1. A method for improving the bursting temperature of superfine magnetite concentrate pellets is characterized by comprising the following steps: mixing part of the superfine magnetite concentrate with the organic-inorganic composite binder and the modified pellet dust for the first time to obtain a primary mixture, mixing the rest of the superfine magnetite concentrate with the primary mixture for the second time to obtain a secondary mixture, and pelletizing the secondary mixture by a disc pelletizer; the modified pellet dust is obtained by wet grinding pellet dust, quick lime and ferrous salt.

2. The method for improving the bursting temperature of the ultrafine magnetite concentrate pellets according to claim 1, wherein the method comprises the following steps: the granularity of the superfine magnetite concentrate meets the following requirements: the mass proportion of the-0.074 mm size fraction accounts for 100%, and the mass proportion of the-0.025 mm size fraction is higher than 80%.

3. The method for improving the bursting temperature of the ultrafine magnetite concentrate pellets according to claim 1, wherein the method comprises the following steps: the mass of the quicklime is 2-5% of that of the pellet dust; the ferrous salt accounts for 0.5-1% of the mass of the pellet dust.

4. The method for improving the bursting temperature of the ultrafine magnetite concentrate pellets according to claim 1, wherein the method comprises the following steps: wet grinding the pellet dust, quicklime and ferrous salt until the granularity meets the following requirements: the mass proportion of the particle size fraction of-0.074 mm accounts for 50 percent.

5. The method for improving the bursting temperature of the ultrafine magnetite concentrate pellets according to claim 1, wherein the method comprises the following steps: the mass of the modified pellet dust is 0.5-1.0% of the total mass of the superfine magnetite concentrate.

6. The method for improving the bursting temperature of the ultrafine magnetite concentrate pellets according to claim 1, wherein the method comprises the following steps: the superfine magnetite concentrate in the primary mixture accounts for 20-30% of the total mass of the superfine magnetite concentrate, and the water content is controlled to be 6.0-7.5%.

7. The method for improving the bursting temperature of the ultrafine magnetite concentrate pellets according to claim 1, wherein the method comprises the following steps: and controlling the water content in the secondary mixture to be 8.5-9.0%.

8. The method for improving the bursting temperature of the ultrafine magnetite concentrate pellets according to claim 1, wherein the method comprises the following steps: the organic-inorganic composite binder is organic modified bentonite, the organic modifier in the organic modified bentonite is humic acid and pelidol, the mass percent of the humic acid in the organic modified bentonite is 5% -10%, and the mass percent of the pelidol is 10% -15%.

Background

The pellet is an ideal blast furnace raw material because of its excellent metallurgical properties and good mechanical strength. At present, the proportion of blast furnace ironmaking pellets in foreign countries exceeds 60 percent and even reaches 100 percent, but the proportion of blast furnace pellets in domestic is generally lower than 20 percent. The main reason is that the raw material supply of domestic high-grade high-quality iron ore concentrate for producing the pellets is insufficient, and the requirement of producing the pellets can be met only by multi-stage grinding-selecting to obtain the iron ore concentrate with high iron grade and low impurity content. However, the Mohs hardness of magnetite is only 5.5-6.5, which is lower than that of common gangue minerals such as quartz, garnet and the like, so that the magnetite is easy to be ground in the grinding process, the granularity of the obtained iron ore concentrate is too fine, and the green ball preparation is influenced. Extensive research in the field of preparation of oxidized pellets has shown that the surface area is about 2000cm²The grain size distribution of concentrate which is suitable for pelletizing is that the grain size of-200 meshes is more than 80 percent, and the rough or fine grain size is not beneficial to green pellet preparation and subsequent oxidizing roasting. In addition, the magnetite has poor surface hydrophilicity, and the high proportion of fine fraction in the iron ore concentrate can obviously influence the balling property of the pelletizing raw material. The raw material granularity is too fine, the internal structure composition of the green pellets becomes compact, the moisture is not beneficial to external diffusion in the drying process, and capillary force is generated when the moisture inside and outside the pellets is not uniformly diffused, so that the pellets are directly crushed and burst. Especially in the current mainstream grate-rotary kiln production process, if a large amount of pellets burst in the air draft drying section of the grate, the air permeability of the pellets in the preheating-roasting process is influenced, and further the subsequent processes of magnetite oxidation, consolidation and the like are influenced. When the green pellet bursting temperature is lower than 300 ℃, the smooth production of the pellets is seriously influenced.

