1 Introduction
1.1 Introduction to the topic
Stone Coal is a presence in the Sinian, Cambrian, Silurian inferior sapropel and other ancient strata of anthracite, Department of algae after the death of lower organisms, formed under shallow water reducing conditions. China's Hunan, Hubei, Henan, Anhui, Shaanxi, Yunnan, Yunnan and other places rich in vanadium-bearing coal, the country's proven vanadium-bearing coal reserves of 6l8.8x10 8 t, its V 2 O 5 grade is more than 0.1% -0.5% Between the total vanadium content is 1.18×10 8 t, accounting for 87% of China's total V 2 O 5 reserves, exceeding the total reserves of vanadium in other countries and regions of the world, of which there is industrial exploitation value (V 2 O 5 content at this stage). 0.8% or more) up to 8 × 10 6 t.
The material composition of vanadium-bearing coal is complex and variable. The vanadium occurrence and valence state are varied and scattered. X-diffraction is generally difficult to clearly and accurately identify the mode of occurrence. The method of mineral processing cannot be used. Enrichment. The valence state analysis of vanadium in stone coal shows that most of the vanadium in stone coal exists in the form of V 3+ in silicate minerals such as vanadium-containing mica , tourmaline , garnet, etc. partial substitution of silica tetrahedron "complex web layer" and an aluminum octahedral Al 3+ "single-ply" in the. Stone Coal may also form a mineral vanadium garnet titanium vanadium, calcium vanadium garnet, vanadium, uranium and other variants; may also exist metal complexes and organic vanadium porphyremia form, may also form a complex anion was adsorbed the mixture present in the iron oxide, clay minerals.
The Institute of Metallurgy of Hunan Nonferrous Metal Research Institute is one of the earliest scientific research units for the research of vanadium extraction from stone coal in the country. In the late 1970s and early 1980s, vanadium-bearing coal from Yueyang Xinkai and Hubei Tongshan was carried out. Detailed process research and factory production. Since the beginning of the new century, especially in the past two years, with the surge in the price of vanadium pentoxide in the international and domestic markets (the price of 98% of the powdered V 2 O 5 international market has increased from 3.3 US dollars / kg in early 2003 to 2005 4 The highest monthly price of 66 US dollars / kg, the domestic market price also rose from 35,000 yuan / t to a maximum of 330,000 yuan / t), and locals have set off a wave of building vanadium. Due to the increasingly strict environmental protection requirements of the country, it is strictly forbidden to discharge excessive emissions of corrosive gases such as HC1, C1 2 and SO 2 which cause serious pollution to the surrounding environment. Since 2005, the State Environmental Protection Administration has stepped up efforts to rectify the small vanadium plant. The small vanadium smelting plant using NaC1 as an additive has been blown up. For example, Hunan Guzhang has destroyed five illegal vanadium plants by the end of June 2005. Xiangxi Autonomous Prefecture has closed 31 small vanadium plants and 45 rectifications; Yueyang in July In the middle of the year, more than a dozen refining vanadium plants were banned; similar reforms were carried out in Hubei, Henan and Shaanxi provinces. Therefore, the search for new technologies and new processes for the control of vanadium without pollution or pollution is a top priority for many investors.
1.2 Formation of traditional process for extracting vanadium from stone coal
In 1958, Hunan Metallurgical Exploration Company discovered a new vanadium mine. The Hunan Metallurgical Research Institute immediately carried out an optional test for the enrichment of vanadium in stone coal, and the conclusion was “not optionalâ€. Since then, the Institute has carried out experimental research on the extraction of vanadium directly from vanadium-bearing coal. From 1961 to 1964, it has completed a small test and a processing capacity of 13,357 tons [dry mining industrial rotary kiln semi-industrial production test. V 2 O 5 590 kg (according to 100%)], the content of V 2 O 5 is 73% to 83%, and the total recovery of vanadium is 44%. Due to the complexity of the process equipment, high technical requirements, large power consumption, gas or heavy oil is also required as fuel, and the investment in construction is large and the construction period is long. Therefore, the domestic vanadium smelters built with this technology have been delayed in production.
In the early 1970s, the Central South Institute of Mining and Metallurgy (now Central South University) mainly engaged in the experimental research work on extracting V 2 O 5 from Anhua Yanzhu Stone Coal, which completed laboratory tests, semi-industrial tests and industry. In the test, the Anhua manufacturer who participated in the test initiated the flat kiln for self-heating sodium roasting of stone coal on the basis of the vertical kiln, and it is still used in various vanadium plants. In 975, the Zijiang Chemical Plant in Anhua County built a small-scale soil test production line, which was renamed as Anhua County Vanadium Plant, and was the first professional vanadium production plant in Hunan.
