Method for preparing pellets using ammonium humate and pellets

Abstract

The present application relates to the technical field of metallurgical engineering materials, and specifically discloses a method for preparing pellets using ammonium humate and the pellets. The method for preparing pellets using ammonium humate provided in the present application comprises the following steps: ammonium humate with a particle size of less than 100 mesh is mixed with iron concentrate in a weight ratio of (0.3-2):100, and water is added, and pelletizing, drying, preheating, and roasting are performed to obtain pellets; further, the weight ratio of the ammonium humate to the iron concentrate is (0.5-1.5):100; the present application also provides pellets prepared using the above preparation method. The method for preparing pellets using ammonium humate provided in the present application does not introduce additional sodium ions, and the obtained pellets have a high TFe grade and excellent compressive strength; the use of the above pellets for subsequent blast furnace smelting will not affect the material column, furnace lining, etc., and can ensure the smooth progress of blast furnace smelting.

Description

Technical Field

[0001] The present application relates to the technical field of metallurgical engineering materials, and in particular to a method for preparing pellets using ammonium humate and the pellets. Background Art

[0002] The steel industry is a key pillar of my country's economic development. In recent years, my country's steel production has ranked first in the world. The main raw materials for steel production include sintered ore, pelletized ore, and lump ore. Currently, with the increasing shortage of iron ore resources, the lump ore resources required to meet ironmaking production requirements are almost depleted. The vast majority of iron ore fines and iron ore concentrates require sintering or pelletizing to meet production requirements. Therefore, the main iron-containing raw materials used in steel production are artificial sintered ore and pelletized ore. Pellets, in particular, account for an increasing proportion of blast furnace charge because they improve the permeability of the blast furnace charge column and the uniformity of airflow distribution.

[0003] Currently, the vast majority of domestic pelletizing plants use inorganic bentonite as a pelletizing binder, with a smaller number using organic binders. However, when inorganic bentonite is used as a binder to produce pellets, approximately 90% of the bentonite remains in the pellets, resulting in a low total iron grade. Conversely, when organic binders are used, the resulting preheated pellets are weak, prone to breakage and pulverization, and generate large amounts of dust in the rotary kiln, posing both operational and environmental hazards. In recent years, researchers have developed an organic / inorganic composite binder, sodium humate. This binder can produce pellets that meet all strength requirements for certain iron ore concentrates, such as vanadium-titanium magnetite. However, the presence of alkali metal sodium ions in the sodium humate binder lowers the softening temperature of the ore, causing the ore to melt and drip before it is fully reduced. In addition, the presence of alkali metal sodium ions worsens the reduction expansion of the pellets, causing the permeability of the material column to deteriorate, affecting the smooth progress of blast furnace smelting. In addition, liquid or solid alkali metal sodium ions will adhere to the furnace lining, which will shorten the service life of the furnace lining in the long run. Moreover, for some multi-metal iron oxide minerals, such as chromite, sodium ions easily form toxic sodium chromate with chromite, which in turn causes harm to humans and the environment. Summary of the Invention

[0004] In order to overcome the shortcomings of the three existing binders and obtain a pellet with high TFe grade and excellent compressive strength, the present application provides a method for preparing pellets using ammonium humate and the pellets.

[0005] In a first aspect, the present application provides a method for preparing pellets, which adopts the following technical solution:

[0006] A method for preparing pellets comprises the following steps: mixing ammonium humate with a particle size of less than 100 mesh and iron concentrate in a weight ratio of (0.3-2):100, adding water, and pelletizing, drying, preheating and roasting to obtain pellets.

[0007] This application uses ammonium humate as a pellet binder. The organic and inorganic substances contained in humic acid can decompose and burn during the preheating and roasting process, so that the TFe grade of the prepared pellets is higher than that of bentonite pellets; and the inorganic substances can react with the oxidized minerals in the pellet raw materials during the preheating and roasting process of the pellets, producing a small amount of liquid phase at a lower temperature. Liquid phase solidification occurs during the cooling process of the pellets, so the compressive strength of the prepared pellets is higher. In this application, the ammonium humate in the green balls can be adsorbed on the surface of the iron concentrate particles. The long chain structure of ammonium humate can form bridges on the surface of the iron concentrate particles, promoting the formation of iron concentrate particles into balls, thereby obtaining excellent green ball drop strength and compressive strength.

