A method for leaching vanadium from vanadium-containing iron ore fines

Abstract

This invention discloses a method for leaching vanadium from vanadium-containing iron ore powder, belonging to the field of metallurgical technology. This invention utilizes existing technology and equipment for blast furnace pellet production. Through step-by-step pelletizing, the vanadium-containing iron ore powder (target for vanadium leaching), pellet binder, and vanadium leaching aids from the iron ore powder are mixed and used as a surface material to encapsulate a pre-formed spherical core of non-target vanadium-leaching iron ore powder, creating a composite pellet with a "core + surface" structure. After oxidative roasting and cooling to a surface temperature close to the boiling point of water, soluble vanadium compounds in the surface layer of the pellets are leached with hot liquid before being used in the blast furnace. The internal heat storage within the pellets maintains the temperature of the leaching hot liquid and dries the pellets after rinsing with purified water. This invention achieves a high overall vanadium extraction rate from vanadium-containing iron ore powder. Compared to vanadium leaching from vanadium-containing iron ore, it has a shorter process, lower investment, and lower cost. The required additional composite pelletizing and vanadium leaching processes, operations, and equipment are simple and mature, resulting in minimal net pollution and extremely low energy consumption.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and more specifically, to a method for preparing blast furnace pellets with a "core + surface" composite material structure using vanadium-containing iron minerals as a surface layer and for online leaching of the vanadium contained therein. Background Technology

[0002] Vanadium, as an important strategic resource, is widely used in many important sectors of the national economy, including steel, non-ferrous metals, chemicals, optics, electronics, energy storage, pharmaceuticals, and atomic energy. Adding a small amount of vanadium to steel can significantly improve its strength, toughness, ductility, wear resistance, and heat resistance. In titanium alloys required by the aerospace industry, vanadium acts as a stabilizer and strengthening agent to give the alloys good ductility and plasticity. In the chemical industry, vanadium is mainly used as a catalyst and colorant, and in recent years it has been increasingly used in vanadium redox flow batteries. Among the 65 major vanadium-bearing minerals, vanadium-bearing magnetite is the most typical, accounting for 88% of the world's annual vanadium production. Its iron concentrate contains 0.2-2.0 wt% vanadium pentoxide (0.11%-1.4% vanadium grade based on elemental vanadium), mainly in the form of (FeO⋅V₂O₃) spinel.

[0003] my country is a major producer and consumer of vanadium and vanadium-containing products globally, and its reserves of vanadium-bearing minerals are abundant, especially vanadium-titanium magnetite, which has proven reserves ranking third in the world. However, the vanadium grade in almost all vanadium-bearing minerals is relatively low. In iron concentrates used as raw materials for iron smelting, the vanadium pentoxide content is only 0.2-0.8 wt% (the vanadium grade, calculated as elemental vanadium, is mostly only 0.11%-0.45%), making extraction difficult and costly. Currently, there are two main methods for extracting vanadium from vanadium-bearing iron concentrates: pyrometallurgical vanadium extraction (accounting for about 70% of the world's vanadium production) and hydrometallurgical vanadium extraction (accounting for about 25% of the world's vanadium production). The so-called "pyrometallurgical vanadium extraction" is a method of extracting vanadium from vanadium-bearing iron ore by combining it with iron to form sinter and / or pellets, which are then used as raw materials for a reduction furnace. This process involves the smelting and refining of iron and steel. First, the vanadium in the ore is simultaneously reduced with iron to vanadium-bearing blast furnace / electric furnace molten iron, or the iron in the ore is directly reduced to vanadium-bearing (vanadium oxide) reduced iron lumps. Second, during the initial blowing stage of steelmaking from the vanadium-bearing molten iron or vanadium-bearing reduced iron lumps, the vanadium in the molten iron is concentrated and oxidized, becoming enriched in the slag. This slag is then promptly separated from the molten iron to become high-vanadium-grade vanadium-extracting slag (generally, the vanadium pentoxide content in the vanadium slag is not less than 10 wt%, and high-grade vanadium slag can contain more than 18 wt%). Then, the vanadium-extracting slag is finely ground, mixed with leaching aids, formed into lumps (balls), oxidized and easily soluble modified by roasting, and then finely ground and roasted again. The vanadium compounds in the vanadium-rich slag are dissolved and leached in the leaching solution in the form of fine powder (the corresponding indicator for evaluating the vanadium acquisition efficiency of the process is the vanadium leaching rate). After extraction and back-extraction or precipitation / precipitation (the corresponding indicators for evaluating the vanadium acquisition efficiency of the process are the vanadium extraction rate / back-extraction rate and vanadium precipitation rate, etc.) and purification, the vanadium extraction rate (synonymous with the yield or recovery rate, defined as "vanadium content in the obtained vanadium-containing material / total vanadium content in the raw material") in this method can be over 80%. However, the overall vanadium extraction rate of the vanadium-containing iron ore used for vanadium extraction in the vanadium-extraction converter is low, especially when using vanadium-titanium magnetite through the blast furnace-converter process, it is generally no more than 50% (there is a certain vanadium loss in the blast furnace reduction and converter oxidation processes), and is mostly only 45% to 50%. The so-called "wet vanadium extraction" method is a method of directly extracting vanadium from iron concentrate powder. In this method, vanadium-containing concentrate powder is granulated or directly powdered and then subjected to high-temperature oxidation and modification roasting similar to the aforementioned treatment of vanadium enrichment slag. After grinding and roasting, the granulated pellets are ground into fine powder and then leached to dissolve and leach vanadium compounds in the leachate. Finally, after extraction and back-extraction or precipitation / precipitation and purification, the overall extraction rate of vanadium in the vanadium-containing iron ore used in this method is generally around 70%.Vanadium extraction is a series of processes that enrich and purify vanadium from vanadium-containing minerals. Whether it is "pyrometallurgical vanadium extraction" or "hydrometallurgical vanadium extraction", it requires the use of flux that can dissolve vanadium compounds contained in vanadium-containing minerals or vanadium-enriched slag to dissolve the vanadium compounds into solutes in the solution. Then, solid vanadium compounds are further extracted from the solution through extraction and back-extraction or precipitation / precipitation. Generally, the process of oxidizing the poorly soluble low-valence vanadium ion compounds in vanadium-containing iron ore (or, under the action of a catalyst) into easily soluble high-valence vanadium ion compounds at high temperature is called "oxidative roasting" or easily soluble "modification". The process of dissolving easily soluble vanadium compounds into solutes in the solution with flux is called "leaching", and the flux is called "leaching solution".

[0004] Problems and shortcomings of pyrometallurgical vanadium extraction. Currently, all companies in the industry using large-scale vanadium extraction plants from low-vanadium-grade vanadium-titanium magnetite, including Panzhihua Iron and Steel Group of Ansteel Group (the world's largest vanadium producer), Chengde Iron and Steel Group of Hebei Iron and Steel Group (a leading global vanadium producer), and Nizhny Tagil Steel Company of Russia, all use the blast furnace-converter process for pyrometallurgical vanadium extraction. Although the top-and-bottom blowing converter method has replaced the ladle method, side-blown converter method, and air atomization method with the oxidation extraction of vanadium from molten iron using the development of related technologies, the overall extraction rate of vanadium from vanadium-bearing iron ore by pyrometallurgical methods is still much lower than that by wet vanadium extraction. The inherent direct causes are: 1) Blast furnace: (1) In the blast furnace, there is a non-equilibrium iron molten iron vanadium and vanadium oxide slag distribution ratio that is less than the equilibrium value when vanadium oxide is melted, reduced and separated from mineral iron oxide in the blast furnace. (2) In order to reduce the problem of excessive titanium oxide content in slag during vanadium-titanium magnetite blast furnace ironmaking, non-vanadium iron ore is added to further reduce the vanadium grade of iron-containing furnace charge, which makes the slag volume corresponding to unit vanadium larger. (3) The oxidation of vanadium in the molten iron during the blast furnace tapping process causes some vanadium to be oxidized into top slag of molten iron ladle / torpedo ladle, which cannot enter the vanadium-removing converter. 2) Converter: (1) After vanadium removal in the converter, the residual vanadium loss in the semi-steel is generally more than 15%. (2) Due to various factors, the semi-steel tapping process is affected by the vanadium content of the vanadium in the molten iron. The impact is that some vanadium extraction slag is lost in the semi-steel ladle; in summary, the vanadium recovery rate in vanadium-bearing iron ore from blast furnace molten iron is generally difficult to exceed 75%, and the vanadium recovery rate in vanadium extraction slag from converter vanadium extraction is generally difficult to exceed 85%. That is to say, when vanadium is enriched and melted and collected into vanadium slag that can be used for subsequent vanadium leaching, more than 35% of the vanadium in the original vanadium-bearing iron ore input into the vanadium extraction process has already been lost. Even if the recovery rate of vanadium in the subsequent vanadium extraction slag reaches 85%, the overall vanadium extraction rate of the vanadium metered in the vanadium-bearing iron ore input into the vanadium extraction converter is only at the level of 50% (which is also the best possible level close to the theoretical value mentioned in recent industry review materials).Furthermore, an indirect reason for the low overall vanadium extraction rate from the vanadium-bearing iron ore used is that, with the increasing scale and efficiency of the steel industry, enterprises using pyrometallurgical vanadium extraction processes will experience insufficient self-produced vanadium-bearing iron ore, requiring the import of large quantities of non-vanadium-bearing iron ore. This is because the blast furnace-converter process, from the raw material yard itself to the sintering, pelletizing, and blast furnace processes, as well as the pyrometallurgical transport of molten iron to the slag removal / desulfurization facilities and then to the dedicated vanadium extraction converter, presents a long process, numerous processes, many pieces of equipment in the same process, extensive cross-path logistics between adjacent process equipment, and complex vanadium extraction planning combinations. The challenges of management, the impact of emergency adjustments before and after vanadium extraction, and the lag in recovery make it difficult to achieve the goal of having all vanadium-containing minerals actually used in the vanadium extraction process. It is also difficult to guarantee that all extractable vanadium-containing molten iron can ultimately be used for vanadium extraction. This will further reduce the overall vanadium extraction rate from vanadium-containing iron ore used in pyrometallurgical vanadium extraction. Even if efforts are made to ensure that 80% of the vanadium-containing molten iron used in the process can enter the vanadium extraction converter to complete the enrichment and smelting of vanadium and be effectively collected, the overall vanadium extraction rate, measured by the total vanadium content of the iron ore used from the source of the raw materials, will only be around 40%, meaning that a large portion of the vanadium resources will be lost. Furthermore, the vanadium slag produced from the vanadium enrichment and smelting of vanadium-containing molten iron in the converter vanadium extraction process appears to be a side operation and byproduct in the iron and steel production process, seemingly with little direct material cost. However, the investment in land and equipment for the vanadium extraction converter in this additional vanadium extraction process is considerable. The additional temperature loss during the vanadium extraction process (the total temperature loss of the semi-steel during the tapping of the vanadium extraction furnace, transportation and waiting, and the process of adding the semi-steel to the decarburization furnace will not be less than 45°C) and the loss of ferrite in the vanadium slag are also significant. The semi-steel is relatively difficult to smelt in subsequent dephosphorization and decarburization processes, and the flux consumption is high. The recovery of related residual energy in the vanadium extraction steelmaking process is also reduced. In addition, further vanadium extraction from the steelmaking vanadium extraction slag still requires corresponding facilities and sites for pre-leaching material mixing, roasting, leaching, and treatment as solid waste tailings. All of these factors contribute to a correspondingly high additional process cost, additional energy consumption, and pollution in pyrometallurgical vanadium extraction.