According to the arrangement of the Science and Technology Commission of Hunan Province, in March 1976, Hunan Metallurgical Research Institute and Houyang Xinkai Commune cooperated to conduct experimental research on the extraction of vanadium from stone coal and establish production. After the experimental study from March to June 1976, the technology of roasting vanadium from stone coal without coal, leaching without alkali, and precipitation of vanadium was not realized. The roasting equipment was selected from the flat kiln of the Anhua Vanadium Plant and improved. A chimney system with a flue gas distribution plate and a smoking system were added, which significantly improved the working conditions and improved the conversion rate of vanadium. Later, the crude vanadium (red vanadium) refining process was experimentally studied. By 1979, the traditional process of adding coal-salt sodium oxide roasting-water immersion-hydrolysis-thawed vanadium-crude vanadium refining-fine vanadium has been formed. The traditional process of extracting vanadium from stone coal has the advantages of not complicated investment equipment, low investment, fast speed and little technical difficulty, and is widely used. At the end of the 1970s, the number of vanadium extraction vanadium manufacturers using this process was up to 59 in Hunan Province, with a production capacity of nearly 10,000 t/a. Due to the change in vanadium prices, by the end of 1982, there were only four remaining in the province. The drawbacks of the traditional process are also obvious: long process flow, low metal recovery rate (<40%), high cost, roasting flue gas and heavy vanadium wastewater seriously pollute the environment.
In the past 20 years, in response to the shortcomings of the traditional process of extracting vanadium from stone coal, the scientific and technological personnel of Hunan universities and research institutes and the technicians of vanadium plants have carried out continuous technological innovations, which has raised the level of vanadium extraction from Hunan's stone coal to a new level.
1.3 Characteristics of calcification roasting process
1 The calcification roasting process is first designed and applied in the mining and metallurgical plant. It has been commissioned by the workshop and is now in production. Through the production practice, the process is technically feasible, the process parameters are easy to operate and control, the index is stable, the vanadium leaching rate is high, the total recovery rate is more than 65%, and the production cost is low, which provides a vanadium industry for the development of stone coal type vanadium ore in China. An economically viable road.
2 Calcification roasting process is suitable for stone coal type vanadium ore containing less acid-consuming substances (such as carbonates, organic matter, etc.) and less ancient iron. It is not suitable for vanadium slag extraction. High acid consumption, high consumption of acid, increased cost, high iron content, iron will be leached into the solution by acid, increasing the amount of extractant regeneration and regeneration costs.
3 This process is an acid operation, and the equipment requires anti-corrosion, so it is 20% to 30% larger than the total investment of the sodium method.
2 Literature review
2.1 Question background
2.1.1 Historical overview
In the 1920s and 1930s, the United States succeeded in extracting vanadium from the Carlin Shale (stone coal) in Nevada. The result was studied by PT Brooks et al. The test results were performed by salt roasting, dilute sulfuric acid leaching, extraction, and precipitation of ammonium metavanadate.
Since the patent publication of Bleecker's sodium salt roasting-water leaching process for the recovery of vanadium in 1912, it has been in use ever since. When roasting, the salt is decomposed to produce harmful gases such as Cl 2 and HCl, which seriously pollutes the environment and corrodes the plant. For example, in the vanadium plants in Yueyang and Chongyang areas of Hunan Province, large areas of grass and trees are dying, and the relationship between agricultural and industrial workers is tense. This process has become a major problem that has plagued the development of vanadium plants. China's awareness of environmental protection is increasing day by day. The factories that add salt roasting have been banned, and research on new environmentally friendly production processes is imperative.
2.1.2 Overview of production at home and abroad
The total production of vanadium in the world is currently about 77,000 tons. The world's three major vanadium producing countries are South Africa, China and Russia. The total amount of vanadium produced accounts for 45.5%, 29.5% and 22.7% of the world's total production respectively. Other countries only account for 2.3. %. The top three manufacturers are: South Africa's second largest steel company Highveld (belonging to the world's second largest mining group Anglo American), China Pangang Group and Swiss mining giant XstrataAG (vanadium mine in South Africa), the three vanadium production total More than 55% of the world total.
Chengde New Vanadium and Titanium Co., Ltd., the second largest vanadium product manufacturer in China, produced 52,200 tons of vanadium slag in 2004, up 20.6% year-on-year; produced 4,220,577 tons of vanadium pentoxide, up 40% year-on-year; 3,203,362t, an increase of 83%. In 2005, the company plans to issue no more than 220 million new shares, raising funds of about 900 million yuan for the comprehensive development and utilization of vanadium and titanium resources, including the preparation of l15,000t / a (added 72,000 t / a) vanadium The slag production line will add 2,500 t/a vanadium pentoxide production line; the new 1,800 t/a 80 vanadium iron production line; the new 2,000 t/a vanadium nitride production line; after the completion of the project, the company will produce vanadium slag. The capacity increased from 43,000 tons before the transformation to 115,000 tons; the vanadium oxide increased from 3,600 tons before the transformation to 9,600 tons; the vanadium product variety increased from the original two (vanadium oxide, 50 vanadium iron) to four ( Added 80 vanadium iron and vanadium nitride). Other large vanadium producers mainly include:
Jinzhou Vanadium Industry Co., Ltd. has an annual production capacity of 5,000 tons of vanadium pentoxide and 5,000 tons of vanadium iron.
Shaanxi Wuzhou Mining Co., Ltd. currently has a monthly capacity of 160t.
Dunhuang Jindi Vanadium Industry Co., Ltd. currently has a production capacity of 600t/a; its three-phase expansion project, which is scheduled to be completed during the year, will expand production capacity to 1,000t/a.
Hubei Chongyang Jinghua Smelting Co., Ltd. will expand its annual production capacity to 1,000 tons.
Hunan Anhua Hualin Vanadium Industry Co., Ltd. (formerly Anhua County Dongping Vanadium Smelter), with a production capacity of 500 t in 2005.