[0008] Compared with the pellets prepared by using inorganic bentonite binders in the related art, the present application obtains pellets with lower inorganic residues and higher TFe grade. Compared with the pellets prepared by using organic binders in the related art, the preheated balls will not break or pulverize, and the compressive strength of the obtained pellets is higher. Compared with the pellets prepared by using sodium humate binders in the related art, no additional sodium ions are introduced during the preparation process, so the reduction expansion of the pellets will not be aggravated, and the material column of blast furnace smelting will not be affected, and there will be no risk of toxic product generation. Therefore, the method for preparing pellets using ammonium humate as a binder provided by the present application will not affect the smelting equipment, ensure the smooth progress of blast furnace smelting, and can obtain pellets with high compressive strength and high TFe grade, and has good application prospects.

[0009] In some embodiments, the weight ratio of ammonium humate to iron concentrate may be (0.3-0.5):100, (0.3-1):100, (0.3-1.5):100, (0.5-1):100, (0.5-1.5):100, (0.5-2):100, (1-1.5):100, (1-2):100, or (1.5-2):100.

[0010] In a specific embodiment, the weight ratio of the ammonium humate to the iron concentrate can also be 0.3:100, 0.5:100, 1:100, 1.5:100 or 2:100.

[0011] In the present application, iron concentrate includes but is not limited to magnetite concentrate, hematite concentrate, specularite and chromite concentrate.

[0012] Preferably, the weight ratio of the ammonium humate to the iron concentrate is (0.5-1.5):100.

[0013] Through research, the present applicants have discovered that the content of ammonium humate has a certain impact on the compressive strength and TFe grade of green balls, preheated balls, and pellets. Therefore, through experimental research, the present applicants have found that further controlling the weight ratio of ammonium humate to iron ore concentrate within the above range can produce pellets with higher compressive strength and TFe grade.

[0014] In the present application, the iron concentrate is selected from magnetite concentrate, hematite concentrate, specularite and chromite concentrate.

[0015] Usually, before the preheating step, the green balls obtained by pelletizing are dried to obtain dry balls.

[0016] Preferably, the preheating conditions are: first calcining at 250-400° C. for 4-7 min, then calcining at 450-600° C. for 4-7 min, and then calcining at 900-980° C. for 4-7 min.

[0017] In this application, the preheating step further adopts a multi-stage preheating process, first calcining the dry balls in stages at low temperature. On the one hand, this slows down the combustion, decomposition, and volatilization reaction rates of ammonium humate, thereby avoiding the looseness of the pellet structure caused by the rapid combustion, decomposition, and volatilization of ammonium humate; on the other hand, it allows a certain reaction time for the initial crystallization reaction of the metal oxide in the pellet to avoid the rapid volume expansion caused by the change of crystal form in a short period of time, which reduces the strength of the preheated balls. Compared with the single-stage preheating process at a single temperature, the above multi-stage preheating can effectively improve the compressive strength of the preheated balls and the compressive strength of the pellets.

[0018] In the present application, the compressive strength of the pellets obtained by using a multi-stage preheating step is significantly better than that obtained by preheating at a single temperature. This is because the humic acid binder will lose weight in the 300-800°C stage during the gradual heating process (the organic components in the humic acid binder will quickly burn, decompose and volatilize). Therefore, directly heating the dry balls to about 900°C for preheating will accelerate the combustion, decomposition and volatilization of the organic components in the humic acid binder, resulting in a loose pellet structure, thereby reducing the strength of the preheated pellets. Therefore, the inventors of the present application further improved the preheating process and used a multi-stage preheating method to preheat the dry balls, significantly improving the compressive strength of the preheated balls and pellets.

[0019] Preferably, the preheating conditions are: first calcining at 300°C for 5 minutes, then calcining at 500°C for 5 minutes, and then calcining at 950°C for 5 minutes.

[0020] In a specific embodiment, the preheating conditions may also be: first calcining at 350°C for 5 minutes, then calcining at 550°C for 5 minutes, and then calcining at 950°C for 5 minutes.

