Experimental study on manganese ore comprehensive pellets

I. Introduction

Pellet method is an ideal manganese ore agglomeration method, studies have shown that manganese pellets (acidic) and compared with sinter ore, manganese content increased on. Some people take the flux of foreign pellets with manganese system, reduce energy consumption and improve metallurgical performance. To further reduce energy consumption and improve productivity, in the former Soviet Union some scholars prepared manganese ore with coal gas into prereduction "Ore - coal" pellets, manganese and iron alloy melting test results show that, with a pre-reduction When the "ore-coal" pellets partially or completely replace the manganese concentrate or sinter in the charge, the electrical energy consumption is reduced by 22%, the manganese recovery rate and the furnace productivity are improved, and in order to reduce the amount of flux and coke added during the smelting, KrCopokhh Wait for others. Subsequently, the "ore-flux-coal" pellets with carbon content of 10% after calcination were developed, that is, the pellets with alkalinity of 1.0-1.1 were prepared by adding manganese concentrate with 20% anthracite and 20% dolomite. Practice has proved that this pellet is not only good in reducing, but also promotes the formation of metals and slag during smelting. There are few domestic manufacturers of manganese ore ore production. Its outstanding features are low yield, high cost and low operating rate. The test will be used to widen the calcination zone of pellets, reduce energy consumption, increase the reduction rate of pellets and manganese. Recovery is a more viable way to improve its production targets.

Second, raw material conditions and test procedures

The raw materials used in the test were manganese carbonate concentrates from Mintan manganese ore, Jidong dolomite and limestone , and Xiangtan coke powder. The chemical compositions of the samples are shown in Table 1.

Table 1 Chemical composition of raw materials (%)

Figure 1 shows the pellet test process. The test equipment includes a mill, a pelletizer, a high temperature roaster, an L-J1000 tensile tester and a reduction tester.

Figure 1 pellet test process

Third, the soft melt weight loss test

Since manganese ore is decomposed into MnO and Mn ₃ O ₄ by heat, it is easy to react with SiO ₂ at high temperature to form a low-melting silicate. The roasting temperature range of manganese ore is narrow, and when the calcination temperature fluctuates greatly (50°C) . This causes the pellet to melt or underfire. To this end, it is necessary to find a way to expand the roasting interval of the manganese ore pellet.

The test was carried out on the SCN802 modeling material fire performance tester. The three-factor quadratic regression orthogonal design was used to arrange the test. The variable design level and test results are shown in Table 2. In order to determine the softening temperature of the sample, the parallel sample is subjected to the weight loss-shrinkage test on the projection type R2Y-1 molten salt comprehensive measuring instrument. The test uses the cylindrical remelting measurement method to measure the thermometer when the cylindrical manganese ore sample starts to be inverted. To soften the onset temperature, the results are shown in Table 2.

Table 2 Head design and test results of soft-melting test

(Note): Y ₁ - softening start temperature; Y ₂ - softening final temperature; Y ₃ - melting end temperature.

According to the test results of the pure melting point pure lead (pure lead ), the inflection point of the temperature-shrinkage curve is the softening end or the melting start temperature, and the temperature at which the sample shrinks by 50% is the melting end temperature. 2. The test results show that the suitable material composition can increase the reflow temperature of the manganese mineral material and expand the reflow zone. If the N012 sample is compared with the original ore, it can be found that although the softening start temperature has not changed, it is 1070 ° C, but the softening end temperature is increased from 1190 ° C to 1270 ° C, and the melting end temperature is increased from 1220 ° C to 1360 ° C, and the soft melt interval is from Increased to 290 ° C at 150 ° C. This may be because the addition of CaO promotes the formation of a high melting point substance, such as CaO-SiO ₂ , which increases the reflow temperature of the manganese mixture. Therefore, it is possible to improve the pellet quality in the production process by producing a flux of manganese ore pellets.

Fourth, comprehensive pellet test results and analysis

(1) Comprehensive pellet test

On the basis of the flux-based comprehensive manganese ore pellets, in order to reduce the smelting coke ratio, the experimental study of the "ore-flux-coal" composite pellets was carried out based on the sample ratio of No. 2 NO12. Table 3 shows "Ore". - Head design of the flux-coal pellet test.

