Extraction of vanadium pentoxide from vanadium ore without salt roasting

I. Introduction

The average vanadium content in the crust is 0.015%, more than copper, nickel, zinc, tin, cobalt, lead and so on, but mainly due to the nature of vanadium to trivalent form is present, and the ionic radius of trivalent vanadium and trivalent The ionic radii of aluminum and ferric iron are very close. Therefore, trivalent vanadium hardly forms its own minerals, but instead replaces ferric and trivalent aluminum in some iron and aluminum minerals, such as the isomorphous part. Vanadium- titanium magnetite and aluminosilicate, which are the main reasons for the high dispersion of vanadium in nature. Traditional vanadium extraction method In order to destroy the structure of vanadium minerals, there is a roasting process in which sodium salt is added as a conversion agent, and most of the NaCI is added. Due to the addition of NaCI, a large amount of exhaust gas containing strong corrosive gases such as HCI and CI ₂ is generated during the roasting process, which is difficult to treat, causing serious pollution to the surrounding environment of the factory and endangering people's lives and property.

Since 2005, the State Environmental Protection Administration has stepped up efforts to rectify small vanadium plants, shutting down and blasting small vanadium smelters using NaCI as additives. Only Hunan has closed and rehabilitated nearly 100 small vanadium plants since June 2005. . Similar remediation actions have been carried out in Hubei, Henan, and Shaanxi provinces. However, vanadium is an indispensable additive in the steel industry and is increasingly used in petrochemical, electronics, glass and ceramics industries. Its price in the international market has steadily increased, such as the vanadium pentoxide grade of 98% since the beginning of 2003. The $1.5/lb rose to $30/lb at the end of April 2005, a 20-fold increase. Although it has fallen back since then, it stabilized at $10/lb in October 2005, which is still six times higher than in early 2003. Its economic value is a treasure trove of wealth for many poor mountainous areas in China that contain vanadium deposits. In recent years, some domestic research and production departments have done a lot of experimental research work to improve the total recovery rate of V ₂ O ₅ in ore, simplify the process flow, reduce the cost of vanadium production, and reduce the environmental pollution caused by “three wastes”. A new process such as direct acid pickling of stone coal, solvent extraction, stone coal oxidizing roasting, alkaline leaching, calcification roasting, carbonation leaching, blank roasting, and acid leaching. When the last two years, entrusted the country more than a dozen vanadium ore or small test samples Pilot Study of Hunan Nonferrous Metal Research Institute of Metallurgy is located, found a class of vanadium ore roasting a salt-free using diffuse out of a sulfuric acid solvent extraction process to extract Vanadium pentoxide, the recovery rate of vanadium in the roasting-leaching section can reach more than 90%, and the recovery rate of vanadium in the whole process reaches 85%, which greatly exceeds the level of 50% recovery of the general vanadium production plant. Because it is salt-free roasting, there is no strong corrosive gas such as HCI and C1 ₂ in the roasting process. Exhaust gas, waste water and waste residue can be discharged to a standard, so it is a promising clean production process. The author carried out a detailed small-scale experimental study on the roasting, leaching and extraction processes of the process, and carried out an extended closed loop test of 2.5 kg.

Second, the test materials

(1) Mineral sample

The main minerals of the vanadium ore sample are chalcedony, quartz , clay minerals, a small amount of feldspar , limonite, hematite, calcite . Vanadium mainly occurs in clay minerals, mainly kaolinite and illite. The results of multi-element chemical analysis of vanadium ore are shown in Table 1, and the results of phase analysis are shown in Table 2. The phase analysis results in Table 2 show that vanadium is mainly present in the mica minerals by replacing the 6-coordinated Al with the V3 isomorphism, secondly in the iron oxide and clay minerals, and a small part in the electrical Stone and garnet. The valence state analysis of vanadium shows that the low-valent vanadium in the sample accounts for the majority, reaching 74.14% of vanadium vanadium 25.86%.

Table 1 Results of multi-element chemical analysis of vanadium ore

Table 2 Analysis results of vanadium ore phase

(2) Reagents

Sulfuric acid: analytically pure (95% to 98%, density 1.84g/mL);

Sodium chlorate: analytically pure;

Ammonia: industrial grade, NH _{3 is} about 20%;

Iron powder: industrial grade;

P2O4: Industrial grade.