[0005] Problems and shortcomings of existing wet vanadium extraction technologies. Unlike the pyrometallurgical vanadium extraction process, which involves enrichment followed by leaching, wet vanadium extraction directly leaches vanadium from the entire amount of vanadium-containing minerals. The process involves fine grinding, mixing with leaching aids, pelletizing (it seems pelletizing is unnecessary when using a rotary kiln for roasting, but high-iron oxide iron ore powder will form rings and lumps above 900℃, affecting uniform roasting and frequently causing production interruptions, making industrial production impossible; high-temperature fluidized bed oxidation roasting also seems to eliminate the need for pelletizing, but due to high energy consumption and low productivity, it has not yet been widely adopted), oxidation and modified roasting, and further fine grinding to leach dissolved vanadium compounds from the fine mineral powder (the leaching principle, process, and technology are almost identical to those of vanadium slag enriched in steelmaking vanadium extraction). Finally, after extraction / precipitation / sedimentation and purification, the overall vanadium extraction rate from the vanadium-containing iron ore used in this method can reach 80%. Although the vanadium extraction process is much shorter and the overall extraction rate is significantly higher, the processing volume of vanadium-bearing minerals is ten to twenty times higher. This results in substantial investment in related equipment, a dramatic increase in energy consumption during the roasting and modification process, and a corresponding increase in the consumption of vanadium leaching aids and / or leachate, as well as the amount of tailings to be treated. The pollution level of the entire vanadium extraction process is also severely aggravated, and the degree of these various negative impacts is directly related to the vanadium grade in the vanadium-bearing minerals; the higher the vanadium content, the lower the cost and pollution. Therefore, under current technology, hydrometallurgical vanadium extraction from vanadium-bearing iron ore is mainly applied to the extraction of vanadium from high-vanadium-grade vanadium-bearing iron ore. It requires at least 1 wt% vanadium pentoxide content in the mineral (relative to a vanadium grade greater than 0.55%) to be commercially viable. Only manufacturers in regions such as South Africa, Australia, and Finland, which possess high-grade vanadium-bearing iron ore and inexpensive energy, can adopt this method.As a special case, there have been reports of attempts to directly leach vanadium in lumps after sodium roasting and lumping of high-vanadium-grade vanadium-titanium magnetite, and then use the vanadium-leached roasted lumps as blast furnace feed. However, due to (1) the long vanadium leaching time and low leaching rate (defined as (initial vanadium content in the material - residual vanadium content in the material after vanadium leaching) / initial vanadium content in the material), (2) the high residual alkali metal sodium content in the sodium leaching pellets with higher leaching rate and easier vanadium leaching, they cannot be used alone as blast furnace feed, and (3) the leaching of vanadium compounds and other substances also causes the lumps to show a strong vanadium leaching effect due to the decrease in apparent density. The aforementioned problems, such as insufficient quality, prevented the efforts from achieving a breakthrough. Another study attempted to leach acid-soluble vanadium from 12mm diameter vanadium-titanium magnetite pellets using optimized sulfuric acid before blast furnace smelting. However, the conclusion was that the optimal leaching time was 6 days (6 days for vanadium leaching rate of 60.3%, and 2 days for about 40%). During this period, the pellets with a strength loss of up to 60% required a second roasting before they could be used. Even without considering the possibility of acid corrosion prevention with 10% sulfuric acid solution for all related equipment, such a long leaching time was simply unsuitable for vanadium leaching in large-scale industrial production. Summary of the Invention

[0006] 1. The problem to be solved

[0007] The purpose of this invention is to utilize the existing technical conditions and current process equipment for blast furnace pellet oxidation roasting, and to optimize the pellet structure and pelletizing process to replace the existing pyrometallurgical vanadium extraction technology with a new wet vanadium extraction technology for low-vanadium iron ore, thereby significantly mitigating the various negative problems associated with the existing vanadium-containing iron ore powder vanadium extraction technology.

[0008] 2. Technical Solution

[0009] In view of the various problems existing in the pyrometallurgical and hydrometallurgical processes for vanadium extraction from vanadium-bearing iron ore powder in the background art, and in light of the current state and development trends of traditional long-process steel production technology, this invention adopts the following technical solution by making full use of existing related technologies, processes and equipment:

[0010] Utilizing existing technology, processes, and equipment in blast furnace pellet production, a composite material pellet with a "core + surface" structure is created by using a mixture of vanadium-containing iron ore powder (target vanadium leaching) and vanadium leaching aids as a surface layer to encapsulate pre-formed non-target vanadium-leaching iron ore powder in a step-by-step pelletizing process. After oxidative roasting and cooling to a surface temperature below the boiling point of water, the soluble vanadium compounds in the pellet surface are leached with hot liquid. Simultaneously, the pellets, after being rinsed with purified water, are pre-dried using residual heat. The main steps are as follows:

[0011] 1) Using conventional pelletizing methods, the mixed material of non-target vanadium leaching iron ore powder is pre-formed into pellet cores with a diameter of 7-11 mm (further optimized to 7-10 mm); the mixed material is a self-fluxing, self-fluxing + high magnesium oxide, high magnesium oxide or acidic pellet type designed entirely based on the requirements of blast furnace ironmaking itself.

[0012] 2) Vanadium-containing iron ore powder (mainly vanadium-titanium magnetite concentrate and vanadium magnetite concentrate) with target vanadium leaching, conventional pellet binder, and appropriate vanadium leaching aids for different types of leaching hydrothermal solutions are used as the pellet surface material. The pellets are grown by spraying to encapsulate the core, forming composite pellets with a "core + surface" structure. The diameter of these pellets is 10-16 mm (further optimized to 11-14 mm), and the thickness of the surface layer is 1.0-3.0 mm (further optimized to 1.5-2.5 mm). The leaching hydrothermal solution is preferably hot water, and the appropriate vanadium leaching aid is preferably sodium carbonate when hot water is used as the leaching solution.

[0013] 3) The green pellets are dried, preheated and oxidized and roasted at 1150-1250℃ in the conventional process of blast furnace pelletizing to become pellets. The oxidation and sintering process of iron in the process simultaneously oxidizes and easily modifies the vanadium in the surface layer to become soluble vanadium compounds in the corresponding leachate.

[0014] 4) When the aforementioned pellets have cooled to a surface temperature of 85-110°C (further optimized to 90-100°C), they are immersed and / or washed in a flowing hot liquid at a temperature of 80-100°C (further optimized to 90-100°C) for 10-60 minutes (further optimized to 15-50 minutes) to dissolve and leach out the soluble vanadium compounds in the modified corresponding hot liquid within the surface layer; the temperature of the leaching hot liquid is maintained by means of the pellet's heat storage.

