Method for improving strength of iron ore pellets by adding ferric chloride

Abstract

The invention belongs to the technical field of iron ore agglomeration, and relates to a method for improving the strength of iron ore pellets by adding ferric chloride. Ferric chloride is added into a pelletizing mixture according to a certain proportion, the iron ore pellets are prepared through the conventional technological processes of pelletizing, drying, preheating, roasting, cooling and the like, and under the condition of the same roasting temperature, the strength of the iron ore pellets prepared from the ferric chloride is obviously improved; under the condition that the requirement of a blast furnace for the pellet strength (not lower than 2000-2500N / piece) is met, the minimum roasting temperature required for preparing the pellets by using ferric chloride is obviously reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of iron ore agglomeration and relates to a method for increasing the strength of iron ore pellets by adding ferric chloride. Background Art

[0002] The steel industry, a fundamental materials industry supporting the development of the national economy, is also a typical high-carbon emission industry. Currently, the steel industry urgently needs to transition to green and low-carbon development. In the entire steel production process, the pre-ironization system is a key link in energy conservation and carbon reduction, and pelletizing is one of the mainstream processes for preparing pre-ironization charge. However, producing pellets of acceptable strength generally suffers from excessive energy consumption and emissions. Therefore, it is necessary to further strengthen the consolidation of iron ore pellets and increase their strength, thereby lowering the minimum roasting temperature for pellet production while still meeting the required pellet strength.

[0003] Literature Ren Jie; Luo Guoping; Zhu Jianguo; Song Wei; Chai Yifan; Effect of iron-containing additives instead of bentonite on the performance of pellets [J]; Mining and Metallurgical Engineering; Issue 04, 2022. Through experimental research, the addition of iron-containing additives with excellent ball-forming properties to magnetite powder can significantly improve the ball-forming property and green ball strength of the ore powder. The appropriate ratio of this additive is 6% to 8%. Within this range, the drop strength of the green ball is greater than 4 times / (0.5m), the compressive strength is greater than 10N / piece, the green ball burst temperature is greater than 600℃, and the roasted ball strength can be greater than 2000N / piece. When the additive ratio increases from 4% to 10%, the reduction degree of the roasted balls increases from 71.46% to 76.04%, and the reduction expansion rate of the pellets decreases from 11.3% to 8.1%, which fully meets the production requirements. Therefore, adding an appropriate amount of iron-containing additive to the pellets instead of bentonite can improve the ball forming property, green ball strength and reduction performance of the pellets, while increasing the grade of the pellets and reducing the production cost of the pellets. The microstructure of the roasted balls shows that when the additive ratio increases from 4% to 10%, the large Fe2O3 crystal areas in the pellets gradually become smaller, and the Fe2O3 obviously changes from large connected crystals to interconnected small crystals. The uniform and fine pores between the crystals gradually aggregate and become larger, resulting in the strength of the roasted balls decreasing from 2425.5N / piece to 1890.6N / piece. If the additive ratio is controlled below 8%, the strength of the roasted balls can be greater than 2000N / piece.

[0004] However, when the thermal system's roasting temperature is too low, the driving force behind the various physical and chemical reactions within the pellets is weak, the reaction rates are slow, and roasting and consolidation are difficult to achieve, resulting in low mechanical strength of the produced pellets. Within a certain range, roasting temperature is the primary factor affecting pellet oxidation and consolidation. To lower the roasting temperature, other factors must be optimized to ensure pellet quality. While extending the roasting time can improve pellet strength, this can affect yield, potentially outweighing the benefits. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a method for increasing the strength of iron ore pellets by adding ferric chloride, which solves the problems existing in the prior art.

[0006] The technical solution adopted by the present invention is a method for improving the strength of iron ore pellets by adding ferric chloride, wherein ferric chloride is added to a pelletizing mixture in a certain proportion, and conventional pelletizing, drying, preheating, roasting and cooling are performed.

[0007] Furthermore, the pelletizing mixture is iron ore concentrate.

