a pelletizing chamber for pelletizing;

[0017] Step E: transporting the green balls to a roasting and cooling system to produce finished pellets.

[0018] A further improvement of the technical solution of the present invention is that in step A, the concentrate powder accounts for 50-65%, the Carrara concentrate accounts for 15-25%, the Brazilian concentrate accounts for 8-15%, the laterite nickel ore accounts for 5-10%, the boron magnesium concentrate accounts for 2-5%, the red mud iron powder accounts for 3%, and the amount of bentonite in step B is ≤1%.

[0019] A further improvement of the technical solution of the present invention is that the moisture content of the raw materials in the drying step in step A is controlled at 7±0.5%.

[0020] A further improvement of the technical solution of the present invention is that the roasting and cooling system in step E includes a green ball distribution screening area, a chain grate area, a rotary kiln area, and a ring cooler area. The temperature in the rotary kiln oxidation roasting process is controlled at 1250-1280°C, and the oxidation roasting time is 25-30 minutes.

[0021] Due to the adoption of the above technical solution, the technical advancements achieved by the present invention are:

[0022] The components of the preparation method of high-silicon and high-hematite pellets in the present application have been updated to construct a ternary main material system of "domestic concentrate powder (50-65%) + Carrara concentrate powder (15-25%) + Brazilian concentrate powder (8-15%)", breaking through the limitation of a single mineral species, and introducing 5-10% dried laterite nickel ore to play a dual role. The laterite nickel ore sticky material containing limonite replaces 30-50% of bentonite (the amount of bentonite in the measured components is ≤1%), reducing the bentonite content in the system, and the magnesium and aluminum oxides therein synergistically regulate the melting characteristics.

[0023] Red mud is a waste product produced during alumina production. It is red in color due to its high content of iron oxide. The iron powder obtained after dealkalization and gravity separation has a Tfe content of approximately 50%. It has a strong water absorption capacity, approximately 1 / 5-1 / 3 that of bentonite, and contains a certain amount of cementing minerals such as goethite, gibbsite, and water glass.

[0024] The addition of high-iron red mud to the components of this application can effectively reduce the amount of bentonite used. When the measured bentonite ratio is ≤1%, the falling strength, compressive strength and dry ball compressive strength of the green ball are much higher than those of the on-site pellets, which can meet production needs.

[0025] When the bentonite content is 0.8%, the compressive strength of the red mud pellets reaches 2600N / piece, which is sufficient for blast furnace use (2500N / piece). In terms of various metallurgical properties, the low-temperature pulverization index of the red mud pellets is better than that of ordinary pellets, while the reducibility, reduction expansion, and remelting performance are all lower than those of ordinary pellets.

[0026] The results of industrial tests show that it is feasible to add 3% high iron red mud to pellets to reduce the amount of bentonite, which can meet the requirements of pellet production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of a method for preparing high-silicon and high-hematite pellets according to the present application. DETAILED DESCRIPTION

[0028] The present invention is described in further detail below in conjunction with the embodiments:

[0029] Example 1

[0030] A method for preparing high-silicon high-hematite pellets comprises the following steps:

[0031] In step A, concentrate powder, Carrara concentrate powder, Brazilian concentrate powder, laterite nickel ore, red mud iron powder, and boron magnesium concentrate powder are mixed, dried, and moist-grinded according to a certain proportion; wherein the concentrate powder accounts for 50-65%, the Carrara concentrate powder accounts for 15-25%, the Brazilian concentrate powder accounts for 8-15%, the laterite nickel ore accounts for 5-10%, the boron magnesium concentrate powder accounts for 2-5%, and the red mud iron powder accounts for 3%. The amount of bentonite in step B is ≤1%.

