Cold-bonded pellet for reduction smelting and production process of cold-bonded pellet

Abstract

The invention discloses a cold-bonded pellet for reduction smelting and a production process of the cold-bonded pellet, and belongs to the technical field of cold-bonded pellet preparation. According to the cold consolidation pellet for reduction smelting, pellet raw materials comprise aggregate and an adhesive, the aggregate comprises modified sintered return ore and magnetite concentrate, and the modified sintered return ore is obtained by modifying the sintered return ore through a modifier containing a silane coupling agent so that the surface of the sintered return ore can be loaded with the silane coupling agent; the adhesive comprises water glass, an organic adhesive and a nano oxide particle nucleating aid, and at least part of the adhesive is connected with the surface of the sintered return mine through a silane coupling agent. According to the method, the sintering return mine is modified in advance, so that the bonding firmness between the sintering return mine and the adhesive can be effectively improved, and the overall structural strength of the obtained cold-bonded pellets is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of cold-bonded pellet preparation, and more specifically, relates to a cold-bonded pellet for reduction smelting and its production process. Background Art

[0002] Sinter is one of the main raw materials for domestic blast furnace smelting production. The production process of sinter has the characteristics of high energy consumption and large pollutant emissions, and is a key process for energy conservation and emission reduction in the iron and steel industry. During the blast furnace production process, about 10% of sinter return ore is generated. The sinter with a particle size > 5mm under the blast furnace trough can be directly used as a finished product for smelting. However, due to problems such as the specifications of the finished product screen and the screen under the trough, and the screening efficiency of the screen powder, there are many sinter with a particle size less than 5mm in the return ore. If these sinter return ores directly enter the blast furnace, they will block the voids of the burden column, hinder the flow of gas in the blast furnace to the furnace top, and too much return ore will also affect the control of the sintering process, resulting in poor strength of the sinter, causing a vicious cycle in sinter production and an increase in ironmaking costs. Therefore, at present, most domestic iron and steel enterprises return these return ores to the sintering burdening, and 30% - 45% of the return ore will enter the sintering system for recycling and re-firing in production practice, which not only wastes manpower and material resources, but also wastes energy.

[0003] Cold-bonded pellets provide an effective solution for the green and efficient treatment of sinter return ore because their preparation process has no high-temperature treatment process, can significantly reduce energy consumption and carbon emissions. However, due to the poor hydrophilicity of the surface of the sinter return ore and the uneven particle size distribution, it is difficult to form pellets by directly adding water to pure sinter return ore, and there is almost no strength. Therefore, in the prior art, it is usually necessary to add a certain amount of binder to the sinter return ore, which can effectively improve the cold strength of the cold-bonded pellets to a certain extent.

[0004] For example, the application case with the Chinese patent application number 201811464869.6 discloses a sinter return ore recycling system and application method. In this application case, small-sized sinter is cold-consolidated and formed under the action of a binder, and then returned to the blast furnace, which can effectively avoid repeated sintering, realize resource recovery and utilization, and reduce energy consumption and costs.

[0005] However, due to the smooth surface and relatively poor hydrophilicity of the sinter return ore, the dried pellets are easily broken at the binder-return ore interface, resulting in a decrease in the strength of the pellets. Therefore, how to effectively improve the bonding firmness between the binder and the sinter return ore and ensure the structural strength of the cold-bonded pellets is of great significance. Summary of the Invention

[0006] Aiming at the technical problem in the prior art that the cold-bonded pellets based on sinter return fines are prone to fracture at the binder-sinter return fines interface, resulting in a decrease in pellet strength, the present invention provides a cold-bonded pellet for reduction smelting and its production process. By pre-modifying the sinter return fines, the present invention can effectively improve the bonding firmness between it and the binder, thereby ensuring the overall structural strength of the obtained cold-bonded pellets.

[0007] To achieve the above object, the technical solution provided by the present invention is as follows:

[0008] In the first aspect of the present invention, there is provided a cold-bonded pellet for reduction smelting used in blast furnace smelting. The pellet raw materials include aggregate and binder. Among them, the aggregate includes modified sinter return fines and magnetite concentrate. The modified sinter return fines are obtained by modifying the sinter return fines with a modifier containing a silane coupling agent so that its surface is loaded with the silane coupling agent.

[0009] The binder includes water glass, organic binder, and nano-oxide particle nucleation aid. At least part of the binder is connected to the surface of the sinter return fines through the silane coupling agent.

