Method for preparing pellets from high pressure roll activated fines and concentrates

Abstract

The application discloses a method for preparing pellets by activating fine ore and concentrate with high-pressure roller mills. The method is to perform first-stage high-pressure roller mill activation treatment on the fine ore, screen out a particle size less than 1 mm and mix the fine ore with the iron concentrate by strong mixing to obtain mixed ore; the mixed ore is subjected to second-stage high-pressure roller mill activation treatment to obtain edge material and medium material; the edge material is returned to the second-stage high-pressure roller mill activation treatment, and the medium material is mixed with a binder and then sequentially subjected to pelletizing, preheating and roasting, so that the pellet ore is obtained. The method realizes efficient activation of multi-element iron-containing raw materials such as 'fine ore + concentrate' through two-stage high-pressure roller mill gradient activation, avoids the problems of over-pulverization or poor activation effect of part of the iron-containing raw materials, improves the quality of the pellet ore, reduces the energy consumption in the pellet production process, and has important significance for expanding the types of iron-containing raw materials of the pellet ore and promoting cost reduction and benefit increase of the pellet industry.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel smelting iron ore pellet preparation, and relates to a method for preparing pellets from high-pressure roller-milled activated fine ore and concentrate. BACKGROUND

[0002] The pellet manufacturing process has the advantages of low energy consumption, low carbon and pollution emissions. The pellet iron grade is high, the strength is good, and the metallurgical performance is excellent. It is not only an important raw material for long process ironmaking, but also a main raw material for short process ironmaking. At present, magnetite concentrate is the main raw material for preparing pellets. With the increase of pellet output and the increase of the proportion of pellets into the furnace, the mining and purchasing cost of high-iron low-silicon high-quality magnetite is increasing. Therefore, broadening the types of iron ore resources and reducing the cost of using ore are the key to supporting the development of the pellet industry.

[0003] The chemical composition of limonite, hematite and other iron ore resources meets the requirements of pellets, and the reserves are abundant and the price is low. Using part of them to replace magnetite to prepare pellets can meet the requirements of economy and product quality. However, most of these iron ore resources have the problems of coarse particle size, small specific surface area and poor balling performance, and need to be pretreated. High-pressure roller milling is an extrusion discharge type pellet pretreatment process that uses layering crushing principle. It can improve the specific surface area of iron-containing raw materials and increase the surface activity, and has the characteristics of selective crushing, high operating capacity and low energy consumption. It has been widely used in the pellet production process.

[0004] In the high-pressure roller milling process, the mutual extrusion effect between particles is the key to affecting the activation effect of roller milling. However, for the multi-element iron-containing raw material system of "fine ore + concentrate", there are great differences in the physical and chemical properties, surface activation energy and internal microcrack expansion stress between limonite, hematite and other fine ores and concentrates. Therefore, their respective suitable roller milling systems and process parameters are different. For example, the suitable roller milling pressure of fine ore is higher, and the suitable moisture content is lower, while the suitable roller milling moisture content of concentrate is higher, but the roller milling pressure should not be too high. If fine ore and concentrate are mixed and high-pressure roller-milled together, there are problems such as over-pulverization or insufficient activation of part of the iron-containing raw materials, and serious particle adhesion and aggregation. When fine ore and concentrate are independently high-pressure roller-milled, there are problems such as long process flow, increased cost and energy consumption.

[0005] Therefore, it is necessary to find a high-efficiency high-pressure roller milling activation method suitable for the multi-element iron-containing raw material system of "fine ore + concentrate", to ensure that the activation degree of concentrate and fine ore is suitable, so as to improve the roller milling efficiency and reduce the roller milling energy consumption. Further, it can improve the quality of pellets, reduce the energy consumption of pellet production, and has important significance for expanding the types of iron-containing raw materials for pellets and promoting the cost reduction and efficiency improvement of the pellet industry. SUMMARY

[0006] The application aims to provide a method for preparing pellets by high-pressure roller milling and activating fine ore and concentrate, which preferentially performs high-pressure roller milling pre-activation on the fine ore, and then performs high-pressure roller milling activation on the pre-activated fine ore and the concentrate after mixing, so as to realize multi-element iron-containing raw material high-efficiency activation through two-stage high-pressure roller milling, and make the activation degree of the fine ore and the concentrate both suitable, thereby improving the roller milling efficiency, reducing the roller milling energy consumption, being beneficial to improving the pellet quality, and reducing the pellet production energy consumption.