[0015] 5) After vanadium leaching is completed, the pellets are rinsed with industrial purified water used to replenish the losses from evaporation and absorption during the leaching process, in order to further recover vanadium and reduce the content of alkali metals and / or acid and alkali substances in the pellets; the purified water before rinsing is heated with the residual heat from the low-temperature section of the pellet cooling or the heat transferred during the cooling of the leaching hot liquid.

[0016] The main aspects of the method of the present invention that need to be explained in conjunction with the above technical solution are as follows:

[0017] 1) Feasibility of vanadium leaching for composite pellets with a "core + surface" structure under the blast furnace pellet production roasting process.

[0018] Vanadium-bearing iron ore is roasted to destroy the mineral structure and oxidize the low-valence vanadium into high-valence vanadium oxide that is easily dissolved by acids / alkalis, and / or modify vanadium into vanadium compounds that are soluble in the corresponding leachate under the action of added vanadium leaching aids. Under the existing technology and equipment conditions for blast furnace pellet production, the vanadium-containing iron ore powder for vanadium leaching is made into composite pellets with a structure of "core + surface". The feasibility of rapidly leaching soluble vanadium compounds in the surface layer of the pellets in online hot liquid is reflected in the following: (1) Vanadium and iron have similar ionic radii. The most important vanadium-containing iron ore is vanadium-containing magnetite, which exists in the form of FeO⋅V2O3 spinel of magnetite. When the pellets are oxidized and roasted at high temperature to destroy the spinel structure of magnetite and oxidize the ferrous oxide in it, they can also oxidize the vanadium trioxide (+3 valence vanadium) in the isomorphous iron-vanadium spinel to become high-valence easily soluble vanadium oxide (+4 or +5 valence vanadium). Moreover, the oxidation roasting of iron in the high-grade iron concentrate used to produce pellets and the pellet sintering are close to the oxidation roasting and leaching modification of the low-valence oxide of vanadium in it. As an extreme case, the pellets used in the existing pyrometallurgical vanadium extraction process to produce vanadium-containing molten iron in the blast furnace can be directly leached by acid or alkali. (1) Vanadium on the surface (but it is difficult to leach vanadium inside the pellets); (2) As the surface layer, the material has the most abundant oxidation conditions, the longest reaction time for oxidation and soluble modification, and can achieve full oxidation and modification; (3) Compared with the interior, the surface material of the same mass has a relatively larger leaching specific surface area; (4) During the drying and preheating process, the gas inside is discharged through the surface layer, making the surface layer relatively permeable, and it also has good liquid permeability during leaching, with multiple diffusion paths for soluble vanadium compounds as solutes; (5) Only vanadium in the thinner surface layer needs to be leached, and the diffusion path of soluble vanadium compounds as solutes is short, which can achieve rapid leaching of vanadium in a shorter time; (6) Compared with vanadium leaching after roasting and modification and grinding into fine powder, the return leaching rate of the surface layer of composite structure pellets is relatively low, but the difference can be controlled within 10 percentage points, which is within the completely acceptable technical and economic range; (7) Vanadium leaching can be carried out at the highest possible temperature close to the boiling point of water. In summary, it is entirely feasible, both in terms of mechanism and technology, to process vanadium-containing iron ore powder with a "core + surface" structure into composite pellets, and then roast them using existing blast furnace pellet production technology. The resulting spherical vanadium compounds are then leached from the corresponding leaching solution in the surface layer.

[0019] 2) Feasibility of using composite pellets with a "core + surface" structure in blast furnaces after vanadium leaching.

[0020] The vanadium-containing iron ore powder leached with the target vanadium is made into composite pellets with a structure of "core + surface". After leaching the soluble vanadium compounds in the surface layer of the pellets, it is used in blast furnaces. Its feasibility is reflected in the following: (1) The core material is a normal blast furnace pellet formula material (without vanadium leaching additives) that is not the target vanadium leaching ore powder. It has the physicochemical properties of conventional pellets such as high density and high strength. It is insoluble in the vanadium leaching solution of the outer layer material or is not dissolved by the vanadium leaching solution through leaching time control. It can serve as the basic support for the pellets to maintain good strength after vanadium leaching in the thin surface layer of the pellets, so that the overall strength performance of the pellets after vanadium leaching is not greatly affected; (2) The core material It can be self-fluxing, self-fluxing + high magnesium oxide, high magnesium oxide or acidic pellets, etc. The pellet core material formula can be designed according to higher basicity self-fluxing, higher basicity self-fluxing + higher high magnesium oxide, higher high magnesium oxide, etc. While supplementing its own strength, it can realize the alkali metallization modification of vanadium on the surface material of acidic pellets. Under the condition of roasting + single water leaching, the pellets can generally supplement the requirements of blast furnace slag for the required basicity to a certain extent; (3) The pellet core material is not equipped with vanadium leaching aid, and it is also controlled to prevent the leaching liquid from penetrating excessively. It can realize the alkali metallization modification of vanadium on the surface material, roasting water leaching, vanadium blank roasting alkali metal alkaline solution / sulfuric acid solution leaching or vanadium Under conditions such as alkaline earth metallization modification roasting and sulfuric acid leaching, the pellets generally have a lower content of alkali metal oxides or sulfur / chlorate, reducing the negative impact on blast furnace operation and the environment; (4) When using vanadium for alkali metallization roasting, especially when using alkali metal carbonates as leaching aids to control environmental pollution, the wear resistance index and room temperature compressive strength of the pellets after preheating and roasting are often low. This is mainly because (a) commonly used alkali metal salts are all water-soluble substances, and some alkali metal salts begin to dissolve after pelleting, resulting in a decrease in the structural density of the green pellet solid material; (b) commonly used sodium carbonate reacts with water and carbon dioxide in the air to generate carbon. Sodium bicarbonate (solid at room temperature) completely decomposes into carbon dioxide and water vapor at 270℃. When the drying heating rate is not right, the additional gas from the decomposition of sodium bicarbonate and other coexisting water vapor during drying will cause defects in the pellet structure. In some cases, the bursting temperature during drying may be less than 300℃. (c) When alkali metal salts are preheated and calcined, the high-temperature decomposition of alkali metal salts releases gases, which further reduces the structural density. (d) The addition of alkali metal salts may interact with the pellet binder, negatively affecting its bonding and consolidation properties, especially composite binders containing organic components. (e) The addition of alkali metal salts will have a certain impact on the sintering of pellets.The aforementioned problems are addressed by (a) dissolving alkali metal carbonates in the spray solution for pellet surface atomization growth in the maximum proportion as a saturated solution to reduce the proportion of carbonates added in solid form, (b) eliminating the possible presence and reaction-generated sodium bicarbonate through physical decomposition / inhibition and / or chemical inhibition during the use of solid sodium carbonate, (c) minimizing the excess alkali during vanadium alkali metallization, (d) optimizing a more suitable pellet binder based on the characteristics of vanadium leaching aids, (e) adding magnesium oxide / magnesium carbonate to the surface material to create a high-magnesium material while appropriately sacrificing a small amount of leaching rate, which helps to improve the surface strength during alkali metallization roasting and when the hot water leaching rate of vanadium has little impact, and also increases the softening strength of the pellets in the blast furnace; (5) leaching of vanadium compounds and other substances (such as silicon contained in the alkali metallization roasted water-leached material). (6) The vanadium leaching also causes the pellets to be leached at the same time, which will further reduce the strength of the pellets after leaching due to structural dissolution and a decrease in apparent density (which will reduce by about 15% depending on the degree). By adjusting the pH value of the leaching solution, controlling the leaching time, and appropriately discarding the vanadium leaching rate, the leaching rate and pellet strength are comprehensively balanced to ensure the smooth operation of the blast furnace while also achieving a high vanadium leaching rate and low iron loss. (7) After vanadium leaching, the micro-density of the pellet surface decreases, which helps to alleviate the degree of pulverization caused by the low-temperature reduction lattice transformation stress of ferric oxide in the blast furnace and is beneficial to compensating for the strength of the pellets. (8) After vanadium leaching, the surface permeability of the pellets increases and the non-iron impurities decrease, which is beneficial to the reduction of iron in the pellets and is beneficial to compensating for the strength of the pellets. (9) Controlling the pellet surface temperature to drop to a level close to the temperature of the target hot leaching solution before starting leaching can minimize the additional thermal shock to the surface. In summary, thanks to the support of high-strength pellet cores with a diameter not less than 60% of the pellet diameter, and by taking measures to control surface strength loss and mitigate low-temperature pellet pulverization, the composite pellets after vanadium leaching can be used normally in blast furnaces.

[0021] 3) Feasibility of pelletizing and online vanadium leaching of composite pellets with a "core + surface" structure under the blast furnace pelletizing process.