[0010] Aiming at the technical problem of relatively low pellet strength in the prior art when making cold-bonded pellets from sinter return fines and applying them to blast furnace smelting, on the one hand, the present invention uses a compound of sinter return fines and magnetite concentrate as the pellet aggregate to make up for the deficiencies of large pores and low strength of sinter return fines; on the other hand, the composition of the binder is optimized. By compounding water glass and organic binder, and adding nano-oxide particles as nucleation aids at the same time, the wet pellet strength and dry pellet strength of the obtained pellets can be effectively improved, meeting the requirements of transportation and automatic batching for pellet strength. Among them, the nano-oxide particles have a small particle size (50-200 nanometers) and can be used as nucleation aids. The surface active hydroxyl groups on them can form a large number of nucleation sites, promoting the heterogeneous nucleation of water glass, thereby accelerating the formation of a three-dimensional network structure. Specifically, when water glass undergoes dehydration condensation, it gradually polymerizes from oligomers to polymers. At this time, the polymers have stronger structural strength, but the exposed chemical sites of the polymers are fewer. By adding nucleation aids: (1) The characteristics of small particle size and many active sites of the nucleation aids can be utilized to attract the surrounding oligomers to combine with themselves, accelerating the dehydration condensation of water glass to form a highly cross-linked three-dimensional network structure; (2) When the nucleation aids dissolve in the water glass solution, they are also a kind of oligomers, which is equivalent to an increase in the number of oligomers constituting the three-dimensional network structure, thereby being beneficial to further increasing the strength and quantity of the network structure.

[0011] In addition, the present invention further modifies the sinter return ore, and a silane coupling agent is loaded on the surface of the sinter return ore. At least part of the binder is connected to the surface of the sinter return ore through the silane coupling agent, thereby effectively increasing the adhesion of the binder to the surface of the sinter return ore, further facilitating an increase in the green compressive strength of the cold-bonded pellets, better exerting the adhesion effect of the binder, especially preventing the pellets from easily breaking at the binder-return ore interface, and enabling the pellets to maintain integrity at high temperatures.

[0012] Specifically, the silane coupling agent is composed of an organic functional group and a silyl group, can form chemical bonds on the surface of the sinter return ore, enhance the hydrophilicity of the surface of the sinter return ore, enhance the adhesion between the sinter return ore and the binder, thereby improving the green compressive strength of the cold-bonded sinter return ore pellets, meeting the requirements for pellet strength in transportation and automatic batching, and maintaining the integrity of the pellets at high temperatures.

[0013] For the cold-bonded pellets according to any one of the technical solutions of the first aspect of the present invention, the silane coupling agent includes at least one of KH550, KH560, and KH570; and / or the mass of the silane coupling agent is 3-5% of the mass of the sinter return ore. It should be noted that the silane coupling agent of the present application includes but is not limited to KH550, KH560, and KH570, but when using KH570, the effect of improving the pellet strength is the best.

[0014] For the cold-bonded pellets according to any one of the technical solutions of the first aspect of the present invention, the modifier further includes formic acid, and the mass of the formic acid is 4-6% of the mass of the sinter return ore. By pretreating the sinter return ore with a formic acid solution, the oxide film, oily substances, impurities, etc. on the surface of the sinter return ore can be decomposed and removed, activating the surface of the sinter return ore, exposing more hydroxyl groups on the surface of the sinter return ore to adhere to the binder, thereby more facilitating the better adhesion of the coupling agent and the binder to the surface of the return ore. Specifically, the sinter return ore can be modified with a silane coupling agent alone, or the sinter return ore can be modified with a formic acid solution alone, or the sinter return ore modified with a formic acid solution can be further modified with a silane coupling agent, and the effect is the best when formic acid and the silane coupling agent are used to modify the sinter return ore in sequence.

[0015] For the cold-bonded pellets according to any one of the technical solutions of the first aspect of the present invention, the grading index m of the aggregate is 0.4-0.6, and the mass ratio of the modified sinter return ore to the magnetite concentrate in the aggregate is (35-55):(45-65).

[0016] By optimizing the grading index of the aggregate and the mass ratio of the modified sintered return fines to magnetite concentrate, the particle distribution of the sintered return fines presents a discontinuous characteristic, eliminating the voids caused by the clogging and supporting effects of smaller particles, minimizing the void ratio of the aggregate, which is not only beneficial to further improving the strength of the obtained pellets, but also has a significant skeleton effect and can effectively save the binder.

[0017] More preferably, the sintered return fines are first screened and classified according to particle sizes: 0-1 mm, 1 mm-2 mm, 2 mm-3 mm, 3 mm-4 mm, 4 mm-5 mm, and the mass ratios of the particles in each particle size range are 38-53%, 16-20%, 12-16%, 9-14%, 8-13% respectively. Then, magnetite concentrate is used to replace the sintered return fines in the 0-1 mm range, that is, the mass ratio of the modified sintered return fines to magnetite concentrate is further preferably (38-53):(47-62).

[0018] For the cold-bonded pellets according to any one of the technical solutions of the first aspect of the present invention, the mass of the binder is 5-9% of the total amount of the aggregate; and / or the modulus of the sodium silicate is 2.3-2.5. The bonding strength of sodium silicate first increases and then decreases with the increase of the modulus. When the modulus is too small, the bonding strength of sodium silicate is too small, and the strength improvement effect of the cold-bonded pellets becomes low; but when the modulus is too high, the solubility of sodium silicate becomes poor, it is difficult to disperse uniformly in the solution, and its curing speed is too fast, resulting in insufficient contact and reaction with the material particles, and the bonding strength decreases instead.