[0007] In order to achieve the above technical purposes, the technical scheme adopted by the application is:

[0008] The method for preparing pellets by high-pressure roller milling and activating fine ore and concentrate, and the key process steps are:

[0009] 1) performing first-stage high-pressure roller milling activation treatment on the fine ore, and screening out a particle size less than 1 mm grade and iron concentrate through strong mixing to obtain mixed ore; the fine ore is at least one of limonite and / or hematite, the particle size of the fine ore is not more than 5 mm, and the mass fraction of the particle size less than 3 mm grade is not less than 70%.

[0010] 2) performing second-stage high-pressure roller milling activation treatment on the mixed ore to obtain edge material and medium material; the moisture content of the mixed ore is controlled to be 5.5-7.0 wt.% before performing the second-stage high-pressure roller milling treatment.

[0011] 3) returning the edge material to the second-stage high-pressure roller milling activation treatment, mixing the medium material with a binder, and then sequentially performing pelletizing, preheating and roasting to obtain the pellet ore; the binder is at least one of bentonite, sodium humate and sodium carboxymethyl cellulose, and the mass of the binder is 0.05%-2% of the mass of the medium material; the pelletizing time is 10-14 min, the moisture content of the green ball is controlled to be 7.5-8.5 wt.%, and the green ball particle size is 11-14 mm; the preheating temperature is 920-940℃, the preheating time is 8-12 min; and the roasting temperature is 1230-1250℃, and the roasting time is 10-15 min.

[0012] Further, the water content of the fine ore in step 1) is controlled to be 3-4 wt.% before performing the first-stage high-pressure roller milling activation treatment.

[0013] Further, the first-stage high-pressure roller milling activation treatment in step 1) is performed under the following conditions: projection pressure is 3.5-4.2 MPa, circular roller rotating speed is 23-26 r / min, and roller spacing is 2-4 mm.

[0014] Further, the mass percentage composition of the fine ore and the iron concentrate in the mixed ore in step 1) is 20-40%:60-80%; the mass fraction of the particle size less than 74 μm in the iron concentrate is not less than 70%, the specific surface area is greater than 1200 cm 2 / g.

[0015] Further: the condition of the high-pressure roller mill activation treatment in the second step) is that the projection pressure is 1.8-2.5 MPa, the circular roller rotation speed is 20-23 r / min, the mass proportion of the circulating edge material is 30-40%, and the roller spacing is 1-2 mm.

[0016] Invention principle:

[0017] The key of the technical scheme of the present application is that according to the roller milling characteristics of the fine ore and the iron concentrate, the fine ore and the iron concentrate are activated in a two-stage high-pressure roller milling mode to realize efficient activation of the multi-element iron-containing raw material, so that the activation degree of the fine ore and the concentrate is appropriate, thereby improving the roller milling efficiency and reducing the roller milling energy consumption, and the activated multi-element iron-containing raw material can reduce the preheating and roasting energy consumption. The present application preferentially performs the first-stage high-pressure roller milling pre-activation on the fine ore, mainly based on the poor hydrophilicity and reaction activity of the fine ore and the high stress required for crack propagation, crack propagation, crushing and preliminary activation mainly occur in the pre-activation stage, the matching of the fine ore and the iron concentrate after the pre-activation treatment is improved, and the fine ore and the iron concentrate can be mixed and then subjected to high-pressure roller milling activation treatment, and the second-stage high-pressure roller milling activation mainly occurs grain interface modification, surface activation energy reduction and generation of internal micro-cracks, which can greatly improve the reaction activity of the iron-containing raw material. Especially, the edge material circulation in the second-stage high-pressure roller milling activation process can solve the problem of uneven distribution of roller surface pressure, i.e. large in the middle and small at both sides, which is beneficial to the full activation of the mixed ore. The present application can avoid the local over-pulverization or insufficient activation of the fine ore and the iron concentrate by adopting the step-by-step activation mode, so that the activation degree of the fine ore and the concentrate is appropriate, thereby improving the roller milling efficiency and reducing the roller milling energy consumption. In addition, the pre-activated fine ore with a particle size less than 1 mm is screened out and mixed with the iron concentrate, and then subjected to the second-stage high-pressure roller milling activation, so that the concentrate particles and the pre-activated fine ore particles are in full contact and uniform distribution, thereby forming a more uniform, dense and reasonable particle packing structure in the high-pressure roller milling layering and crushing process, which is beneficial to the efficient and full activation of the fine ore and the concentrate and improves the roller milling efficiency.

[0018] The water content of the fine ore is controlled to be 3-4 wt.% before the first-stage high-pressure roller milling activation treatment. The water content should not be too high when the fine ore is pre-activated by high-pressure roller milling. On the one hand, based on the low maximum capillary water content of the fine ore, the high water content significantly increases the plastic deformation of the layering and crushing process, thereby reducing the roller milling activation efficiency. On the other hand, too high water content will cause particle aggregation and bonding, which is not conducive to subsequent screening.

