Magnetized roasting test of a braided high-phosphorus red and limonite rotary kiln

Iron and steel industry is one of the pillar industries of the national economy, especially the economy is in rapid development of China's steel industry is even more important. There are two ways to solve the shortage of iron ore raw materials and make up for the gap between supply and demand. One is to find and develop new iron ore raw material bases; the other is to continue to use foreign iron ore resources. Among the iron ore resources in China, iron ore with easy selection, low impurity content, high iron content and simple beneficiation process is gradually facing depletion; on the contrary, it has high impurity content (mainly P and S) and iron content. The refractory iron ore resources with low characteristics and fine grain size are still not properly developed and utilized.

At present, the ore-like high- phosphorus red and limonite in the refractory iron ore is complicated by the ore dressing process, and the obtained iron concentrate product has a low iron grade, and the phosphorus-containing high still has no reasonable beneficiation process to utilize this valuable iron ore resource. Therefore, it is of great practical significance to develop a reasonable new beneficiation process for the treatment of braided high-phosphorus red and limonite.

First, the nature of the sample

The semi-industrial test sample was from a certain area of ​​Sichuan, and the high-phosphorus-like red and limonite with fine grain size was embedded. The ore was massive and hard. The maximum grain size of the ore is about 20% below 50mm, and some of it is about 35% under 25mm. The rest are below m15mm. The gangue ( quartz , calcite, etc.) in the ore is more visible from the naked eye. At the same time, it is densely distributed, and the shape of the wart is obvious. The ore grade is 39.38% and the phosphorus content is 0.763%. The main iron minerals of the ore are red and limonite, followed by magnetite, silicate iron ore, siderite, pyrite, etc. The main ore minerals of the ore are quartz, calcite, diopside and ordinary pyroxene. , chlorite, aragonite, garnet, etc. In order to meet the requirements of industrial tests, the samples were processed to a wavelength of -10 mm or less for spectral analysis, multi-element analysis, iron phase analysis and screening test. The test results are shown in Tables 1 to 4.

Table 1 Spectral analysis results of samples %

Table 2 Multi-element chemical analysis results of samples

Note: As unit is ×10 ^-6

Table 3 Sample iron phase analysis results

Table 4 Sample screening test results

From the results of spectral analysis, multi-element analysis, and iron phase analysis of Tables 1 to 3, it is known that the main element recovered in the sample is iron, and other valuable elements such as copper , zinc , lead , molybdenum , nickel , cobalt , and titanium. The content of gold , silver and other are low, and there is no comprehensive recovery value; the content of harmful elements such as sulfur and arsenic does not exceed the standard, but the phosphorus exceeds the standard by 0.763%. The optional iron in the sample is red, limonite, siderite and magnetic iron, which account for 84.99% of the original ore. Therefore, the ore is mainly obtained by iron and phosphorus reduction to obtain qualified iron concentrate.

It can be seen from Table 4 that the distribution of iron is not very large with the change of the particle size, and the distribution of phosphorus is also small as the particle size decreases.

Second, the main equipment for testing and phosphorus-reducing agents

Test equipment for the main φ800mm × 9000mm rotary kiln, the auger feeder, a jaw crusher, a roll crusher, vibrating screen, Raymond, fine coal to coal, spiral classifier, hydrocyclone, 2 900mm×1800mm ball mill , barrel magnetic separator (B=0.30T), permanent magnet cylinder magnetic separator (B=0.15T), water quenching spiral continuous conveyor (developed by itself) and auxiliary equipment.

In this test, the rotary kiln magnetization roasting was carried out. The process mineralogy research of the ore was used to show that the phosphorus in the sample was present in the ore in the form of colloidal phosphate. The colloidal phosphate was characterized by a fine grain size and iron ore. The objects are symbiotic in the form of lattice substitution. At the same time, iron is embedded in the ore in the form of a scorpion, and the particle size is also relatively fine. This determines that the conventional magnetization roasting is difficult to achieve the ideal effect of iron and phosphorus reduction. Therefore, the self-developed composite roasting phosphorus-reducing agent (code name LCP) is used for phosphorus reduction.

The agent belongs to a salt inorganic compound and has the characteristics of low melting point, pro-phosphorus minerality and low degree of interference. The main mechanism is that LCP rapidly reacts with phosphorus minerals in iron ore at a calcination temperature of 900-1100 °C. The formation of a new mineral, the effective transformation of phosphorus minerals, and ultimately the effective separation of iron minerals.