[0019] For the cold-bonded pellets according to any one of the technical solutions of the first aspect of the present invention, the mass ratio of the sodium silicate, the organic binder and the nano-oxide particle nucleating aid is (4-8.5):(0.3-0.7):(0.1-0.3).

[0020] For the cold-bonded pellets according to any one of the technical solutions of the first aspect of the present invention, the organic binder includes one or more of sodium carboxymethylcellulose, starch, and organic resin binders; and / or the nano-oxide particle nucleating aid includes at least one of nano-silica and nano-alumina.

[0021] For the cold-bonded pellets according to any one of the technical solutions of the first aspect of the present invention, the sodium silicate adopts a boric acid and / or formic acid modified sodium silicate solution, and the modified sodium silicate solution uses anhydrous ethanol as a solvent.

[0022] When sodium silicate is used as the binder, the Na it contains +It will cause an excessive amount of alkali metals to enter the blast furnace, thereby reducing the permeability of the blast furnace and corroding refractory materials, etc. Therefore, in the present invention, water glass is modified by using boric acid and / or formic acid. Boric acid and / or formic acid can react with water glass to form water-insoluble silicate glue and sodium salts. Since sodium ions can dissolve in water, during the subsequent process of cold-pressed pellet forming, the sodium ions are extruded together with the solvent, while the silicate glue remains in the pellets due to its low fluidity, thereby effectively reducing the alkali metal content in the pellets; among them, the best effect is achieved when a mixed acid of boric acid and formic acid is used for modification.

[0023] However, it should be noted that the removal of alkali metals will cause a certain degree of loss of pellet strength. Therefore, in the present invention, by using a composite binder, that is, through the coordinated action of water glass, organic binder and nucleating agent, the influence of alkali metal removal on pellet strength can also be compensated, thereby effectively ensuring the wet pellet strength and dry pellet strength of the pellets.

[0024] In addition, the modulus of water glass will also affect its modification effect, that is, the removal effect of sodium ions. When its modulus is too high, the solubility of water glass becomes poor and it is difficult to be evenly dispersed in the solution, and Na + is wrapped, which is not conducive to the reaction between water glass and boric acid or formic acid, thus affecting the removal of alkali metals. Therefore, in the present invention, by optimizing the design of the modulus of water glass, not only can the strength of the pellets be effectively guaranteed, but also the adverse effect on the removal effect of sodium ions can be avoided.

[0025] For the cold-bonded pellets according to any technical solution of the first aspect of the present invention, the mass ratio of the boric acid and / or formic acid (total amount of acid) to water glass is (1-3):(4-5). By controlling the mass ratio of boric acid and / or formic acid to water glass, the modification degree of water glass can be controlled to improve the removal rate of sodium ions while minimizing the influence on the bonding effect of water glass, that is, only part of the water glass reacts with the acid to form silicic acid.

[0026] The second aspect of the present invention also provides a preparation method of the cold-bonded pellets according to any technical solution of the first aspect, including: subjecting pellet raw materials including modified sinter return, magnetite concentrate and binder to cold pressing and forming to obtain cold-bonded pellets.

[0027] For the preparation method according to any technical solution of the second aspect of the present invention, the modification process of the modified sinter return includes: fully contacting / mixing the sinter return raw material with the hydrolyzed solution of the silane coupling agent so that the silane coupling agent is grafted onto the surface of the sinter return.

[0028] Further, the hydrolyzed solution of the silane coupling agent is composed of a silane coupling agent, ethanol, and distilled water. The hydrolyzed solution of the silane coupling agent is slowly added dropwise to the sintered return fines and stirred evenly, and then dried to obtain the silane coupling agent-modified sintered return fines.

[0029] The cold-bonded pellets according to any one of the technical solutions of the first aspect of the present invention further include: before the sintered return fines are modified with a silane coupling agent, the sintered return fines are pretreated with a formic acid-modified solution. Through the pretreatment with the formic acid aqueous solution, the oxide film, oily substances, impurities, etc. on the surface of the sintered return fines can be decomposed and removed, so that more hydroxyl groups on the surface of the sintered return fines are exposed to adhere to the binder, which is beneficial to further improving the bonding strength between the binder and the sintered return fines.

[0030] According to the preparation method of any one of the technical solutions of the second aspect of the present invention, the forming pressure of the cold pressing and forming into pellets is 30-90 MPa, and the pressing time is 30-45 s. By strictly controlling the forming pressure, Na + can be extruded out with the solvent, while the gel-like substance silicic acid remains in the cold-bonded pellets because its fluidity is lower than that of ethanol, and a good coordination is achieved between the pellet strength and the Na + removal rate.