Therefore, the development of the method for improving the burst temperature of the superfine magnetite concentrate pellet has great significance for optimizing the pellet preparation process and improving the quality of the oxidized pellet.

Disclosure of Invention

Aiming at the current production situations of large specific surface area, poor balling performance, low pellet bursting temperature and the like of the superfine magnetite concentrate in the prior art, the invention aims to provide the method for improving the pellet bursting temperature of the superfine magnetite concentrate, which can prepare green pellets with strength meeting the production requirement by optimizing process parameters, improving the surface hydrophilicity of magnetite and reducing green pellet moisture on the premise of not using a high-proportion binder, compared with the conventional process, the method can improve the green pellet bursting temperature by 70-110 ℃, is simple to operate, low in production cost and environment-friendly, and meets the industrial production requirement.

In order to achieve the technical purpose, the invention provides a method for improving the burst temperature of superfine magnetite concentrate pellets, which comprises the steps of uniformly mixing part of superfine magnetite concentrate with organic-inorganic composite binder and modified pellet dust for the first time to obtain a primary mixture, uniformly mixing the rest part of superfine magnetite concentrate with the primary mixture for the second time to obtain a secondary mixture, and pelletizing the secondary mixture by a disc pelletizer; the modified pellet dust is obtained by wet grinding pellet dust, quick lime and ferrous salt.

As a preferred scheme, the particle size of the superfine magnetite concentrate satisfies: the mass proportion of the-0.074 mm size fraction accounts for 100%, and the mass proportion of the-0.025 mm size fraction is higher than 80%. The superfine magnetite concentrate raw material related by the invention has the advantages of excessively fine granularity, poor surface hydrophilicity and difficult pelletizing, and the raw pellets become compact due to the internal structure composition in the process of preparing the pellet material, so that the external diffusion of moisture in the drying process is not facilitated, and when the moisture inside and outside the pellet is not uniformly diffused, capillary force is generated, so that the pellet is easily crushed and burst.

As a preferable scheme, the mass of the quicklime is 2-5% of that of the pellet dust; the ferrous salt accounts for 0.5-1% of the mass of the pellet dust. According to the technical scheme, quicklime and ferrous salt are added as activating agents, so that the surface activity of pellet dust activated by mechanical force can be enhanced in the wet grinding process, the surface bonding effect of mineral particles and a binder in the pelletizing process is improved, and the performance of the pellet dust participating in pelletizing is improved. The quicklime and ferrous salt have large specific surface area, good hydrophilicity, high surface activity and natural cementing capability. In the process of balling the mixed material particles, the particle spacing is reduced, the porosity is reduced, the contact angle of the bridge liquid on the particle surface is reduced, the molecular bonding force and the capillary force between the materials can be improved, and the balling speed is accelerated. Meanwhile, the plasticity of green pellets can be improved by adding quicklime, the ion dissociation of magnetite surfaces can be obviously improved by adding ferrous ions, the magnetite surfaces are bonded with binder molecules, the physical binding force and bonding effect between particles are mutually synergistic, and the green pellet strength is obviously improved. The ferrous salt is common ferrous salts such as ferrous nitrate.

As a preferred scheme, the pellet dust is wet-milled with quick lime and ferrous salt until the particle size satisfies the following conditions: the mass proportion of the particle size fraction of-0.074 mm accounts for 50 percent. According to the technical scheme, the compact distribution state among fine-grained magnetite particles in green pellets can be improved by controlling the dust grinding particle size, pellet size matching is improved by +0.074mm particles in the pellets, a channel for water vapor to diffuse outwards in the drying process is facilitated to be formed, and the dust grinding particle size control method has great significance for improving the pellet bursting temperature.

