China's vanadium resources are extremely rich, but most of them are low in quality, and most of them have not been fully exploited. Vanadium predominantly in the form of trivalent and pentavalent in ore, wherein the trivalent vanadium almost mainly containing iron minerals or mineral containing aluminum, there is no independent minerals; pentavalent vanadium is generally formed independently of the mineral - vanadate, often associated with uranium and phosphorus mineral association. When the vanadium in the ore is present in the silicate mineral in a trivalent state, the additive is usually calcined at a high temperature to destroy the structure of the vanadium mineral, and the trivalent vanadium is oxidized to pentavalent vanadium for leaching. However, high temperature roasting has large pollution, high energy consumption and large investment.
The V 2 O 5 of a vanadium ore in Northwest China has an average grade of 0.75%. The mineral composition is complex and the phosphorus content is high. The traditional roasting process is used for oxidative roasting. The vanadium conversion rate is low, so the resource has not been well developed. . The experiment studied the direct acid leaching of the ore and determined the feasible process conditions.
I. Ore type and material composition
(1) Ore type
The composition of the ore is very complicated. Vanadium is adsorbed in argillaceous rocks and colloidal limonite, and there is no corresponding independent mineral. The carrier materials of vanadium are mostly in the form of muddy internal debris. The gangue minerals are mainly calcite , quartz and mud, and the surrounding rock is carbonate rock. The apatite is mostly in the form of clastic cement in the colloidal phosphate ore, which is a microcrystalline apatite formed by colloidal dehydration.
(2) Ore composition
The results of multi-element chemical analysis of the ore are shown in Table 1. The X-ray diffraction analysis results of the ore are shown in Table 2.
Table 1 Multi-element chemical analysis results of ore
Table 2 X-ray diffraction analysis results of vanadium ore
Second, the principle of testing
Argillaceous rocks and ores destroy the structure of the gum limonite oxidizing acid, into the mineral crystal lattice hydrogen ions replace the corresponding metal ions, changes in the structure of fossil, vanadium released, and it is oxidized to tetravalent vanadium. Tetravalent vanadium is easily soluble in acid and forms vanadium oxide ion (VO) 2+ . The reaction formula is:
Third, test equipment and methods
(1) Test equipment
The test equipment mainly includes HH-2 type electric heating constant temperature water bath, JJ-1 type precision booster electric mixer, 2X2-2 type rotary vane type vacuum pump and so on.
(2) Test methods
Take a certain concentration of sulfuric acid solution in a four-necked bottle, and heat it to a certain temperature in a water bath; weigh a certain amount of raw ore into a four-necked bottle containing acid, continue to heat and stir; stop stirring after a period of reaction , filter, wash. The filter residue and filtrate were separately measured and analyzed.
Fourth, test results and discussion
(1) Orthogonal test of direct acid leaching of raw ore
The ore is directly leached with sulfuric acid, and the vanadium leaching rate is mainly affected by the concentration of the leaching agent, the leaching temperature, the mass ratio of the liquid solid product, the leaching time, and the ore particle size. Select these 5 factors, 3 factors per factor, and arrange the L27 (313) orthogonal test. The factors and levels are shown in Table 3. The test results are shown in Table 4 and Figures 1-4.
Table 3 Test factors and levels
Table 4 Orthogonal test results
Fig.1 Effect of mass concentration of H 2 SO 4 on vanadium leaching rate
Fig. 2 Effect of mass ratio of liquid solid product on vanadium leaching rate
Figure 3 Effect of leaching time on vanadium leaching rate
Figure 4 Effect of leaching temperature on vanadium leaching rate
Figure 5 Effect of ore particle size on vanadium leaching rate
It can be seen that the raw ore is directly subjected to acid leaching, and the order of influence of each factor is: leaching temperature > liquid solid product mass ratio > sulfuric acid mass concentration > leaching time > raw ore size; preferred process parameters are: leaching temperature 90 ° C, liquid solid product The mass ratio is 3:1, the H 2 SO 4 concentration is 250 g/L, the leaching time is 6 h, and the ore particle size is less than 0.175 mm. The temperature and liquid solid mass ratio are the main factors affecting vanadium leaching: the temperature rise is beneficial to the leaching reaction, but the temperature is too high, which is unfavorable for operation, not higher than 90 °C; the liquid solid product quality is relatively large. Higher leaching rate can be obtained, but the mass concentration of vanadium in the leachate is also reduced, which affects subsequent purification and enrichment, which is more suitable for 2:1; H 2 SO 4 mass concentration increases, vanadium leaching rate increases, but acidity It is economically uneconomical to reduce the pH value of the solution and affect the subsequent process. Therefore, the mass concentration of H 2 SO 4 is determined to be 250 g/L.
(2) Verification test
According to the orthogonal test results of direct ore leaching of raw ore, the verification test was carried out under the most suitable conditions. The vanadium leaching rate was 90.72%-92.56%, and the average value was 91.81%, which had good results.
V. Conclusion
It is feasible to leach vanadium by direct sulfuric acid leaching of high phosphorus vanadium ore. The optimum conditions for direct acid leaching are: leaching temperature 90 ° C, liquid solid product mass ratio 2:1, H 2 SO 4 mass concentration 250 g / L, leaching time 6 h, ore particle size less than 0.175 mm, vanadium leaching rate under this condition Up to 90.72% to 92.56%.
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