[0031] Adopting the technical solution provided by the present invention, compared with the prior art, it has the following beneficial effects:

[0032] (1) By using a silane coupling agent to perform surface modification on the sintered return fines, the present invention can make the sintered return fines have better hydrophilicity, and can better adhere to the binder during the pellet pressing process, thereby preventing the pellets from breaking at the sintered return fines / binder interface. On the premise of ensuring the dry ball compressive strength of the green pellets, it is beneficial to reduce the usage amount of sodium silicate binder, and thus can also reduce the entry of alkali metals into the blast furnace.

[0033] (2) The present invention further compounded the modified sintered return fines with magnetite concentrate as the aggregate of the cold-bonded pellets, and optimized the composition of the binder, which is beneficial to further improving and ensuring the structural strength of the pellets, especially meeting the use requirements of the blast furnace.

[0034] (3) Before using a silane coupling agent to modify the sintered return fines, the present invention first pretreats the surface of the return fines with a formic acid solution, so as to decompose and remove the oxide film, oily substances, impurities, etc. on the surface of the sintered return fines, and expose more hydroxyl groups on the surface of the sintered return fines to adhere to the binder, which is beneficial to further improving the strength of the obtained pellets.

[0035] (4) The present invention further modifies sodium silicate, so that boric acid and / or formic acid react with sodium silicate to generate silicic acid and sodium salts that are insoluble in water and ethanol. Among them, sodium ions dissolve in absolute ethanol. Since the fluidity of silicic acid is significantly lower than that of ethanol, it is convenient to extrude sodium ions together with ethanol during subsequent pelletizing, while silicic acid remains in the pellets, thus effectively removing sodium ions and preventing sodium ions in sodium silicate from affecting normal production in the blast furnace. Detailed implementation mode

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this invention belongs; the term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0037] To further understand the content of the present invention, the present invention will be described in detail below in conjunction with specific embodiments. It should be noted that due to limited space, only some embodiments are listed here, and the protection scope of the present invention is not limited to the following specific embodiments. For example, the numerical ranges of the various parameters in the present invention not only include the numerical values clearly stated as the range limits, but also include all individual numerical values or sub-ranges covered within the said range, as if each numerical value and sub-range were clearly stated. For example, the cold pressing forming pressure is 30 - 90 MPa, and it should be understood that the numerical value of the cold pressing forming pressure not only includes range values such as 30 - 45 MPa, 40 - 60 MPa, 65 - 80 MPa, 70 - 90 MPa, etc., but also includes specific numerical values such as 30 MPa, 45 MPa, 60 MPa, 70 MPa, 90 MPa, etc.

[0038] At the same time, the specific component compositions of sinter return ore and magnetite concentrate powder in this application are not restricted. Among them, the components of sinter return ore are preferably: wTFe: 55 - 60%, wFeO: 5 - 10%, wCaO: 8 - 12%; the components of magnetite concentrate powder are preferably: wTFe: 65 - 70%, wFeO: 20 - 30%, wSiO 2 : 1 - 2%, and more preferably its particle size composition is: the mass ratio of particles less than 200 mesh accounts for 25% - 30%, the mass ratio of particles from 200 mesh to 400 mesh accounts for 50% - 70%, and the particle size of the remaining particles is greater than 400 mesh.

[0039] Example 1

[0040] This embodiment provides a cold-bonded pellet for reduction smelting in blast furnace smelting. The pellet raw materials include modified sinter return fines, magnetite concentrate, and a binder. Among them, the modified sinter return fines are sinter return fines surface-modified with a silane coupling agent. In this embodiment, the silane coupling agent specifically uses FA-KH570 silane coupling agent. The binder is connected to the sinter return fines through the silane coupling agent, which can effectively improve the bonding firmness between the binder and the sinter return fines, prevent the pellet from breaking at the binder / sinter return fines interface, and affect the pellet strength. By compounding the sinter return fines and magnetite concentrate, the cold compressive strength of the obtained pellet can be further improved.

[0041] Specifically, the chemical composition of the sinter return fines in this embodiment is shown in Table 1 below, and screening and grading are carried out according to the grading scheme in Table 2 below. Then, magnetite concentrate is used to replace the sinter return fines particles in the range of 0-1 mm in Table 2. Through the optimization of the particle grading of the aggregate (sinter return fines + magnetite concentrate), the porosity of the aggregate can be effectively reduced, and it helps to further improve the compactness and structural strength of the obtained pellet.