[0019] The conditions of the first-stage high-pressure roller mill activation treatment are that the projection pressure is 3.5-4.2 MPa, the rotating speed of the circular roller is 23-26 r / min, and the roller spacing is 2-4 mm. Since the crack propagation stress of the fine ore particles is large and the surface activation energy is high, sufficient roller mill pressure is required. Maintaining a certain roller spacing can reduce the wear of the coarse ore particles on the roller surface while not affecting the interaction between the particles in the extrusion process of the material layer. The activation treatment of the fine ore by the high-pressure roller mill can make the fine ore particles crack, break and be preliminarily activated, and the matching with the iron concentrate is improved, which is beneficial to the subsequent second-stage high-pressure roller mill activation.

[0020] After the first-stage high-pressure roller mill treatment of the fine ore, the particle size of the fine ore is greater than 1 mm, and the particle size of the fine ore is less than 1 mm. The fine ore and the iron concentrate are uniformly mixed to make the mass percentage composition of the fine ore and the iron concentrate in the mixed ore (20%-40%) / (60%-80%). On the one hand, returning the particle size of the fine ore greater than 1 mm to the first-stage high-pressure roller mill is beneficial to fully exert the pre-activation effect. On the other hand, the fine ore with a particle size less than 1 mm and the iron concentrate are uniformly mixed to make the particles of the fine ore and the pre-activated fine ore particles fully contact and uniformly distribute. Further controlling the ratio of the fine ore and the iron concentrate in the appropriate range is beneficial to the formation of a more dense and reasonable particle packing structure in the material cake in the high-pressure roller mill layering crushing process, the transmission and action of the roller surface pressure in the material cake are strengthened, and the activation efficiency is improved.

[0021] The moisture content of the mixed ore is controlled to be 5.5-7.0 wt.% before the second-stage high-pressure roller mill treatment. After the first-stage high-pressure roller mill pre-activation, the surface free energy of the fine ore increases, and the hydrophilic performance of the particles is enhanced. Increasing the moisture content in the appropriate range can increase the molecular and capillary forces between the particles, so that greater inter-particle shear stress can be obtained in the high-pressure roller mill process, and the activation efficiency is improved.

[0022] The conditions of the second-stage high-pressure roller mill activation treatment are that the projection pressure is 1.8-2.5 MPa, the rotating speed of the circular roller is 20-23 r / min, the mass percentage of the circulating edge material is 30-40%, and the roller spacing is 1-2 mm. The appropriate roller mill pressure of the mixed ore should not be too high, otherwise there is a problem of over-crushing, which makes the densification degree of the activated iron-containing raw material increase, and the thermal stability is poor. In addition, circulating a proper proportion of the edge material in the second-stage high-pressure roller mill activation treatment process can solve the problem of uneven distribution of the roller surface pressure, which is beneficial to the full activation of the mixed ore, but too high a circulating proportion also has the problems of over-crushing and reduced work efficiency. In addition, reducing the roller spacing in the appropriate range is beneficial to the interaction between the particles in the layering crushing process.

[0023] The mixing process of the medium material and the binder is realized by a strong mixer. The paddle rotation speed of the strong mixer is 700-1200 r / min. It is necessary to use the strong mixer and maintain sufficient paddle rotation speed, which is beneficial to fully disperse the roll-milled cake and mix the binder and the iron-containing raw material uniformly, and can improve the stability of the chemical composition and quality index of the pellet. However, too fast paddle rotation speed can reduce the service life, and the pellet material is more likely to stick to the side wall.

[0024] Based on the roll-milling characteristics of the fine ore and the concentrate, the two-stage high-pressure roll-milling gradient activation method is adopted, and further combined with appropriate roll-milling, balling, preheating and roasting process systems and parameters, the efficient activation of the multi-element iron-containing raw material of the "fine ore + concentrate" can be realized, the problems of over-crushing or insufficient activation degree can be avoided, the roll-milling process flow is reduced, the adverse effects of the fine ore on the pellet preparation are solved, and the energy consumption in the production process can be reduced under the premise of ensuring the quality of the pellet. Compared with the prior art, the advantages of the present application are:

[0025] (1) The high-pressure roll-milling activation process of the fine ore and the iron concentrate in the present application is mainly based on the roll-milling characteristics of the fine ore and the iron concentrate. The key is to first pre-activate the fine ore by high-pressure roll-milling, then mix the pre-activated fine ore with the concentrate, and then perform high-pressure roll-milling activation. The fine ore and the iron concentrate are subjected to gradient activation by two-stage high-pressure roll-milling, efficient activation of multi-element iron-containing raw material is realized, the problems of local over-crushing or poor and uneven activation of the fine ore and the iron concentrate are effectively avoided, the activation degree of the two is suitable, the activation degree of the fine ore and the iron concentrate is suitable, and the roll-milling efficiency is improved, the roll-milling process flow is reduced, the roll-milling energy consumption is reduced, and the pellet quality is improved and the pellet production energy consumption is reduced.