Hunan Huaihua Shuangxi Coal Mine has an annual production capacity of 400t, a production of 352t in 2004, and 120t in January-April 2005.
Yueyang Xiang Vanadium Chemical Co., Ltd. has a monthly capacity of 40t.
Jiangxi Jiujiang City Baiyu Vanadium Factory, with an annual output of 300t.
Hubei Chongyang Shaping Vanadium Factory, with an annual output of 300t.
Hubei Chongyang Golden Vanadium Chemical Co., Ltd., with an annual output of 200t.
2.2 Application and development prospects of vanadium
Vanadium is a rare metal, and vanadium is transliterated from the English Vanadium. The chemical symbol for vanadium is V, which has an atomic number of 23. Vanadium is very chemically stable and will not be oxidized at normal temperatures. Vanadium has a high degree of corrosion resistance to salt solutions and seawater. Alkali solution and sulfuric acid do not work for it, hydrofluoric acid, hot concentrated sulfuric acid and nitric acid, and aqua regia can dissolve vanadium. The molten alkali, potassium carbonate, potassium nitrate can dissolve vanadium and form vanadium vanadium with silicides and carbides formed of silicon and carbon with high hardness and chemical stability.
Vanadium is oxidized to vanadium pentoxide V 2 O 5 at temperatures above 933 K (660 ° C). The structural strength of vanadium is quite high, but highly flammable, vanadium compounds are highly toxic, and vanadium-containing dust can cause lung cancer when inhaled. Vanadium is generally +5 valence in the oxide, but there are also oxides of the valence of +2, +3 and +4, although they are more susceptible to transition to +5 valence oxides. The divalent and trivalent vanadium oxides are basic, the tetravalent oxides are amphoteric, and the pentavalent oxides are acidic.
In nature, vanadium minerals are generally symbiotic with other metal minerals. Vanadium is generally in the form of a compound
There are about 65 vanadium compounds in nature. In nature, bauxite is found in bauxite, petroleum , coal and oil shale . Spectroscopic analysis revealed vanadium on the surface of the sun and some stars.
The blunt metal vanadium is prepared by reducing calcium pentoxide in a steel vessel. The obtained metal vanadium particles were washed and melted in a vacuum furnace, and the thus obtained metal contained 99.99% of vanadium. However, most vanadium comes from by-products of other mineral processing.
Stone coal is a kind of inferior anthracite with less carbon and low calorific value. It is also a low-grade polymetallic symbiotic ore. Vanadium is the most important valuable metal element. The vanadium-bearing coal is distributed in more than 20 provinces and autonomous regions such as Hunan, Hubei, Sichuan, Guizhou, Zhejiang, Guangxi, Guizhou, Guizhou, Shaanxi, Shanxi, Henan and Gansu, and most of them are in economically backward areas. According to relevant statistics, the total reserves of vanadium in stone coal is 7 times of the total vanadium reserves in the famous vanadium-titanium magnetite in China. Only a stone mine with a length of more than 1,600 kilometers from Zhejiang to Guangxi contains 100 million. More than tons of vanadium pentoxide. It can be seen that the development and utilization of such rich and valuable vanadium-bearing coal resources has enormous economic potential and social benefits.
2.2.1 Main application
In China, about 90% of vanadium is used in the steel industry. The application of vanadium in steel is mainly to increase the strength and toughness by adding vanadium. Adding 0.1% vanadium to the structural steel can increase the strength by 10%-20%, reduce the structural weight by 15%-25%, and reduce the cost by 8%-10%. Because vanadium steel has the characteristics of high strength, toughness, wear resistance and corrosion resistance, it is widely used in oil and gas (gas) pipelines, buildings, bridges, rails and pressure vessels. In 2000, the application amount of vanadium steel in China has reached 1.2 million t/a, and the application volume of vanadium-containing steel has increased by 10% annually.
Vanadium and titanium constitute an important metal alloy Ti-6Al-4V for aircraft engines, aerospace cabin skeletons, missiles, warships and introducers of warships, steam turbine blades, rocket engine casings, etc. In addition, vanadium alloy
Also used in magnetic materials, cemented carbide, superconducting materials (such as V, Ca) and nuclear reactor materials. The domestic enterprises producing vanadium-aluminum intermediate alloys include Baoji Nonferrous Metals Processing Factory and Jinzhou Ferroalloy Factory. The domestic production of vanadium and aluminum alloys cannot fully meet domestic needs. Each year, some parts need to be imported from abroad, and the market potential of vanadium-aluminum intermediate alloys is quite large.
The vanadium products mainly used in the chemical industry include deep processing products V 2 O 5 , (98%-99.99%), NH 4 VO 3 (ammonium metavanadate), NaVO 3 and KVO 3 . They are used in catalysts, ceramic colorants, developers, desiccants, and raw materials for the production of high-purity vanadium oxide or ferrovanadium. V 2 O 5 is a catalyst with special activity, and other elements are difficult to replace. Domestic powdered V 2 O 5 is now mainly extracted from stone coal. Due to the small scale and low output of domestic related enterprises, it is difficult to produce high-end products. Therefore, this part of high-end products is mainly solved by imports.