[0021] Preferably, the calcination temperature is 1200-1300° C., and the calcination time is 5-10 minutes.

[0022] In a specific embodiment, the calcination temperature is 1250° C. and the calcination time is 10 minutes.

[0023] In the present application, ammonium humate can be commercially available or can be prepared by the following method.

[0024] Preferably, the preparation method of ammonium humate comprises the following steps: mixing low-grade lignite powder with a particle size of less than 100 mesh with ammonia water with a mass concentration of 2-8% at a solid-liquid ratio of 1:(5-10) to obtain a mixed solution; stirring the mixed solution at 50-85° C., then letting it stand, separating the layers and taking the upper layer liquid; drying and grinding the upper layer liquid to obtain ammonium humate with a particle size of less than 100 mesh.

[0025] In the present application, in the preparation method of ammonium humate, by controlling the concentration of ammonia water and the liquid-solid ratio of low-grade lignite powder to ammonia water within the above range, the viscosity and water solubility of the obtained ammonium humate are better, and the compressive strength of the final pellets is high.

[0026] In some embodiments, the mass concentration of the aqueous ammonia may be 2-4%, 2-5%, 2-6%, 4-5%, 4-6%, 4-8%, 5-6%, 5-8% or 6-8%.

[0027] In a specific embodiment, the mass concentration of the ammonia water may also be 2%, 4%, 5%, 6% or 8%.

[0028] Preferably, the mass concentration of the ammonia water is 4-6%.

[0029] The present application has found through experimental exploration that the concentration of ammonia water affects the quality of ammonium humate, and then affects the quality of pellets. When the concentration of ammonia water is too low, the humic acid content in the obtained ammonium humate is low, and the strength of the pellets obtained is poor; and when the ammonia water concentration is too high, a large amount of volatile ammonia and heat will be produced during the extraction process, and carbon dioxide gas will be released at the same time. The ammonia and carbon dioxide produced will promote the generation of unnecessary by-products such as styrene and propylene, seriously affecting the humic acid content in the binder, and the strength of the pellets obtained is low. Therefore, the present application controls the concentration of ammonia water within the above range, and can obtain a binder with a higher humic acid content, and the compressive strength of the pellets obtained using the ammonium humate is more excellent.

[0030] In a second aspect, the present application provides a pelletized ore.

[0031] A pellet is prepared by utilizing a method for preparing pellets using ammonium humate.

[0032] In the present application, since the pellet binder used is ammonium humate, no additional sodium ions are introduced into the produced pellets. The use of the pellets for subsequent steel smelting will not worsen the reduction expansion of the pellets, will not affect the permeability of the material column, and can ensure the smooth progress of blast furnace smelting. Moreover, when ferrochromium concentrate is used as the raw material, the produced pellets do not contain harmful substances such as sodium chromate, and therefore will not cause harm to the human body and the environment.

[0033] In summary, this application has the following beneficial effects:

[0034] 1. The pellets provided in this application are prepared using ammonium humate. The organic matter contained in this ammonium humate decomposes, burns, and volatilizes during the preheating and roasting process of the metal oxide ore agglomerates. Therefore, the pellets produced by this method contain much less residual inorganic matter than pellets produced using inorganic binders. As a result, the TFe grade of the pellets produced is higher than that of pellets produced using inorganic binders. In addition, the ammonium humate also contains a small amount of inorganic matter. Compared with organic binders, these inorganic substances can react with the oxide minerals in the pellet raw materials during preheating and roasting, generating a small amount of liquid phase at a lower temperature, promoting liquid phase consolidation of the pellets and thus improving the compressive strength of the pellets.

[0035] 2. The preparation method of the pellets provided in this application uses ammonium humate as a binder. No additional sodium ions are introduced during the preparation process, so the reduction expansion properties of the pellets will not be deteriorated, and the material column of blast furnace smelting will not be affected. Moreover, when the iron concentrate is chromite, there is no risk of the generation of toxic products (sodium chromate). It is an environmentally friendly and efficient binder; and the compressive strength and TFe grade of the above-mentioned pellets are high, which can fully meet the subsequent production needs.