[0032] The concentrate powder is domestic concentrate powder, and the Carrara concentrate powder is high-silicon Carrara concentrate powder (SiO2 ≥ 11%). Since the particle size of laterite nickel ore is relatively coarse, generally 0-20mm, it is traditionally considered unsuitable for pellet production. Laterite nickel ore and red mud iron powder contain muddy substances with high viscosity, and the characteristics of burn-out and high moisture content make the green ball drying process extremely difficult to control, and the green ball bursting temperature is low. During the roasting and drying process, green balls are prone to cracking or bursting and pulverization. The Brazilian hematite concentrate has a smooth surface, a compact structure and a coarse particle size. It has extremely poor hydrophilicity and pelletizing properties, which is not conducive to pelletizing. Considering the characteristics of limonite, such as high viscosity, high moisture content, and low green ball bursting temperature, and the good hydrophobicity and coarse particle size of the concentrate iron ore, the two are combined to improve the particle size composition of the mixture, which can effectively solve the problems of filtration and bursting.

[0033] Adding a small amount of boron-magnesium concentrate can improve pellet roasting performance, reduce gas and energy consumption, and promote consolidation reactions, improving the quality of the finished pellets. While hematite generally consolidates at a high temperature, the B₂O₃ in boron-magnesium concentrate and the CaO in the components form low-melting-point compounds during pellet roasting. These low-melting-point compounds begin to form an initial liquid phase at relatively low roasting temperatures. Although the liquid phase is small, it plays a significant role in the consolidation reaction. On the one hand, this small amount of liquid phase can cause pellet shrinkage during roasting, densifying the structure and improving the strength of the finished pellets. On the other hand, the presence of a small amount of liquid phase at low temperatures can promote the diffusion of solid particles and accelerate crystallization, thereby reducing heat consumption during the roasting process. During the experiment, the roasting temperature was reduced from 1290°C to 1230°C before and after the addition of boron-magnesium concentrate, and the compressive strength of the finished pellets still exceeded 2500 N / P. Furthermore, since boron-magnesium concentrate, fine ore concentrate, or blast furnace return ore all contain a certain amount of MgO, it can effectively reduce reduction expansion of the finished pellets. However, the ratio of boron magnesium concentrate should not be too high, otherwise a large amount of liquid phase will be produced, which will not only fail to improve the quality of the finished pellets, but will also make the pellets "brittle" and reduce the compressive strength. Excessive liquid phase will also affect the oxidation process and reduce the reduction degree of the pellets.

[0034] During the drying process in step A, the raw material is transported to the drying chamber via a belt conveyor and fed through a sealed chute into the rear end of the drying drum. The drying system utilizes a countercurrent drying process, whereby the drying heat medium (high-temperature flue gas) enters the dryer head, the iron ore concentrate enters the dryer tail, and exits the dryer head. A cylindrical dryer is located within the drying chamber to dry the iron ore concentrate.

[0035] Stabilize drying efficiency, maintain stable moisture content of the mixture, and ensure that the moisture content of the raw materials is stably controlled at 7±0.5%;

[0036] During the damp grinding process, adjust the grinding machine's steel ball gradation and loading. Increase the diameter of the steel balls entering the mill from Φ100mm to Φ110mm to enhance the impact and unloading effect of the steel balls, increase the abrasive medium filling rate, and improve the abrasive volume and damp grinding efficiency. Appropriately increase the steel ball loading to increase the grinding surface area.

[0037] Enhance the mill dehumidification effect. A new dehumidification pipe is added next to the original mill steam pipe. The material humidity is reduced, the material flow rate is increased, a large amount of water vapor in the mixture is carried away, the adhesion phenomenon is reduced, the material is eliminated from sticking to the grate plate, and the mill efficiency is improved.

[0038] Step B: Add bentonite in proportion to the material ground in step A to prepare the secondary batching; the secondary batching chamber is equipped with a high-pressure roller mill.

[0039] By combining high-silicon Carrara fines with Brazilian fines (TFe ≥ 63%), the proportion of high-priced ore is reduced while maintaining a TFe ≥ 62%. Dried nickel ore (priced 40-50% lower than iron ore concentrate) accounts for 5-10% of the pellets, reducing the cost per ton of pellets by approximately 25-50 RMB. Red mud iron ore (priced 70-75% lower than iron ore concentrate) accounts for 3%, reducing the cost per ton of pellets by approximately 22.5 RMB. Bentonite consumption is reduced from 1.5% to 1%, reducing consumption by approximately 4kg per ton of pellets and increasing pellet grade by approximately 0.3-0.4%.