[0022] Regarding the step-by-step pelletizing of different materials to produce composite pellets with a "core + surface" structure, it should be said that with the continuous increase in the pellet ratio in blast furnace smelting, in order to obtain better physicochemical properties of pellets for blast furnace smelting or to utilize some of the high-iron-grade recovery resources originally added to sintered ore raw materials, the industry has carried out a large amount of research related to pellets. Some of these studies involve cases of pellets made from different materials with different structures. For example, some studies have added about 1 wt% coke powder to the core material of the pellets to produce composite pellets with a "core + surface" structure in order to reduce the reduction expansion problem of blast furnace pellets and reduce energy consumption; others have concentrated the alkali metal salt flux in solvent-based pellets into the core to produce double-layer pellets with an acidic outer layer (concentrate powder + binder) in order to improve the reducibility of the pellets; still others have produced pellets for direct reduction in rotary hearth furnaces with carbon added, which are made into pellets with a carbon-free outer layer, a high carbon content in the core, and a high iron grade for recycling solid waste, thereby improving the drop strength index of green pellets and the utilization rate of reduced carbon, etc. Correspondingly, various composite materials have also been developed. The pelletizing technology and equipment include: (1) Step-by-step pelletizing with the same equipment, that is, first add the core material for dripping water nucleation, then switch to spraying water mist to grow to the set core diameter and after the core material in the disc is exhausted through a compact consumption process, switch to the outer layer material, continue to spray water mist to grow to the target pellet diameter or target outer layer thickness, and then compactly exhaust the outer layer material to become a green pellet. However, this method is inefficient, the pellet diameter is uneven, the outer layer thickness deviation is large, and it is easy to cause a certain degree of mixing due to the inability to completely consume the core or outer layer material; (2) Linked continuous pelletizing, that is, a set of pelletizing equipment is connected in series, first making and screening out the core of the designed size (when using a disc granulator, the large diameter core can be automatically separated, and the undersized small balls can be returned to the granulator to continue growing), and then transferring to the subsequent outer layer material compounding pelletizing machine to continue growing to the designed target pellet size. This method has high production efficiency, small pellet diameter difference and relatively uniform outer layer thickness. There are already relatively mature corresponding large-scale industrial production equipment available on the market. Although the purpose, additives, and subsequent processing of the "core + surface" composite pellets of this invention are quite different, their structure is basically the same as the aforementioned double-layer pellets, and the materials used and their characteristics are the same or similar to those of conventional pellets: (1) The core part is the conventional pellet material; (2) When vanadium is leached with acid, the vanadium leaching additive added to the surface is an alkaline earth metal carbonate, and the flux and corresponding amount added to the conventional self-fluxing pellets for vanadium-containing iron ore with low vanadium content are the same; (3) When vanadium is leached using acid / alkali solutions, no special material is added to the surface layer; only blank oxidative roasting of vanadium is performed. The surface material is the conventional acidic vanadium-containing magnetite pellets. The only major difference is that when water is chosen as the leaching solution for vanadium leaching and alkali metallization roasting is applied to the vanadium in the iron ore powder, alkali metal salts need to be added to the surface material and / or alkali metal salts are added to the spray solution that continues to grow on the pellet core to form a near-saturated aqueous solution. Conventional pellet growth generally only requires water spraying.

[0023] In principle, there is no problem with vanadium leaching on the surface of composite pellets with a "core + surface" structure. However, since the vanadium-containing iron ore powder for vanadium leaching is oxidized and modified as the surface layer of the pellets during the roasting process in the blast furnace, the non-target leaching iron minerals in the internal core are also leached online together. The mass of the leaching process is enormous. From the perspective of process flow, industrial facilities and process practice, the feasibility of realizing online vanadium leaching is as follows: (1) After normal pellet roasting, it needs to be forcibly cooled to below 140°C to adapt to subsequent conveyor belt transportation. The pellets can be transferred to the vanadium leaching pool at this point, and its temperature is just right for the hot liquid vanadium leaching based on the heat storage of the leaching pellets in the method of this invention. It is only necessary to control the pellets to prevent severe boiling of the leaching liquid on the outer surface when they are immersed, so as to prevent the peeling of the pellet skin and the impact on the strength of the pellets caused by the sudden steam in the shallow layer. That is, the actual control is to take the higher value of the pellet surface temperature when the water temperature is low, and the pellet surface temperature should not exceed 100°C when the water temperature is near the boiling point; (2) Since the total time for the thin surface leaching is at most one hour, Based on the output of a chain grate machine + rotary kiln or belt roaster with an hourly output of 600 tons, the pellet accumulation during the 60-minute leaching process is only a maximum of 600 tons. According to the apparent liquid-solid ratio of 4:1 (the actual liquid-solid ratio relative to the surface material is about 10:1), the total amount of leaching liquid in the system during the leaching process is 2400 tons. There are no engineering problems in the continuous circulation washing of single or multiple series and parallel leaching tanks + storage tanks. It would be even simpler if it were matched with a chain grate machine + rotary kiln or belt roaster or vertical kiln with a smaller output. (3) Since the number of pellets "full leaching" is large, it is advisable to adopt the continuous leaching method. The continuous leaching of vanadium can be carried out in various forms such as cage filter conveying equipment or "sedimentation + lifting multi-tank continuous leaching" device.

[0024] In conclusion, it is technically and engineeringally feasible to use different materials to form pellets in stages and "embed" them into the blast furnace pelletizing process, as well as to use the vanadium leaching process and corresponding equipment after pellet roasting as a "bypass addition" to the existing output process of blast furnace pellet production, and then operate it as the main process.

[0025] 4) Selection and determination of leaching method

[0026] Vanadium in minerals, after high-temperature oxidation roasting and readily soluble modification with appropriate vanadium leaching aids, can be leached into vanadium in various possible vanadium leaching solutions with optimized methods. Currently, widely used methods for leaching vanadium from vanadium-bearing iron ore powder include:

[0027] (1) When vanadium is leached with hot water, alkali metal salts are needed as vanadium leaching aids to oxidize and alkali metallize the vanadium in the vanadium-containing iron ore powder with iron-vanadium spinel at high temperature and roast it to oxidize the low oxidation state (+3) vanadium to be leached and generate water-soluble alkali metal vanadate compounds with high oxidation state (+4 or +5) so as to facilitate leaching. The vanadium oxide volatilization during roasting is low. Sodium roasting is often used to extract vanadium. This is also the oldest, most mature and relatively effective method for extracting vanadium. However, traditional methods often use salt or sodium sulfate (or sodium sulfite). The chlorine or oxysulfide gas released during roasting has a large negative impact on the environment.

[0028] (2) Vanadium leaching is carried out using dilute acid. Alkaline earth metal salts are used as vanadium leaching aids to oxidize and roast vanadium-containing iron ore powder at high temperature and alkaline earth metallization. This makes the vanadium to be leached into alkaline earth metal salt vanadates that are soluble in dilute acid so that they can be leached. Calcification roasting is often used to extract vanadium. Since limestone or dolomite is often used, the roasting process has relatively little environmental pollution. However, the acid consumption for leaching low-vanadium grade iron ore powder is relatively large.

[0029] (3) Vanadium leaching is carried out using strong alkali / or concentrated acid. In order to obtain a higher vanadium leaching rate, it is also necessary to use salt-free high-temperature oxidation blank roasting of vanadium-containing iron ore powder to destroy the iron-vanadium spinel mineral structure of the target vanadium to be leached and to oxidize from low-valence vanadium to generate high-valence vanadium oxides so as to facilitate dissolution and leaching. However, the higher temperature during salt-free roasting will cause more vanadium oxides to volatilize. Lowering the roasting temperature will cause the leaching rate to decrease due to incomplete destruction of the vanadium symbiotic mineral structure. In addition, while dissolving vanadium compounds, iron, silicon and other compounds in the pellets will be dissolved, which will seriously reduce the overall strength of the pellets. Furthermore, the acid / alkali consumption for leaching low-vanadium grade iron ore powder is huge.

[0030] There are other methods that have been explored and tried, such as directly acid leaching vanadium from vanadium-bearing minerals after fine grinding, but these are not suitable for low-vanadium-grade iron minerals and will not be listed here.

[0031] The above methods can be used for vanadium leaching of the surface layer of composite pellets with "core + surface layer". Since it is vanadium leaching of the surface layer of high-strength sintered pellets, the leaching solution penetrates less into the internal core of the pellets under the premise of controlling the leaching time, and the consumption of leaching solution can be relatively reduced.

[0032] It needs further clarification that the rapid vanadium leaching of the pellet surface, as an online step in the blast furnace pelleting process, must also consider the impact of residual leaching solution and leaching aids on the physicochemical properties of the pellets themselves and their subsequent smelting process in the blast furnace. The negative impacts of the leaching solution on all process-related leaching equipment and the environment must also be considered. Clearly, while concentrated acids and strong alkalis may be more environmentally friendly during roasting and have fewer adverse effects on pellet indicators and blast furnace production, considering their corrosive effects on process equipment during large-scale industrial leaching, equipment investment increases dramatically, operating costs are very high, and implementation is extremely difficult. Using dilute acids and weak alkalis as leaching solutions may make equipment corrosion prevention relatively easier, but implementation is still very challenging. Taking all factors into account, the only optimal leaching method is to achieve a more environmentally friendly, energy-saving, economical, efficient, high-yield, and convenient optimization of the entire process, while prioritizing water as the leaching solution.