[0036] 3. During the pellet preparation process, this application further utilizes a multi-stage preheating method to preheat the dry balls. This, on the one hand, slows the decomposition, combustion, and volatilization rates of ammonium humate, preventing the pellet structure from becoming loose over a short period of time. On the other hand, it allows the initial crystallization of the oxide mineral particles in the pellets a certain reaction time, allowing their lattice structure to slowly change under a certain temperature gradient, transforming into a stable, regular crystal form. Therefore, the multi-stage preheating method provided by this application effectively avoids the disadvantage of low preheated ball strength caused by rapid temperature increases during the preheating stage, significantly improving the strength of preheated balls and pellets prepared using ammonium humate. DETAILED DESCRIPTION

[0037] The present application provides a method for preparing pellets using ammonium humate, comprising the following steps:

[0038] (1) Raw material preparation: Ammonium humate with a particle size of less than 100 mesh and iron ore concentrate with a particle size of less than 200 mesh are mixed in a weight ratio of (0.3-2):100, and an appropriate amount of water is added to adjust the moisture content of the mixture to about 6%. The mixture is then pre-treated by wet grinding in a wet mill for 5 minutes to obtain a raw material for pelletizing. Furthermore, the weight ratio of ammonium humate to iron ore concentrate can also be (0.5-1.5):100.

[0039] (2) Ball Forming: The raw materials are pelletized using a disc pelletizer. During the pelletizing process, the disc speed is maintained at 18 rpm, the disc inclination angle is 45°, and the pelletizing time is fixed at 12 minutes. Qualified green balls with a diameter of 10-12 mm are finally obtained. The moisture content of the green balls is controlled at approximately 8-10% during the pelletizing process.

[0040] (3) Preheating: Dry the green balls obtained from pelletizing at 100±5°C to constant weight to obtain dry balls; then preheat the dry balls at 250-980°C for 5-10 minutes to obtain preheated balls.

[0041] Furthermore, the preheating step can also be: drying the green balls obtained by ball making at 100±5°C to constant weight to obtain dry balls; then calcining the dry balls at 250-400°C for 4-7 minutes, 450-600°C for 4-7 minutes, and 900-980°C for 4-7 minutes in sequence to obtain preheated balls.

[0042] (4) Calcination: Calcinate the preheated pellets at 1200-1300°C for 5-10 minutes. After calcination, pellets are obtained.

[0043] In this application, ammonium humate was either homemade or commercially available;

[0044] The homemade ammonium humate production process includes the following steps: drying and grinding low-rank lignite (from Guizhou, with a humic acid content of 45 wt%) to a particle size of less than 100 mesh; then mixing the lignite powder with 2-8% ammonia water at a solid-to-liquid ratio of 1:5-10 to obtain a mixed solution; heating the mixed solution in a water bath at 50-85°C while stirring at a speed of 200-600 rpm for 1-2 hours. After stirring, the mixed solution is allowed to stand until layers separate. The upper layer is poured into a clean container and dried at 75-85°C to obtain a solid product. The solid product is then ground in an agate mortar to obtain ammonium humate with a particle size of less than 100 mesh.

[0045] In this application, the sources and component contents of the iron ore concentrate used are shown in Table 1 below, and other reagents, solvents, etc. used can be obtained commercially.

[0046] Table 1 Source and component content of iron ore concentrate

[0047]

[0048] The present application is further described in detail below with reference to preparation examples, embodiments and performance testing experiments.

[0049] Preparation Example 1

[0050] Preparation Example 1 provides an ammonium humate.

[0051] The preparation method of the above-mentioned ammonium humate comprises the following steps:

[0052] Low-rank lignite raw material was dried and ground to a particle size of less than 100 mesh. The lignite powder was then mixed with 2% ammonia water at a solid-to-liquid ratio of 1:5 to obtain a mixed solution. The mixed solution was heated in a water bath at 50°C while stirring at a speed of 200 r / min for 1 hour. After stirring, the mixed solution was allowed to stand until layers separated. The upper layer was poured into a clean container and dried at 75°C to obtain a solid product. The solid product was then ground in an agate mortar to obtain ammonium humate with a particle size of less than 100 mesh.

[0053] Preparation Example 2-5

[0054] Preparation Examples 2-5 each provide an ammonium humate.

