Mechanism of Reduction and Roasting of Oyster Hematite in Western Hubei and Analysis of Effective Ways of Sorting

Oolitic hematite iron ore is an important form of occurrence, data show that Europe Oolitic reserves of as much as 14 billion t, while in China there are 40 to 5 billion t. The use of this ore by humans has continued for nearly a hundred years, but it has not made significant technological progress due to the complex nature of the ore.

The rising price of international iron ore and the relatively high grade of braided hematite in China, and the certain differences in the structure of useful minerals and gangue minerals have made the study of the utilization of braided hematite in China. Very active. The study considers that magnetization roasting-magnetic separation-flotation is an effective beneficiation method for the use of the western Hematite hematite, and the flash roasting technology developed by the research team led by Academician Yu Yongfu has the characteristics of short process flow and low energy consumption. Have a better future. At present, this research has not only achieved good results in the laboratory, but also in industrial trials, making it possible to utilize the helium-shaped hematite in western Hubei.

In the study of flash magnetization roasting, it is found that under the same conditions, the magnetization roasting of the western Hematite hematite and hematite, limonite and siderite is quite different in time. The mechanism of reduction roasting of hafnium hematite and effective sorting pathway were discussed and analyzed.

I. Ore-like hematite ore properties in western Hubei

The results of chemical multi-element analysis and iron phase analysis of raw ore (composite sample) are listed in Table 1 and Table 2, respectively. The main mineral contents in the ore are shown in Table 3. The surface of the 鲕-like hematite particles and Si, P, Al, Fe The SEM image is shown in Figure 1.

Table 1 Multi-element analysis results of ore chemistry

Table 2 Analysis results of ore iron phase %

Table 3 Main mineral content in ore %

Fig.1 Scanning electron microscopy image of the surface of braided hematite particles and Si, P, Al and Fe

It can be seen from Table 1 to Table 3 that the main recovery component in the ore is iron, the ratio of TFe to FeO content is 18.86; the acidity and alkalinity coefficient of the ore is 0.17, indicating that the ore is acidic oxidized ore; the ore contains low sulfur, but containing high phosphorus.

It can be seen from the image of the scanning electron microscope that in the range of bismuth grains, the minerals composed of Fe, P, Si and Al elements are concentrically wrapped around each other, and the iron is finely distributed in the granules. In the middle and outer rings, the phosphate rock is mainly distributed close to the nucleus of the nucleus. Quartz and silicate are mainly concentrated in the nucleus and the middle zonal.

Second, the test device

The reduction roasting of the western Hematite hematite is completed in a flash magnetization roaster, and the flash magnetization roaster is shown in Fig. 2. The test tube is installed in the electric heater. When the temperature inside the test tube reaches the test demand, the ore is fed from the upper part of the test tube. By adjusting the rising rate of the reduced gas flow, the ore can be suspended in the test tube at different time conditions. Under the iron minerals with different degrees of magnetization can be obtained. The degree of magnetization of the iron mineral under various test conditions can be known by magnetic separation test.

Figure 2 shows the flash magnetization roasting small test furnace

1- air blower; 2- coal gas furnace; 3- stoker opening; 4- gas distribution plate;

5- electric furnace wire; 6-reduction furnace switching valve; 7-bypass switching valve; 8-reduction furnace regulating valve;

9-insulation layer; 10-water sealing hopper; 11-exhaust chimney; 12-discharging tube; 13-feeding hopper;

14-reduction furnace; 15-silicon carbon rod; 16-refractory brick; 17-filter;

18-temperature measuring port; 19-gas distribution plate differential pressure measuring point

Third, the test and results

The ore is ground to 0.2 to 0 mm and dried into a loose powder. When the calcination temperature is 800 to 900 ° C, the CO concentration is 3% to 12%, and the fluidization velocity is 0.4 m/s, the ore is given to the test tube and timed. The calcined product is then magnetically selected to give a corresponding sorting result.