[0033] 5) Selection and determination of vanadium leaching aids

[0034] In the oxidative roasting process, alkaline substances, acting as leaching aids for vanadium, function as catalysts. When vanadium spinel in iron ore is heated and oxidized, alkali metals are simultaneously formed into soluble vanadates. The leaching solution is then used as a solvent to leach these soluble vanadates into the solvent, separating them from the iron ore powder pellets. The catalytic mechanism of the alkaline substances involves alkali metal or alkaline earth metal ions penetrating the spinel lattice in the vanadium slag, increasing the concentration of electron vacancies and ion vacancies. The order of catalytic activity from strongest to weakest is: chlorate > carbonate > nitrate. Within the salts, the catalytic activity of alkali metal elements is: cesium > rubidium > potassium > sodium. This is because the ionic radius decreases sequentially, leading to a decrease in the concentration of electrons and ion vacancies within the spinel lattice, thus weakening the catalytic effect. Under the premise of hot water leaching, conventional vanadium leaching aids can only be alkali metal oxides and alkali metal salts, which react with high-valence vanadium through high-temperature oxidative roasting to generate water-soluble vanadates. Alkali metal oxides readily hydrate into strong alkalis and cannot be used in large-scale industrial production. Suitable alkali metal salts include sodium chloride, potassium chloride, potassium carbonate, sodium carbonate, sodium bicarbonate, sodium sulfate, and sodium sulfite. Sulfates and chlorates, which produce harmful gases during thermal decomposition and reaction, are unsuitable. Sodium bicarbonate is unstable and produces excessive carbon dioxide and water vapor upon thermal decomposition after pelletizing, making it also unsuitable. Carbonates release carbon dioxide, a greenhouse gas, during thermal decomposition and reaction, but this is slightly less harmful than the presence of toxic gases. Although sodium salts do not catalyze as effectively as cesium, rubidium, or potassium salts, they can still play a catalytic role in pellet oxidation. Furthermore, sodium carbonate is more readily available and economical than potassium carbonate and other alkali metal carbonates. Sodium also has the smallest atomic weight, allowing it to bind more vanadium to the same mass of pellets, making it relatively more economical. Sodium carbonate was selected as the vanadium leaching aid after comprehensive comparison. In particular, the sodium hydroxide solution extracted after the vanadium precipitation liquid treatment can be passed into the roasting flue gas. When the sodium hydroxide absorbs carbon dioxide and becomes a recyclable sodium carbonate solution, it can achieve a certain degree of cyclical balance of emitted carbon dioxide.

[0035] 6) Use of sodium carbonate as a vanadium leaching aid

[0036] As a vanadium leaching aid using hot water as the leaching solution, the addition of sodium carbonate has a significant impact on the drying, preheating, and calcination strength of pellets, as well as the strength of vanadium after leaching. It can also have certain negative effects on blast furnace production, and its adverse effects must be minimized as much as possible. The main problems that may arise from the use of sodium carbonate include:

[0037] (1) Sodium carbonate will react with water (water vapor) and carbon dioxide in its environment during storage and processing at room temperature, especially when it is added to the surface material and finely ground, to form solid / liquid sodium bicarbonate. It begins to decompose at 50°C and completely decomposes to release carbon dioxide and water vapor at 270°C. If the drying and heating rate is not right, the gas from the decomposition of sodium bicarbonate and other coexisting water vapor during drying will work together to cause defects in the pellet structure, and even the bursting temperature may be less than 300°C.

[0038] (2) Sodium carbonate and other commonly used alkali metal salts are water-soluble substances. When added to iron ore powder in solid form according to the dosage, the free water contained in the material is far from enough to dissolve sodium carbonate. A large amount of undissolved solid sodium carbonate added to the surface material will dissolve in the spray water during the growth of the spheres. Some of it will only begin to dissolve and liquefy after the microstructure of the spheres has been formed, resulting in a decrease in the density of the solid material structure of the green spheres, which reduces the strength of the green spheres and causes certain breakage losses.

[0039] (3) All solid sodium carbonate that begins to dissolve and liquefy after the microstructure of the grown pellets has been formed not only leaves voids that reduce the strength of the green pellets, but also forms micro-regions of local excess sodium carbonate in the voids after drying and water loss. This not only increases the consumption and pollution of sodium carbonate and reduces the pellet density, affecting the pellet strength, but also causes the "sodiumization" of other elements to leach out along with vanadium due to the excess sodium carbonate, further reducing the strength of the pellets after vanadium leaching.

[0040] (4) Among the various alkali metal salts used in the existing vanadium leaching technology, only the aqueous solution of sodium carbonate is strongly alkaline (the others are weakly alkaline or neutral to alkaline). After being added and dissolved, it may have a great adverse effect on the relevant materials, especially on the organic components in the composite binder.

[0041] In summary, while adding a large excess of sodium carbonate can maximize vanadium leaching, the overall excess of sodium carbonate needs to be controlled due to the requirements of subsequent blast furnace smelting on pellet strength and alkali metal content. This requires sacrificing a small amount of vanadium leaching rate to meet the requirements of blast furnace smelting on pellet strength.

[0042] Therefore, when using sodium carbonate as a vanadium leaching aid, the following should be noted:

[0043] (1) Before using solid sodium carbonate, heat it to decompose any possible sodium bicarbonate, add sodium carbonate and mix it to keep the material at a temperature above 55°C, or add a small amount of sodium hydroxide to the atomizing liquid containing sodium carbonate to eliminate the possible sodium bicarbonate that may be present and produced by the reaction through physical decomposition / inhibition and / or chemical decomposition / inhibition.

[0044] (2) While heating the material to suppress the formation of sodium bicarbonate from sodium carbonate, reduce the water content in the material and dissolve sodium carbonate in the spray liquid for atomization and growth of the pellet surface in the form of a sodium carbonate saturated solution as much as possible, in order to reduce the amount of sodium carbonate added in solid state.

[0045] (3) It is necessary to sort out the pellet binders commonly used in the existing technology. Before screening and developing a pellet binder that is more suitable for maintaining and improving the strength of pellets after adding sodium carbonate leaching aid and hot water leaching vanadium, traditional inorganic pellet binders, such as bentonite, which are relatively more stable and reliable even though the amount added is slightly higher, should be selected.

[0046] (4) Explore and find the optimal amount of sodium carbonate added and related pelleting process and vanadium leaching process that take into account both vanadium leaching rate and pellet strength after leaching through experiments;

[0047] (5) In order to control the possible combination of carbonates and moisture in the atmosphere where carbon dioxide is generated and the water vapor and carbon dioxide gas decompose at 270°C combine with the moisture in the pellets and cause the pellets to burst, the conventional green pellet drying air temperature should be reduced from about 400°C to 230-250°C.

[0048] 7) Factors determining the pellet diameter and surface thickness

[0049] Blast furnace pellets, as a mature blast furnace charge, have established unified technical specifications based on factors such as pellet diameter / calcination energy consumption, pellet diameter / pelleting efficiency, pellet diameter / green pellet strength relationship, and cooling efficiency in the pellet production process. This invention, following relevant blast furnace pellet standards and based on pellet diameter values ​​(generally considered optimal at 11-14mm considering pellet production efficiency, calcination energy saving, and performance within the blast furnace), establishes structural parameters for "core + surface" composite pellets used in online surface vanadium leaching. The surface thickness (δ) is a key indicator related to vanadium leaching. Important aspects related to the pellet diameter (D) in conjunction with the surface thickness (δ) include:

[0050] (1) The surface thickness alone determines the shortest time for effective vanadium leaching under the same conditions. Obviously, the smaller the thickness, the shorter the effective leaching time of vanadium, and the better the degree of pellet formation after internal heat storage, drying and rinsing.

[0051] (2) The diameter of the pellet determines the amount of heat stored inside the pellet when it is cooled to below the boiling point of water after roasting. Obviously, the smaller the diameter, the less heat energy can be used inside the pellet (the lower the temperature inside the pellet core).

[0052] (3) The ratio of pellet diameter to surface thickness qualitatively indicates the strength performance of the pellet in the blast furnace. A larger ratio indicates higher overall compressive strength of the pellet.

[0053] (4) The surface thickness combined with a certain pellet diameter can roughly determine the ratio of the target vanadium leaching iron ore powder to the non-target vanadium leaching iron ore powder in the composite material. Based on the resource amount of vanadium-containing iron ore powder, the resource amount of non-target iron ore powder, and the desired vanadium leaching time, the optimized pellet production and vanadium leaching composite material pellet parameters, such as the target pellet core diameter (D-2δ), can be determined. Obviously, the thicker the surface layer, the smaller the pellet diameter, and the more vanadium-containing iron ore powder can be used for vanadium leaching.

[0054] 8) Energy saving

[0055] The high energy consumption of vanadium enrichment and leaching is a common problem in existing pyrometallurgical and hydrometallurgical processes for vanadium extraction from vanadium-containing iron ore powder, especially for iron ore powder with lower vanadium grades. The energy-saving considerations of the method in this invention are as follows:

[0056] (1) Using the normal pellet production process for roasting, the additional energy consumption of the oxidative roasting and modification process of vanadium minerals is almost zero, while the existing wet vanadium extraction process has extremely high energy consumption of oxidative roasting. The iron ore powder after vanadium leaching is used as a steelmaking raw material and enters the steel manufacturing process from scratch.

[0057] (2) Vanadium can be directly leached from the pellets after roasting, unlike existing pyrometallurgical vanadium extraction technology. Even pellets made from vanadium-containing iron ore powder need to go through ironmaking and steelmaking to extract vanadium into vanadium-enriched slag, and then be broken, finely ground, pelletized, roasted, and then crushed / finely ground again before vanadium can be leached.