[0026] (2) The process system and parameters of the first-stage high-pressure roll-milling in the present application are set based on the characteristics of the fine ore in terms of interfacial physical and chemical properties, surface activation energy, and stress required for internal micro-crack propagation. The use of higher roll-milling projection pressure, lower feed moisture, and reasonable control of roll spacing, combined with the inspection and screening process, can make the pre-activation more efficient and sufficient. Among them, controlling the moisture content of the fine ore is beneficial to improving the mechanical activation effect on the one hand, and on the other hand, it can avoid the aggregation and sticking of the roll-milled cake, thereby affecting the subsequent inspection and screening.

[0027] (3) In the present application, the fine ore with a particle size less than 1 mm is screened out, the iron concentrate and the pre-activated fine ore are subjected to strong mixing, and then the second-stage high-pressure roll-milling is performed, so that the concentrate particles and the pre-activated fine ore particles are in full contact and uniform distribution, thereby forming a more uniform, dense and reasonable particle packing structure during the high-pressure roll-milling layering crushing process, which is beneficial to the efficient and sufficient activation of the fine ore and the concentrate, and improves the roll-milling efficiency.

[0028] (4) After two-stage high-pressure roller grinding activation, the interaction force between the iron-containing raw material particles is enhanced, and the surface free energy is increased, and the reaction activity is improved. This improves the quality of green balls, is also beneficial to the oxidation and consolidation of the pellets, and can reduce the adverse effects of powder ore on the pellets. And it makes it possible to reduce the amount of organic binder, the amount of binder and the preheating and roasting temperature, which is beneficial to the preparation of higher quality pellets and reduces the energy consumption of pellet production. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 Process flow chart for preparing pellets from high-pressure roller grinding activated powder ore and concentrate. DETAILED DESCRIPTION

[0030] The following examples and comparative examples will be further described.

[0031] The particle size distribution of the iron-containing raw material used in the method of preparing pellets from high-pressure roller grinding activated powder ore and concentrate is shown in Table 1.

[0032] Table 1 Particle size composition of iron-containing raw material / wt.%

[0033] Example 1

[0034] The hematite powder was controlled to have a moisture content of 3%, and was subjected to first-stage high-pressure roller grinding treatment at a projection pressure of 3.5 MPa, a circular roller speed of 23 r / min, and a roller gap of 4 mm. After roller grinding, the particle size greater than 1 mm was returned to the first-stage high-pressure roller grinding, and the particle size less than 1 mm was mixed with the magnetite concentrate in a ratio of 3:7, and then the moisture content was adjusted to 5.5% for second-stage high-pressure roller grinding treatment at a projection pressure of 1.8 MPa, a circular roller speed of 23 r / min, and a roller gap of 1 mm. The edge material after roller grinding was returned to the second-stage high-pressure roller grinding, and the obtained medium material was the activated iron-containing raw material.

[0035] The activated iron-containing raw material was mixed with 1.2% by mass of bentonite in a high-speed mixer at a paddle speed of 1200 r / min. The mixed pellet raw material was prepared into 11-14 mm green balls, with a balling time of 12 min and a green ball moisture content of 8.0%. The green ball had a drop strength of 4.8 times / 0.5 m, a compressive strength of 14.7 N / piece, and a burst temperature of 475°C. Under the conditions of preheating at 940°C for 8 min and roasting at 1250°C for 12 min, the preheated pellet had a strength of 465 N, and the roasted pellet had a strength of 2753 N. Example 2

[0036] The limonite powder is controlled to have a moisture of 4%, and is subjected to a first-stage high-pressure roller grinding treatment, a projection pressure of 4 MPa, a circular roller rotation speed of 26 r / min, and a roller spacing of 2 mm. After the roller grinding, a particle size of greater than 1 mm is screened out and returned to the first-stage high-pressure roller grinding, and a particle size of less than 1 mm is mixed with the magnetite concentrate at a ratio of 2:8, and then the moisture is adjusted to 7% to perform a second-stage high-pressure roller grinding treatment, a projection pressure of 2.2 MPa, a circular roller rotation speed of 20 r / min, a side material circulation ratio of 30%, and a roller spacing of 1 mm. After the roller grinding, the side material is returned to the second-stage high-pressure roller grinding, and the obtained medium material is the activated iron-containing raw material.