[0055] Preparation Examples 2-5 were prepared according to the method of Preparation Example 1, except that the concentration of ammonia water was as shown in Table 2.

[0056] Table 2 Concentration of ammonia water in the preparation method of ammonium humate provided in Preparation Examples 1-5

[0057] Preparation Example Mass concentration of ammonia water (%) 1 2 2 4 3 5 4 6 5 8

[0058] Examples 1-5

[0059] Examples 1-5 respectively provide a method for preparing pellets using ammonium humate, the difference being that the weight ratio of ammonium humate to iron ore concentrate is specifically shown in Table 3.

[0060] The method for preparing the pellets comprises the following steps:

[0061] (1) Raw material pre-preparation: 50 g of ammonium humate with a particle size of less than 100 mesh (purchased from Shandong Guohua Chemical Co., Ltd.) was mixed with 5 kg (dry weight) of iron concentrate (magnetite concentrate, with a particle size of less than 200 mesh accounting for 90.5%, 3% moisture, and TFe grade of 65.98%), and an appropriate amount of water was added to make the water content of the mixture 5%; then the mixture was pre-treated by milling for 5 minutes using a mill to obtain a raw material for pelletizing.

[0062] (2) Ball Forming: The raw materials are pelletized using a disc pelletizer. During the pelletizing process, the disc speed is maintained at 18 rpm, the disc inclination angle is 45°, and the pelletizing time is fixed at 12 minutes. Qualified green balls with a diameter of 10-12 mm are finally obtained. The moisture content of the green balls is controlled at approximately 8-10% during the pelletizing process.

[0063] (3) Preheating: Dry the green balls obtained from pelletizing at 100±5°C to constant weight to obtain dry balls; then preheat the dry balls at 950°C for 5-10 minutes to obtain preheated balls.

[0064] (4) Calcination: Calcinate the preheated pellets at 1250°C for 10 min. After calcination, pellets are obtained.

[0065] Table 3 Weight ratio of ammonium humate to iron concentrate in the preparation methods provided in Examples 1-5

[0066]

[0067] Examples 6-10

[0068] Examples 6-10 were carried out according to the method of Example 3, except that in Examples 6-10, ammonium humate was derived from Preparation Examples 1-5, respectively.

[0069] Example 11

[0070] Example 11 was carried out according to the method of Example 8, except that the preheating step was as follows:

[0071] (3) Preheating: Dry the green balls obtained at 100±5°C to constant weight to obtain dry balls; then calcine the dry balls at 500°C for 5 minutes and then at 950°C for 5 minutes to obtain preheated balls.

[0072] Example 12

[0073] Example 12 was carried out according to the method of Example 8, except that the preheating step was as follows:

[0074] (3) Preheating: Dry the green balls obtained at 100±5°C to constant weight to obtain dry balls; then calcine the dry balls at 300°C for 5 minutes and 950°C for 5 minutes to obtain preheated balls.

[0075] Example 13

[0076] Example 13 was carried out according to the method of Example 8, except that the preheating step was as follows:

[0077] (3) Preheating: Dry the green balls obtained at 100±5°C to constant weight to obtain dry balls; then calcine the dry balls at 300°C for 5 min, 500°C for 5 min, and 950°C for 5 min to obtain preheated balls.

[0078] Example 14

[0079] Example 14 was carried out according to the method of Example 8, except that the preheating step was as follows:

[0080] (3) Preheating: Dry the green balls obtained at 100±5°C to constant weight to obtain dry balls; then calcine the dry balls at 350°C for 4-7 min, 550°C for 5 min, and 950°C for 5 min to obtain preheated balls.

[0081] Example 15

[0082] Example 15 was carried out according to the method of Example 8, except that the iron concentrate in Example 15 was hematite concentrate (hematite concentrate powder with a particle size less than 200 mesh accounted for 95.3%, moisture 5%, and TFe grade was 67.84%).

[0083] Example 16

[0084] Example 16 was carried out according to the method of Example 8, except that the iron concentrate in Example 16 was specularite (specularite powder with a particle size less than 200 mesh accounted for 97.2%, moisture 4%, and TFe grade was 68.74%).

