Experiment on extracting vanadium from a stone coal vanadium mine

Stone coal is a unique vanadium resource that can be exploited as a separate deposit in China. Its ore type is mainly carbonaceous and siliceous, and vanadium is almost entirely present in clay minerals such as vanadium-bearing mica (illite) and kaolinite. It exists in the mineral lattice with aluminum , potassium and iron in the same form as the analogy. It is very difficult to extract directly. A certain stone coal vanadium deposit in the northwest belongs to the siliceous rock-bearing carbonaceous mudstone type, and vanadium exists in the hydromica in the form of isomorphism. The oxidized roasting-sulfuric acid leaching-reduction-solvent extraction-ammonium salt precipitation process was used to extract vanadium pentoxide from the ore and the optimum extraction conditions were determined.

I. Ore and reagents

The main chemical composition of the ore is: 1.07% V ₂ O ₅ , 78.60% SiO ₂ , 2.60% Fe ₂ O ₃ , 3.13% Al ₂ O ₃ , 0.97% CaO, 0.68% K ₂ O, 0.47% P ₂ O ₅ , 0.95 % S, 1.40% C, loss on ignition 3.94%.

Reagents: sulfuric acid, ammonia water, sodium chlorate, were of analytical grade; iron, P ₂ O ₄ (bis (2-ethylhexyl) phosphoric acid, tributyl phosphate, aliphatic TBP), sulfonated kerosene, are industrial grade.

Second, the test method

By calcination, V(III) is first oxidized to V(IV) or V(V) and then dissolved with an acid, then extracted with P ₂ O ₄ having high selectivity to tetravalent vanadium, and then back extracted with an aqueous solution of sulfuric acid. After the V(IV) in the stripping solution is oxidized to V(V), the red vanadium is precipitated by ammonium salt precipitation, and the precipitated red vanadium is washed, dried and pyrolyzed to obtain a vanadium pentoxide product. The process flow is shown in Figure 1.

Third, the test results discussion

(1) Leaching exploration test,

The ore particle size is 0.089 mm and the temperature is 95 ° C. The direct acid leaching test results (see Table 1) indicate that the leaching rate of vanadium pentoxide is lower under enhanced leaching conditions. After the ore is pelletized, it is calcined and then leached with sulfuric acid (raw material size: 0.124 mm, pelletized Φ10 mm; leaching temperature: 90 ° C, leaching particle size - 0.71 mm, liquid solid product mass ratio of 1.2, leaching for 2 h). The test results (see Table 2) indicate: The ore is treated by an oxidizing roasting-acid leaching process, and the leaching rate of vanadium pentoxide is significantly improved compared with the direct acid leaching.

Table 1 Direct acid leaching exploration test results

Table 2 Results of pelleting-baking-leaching exploration test

(two) roasting test

The ore is ground to -0.074 mm for 90%, and the ball is Φ10 to 20 mm. It is calcined after drying. The leaching temperature was 90 ° C, the leaching ore sample size was -0.71 mm, the sulfuric acid amount was 25%, and the leaching time was 2 h.

1. Effect of calcination temperature

The calcination time is 2 h, and the effect of calcination temperature on the leaching rate of vanadium pentoxide is shown in Fig. 2. It can be seen that as the calcination temperature increases, the leaching rate of vanadium pentoxide increases, but after the temperature rises to 900 °C, the leaching rate tends to be stable, which may be because the vanadium is encapsulated or the vanadium bound by vanadium is formed by sintering. Stones and nepheline minerals make it difficult for vanadium to leach; however, the lower calcination temperature is not enough to completely oxidize low-valent vanadium, resulting in a low vanadium leaching rate. The test determines that the calcination temperature is preferably 900 °C.

2, the impact of roasting time

The calcination temperature is 900 ° C, and the effect of calcination time on the leaching rate of vanadium pentoxide is shown in Fig. 3. It can be seen that: after calcination for 1 h, the leaching rate of vanadium pentoxide is only 84.61%, and the vanadium leaching is incomplete. This may be due to insufficient calcination time and insufficient complete destruction of the mineral structure, resulting in insufficient oxidation of low-valent vanadium; roasting for 1.5 h, vanadium The leaching rate reached 92.43%, and the roasting time was extended, and the leaching rate did not change much. The calcination time was determined to be 1.5 h.

(3) Determination of leaching conditions

The calcination temperature was determined to be 900 ° C, the calcination time was 1.5 h; the calcination was broken to -0.71 mm, and the liquid solid product mass ratio was 1.2.

1, the impact of sulfuric acid dosage

The leaching temperature of 90 ° C, time 2 h, the effect of sulfuric acid dosage on vanadium leaching rate is shown in Figure 4. It can be seen that after the ore is calcined, a higher acidity is still required to obtain an ideal leaching rate, which may be due to more acid-consuming substances in the ore. When the pH of the leachate rises, the leached pentavalent vanadium is hydrolyzed and precipitated, so that the leaching rate of vanadium pentoxide is lowered. The amount of acid selected for the test was 20%.

2, the impact of leaching temperature

The leaching time is 1 h, the amount of sulfuric acid is 20%, and the effect of the leaching temperature on the leaching rate of vanadium pentoxide is shown in Fig. 5.

It can be seen from Figure 5 that the effect of temperature on the leaching rate of vanadium pentoxide is not significant. In order to reduce the energy consumption and reduce the temperature requirements for the equipment, the test was selected to leaching at room temperature.

3, the impact of leaching time

The effect of the leaching time on the leaching rate of vanadium pentoxide at room temperature is 20%, and the test results are shown in Fig. 6.

It can be seen from Fig. 6 that the leaching rate of vanadium pentoxide is slightly increased with the increase of leaching time; after 2 hours of leaching, the leaching rate tends to be stable. The test determined that the leaching time was 2 h.