(1) Experimental study on typical refractory iron ore in China

Firstly, several typical refractory iron ores in China were subjected to fluidized roasting (70g/time) one-time magnetic separation test. The results are shown in Table 4.

Table 4 Fluidized magnetic separation test results of typical refractory iron ore

It can be seen from Table 4 that these typical refractory iron ores represent the ore types mainly composed of hematite, siderite and limonite, and the magnetization roasting effect is good. After 1 rough magnetic separation. A concentrate with an iron grade of 57% to 61% and an operation recovery rate of over 90% is obtained.

(II) Experimental study on beneficiation of ore-like hematite in western Hubei

The magnetic separation indexes of the Hexi Hematite hematite with different particle size and different roasting time were studied. The test results are shown in Table 5.

Table 5 Results of roasting-magnetic separation test of braided hematite in western Hubei

Table 5 can be seen from Table 4, although the magnetization roasting time of the stellite hematite is prolonged, the magnetization roasting-magnetic separation effect is still not as good as the other iron ore in Table 4, and the concentrate iron grade is between 54.22% and 57.00%. The recovery rate is between 74.21% and 83.79%. However, the finer calcination size and longer calcination time are beneficial to improve the concentrate grade and recovery rate.

Fourth, the mechanism of magnetization roasting

(1) Hematite reduction thermodynamics

Theoretical analysis of thermodynamics indicates that the reduction of iron oxide is carried out step by step, that is, the reduction of Fe 2 O 3 to form Fe is a stepwise reaction. This study mainly discusses the process of Fe 2 O 3 reduction to Fe 3 O 4 . Figure 3 is the equilibrium relationship between various valence states of iron under different CO concentrations and temperature conditions.

Figure 3 shows the balance of CO reduction of iron oxide

The reaction curve (1) of Fig. 3 reflects the process of reduction of Fe 2 O 3 to Fe 3 O 4 , which is close to the horizontal axis, indicating that CO at a very low concentration can reduce Fe 2 O 3 at any temperature. It became Fe 3 O 4 (see Table 6), so the reaction was actually irreversible. At the same time, it can also be seen from Fig. 3 that limiting the CO concentration can prevent further reduction of Fe 3 O 4 .

Table 6 K p (CO 2 /CO) and CO equilibrium concentration of reaction (1)

The above analysis shows that the conversion of iron oxide (Fe 2 O 3 ) to Fe 3 O 4 by reduction roasting is relatively easy to achieve.

(2) Hematite reduction kinetics

The reaction of reducing the calcination of hematite ore to form magnetite is also carried out according to the unreacted core model (shrinkage model). The magnetization roasting reaction process is shown in Figure 4. References, it can be considered that the reaction of hematite reduction roasting to form magnetite mainly goes through the following links:

1. The mineral particles are heated in a hot reducing gas stream.

2. When the reaction temperature is reached, CO diffuses and adsorbs on the surface of hematite and reacts with surface hematite to form magnetite Fe 3 O 4 and CO 2 .

3. CO continues to adsorb on the surface, and the outer Fe 2+ and electrons diffuse into the inner layer Fe 2 O 3 through the lattice vacancies, and undergo lattice reconstruction to transform into magnetite Fe 3 O 4 ; and inner layer O 2 - Diffusion to the outer layer, which reacts with CO to form CO 2 and is continuously removed.

4. The previous process proceeds in depth, and the reaction is continuously pushed to the inner layer, and finally the particles are completely reduced to form magnetite particles.

