Stone coal extraction vanadium coal blending technology

The vanadium in stone coal is mainly trivalent, and the trivalent vanadium exists in the silicon tetrahedral structure of clay minerals in the form of isomorphism. The combination is strong and insoluble in acid and alkali, only under the action of high temperature and additives. Conversion to soluble pentavalent vanadium, so roasting is an indispensable process for extracting vanadium from stone coal .

The high-temperature oxidative roasting process in the laboratory for the vanadium extraction process is mostly carried out by electric heating of the muffle furnace. Due to the uneven temperature distribution in the furnace, the temperature of some ore samples is low and the oxidation is insufficient. At the same time, the roasting temperature is higher and the time is higher. Long, high energy consumption and other shortcomings. In view of the above problems, it is considered to add an appropriate amount of anthracite in the roasting process, which does not affect the oxidizing atmosphere, and can cause point-to-point contact heat transfer with the coal coal during combustion, increase the temperature of some ore samples, accelerate the oxidation reaction process, thereby lowering the roasting temperature, Shorten the reaction time. Therefore, research on the oxidation roasting of stone coal blending coal has certain guiding significance for improving the conversion rate, improving the roasting conditions, reducing the roasting energy consumption and optimizing the vanadium production.

First, the test part

(1) Test materials

The ore sample used in this experiment was taken from a vanadium mine in a certain area of ​​Jiangxi. The main chemical composition is shown in Table 1.

Table 1 Stone coal chemical composition (mass fraction) /%

(2) Test reagents and instruments

The experimental materials are sodium salt composite additive (MX) and anthracite coal (Jincheng, Shanxi); the experimental instruments are SXZ-10-B muffle furnace, 101-3 type drying oven, XZM-100 vibration grinding sample machine, SHB-III circulating water vacuum pump, etc. .

(3) Test methods

Under the conditions of the best decarburization, grinding and compounding additives determined in the previous test, a certain amount of raw ore is crushed to 0~5mm, decarburized at 700°C for 30min, and the original or decarburization sample is ground to 0~0.125mm. Add 12% composite additive, add a certain amount of anthracite coal during coal blending test, mix well, and then put it in a muffle furnace at a certain temperature (baking temperature refers to the set temperature of the roasting equipment meter) for roasting. The clinker was immersed for 40 min at a liquid-solid ratio of 2.5..1 and 90 ° C; the leaching residue was immersed in 1% HCl for 60 min at 40 ° C. Determination of leachate concentration of vanadium, vanadium leaching rate calculation method using ferrous capacity. The leaching rate is calculated as:

(four) test principle

The free energy-temperature relationship of carbon vanadium oxide is shown in Figure 1.

It can be seen from Fig. 1 that carbon combustion is smaller than the Gibbs free energy of vanadium oxidation. Therefore, in the roasting process, the first reaction is carbon combustion; when the carbon amount is low, the oxidation process of trivalent vanadium begins. Before the ash roasting of the stone coal, the ore is generally subjected to pre-decarburization treatment. When high temperature oxidation roasting of stone coal and composite sodium salt additives, the main chemical reactions are:

C+1/20 ₂ ==CO (1)

CO+1/20 ₂ ==CO ₂ (2)

V ₂ 0 ₃ +O ₂ ==2V0 ₂ (3)

2V0 ₂ +1/20 ₂ ==V ₂ 0 ₅ (4)

2NaCl==2Na+Cl ₂ (5)

2Na+1/20 ₂ ==Na ₂ O (6)

xNa ₂ 0+yV ₂ O ₅ ==xNa ₂ 0·yV ₂ 0 ₅ (7)

Stone coal sodium oxidizing roasting is mainly divided into four steps: carbon oxidation, vanadium conversion from low price to high price, salt decomposition and oxidation, and combination of sodium oxide and vanadium pentoxide.

Second, the test results and discussion

(1) Comparative test of stone coal ore and decarburization oxidative roasting

The effect of different calcination temperatures on the leaching rate is shown in Figure 2 when the composite additive is 12% and the calcination time is 1.5h. When the calcination temperature of the decarburization sample is 850 ° C and the calcination temperature of the ore is 790 ° C, the effect of different calcination time on the leaching rate is shown in FIG. 3 .

It can be seen from Fig. 2 and Fig. 3 that the oxidative roasting of the ore after decarburization is better than the direct oxidation roasting of the ore. This is because after the demineralization of the ore, some organic matter, carbon and some reducing minerals are oxidized, so that it does not affect the conversion reaction of vanadium during high temperature oxidative roasting; another decarburization can improve the grade of vanadium and loosen the original ore structure. The decarburization sample is more easily contacted with the oxidizing gas to cause an oxidation reaction. Therefore, the ore needs to be decarburized and then oxidized and roasted.

