Oolitic hematite mineral because of its unique structural features, using conventional sorting methods (mainly for the domestic magnetic - reverse flotation, magnetic - research beneficiation methods of re-election, flotation, reverse flotation, etc.) it is difficult to Get better selection indicators. The Mineral Processing Laboratory of Beijing University of Science and Technology has developed a new process of deep reduction-magnetic separation on the basis of sufficient analysis of a difficult ore-selective ore-like ore-bearing lithofacies in China, which destroys the symptoms of hematite under high-temperature reducing atmosphere. structure, change the mode of occurrence of iron, the metallic iron accumulation in some way, mergers and growth, improve the optional iron, then get high-quality iron by grinding and magnetic separation operations. The prerequisite for efficient separation of iron slag in this process is the aggregation, merger and growth of iron grains. First, the nature of the ore (1) Structural characteristics of the ore The main raw material used in the test is the difficult selection of ore-like hematite ore in a certain place in China. From the appearance, most of the ore is irregular angular red particles with a particle size of between 0.04 and 0.2 mm. Optical micrographs of braided hematite ore are shown in Figures 1 and 2. Fig.1 Distribution and morphology of hazelnut hematite ore Figure 2 Quartz and hematite adjacent to the mosaic It can be seen from the picture that the iron oxides in the ore and the gangue minerals such as quartz are cemented together in a mosaic form to form a typical braided structure of varying sizes and shapes, and the main mineral forming these structures is hematite. Most of the hematite is distributed in the filler between the outer shell of the granule and the granule; the secondary mineral is mainly magnetite and siderite, and the siderite is mainly used as cement; the gangue mineral is mostly composed of quartz. Mineral composition such as clay . The inlaid particle size of hematite is 5 to 300 μm, and the grain size of the quartz particles is coarse, generally 5 to 500 μm, and the maximum is 1 800 μm. (II) Chemical multi-element analysis and phase analysis of ore The results of chemical multi-element analysis of ore are shown in Table 1, and the results of iron phase analysis are shown in Table 2. Table 1 Chemical composition of braided hematite ore Table 2 Iron phase analysis of braided hematite ore It can be seen from Table 1 that the main valuable metal in the ore is iron, and the content is 47.66%. It can be seen from Table 2 that the iron in the ore is mainly in the form of hematite. Second, test equipment and auxiliary materials The iron ore is crushed to a suitable particle size, and is mixed with coke , quicklime, etc. in a set ratio, and is placed in a ball mill for grinding to thoroughly mix the various ingredients, and then the uniformly mixed batch is placed in a graphite crucible until the electric resistance furnace When rising to a certain temperature, the crucible containing the batch material is placed in the electric furnace to reach the preset temperature and the crucible is taken out after being kept for a certain period of time, and then the reduction product is subjected to grinding, magnetic separation and product analysis. (1) Test equipment and testing means 1. Raw material weighing and mixing equipment: electronic balance, ball mill. 2. Reduction and calcination reaction equipment: silicon molybdenum rod muffle furnace, the maximum working temperature is 1700 °C. 3. Reduction reaction device: graphite crucible. 4, phase detection means: XRD tester, the instrument used is the Japanese Mac XRD tester. (2) Auxiliary raw materials 1. The reducing agent used in the test is metallurgical secondary coke, which is provided by Shougang Co., Ltd., with fixed carbon of 86%, volatile content of 1.2%, ash content of ≤12.5%, sulfur content of ≤0.6%, and 10-40 mm particle size of 90%. %. 2. The quicklime used in the test is primary lime powder for chemical industry, with CaO content of 97% and fineness of 200-300 mesh (75-50 μm). Third, the test results and discussion (1) Analysis of calcined products Under the condition of reduction temperature of 1200 °C, the iron ore batch with binary basicity of 0.2 and coke excess coefficient of 1.5 was placed in an electric resistance furnace for deep reduction roasting. When the reduction time was 60 min, the calcined product was taken out. Conduct research analysis. Figure 3 is a SEM scanning electron micrograph of the deep reduction calcined product of the 鲕-like hematite. Figure 4 is a graph showing the energy spectrum of particles in a scanning electron microscope photograph. Figure 3 SEM photograph of the calcined sample Figure 4 Energy spectrum analysis of particles in SEM images Comparing Fig. 3 with Fig. 1 and Fig. 2, it can be seen that the braided structure in the ore is no longer present, and the light-colored spherical or spheroidal particles generated by the reduction process are wrapped by light gray floc. The energy spectrum analysis of the particulate matter shows that the main component of the spherical or spheroidal particles is metallic iron, while the light gray flocculent is mainly Fe, Si, O, Ca, Al and a small amount of Mg. The phase analysis showed that the spherical or