The color of the vanadium salt is five colors, green, red, black, yellow, and the like. For example, the divalent vanadium salt is usually purple; the trivalent vanadium salt is green, the tetravalent vanadium salt is light blue, the tetravalent vanadium basic derivative is often brown or black, and the vanadium pentoxide is red. These colorful vanadium compounds are made into bright pigments, such as glass, which can be made into colored glass or used to make a variety of inks.
In addition, vanadium dioxide thin films and ultrafine powders can be widely used in electrical and optical switching devices, solar control materials, optical disk dielectric materials, coatings, thermistors, etc. due to their unique phase change characteristics; Tejing Technology Co., Ltd. has developed a bismuth vanadate crystal material for long-distance fiber optic communication, which has a large birefringence, high transmittance, and good light transmission, and is a birefringent crystal with excellent performance.
2.2.2 Development prospects
It is expected that China will become the world's most promising vanadium product market in the future. Even if it only meets the consumption of vanadium products in steel production, vanadium products must increase production by more than 30% per year. However, as domestic demand for vanadium products continues to expand, the growth rate of domestic vanadium products is difficult to meet the growth rate of demand. In 2005, China has changed from a exporter of vanadium products to a net importer. According to relevant forecasts, it is estimated that by 2009, the supply and demand gap of China's vanadium products will reach 26,300 tons.
China's vanadium resources are very rich, especially China's unique vanadium mine - stone coal reserves are quite large, but because of its low grade, development and utilization is difficult. In recent decades, China's stone coal vanadium extraction technology has made great progress, and it is also in a leading position in the world, but there are still problems such as low extraction rate, low industrialization level and serious environmental pollution. Therefore, the development of high-efficiency and environmentally friendly new technologies and processes for extracting vanadium from stone coal has broad research prospects.
3 test conditions
3.1 Test raw materials
The ore is taken from the vanadium mine of Huayuan County, Huaihua County, Hunan Province, and the ore is taupe.
3.2 Test materials and equipment
1 Test materials:
Containing vanadium stone coal, CaO, H 2 SO 4 , sulfonated kerosene, N-235, TBP, Na 2 CO 3 .
2 Test equipment:
Jaw crusher, mining equipment plant Tianjin
Sample ball mill , Nanjing Nanda Electronic Surveying and Mapping Factory Branch
Oven, Tianjin Test Instrument Factory
Mesh screen, Zhejiang Guotai Standard Screen Factory
11-1 type booster electric mixer
SX3-10-14 type fast heating resistance furnace
XMT-DA digital display regulator
SHB-111 circulating water multi-purpose vacuum pump
Electric thermostatic water bath
3.3 Test plan
3.3.1 Purpose
The purpose of this test is to achieve that the roasting does not produce toxic and harmful gases, the extraction and vanadium-vanel wastewater are circulated in the system to achieve zero or low emission requirements, and the best process parameters for extracting vanadium from stone coal are obtained, and the intellectual property rights are formed. .
3.3.2 Research methods and routing
1 Research methods
1) pulverized: ore directly into the jaw crusher, crushing to 20 ~ 30mm; abrasive disk and then enters the dryer, ground to -60 mesh and -120 mesh, and then sent to the testing chamber assay components.
2) Ingredients: Weigh a certain amount of materials with the balance, and then weigh the additives according to the designed proportion, and mix them in the mortar for use. Weigh a certain amount of material with the balance, and then weigh the additive (calcium oxide) according to the designed ratio, and mix it in the mortar for use. The ratio of the two particle size additives (calcium oxide) is stone coal: additive (calcium oxide) = 100:0, 2, 4, 6, 8, 10. Put them in six rafts for use.
3) Calcination: Oxidation and calcification calcination are carried out according to the set calcination conditions, and are prepared for leaching.
4) Leaching: Weigh a certain amount of calcined dip, compare the acid leaching conditions with the room temperature immersion conditions in a water bath, analyze the vanadium content of the solution and the leaching slag, and calculate the conversion rate.
5) Extraction: a certain composition of the organic phase and a certain amount of purified leachate (aqueous phase) are placed in a separatory funnel, and shaken at a constant speed for a predetermined period of time, and the raffinate is discharged into the organic phase. Perform stripping.
6) Shen vanadium: Analyze the vanadium content in the stripping solution. After metering, add ammonium salt to precipitate vanadium. The precipitated ammonium vanadate is calcined in a muffle furnace to eventually become a V 2 O 5 product.
2 Process Roadmap
Figure 3.1 Calcification roasting process
3.3.3 Test conditions
1 Ingredients: The ratio of the two particle size additives is stone coal: additive = 100:0, 2, 4, 6, 8, 10
2 Roasting: roasting temperature, heating time 90min, respectively, to 800, 850, 900, 950, 1000 °C roasting time, select and determine the optimal temperature, respectively, 30, 60, 90, 120, 180, 240min.
3 Leaching: a: Different acidity leaching test, weight ratio of wt 5%, 8%, 10%.
b: The immersion material is immersed at room temperature for 5, 10, 15, 20, 25, 30 h, and the elements such as TV and other impurities in the leaching solution, the washing liquid, the waste slag are analyzed after washing.
c: leaching temperature, the temperature is controlled by a constant temperature water bath, and the electric stirrer is stirred at temperatures of 70 ° C, 75 ° C, 80 ° C, 85 ° C, and 90 ° C, respectively.
d: leaching time, after selecting and determining the optimum leaching temperature, the time is 1, 2, 3, 4h.