[0037] The activated iron-containing raw material is mixed with bentonite at a mass fraction of 2% in a strong mixer at a paddle rotation speed of 700 r / min. The mixed pellet raw material is prepared into green balls of 11-14 mm, a balling time of 10 min, and a green ball moisture of 8.5%. The obtained green ball has a drop strength of 5.3 times / 0.5 m, a compressive strength of 15.2 N / piece, and a shatter temperature of 488°C. Under the conditions of preheating at 940°C for 12 min and roasting at 1230°C for 10 min, the preheated ball has a strength of 482 N, and the roasted ball has a strength of 2831 N. Example 3

[0038] The hematite powder is controlled to have a moisture of 3.5%, and is subjected to a first-stage high-pressure roller grinding treatment, a projection pressure of 4.2 MPa, a circular roller rotation speed of 23 r / min, and a roller spacing of 4 mm. After the roller grinding, a particle size of greater than 1 mm is screened out and returned to the first-stage high-pressure roller grinding, and a particle size of less than 1 mm is mixed with the magnetite concentrate at a ratio of 4:6, and then the moisture is adjusted to 6% to perform a second-stage high-pressure roller grinding treatment, a projection pressure of 2.5 MPa, a circular roller rotation speed of 20 r / min, a side material circulation ratio of 40%, and a roller spacing of 1 mm. After the roller grinding, the side material is returned to the second-stage high-pressure roller grinding, and the obtained medium material is the activated iron-containing raw material.

[0039] The activated iron-containing raw material is mixed with sodium carboxymethyl cellulose at a mass fraction of 0.08% and bentonite at a mass fraction of 0.5% in a strong mixer at a paddle rotation speed of 1200 r / min. The mixed pellet raw material is prepared into green balls of 11-14 mm, a balling time of 14 min, and a green ball moisture of 7.5%. The obtained green ball has a drop strength of 4.5 times / 0.5 m, a compressive strength of 14.1 N / piece, and a shatter temperature of 515°C. Under the conditions of preheating at 920°C for 12 min and roasting at 1250°C for 15 min, the preheated ball has a strength of 455 N, and the roasted ball has a strength of 2622 N. Example 4

[0040] The hematite powder is controlled to have a water content of 3.5%, and is subjected to the first-stage high-pressure roller milling treatment, with a projection pressure of 4.2 MPa, a round roller rotating speed of 23 r / min, and a roller spacing of 4 mm. After the roller milling, the particle size of more than 1 mm is returned to the first-stage high-pressure roller milling, and the hematite with a particle size of less than 1 mm is mixed with the magnetite concentrate at a ratio of 4:6, and then the water content is adjusted to 6.5% for the second-stage high-pressure roller milling treatment, with a projection pressure of 2.5 MPa, a round roller rotating speed of 20 r / min, a side material circulation ratio of 40%, and a roller spacing of 2 mm. After the roller milling, the side material is returned to the second-stage high-pressure roller milling, and the obtained medium material is the activated iron-containing raw material.

[0041] The activated iron-containing raw material is mixed with 0.05% sodium humate by mass fraction in a strong mixer with a paddle rotating speed of 1200 r / min. The mixed pellet raw material is prepared into green balls with a size of 11-14 mm, with a balling time of 12 min and a green ball water content of 8.5%. The obtained green ball has a drop strength of 5.5 times / 0.5 m, a compressive strength of 12.8 N / piece, and a shatter temperature of 477 ℃. Under the conditions of preheating at 940 ℃ for 12 min and roasting at 1250 ℃ for 15 min, the preheated ball has a strength of 472 N, and the roasted ball has a strength of 2553 N.

[0042] Comparative Example 1

[0043] The hematite powder is controlled to have a water content of 3%, and is subjected to the first-stage high-pressure roller milling treatment, with a projection pressure of 3.5 MPa, a round roller rotating speed of 23 r / min, and a roller spacing of 4 mm. After the roller milling, the particle size of more than 1 mm is returned to the first-stage high-pressure roller milling, and the water content of the particle size of less than 1 mm is adjusted to 5.5% for the second-stage high-pressure roller milling treatment, with a projection pressure of 1.8 MPa, a round roller rotating speed of 23 r / min, a side material circulation ratio of 30%, and a roller spacing of 1 mm. After the roller milling, the side material is returned to the second-stage high-pressure roller milling, and the obtained medium material is the activated hematite.