The test results can be processed to obtain the following equation:

The F test results show that the regression equation obtained is significant.

Table 3 Integrated pellet design variable level

(II) Analysis of strength and porosity of integrated pellets

It can be seen from the formulas (1) and (2) that the factors affecting the strength and the porosity are the firing temperature (X ₁ ), the calcination time (X ₃ ) and the interaction between the two, and the preheating time has little effect.

It can be seen from Fig. 2 and Fig. 3 that as the calcination temperature increases, the compressive strength of the pellets increases significantly, while the porosity decreases. When the preheating time, the calcination time and the calcination temperature are 20 min, 15 min and 1150 ° C, respectively, The compressive strength is 147 N/piece, and the porosity is 56%. When the temperature is raised to 1200 ° C, the compressive strength increases to 245 N/piece, and the porosity decreases to 54%. Compared with ordinary pellets, the "ore-flux-coal" pellets have lower strength, and the highest test is 325.85 N/piece. The photomicrograph (slightly) shows the "ore-flux-coal" composite pellet. It is mainly composed of spheroidal manganese ore and stellite aggregates (see Table 4), while the porphyrite ore is porous honeycomb structure, and its pressure hardness averages 4391 N/mm ² , so the "ore-flux-coal" composite pellet The porosity is large and the strength is not ideal.

Figure 2 Equivalent graph of compressive strength of pellets after 15 minutes of roasting

Fig. 3 Equivalent diagram of porosity of pellets after roasting for 20 min

Table 4 Mineral composition microstructure

In the table: T-baking temperature; t ¹ - preheating time; t-baking time

(III) Analysis of residual carbon in integrated pellets

It can be known from equation (3) that the main factors affecting the integrated pellets are calcination temperature, preheating time and calcination time. Figure 4 is the equivalent diagram of the residual carbon of the pellets when the calcination temperature is constant.

Figure 4 "Ore-flux-coal" pellets residual carbon equivalent map

As seen from Fig. 4, the increase in the calcination temperature and the prolongation of the preheating time reduce the amount of residual carbon. The residual carbon in the pellets can be used as a reducing agent during the refining, which can save the smelting coke ratio and power consumption. However, the excessive carbon residue will affect the strength of the pellets, and the residual carbon in the pellets should be strictly controlled. the amount.

(IV) Reductive analysis of comprehensive pellets

Kinetic studies and thermal analysis of "ore-coal" pellet reduction indicate that direct reduction of carbon by MnO ₂ is an exothermic reaction, so the temperature of the calcined sphere is higher than the temperature of the furnace. In addition, since the thermal decomposition of coal has a great influence on the reduction of high-priced manganese oxide, the reduction rate of the pellets is greatly accelerated. Therefore, the carbon in the pellets greatly enhances the reduction process of manganese minerals. The mineral identification of the pellets is shown (see Table 5). The main mineral of the comprehensive pellet mine is the manganese ore. The other pellets and sinter are mainly manganite. The mineral characteristics of the integrated pellets are favorable for accelerating the reduction process.

Table 5 Mineral identification of pellets and sinter

(5) Separation characteristics of metal and slag during smelting of integrated pellets

Table 6 shows the results of the comprehensive pellet smelting test, which shows that the uniform carbonized fine particles in the pellets can significantly promote the formation of metals during smelting.

Table 6 Integrated pellet smelting products (%)

V. Conclusion

(1) The addition of additives to the mixture can widen the soft melt interval, which overcomes the shortcomings of the pellets being difficult to operate due to the narrow melting zone.

(2) The integrated pellets have good smelting performance and are ideal for the smelting of electric furnaces. However, due to their low strength, the current research results cannot be used as raw materials for blast furnaces.

(3) The research on the strength of the integrated pellets should be strengthened (for example, the double-layer pellet method can be considered for testing, and the inner and outer layers of the pellets are added with different amounts of coal and flux) to increase the strength and make the composite ball. The mine has become an excellent raw material for smelting.

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