As a preferable scheme, the mass of the modified pellet dust is 0.5-1.0% of the total mass of the superfine magnetite concentrate. The pellet dust comes from the return powder of the pellet production field. The particle size of the pellet dust is coarser than that of the superfine magnetite concentrate, and after high-temperature roasting, the pellet dust shows that the pellet dust has more hydrophobic properties and is not suitable for pelletizing production, quicklime and ferrite are added as activating agents, in the wet grinding process, the surface activity of the pellet dust is activated by mechanical force, the surface bonding effect of mineral particles and binders in the pelletizing process is improved, the mineral particles can participate in pelletizing, the compact distribution state among fine-grained magnetite particles in green pellets can be improved by controlling the particle size of dust grinding, pellet size matching is improved in pellets by particles with the size of +0.074mm, the formation of a channel for water vapor external diffusion in the drying process is facilitated, the bursting temperature of the pellets is improved, but the adding proportion cannot be too high, and the performance of the pellets can be influenced.

As a preferable scheme, the superfine magnetite concentrate in the primary mixture accounts for 20-30% of the total mass of the superfine magnetite concentrate, and the water content is controlled to be 6.0-7.5%. A small part of superfine magnetite concentrate is mixed with the organic-inorganic composite binder uniformly in advance, so that the organic-inorganic composite binder is favorably dispersed in the whole superfine magnetite concentrate raw material, and the balling property of the concentrate is improved.

As a preferable scheme, the water content of the secondary mixture is controlled to be 8.5-9.0%.

According to the technical scheme, the moisture control of two-stage uniform mixing is adopted, so that the problems of insufficient uniform mixing, poor binder dispersibility and the like caused by overhigh raw material moisture are avoided, and the pellet bursting temperature can be optimized to a certain extent.

As a preferable scheme, the organic modifier in the organic modified bentonite is humic acid and pelidol, the humic acid content in the organic modified bentonite accounts for 5-10% by mass, and the pelidol content in the organic modified bentonite accounts for 10-15% by mass. Because the specific surface area of super magnetite concentrate is big, the granularity is thin, on the one hand, if adopt single organic binder inevitably to cause the inseparable bonding of partial magnetite concentrate granule, be unfavorable for dispersion and the evenly distributed of binder in the material, cause binder segregation in the material, unfavorable to the pelletization process, need improve the binder quantity, influence green ball intensity, on the other hand, super magnetite concentrate raw materials granularity is too thin, cause green ball inner structure to constitute and become closely knit, be unfavorable for the outer diffusion of drying process moisture, will produce the capillary force when the inhomogeneous diffusion of outside moisture in the pellet, thereby directly lead to the pellet breakage, burst. According to the technical scheme, the modified bentonite binder is preferably adopted, the inorganic bentonite is phyllosilicate, the modified bentonite binder has good water retention and a gap structure, a large amount of water is adsorbed in the pelletizing process, the situations of local over-wetting and the like are avoided, the binder is favorable for dispersing, the pelletizing property of the concentrate is improved, meanwhile, the main functional component of the bentonite is montmorillonite which is a natural phyllosilicate mineral, the volume is obviously expanded after water absorption, the modified bentonite binder has good stability and water retention in the drying process, and the pellet bursting can be relieved to a certain extent.

According to the technical scheme, the pellet bursting temperature is increased while the pelletizing performance of the superfine magnetite concentrate is improved by optimizing process parameters, improving the surface hydrophilicity of magnetite, reducing the green pellet moisture and improving the pellet size fraction matching on the premise of not using a high-proportion binder, the strength of the prepared green pellets meets the production requirement, and the bursting temperature is increased by 70-110 ℃. The key factors influencing the bursting temperature of the green pellets are the granularity of raw materials, moisture, the surface properties of minerals and the like, the surface of the natural magnetite concentrate is hydrophobic, the adhesion of the moisture is not facilitated, the bursting temperature of the green pellets in the drying process is relatively low, the superfine magnetite concentrate is too fine in granularity, the internal structure of the green pellets becomes compact in the process of preparing the pellet materials, the external diffusion of the moisture in the drying process is not facilitated, the capillary force is generated when the moisture inside and outside the pellet is unevenly diffused, and the pellet is easily and directly broken and burst. On one hand, the improvement of the technical scheme of the invention is that the organic-inorganic composite binder is introduced, the modified bentonite has good stability and water retention property in the drying process due to the obvious volume expansion after absorbing water, the pellet bursting can be relieved to a certain extent, and meanwhile, the modified bentonite absorbs a large amount of water in the pelletizing process, so that the occurrence of local over-wet and other conditions is avoided, thereby being beneficial to the dispersion of the binder and improving the pelletizing property of the concentrate; on the other hand, modified pellet dust is introduced, after special activation treatment, the pellet dust is good in surface performance and can be used as an iron-containing raw material to participate pelletizing, the particle size of the modified pellet is moderate, the particle size matching of materials can be improved by partial coarse fraction, the modified pellet dust is beneficial to the drying process of the pellet, and the pellet is effectively relieved from being broken and cracked at low temperature.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

