An example of vanadium extraction from stone coal

China's Hunan, Hubei, Zhejiang, Anhui, Guizhou, Guangxi, Sichuan, Shaanxi and Anhui provinces are rich in stone coal . The V ₂ O ₅ grade in stone coal is between 0.3% and 1%. Although the grade is not high, the reserves account for 87% of the country's vanadium reserves, reaching 118 million t V ₂ O ₅ .

Vanadium in stone coal mainly occurs in vanadium mica and vanadium-containing clay. Vanadium exists in the trivalent state in vanadium mica and in the pentavalent state in clay. Therefore, oxidative roasting is required in the extraction of vanadium from stone coal to oxidize low-valent vanadium into pentavalent vanadium. From the perspective of typical stone coal mines in China, about 70% to 80% exist in the state of trivalent vanadium. The status quo of vanadium extraction from stone coal in China is as follows:

First, add salt sodium oxide roasting

By the end of the 1970s, China's traditional vanadium extraction process was the addition of salt to sodium oxide roasting. The amount of salt added per 100 kg of ore is about 10-20 kg (individually, Na ₂ SO _{4 is} also added). The temperature is 750 to 850 ° C, the time is 1 to 4 h, and the conversion rate is 60% to 78%. Flat kiln for roasting. The water leaching rate of the calcined material is 88% to 93%. Hydrolyzed vanadium, vanadium yield 92% ~ 96%, product V ₂ O ₅ purity greater than 98.5%, the total recovery is less than 50%.

The process is simple and easy to operate, with less investment and quick results. The main disadvantage is that the vanadium recovery rate is low, and the HCl, Cl ₂ , SO ₂ gas and acid hydrolysis vanadium waste liquid generated by calcination are seriously polluting the environment.

Second, fluidized roasting, acid leaching, ion exchange process

Coal Research Institute jointly developed by Hunan Changsha Nonferrous Metallurgy Design Institute, and has been produced in Hubei, the vanadium recovery rate has improved significantly. The total recovery of vanadium is about 65%, and the refined V ₂ O ₅ grade is greater than 99%.

3. Stone coal without salt roasting, acid leaching, solvent extraction

Developed by Hunan Coal Research Institute and Xiangxi Shuangxi Coal Mine and put into production. The process flow is shown in Figure 1. The leachant is sulfuric acid, and the extractant is 15% N263, 3% octanoic acid, and 82% sulfonated kerosene. pH=7, compared to O/A=2/1, primary extraction for 30 min. The stripping solution used 2% NH ₄ Cl + 1% NH ₄ OH, compared to O/A = 2/1, grade 1 grade. The roasting conversion rate is more than 55%, the acid leaching rate is 98%, the extraction rate is 99.8%, and the total vanadium yield is about 50%. The cost is reduced by 20% to 25%, gas pollution is reduced, and wastewater is reduced.

Figure 1 Stone coal salt-free roasting extraction process

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