[0044] The magnetite concentrate is mixed with the activated hematite at a ratio of 7:3, and is mixed with 1.2% bentonite by mass fraction in a strong mixer with a paddle rotating speed of 1200 r / min. The mixed pellet raw material is prepared into green balls with a size of 11-14 mm, with a balling time of 12 min and a green ball water content of 8.0%. The obtained green ball has a drop strength of 3.6 times / 0.5 m, a compressive strength of 10.7 N / piece, and a shatter temperature of 407 ℃. Under the conditions of preheating at 940 ℃ for 8 min and roasting at 1250 ℃ for 12 min, the preheated ball has a strength of 368 N, and the roasted ball has a strength of 2352 N.

[0045] Comparative Example 1, only the two-stage high-pressure roller mill activation is carried out on the fine ore. The cake structure formed in the high-pressure roller mill lamination crushing process in the second stage is relatively loose, and part of the roller surface pressure is on the air discharge between the fine ore particles and the cake compaction, so that the iron-containing raw material is not fully activated, the strength of the prepared green ball is reduced, the burst temperature is reduced, and the strength of the preheated ball and the calcined ball is also lower.

[0046] Comparative Example 2:

[0047] The hematite powder is controlled to have a water content of 3%, and is subjected to the first-stage high-pressure roller mill treatment, with a projection pressure of 3.5 MPa, a circular roller speed of 23 r / min, and a roller spacing of 4 mm. After the roller milling, the particle size greater than 1 mm is returned to the first-stage high-pressure roller mill, and the particle size less than 1 mm is adjusted to have a water content of 5.5%, and then is subjected to the second-stage high-pressure roller mill treatment, with a projection pressure of 1.8 MPa, a circular roller speed of 23 r / min, a side material circulation ratio of 30%, and a roller spacing of 1 mm. After the roller milling, the side material is returned to the second-stage high-pressure roller mill, and the obtained middle material is the activated hematite. The magnetite concentrate is controlled to have a water content of 5.5%, and is subjected to the high-pressure roller mill treatment, with a projection pressure of 1.8 MPa, a circular roller speed of 23 r / min, a side material circulation ratio of 30%, and a roller spacing of 1 mm. The obtained middle material is the activated magnetite concentrate.

[0048] The activated magnetite concentrate and the activated hematite are mixed in a ratio of 7:3, and then are mixed with bentonite having a mass fraction of 1.2% in a strong mixer with a paddle speed of 1200 r / min. The mixed balling raw material is prepared into green balls having a diameter of 11-14 mm, with a balling time of 12 min and a green ball water content of 8.0%. The green ball has a drop strength of 4.5 times / 0.5 m and a compression strength of 13.9 N / piece, and a burst temperature of 437°C. Under the conditions of preheating at 940°C for 8 min and calcining at 1250°C for 12 min, the preheated ball has a strength of 412 N, and the calcined ball has a strength of 2513 N.

[0049] Comparative Example 1, the fine ore and the concentrate are subjected to two-stage roller mill activation and one-stage roller mill activation, respectively. On the one hand, the fine ore is subjected to activation treatment in the second-stage high-pressure roller mill, and the cake structure is loose and the activation is not sufficient. On the other hand, the cake structure is too dense in the concentrate roller mill activation process, and there is a problem of over-crushing. This results in a decrease in the strength of the green ball, a decrease in the burst temperature, and a decrease in the strength of the pellet. In addition, it also leads to a longer roller mill process flow and higher energy consumption.

[0050] Comparative Example 3:

[0051] The 30% hematite powder and 70% magnetite concentrate are mixed and the moisture content is controlled to be 3% for the first stage high pressure roller grinding treatment. The projection pressure is 3.5 MPa, the round roller rotating speed is 23 r / min, and the roller spacing is 4 mm. After the roller grinding, the particle size greater than 1 mm is returned to the first stage high pressure roller grinding, and the moisture of the particle size less than 1 mm is adjusted to be 5.5% for the second stage high pressure roller grinding treatment. The projection pressure is 1.8 MPa, the round roller rotating speed is 23 r / min, the edge material circulation ratio is 30%, and the roller spacing is 1 mm. After the roller grinding, the edge material is returned to the second stage high pressure roller grinding, and the obtained medium material is the activated iron-containing raw material.

[0052] The bentonite with a mass fraction of 1.2% is added into the activated iron-containing raw material and is uniformly mixed in a strong mixer with a paddle rotating speed of 1200 r / min. The mixed pellet raw material is prepared into green balls with a size of 11-14 mm, the balling time is 12 min, and the green ball moisture is 8.0%. The green ball falling strength is 5.5 times / 0.5 m, the compression strength is 15.3 N / piece, and the burst temperature is 370°C. Under the conditions of preheating at 940°C for 8 min and roasting at 1250°C for 12 min, the preheated ball strength is 437 N, and the roasted ball strength is 2572 N.