1) the technical scheme of the invention has the greatest advantage that under the premise of not using a high-proportion binder, by means of the measures of optimizing process parameters, regulating and controlling the surface property of magnetite, controlling water, strengthening and mixing two sections, and the like, compared with the conventional process, the method can prepare the green pellets with the strength meeting the production requirement from the superfine magnetite concentrate, and simultaneously, the burst temperature of the green pellets is increased by 70-110 ℃.

2) The technical scheme provided by the invention is simple, low in cost and feasible in operation, does not increase new equipment, and meets the requirements of industrial production.

Detailed Description

The following examples are intended to further illustrate the present disclosure, but not to limit the scope of the claims.

Comparative example 1

The traditional process is adopted, the organic modified bentonite is used as a binder, and the materials are directly mixed.

The method comprises the following steps of taking a certain high-grade superfine magnetite concentrate as a raw material (the granularity is 100% in a proportion of-0.074 mm and 85% in a proportion of-0.025 mm), controlling the mass percent of humic acid serving as an organic modifier in organic modified bentonite to be 8.9%, controlling the mass percent of pelidol to be 13%, adding 1.5% of organic modified bentonite, uniformly mixing, adding a proper amount of water, preparing green pellets with the diameter of 8-12 mm in a disc pelletizer, wherein the green pellet moisture is 10.3%, the falling strength of the green pellets is 3.2 times (0.5m is one) -1, the compressive strength is 11.5N is one-1, and the bursting temperature of the green pellets is 300 ℃.

Comparative example 2

The pellet dust is directly added after being wet-milled.

Taking a certain high-grade superfine magnetite concentrate as a raw material (the granularity is 100 percent to 0.074mm, the proportion is 100 percent to 0.025mm, the proportion is 85 percent), controlling the mass percent content of humic acid serving as an organic modifier in the organic modified bentonite to be 8 percent and the mass percent content of pellitol to be 13 percent, and adding 1.5 percent of the organic modified bentonite and 0.7 percent of directly ground pellet dust (the granularity is 50 percent and is less than 0.074mm) into 20 percent of the mass percent of the raw material for pelletizing magnetite concentrate for one-time blending and strong uniform mixing; then, the partial material and the iron ore concentrate with the rest proportion are mixed uniformly for the second time, and the mixture is adjusted to be proper in moisture content; controlling the moisture content of the primary mixing to be 7 percent and the moisture content of the secondary mixing to be 9 percent, finally preparing the mixed material into green pellets with the diameter of 8-12 mm in a disc pelletizer, and controlling the falling strength of the green pellets to be 3.6 times (0.5 m. pieces)^-1Compressive strength of 12.5 N.^-1The green pellet burst temperature was 295 ℃.

Comparative example 3

Only quicklime is added to modify the pellet dust.

Taking a certain high-grade superfine magnetite concentrate as a raw material (the granularity is 100 percent in a proportion of 0.074mm and 85 percent in a proportion of 0.025 mm), controlling the mass percent content of humic acid serving as an organic modifier in the organic modified bentonite to be 8 percent and the mass percent content of pellitol to be 13 percent, and adding 1.5 percent of the organic modified bentonite and 0.7 percent of pretreated pellet dust into 20 percent of the raw material mass fraction of the pelletizing magnetite concentrate for primary batching and strong mixing; the pellet dust pretreatment mode is that 2 percent of quicklime is added and then wet grinding is carried out until the granularity is 50 percent and is less than 0.074 mm; then, the partial material and the iron ore concentrate with the rest proportion are mixed uniformly for the second time, and the mixture is adjusted to be proper in moisture content; controlling the moisture content of the primary mixing to be 7 percent and the moisture content of the secondary mixing to be 9 percent, finally preparing the mixed material into green pellets with the diameter of 8-12 mm in a disc pelletizer, and controlling the falling strength of the green pellets to be 3.5 times (0.5 m. pieces)^-1Compressive strength of 11.2 N.^-1Green pellet burst temperature 293 ℃.