Third, semi-industrial experimental research

After preliminary small-scale experimental research and expanded experimental research, it is concluded that the process suitable for the ore is a one-two or two-stage magnetic separation process of magnetized roasting, and a self-developed LCP combined phosphorus-reducing agent is obtained through a magnetization roasting process. The ore dressing index of iron grade 65%, phosphorus content ≤0.30%, iron recovery rate ≥75%. Therefore, the semi-industrial test of rotary kiln (small 800mm × 9000mm) is carried out by magnetic ore roasting one or two grinding or one or two magnetic separation process, and the process parameters are adjusted according to the problems and test results in the semi-industrial test process. Seeking the optimal process parameters to obtain the ideal iron concentrate product indicators, the semi-industrial test process is shown in Figure 1.

Figure 1 Semi-industrial test process

(1) Roasting condition test

Calcination is one of the key factors in the whole process. The calcination conditions include calcination temperature, calcination time (time difference from material entering rotary kiln to discharge), coke dosage, amount of phosphorus-lowering agent (LCP), coke particle size, pellets. diameter. The calcination temperature is reflected by the temperature sensor (A, B, C, D, E) installed on the rotary kiln, the high temperature zone is A ~ B, the length is 2 m, the calcination reaction zone is B ~ C, the length is 4 m, the drying zone It is C~E, the length is 3m, the roasting time is controlled by adjusting the rotation speed of the rotary kiln. The different speeds of the rotary kiln are realized by adjusting the frequency f of the inverter. The relationship between the different firing frequencies of the inverter is shown in Table 5.

Table 5 The frequency of the inverter corresponds to the roasting time

1. Calcination temperature test

The calcination temperature is controlled by a temperature sensor of the rotary kiln. Rotary kiln inverter f=30Hz (baking time is 60min), LCP dosage is 10%, coke dosage is 8%, coke particle size is -1mm, pellet diameter is -20+5mm, weak magnetic selection magnetic induction intensity B1=0.30 T, B2=0.12T, The grinding process temperature test is carried out under the condition that the grinding fineness -0.100mm accounts for 95% and the second-stage grinding fineness -0.045mm accounts for more than 80%. The test process is shown in Figure 1. The test results are shown in Figure 2.

Figure 2 Roasting temperature test results

■-Fe grade; ▲-Fe recovery rate; ◆-P grade (×10 ^-2 ); ●-P recovery rate

It can be seen from Fig. 2 that the temperature is between 900 °C and 1000 °C. As the calcination temperature increases, the iron grade gradually increases and the iron recovery rate also increases. When the temperature rises to 1050 °C, the iron grade decreases. The iron recovery rate has also been reduced. The phosphorus content in the iron concentrate changes first and then increases with the increase of the calcination temperature. Considering that the calcination temperature is 1000 °C, the ore dressing index of iron grade is 65.74%, phosphorus content is 0.236%, and iron recovery rate is 78.11%.

2, roasting time test

The calcination temperature test shows that the calcination temperature is 1000 °C, so the temperature of the rotary kiln is controlled at 1000 ° C, the LCP dosage is 10%, the coke dosage is 8%, the particle size is -1 mm, the pellet diameter is -20+5 mm, and the weak magnetic separation magnetic induction strength is obtained. B ₁ =0.30T, B ₂ =0.12T, a grinding fineness of -0.10mm accounted for 95%, and a second-stage grinding fineness of -0.045mm accounted for more than 80%, and the calcination time test was carried out. The test process flow is shown in Figure 1. The test results are shown in Figure 3.

Figure 3 Roasting time test results

■-Fe grade; ▲-Fe recovery rate; ◆-P grade (×10 ^-2 ); ●-P recovery rate

It can be seen from Fig. 3 that as the calcination time increases, the iron grade gradually decreases, and the iron recovery rate also gradually decreases. During the whole change process, when f=40 Hz, an extreme point appears, and the corresponding calcination time is 45 min (Table) 5); increase the phosphorus grade in time, increase the phosphorus grade in time, and there is a trend of high and low in both ends. Selecting the roasting time of 45 min can obtain the ore dressing index of iron grade 66.01%, phosphorus content 0.225% and iron recovery rate of 79.09%.

