Process for the preparation of a low smectite content bentonite for use as a binder for metallurgical pellets

Abstract

The application discloses a process for preparing a metallurgical pellet binder from bentonite with low montmorillonite content. The process adopts a twice wet modification process. After the first modification, the basis is converted. In the second modification, calcium oxide and hydrolyzed polyacrylonitrile sodium salt are innovatively introduced. The calcium ion bridging effect is used to enhance the interaction force between the organic and inorganic, fill the interlayer defects of the montmorillonite, and enhance the binding network. The low-grade bentonite montmorillonite can be converted into a high-performance metallurgical pellet binder, and the performance requirements of the metallurgical pellet binder can be met, so that the efficient utilization of low-value mineral resources is realized.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical pellet binder preparation technology, specifically relating to a process method for preparing metallurgical pellet binders using bentonite with low montmorillonite content through a two-step wet modification. Background Technology

[0002] Sodium-based bentonite has become the industry's preferred choice due to its superior swelling and water absorption properties compared to calcium-based bentonite. A typical process involves modifying calcium-based bentonite by adding sodium carbonate to improve its colloidal properties. This significantly reduces the amount of binder required and increases the iron content in the pellets. Mainstream technologies require bentonite with a montmorillonite content ≥65% to ensure that the swelling capacity and colloidal value meet national standards after conversion. This results in low-grade ore (montmorillonite <50%) being discarded or downgraded due to substandard performance.

[0003] The core reason is that bentonite with low montmorillonite content (such as the 47% montmorillonite ore from Linli County, Hunan Province) has low interlayer charge density and weak cation exchange capacity. During conventional sodium alteration, sodium carbonate is insufficient to fully replace interlayer calcium ions, resulting in low modification efficiency. To improve performance, the industry has attempted to add organic polymers (such as CMC and sodium polyacrylate), but low-grade bentonite has many impurities and a small specific surface area, making it difficult for organic matter to be effectively grafted. For example, a modification scheme that directly blends 2% CMC results in uneven dispersion in bentonite with less than 47% montmorillonite, leading to a decrease in the strength of the binder pellets.

[0004] Furthermore, existing traditional wet processes only involve one sodium conversion, with an aging period of 4-10 days. Low-grade bentonite, due to impurities (quartz, feldspar) hindering ion diffusion, still retains a large amount of unconverted calcium-based montmorillonite after sodium conversion, resulting in poor performance. Although attempts have been made to add sodium fluoride or lightly calcined magnesia (such as adding 0.5% lightly calcined magnesia to increase the cracking temperature), the core problem of low conversion rate of low-grade ore has not been solved.

[0005] Therefore, there is an urgent need in the field for a process to prepare a qualified binder using low-grade bentonite (montmorillonite <50%). Summary of the Invention

[0006] To address the shortcomings of existing technologies, the technical solution provided by this invention is as follows:

[0007] S1: Crush the wet calcium-based bentonite ore into blocks, and then dry the crushed block calcium-based bentonite ore to a moisture content of ≤10%;

[0008] S2: After thoroughly mixing the dried blocky calcium-based bentonite wet ore with 2%-3% soda ash, it is put into an automatic spraying system and sprayed at 25-35℃ with a water-to-soil ratio of 1:4, and then fully compressed.

[0009] S3: Aged at 20-30℃ for 7 days, then sun-dried or oven-dried until the moisture content is ≤10% to obtain primary modified mineral powder;

[0010] S4: After thoroughly mixing the modified mineral powder with 0.4%-0.7% calcium oxide and 0.1%-0.3% hydrolyzed sodium polyacrylonitrile, the mixture is put into an automatic spraying system and sprayed at 25-35℃ with a water-to-soil ratio of 1:4, and then fully compressed.

[0011] S5: After aging again at 20-30℃ for 7 days, dry until the moisture content is ≤13% to obtain the finished adhesive;

[0012] S6: Crush the finished adhesive and package and seal it.

[0013] Preferably, in steps S1 and S5 of the above preparation process, the drying method is natural sun drying or drying in a dryer, and the drying temperature of the dryer is 100-105℃.

[0014] Preferably, in steps S2 and S4 of the above preparation process, the extrusion method is wet extrusion, and the extrusion time is 40 min.

[0015] Preferably, in step S1 of the above preparation process, a rotary tiller is used to crush the wet raw calcium-based bentonite ore into 15cm blocks.

[0016] Preferably, in step S6 of the above preparation process, the finished adhesive is pulverized to 200 mesh.

[0017] Under the above-mentioned secondary modification preparation process, this invention uses a specific combination of additives and process timing design to achieve calcium-based to sodium-based conversion with soda ash, and introduces CaO and polymers in a secondary process to synergistically enhance the effect. CaO improves structural stability, and hydrolyzed sodium polyacrylonitrile fills the interlayer defects of montmorillonite and strengthens the bonding network.