[0085] Example 17

[0086] Example 17 was carried out according to the method of Example 8, except that the iron concentrate in Example 17 was chromite concentrate (chromite concentrate powder with a particle size less than 200 mesh accounted for 93.5%, moisture 2%, and TFe grade was 27.64%).

[0087] Comparative Example 1

[0088] Comparative Example 1 provides a method for preparing pellets using bentonite, and the specific steps are as follows:

[0089] (1) Raw material pre-preparation: 100 g of bentonite was mixed with 5 kg (dry weight) of iron concentrate with a particle size of less than 200 mesh (magnetite concentrate, 90.5% of which is less than 200 mesh, 3% of which is moisture, and 65.98% of which is TFe grade), and an appropriate amount of water was added to make the water content of the mixture 5%; the mixture was then pre-milled for 5 min using a mill to obtain a raw material for pelletizing.

[0090] (2) Ball Forming: The raw materials are pelletized using a disc pelletizer. During the pelletizing process, the disc speed is maintained at 18 rpm, the disc inclination angle is 45°, and the pelletizing time is fixed at 12 minutes. Qualified green balls with a diameter of 10-12 mm are finally obtained. The moisture content of the green balls is controlled at approximately 8-10% during the pelletizing process.

[0091] (3) Preheating: Dry the green balls obtained at 100±5°C to constant weight to obtain dry balls; then preheat the dry balls at 950°C for 10 minutes to obtain preheated balls.

[0092] (4) Calcination: Calcinate the preheated pellets at 1250°C for 10 min. After calcination, pellets are obtained.

[0093] Comparative Example 2

[0094] Comparative Example 2 provides a method for preparing pellets using a CMC binder, and the specific steps are as follows:

[0095] (1) Raw material pre-preparation: 50 g of CMC binder was mixed with 5 kg (dry weight) of iron concentrate with a particle size of less than 200 mesh (magnetite concentrate, 90.5% of which is less than 200 mesh, 3% of which is moisture, and 65.98% of which is TFe grade), and an appropriate amount of water was added to make the water content of the mixture 6%. The mixture was then pre-milled for 5 min using a mill to obtain the raw material for pelletizing.

[0096] (2) Ball Forming: The raw materials are pelletized using a disc pelletizer. During the pelletizing process, the disc speed is maintained at 18 rpm, the disc inclination angle is 45°, and the pelletizing time is fixed at 12 minutes. Qualified green balls with a diameter of 10-12 mm are finally obtained. The moisture content of the green balls is controlled at approximately 8-10% during the pelletizing process.

[0097] (3) Preheating: Dry the green balls obtained at 100±5°C to constant weight to obtain dry balls; then preheat the dry balls at 950°C for 10 minutes to obtain preheated balls.

[0098] (4) Calcination: Calcinate the preheated pellets at 1250°C for 10 min. After calcination, pellets are obtained.

[0099] Comparative Example 3

[0100] Comparative Example 3 provides a method for preparing pellets using sodium humate binder, and the specific steps are as follows:

[0101] (1) Raw material pre-preparation: 50 g of sodium humate binder (purchased from Yichun Zhongxiang Biotechnology Co., Ltd.) was mixed with 5 kg (dry weight) of chromite concentrate with a particle size of less than 200 mesh (chromite concentrate, chromite concentrate with a particle size less than 200 mesh accounts for 93.5%, moisture 2%, and TFe grade is 27.64%), and an appropriate amount of water was added to make the water content of the mixture 6%; then the mixture was pre-treated by milling for 5 minutes using a mill to obtain a raw material for pelletizing.

[0102] (2) Ball Forming: The raw materials are pelletized using a disc pelletizer. During the pelletizing process, the disc speed is maintained at 18 rpm, the disc inclination angle is 45°, and the pelletizing time is fixed at 12 minutes. Qualified green balls with a diameter of 10-12 mm are finally obtained. The moisture content of the green balls is controlled at approximately 8-10% during the pelletizing process.

[0103] (3) Preheating: Dry the green balls obtained at 100±5°C to constant weight to obtain dry balls; then preheat the dry balls at 950°C for 10 minutes to obtain preheated balls.