[0042] Table 1 Chemical composition (wt.%) of sinter return fines and modified sinter ore in Examples 1-3

[0043]

[0044] Table 2 Grading scheme of sinter return fines

[0045]

[0046] Further preferably, the binder includes sodium silicate, an organic binder, and a nano-oxide particle nucleating aid. The addition amounts of the components in the binder are 4%, 0.7%, and 0.3% of the total amount of the aggregate (modified sinter return fines + magnetite concentrate) respectively. Among them, the modulus of the sodium silicate is 2.5; the organic binder includes, but is not limited to, sodium carboxymethyl cellulose, starch, and organic resin binders. In this embodiment, the organic binder specifically uses sodium carboxymethyl cellulose; the nano-oxide particle nucleating aid includes, but is not limited to, nano-silica and nano-aluminum oxide. In this embodiment, nano-silica particles (particle size 50-100 nm) are specifically used. It can be used as a nucleating aid, and its surface active hydroxyl groups can form a large number of nucleation sites, promoting the heterogeneous nucleation of sodium silicate, thereby accelerating the formation of a three-dimensional network structure. Through the compounding of sodium silicate and the organic binder and the combined addition of the nano-oxide particle nucleating aid, the mechanical strength of the obtained pellet can be further improved, enabling it to meet the requirements of blast furnace use. At the same time, the addition amount of sodium silicate can be reduced on the basis of meeting the requirements of blast furnace use.

[0047] This embodiment also provides a preparation method for cold-bonded pellets for reduction smelting, including:

[0048] Step 1: Screen and classify the raw sinter return fines, and prepare them according to the particle size grading requirements shown in Table 2. Among them, the sinter return fines with a particle size of 0 - 1 mm are replaced with magnetite concentrate.

[0049] Step 2: Conduct a modification pretreatment on the sinter return fines raw material.

[0050] Specifically, fully stir KH570, distilled water, and an appropriate amount of ethanol for 5 min and then let it stand for 30 min to prepare a silane coupling agent hydrolysis solution (the mass concentration of KH570 is 50%, and the addition amount of the silane coupling agent is 5% of the mass of the sinter return fines); then use a high - speed mixer to stir the sinter return fines at a speed of 500 r / min and slowly drop the silane coupling agent hydrolysis solution. After stirring for more than 1 h, place it in a drying oven at 65 °C and dry for 6 h to obtain the sinter return fines grafted with the silane coupling agent on the surface.

[0051] Step 3: Mix the modified sinter return fines, magnetite concentrate, and binder in proportion to prepare a mixture.

[0052] Step 4: Prepare cold - bonded pellets.

[0053] Use a ZYP - 20TS full - automatic powder tableting machine to prepare cold - pressed pellets. Set the forming pressure to 60 MPa, the mold diameter to 20 mm, and the pressing time to 40 s. During the pelletizing process, add pure water to the mixture, and the total amount of water added accounts for 7% of the total mass of the aggregate.

[0054] Step 5: Dry the obtained cold - bonded pellets by drying in an oven or air - drying to obtain the final product pellets.

[0055] Example 2

[0056] The cold - bonded pellets for reduction smelting in this example are mainly different from those in Example 1 in that: in this example, a formic acid solution is used to pretreat the sinter return fines, and other operations are the same as in Example 1. Specifically, when using the formic acid solution to pretreat the sinter return fines, first fully stir the formic acid solution and ethanol for 5 min and let it stand for 30 min to prepare a formic acid - modified solution (the mass concentration of formic acid is 66%); then use a high - speed mixer to stir the sinter return fines at a speed of 500 r / min and slowly drop the formic acid - modified solution. After stirring for more than 1 h, place it in a drying oven at 65 °C and dry for 6 h to obtain the sinter return fines pretreated with the formic acid solution (FA - modified sinter return fines), and its chemical composition is shown in Table 1 for details.

[0057] Example 3

[0058] The cold-bonded pellets for reduction smelting in this example are mainly different from those in Example 1 in that: before using the silane coupling agent to modify the sintered ore fines in this example, the sintered ore fines are pretreated with formic acid solution first. The operation of pretreating the sintered ore fines with formic acid solution is the same as that in Example 2. The chemical composition of the obtained FA-KH570 modified sintered ore fines in this example is shown in Table 1.

[0059] Comparative Example 1

[0060] The cold-bonded pellets in this comparative example have the same raw material composition and pellet preparation process as those in Example 1, and the main difference is that: the sintered ore fines in this comparative example are not subjected to any modification treatment.

[0061] Comparative Example 2

[0062] The cold-bonded pellets in this comparative example have the same raw material composition and pellet preparation process as those in Example 1, and the main difference is that: magnetite concentrate is not added in this comparative example.

[0063] Comparative Example 3

[0064] The cold-bonded pellets in this comparative example have the same raw material composition and pellet preparation process as those in Example 1, and the main difference is that: only sodium silicate is used as the binder in this comparative example.

[0065] Comparative Example 4

[0066] The cold-bonded pellets in this comparative example have the same raw material composition and pellet preparation process as those in Example 1, and the main difference is that: sodium silicate and sodium carboxymethylcellulose are used as the binder in this comparative example, and the nano-oxide particle nucleating aid is not added.

[0067] Comparative Example 5

[0068] The cold-bonded pellets in this comparative example have the same raw material composition and pellet preparation process as those in Example 1, and the main difference is that: the binder in this comparative example contains sodium silicate and the nano-oxide particle nucleating aid, and sodium carboxymethylcellulose is not added.