[0040] The raw material ratio is shown in the following table.

[0041]

[0042] In step C, the materials in step B are transported to a vertical mixer for strong mixing. After the various materials in step B are mixed according to the set ratio, they are directly transported to the mixing chamber via a belt conveyor. The mixing and screening chamber is equipped with a vertical strong mixer.

[0043] Step D: transport the mixed material to the pelletizing room for pelletizing. Equipment: disc pelletizing machine; the raw balls made by the pelletizing disc are transported to the comprehensive roller screen in the screening room for screening through the L-1 collecting belt conveyor. Unqualified raw balls larger than 16 mm and unqualified raw balls smaller than 8 mm are returned to the Q-1 belt conveyor through the SF-2 belt conveyor. Qualified raw balls are transported to the shuttle distributor through the L-2 belt conveyor and then to the chain grate room for distribution. The L-2 belt conveyor detects the output of raw balls and controls the material thickness of the chain grate.

[0044] Step E: transporting the green balls to a roasting and cooling system to produce finished pellets.

[0045] The roasting system consists of three main machines: a chain grate, a rotary kiln, and a ring cooler. The green pellets are dried and preheated on the chain grate, roasted and consolidated in the rotary kiln, and cooled in the ring cooler.

[0046] Under the high-proportion hematite pellet production model, the key to roasting control is to strengthen the drying process, reasonably control the chain grate speed, and the thickness of the bottom material and the total material layer, to ensure that the green balls have a longer drying time and oxidation roasting time. The exhaust drying section should adopt low air temperature, high negative pressure, and high air volume to ensure that the entire material layer is fully dried, improve permeability, and promote heat conduction, and avoid the occurrence of an over-wet layer that causes green balls to burst, worsen permeability, and cause compaction. The roasting temperature is controlled at 1250-1280℃, and the oxidation roasting time of 25-30 minutes is sufficient to achieve an FeO conversion rate of ≥95%, a densified Fe2O3 microcrystalline structure, and a compressive strength fluctuation rate of ≤5%, thereby improving the quality of the finished balls.

[0047] The final pellets were tested and the results were as follows:

[0048]

[0049] The compressive strength of the finished ball can reach more than 2500N / P, and the green ball can drop 7-8 times. The finished ball is supplied to 1780 blast furnace production with good results.

Claims

1. A method for preparing high-silicon high-hematite pellets, characterized in that The following steps are involved: Step A, mixing, drying and grinding the concentrate powder, Carrara concentrate powder, Brazilian concentrate powder, laterite nickel ore, red mud iron powder and boron magnesium concentrate powder according to a certain proportion; Step B, adding bentonite in proportion to the material ground in step A to form a secondary batch; Step C, conveying the materials in step B to a vertical mixer for strong mixing; Step D, transporting the mixed material to a pelletizing chamber for pelletizing; Step E: transporting the green balls to a roasting and cooling system to produce finished pellets.

2. The method for preparing high-silicon high-hematite pellets according to claim 1, wherein: In step A, the concentrate powder accounts for 50-65%, the Carrara concentrate accounts for 15-25%, the Brazilian concentrate accounts for 8-15%, the laterite nickel ore accounts for 5-10%, the boron magnesium concentrate accounts for 2-5%, the red mud iron powder accounts for 3%, and the bentonite dosage in step B is ≤1%.

3. The method for preparing high-silicon high-hematite pellets according to claim 1, wherein: The drying step in step A controls the moisture content of the raw materials to 7±0.5%.

4. The method for preparing high-silicon high-hematite pellets according to claim 1, wherein: The roasting cooling system in step E includes a chain grate area, a rotary kiln area, and an annular cooler area. The temperature of the rotary kiln oxidation roasting process is controlled at 1250-1280° C., and the oxidation roasting time is 25-30 minutes.

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