[0058] (3) Because the pellets are leached as a whole, the roasted pellets can be leached with hot vanadium while they are still hot, and the heat storage of the hot pellets can be fully utilized to keep the leaching liquid and washing water at a level close to the boiling point. The surface of the pellets is kept close to the boiling point. After the final rinsing is completed, there is still a certain amount of heat storage to dry or pre-dry the pellets. There is no need to grind the roasted vanadium-containing material pellets into fine powder for vanadium leaching as in the existing technology. It is impossible to realize any low-temperature heat storage utilization during pellet leaching. The vanadium leaching hot liquid needs to be continuously heated with energy consumption. On the contrary, the iron ore powder / residue after vanadium leaching will also carry out the heat supplied to the leaching liquid.

[0059] (4) Fine grinding is a major energy consumer. Since it does not require fine grinding of roasted pellets as in the existing wet vanadium extraction process, nor does it require fine grinding of vanadium slag before roasting and roasted pellets as in the existing pyrometallurgical vanadium extraction process, it has a significant energy-saving effect.

[0060] (5) At the very end of pellet cooling, the temperature is too low, and conventional waste heat recovery that requires further conversion is difficult to be efficient. It can be used to preheat the leachate and also as a leachate compensation water for rinsing after pellet leaching.

[0061] (6) The heat storage inside the pellets used for vanadium leaching can be used to heat and maintain the temperature of the leaching solution;

[0062] (7) When the temperature of the leachate is too high and it boils, a clean water circulation pipeline can be installed at the bottom of the pipeline. The leachate is cooled by heat exchange through the pipe wall while the rinsing solution that needs to be preheated is heated.

[0063] 9) Pollution control

[0064] (1) The high-temperature oxidation roasting of vanadium in vanadium-containing iron ore is completed directly using the blast furnace pellet production process. Except for the small amount of vanadium leaching additives decomposed and emitted during the roasting process, which needs to be treated simultaneously with the existing pellet production line's complete and compliant pollution control facilities, there is no other additional pollution.

[0065] (2) When carbonate is selected as vanadium leaching aid, the carbon dioxide produced by its roasting decomposition is relatively less harmful to the environment than sulfide gas, halogen gas, etc. Furthermore, after the vanadium extraction liquid of the leaching liquid is treated with sodium hydroxide and then roasting flue gas is introduced into it, the sodium hydroxide absorbs carbon dioxide and becomes a recycled sodium carbonate solution, which can achieve a certain degree of recycling balance of the emitted carbon dioxide.

[0066] (3) The sediment in the leaching solution is mainly the washing and stripping material on the surface of the pellets during the leaching process. Its composition is basically similar to that of iron concentrate powder and can be directly used to make pellet core material. In other words, there is no need to discharge sediment outside the blast furnace production process.

[0067] Refer to the instruction manual. Figure 1 A comparative flow diagram of the vanadium leaching method for vanadium-containing iron ore powder of this invention with conventional methods shows that, compared to existing technologies, this invention utilizes the existing technology and equipment for blast furnace pellet oxidation roasting to produce composite pellets with a "core + surface" structure from the vanadium-containing iron ore powder to be leached, and then supplies these pellets to the blast furnace after leaching out the soluble vanadium. The advantages of this method are as follows:

[0068] 1) The present invention provides a method for leaching vanadium from vanadium-containing iron ore powder. This method fully utilizes existing blast furnace pellet oxidative roasting production technology and equipment. By improving the pelletizing process and adding online vanadium leaching facilities, the vanadium leaching of vanadium-containing iron ore powder in the pellets is completed during the production process of blast furnace pellets. Compared with the existing pyrometallurgical vanadium extraction technology, the entire vanadium leaching process is shorter, has fewer steps, less interference, and lower cost, resulting in a very low overall investment for vanadium leaching. Compared with the existing hydrometallurgical vanadium extraction technology, the entire vanadium leaching process is simplified, requires less land, and has extremely low cost, resulting in a very low overall investment for vanadium leaching.

[0069] 2) The vanadium leaching method of the present invention for vanadium-containing iron ore powder utilizes the high-temperature roasting process of blast furnace pellets to simultaneously oxidize and modify the vanadium for easy solubility. It also utilizes the residual energy of the roasted pellets to preheat the leaching solution and replenish the water. The entire process of roasting and leaching vanadium-containing iron ore does not generate any additional energy consumption for heating the materials involved (significantly different from existing wet vanadium extraction technology and pyrometallurgical vanadium slag extraction technology), nor does it generate a large amount of heat energy loss due to the enrichment of vanadium (significantly different from existing pyrometallurgical vanadium extraction technology). The energy-saving advantage is very significant.

[0070] 3) The vanadium leaching method of the present invention for vanadium-containing iron ore powder has low pollution and low environmental protection investment and cost. It is mainly reflected in: (1) using environmental protection technology and equipment produced by blast furnace pellet production with complete facilities and compliant emissions to complete the high-temperature roasting process of vanadium in the blast furnace pellets; (2) using sodium carbonate as vanadium leaching aid, the roasting process does not produce toxic or harmful gases; (3) using vanadium water leaching process with relatively low environmental harm, the residual liquid after further vanadium extraction of sodium vanadate water leaching liquid can be recycled and modified for reuse; (4) after vanadium leaching, the pellets are dried and directly supplied to the blast furnace. The very small amount of sediment bottom mud in the leaching pool has the same main components as iron ore concentrate and can be used as pellet core material. There is no solid waste such as vanadium leaching tailings that need to be discharged.

[0071] 4) The present invention provides a method for leaching vanadium from vanadium-containing iron ore powder. The vanadium-containing iron ore powder for vanadium leaching is made into a composite material pellet with a structure of "core + surface". The outer surface of the pellet is thin and leached with sodium-roasted hot water. The modified water-soluble vanadium compound dissolves rapidly and has multiple channels and short paths to diffuse into the leaching solution. This allows for rapid online vanadium leaching of the entire pellet. While taking into account the physicochemical performance of the pellet in the blast furnace, the vanadium leaching rate in the surface vanadium-containing iron ore powder can reach 56-62% under large-scale industrial production conditions, with a corresponding comprehensive extraction rate of 52-60%.

[0072] 5) The present invention provides a method for leaching vanadium from vanadium-containing iron ore powder, wherein the iron ore powder that is not leached with vanadium is made into a composite material pellet with a structure of "core + surface". The core serves as the basis and backbone for maintaining the pellet's characteristics for use in blast furnaces, and supports and maintains the surface of the pellet to prevent excessive loss of strength performance for use in blast furnaces due to vanadium leaching. It can also compensate for the lack of overall alkalinity of the pellet caused by the inability to add calcium oxides or calcium carbonate salts due to water leaching of vanadium through formula adjustment.

[0073] 6) The present invention provides a method for leaching vanadium from vanadium-containing iron ore powder. The leaching cost of vanadium from vanadium-containing iron ore powder is relatively low. It can also conveniently recover vanadium from iron ore with relatively lower vanadium content that cannot be recovered under existing technologies due to economic issues, thereby making better use of valuable vanadium resources.

[0074] 7) The vanadium leaching method of the present invention for vanadium-containing iron ore powder has simple additional composite pelletizing and vanadium leaching processes, operations and equipment. It is easy to switch between traditional pelletizing and composite pelletizing methods on the same production line. The open circuit and closed circuit of the vanadium leaching system can be quickly changed and can be flexibly adjusted at any time according to resources and needs. Attached Figure Description

[0075] Figure 1 A flowchart comparing the vanadium leaching method for vanadium-containing iron ore powder of the present invention with that of conventional methods;

[0076] Figure 2 A schematic diagram of the central cross-section of a composite pellet with a "core + surface" structure in a vanadium leaching method for vanadium-containing iron ore powder according to the present invention.

[0077] In the diagram: 1. Composite pellets with a "core + surface" structure; 2. Surface (target vanadium leached iron ore powder); 3. Core (non-vanadium leached iron ore powder). Implementation

[0078] The present invention discloses a method for leaching vanadium from vanadium-containing iron ore powder, characterized in that: during the pelletizing process in a blast furnace, the vanadium-containing iron ore powder for which vanadium is to be leached is used as a surface layer to form composite pellets with a structure of "core + surface layer," and soluble vanadium compounds in the surface layer of the roasted pellets are rapidly leached online; the main steps are as follows:

[0079] 1) Use conventional pelletizing methods to homogenize non-target vanadium leached iron ore powder. The homogenized material is of the self-fluxing, self-fluxing + high magnesium oxide, high magnesium oxide or acidic pellet type. Pre-form pellet cores by drip nucleation and spray growth. The pellet core diameter ranges from 7 to 11 mm.