[0069] Performance test results:

[0070] As shown in Table 3 and Table 4 below, the physical property parameters of the pellets in Examples 1-3 and Comparative Examples 1-5 are respectively presented. It can be seen from the table that by modifying the sinter return fines with a silane coupling agent or pretreating the sinter return fines with a formic acid solution, and using them together with magnetite concentrate as the pellet skeleton, while using sodium silicate and an organic binder as a composite binder and adding some nano-oxide particle nucleating aids, the green pellet and dry pellet compressive strengths of the obtained pellets can be effectively improved to meet the usage requirements of the blast furnace. Among them, when the sinter return fines are modified with formic acid and a silane coupling agent in sequence, the improvement effect on the dry pellet compressive strength is the best. Since the fluctuation range of the compressive strength of each green pellet is relatively large, the average value of the green pellet compressive strength has weak regularity, while the addition of the organic binder has a great improvement effect on the green pellet drop strength, so the improvement effect on the green pellet compressive strength is relatively obvious.

[0071] Table 3 Comparison data of the wet pellet strength of the pellets obtained in Examples 1-3 and Comparative Examples 1-5

[0072]

[0073] Table 4 Comparison data of the dry pellet compressive strength and sodium removal rate of the pellets obtained in Examples 1-3 and Comparative Examples 1-5

[0074]

[0075]

[0076] Example 4

[0077] The cold-bonded pellet for reduction smelting in this example is mainly different from that in Example 1 in that: in this example, the silane coupling agent used is KH550.

[0078] Example 5

[0079] The cold-bonded pellet for reduction smelting in this example is mainly different from that in Example 1 in that: in this example, the silane coupling agent used is KH560.

[0080] Example 6

[0081] The cold-bonded pellet for reduction smelting in this example is mainly different from that in Example 1 in that: in this example, the grading index m of the sinter return fines is 0.4, and magnetite concentrate is used to replace the 0-1 mm sinter return fines, that is, the mass proportion of magnetite concentrate in the aggregate is 52.53%.

[0082] Table 5 Grading scheme of the sinter return fines

[0083]

[0084] Example 7

[0085] The cold-bonded pellets of this example have basically the same component composition as that of Example 1, with the main difference being that: in this example, the grading index m of the sinter return is 0.6, and magnetite concentrate is used to replace the 0-1mm sinter return, that is, the mass proportion of magnetite concentrate in the aggregate is 38.07%.

[0086] Table 6 Grading scheme of sinter return

[0087]

[0088] Comparative Example 6

[0089] The cold-bonded pellets of this comparative example are mainly different from those of Example 1 in that: in this comparative example, the grading index m of the aggregate is 0.3.

[0090] Comparative Example 7

[0091] The cold-bonded pellets of this comparative example are mainly different from those of Example 1 in that: in this comparative example, the grading index m of the aggregate is 0.7.

[0092] Example 8

[0093] The cold-bonded pellets of this example have basically the same component composition as that of Example 1, with the main difference being that: in this example, the modulus n of the water glass Na 2 O·nSiO 2 is 2.3.

[0094] Example 9

[0095] The cold-bonded pellets of this example have basically the same component composition as that of Example 1, with the main difference being that: in this example, the modulus n of the water glass Na 2 O·nSiO 2 is 2.4.

[0096] Comparative Example 8

[0097] The cold-bonded pellets of this comparative example are mainly different from those of Example 1 in that: in this comparative example, the modulus n of the water glass Na 2 O·nSiO 2 is 2.

[0098] Comparative Example 9

[0099] The cold-bonded pellets of this comparative example are mainly different from those of Example 1 in that: in this comparative example, the modulus n of the water glass Na 2 O·nSiO 2 is 3.

[0100] The physical property parameters of the pellets obtained in Examples 4-9 and Comparative Examples 6-9 are shown in Table 7 below. It can be seen from the table that although using KH550 and KH560 as silane coupling agents can also improve the strength of the obtained pellets, the improvement effect is significantly worse than that of KH570. At the same time, when the modulus of the water glass is 2.4-2.6 and / or the grading index of the aggregate is 0.4-0.6, the strength of the obtained pellets is higher. When the modulus of the water glass or the grading index of the aggregate is not properly selected, under the condition of adding the same amount of binder, it will have an adverse effect on the overall strength of the obtained pellets. Therefore, in the case of modifying the sintered ore fines, it is preferably to select the modulus of the water glass to be 2.4-2.6 and the grading index of the aggregate to be 0.4-0.6, so as to minimize the use amount of the binder on the basis of ensuring the structural strength of the pellets, and further facilitate reducing the entry of sodium ions in the water glass into the blast furnace.