[0104] (4) Calcination: Calcinate the preheated pellets at 1250°C for 10 min. After calcination, pellets are obtained.

[0105] Comparative Example 4

[0106] Comparative Example 4 was prepared according to the preparation method of Example 1, except that the amount of ammonium humate added was 10 g; and the weight ratio of ammonium humate to iron concentrate was 0.2:100.

[0107] Comparative Example 5

[0108] Comparative Example 5 was prepared according to the preparation method of Example 1, except that the amount of ammonium humate added was 125 g; and the weight ratio of ammonium humate to iron concentrate was 2.5:100.

[0109] Performance testing

[0110] The drop strength and compressive strength of the green balls obtained in Examples 1-17 and Comparative Examples 1-5, the compressive strength of the preheated balls and pellets, and the TFe grade of the pellets were tested. The test results are shown in Table 4 below. The test method is as follows:

[0111] (1) Drop Strength: Ten green balls with a diameter of 10-12 mm were prepared according to the methods of Examples 1-17 and Comparative Examples 1-5. The green balls were allowed to freely drop from a height of 0.5 m onto a 10 mm thick steel plate. This was repeated until the green balls showed obvious cracks or broke. The number of drops until the balls broke was the drop strength, and the average number of drops for the ten balls was used as the drop strength index.

[0112] (2) Compressive strength: The test method refers to GB / T14201-1993.

[0113] (3) TFe grade: The detection method refers to GB / T 6730.6-2016.

[0114] (4)Cr 6+ Content detection: Diphenylcarbazide spectrophotometry was used to detect whether the pellets obtained in Example 17 and Comparative Example 3 contained Cr. 6+ , for specific detection methods, please refer to GB / T 31931-2015.

[0115] Table 4 Performance test results of green balls, preheated balls and pellets obtained in Examples 1-17 and Comparative Examples 1-5

[0116]

[0117]

[0118] According to the test results of Examples 1-17 and Comparative Examples 1-5, the present application uses ammonium humate as a pellet binder, and the compressive strength of the pellets obtained is ≥2500N / piece. In addition, the preparation method of the pellets provided in the present application does not introduce additional alkali metal sodium ions and does not cause harm to blast furnace smelting equipment, the environment, and the human body. On the other hand, the pellets obtained by this method also have excellent compressive strength and can fully meet the subsequent steel smelting production needs.

[0119] The pellets prepared using bentonite in Comparative Example 1 have excellent compressive strength, but the amount of bentonite remaining in the pellets after calcination is relatively high, resulting in a TFe grade of only 63.60% in the pellets.

[0120] In Comparative Example 2, the preheated balls and roasted balls produced using CMC binder have relatively low compressive strengths of only 357 N / piece and 1879 N / piece, respectively. Pellets of this strength are difficult to meet the production requirements of subsequent steelmaking. In Comparative Example 3, the pellets produced using sodium humate binder have relatively excellent compressive strength and TFe grade. However, this method introduces sodium ions during the preparation process, so the obtained pellets contain sodium chromate, which can be harmful to blast furnace smelting equipment, the environment, and the human body, and therefore do not meet the use requirements.

[0121] The test results of Examples 1-5 and Comparative Examples 4-5 show that in Comparative Example 4, when the weight ratio of ammonium humate to magnetite concentrate was controlled at 0.2:100, the pellets produced had a higher TFe grade, but their compressive strength was only 1734 N / pellet. In Comparative Example 5, when the weight ratio of ammonium humate to magnetite concentrate was controlled at 2.5:100, the pellets produced had a compressive strength of 2129 N / pellet, but the TFe grade was only 63.81%. In Examples 1-5, when the weight ratio of ammonium humate to magnetite concentrate is controlled to (0.5-1.5):100, the compressive strength of the obtained pellets is 2510-2617N / piece, and the TFe grade is 64.12-65.58%. Therefore, it is explained that the addition amount of ammonium humate affects the compressive strength and TFe grade of the pellets. In the present application, the weight ratio of ammonium humate to iron concentrate is controlled to (0.3-2):100, and pellets with excellent compressive strength and TFe grade can be obtained.