[0053] In the comparative example 1, the powder ore and the concentrate are activated by two-stage high pressure roller grinding. Although the powder ore and the concentrate are fully activated, the concentrate is over-crushed and more fine particles are generated. The full activation of the iron-containing raw material improves the green ball strength, but the compact structure and the low porosity of the green ball reduce the burst temperature. The compact pellet structure also affects the oxygen diffusion, and in addition, the solidification between the particles occurs too early, which leads to the non-uniform internal oxidation and solidification of the pellet, and the preheated ball and the roasted ball strength are reduced.

[0054] Comparative example 4:

[0055] The hematite powder is controlled to have a moisture of 2.5% for the first stage high pressure roller grinding treatment. The projection pressure is 2.8 MPa, the round roller rotating speed is 23 r / min, and the roller spacing is 4 mm. After the roller grinding, the particle size greater than 1 mm is returned to the first stage high pressure roller grinding. The particle size less than 1 mm is mixed with the magnetite concentrate at a ratio of 3:7, and then the moisture is adjusted to be 5% for the second stage high pressure roller grinding treatment. The projection pressure is 1.2 MPa, the round roller rotating speed is 23 r / min, the edge material circulation ratio is 30%, and the roller spacing is 1 mm. After the roller grinding, the edge material is returned to the second stage high pressure roller grinding, and the obtained medium material is the activated iron-containing raw material.

[0056] The activated iron-containing raw material is mixed with 1.2% bentonite by mass fraction in a high-speed mixer with a paddle speed of 1200 r / min. The mixed pellet raw material is prepared into green balls with a size of 11-14 mm, a balling time of 12 min, and a green ball moisture of 8.0%. The green ball strength is 3.8 times / 0.5 m, the compression strength is 10.3 N / piece, and the burst temperature is 467°C. Under the conditions of preheating at 940°C for 8 min and roasting at 1250°C for 12 min, the preheated ball strength is 417 N, and the roasted ball strength is 2438 N.

[0057] In Comparative Example 1, two-stage high-pressure roller milling activation is performed with lower roller milling pressure and moisture. On the one hand, the lower roller milling pressure makes it difficult for the iron-containing raw material to be fully activated. On the other hand, the lower roller milling moisture makes the cake structure loose during roller milling, and part of the roller milling pressure acts on the air between the particles, which reduces the roller milling efficiency. Therefore, the green ball strength decreases, and the preheated ball and roasted ball strengths are low.

[0058] Comparative Example 5:

[0059] The hematite powder is controlled to have a moisture of 4.5%, and is subjected to first-stage high-pressure roller milling treatment with a projection pressure of 5.5 MPa, a circular roller speed of 23 r / min, and a roller spacing of 4 mm. After roller milling, the particle size greater than 1 mm is returned to the first-stage high-pressure roller milling, and the particle size less than 1 mm is subjected to high-speed mixing with magnetite concentrate at a ratio of 3:7, and then the moisture is adjusted to 7.5% for second-stage high-pressure roller milling treatment with a projection pressure of 3 MPa, a circular roller speed of 23 r / min, a side material circulation ratio of 30%, and a roller spacing of 1 mm. The side material after roller milling is returned to the second-stage high-pressure roller milling, and the obtained intermediate material is the activated iron-containing raw material.

[0060] The activated iron-containing raw material is mixed with 1.2% bentonite by mass fraction in a high-speed mixer with a paddle speed of 1200 r / min. The mixed pellet raw material is prepared into green balls with a size of 11-14 mm, a balling time of 12 min, and a green ball moisture of 8.0%. The green ball strength is 3.8 times / 0.5 m, the compression strength is 10.3 N / piece, and the burst temperature is 467°C. Under the conditions of preheating at 940°C for 8 min and roasting at 1250°C for 12 min, the preheated ball strength is 417 N, and the roasted ball strength is 2438 N.

[0061] In Comparative Example 1, two-stage high-pressure roller milling treatment is performed with higher roller milling pressure and moisture. Higher roller milling pressure is beneficial to the full activation of the iron-containing raw material and the improvement of pellet strength, but it is more likely to cause over-crushing and produce a large amount of fine particles. Higher moisture will affect the screening efficiency after the first-stage high-pressure roller milling, causing part of the -1 mm particle size to enter the sieve, and also causing over-crushing. Therefore, the green ball strength is improved, but the burst temperature decreases, and the preheated ball and roasted ball strengths decrease.