3, coke dosage test

There are many types of reducing agents, such as lignite, anthracite, bituminous coal, etc. These reducing agents generally contain high (sulfur, phosphorus, arsenic, etc.) and are easy to bring into the concentrate to affect the quality of the product. Therefore, only coke is selected as the reducing agent. experimenting. Coke plays a dual role in providing a reducing atmosphere and a reducing carrier throughout the calcination process, and the amount of coke directly affects the quality of the calcined product. Therefore, the rotary kiln inverter f = 40Hz (baking time 45min), LCP dosage 10%, coke particle size -1mm, pellet diameter -30 + 5mm, weak magnetic selection magnetic induction strength B1 = 0.30T, B2 = 0.12T, a section of grinding fine The degree of -0.10mm is 95%, and the second-stage grinding fineness -0.045mm accounts for more than 80%. The coke dosage test is carried out. The test process is shown in Figure 1. The test results are shown in Figure 4.

Figure 4 Reductant dosage test results

■-Fe grade; ▲-Fe recovery rate; ◆-P grade (×10 ^-2 ); ●-P recovery rate

It can be seen from Fig. 4 that the amount of coke is increased, the iron grade is increased, the phosphorus content is decreased, and the iron recovery rate is increased. However, when the dosage is increased to 8% and the dosage is continuously increased, the iron grade, the phosphorus grade, and the iron recovery rate are relatively small, so Choosing coke consumption of 8% is reasonable, and can obtain the ore dressing index of iron grade 65.98%, phosphorus content 0.215% and iron recovery rate of 78.89%.

4, coke particle size test

The coke particle size is mainly reflected by the specific surface properties of coke. The larger the particle size, the smaller the specific surface area; conversely, the larger the specific surface area. In addition, since the sample needs to be pelletized, the larger the particle size, the corresponding uniformity is insufficient; the finer the particle size, the larger the contact area with the sample. At the calcination temperature of 1000 ° C (rotary kiln temperature sensor), rotary kiln inverter f = 40 Hz (baking time 45 min), LCP dosage 10%, coke consumption 8%, pellet diameter -20 + 5 mm, weak magnetic selection magnetic induction B ₁ = 0.30T, B ₂ =0.12T, a grinding fineness -0.100mm accounted for 95%, and the second-stage grinding fineness -0.045 mm accounted for more than 80%, the coke dosage test was carried out, and the test process flow is shown in Figure 1. The test results are shown in Figure 5.

Figure 5 Reductant particle size test results

■-Fe grade; ▲-Fe recovery rate; ◆-P grade (×10 ^-2 ); ●-P recovery rate

It can be seen from Fig. 5 that the beneficiation index of iron grade greater than 65%, phosphorus content less than 0.3%, iron recovery rate higher than 78%, and coke grain size increase to +1 mm, in the iron concentrate, can be obtained below -1 mm. Phosphorus increased to 0.328%. Therefore, it is reasonable for the coke particles to be -1 mm.

5, pellet diameter test

The diameter of the pellet mainly affects the firing time. The larger the diameter, the longer the firing time; conversely, the shorter the firing time. In addition, the excessive baking time affects the unit throughput of the rotary kiln, and the ore dressing cost is increased under the same conditions. Therefore, the diameter of the pellet should not be too large or too small. At the calcination temperature of 1000 ° C, rotary kiln inverter f = 40 Hz (baking time 45 min), LCP dosage 10%, coke dosage 8%, coke particle size -1 mm, weak magnetic separation magnetic field strength B1 = 0.30T, B2 = 0.12T, a section Weak magnetic separation grinding fineness -0.10mm accounted for 95%, two-stage weak magnetic separation grinding fineness -0.045mm accounted for more than 80%, the pellet diameter test was carried out, the test process is shown in Figure 1, the test results See Figure 6.

Figure 6 Pellet diameter test results

■-Fe grade; ▲-Fe recovery rate; ◆-P grade (×10 ^-2 ); ●-P recovery rate

It can be seen from Fig. 6 that the diameter of the pellet is suitably between -30+5 mm, the iron grade in the obtained iron concentrate is more than 65%, the phosphorus content is less than 0.3%, and the iron recovery rate is higher than 78%. However, it is found that the -10 +5mm phenomenon has a "ringing" phenomenon during the roasting process. Therefore, it is reasonable to control the diameter of the pellets between -30+10mm, so that better beneficiation index can be obtained, and the degree of "ringing" of the rotary kiln can be reduced. .