spheroidal particles were mainly metallic iron, and the light gray flocculent materials were fayalite, iron spinel and coexisting phases formed by them. (2) Factors affecting the growth of iron particles in the calcined product 1, reduction temperature The effect of the reduction temperature on the growth of iron particles is shown in Figures 5 and 6. Figure 5 is a photomicrograph of the calcined product at a binary basicity of 0.2, a coke excess of 1.5, a reduction time of 30 min, and a temperature of 1100 °C; Figure 6 shows a binary basicity of 0.2, a coke excess of 1.5, a reduction time of 30 min, and a temperature of 1200 °C. Photomicrograph of the calcined product under the conditions. Figure 5 Photomicrograph of the calcined product at 1100 ° C Figure 6 Photomicrograph of the calcined product at 1200 °C During the reduction reaction, the reduction temperature has an important influence on the aggregation, merger and growth of iron grains. As the temperature increases, the diffusion and migration of iron accelerate and the carburization accelerates, which is beneficial to the diffusion of iron phase. It can be seen from Fig. 5 that when the reduction temperature is 1100 ° C, a large number of fine and widely distributed round bright white iron particles start to appear in the calcined product, and the particle diameter is below 1 μm, and the bright white iron particles are mostly dark gray flocculent. Wrapped in things. When the reduction temperature is raised to 1200 ° C, the particle size of the bright white dots begins to increase significantly (as shown in Figure 6). The bright white large dots clearly visible in Figure 6 are the iron formed by the reduction reaction. The granules have a wide distribution area throughout the entire field of view. A small number of bright white iron particles are connected together to form large particles, and some of the larger bright white iron particles have a particle size of about 11 μm. Overall, as the temperature increases, the particle size of iron particles increases significantly. 2, restore time The effect of reduction time on the growth of iron particles is shown in Figures 7 and 8. Figure 7 is a photomicrograph of the calcined product at a binary basicity of 0.8, an excess coefficient of coke of 1.5, a reduction time of 30 min, and a temperature of 1200 °C; Figure 8 is a binary alkalinity of 0.8, an excess coefficient of coke of 1.5, a reduction time of 60 min, 1200. Photomicrograph of the calcined product at °C. Figure 7 Photomicrograph of the calcined product under reduction for 30 min Figure 8 Photomicrograph of the calcined product after 60 min reduction It can be seen from the comparative analysis of Fig. 7 and Fig. 8 that, under the same conditions, the particle size of the iron particles is significantly increased as the reduction time is extended. When the reduction time is 30 min, there are widely densely distributed round bright white iron particles in the calcined product. The iron particle size is about 1 μm, and when the reduction time is extended to 60 min (as shown in Fig. 8), it is bright. The particle size of the white iron particles is significantly increased, and most of the bright white iron particles are joined together to form larger iron particles having a particle size of up to 20 μm. It can be seen that prolonging the reaction time is conducive to the aggregation and growth of iron particles. However, the reduction time is excessively prolonged, and since the reducing agent is continuously consumed, the reducing atmosphere in the crucible is continuously lowered, and the oxidizing atmosphere is gradually enhanced, and it is possible to reoxidize the reduced ore. 3, binary alkalinity The effect of binary alkalinity on iron particle growth is shown in Figures 6 and 7. From the comparative analysis of Fig. 6 and Fig. 7, it can be seen that, under the same conditions, the particle size of the iron particles shows a significant trend with the increase of the binary alkalinity. The iron particles in Fig. 6 have a large particle size of up to about 11 μm, but the distribution thereof is relatively sparse; the iron particles in Fig. 7 are small, with an average of about 1 μm, but the distribution is relatively dense. Overall, too high a binary alkalinity is not conducive to the growth of iron particles. (3) Behavior and special occupation of metal iron particles growing during deep reduction The highest valence oxide of iron is Fe 2 O 3 . The reduction of iron oxides is carried out stepwise, in the reverse order of oxide formation. The reduction history below 570 ° C is Fe 2 O 3 →Fe 3 O 4 →Fe, The reduction history above 570 °C is Fe 2 O 3 →Fe 3 O 4 →FeO→Fe. Since the reaction temperature of this test is above 1100 ° C, and Fe and low-valent iron oxides in this high-temperature reducing atmosphere have high activity, it can be speculated that in the deep reduction process of the stellate hematite, iron At the same time that the high-valent oxide undergoes a reduction phase transition, Fe and the low-valent iron oxide react with the oxides such as SiO 2 and Al 2 O 3 in the ore to form a fayalite and iron spinel. The generation reaction may be performed as follows: In the initial stage of the reduction reaction, the reduction phase change is only carried out on some of the surface of the iron oxide in the ore, and the metal iron