[0122] According to the test results of Example 3 and Examples 6-10, the compressive strength of the pellets obtained by Examples 6-10 using the ammonium humate prepared by the present application is ≥2609N / piece, and the TFe grade is ≥64.17%; and as the concentration of ammonia water increases during the preparation of ammonium humate, the TFe grade of the pellets shows a trend of first increasing and then decreasing. Further comparison shows that when the mass concentration of ammonia water is controlled within the range of 4-6% in Examples 7-9, the pellets obtained are even better, with a compressive strength of ≥2708N / piece and a TFe grade of ≥64.36%.

[0123] The test results of Examples 8 and 11-14 show that the compressive strength of the pellets obtained in Examples 11-14, which employ a multi-stage calcination preheating method, is improved. In particular, Examples 13-14, which employ a three-stage calcination preheating method, achieve a compressive strength of >2850 N / pellet. This demonstrates that the multi-stage calcination preheating method employed in the pellet preparation method provided by the application can further improve the pellet strength.

[0124] In Example 15, pellets were prepared using hematite concentrate as raw material. The drop strength of the obtained green balls was 5.4 times / piece, the compressive strength of the preheated balls was 478N / piece, the compressive strength of the pellets was 2891N / piece, and the TFe grade was 67.19%.

[0125] Example 16: Pellets were prepared using specularite as raw material. The drop strength of the obtained green balls was 5.1 times / piece, the compressive strength of the preheated balls was 465N / piece, the compressive strength of the pellets was 2688N / piece, and the TFe grade was 68.09%.

[0126] In Example 17 and Comparative Example 3, pellets were prepared using chromite concentrate as raw material. The drop strength of the green balls obtained was 5.8-6.0 times / piece, the compressive strength of the preheated balls was 450-453N / piece, the compressive strength of the pellets was 2612-3012N / piece, and the TFe grade was 26.89%. However, by measuring the hexavalent chromium in the two pellets, it was found that the pellets prepared in Example 17 did not contain Cr. 6+ , while the pellets prepared in Comparative Example 3 contain Cr 6+ This shows that in the process of preparing pellets using chromite concentrate and sodium humate binder in Comparative Example 3, the chromite concentrate reacted with sodium humate, causing the Cr in the chromite concentrate to 2+ Converted into Cr 6+ , that is, the harmful substance sodium chromate is generated. Therefore, when chromite concentrate is used to prepare pellets, sodium chromate is easily generated when sodium humate is used as the pellet binder, which in turn has an impact on the environment and human body. However, when the ammonium humate provided by this application is used as the pellet binder, there is no risk of the formation of toxic products (sodium chromate).

[0127] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for preparing pellets using ammonium humate, characterized in that: The method comprises the following steps: The ammonium humate with a particle size of less than 100 mesh and the iron ore concentrate are mixed in a weight ratio of (0.5-1.5):100, and water is added, and pelletizing, drying, preheating and roasting are performed to obtain pellets; The preparation method of ammonium humate comprises the following steps: mixing low-grade brown coal powder with a particle size of less than 100 mesh and ammonia water with a mass concentration of 5-6% at a solid-liquid ratio of 1:(5-10) to obtain a mixed solution; stirring the mixed solution at 50-85° C., then standing and separating the mixed solution into layers, and collecting the upper layer liquid; drying and grinding the upper layer liquid to obtain ammonium humate with a particle size of less than 100 mesh; The preheating conditions are: first calcining at 250-400° C. for 4-7 min, then calcining at 450-600° C. for 4-7 min, and then calcining at 900-980° C. for 4-7 min.

2. The method for preparing pellets using ammonium humate according to claim 1, wherein: The iron concentrate is selected from magnetite concentrate, hematite concentrate and chromite concentrate.

3. The method for preparing pellets using ammonium humate according to claim 1, wherein: The preheating conditions are: first calcining at 300° C. for 5 min, then calcining at 500° C. for 5 min, and then calcining at 950° C. for 5 min.

4. The method for preparing pellets using ammonium humate according to claim 1, wherein: The calcination temperature is 1200-1300° C., and the calcination time is 5-10 minutes.

5. A pelletized ore, characterized in that: The pellets are prepared by the method for preparing pellets using ammonium humate according to any one of claims 1 to 4.

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