[0008] Furthermore, the certain ratio is a mass ratio of iron ore concentrate to ferric chloride of 1:0.01 to 0.12.

[0009] Preferably, the certain ratio is a mass ratio of iron ore concentrate to ferric chloride of 1:0.04 to 0.12.

[0010] Furthermore, the calcination temperature is not less than 1170°C.

[0011] Furthermore, the ball making time is 9-15 minutes, the rotation speed of the disc ball making machine is 15-25r / min, the ball making moisture is 7.5-8.5%, and green balls with a diameter of 12 to 15 mm are prepared. The qualified green balls are dried in an oven at a temperature of 100-140°C, and the dried balls are preheated at a preheating temperature of 720-1120°C for 5-15 minutes and roasted for 15-25 minutes.

[0012] The beneficial effects of the present invention are:

[0013] (1) The ferric chloride additive used in the present invention can effectively strengthen the oxidative consolidation of pellets. Under the condition of meeting the blast furnace's requirements for pellet consolidation strength, the minimum roasting temperature of pellet production can be reduced or the roasting time of pellet production can be shortened.

[0014] (2) The ferric chloride used in the present invention has a certain adhesiveness, which can effectively strengthen the adhesion between the iron ore particles inside the pellets, improve the green ball strength, and strengthen the crystallization of the internal hematite during the preheating and roasting process of the pellets, thereby improving the compressive strength of the pellets. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 This is a micrograph of the mineral phase inside the oxidized pellets prepared in Example 1;

[0017] Figure 2 This is a micrograph of the internal mineral phase of the oxidized pellets prepared in Comparative Example 1. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] The pellets of the embodiment and comparative example were tested and analyzed according to the national standard GB / T14201-1993 "Determination of compressive strength of iron ore pellets". The finished pellets were placed on a compressive strength testing instrument, and a vertical downward pressure was slowly applied to the upper part until the finished pellets broke. The pressure value displayed by the equipment at this time was the compressive strength of the finished pellets. 10 finished balls were measured each time, and the average value was taken as the compressive strength of the pellet sample batch (unit: N / piece).

[0020] Example 1:

[0021] 60g of bentonite and 200g of ferric chloride were added to 5kg of mixed iron concentrate and mixed evenly. The ball making time was controlled to be 12min, the rotation speed of the disc ball making machine was 20r / min, the ball making moisture was 8%, and green balls with a diameter of 12-15mm were prepared. The qualified green balls were first dried in an oven at a temperature of 120°C, and the dried balls were preheated at a preheating temperature of 920°C for 10min, and then roasted at a roasting temperature of 1200°C for 20min, and finally cooled to room temperature to obtain pellets.

[0022] The compressive strength of the pellets obtained according to the above method is 2812N / piece, and the micrograph of the mineral phase inside the oxidized pellets is as follows: Figure 1 As shown in Figure 2, pellets prepared with ferric chloride exhibit a higher degree of iron oxide inter-crystallization and a denser internal structure, indicating a higher degree of oxidation. This is because ferric chloride has a certain degree of adhesion, which can strengthen the bonding of iron ore particles within the pellets, thereby strengthening the degree of hematite inter-crystallization within the pellets and improving the pellet strength.

[0023] Example 2: The roasting temperature in Example 1 was changed to 1230°C, while other conditions remained unchanged. The compressive strength of the pellets was 3225N / piece.

[0024] Example 3: The roasting temperature in Example 1 was changed to 1170°C, while other conditions remained unchanged. The compressive strength of the pellets was 2619N / piece.

[0025] Example 4: The amount of ferric chloride added in Example 1 was changed to 50 g, while other conditions remained unchanged. The compressive strength of the pellets was 2509 N / piece.

[0026] Example 5: The amount of ferric chloride added in Example 1 was changed to 400 g, while other conditions remained unchanged. The compressive strength of the pellets was 3189 N / piece.