The calcination temperature and time are the main influencing factors of oxidative roasting. When the calcination temperature is less than 760 ° C, mainly the oxidation of other reducing substances inhibits the oxidation reaction of vanadium, resulting in low conversion of vanadium; when the temperature rises, the firm lattice structure of the silicon tetrahedron is destroyed, vanadium is free from binding, Most of V(III) and V(IV) are converted to V(V); when the temperature is higher than 850 °C, the high-valence vanadium undergoes a secondary reaction to form insoluble vanadate, which also reacts with the stone coal components, especially SiO. ₂ Participate in the reaction to form complex and insoluble silicates, affecting the leaching rate of vanadium. When the oxidizing roasting time is less than 1.5 h, the reaction is insufficient and the leaching rate is low; after the calcination time is more than 2.5 h, the side reaction occurs and the production cycle is affected. The experimental results show that the ore is decarburized and calcined at 850 °C for 1.5 h, the leaching rate can reach 80.12%; the ore is directly calcined at 790 °C for 1.5 h, and the leaching rate is up to 68.41%.

(2) Coal blending roasting test

Anthracite has the characteristics of high degree of coalification, low volatile content, high density, high ignition point and no cohesiveness. Therefore, anthracite is selected as the coal type for coal blending test. The carbon content of anthracite used in this experiment was 92.61%, the volatile content was 3.28%, the ash was 4.11%, and the calorific value was 31500kJ/kg.

1. Coal-fired ore blending test

Adding a certain amount of anthracite roasting can make the coal coal and anthracite fully contact and point-to-point heat transfer, which is beneficial to the oxidation of vanadium, but the combustion requires a large amount of oxygen, which will inhibit the oxidation of vanadium; therefore, it is feasible to investigate whether the coal-fired coal-fired roasting is feasible.

The ore is mixed with a certain amount of anthracite and 12% composite additive, and calcined at 790 °C for 1.5 h. The effect of different anthracite addition on the leaching rate is shown in Fig. 4.

It can be seen from Fig. 4 that the original ore is added with anthracite oxidative roasting, and the leaching rate is larger than that of unalloyed coal. Since the carbon oxidation reaction occurs first in the calcination process, followed by the oxidation of vanadium, although the addition of anthracite can provide a certain amount of heat for roasting, the carbon combustion in the ore and anthracite requires a large amount of oxygen, which affects the oxidizing atmosphere of vanadium turnover. The reducibility of anthracite in this process is the dominant factor. Therefore, the ore should not be blended with coal oxidizing roasting.

2, decarburization sample coal roasting test

The decarburization sample was mixed with a certain amount of anthracite and 12% composite additive, and calcined at 820 ° C for 1 h. The effect of different anthracite addition on the leaching rate is shown in Fig. 5.

It can be seen from Fig. 5 that the leaching rate increases slightly with the increase of anthracite dosage. When the anthracite dosage is 5%, the total leaching rate is 81.96%, which indicates that point-to-point contact heat transfer between anthracite and stone coal is beneficial to vanadium oxidation. Does not affect the oxidation atmosphere required for vanadium oxidation; continue to increase the amount of coal, the leaching rate decreases, indicating that the amount of anthracite is too much, the amount of oxygen required for combustion exotherm increases, destroying the oxidizing atmosphere of roasting, and the amount of coal is too large, easily causing local The temperature is too high to cause the ore sample to be partially sintered. Therefore, the optimum amount of anthracite added is 5%.

The decarburization sample was mixed with 5% anthracite and 12% composite additive, and calcined at different temperatures for 1 h. The effect of calcination temperature on the leaching rate is shown in Fig. 6.

It can be seen from Fig. 6 that the leaching rate of decarburization sample plus 5% anthracite calcined at 820 °C for 1 h can reach 81.96%. Compared with Fig. 2, the leaching rate of decarburization sample unmatched coal at 850 °C for 1.5 h is 80.12%. After adding a certain amount of anthracite, it can provide heat for oxidizing roasting, reduce the external environment temperature, and does not affect the vanadium price conversion effect. Therefore, after adding 5% anthracite, the calcination temperature can be lowered by 30 ° C, and the total leaching rate is slightly increased.

The decarburization sample was mixed with 5% anthracite and 12% composite additive, and calcined at 820 ° C. The effect of baking time on the leaching rate is shown in Fig. 7.

It can be seen from Fig. 7 that the decarburization sample is 5% anthracite coal calcined at 820 ° C for 1.5 h, the leaching rate is 82.08%; when the calcination time is 1 h, the leaching rate is 81.96%. Decarburization sample plus anthracite high temperature roasting, this point-to-point contact heat transfer is beneficial to vanadium oxidation and accelerate the price conversion process of vanadium. After the decarburization sample is added with anthracite, the calcination temperature can be reduced by 30 °C, the calcination time can be shortened by 0.5 h, and the leaching rate is not affected, and the roasting energy consumption is greatly reduced.

Third, the conclusion

(1) The leaching rate of oxidizing roasting of the ore after decarburization can reach 80.12%, which is 11.71% higher than the direct oxidizing roasting leaching rate of the ore. Therefore, the stone coal ore needs to be decarburized and reoxidized and calcined.

(2) When the raw ore is oxidized and roasted with anthracite as the added coal, the leaching rate is low, so the stone coal ore is not suitable for coal blending.

(3) Decarburization sample with 5% anthracite oxidative roasting, the calcination temperature is reduced from 850 °C to 820 °C, the roasting time is shortened from 1.5 h to 1 h, the leaching rate is 81.96%, and the leaching rate is slightly increased compared with the non-coal roasting. And greatly reduce the energy consumption of roasting.

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