4 Purification: Add a certain amount of ammonia water to the leachate and stir. Remove the impurities by adjusting the pH value, and place it for 24 hours to filter. The purified liquid is ready for use.
5 Extraction: The extraction process is relatively mature, and the preliminary test results are directly applied in the test.
Extractant (amine salt) 10%
Helper extractant TBP 5%
Industrial kerosene more than 85% organic phase (O)
Acid qualified leachate: SiO 2 ≤ 4%, V 2 O 5 ≥ 3%, pH between 2 and 3, and as an extraction raw material, it becomes an aqueous phase (A). The extraction was compared with O:A=1:4, placed in a shake flask and shaken at a constant speed for 5 min. After standing, the layer was separated into an extract and a raffinate. The extract went to the next step, and the raffinate returned to the leaching process.
6 Stripping: The stripping agent is 0.5~0.7M Na 2 CO 3 , and the solvent temperature is about 40 °C. Stripping agent: extract = 1:3~5, placed in a shake flask and shaken at a constant speed for 5~10min. The organic phase is returned for use and the stripping solution is used as a vanadium-bearing mother liquor.
7 Shen vanadium: the stripping solution pH ≈10, can directly carry out the operation of alkali ammonium vanadium precipitation.
8 Calcination: The precipitated ammonium metavanadate is used as a raw material, placed in a muffle furnace, and calcined at 500 ° C ~ 550 ° C for 30 ~ 90min. The product is powdered V 2 O 5 .
Pay attention to safety: pay attention to burns and calcination, burns on the face and other parts; pay attention to acid and alkali to erode skin and clothes during leaching and hydrometallurgy.
3.4 Test principle
In order to make vanadium leaching, the mica structure must be destroyed, so that hydrogen ions can enter the mica structure to replace Al 3+ , and the ionic radius changes. Thereby, the vanadium is released and oxidized to a tetravalent acid to be dissolved, and the general formula is:
(V 2 O 3 )·X + 2H 2 SO 4 ·1/2O 2 = V 2 O 2 (SO 4 ) + 2 H 2 O + XO Formula (3.1)
V 2 O 2 (OH) 4 + 2H 2 SO 4 = V 2 O 2 (SO 4 + 2H 2 O formula (3.2)
The product was a vanadyl sulfate blue solution.
Roasting is an effective way to destroy the structure of vanadium-bearing coal mines. The vanadium-containing raw material is directly or after being mixed with an additive and calcined at a high temperature in an oxidizing atmosphere to oxidize trivalent or tetravalent vanadium to tetravalent and pentavalent vanadium, and to form vanadate with an additive or an oxide decomposed by the ore itself. The Fe(VO 3 ) 3 , Mn(VO 3 ) 2 , Ca(VO 3 ) 2 and the incompletely oxidized tetravalent vanadium compound formed during the calcination are insoluble in water but soluble in acid. In the conventional process, there is a practice of sublimating the sodium-sintered roasting residue after water immersion with an acid solution to increase the vanadium recovery rate. Acid leaching is effective for increasing the leaching rate of vanadium.
In the roasting process, the stone coal is first heated under oxidizing conditions, and the carbonaceous material is substantially burned out at about 380 °C. At this time, the oxidation potential of the material changed greatly, and the valence state of vanadium also partially changed. Figure 3.2 shows the standard free-form curves for some oxides. It can be seen from the figure that the oxidation curve of V(IV) is below the oxidation curve of carbon, so when the system is in equilibrium, V(III) is likely to be oxidized to V(IV) only after carbonaceous combustion. . In addition, the oxidation curve of Fe is below the oxidation curve of trivalent vanadium. Due to the presence of pyrite in vanadium-bearing coal, the divalent iron will be preferentially chemicalized. Therefore, the reduction of pyrite in stone coal has an inhibitory effect on the oxidation of vanadium during the calcination of stone coal. If the pyrite is removed from the stone coal, the V(III) to V(IV) and V(IV) can be further oxidized to V(V), so that the calcination efficiency can be remarkably improved.
Figure 3.2 Oxide Standard Generation ç„“-Temperature Chart
Oxidation and calcification calcination were carried out according to the set calcination conditions to prepare a leaching preparation. The calcination temperature and the temperature rise time were 90 min, and were raised to 800, 850, 900, 950, and 1000 ° C, respectively. The valence state of vanadium was determined by potentiometric titration, and the vanadium state change curve during the calcination of stone coal was obtained (Fig. 3.3).
Figure 3.3 Curve of vanadium valence state during stone coal roasting
As can be seen from the figure:
1 At temperatures below 300 °C, the reducing substances such as organic matter and pyrite in stone coal are not completely oxidized, and the presence of a large amount of reducing substances makes it difficult to oxidize V(III) in stone coal to V(IV). . The conversion of V(III) to V(IV) is small (<10%).
2 When the temperature rises to 500 ° C, the reduction of stone coal is rapidly oxidized. At the same time, the oxidation reaction of vanadium is accelerated. Most of the V (III) is oxidized to V (IV) at about 400 ° C to 500 ° C.
3 When the temperature rises to 800 °C, the formed V(IV) in the stone coal is further oxidized to V(V).
4 After the calcination temperature reaches 800 ° C, the temperature is further increased to 1000 ° C, the valence conversion of vanadium tends to be constant, and the oxidation of vanadium reaches an equilibrium state.