[0027] Example 6: The amount of ferric chloride added in Example 1 was changed to 600 g, while other conditions remained unchanged. The compressive strength of the pellets was 3381 N / piece.

[0028] Comparative Example 1:

[0029] 60 g of bentonite was added to 5 kg of mixed iron concentrate and mixed evenly. The ball making time was controlled to be 12 min, the rotation speed of the disc ball making machine was 20 r / min, the ball making moisture was 8%, and green balls with a diameter of 12 to 15 mm were prepared. The qualified green balls were first dried in an oven at a temperature of 120°C, and the dried balls were preheated at a preheating temperature of 920°C for 10 min, and then roasted at a roasting temperature of 1200°C for 20 min, and finally cooled to room temperature to obtain pellets.

[0030] The compressive strength of the pellets obtained by the above method is 2356N / piece, which does not meet the blast furnace requirement of pellet compressive strength of not less than 2500N / piece. Figure 2 shown.

[0031] Comparative Example 2:

[0032] When the roasting temperature in Comparative Example 1 was increased to 1230°C and other conditions remained unchanged, the pellet strength was 2579N / piece.

[0033] Comparative Example 3:

[0034] The ferric chloride in Example 1 was changed to ferrous chloride, while other conditions remained unchanged.

[0035] The compressive strength of the pellets is 2293 N / piece, which does not meet the blast furnace requirement of a compressive strength of at least 2500 N / piece. This shows that adding ferrous chloride does not improve the strength of the roasted pellets under the same conditions.

[0036] Comparative Example 4: The ferric chloride in Example 1 was changed to ferric nitrate, while other conditions remained unchanged.

[0037] The compressive strength of the pellets is 2329 N / piece, which does not meet the blast furnace requirement of a compressive strength of at least 2500 N / piece. This shows that adding ferric nitrate does not improve the strength of the roasted pellets under the same conditions.

[0038] Comparative Example 5: The ferric chloride in Example 1 was changed to iron-containing red mud, while other conditions remained unchanged.

[0039] The compressive strength of the pellets is 1951 N / piece, which does not meet the blast furnace requirement of a compressive strength of at least 2500 N / piece. This shows that adding iron-containing red mud does not improve the strength of the roasted pellets under the same conditions.

[0040] In summary, compared with not adding ferric chloride, under the same preparation conditions, the pellets prepared with ferric chloride have higher strength; under the condition of meeting the blast furnace's requirements for pellet strength, the minimum roasting temperature of pellets prepared with ferric chloride is lower.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A method for increasing the strength of iron ore pellets by adding ferric chloride, characterized in that: Ferric chloride is added to the pelletizing mixture in a certain proportion, and then the mixture is pelletized, dried, preheated, calcined and cooled in a conventional manner.

2. The method for increasing the strength of iron ore pellets by adding ferric chloride as claimed in claim 1, wherein: The pelletizing mixture is iron ore concentrate.

3. A method for increasing the strength of iron ore pellets by adding ferric chloride as claimed in claim 2, characterized in that: The certain ratio is a mass ratio of iron ore concentrate to ferric chloride of 1:0.01 to 0.

12.

4. A method for increasing the strength of iron ore pellets by adding ferric chloride as claimed in claim 3, characterized in that: The certain ratio is a mass ratio of iron ore concentrate to ferric chloride of 1:0.04 to 0.

12.

5. A method for increasing the strength of iron ore pellets by adding ferric chloride as claimed in claim 4, characterized in that: The calcination temperature is not less than 1170°C.

6. A method for increasing the strength of iron ore pellets by adding ferric chloride as claimed in claim 5, characterized in that: The ball making time is 9-15 minutes, the rotation speed of the disc ball making machine is 15-25r / min, the ball making moisture content is 7.5-8.5%, and green balls with a diameter of 12-15 mm are prepared. The qualified green balls are dried in an oven at a temperature of 100-140°C, and the dried balls are preheated at a preheating temperature of 720-1120°C for 5-15 minutes and roasted for 15-25 minutes.

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