[0062] Comparative Example 6:

[0063] The moisture content of hematite powder was controlled to 3%, and it underwent the first stage of high-pressure roller milling at a projected pressure of 3.5 MPa, a roller speed of 23 r / min, and a roller spacing of 4 mm. Particles larger than 2 mm after roller milling were returned to the first stage of high-pressure roller milling. Hematite particles smaller than 2 mm were then vigorously mixed with magnetite concentrate at a ratio of 3:7, and the moisture content was adjusted to 5.5%. This mixture underwent the second stage of high-pressure roller milling at a projected pressure of 1.8 MPa, a roller speed of 23 r / min, a scrap recycling rate of 30%, and a roller spacing of 1 mm. The scrap from the second stage of high-pressure roller milling was returned to the second stage of high-pressure roller milling, and the resulting medium-grade material was the activated iron-containing raw material.

[0064] Activated iron-containing raw materials were mixed with 1.2% bentonite by mass and thoroughly mixed in a high-powered mixer with a paddle speed of 1200 r / min. The mixed raw materials were then processed into green pellets of 11-14 mm in 12 min, with a moisture content of 8.0%. The resulting green pellets had a drop strength of 3.2 drops / 0.5 m, a compressive strength of 11.2 N / pellet, and a bursting temperature of 411 °C. Under the conditions of preheating at 940 °C for 8 min and calcining at 1250 °C for 12 min, the preheated pellets had a strength of 397 N, and the calcined pellets had a strength of 2283 N.

[0065] Compared to Example 1, the upper limit of the particle size of the ore powder in the second stage of high-pressure roller milling was increased, meaning that ore powder with a particle size of less than 2mm was screened out after the first stage of high-pressure roller milling and then subjected to subsequent roller milling. This resulted in difficulty in forming a dense cake with a reasonable particle packing structure during the roller milling process, leading to lower roller milling efficiency and incomplete activation of the ore powder. The strength of the green pellets decreased, the bursting temperature dropped, and the strength of the preheated and roasted pellets also decreased.

Claims

1. A method for preparing pellets from high pressure roll activated fines and concentrates, characterized in that Key process steps are: 1) the fine ore is subjected to a first-stage high-pressure roller mill activation treatment, and a particle size less than 1 mm is screened out and mixed with iron concentrate by strong mixing to obtain a mixed ore; the fine ore is limonite and / or hematite, the particle size of the fine ore is not more than 5 mm, and the mass fraction of the particle size less than 3 mm is not less than 70%; the mass percentage composition of the fine ore and the iron concentrate in the mixed ore is (20% to 40%) / (60% to 80%); 2) the mixed ore is subjected to a second-stage high-pressure roller mill activation treatment to obtain side material and medium material; the moisture content of the mixed ore is controlled to 5.5 to 7.0 wt% before the second-stage high-pressure roller mill treatment; 3) the side material is returned to the second-stage high-pressure roller mill activation treatment, and the medium material is mixed with a binder and then subjected to balling, preheating and roasting in sequence to obtain the pellet; the binder is at least one of bentonite, sodium humate and sodium carboxymethyl cellulose, and the mass of the binder is 0.05% to 2% of the mass of the medium material; the balling time is 10 to 14 min, the moisture content of the green ball is controlled to 7.5 to 8.5 wt.%, and the particle size of the green ball is 11 to 14 mm; the preheating temperature is 920 to 940℃, and the preheating time is 8 to 12 min; the roasting temperature is 1230 to 1250℃, and the roasting time is 10 to 15 min; In step 1), the first-stage high-pressure roller mill activation treatment has a projection pressure of 3.5 to 4.2 MPa, a circular roller speed of 23 to 26 r / min, and a roller spacing of 2 to 4 mm.

2. The process of producing pellets by activating fine ore with concentrate using high pressure roller mill as claimed in claim 1 wherein: In step 1), the water content of the fine ore is controlled to 3 to 4 wt% before the first-stage high-pressure roller mill activation treatment.

3. The method of producing pellets by activating fine ore with high pressure roller grinding along with concentrate as claimed in claim 1 wherein: The mass fraction of the iron ore concentrate described in step 1) having a particle size of less than 74 μm is not less than 70%, and the specific surface area is greater than 1200 cm 2 / g.

4. The process of producing pellets by activating fine ore with concentrate using high pressure roller mill as claimed in claim 1 wherein: In step 2), the second-stage high-pressure roller mill activation treatment has a projection pressure of 1.8 to 2.5 MPa, a circular roller speed of 20 to 23 r / min, a mass ratio of the circulating side material of 30 to 40%, and a roller spacing of 1 to 2 mm.

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