Third, the test principle and method

The vanadium present in the mica lattice in the aluminosilicate mineral in the V3 isomorphous form to replace the sub-coordinated AP must destroy the mica structure and oxidize it to dissolve. The vanadium-containing raw material is directly or mixed with an additive and then calcined at a high temperature in an oxidizing atmosphere for the purpose of destroying the structure of the vanadium mineral, oxidizing the trivalent or tetravalent vanadium to vanadium vanadium, and decomposing with the additive or the ore itself. The product produces metavanadate. The alkali metal and magnesium metavanadate formed during calcination are soluble in water and acid, Fe(VO ₃ ) ₂ , Fe(VO ₃ ) ₃ , Mn(VO ₃ ) ₂ , Ca(VO ₃ ) ₂ and The fully oxidized tetravalent vanadium compound is insoluble in water but soluble in acid.

The acid leaching process is not selective. In addition to the dissolution of the vanadium compound, many impurities are also dissolved into the human solution, so that the resulting leaching solution has more impurities and needs to be further purified. There are various methods for purifying the vanadium ore sulfuric acid leaching solution, which can be directly dried by vanadium precipitation, or purified by ion exchange, or purified by solvent extraction. This test uses P2O4 (bis (2-ethylhexyl) phosphoric acid) method with TBP (tributyl phosphate) sulfonated kerosene solution extraction, P2O4 extractable tetravalent or pentavalent vanadium cation and the extraction V ^{4 +} Ability is stronger than V ^{5 +} . The extraction coefficient of P ⁴ O ⁴ to V ^{4 +} is quite large, and the extraction reaction can be expressed as:

(1)

In the formula, HA is P2O4. When nl>1, a multinuclear complex is formed during the extraction.

In the actual extraction process, the concentration of P2O4 is generally 10% to 20%, and 5% is added. TBP synergistic extraction, the amount of sulfonated kerosene is 75% to 85%. The pH of the extraction process is maintained at around 2. The solution before extraction is treated with iron powder, sodium sulfide or sodium hydrosulfide, and v ^{5 +} in the solution is reduced to. Fe ^{3 +} in the solution is also reduced to Fe ^{2 + in a} non-extracted state. The vanadium in the stripping P2O4 is generally treated with 15% sulfuric acid solution or 10% sodium carbonate solution. In this test, 15% sulfuric acid solution is used as the stripping agent.

The vanadium in the stripping solution exists in a tetravalent form and must be oxidized to a vanadium vanadium to form an ammonium salt to form vanadium. This test uses sodium chlorate as the oxidant. V ₂ O ₅ has the lowest solubility under the condition of pH=1.9-2.2, which is also the optimum acidity of vanadium precipitation. Because the stripping agent is sulfuric acid solution, the pH value is adjusted with ammonia water when vanadium is precipitated, and the solution neutralizes excessive sulfuric acid. Ammonium, so adjust the pH to 2.2 with ammonia to achieve vanadium precipitation. Increasing the temperature accelerates the precipitation of vanadium. Generally, the precipitation rate can be accelerated by 1.6 to 2 times for every 10 °C increase. Stirring can evenly spread the precipitate and increase the reaction speed. Especially when the vanadium concentration in the late vanadium solution is continuously reduced, the effect of stirring is more obvious. In addition, adding some pre-precipitated vanadium compounds as seed crystals during precipitation of vanadium can accelerate the precipitation process and increase the precipitation rate. The precipitated red vanadium is dried and calcined in a muffle furnace at a temperature of 550 ° C for 3 h to obtain a V ₂ O ₅ product.

The small test uses single factor condition test to determine the calcination temperature, calcination time, leaching temperature and other process parameters, and expands the closed loop test using the best conditions obtained by small experiments. The expanded test process is shown in Figure 1.

Fourth, test results and analysis

(1) Grinding particle size

1. Raw ore grinding grain size

The ore grinding grain size has a great influence on the vanadium leaching rate, because in the aluminosilicate mineral, vanadium is replaced by the V ^{3 +} isomorphous form in the 6-coordinated Al and exists in the mica lattice. The finer it is, the easier it is to destroy the mica structure, and the vanadium is more susceptible to oxidation.

The condition test of the ore grinding grain size was done in two groups: 1 the original ore was ground to less than 0.074 mml (hereinafter referred to as -0.074 mm), and the vanadium leaching rate was 76.2% when 50% was occupied; 2 the ore was ground to -0.074 mm, accounting for 71.5%. The vanadium leaching rate was 94.39%. The smaller the grinding particle size, the higher the grinding cost, and the vanadium leaching rate of more than 90% has been achieved under the condition of -0.074 mm and 71.5% of the particle size. Therefore, it is not necessary to use a finer particle size for the test. Therefore, the original ore grinding grain size is selected to be -0.07mm, which accounts for 71.5%.