Comparative example 4

Only ferrous nitrate is added to modify the pellet dust.

Taking a certain high-grade superfine magnetite concentrate as a raw material (the granularity is 100 percent in a proportion of 0.074mm and 85 percent in a proportion of 0.025 mm), controlling the mass percent content of humic acid serving as an organic modifier in the organic modified bentonite to be 8 percent and the mass percent content of pellitol to be 13 percent, and adding 1.5 percent of the organic modified bentonite and 0.7 percent of pretreated pellet dust into 20 percent of the raw material mass fraction of the pelletizing magnetite concentrate for primary batching and strong mixing; the pellet dust pretreatment mode is that 1 percent of ferrous nitrate is added and then wet grinding is carried out until the granularity of 50 percent is less than 0.074 mm; then, the partial material and the iron ore concentrate with the rest proportion are mixed uniformly for the second time, and the mixture is adjusted to be proper in moisture content; controlling the moisture content of the primary mixing to be 7 percent and the moisture content of the secondary mixing to be 9 percent, finally preparing the mixed material into green pellets with the diameter of 8-12 mm in a disc pelletizer, and controlling the falling strength of the green pellets to be 3.7 times (0.5 m. pieces)^-1Compressive strength of 11.9 N.^-1The green pellet burst temperature was 288 ℃.

Comparative example 5

All raw materials are mixed in one stage.

Taking a certain high-grade superfine magnetite concentrate as a raw material (the granularity is 100 percent in a proportion of 0.074mm and 85 percent in a proportion of 0.025 mm), controlling the mass percent of humic acid serving as an organic modifier in the organic modified bentonite to be 8 percent and the mass percent of pellitol to be 13 percent, adding 1.5 percent of the organic modified bentonite and 0.7 percent of the pretreated pellet dust, and strongly mixing and uniformly mixing; the pellet dust pretreatment mode is that 2 percent of quicklime and 1 percent of ferrous nitrate are added and then wet-milled until the granularity of 50 percent is less than 0.074 mm; then adding a proper amount of water into the mixed material, and preparing the raw pellets with the diameter of 8-12 mm in a disc pelletizer, wherein the water content of the raw pellets is 9.8 percent, and the falling strength of the raw pellets is 3.2 times (0.5 m. pieces)^-1Compressive strength of 10.3 N.^-1And green pellet burst temperature of 285 ℃.

Example 1

Taking a certain high-grade superfine magnetite concentrate as a raw material (the granularity is 100 percent to 0.074mm, the proportion is 100 percent to 0.025mm, the proportion is 85 percent), controlling the mass percent of humic acid serving as an organic modifier in the organic modified bentonite to be 8 percent and the mass percent of pellitol to be 13 percent, and mixing 20 percent of the mass percent of the raw material for pelletizing magnetite concentrate with pretreated pellet dust of 0.5 percent and 0.9 percent of the modified bentonite for one time and mixing the mixture by strong force; the pellet dust pretreatment mode is that 2 percent of quicklime and 1 percent of ferrous nitrate are added and then wet-milled until the granularity of 50 percent is less than 0.074 mm; then, the partial material and the iron ore concentrate with the rest proportion are mixed uniformly for the second time and are adjusted to proper pelletizing moisture; the water content of the primary mixing is controlled to be 7.5 percent, and the water content of the secondary mixing is controlled to be 9.0 percent. Finally, the uniformly mixed material is put into a disc pelletizer to prepare green pellets with the diameter of 8-12 mm, the moisture of the green pellets is 9.5 percent, and the falling strength of the green pellets is 3.6 times (0.5 m. pieces)^-1Compressive strength of 12.5 N.^-1And green pellet bursting temperature of 370 ℃.