must overcome the nucleation barrier to form, which is more difficult. In addition, since the metal iron and the low-valent iron oxide generated during the reduction migrate and diffuse to Al 2 O 3 , the surface of the oxide such as SiO 2 undergoes a solid phase reaction and disappears, which makes the formation of the metallic iron phase more difficult. When the new metallic iron phase, the fayalite phase and the iron spinel phase are formed, the fayalite and iron spinel act as nucleating agents, which lowers the nucleation barrier of metallic iron. At the same time, metallic iron begins to diffuse to the interface of the fayalite and iron spinel and grows at its interface. Complex oxides such as fayalite have high stability and are difficult to re-reductive. The main reduction reaction of fayalite is as follows: From the calculation of the reaction formula (7), the reduction starting temperature of Fe 2 SiO 4 is 1037 K (764 ° C), and it is known from the reaction (1) that the reduction starting temperature of FeO is 992 K (719 ° C), and Fe 2 SiO 4 can be seen. More difficult to restore than FeO. Since the reactions (5) and (7) are both strong endothermic reactions, raising the reduction calcination temperature is advantageous for accelerating the reduction reaction rate. Substantially the reaction (5) is synthesized by the reaction (8) and the reaction (9), that is, When the reduction temperature increases, the reactivity of the reducing agent is increased, CO concentration in the reactor is increased, a reducing atmosphere to enhance, facilitate the reaction (8) in the positive direction; the same time, the reaction (9) the system of CO 2 The concentration is very low, so the negative value of Δ r G m in reaction (8) is large, and the reaction (5) is more easily carried out to the right. Therefore, raising the reduction roasting temperature can increase the separation rate of slag iron and reduce the content of gangue in iron concentrate. Promote the migration and diffusion of iron phases, which is conducive to the aggregation and growth of iron particles. Therefore, in Fig. 5 and Fig. 6, when the reduction temperature is raised from 1100 °C to 1200 °C, the particle size of iron particles increases significantly. However, too high a reaction temperature will soften and melt the minerals, causing adhesion between the minerals, resulting in deterioration of the reduction kinetic conditions. When reducing iron silicate with carbon, an alkaline flux (such as quicklime) may be added to promote decomposition, increase the activity of the main metal oxide, and lower the reduction initiation temperature: The binding force between CaO and SiO 2 is greater than the binding force between FeO and SiO 2 . The addition of appropriate amount of quicklime during the deep reduction of the stellite hematite can strengthen the combination of CaO and SiO 2 to release FeO, which is beneficial to the reduction of FeO. In the reaction (10), FeO in Fe 2 SiO 4 is substituted by CaO, and FeO is in a free state, and Fe 2 SiO 4 is easily reduced due to high FeO activity in a free state, and Gibbs is free in the reaction (12). The relationship shows that the reduction starting temperature of Fe 2 SiO 4 decreases from 1037K (764 ° C) to 734 K (461 ° C) due to the addition of CaO. Therefore, appropriately adjusting the alkalinity and increasing the amount of CaO added are conducive to improving the product index. However, when the binary alkalinity is low, the content of SiO 2 and Al 2 O 3 in the slag phase is relatively large, and the iron oxide easily reacts with the solid phase to cause an increase in the liquid phase in the slag phase, which is favorable for the iron phase. Migration, diffusion and aggregation. With the increase of the binary alkalinity, the amount of Ca 2 SiO 4 and other substances in the slag phase also begins to increase, and the increase of the slag amount makes the distance between the iron phases become larger, which causes the migration and diffusion of the iron phase. Aggregation has become more difficult. Therefore, under the same reaction conditions, proper adjustment of alkalinity is beneficial to the growth of iron particles. However, when the alkalinity is too high, it is not conducive to the aggregation of the iron phase. Therefore, in Fig. 6 and Fig. 7, the iron particle diameter at a binary basicity of 0.8 is significantly smaller than the iron particle diameter at a binary basicity of 0.2. Fourth, the conclusion (1) The hematite ore in a certain place has a typical braided structure, the ore structure is complex, and the inlay size is extremely fine. It is not easy to obtain a good sorting index by conventional ore dressing method. (2) The deep reduction process destroys the braided structure in the ore, and the particle size of the produced iron particles grows from less than 1 μm to several tens of micrometers, which creates conditions for efficient separation and enrichment of weak magnetic separation. (3) Increasing the reduction temperature and prolonging the reaction time are conducive to the aggregation and growth of iron particles, while the excessively high binary alkalinity is not conducive to the growth of iron particles. Outdoor Storage Tent,Heavy Duty Storage Tent,Commercial Storage Tents,Tarp Storage Shed Bestway Industries (Group) Co., Limited , https://www.military-tents.com