2. Roasting ore grinding grain size

The effect of the grinding grain size on the leaching rate of vanadium after calcination (sinter ore) shows that the calcined ore is finer to less than 1.19 mm (hereinafter referred to as -1.19 mm), 50%, vanadium leaching rate is 82.4%; roasting ore Grinding to -1.19mm accounted for 84%, vanadium leaching rate can reach more than 90%; finer particle size, the increase of vanadium leaching rate is not obvious. Therefore, the grinding grain size of the calcined ore is selected to be -1.19 mm, accounting for 84%.

(2) Roasting system

The original vanadium ore is ground to -0.074mm to occupy 71.5%, and water is added to make φ8mm~φ20mm particles, which are dried and calcined to determine the best roasting system.

1. Calcination temperature

The effects of different calcination temperatures (650, 750, 800, 850, 950, 1050 °C, calcination time 1 h) on vanadium leaching rate were tested. The results are shown in Fig. 2. It can be seen from Fig. 2 that the vanadium leaching rate is only 48% when the calcination temperature is 650 °C; the vanadium leaching rate is 86.2% at 750 °C; the vanadium leaching rate is the highest at 800 °C, up to 93.8%, and then the calcination temperature vanadium leaching rate is increased. Instead, it decreases. This is because the sintering of the material causes the vanadium to be wrapped or the vanadium-bearing and sodalite-like minerals that bind the vanadium, making the vanadium difficult to dip.

Out. The lower calcination temperature of the low-valent vanadium oxidation is incomplete, resulting in a low leaching rate. Therefore, 800 ° C is selected as the reference baking temperature.

2, roasting time

The effects of different calcination times (1.0, 1.5, 2.0, 3.0 h, calcination temperature 800 °C) on vanadium leaching rate were tested. The results are shown in Fig. 3. It can be seen from Fig. 3 that the calcination time is only 87%, and the vanadium leaching rate is only 87%. It is obvious that the calcination time is insufficient and the mineral structure is not completely destroyed, resulting in insufficient oxidation of the low-valent vanadium and making the vanadium difficult to leach; roasting for 1.5 h, vanadium leaching The highest rate is 94.4%; the calcination time is increased, the vanadium leaching rate is not increased, and more energy is consumed. Therefore, the calcination time was chosen to be 1.5 h.

(3) Determination of leaching conditions

The calcined ore was finely ground to -1.19 mln to 84%, and the leaching test was carried out under the conditions of liquid:solid = 1.2:1.

1, the amount of sulfuric acid added

The effect of different sulfuric acid addition amount (according to 2%, 4%, 6%, 8%, 10%, and 12% of the calcined ore) on the leaching rate of vanadium was tested. The results are shown in Fig. 4. It can be seen from Fig. 4 that only 90% of the leaching effect can be achieved by adding 6% sulfuric acid to the calcined ore. When the vanadium concentration in the solution is greater than 2.55 g/L and the pH is 2-3, the V ₂ O _{5 is} hydrolyzed and precipitated; when the pH is about 1.8, the solubility of V ₂ O _{5 is} the smallest. Up to 65% of the water-soluble vanadium is present in the calcined ore, and the calcined ore contains a certain amount of acid-consuming substances. Therefore, when the amount of sulfuric acid added is reduced to 2% to 4%, the pH of the leachate is raised to 1 .8-3, which causes the leaching of pentavalent vanadium to hydrolyze and precipitate, so that the leaching rate of vanadium is greatly reduced. When the amount of sulfuric acid was increased on the basis of 6%, the increase of vanadium leaching rate was not obvious. Therefore, the amount of acid selected for leaching is 6% of the calcined ore.

2, leaching temperature

The effect of different leaching temperatures (30, 60, 90 ° C) on vanadium leaching rate is shown in Figure 5. It can be seen from Fig. 5 that the effect of temperature on vanadium leaching rate is not obvious. The leaching rate of vanadium at all temperature conditions (30-90 °C) is above 90%, considering the energy consumption during high temperature leaching and the leaching equipment. High requirements, the test was selected for room temperature leaching.

3, leaching time

The effects of different leaching times (0.5, 0.67, 1.0, 2.0, 12 h) on vanadium leaching rate were tested. The results are shown in Fig. 6. It can be seen from Fig. 6 that the leaching time is 0.5h, the vanadium leaching rate is only 72.5%; the leaching time is 0.67h, the vanadium leaching rate is 87.54%; the leaching time is 1h, the vanadium leaching rate is 93.4%; and the leaching time is extended, the vanadium leaching rate is not improved much. Therefore, the selected leaching time is 1 h.