The lime coal is added to the high temperature heating roasting, and the low-valent vanadium is converted into high-valent vanadium. High-valent vanadium reacts with calcium oxide to form calcium polyvanadate. The calcification roasting reaction is as follows:
V 2 O 3 + O 2 = V 2 O 5 (3.3)
2V 2 O 4 + O 2 = 2V 2 O 5 (3.4)
V 2 O 5 + V 2 O 3 + 4CaO + O 2 = 2Ca 2 V 2 O 7 (3.5)
V 2 O 5 + V 2 O 3 + 6CaO + O 2 = 2Ca 3 (VO 4 ) 2 (3.6)
Stone coal vanadium is mainly present in different rocks in the form of fine grain adsorption and isomorphism. Vanadium present in rocks in the same state is a more difficult to dip vanadium. Such vanadium is replaced by a low-valent vanadium ion in part of A1 3+ in the illite lattice. The principle of acid leaching is: H + The ions enter the illite lattice, causing the ionic radius to change and the lattice to break, thereby releasing vanadium from the illite, and the vanadium is oxidized to tetravalent and leached by the acid. The reaction formula is as follows:
V 2 O 3 +2H 2 SO 4 →2VOSO 4 +2H 2 O. Equation (3.7)
In the acid leaching process, iron, aluminum, calcium, magnesium, etc. in the stone coal are also reacted with the acid to dissolve. Because the mine contains iron, aluminum, calcium, magnesium and other acid-consuming elements, the immersion liquid is not high after direct acid leaching. This is a favorable factor for direct acid leaching.
Because stone coal has high carbon content and carbon is hydrophobic, direct acid leaching is due to hydrophobicity, causing minerals covered by carbon to float on the liquid surface, which is unfavorable for the leaching of vanadium. At the same time, carbon is a mineral with strong adsorption capacity. After immersion, the carbon will adsorb vanadium, so that the vanadium is not easily washed out when the slag is washed. Therefore, decarburization before acid leaching is an effective measure to increase the vanadium leaching rate.
There are two main methods for decarburization of stone coal: one is direct roasting; the other is through beneficiation . After partial carbon removal by flotation, the leaching rate of vanadium in the decarburized tailings acid is significantly higher than that of the original ore. Moreover, the carbon extracted by flotation can be used to burn the boiler instead of the purchased coal, thereby saving production costs.
The leaching system was filtered to give a filtrate which was light blue. In a strongly acidic solution, pentavalent vanadium exists in the form of VO 3+ and tetravalent vanadium is VO 2+ . It has been shown by electrochemical studies in acidic media:
VO 2+ +2H + +e- = VO 2+ +H 2 O Formula (3.8)
When the pH of the acid leaching solution is 2.5, the system is oxidized by KMnO 4 oxidation, and the oxidation occurs as follows:
MnO 4 - +5VO 2+ +8H + = 5VO 3 - +Mn 5+ +4H 2 O Formula (3.9)
The acid leaching reaction is as follows:
Ca 2 V 2 O 7 + 3H 2 SO 4 = 2CaSO 4 +( V0 2 ) 2 SO 4 + 3H 2 O Formula (3.10)
Ca 3 (VO 4 ) 2 + 4 H 2 SO 4 = 3CaSO 4 + (VO 2 ) 2 SO 4 + 4H 2 O Formula (3.11)
2VO 2 + + 2H 2 O = V 2 0 5 H 2 O + 2H + (3.12)
5V 2 O 5 H 2 O = H 2 V 10 O 28 +4H + +2H 2 O Formula (3.13)
H 2 V 10 O 28 4 a = HV l0 O 28 5 a + H + of formula (3.14)
HV l0 O 28 5- = V 10 O 28 6- + H + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Equation (3.15)
During the extraction process, the organic phase competes with the water phase for the basic reaction of the extract. When the amount of the extract transferred from the aqueous phase to the organic phase and from the organic phase to the aqueous phase is equal, the extraction system is in a temporary relative equilibrium. If the conditions change, the original equilibrium is destroyed, and a new equilibrium is established. The extraction process is the redistribution of the extract between the aqueous phase and the organic phase; after the extraction equilibrium is reached, the extract is bound in both the organic phase and the aqueous phase. concentration.
4 test results and analysis
4.1 Physical and chemical properties of raw materials
The chemical analysis results of raw ore and roast clinker are shown in Table 4.1.
Table 4.1 Results of chemical analysis of ore and clinker (%)
V 2 O 5 | SiO 2 | Al 2 O 3 | C | CaO | TFe | Fe 2 O | S | K 2 O | MgO | |
Raw ore | 0.91 | 75.40 | 3.68 | 0.11 | 2.30 | 3.05 | 3.29 | 3.29 | 3.06 | 1.93 |
Clinker | 1.09 | 75.93 | 6.83 | 0.33 | 2.86 | —— | 4.22 | 4.22 | 3.14 | 2.18 |
Phase analysis: XRD analysis results The main phase of the ore is SiO 2 vanadium inclusions in the crystal lattice of the silicate. The main phases of the clinker were SiO 2 and Fe 2 O 3 ; the weight loss rate at 850 ° C for 3 h was 8.3%.