[0080] 2) Vanadium-containing iron ore powder for target vanadium leaching, commonly used pellet binders, and appropriate vanadium leaching aids for the type of hydrothermal leaching solution containing vanadium are used as the pellet surface material; when water-soluble vanadium leaching aids are used, the amount of spray growth water is added according to their solubility, a portion of the vanadium leaching aid is added to the spray water to form a near-saturated solution, and the remaining portion is added to the surface material in solid form and finely ground / mixed together; the surface material is used to coat the pellet core through spray growth to form composite material pellets with a structure of "pelle core + surface layer", with a diameter of 10-16 mm and a surface layer thickness of 1.0-3.0 mm;

[0081] 3) The green pellets are dried, preheated and calcined at a high temperature of 1150-1280℃ to become pellets, in which the vanadium in the surface layer is simultaneously oxidized and modified by the iron oxidation and sintering process.

[0082] 4) When the pellets are cooled to a surface temperature of 85-110°C, they are immersed and / or washed in the leaching hot liquid described in step 2 at a temperature of 80-100°C for 10-60 minutes to dissolve and leach out the soluble vanadium compounds in the leaching hot liquid modified by the corresponding vanadium leaching aid described in step 2 in the surface layer.

[0083] Furthermore, the vanadium-containing iron ore powder is vanadium-titanium magnetite concentrate or vanadium magnetite concentrate, wherein the iron content is greater than 62%, the vanadium content is not less than 0.10%, the proportion of ore powder particles with a diameter less than 0.074 mm is greater than 65%, and the specific surface area is greater than 1050 cm². 2 / g.

[0084] Furthermore, the vanadium leaching hot liquid in step 2 is preferably hot water, and the corresponding vanadium leaching aid is preferably sodium carbonate.

[0085] Furthermore, the green pellet structure of the composite structure pellet is further optimized to have the following dimensions: a diameter of 11-14 mm, a core diameter of 7-10 mm, and a surface thickness of 1.5-2.5 mm.

[0086] Furthermore, step 4 is optimized to soaking and / or washing the pellets in a flowing hot liquid at a temperature of 90-100°C after the pellets have cooled to a surface temperature of 90-100°C.

[0087] Furthermore, the temperature rise of the hydrothermal liquid before vanadium leaching in step 4 can be maintained by utilizing the residual heat of the low-temperature section cooled by the pellets and by the heat stored within the pellets where vanadium leaching is performed.

[0088] Furthermore, the leaching time for the vanadium compound in step 4, involving immersion and washing in flowing hydrothermal fluid, is optimized to 15-50 minutes.

[0089] Furthermore, after step 4 is completed, the pellets are rinsed with purified water to replenish the losses from evaporation and absorption during the leaching process. The purified water is heated by the residual heat from the low-temperature section of the pellet cooling process or by the heat transferred during the cooling of the leaching hot liquid.

[0090] Furthermore, after the rinsing is completed, the pellets are pre-dried using the residual heat inside before being used in the blast furnace.

[0091] For core pellets of different diameters, a more uniform surface thickness can be controlled, which correspondingly makes the leaching time of pellets with different outer diameters tend to be the same.

[0092] The present invention will be further described below with reference to specific embodiments or implementation schemes. Example

[0093] This embodiment describes a method for leaching vanadium from vanadium-containing iron ore powder. The surface target vanadium leaching vanadium-titanium magnetite concentrate used has an iron content of 67.07%, a vanadium content of 0.2%, and approximately 65% ​​of the ore powder particles have a particle size less than 0.074 mm, with a specific surface area of ​​1050 cm². 2 / g; the binder is sodium-based bentonite, with an addition amount of 0.8% of the above iron ore powder mass; the vanadium leaching aid is sodium carbonate, with a total addition amount of 5% of the above iron ore powder mass, of which 60% is added to the ore powder and 40% is dissolved in the pellet growth spray solution; continuous pelletizing is carried out, firstly, a disc granulator forms non-vanadium leached iron ore powder self-fluxing material with a diameter of 7-10mm, then it is transferred to a disc granulator with near-saturated sodium carbonate aqueous solution spray and target vanadium leaching ore powder feeding to wrap the pellet core and continue to grow, with a surface layer thickness of 2.5-3mm, and the final composite material pellet diameter is 12-16mm; the pellet drying temperature is 220℃, the calcination temperature is 1280℃; cooling to the pellet surface temperature Vanadium leaching is performed by immersing the pellets in hot water heated to 60°C using waste heat steam from the low-temperature cooling section of the pellets at 100-110°C. The initial 60°C hot water is gradually heated to above 90°C with the help of heat storage in the pellets, and the leaching time is 40-60 minutes. After leaching, the pellets are rinsed with clean water, which is preheated by the pipe walls located in the leaching tank. The surface vanadium leaching rate {[(original vanadium content on the pellet surface - vanadium content after leaching) / original vanadium content on the pellet surface] * 100%} is 50-62%, and the pellet compressive strength loss {[(original compressive strength of the pellet - compressive strength of the pellet after leaching) / original compressive strength of the pellet] * 100%} is 3-5%. Example

[0094] This embodiment describes a method for leaching vanadium from vanadium-containing iron ore powder. The surface target vanadium leaching vanadium magnetite concentrate used has an iron content of 67.07%, a vanadium content of 0.2%, and approximately 65% ​​of the ore powder particles have a particle size less than 0.074 mm, with a specific surface area of ​​1050 cm². 2 / g; the binder is sodium-based bentonite, added at 0.8% of the mass of the iron ore powder; the vanadium leaching aid is sodium carbonate, added in a total amount of 4.5% of the mass of the iron ore powder, of which 60% is added to the ore powder and 40% is dissolved in the pellet growth spray solution; first, non-target vanadium leaching iron ore powder is used to make pellet cores with a diameter of 8-9mm, and then a near-saturated sodium carbonate aqueous solution is sprayed to coat the pellet cores for continued growth, producing composite pellets with surface thicknesses of 1.0, 2.0 and 3.0mm respectively; vanadium magnetite with the same target vanadium leaching as described above is used. The refined powder and spray liquid were used to make single-material pellets with a final diameter of 13 mm; the pellets were dried at 240℃ and calcined at 1250℃; when the pellet surface temperature was cooled to 100℃, some of the single-material pellets were crushed (particle size less than 200 mesh or 74μm) and then separately mixed with whole single-material pellets and composite material pellets and immersed in hot water at 95℃ for vanadium leaching for 60 minutes. After leaching, the pellets were rinsed in clean water. The vanadium leaching rates of the whole pellets and the crushed single-material pellets were as follows:

[0095] type Single material Single material Compound material Compound material Compound material Surface thickness (mm) 6.5 (whole ball) 0.037 (fine powder) 3.0 2.0 1.0 Surface vanadium leaching rate (%) 50 61 57 59 60 Example

[0096] This embodiment describes a method for leaching vanadium from vanadium-bearing iron ore powder. The surface target vanadium leaching concentrate used has an iron content of 62%, a vanadium content of 0.10%, and approximately 75% of the ore powder particles have a particle size less than 0.074 mm and a specific surface area of ​​1400 cm². 2 / g; the binder is sodium-based bentonite, with an addition amount of 0.7% of the above iron ore powder mass; the vanadium leaching aid is sodium carbonate, with a total addition amount of 4.5% of the above iron ore powder mass, of which 60% is added to the ore powder and 40% is dissolved in the pellet growth spray solution; the linkage continuous pelletizing process first uses a disc granulator to form non-vanadium leached iron ore powder self-fluxing material with a diameter of 9-10mm, and then transfers it to a disc for near-saturated sodium carbonate aqueous solution spraying and target vanadium leaching ore powder feeding. The pelletizer encapsulates the core pellets, which continue to grow, with a surface layer thickness of 1.0-1.5 mm, resulting in final composite pellet diameters of 11-13 mm. The pellets are dried at 250℃ and calcined at 1150℃. After cooling to a surface temperature of 90-100℃, the pellets are immersed in a hot water tank at 92℃ for continuous vanadium leaching for 10-60 minutes. After leaching, the pellets are rinsed with clean water, which is preheated through pipes within the leaching tank. The surface vanadium leaching rate is: Example

[0097] This embodiment describes a method for leaching vanadium from vanadium-containing iron ore powder. The surface target vanadium leaching concentrate used has an iron content of 66%, a vanadium content of 0.35%, and approximately 75% of the ore powder particles have a particle size less than 0.074 mm, with a specific surface area of ​​1450 cm². 2 / g; the binder is sodium-based bentonite, added at 0.9% of the mass of the iron ore powder; the vanadium leaching aid is sodium carbonate, added at a total amount of 4% of the mass of the iron ore powder. Of the total amount of vanadium leaching material, 2 / 3 is added to the ore powder and 1 / 3 is dissolved in the pellet growth spray solution. A continuous pelletizing process is employed, first using a disc granulator to form 8-10mm diameter pellets of non-vanadium leaching iron ore powder self-fluxing material. These pellets are then transferred to a disc granulator with near-saturated sodium carbonate aqueous solution spray and target vanadium leaching ore powder feeding to further encapsulate the pellets and grow them, achieving a surface layer thickness of 2.5mm. The final composite pellet diameter is 10-14mm. The pellets are dried at 250℃ and calcined at 1240℃. When the pellet surface temperature is cooled to 80-90℃, they are immersed in 95℃ hot water for vanadium leaching for 35 minutes. The leaching solution is preheated by the residual heat from the low-temperature section of the pellet cooling process. After leaching, the pellets are rinsed with clean water, which is preheated through the pipe walls within the leaching pool. The surface vanadium leaching rate is 58%. Example