[0101] Table 7 Physical property parameters of the pellets obtained in Examples 4-9 and Comparative Examples 6-9

[0102]

[0103]

[0104] Example 10

[0105] The cold-bonded pellets for reduction smelting in this example are mainly different from those in Example 1 in that: in this example, boric acid is used to modify the water glass, and absolute ethanol is added as a solvent during the modification treatment. After modification, a colloidal silicic acid and sodium salt insoluble in water and ethanol are obtained, and the sodium ions are dissolved in ethanol. Specifically, in this example, the mass ratio of water glass Na 2 O·nSiO 2 to the aggregate is 4%, the proportion of boric acid is 1%, the proportion of the organic binder is 0.7%, the proportion of the nucleation aid is 0.3%, and the added mass of absolute ethanol during the modification treatment of the water glass accounts for 2% of the total mass of the water glass and boric acid.

[0106] Example 11

[0107] The cold-bonded pellets for reduction smelting in this example are mainly different from those in Example 10 in that: in this example, formic acid is used to modify the water glass.

[0108] Example 12

[0109] The cold-bonded pellets for reduction smelting in this example are mainly different from those in Example 10 in that: in this example, a mixed acid of formic acid and boric acid (mass ratio 1:1) is used to modify the water glass.

[0110] Example 13

[0111] The cold-bonded pellets for reduction smelting in this example are mainly different from those in Example 2 in that: in this example, boric acid is used to modify sodium silicate, and absolute ethanol is added as a solvent during the modification process. After modification, a colloidal silicic acid and sodium salt that are insoluble in water and ethanol are obtained, and the sodium ions are dissolved in ethanol. Specifically, in this example, the mass ratio of sodium silicate Na 2 O·nSiO 2 relative to the aggregate is 4%, the boric acid ratio is 1%, the organic binder ratio is 0.7%, the nucleation aid ratio is 0.3%, and the added mass of absolute ethanol during the modification of sodium silicate accounts for 2% of the total mass of sodium silicate and boric acid.

[0112] Example 14

[0113] The cold-bonded pellets for reduction smelting in this example are mainly different from those in Example 3 in that: in this example, boric acid is used to modify sodium silicate, and absolute ethanol is added as a solvent during the modification process. After modification, a colloidal silicic acid and sodium salt that are insoluble in water and ethanol are obtained, and the sodium ions are dissolved in ethanol. Specifically, in this example, the mass ratio of sodium silicate Na 2 O·nSiO 2 relative to the aggregate is 4%, the boric acid ratio is 1%, the organic binder ratio is 0.7%, the nucleation aid ratio is 0.3%, and the added mass of absolute ethanol during the modification of sodium silicate accounts for 2% of the total mass of sodium silicate and boric acid.

[0114] Example 15

[0115] The cold-bonded pellets for reduction smelting in this example are mainly different from those in Example 10 in that: in the composite binder of this example, the organic binder is starch, and the nucleation aid is nano-aluminum oxide with a particle size of 100-200 nanometers; the addition amounts of the components in the binder are calculated as mass percentages of the aggregate. The mass ratio of sodium silicate Na 2 O·nSiO 2 (n is taken as 2.5) is 5%, the boric acid ratio is 2%, the organic binder ratio is 0.3%, the nucleation aid ratio is 0.1%, and the addition amount of absolute ethanol during the modification of sodium silicate accounts for 4% of the total mass of sodium silicate and boric acid.

[0116] The preparation method of the cold-bonded pellets in this example includes the following steps:

[0117] Step 1: Screen the sintered ore fines according to particle size classification and formulate according to particle size distribution;

[0118] Step 2: Perform pre-modification treatment on the sintered ore fines and sodium silicate in the composite binder respectively, where the mass of the silane coupling agent is 3% of the mass of the sintered ore fines;

[0119] Step 3: Mix the modified sinter return fines, magnetite concentrate, modified sodium silicate solution, organic binder and nucleating aid in proportion to prepare a mixture. At the same time, add an appropriate amount of pure water to the mixture, and the total amount of water added accounts for 9% of the total mass of the mineral raw materials.

[0120] Step 4: Use a pelletizing machine to prepare cold-bonded pellets.

[0121] The cold-pressed pellets are prepared by a ZYP-20TS full-automatic powder tabletting machine, with the setting of the forming pressure being 90 MPa, the die diameter being 20 mm, and the pressing time being 30 s.

[0122] Step 4: Dry the cold-bonded pellets under the condition of 110 °C for 7 h to obtain dry cold-bonded pellets.

[0123] Example 16

[0124] The cold-bonded pellets for reduction smelting in this example are mainly different from those in Example 10 in that in the composite binder of this example, the organic binder uses sodium carboxymethylcellulose and an organic resin binder (mixing mass ratio 1:1), the nucleating aid uses nano-silica and nano-aluminum oxide (mixing mass ratio 2:1), and the addition amount of each component in the binder is calculated based on the mass percentage of the aggregate. Sodium silicate Na 2 O·nSiO 2 accounts for 4.5%, formic acid accounts for 3%, the organic binder accounts for 0.5%, the nucleating aid accounts for 0.2%, and the addition amount of absolute ethanol when modifying sodium silicate accounts for 3% of the total mass of sodium silicate and formic acid.