4.2 Roasting
4.2.1 Lime addition amount
The ratio of the vanadium-containing material and the additive is stone coal: CaO=100:0, 2,4,6,8,10, and the temperature is raised from room temperature to 90 minutes at 950 ° C for 120 minutes. The test results of the amount of calcium oxide added and the conversion rate are shown in Fig. 4.1.
It can be seen from Fig. 4.1 that the conversion rate increases with the increase of the amount of calcium oxide added. When the ratio of stone coal to calcium oxide is 100:8, the conversion rate is higher, and when the amount of calcium oxide is too much, the conversion rate is not obvious.
4.2.2 Calcination temperature
Stone coal: CaO=100:8, heating for 90min, respectively to the predetermined temperature of 800 ° C, 850 ° C, 900 ° C, 950 ° C, 1000 ° C, were kept warm for 120 min. The relationship between the conversion rate and the baking temperature is shown in Table 4.2.
Table 4.2 Relationship between conversion rate and calcination temperature
Calcination temperature / °C | 800 | 850 | 900 | 950 | 1000 |
Transfer rate /% | 20.78 | 26.51 | 35.92 | 48.73 | 45.31 |
It can be seen from Table 4.2 that the leaching rate increases with increasing temperature, indicating that the silicate composed of SiO 2 is decomposed in the material, releasing V(III) bare to allow vanadium to continue to oxidize, and the temperature is too low to destroy The structure of the vanadium-bearing mineral, but the temperature is too high to cause the calcination to be sintered, and may cause the volatilization loss of the pentavalent vanadium, and the calcination temperature is higher at a conversion rate of about 950 °C.
4.2.3 Roasting time
The calcination time also has a great influence on the conversion rate. When the time is too short, the conversion is incomplete, and when it is too long, it is easy to agglomerate, the volatilization loss of pentavalent vanadium increases, and the leachate is difficult to filter. The temperature was raised from room temperature to 950 ° C for 90 min, and samples were taken after 1 h, 2 h, 3 h, 4 h, and 5 h respectively. There was no sintering phenomenon, indicating that the minerals were highly resistant to roasting. The leaching was carried out with wt10% H 2 SO 4 medium, and immersed in a water bath at 85 ° C for 3 h with a liquid-solid ratio of 1.5:1. The relationship between the conversion rate and the baking time is shown in Fig. 4.2.
It can be seen from Fig. 4.2 that with the extension of the calcination time, the V oxidation tends to be sufficient, the conversion rate reaches 35% when the calcination time is 3h, and the conversion rate reaches 45% or more at 4h, and the effect of continuing to extend the roasting time is not obvious. It has been found through experiments that the calcination time is optimal around 4h.
4.3 Leaching
4.3.1 Effect of sulfuric acid concentration on leaching rate
Stone coal: CaO=100:8, calcined at 950°C, kept for 120min, the clinker was stirred at 85°C in water bath for 3h, and leached with 0%, 5%, 10% and 15% sulfuric acid concentrations respectively. The test results are shown in Figure 4.3. .
As can be seen from Figure 4.3: As the amount of acid increases, the acidity per unit volume increases and the vanadium leaching rate increases. Due to the increase in the amount of sulfuric acid, it is advantageous to destroy the internal structure of illite, thereby increasing the acid leaching rate of vanadium. When the sulfuric acid concentration was 10%, the leaching rate was 50.8%. When the sulfuric acid concentration reaches 15%, the vanadium leaching rate is not improved.
4.3.2 Effect of leaching solution ratio on leaching rate
The effect of the leachate solid L/S on the vanadium leaching rate is actually the acidity test. The liquid-solid ratio is large, and the acidity per unit volume is small under a certain amount of acid. Stone coal: CaO = 100:8, calcined at 950 ° C, held for 120 min, stirred in a water bath at 85 ° C for 3 h, leaching with wt 10% H 2 SO 4 medium, L / S were 1.8, 1.6, 1.4, 1.2, 1.0, respectively. The test results are shown in Figure 4.4.
It can be seen from the test results that the smaller the liquid-solid ratio, the better the leaching effect, which indicates that the higher the acidity per unit volume, the more favorable the leaching of vanadium. Therefore, under the condition that the leaching effect is not affected, the leaching conditions of low liquid-solid ratio should be selected as much as possible to save the amount of sulfuric acid. For comprehensive consideration, a liquid to solid ratio of 1.5:1 should be selected.
4.3.3 Effect of soaking time on leaching rate
Heating and stirring leaching can shorten the operation time, but heating requires a certain amount of equipment and energy consumption. After immersing for a certain time at room temperature, the dip rate is close to 50%, which can be said to be a better leaching method. This test is to investigate the effect of room temperature leaching time on the rate of conversion. Soaked with wt10% H 2 SO 4 for 5h, 10h, 15h, 20h, 25h, 30h, and other conditions are the same as 4.3.2. The test results are shown in Figure 4.5.
As seen in Figure 4.5, the longer the constant temperature time, the higher the leaching rate. It can reach more than 45% after 30h.
4.3.4 Effect of leaching temperature on leaching rate
Leaching conditions L / S = 1.5 / 1, sulfuric acid 10%, clinker conditions are the same as 4.3.2. The materials were leached for 3 h at 70 ° C, 75 ° C, 80 ° C, 85 ° C, and 90 ° C in a water bath. The effect of temperature on the leaching rate is shown in Table 4.3.
