Table 1 Chemical composition of test material% Ore code TFe FeO SiO 2 CaO MgO Al 2 O 3 S P Burnt out A 67.72 0.22 0.58 0.018 0.02 0.74 0.003 0.048 1.61 B 68.7 0.26 1.05 0.11 0.06 0.34 0.003 0.018 0.44 C 67 0.26 1.4 0.32 0.073 1.3 0.018 0.046 1.18 D 66.02 0.29 3.36 0.31 0.043 0.71 0.01 0.026 1.18 E 63.46 0.15 3.03 0.031 0.04 1.97 0.005 0.078 3.79 F 64.9 0.77 3.15 0.04 0.06 1.83 0.008 0.07 2.55 G 57.95 0.9 4.15 0.011 0.08 1.12 0.008 0.04 11.61 H 56.9 1.16 5.34 0.41 0.19 2.36 0.006 0.039 10.32 I 56.9 1.16 5.34 0.41 0.19 2.36 0.006 0.039 10.32 J 62.46 0.22 2.44 0.031 0.034 1.7 0.002 0.072 5.51 Table 2 Test temperature and atmosphere control Temperature / °C Time /min atmosphere Room temperature → 600 4 air 600→1000 1 Nitrogen 1000→1150 1.5 Nitrogen 1150→ test temperature 1 Nitrogen Test temperature 4 Nitrogen Test temperature → 1150 2 air 1150→1000 1.5 air 1000→ room temperature Power off and cool down naturally air Note: Both nitrogen and air flow are 3L/min. 3 Test results and analysis 3.1 The highest SFCA content in G and H mines Among the 10 kinds of iron ore, the SFCA content of G and H samples is the highest, reaching 40% and 35% respectively. Main reasons: (1) Both iron ores are limonite, and the burning loss is relatively high. At a certain temperature, the crystal water is evaporated by heat, leaving residual pores in the limonite, so that the iron ore structure Looseness accelerates the diffusion of Ca 2+ into iron ore, and iron mineral ions are also easy to diffuse, making the reaction easier to carry out, which is beneficial to the formation of a large number of low-melting compounds, thus contributing to the increase of SFCA production. (2) The ratio of Al 2 O 3 /SiO 2 of the two kinds of iron ore is suitable, which is beneficial to the formation of calcium ferrite. (3) The content of Al 2 O 3 and SiO 2 of these two kinds of iron ore is relatively high, and the structure is relatively loose, which is very beneficial to the formation of SFCA. 4 blades PDC Bit is also one of steel body PDC bit, it has better stability in drilling and can drill more harder formation when compared with 3 Blades PDC Bit, they both have advantage of fast drilling footage in soft formation. Lower cost with long service life makes our 4 blades PDC bit widely used in mining, water well drilling, dam construction, bridge and water conservansy etc. Welcome to purchase quality 4 blades PDC bit with factory price from us if you need them. 4 Blades Pdc Bit,4 Blades 6 Inch Pdc Bit,4 Blades 152Mm Pdc Bit,Non-Coring 4 Blades Pdc Bit Xi'an Heaven Abundant Mining Equipment CO.,LTD , https://www.tydrillingbits.com
In recent years, research on the reduction of sinter has been widely emphasized, and the reduction of the blast furnace charge has greatly reduced the coke ratio and improved productivity. In other properties to ensure sinter (e.g., cold strength, softening temperature and reduced powder etc.) at the same time, should increase the reduction of sintered ore, iron and calcium are important factors reducing sintered ore, therefore, it is necessary The formation characteristics of calcium ferrite during the sintering process of iron ore were studied.
There are many studies at home and abroad about the composition and structure of calcium ferrite. It was originally thought to be a binary system of calcium ferrite, and its composition is CaO.Fe 2 O 3 , 2CaO.Fe 2 O 3 , CaO.2Fe 2 O 3 . With the deepening of the research, it was found that the calcium ferrite in the sinter is mainly a ternary system, a quaternary system and a solid solution thereof, because the SiO 2 and Al 2 O 3 present in the raw material dissolve calcium ferrite during the sintering process. Therefore, it is called a composite or a silicon iron aluminum, iron, calcium, calcium referred SFCA.
Dawson et al. believe that the formation of SFCA is the result of several reactions:
CaO.Fe 2 O 3 formation (1050 ~ 1150 ° C);
Al 2 O 3 reacts with CaO to form calcium aluminate (1100～1150°C);
Calcium aluminate is melted in CaO.Fe 2 O 3 (1100～1150°C) to form monocalcium aluminoaluminate;
Calcium aluminosilicate melts and reacts with Fe 2 O 3 to form iron aluminophosphate hemi-calcium (1200-1250 ° C);
Subsequent reaction with SiO 2 forms SFCA (1200 to 1250 ° C).