(4) Extraction-back extraction-ammonium salt vanadium

1. Extraction-back extraction

The leachate was neutralized by ammonia and iron scraps to obtain a liquid extract. The neutralization and reduction recovery of V ₂ O ₅ was 97.52%. The concentration of the raw liquid V ₂ O ₅ is 5-6 g/L, and the pH is 2.2 to 2.45. The mixing time single-stage extraction test results are shown in Table 3; the raw material pH value single-stage extraction test results are shown in Table 4; the extractant concentration single-stage extraction test results are shown in Table 5.

Table 3 Mixed-time single-stage extraction test results

Test conditions: extract ρV ₂ O ₅ = 5.88 g / L; compared (Va / Vo) = 1; extractant V (P2O4), V (TBP), V (kerosene) = 15.. 5.. 80; clarification time 7 min; feed pH = 2.2.

Table 4 Single-stage extraction results of raw material pH

Test conditions: extract ρV ₂ O ₅ = 5.88 g / L; compared (Va / Vo) = 1; extractant V (P2O4), V (TBP), V (kerosene) = 15.. 5.. 80; mixing time 5 min; clarification time 7 min.

Table 5 Single-stage extraction results of extractant concentration

Test conditions: extraction liquid ρV ₂ O ₅ = 5.88 g / L; compared (Va / Vo) = 1; mixing time 5 min; clarification time 7 min; pH value of the feed 2.38.

It can be seen from Table 3 that the extraction reaction is very fast, and the contact time of the two phases is within 5 min to reach the extraction equilibrium. The test determined that the extraction mixing time was 5 min and the clarification time was 7 min.

It can be seen from Table 4 that as the pH of the feed liquid increases, the extraction rate of vanadium pentoxide increases, but when the pH reaches 2.5, a small amount of floc starts to appear, which may be impurities in the aqueous phase such as iron and aluminum. To. The pH control is preferably between 2.3 and 2.5.

As seen from Table 5, in the single-stage extraction, the optimum composition of the extractant is 15% P2O4 + 10% TBP + 75% kerosene.

A 5-stage countercurrent extraction was carried out under optimal conditions, and the results are shown in Table 6.

Table 6 Results of the 5th-stage countercurrent extraction test

Extraction conditions: the concentration of V ₂ O _{5 was} 5.19 g/L, and the extractant was 75% sulfonated kerosene + 15% P2O4 + 10% TBP, compared with (Va/Vo)=1..1,1, mixing time 5 min, clarification time 7min.

After the 5-stage countercurrent extraction, the extraction rate of V ₂ O _{5 is} 98.48%, and the concentration of the supported organic phase V ₂ O ₅ is 5.28 g/L. The extractant can be recycled after being treated. The extracted organic phase after extraction was back-extracted by a 5-stage countercurrent with 1.5 mol/L sulfuric acid solution. The results are shown in Table 7.

Table 7 Results of the 5th-level countercurrent back extraction test

Test conditions: Va/Vo=8..1, mixing time 10 min, clarification time 10 min.

After the 5-stage countercurrent stripping, the V ₂ O ₅ concentration in the lean organic phase is 0.001 g/L, the V ₂ O ₅ stripping rate is 99.98%, and the V ₂ O ₅ mass concentration in the stripping solution is above 45 g/L.

2. Preparation of product vanadium pentoxide

Red vanadium was precipitated by ammonium salt precipitation. The test conditions are as follows: the concentration of V ₂ O ₅ in the stripping solution is 47.08 g / L, adding sodium chlorate solution with a mass concentration of 200 g / L, stirring at 60 ° C for 1 h, controlling the oxidation-reduction potential above -900 MV; adjusting the pH with ammonia water To 2.1, stirred at about 92 ° C for 2 h, precipitated red vanadium; red vanadium after washing, drying, pyrolysis, to obtain a brownish yellow powdery product. In the vanadium precipitation process, the V ₂ O ₅ precipitation rate was 97.50%, and the V ₂ O ₅ calcination recovery rate was 98.50%. The final product composition analysis results were: 98.78% V ₂ O ₅ , 0.11% Si, 0.30% Fe, 0.0093% As, 0.05% P, 0.003% S, (0.026+0.041)% (Na ₂ O+K ₂ O), product GB3283-1987 metallurgical quality to meet 98 standards.

Fourth, the conclusion

(1) Extracting V ₂ O ₅ from a certain stone coal and vanadium mine in the northwest by using a pellet-oxidation roasting-leaching-neutralization-reduction-extraction-oxide vanadium-calcination process. The ore is ground to 0.074mm and accounts for more than 90%. After pelletizing, it is oxidized and calcined at 900 °C for 1.5 h, the calcined sand is crushed to 0.84 mm, and leached with sulfuric acid solution at room temperature for 1 h, and vanadium is substantially completely leached.

(2) After neutralization and reduction treatment, the leachate is extracted with 15% P2O4 + 10% TBP + 75% sulfonated kerosene system and back extracted with 1.5 mol/L sulfuric acid solution. The anti-extract solution is precipitated with red vanadium by salt, and red vanadium is at 550 ° C. Calcined to obtain a qualified product.

(3) The leaching rate of vanadium pentoxide in the process is 88.66%, the recovery rate of neutralization reduction is 97.52%, the extraction rate is 98.48%, the stripping rate is 99.98%, the precipitation rate is 97.50%, the recovery rate of calcination is 98.5%, and the total vanadium pentoxide is The recovery rate was 81.76%.

(4) With this process, the recovery rate of vanadium pentoxide is greatly improved compared with the traditional sodium roasting process, and it meets environmental protection requirements, which is conducive to industrialization.

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