Table 4.3 Effect of Different Leaching Temperatures on Leaching Rate
Leaching temperature / °C | 70 | 75 | 80 | 85 | 90 |
Leach rate /% | 70.3 | 75.2 | 85.6 | 87.2 | 87.0 |
As can be seen from Table 4.3, as the leaching temperature increases, the leaching rate also increases. The leaching temperature is preferably 85 °C.
4.4 Extraction and stripping
4.4.1 pH of the extract
Stone coal: CaO=100:8, heated to 950 °C for 90 minutes, heat for 4h, 500g per time, add acid soaking solution wt10% H 2 SO 4 750ml, leaching is to use 5000ml beaker, stir in water bath at 85 ° C for 3h . The clinker was 0.42kg, and the clinker contained TV0.611% on average. 3500 ml of the leachate was prepared, and the composition of the solution is shown in Table 4.4.
Table 4.4 Chemical composition of leachate (g/l)
ingredient | TV | SiO 2 | Al 2 O 3 | Fe | P |
content | 0.931 | 2.023 | 7.050 | 0.391 | 4.370 |
The leachate cannot be used directly for vanadium precipitation and needs to be enriched first. N-235 is used as extractant, TBP is used as auxiliary agent, and sulfonated kerosene is used as extraction solvent. The extraction conditions were 10% N-235 + 5% TBP + 85% sulfonated kerosene, the pH of the extract was 2.5, 3.5, 4.5, O:A=1:4, placed in a shake flask and shaken at a constant speed for 5 min, and then allowed to stand for 5 min. The results are shown in Table 4.5.
Table 4.5 Extraction pH test results
pH | 2.5 | 3.5 | 4.5 |
Extraction rate /% | 98.02 | 84.21 | 20.13 |
It can be seen from Table 4.5 that the pH of the extract is preferably 2.5.
4.4.2 Selection of stripping agent
The stripping agents selected were: NaOH, Na 2 CO 3 , NH 4 OH, NH 4 Cl+NH 4 OH, and the test results are shown in Table 4.6.
Table 4.6 Test results of different stripping agents
Stripping agent | Stripping rate /% | pH |
NaOH | 90.12 | 8~9 |
Na 2 CO 3 | 98.21 | 8~9 |
NH 4 OH | 54.23 | 12 |
NH 4 Cl + NH 4 OH | 20.09 | 8~9 |
The test results show that the best effect is obtained by using Na 2 CO 3 as the stripping agent. Using Na 2 CO 3 as a stripping agent, the components of the stripping solution are shown in Table 4.7.
Table 4.7 Composition of the stripping solution (%)
ingredient | V 2 O 5 | SiO 2 | Al 2 O 3 | Fe | P |
content | 4.140 | 0.073 | <0.010 | <0.010 | 0.034 |
The results show that the extraction and stripping can effectively enrich vanadium and achieve separation with impurities, and the contents of SiO 2 , Al 2 O 3 , Fe and P are significantly reduced.
4.5 Vanadium and calcination
The ammonium metavanadate precipitates by adding ammonium chloride to the enriched solution. The vanadium is carried out at room temperature. In order to facilitate the crystallization of NH 4 VO 3 for 45 min, after standing for 12 h, the V 2 O 5 product can be obtained by calcination and deamination at 520 ° C to 550 ° C after vacuum extraction and drying. The chemical composition analysis results are shown in Table 4.8.
Table 4.8 Results of chemical analysis of powdered V 2 O 5 (%)
ingredient | V 2 O 5 | SiO 2 | As | Fe | P | Na 2 O+K 2 O |
content | 96.770 | 1.250 | 0.010 | 0.010 | 0.015 | 0.010 |
The V 2 O 5 product has a relatively low grade, and further purification is required if the grade is 99% (high purity V 2 O 5 ).
The yield of each step is shown in Table 4.9.
Table 4.9 Yield of each process (%)
Process | Roasting leaching | Purification | extraction | Stripping | Shen vanadium |
Yield | 50 | 98 | 98 | 96 | 98 |
The total yield = 50% × 98% × 98% × 96% × 98% = 45.18% extraction, stripping, the liquid produced by the vanadium precipitation process can be recycled, vanadium can be regarded as no loss. If the process of purifying vanadium is used, a part of sodium salt is generated, which is not conducive to system circulation.
4.6 Questions and Discussion
When a calcium oxide calcification roasting-acid leaching process is carried out using a boiling furnace, it is possible that the total yield in industrial production reaches a level of 60%. Manufacturers using flat kiln roasting, regardless of the process used, the total yield of V 2 O 5 is generally only 40%, and sometimes it can reach 50%. The main reason is that the conversion rate of vanadium during calcination is low. To increase the conversion of vanadium during roasting, at least the following should be done:
1 Strengthen the research on the mechanism of vanadium-bearing stone roasting process. Using advanced testing instruments such as high temperature microscope, XRB, SEM, EDAX, etc. to study the roasting process of vanadium-bearing coal, to understand the changes and changes of vanadium-bearing coal components during roasting, and to study the effects of additives on these processes. To guide the screening of the roasting additive.
2 Improve the process, strengthen testing , and stabilize operation to achieve stable production conditions and stabilize technical indicators .
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