6, LCP phosphorus dosage test

The LCP phosphorus-reducing agent belongs to a composite agent. According to the market price of its components, the comprehensive price is about 400 yuan/t. The amount of the amount not only affects the phosphorus content in the iron concentrate, but also affects the cost of the ore dressing. At the calcination temperature of 1000 ° C, the rotary kiln inverter f = 40 Hz (baking time 45 min), coke consumption 8%, coke particle size -1 mm, pellet diameter -30 + 10 mm, weak magnetic magnetic induction strength B ₁ = 0.30 T, B ₂ = 0.12 T, a section of grinding fineness -0.10mm accounted for 95%, the second section of grinding fineness -0.045mm accounted for more than 80% of the conditions, the pellet diameter test, the test process is shown in Figure 1, the test results are shown in Figure 7. .

Figure 7 LCP dosage test results

■-Fe grade; ▲-Fe recovery rate; ◆-P grade (×10 ^-2 ); ●-P recovery rate

It can be seen from Fig. 7 that as the amount of LCP increases, the phosphorus content in the iron concentrate gradually decreases to 0.109%, but the iron grade and iron recovery rate first increase and then decrease. When the amount of LCP is 15%, the iron grade is 63.65%, the phosphorus content is 0.109%, and the iron recovery rate is 71.68%. Therefore, considering the iron concentrate grade, iron recovery rate, phosphorus content and other factors, the LCP dosage is 10%, and the ore dressing index of iron grade 65.71%, phosphorus content 0.223% and iron recovery rate 78.91% can be obtained.

(2) Continuous calcination process test

The roasting conditions of the magnetization roasting-weak magnetic separation (stage grinding stage selection) process were obtained by the main process parameters of the rotary kiln roasting: roasting temperature 1 000 ° C, f = 40 Hz (baking time 45 min), coke dosage 8%, coke particle size -1mm, pellet diameter -30+10mm, LCP dosage 10%, weak magnetic separation magnetic induction strength B _l =0.30T, B ₂ =0.12T, one section grinding fineness -0.100mm accounted for 95%, two sections Grinding fineness -0.045 mm accounted for more than 80%. In order to investigate the reliability and stability of the obtained process parameters, the whole process test of the continuous 72h process flow was carried out under the obtained roasting conditions. The test process flow is shown in Figure 1, and the test results are shown in Table 6.

Table 6 Results of the whole process test for continuous 72h roasting

It can be seen from Table 6 that a beneficiation index with a yield of 50.41%, an iron grade of 65.93%, a phosphorus content of 0.225%, and an iron recovery rate of 78.91% can be obtained, and the difference between the index and the calcination condition test is small, so the obtained process parameters are obtained. It is more reliable, reproducible, and the product index is stable. In addition, there is no “ringing” phenomenon during the continuous 72 h rotary kiln roasting process, and the entire continuous process equipment is operating normally.

Fourth, the conclusion

(1) Through the experimental research on the magnetization roasting of φ800 mm×9000mm rotary kiln, the ore dressing index with iron grade greater than 65%, phosphorus content less than 0.25% and iron recovery rate higher than 78% was obtained.

(2) The self-developed LCP compound phosphorus-reducing agent effectively reduced the phosphorus content in the iron concentrate and obtained the high-quality iron concentrate product. LCP has the characteristics of low melting point, low price, convenient source and low pollution. Adding a certain amount in the process of high-phosphorus iron ore roasting can effectively reduce the phosphorus content in iron concentrate. In addition, a large number of experimental studies have been carried out on other types of high-phosphorus iron ore by LCP, and a better phosphorus-reducing effect has also been obtained.

(3) The success of the process of magnetization roasting (adding LCP to reduce phosphorus) and weak magnetic separation (stage grinding stage selection) provides a new idea for the development and utilization of refractory high-phosphorus iron ore.

(4) Under the situation of easy selection, high iron content, low impurity content and simple process of iron ore resources, it is an inevitable trend to develop and utilize difficult iron ore resources. Therefore, it will be of great practical significance to develop new technologies and processes to deal with this valuable iron ore resource.

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