[0018] The carboxyl groups (—COO⁻) and nitrile groups (—CN) on the molecular chain of hydrolyzed sodium polyacrylonitrile (Na-HPAN) have strong polarity and can be inserted into the interlayer domain of bentonite. They can form hydrogen bonds or electrostatic adsorption with the hydroxyl groups on the surface of montmorillonite sheets, thereby strengthening the interlayer bonding force. At high temperatures, its molecular chain can form a cross-linked network, which together with the bentonite sheets constructs a "skeleton-filler" structure and inhibits cracking during the pellet roasting process.

[0019] Based on the above-mentioned secondary modification process and the addition of hydrolyzed sodium polyacrylonitrile (Na-HPAN), low-grade bentonite (47% montmorillonite) is transformed into a high-performance metallurgical pellet binder.

[0020] The present invention has the following beneficial effects:

[0021] 1. The present invention, through the above technical solution, firstly modifies the material by wet extrusion sodium salt with soda ash for a basic transformation, and then innovatively introduces calcium oxide and hydrolyzed polyacrylonitrile sodium salt to enhance the organic-inorganic phase interaction through the calcium ion bridging effect for a second modification. This transforms low-grade bentonite (47% montmorillonite) into a high-performance metallurgical pellet binder, making it meet the performance requirements of metallurgical pellet binders and achieving efficient utilization of low-value minerals.

[0022] 2. In this invention, the introduction of hydrolyzed sodium polyacrylonitrile in the secondary modification allows CaO and the polymer to work synergistically. The hydrolyzed sodium polyacrylonitrile fills the interlayer defects of montmorillonite and strengthens the bonding network, thereby enhancing the interlayer bonding force, inhibiting cracking during pellet calcination, and significantly improving compressive strength. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the manufacturing process of the present invention. Detailed Implementation

[0024] To better understand the present invention, the following embodiments further illustrate the content of the invention, but the scope of protection of the present invention is not limited to the following embodiments. Numerous specific details are set forth in the following description to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the present invention can be practiced without one or more of these details.

[0025] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0026] The following examples use various raw materials. Unless otherwise stated, the bentonite used in the following examples is Hunan Linli calcium-based bentonite wet ore with a montmorillonite content of 47%, which is less than 50% and is a low-grade ore.

[0027] Example 1

[0028] A process for preparing metallurgical pellet binders from bentonite with low montmorillonite content includes the following steps:

[0029] S1: Use a rotary tiller to crush 1 ton of wet calcium-based bentonite ore into blocks, and then let the crushed blocks of wet calcium-based bentonite ore dry naturally until the moisture content is ≤10%;

[0030] S2: After thoroughly mixing the dried blocky calcium-based bentonite wet ore with 25 kg of soda ash, put it into an automatic spraying system and spray it at 25°C with a water-to-soil ratio of 1:4, and then wet extrusion for 40 minutes.

[0031] S3: Aged at 25℃ for 7 days, then naturally dried until the moisture content is ≤10% to obtain primary modified mineral powder;

[0032] S4: After thoroughly mixing the modified mineral powder with 5kg of calcium oxide and 2kg of hydrolyzed sodium polyacrylonitrile, the hydrolyzed sodium polyacrylonitrile has a molecular weight of 10 million. The mixture is then put into an automatic spraying system and sprayed at 25°C with a water-to-soil ratio of 1:4. The mixture is then wet-extruded for 40 minutes.

[0033] S5: After aging again at 25℃ for 7 days, naturally dry until the moisture content is ≤13% to obtain the finished adhesive;

[0034] S6: Crush the finished adhesive to 200 mesh, then package and seal it.

[0035] Example 2

[0036] A process for preparing metallurgical pellet binders from bentonite with low montmorillonite content includes the following steps:

[0037] S1: Use a rotary tiller to crush 1 ton of wet calcium-based bentonite ore into blocks, and then let the crushed blocks of wet calcium-based bentonite ore dry naturally until the moisture content is ≤10%;

[0038] S2: After thoroughly mixing the dried blocky calcium-based bentonite wet ore with 20 kg of soda ash, it is put into an automatic spraying system and sprayed at 20°C with a water-to-soil ratio of 1:4. Then, it is wet-pressed for 40 minutes.

[0039] S3: Aged at 25℃ for 7 days, then naturally dried until the moisture content is ≤10% to obtain primary modified mineral powder;

[0040] S4: After thoroughly mixing the modified mineral powder with 4kg of calcium oxide and 1kg of hydrolyzed sodium polyacrylonitrile, the molecular weight of the hydrolyzed sodium polyacrylonitrile is 8 million. The mixture is then put into an automatic spraying system and sprayed at 20℃ with a water-to-soil ratio of 1:4. The mixture is then wet-extruded for 40 minutes.

[0041] S5: After aging again at 25℃ for 7 days, naturally dry until the moisture content is ≤13% to obtain the finished adhesive;

[0042] S6: Crush the finished adhesive to 200 mesh, then package and seal it.