[0125] The preparation method of the cold-bonded pellets in this example includes the following steps:

[0126] Step 1: Screen the sinter return fines according to particle size classification and formulate according to particle size distribution.

[0127] Step 2: Perform pre-modification treatment on the sinter return fines and sodium silicate in the composite binder respectively; the mass of the silane coupling agent is 4% of the mass of the sinter return fines.

[0128] Step 3: Mix the modified sinter return fines, magnetite concentrate, modified sodium silicate solution, organic binder and nucleating aid in proportion to prepare a mixture. At the same time, add an appropriate amount of pure water to the mixture, and the total amount of water added accounts for 5% of the total mass of the mineral raw materials.

[0129] Step 4: Use a pelletizing machine to prepare cold-bonded pellets.

[0130] The cold-pressed pellets are prepared by a ZYP-20TS full-automatic powder tabletting machine, with the setting of the forming pressure being 30 MPa, the die diameter being 20 mm, and the pressing time being 45 s.

[0131] Step 4: Place the cold-bonded pellets under the condition of 95°C and dry them for 9 h to obtain dry cold-bonded pellets.

[0132] The physical property parameters of the pellets obtained in Examples 10-16 are shown in Table 8 and Table 9 below. It can be seen from the table that by further modifying the sodium silicate in the binder, the sodium ions in the sodium silicate can be effectively removed, preventing excessive sodium ions from entering the blast furnace and having an adverse effect on blast furnace production.

[0133] Table 8 Comparison data of the wet ball strength of the pellets obtained in Examples 10-16

[0134]

[0135] Table 4 Comparison data of the dry ball compressive strength and sodium removal rate of the pellets obtained in Examples 10-16

[0136]

Claims

1. A cold-consolidated pellet for reduction smelting, characterized in that: The pellet raw material comprises aggregate and adhesive, wherein the aggregate comprises modified sintered return ore and magnetite concentrate, and the modified sintered return ore is obtained by modifying the sintered return ore with a modifier comprising a silane coupling agent; The adhesive comprises water glass, an organic adhesive and a nano-oxide particle nucleation aid, and at least part of the adhesive is connected to the surface of the sintered return ore through a silane coupling agent.

2. The cold-consolidated pellets for reduction smelting according to claim 1, characterized in that: The silane coupling agent comprises at least one of KH550, KH560 and KH570; and / or the mass of the silane coupling agent is 3-5% of the mass of the sintered ore.

3. The cold-consolidated pellets for reduction smelting according to claim 1, characterized in that: The modifier further comprises formic acid, and the mass of the formic acid is 4-6% of the mass of the sintered ore.

4. The cold-consolidated pellets for reduction smelting according to any one of claims 1 to 3, characterized in that: The grading index m of the aggregate is 0.4-0.6, and the mass ratio of the modified sintered return ore to the magnetite concentrate in the aggregate is (35-55):(45-65).

5. The cold-consolidated pellets for reduction smelting according to any one of claims 1 to 3, characterized in that: The mass of the adhesive is 5-9% of the total amount of aggregate; and / or the modulus of the water glass is 2.3 to 2.5; and / or the mass ratio of the water glass, the organic binder and the nano-oxide particle nucleation aid is (4-8.5): (0.3-0.7): (0.1-0.3); and / or the organic binder comprises one or more of sodium carboxymethyl cellulose, starch, and organic resin adhesives; and / or the particle size of the nano oxide particle nucleation aid is 50 to 200 nm; And / or the nano oxide particle nucleation aid comprises at least one of nano silicon dioxide and nano aluminum oxide.

6. The cold-consolidated pellets for reduction smelting according to any one of claims 1 to 3, characterized in that: The water glass adopts boric acid and / or formic acid modified water glass solution, and the modified water glass solution uses anhydrous ethanol as a solvent.

7. The cold-consolidated pellets for reduction smelting according to claim 6, characterized in that: The mass ratio of the boric acid and / or formic acid to water glass is (1-3):(4-5).

8. A method for preparing cold-consolidated pellets for reduction smelting according to any one of claims 1 to 7, characterized in that: include: The pellet raw materials including modified sintered return ore, magnetite concentrate and adhesive are subjected to cold pressing and pelletizing treatment to obtain cold consolidated pellets.

9. The preparation method according to claim 8, characterized in that: The modification process of the modified sintered return ore comprises: fully contacting / mixing the sintered return ore raw material with a silane coupling agent hydrolysis solution so that the silane coupling agent is grafted onto the surface of the sintered return ore; And / or the molding pressure of the cold pressing pelletizing is 30-90 MPa, and the pressing time is 30-45 s.

10. The preparation method according to claim 9, characterized in that: Also includes: Before the sintered return ore is modified by using a silane coupling agent, the sintered return ore is pretreated by using a formic acid modification solution.

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