There are many factors affecting the formation characteristics of iron ferrite in iron ore, including the following two aspects: (1) the influence of sintering process parameters, including sintering temperature, sintering atmosphere and carbon content. A lower sintering temperature and a stronger oxidizing atmosphere promote the formation of calcium ferrite. (2) The nature of iron ore, that is, its own characteristics, is an intrinsic factor that determines the composition of different minerals in sinter. The type, particle size composition, compactness, alkalinity and chemical composition (including CaO, MgO, SiO 2 and Al 2 O 3 ) of iron ore fines directly affect the uniformity of the mineral phase composition and distribution of the sintered ore. The self-characteristics of iron ore fines are important factors influencing the ability of SFCA to form. [next]
2 Test materials and methods 2.1 Sample preparation
Part of the iron ore fines used in the test came from the Jinan Iron and Steel Group Corporation (Jigang) raw material plant and the first sintering plant, some of which were supplied by iron ore distributors; CaO was a chemically pure reagent. The sampling of iron ore fines adopts the “four-point selection method†to ensure the representativeness of the samples. The iron ore fines used in the test were dried in an oven at 110 ° C for 2 h, and then placed in a drying dish in a timely manner after cooling. The dried iron ore is ground to a powder of less than 0.15 mm and stored in a drying dish. The CaO reagent is ground to a powder of less than 0.15 mm and stored in a drying dish. The weight of the small cake sample is an electronic balance with an accuracy of one ten thousandth. It is pressed by "dry powder pressing method", the pressure is 10 MPa, and the pressure is kept for 2 min.
2.2 Test equipment
The main equipment used in the test is a weighing device, a crushing strength device, a pressure test device and a micro sintering test device. The micro-sintering test device mainly includes RHL-410P type infrared rapid high temperature test furnace (mainly composed of quartz protection tube and infrared lamp heating element), TPC-1000 type temperature program control instrument, cooling water controller, sample table automatic lifting device , furnace support and control system, test gas control system, temperature measurement and control system.
2.3 Test methods
The test uses a micro-sintering method and a micro-mineral phase test method. The micro-sintering method was used to calcine the cake samples made of each mineral powder under a certain sintering system; the sintered cake samples were ground, and the formation of SFCA and the mineral phase structure in each sample were observed under the microscope. Wait. The quantitative analysis of the mineral phase composition was carried out by visual inspection.
 The specific scheme uses a basicity of 2.0 and a test temperature of 1280 ° C. The chemical composition of the raw materials for the test is shown in Table 1. The test cake sample was 5 mm high and 8 mm in diameter based on height. The test temperature and atmosphere control are shown in Table 2. [next]
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The order of the columns is: G, H, E, F, D, J, I, B, C, A mine.
The mineral composition and microstructure characteristics of 10 kinds of iron ore are shown in Table 3 and Figures 1 to 10. Rows of calcium ferrite in the ore sample from high to low: [next] 
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3.2 The content of SFCA in E, F and D mines is higher
Among the 10 types of iron ore, the SFCA content of the three ore samples E, F and D is relatively high (between 29% and 31%). Main reasons: (1) The SiO 2 content of these three ores is relatively high. Under the same alkalinity conditions, the amount of CaO is higher, and all three mines are hematite, so CaO and Fe 2 O 3 The probability of contact increases and the amount of SFCA generated increases. (2) These three types of ore structures are relatively loose, which is conducive to the diffusion reaction, which is conducive to the formation of calcium ferrite. In addition, the ratio of Al 2 O 3 /SiO 2 in D ore is suitable, which is beneficial to the formation of calcium ferrite, which is also an important reason for the high amount of SFCA in D mine.
3.3 J, I, B, C mines have lower SFCA content
Among the 10 kinds of iron ore, the main reasons for the low production of calcium ferrite in J, I, B and C are: (1) The grade of I ore is low and the content of SiO 2 is high, reaching 5.34%. When the sinter contains higher SiO 2 , the reaction of 2Fe 3 O 4 +3SiO 2 =3(2FeO.SiO 2 ) + O 2 will occur, which will accelerate the decomposition of magnetite and hematite, which is not conducive to The formation of calcium ferrite. In addition, the higher content of SiO 2 in the sinter will produce more 2CaO.SiO 2 , and the formation of a large amount of 2CaO.SiO 2 means that the chance of Fe 2 O 3 and CaO bonding is relatively reduced, which is not conducive to ferric acid. Calcium production. (2) The content of SiO-2 in the three minerals of J, B and C is relatively low. Under the same alkalinity condition, the amount of CaO is also less, and the probability of generating SFCA is reduced. [next]
Among the 10 kinds of iron ore, the A has the lowest SFCA content, only 5%. The reason is as follows: the SiO 2 content of the ore is the lowest, only 0.58%, so that under the same alkalinity condition, the amount of CaO is also minimized, and thus the content of calcium ferrite formed is the least. In addition, the structure of the mine is relatively dense, which is not conducive to the diffusion of Fe 2 O 3 and CaO, and is not conducive to the oxidation process of low-valent oxides, thus affecting the formation of calcium ferrite to some extent.
4 Conclusions 4.1 The formation characteristics of iron ferrite in iron ore are the result of a combination of factors. In addition to the calcination temperature, calcination atmosphere, alkalinity and other factors, it is also affected by the iron ore's own properties, such as Fe 2 O 3 content, CaO content, SiO 2 content, MgO content, Al 2 O 3 /SiO 2 ratio. And the influence of factors such as compactness, these factors affect each other and interact with each other.
4.2 Different iron ore, calcium ferrite formation characteristics are different. In the case of alkalinity of 2.0 and other conditions, loose limonite, hematite and higher content of Al 2 O 3 and SiO 2 are beneficial to the formation of SFCA.
4.3 The formation characteristics of iron ferrite in iron ore is a factor that must be considered in sintering ore blending, and it has an important guiding role in optimizing ore blending. Properly adding a certain proportion of G ore and H ore and loose hematite powder in the sinter can improve the strength and degree of reduction of the sinter.
Study on the Formation Characteristics of Calcium Ferrite Sintered by Iron Ore
1 Foreword