T 0 - initial moment of magnetization; T E - magnetization completion time; T-magnetization time

When Fe 2 O 3 is reduced to magnetite Fe 3 O 4 , the CO adsorbed on the surface of Fe 2 O 3 is slightly deformed, so that the activated CO molecules turn to the surface of Fe 2 O 3 lattice in different directions, and O 2 - Generates CO 2 , carries away O 2 - leaves 2 electrons, and 2 electrons remain in the crystal lattice to promote the reduction of Fe 3+ to Fe 2+ :

The Fe 2 O 3 lattice is deformed and undergoes lattice reconstruction to form magnetite Fe 3 O 4 :

The above reaction indicates that the reduction of the iron oxide mineral is a reduction reaction of CO with the surface of the iron oxide mineral, and is carried out by diffusion migration of Fe 2+ (including electrons) and O 2 - in the crystal of the reduction product. This process is carried out from the outside to the inside of the mineral layer in which magnetite and hematite are closely connected.

5. Reasons for the difficulty of magnetization roasting in the western Heilongjiang hematite ore and improvement measures

(1) Analysis of the reasons why it is difficult to magnetize roasting in the western Heilongjiang

The braided hematite ore in western Hubei is a braided iron mineral with quartzite mineral as the core and colloidal phosphate, fine-grained clay and red limonite as the ring zone, and this layered ring is wrapped with each other. . It can be assumed that in the process of CO reduction from helium to the inside, after completion of the reduction of the first (outermost) hematite, the CO will face the second (secondary) quartz silicate mineral. The barrier of the annulus layer acts as a barrier to the normal diffusion and migration of Fe 2+ ions, electrons and oxygen ions. The hematite in the third layer and below is difficult to be reduced by CO, so the reduction effect of the stellite hematite not good.

(2) Measures to improve the effect of magnetization roasting

Studies have shown that reducing the particle size of the magnetization roasting of the stellite hematite and prolonging the time of magnetization roasting can improve the reduction roasting effect of the ore.

At present, the circulating preheating fluidized magnetization roasting (flash magnetization roasting) process is under study, the feed size is reduced to less than 0.2 mm, which is smaller than the grain size of the shaft furnace magnetization roasting process (<75 mm) and the rotary kiln magnetization roasting process. The particle size (<15mm) is much smaller. The fluidized magnetization roasting of less than 0.2mm material makes the particles more fully contact with the reducing atmosphere, and improves the heat transfer and mass transfer effect of the reaction, so that the original ring is covered by the quartz ring band, the clay ring band or the phosphorus mineral ring band. The surface of the hematite is also exposed, or mostly exposed, increasing the chance of contact with the CO gas, thereby improving and enhancing the reduction roasting effect. The results of the magnetization roasting-magnetic separation test of the shaft furnace or rotary kiln of the ore fully demonstrate the advanced nature of the circulating preheating fluidized magnetization roasting process.

Conclusion

(1) The reduction of hematite minerals is the reduction reaction between CO and mineral surface. The internal principle is also the process of diffusion, migration and chemical reaction of Fe 2+ ions, electrons and O 2 - in the crystal lattice of magnet mineral layer.

(2) Fluidized reduction roasting, the input particles are less than 0.2mm, which can be regarded as homogeneous particles, or partially homogenized, with rapid heat transfer and mass transfer, so for hematite, limonite, and Iron ore reacts quickly and can be converted into magnetite in general for 30 to 60 seconds.

(3) Western Hubei Hematite Hematite due to the annular banding of other minerals in the mineral, the general magnetization roasting method (shaft furnace, rotary kiln) is adopted, even if the temperature of magnetization roasting is reached, but other minerals (such as SiO 2 ) The presence of an annulus layer of clay minerals, colloidal phosphorus minerals, hinders the contact of iron minerals with CO gas, and the diffusion and migration of Fe 2+ ions, electrons and O 2 - in the inner layer of minerals, thus making this class The effect of the magnetization roasting of the ore is deteriorated and the speed is slow.

(4) The western-style braided high-phosphorus hematite is subjected to flash magnetization roasting method, and the ore is crushed to below 0.2 mm, so that most of the surface of the hematite in the braided iron ore is exposed to the outside, which is easy to react with the reducing gas. The reaction of CO and the like to improve the effect of reduction roasting-magnetic separation is a promising direction and route for the ore dressing of the western Heilongjiang.

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