Example 2

The high-grade superfine magnetite concentrate is used as raw material (granularity-0.074 mm is 100%, -0.025mm is 85%), the water content of raw material is 8.9%, and the organic content in organic modified bentonite is controlled5 percent of modifier humic acid and 15 percent of Pelidol, and mixing 30 percent of raw material mass fraction of the pelletizing magnetite concentrate with 1.0 percent of pretreated pellet dust and 1.0 percent of modified bentonite for one-time blending and strong mixing; the pellet dust pretreatment mode is that 5 percent of quicklime and 0.5 percent of ferrous nitrate are added and then wet-milled until the granularity of 50 percent is less than 0.074 mm; then, the partial material and the iron ore concentrate with the rest proportion are mixed uniformly for the second time and are adjusted to proper pelletizing moisture; the water content of the primary mixing is controlled to be 6.0 percent, and the water content of the secondary mixing is controlled to be 8.5 percent. Finally, the uniformly mixed material is put into a disc pelletizer to prepare green pellets with the diameter of 8-12 mm, the moisture of the green pellets is 9.8 percent, and the falling strength of the green pellets is 3.4 times (0.5 m. pieces)^-1Compressive strength of 12.8 N.^-1Green pellet burst temperature 395 ℃.

Example 3

Taking a certain high-grade superfine magnetite concentrate as a raw material (the granularity is 100 percent in a proportion of 0.074mm and 90 percent in a proportion of 0.025 mm), controlling the mass percent content of humic acid serving as an organic modifier in the organic modified bentonite to be 10 percent and the mass percent content of pellitol to be 10 percent, and carrying out primary burdening, strong mixing and uniform mixing on 25 percent of the mass fraction of the raw material of the pelletizing magnetite concentrate, 0.75 percent of pre-treated pellet dust and 0.8 percent of modified bentonite; the pellet dust pretreatment mode is that after 4 percent of quicklime and 0.7 percent of ferrous nitrate are added, wet grinding is carried out until the granularity of 50 percent is less than 0.074 mm; then, the partial material and the iron ore concentrate with the rest proportion are mixed uniformly for the second time and are adjusted to proper pelletizing moisture; the water content of the primary mixing is controlled to be 7.0 percent, and the water content of the secondary mixing is controlled to be 8.7 percent. Finally, the uniformly mixed material is put into a disc pelletizer to prepare green pellets with the diameter of 8-12 mm, the moisture of the green pellets is 9.6 percent, and the falling strength of the green pellets is 3.6 times (0.5 m. pieces)^-1Compressive strength of 11.6 N.^-1The green pellet burst temperature is 398 ℃.

Example 4

Taking a certain high-grade superfine magnetite concentrate as a raw material (the granularity is 100 percent in a proportion of 0.074mm and 90 percent in a proportion of 0.025 mm), controlling the content of organic modifier humic acid in the organically modified bentonite according to the mass percent, wherein the water content of the raw material is 8.9 percent10 percent of the raw material, 13 percent of the pellitorin in percentage by mass, and mixing 20 percent of the mass fraction of the raw material of the pelletizing magnetite concentrate with 0.70 percent of the pretreated pellet dust and 0.9 percent of the modified bentonite for one time, strongly mixing and uniformly mixing; the pellet dust pretreatment mode is that 3 percent of quicklime and 0.8 percent of ferrous nitrate are added and then wet-milled until the granularity of 50 percent is less than 0.074 mm; then, the partial material and the iron ore concentrate with the rest proportion are mixed uniformly for the second time and are adjusted to proper pelletizing moisture; the water content of the primary mixing is controlled to be 6.5 percent, and the water content of the secondary mixing is controlled to be 8.8 percent. Finally, the uniformly mixed material is put into a disc pelletizer to prepare green pellets with the diameter of 8-12 mm, the moisture of the green pellets is 9.4 percent, and the falling strength of the green pellets is 3.7 times (0.5 m. pieces)^-1Compressive strength of 13.2 N.^-1Green pellet burst temperature 386 ℃.