[0043] Example 3

[0044] A process for preparing metallurgical pellet binders from bentonite with low montmorillonite content includes the following steps:

[0045] S1: Use a rotary tiller to crush 1 ton of wet calcium-based bentonite ore into blocks, and then dry the crushed blocks of wet calcium-based bentonite ore until the moisture content is ≤10%;

[0046] S2: After thoroughly mixing the dried blocky calcium-based bentonite wet ore with 30 kg of soda ash, put it into an automatic spraying system and spray it at 30°C with a water-to-soil ratio of 1:4, and then wet extrusion for 40 minutes.

[0047] S3: Aged at 25℃ for 7 days, then dried in a dryer until the moisture content is ≤10% at a drying temperature of 105℃ to obtain primary modified mineral powder;

[0048] S4: After thoroughly mixing the modified mineral powder with 7kg of calcium oxide and 3kg of hydrolyzed sodium polyacrylonitrile, the molecular weight of the hydrolyzed sodium polyacrylonitrile is 12 million. The mixture is then put into an automatic spraying system and sprayed at 25℃ with a water-to-soil ratio of 1:4. The mixture is then wet-extruded for 40 minutes.

[0049] S5: After aging again at 25℃ for 7 days, naturally dry until the moisture content is ≤13% to obtain the finished adhesive;

[0050] S6: Crush the finished adhesive to 200 mesh, then package and seal it.

[0051] Comparative Example 1

[0052] S1: Use a rotary tiller to crush 1 ton of wet calcium-based bentonite ore into blocks, and then let the crushed blocks of wet calcium-based bentonite ore dry naturally until the moisture content is ≤10%;

[0053] S2: After thoroughly mixing the dried blocky calcium-based bentonite wet ore with 30 kg of soda ash, it is put into an automatic spraying system and sprayed at 20°C with a water-to-soil ratio of 1:4. Then, it is wet-pressed for 40 minutes.

[0054] S3: Aged at 25℃ for 7 days, then dried in a dryer to a moisture content of ≤13% at a drying temperature of 105℃ to obtain primary modified mineral powder;

[0055] S4: After thoroughly mixing the modified mineral powder with 5kg of lightly calcined magnesia and 2kg of CMC, directly pulverize it to 200 mesh, and then package and seal it.

[0056] Compared with Comparative Example 1, Example 1 significantly improved the water absorption rate, swelling capacity, and colloidal value of low-grade bentonite when using low-grade ore for preparation without significantly increasing the bluing capacity, so as to meet the performance requirements of metallurgical pellet binder. The water absorption rate was increased to 450%, the colloidal value was increased to 500 ml / 15g, and the swelling capacity was increased by 50 ml / g.

[0057] Among them, the water absorption rate is ≥400%, the expansion volume is ≥45ml / g, and the gel value is ≥480ml / 15g, which far exceeds the national standard (GB / T20973-2020).

[0058] Finally, it should be noted that the above embodiments do not limit the present invention in any way. Those skilled in the art can make modifications and improvements based on the present invention. Therefore, any modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A process for preparing metallurgical pellet binders from bentonite with low montmorillonite content, characterized in that, The preparation process includes the following steps: S1: Crush the wet calcium-based bentonite ore into blocks, and then dry the crushed block calcium-based bentonite ore to a moisture content of ≤10%; S2: After thoroughly mixing the dried blocky calcium-based bentonite wet ore with 2%-3% soda ash, it is put into an automatic spraying system and sprayed at 25-35℃ with a water-to-soil ratio of 1:4, and then fully compressed. S3: Aged at 20-30℃ for 7 days, then sun-dried or oven-dried until the moisture content is ≤10% to obtain primary modified mineral powder; S4: After thoroughly mixing the modified mineral powder with 0.4%-0.7% calcium oxide and 0.1%-0.3% hydrolyzed sodium polyacrylonitrile, the mixture is put into an automatic spraying system and sprayed at 25-35℃ with a water-to-soil ratio of 1:4, and then fully compressed. S5: After aging again at 20-30℃ for 7 days, dry until the moisture content is ≤13% to obtain the finished adhesive; S6: Crush the finished adhesive and package and seal it.

2. The process for preparing metallurgical pellet binder from low-montmorillonite bentonite according to claim 1, characterized in that: In steps S1 and S5, the drying method is natural sun drying or drying in a dryer, wherein the drying temperature is 100-105℃.

3. The process for preparing metallurgical pellet binder from low-montmorillonite bentonite according to claim 1, characterized in that: In steps S2 and S4, the extrusion method is wet extrusion, and the extrusion time is 40 minutes.

4. The process for preparing metallurgical pellet binder from low-montmorillonite bentonite according to claim 1, characterized in that: In step S1, a rotary tiller is used to crush the wet raw calcium-based bentonite ore into 15cm blocks.

5. The process for preparing metallurgical pellet binder from low-montmorillonite bentonite according to claim 1, characterized in that: In step S6, the finished adhesive is pulverized to 200 mesh.

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