The optimum conditions obtained in the above test are as follows: the original vanadium ore is ground to a thickness of 0.074 mm, accounting for 71.5%, and water granulation (particle size φ8 mm to φ20 mm) is added, and dried and calcined. The calcination temperature is 800 ° C, the time is 1.5 h; the calcined ore mill is fine to -1.19 mm, 84%; the leaching temperature is normal temperature, time 1 h; the leachate: solid = 1.2:1; the amount of sulfuric acid used in the leaching is 6% of the calcined ore.

(4) Full process expansion test

According to the optimal conditions obtained by the above single factor condition test, a full flow expansion (closed circuit) test of 2.5 kg was carried out. The test flow is shown in Figure 1. The index of the expanded test is: the vanadium leaching rate is 91.6l% on average, reaching the level of the condition test; the vanadium loss rate during the neutralization reduction process is 3.97%; the sixth-stage extraction (A/O=1), the vanadium extraction rate is 99.44%; six-stage stripping (A/O=10), the stripping rate of vanadium is 99.23%; adding vanadium with ammonia, the vanadium precipitation rate is 99.05%; the vanadium recovery rate during calcination is 99.24%. The test product V ₂ O ₅ content is 98.74%, and the product quality has reached the national GB3283-1987 metallurgical vanadium pentoxide quality standard. The recovery rate of vanadium in the extended test (closed circuit) was 85.33%. If the recycling of some of the solutions is considered, the total recovery of vanadium can be further increased.

The main components of the test leaching waste residue were (%): V ₂ O ₅ 0.10, Si0 ₂ 56.84, TFe 1.56, A1 ₂ 0 ₃ 1.59. Since no other reagents were added during the roasting and leaching, the waste residue was free of contaminants. The pH value of the waste residue is 3-4, and after adding lime to pH=7, it can reach the national GB8978-1996 industrial waste residue discharge standard.

The wastewater generated by this process is mainly the raffinate water phase. Others such as organic phase washing water, vanadium precipitation mother liquor, red vanadium washing water, etc. can be returned to the configuration leachate or washing leach residue, so only the raffinate water phase needs to be treated. . The raffinate aqueous phase can be considered for partial return leaching, and the remaining lime is neutralized to pH > 7, impurities such as iron and aluminum are precipitated as hydroxide, and sulfate is precipitated as calcium sulfate. Since both ferric hydroxide and aluminum hydroxide have a certain flocculation effect, other harmful elements can be co-precipitated during the precipitation process, so other harmful elements in the water are also purified. The treated wastewater is clear and transparent, and the harmful element content meets the national industrial wastewater discharge standard. The results of multi-element test of wastewater are shown in Table 3.

Table 3 Chemical composition of wastewater and related national standards

There are two places where exhaust gas is produced during the process test.

1. Raw ball roasting process

According to the calcination of vanadium ore balls in a rotary kiln of a similar vanadium plant of φ2.4m×45m, the composition of the exhaust gas produced by the green ball roasting process is (volume percent, %): CO ₂ 9.43, S0 ₂ 0.031, O ₂ 5.17, N ₂ 71.3, H ₂ Ol4.02. In the case of strict control of the sulfur content of coal combustion in industrial production, the waste can be discharged directly from the chimney after being treated by the dust collector.

2. The vanadium pentoxide is formed by vanadium sulphate, and the calcination reaction is as follows:

The tetravalent vanadium is oxidized to pentavalent vanadium in an oxidizing atmosphere. When the ammonium hexa-vanadate is calcined, nitrogen and water vapor which are free from pollution to the environment are discharged. Considering that the industrial production is not clean because of washing, the red vanadium precipitated may carry a trace amount of ammonium sulfate. The ammonium sulfate decomposes during the calcination process to release ammonia gas and sulfur dioxide, and a first-stage water spray absorption tower can be designed to be absorbed.

V. Conclusion

(A) the vanadium ore roasting a salt-free sulfuric acid leaching process to extract an organic solvent extraction of vanadium pentoxide, vanadium leaching stage roasting a recovery rate of 90% or more, the whole process vanadium recovery rate 85.33% V ₂ Test Product The O ₅ content is 98.74%, and the product quality has reached the national GB3283-1987 metallurgical vanadium pentoxide quality standard.

(II) Compared with other vanadium extraction processes in current industrial production applications, the vanadium recovery rate of this process is high, and the exhaust gas, waste water and waste residue produced can be discharged to a standard with a slight treatment. The technical indicators exceed the production level of the general vanadium plant. Promising clean production process.

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