[0098] This embodiment describes a method for leaching vanadium from vanadium-containing iron ore powder. The surface target vanadium leaching vanadium-titanium magnetite concentrate used has an iron content of 66%, a vanadium content of 0.30%, and approximately 75% of the ore powder particles have a particle size less than 0.074 mm and a specific surface area of ​​1150 cm². 2 / g; the binder is sodium-based bentonite, with an addition amount of 0.9% of the above iron ore powder mass; the vanadium leaching aid is potassium carbonate, with a total addition amount of 5% of the above iron ore powder mass, of which 60% is added to the ore powder and 40% is dissolved in the pellet growth spray solution; continuous pelletizing is carried out, firstly, non-vanadium leaching iron ore powder self-fluxing material with a diameter of 8-10mm is formed by a disc granulator, and then transferred to a disc granulator with near-saturated sodium carbonate aqueous solution spray and target vanadium leaching ore powder feeding to wrap the pellet core and continue to grow, with a surface layer thickness of 2.0 mm, and the final composite material pellet diameter is 10-14mm; the pellet drying temperature is 250℃ and the calcination temperature is 1240℃; when the pellet surface temperature is cooled to 80-90℃, it is immersed in hot water at 95℃ for vanadium leaching, with a leaching time of 30 minutes, and the pellet is rinsed with clean water after leaching; the surface vanadium leaching rate is 57%. Example

[0099] This embodiment describes a method for leaching vanadium from vanadium-containing iron ore powder. The surface target vanadium leaching vanadium-titanium magnetite concentrate used has an iron content of 66%, a vanadium content of 0.30%, and approximately 75% of the ore powder particles have a particle size less than 0.074 mm and a specific surface area of ​​1150 cm². 2 / g; Dolomite is added as a vanadium leaching aid at 3.0% of the iron ore mass; the binder is an organic commercial composite binder with aluminum oxide and silicon dioxide as the main inorganic components or calcium-based bentonite, with an addition amount of 0.3% or 0.8% of the above iron ore powder mass, respectively; continuous pelletizing is carried out, firstly, the self-fluxing properties of the non-target vanadium leaching iron ore powder + high magnesium oxide material are used to make a 9mm diameter pellet core, then water mist is sprayed and the pellet core is wrapped with feed to continue growing, making a composite material pellet with a surface thickness of 1.5mm, and the final composite material pellet diameter is 12mm; the pellet drying temperature is 380℃, and the oxidation and calcification roasting temperature is 1150℃; when the pellet surface temperature is cooled to 80-85℃, it is placed in a cage and immersed in a hot sulfuric acid pool with a concentration of 1.5mol / L and a temperature of 90℃ for continuous vanadium leaching for 60 minutes, and the pellet is rinsed with clean water cage after leaching; the surface vanadium leaching rate is 55%. Example

[0100] This embodiment describes a method for leaching vanadium from vanadium-containing iron ore powder. The surface target vanadium leaching vanadium magnetite concentrate used has an iron content of 66%, a vanadium content of 0.30%, and approximately 75% of the ore powder particles have a particle size less than 0.074 mm and a specific surface area of ​​1350 cm². 2 / g; Magnesium carbonate is added to prepare a high-magnesium surface material, with an addition amount of 2.2% of the iron ore powder mass; Sodium-based bentonite is used as a binder, with an addition amount of 0.8% of the iron ore powder mass; Sodium carbonate is used as a vanadium leaching aid, with a total addition amount of 4% of the iron ore powder mass, of which 60% is added to the ore powder and 40% is dissolved in the pellet growth spray solution; Continuous pelletizing is performed, firstly by a disc granulator to form non-vanadium leaching iron ore powder acidic material with a diameter of 7-8mm, then transferred to a disc granulator with near-saturated sodium carbonate aqueous solution spray and target vanadium leaching ore powder feeding to wrap the pellet core for continued growth, with a surface layer thickness of 2.5-3.0. The final composite pellet diameter is 13-14 mm; small core and large surface layer thickness are used to increase the proportion of vanadium magnetite powder in the pellets; the pellet drying temperature is 240℃ and the roasting temperature is 1200℃; when the pellet surface temperature is cooled to 95℃, it is immersed in hot water at 96℃ for continuous vanadium leaching for 50 minutes, and the pellets are rinsed with clean water after leaching; the surface vanadium leaching rate is 59%. Example

[0101] This embodiment describes a method for leaching vanadium from vanadium-containing iron ore powder. The high-titanium vanadium-titanium magnetite concentrate used for surface vanadium leaching has an iron content of 66%, a vanadium content of 0.32%, and approximately 75% of the ore powder particles have a particle size less than 0.074 mm and a specific surface area of ​​1450 cm². 2 / g; the binder is sodium-based bentonite, added at 0.8% of the mass of the iron ore powder; the vanadium leaching aid is sodium carbonate, added at 4% of the mass of the iron ore powder, of which 60% is added to the ore powder and 40% is dissolved in the pellet growth spray solution; a continuous pelletizing process is used, first forming 7-8mm diameter pellets from low-titanium non-vanadium leached iron ore powder self-fluxing material by a disc granulator, then transferring them to a disc granulator with near-saturated sodium carbonate aqueous solution spray and target vanadium leaching powder feeding to encapsulate the pellet cores and continue growing, with a surface layer thickness of 2.5-3.0. The final composite pellet diameter is 12-14 mm; small core and large surface thickness are used to reduce the titanium dioxide content of blast furnace slag; the pellet drying temperature is 225℃ and the calcination temperature is 1250℃; when the pellet surface temperature is cooled to an average of about 92℃, it is immersed in a hot water tank with a water temperature of 96℃ for continuous vanadium leaching for 40 minutes. After leaching, the pellets are rinsed with clean water; the surface vanadium leaching rate is 56%.

[0102] This specification describes the invention in detail with reference to specific exemplary embodiments. However, it should be understood that various modifications and variations can be made without departing from the scope of the invention as defined by the appended claims. The detailed description and drawings are provided only to complement the content disclosed in this specification for those skilled in the art to understand and read, and should be considered illustrative only, not intended to limit the conditions under which the invention can be implemented, and therefore have no substantial technical significance. Any related modifications and adjustments, without affecting the effects and objectives that the invention can achieve, should still fall within the scope of the technical content disclosed in this invention. Furthermore, the background art is intended to illustrate the current state of research and development and significance of the technology, and is not intended to limit the invention or the application field of this invention. More specifically, although exemplary embodiments of the invention have been described herein, the invention is not limited to these embodiments, but includes any and all embodiments modified, omitted, such as combinations, adaptive changes and / or substitutions between embodiments, as would be recognized by those skilled in the art from the foregoing detailed description. The limitations in the claims can be interpreted broadly according to the language used in the claims, and are not limited to the examples described in the foregoing detailed description or during the implementation of this application, which should be considered non-exclusive. Any step listed in any method or process claim may be performed in any order and is not limited to the order set forth in the claims. Therefore, the scope of the invention should be determined solely by the appended claims and their legal equivalents, and not by the description and examples given above.

[0103] The structures, proportions, and sizes illustrated in the accompanying drawings are merely for illustrative purposes and to aid those skilled in the art in understanding and reading the invention. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed herein. Furthermore, terms such as "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity and not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention's implementation.

[0104] It should be understood that the term "and / or" used in this article is a description of the relationship between related objects, and is defined to indicate that there can be three relationships. For example, a and / or b can represent three cases: a exists alone, a and b exist simultaneously, and b exists alone. The character " / " in this article is defined to represent an "or" relationship between the preceding and following related objects.

Claims

1. A method for leaching vanadium from vanadium-containing iron ore powder, characterized in that: In the production of blast furnace pellets, vanadium-containing iron ore powder with vanadium leaching target is used as the main surface material to make composite pellets with a structure of "core + surface". Soluble vanadium compounds in the surface of the pellets after online leaching and roasting are also leached. The steps are as follows: 1) Using conventional pelletizing methods, the mixed material of non-target vanadium leaching iron ore powder is pre-formed into pellet cores with a diameter of 7-11 mm. The mixed material is a self-fluxing, self-fluxing + high magnesium oxide, high magnesium oxide or acidic pellet type. 2) Using vanadium-containing iron ore powder for target vanadium leaching, common pellet binders, and appropriate vanadium leaching aids for different types of hydrothermal leaching solutions as pellet surface materials, the pellets are grown by spraying and encapsulating the core through conventional pelletizing processes to form composite pellets with a "core + surface" structure. The diameter of the pellets is 10-16 mm, and the thickness of the surface layer is 1.0-3.0 mm. 3) The green pellets are dried, preheated and calcined at a high temperature of 1150-1280℃ to become pellets, in which the vanadium in the surface layer is oxidized and modified by the oxidation and sintering process of iron. 4) When the pellets are cooled to a surface temperature of 85-110°C, they are immersed and / or washed in the leaching hot liquid of step 2 at a temperature of 80-100°C for 10-60 minutes to dissolve and leach the soluble vanadium compounds modified by the calcination of the corresponding vanadium leaching aid described in step 2 in the surface layer. The temperature of the hot liquid is maintained by the heat storage inside the pellets where vanadium leaching is performed. The vanadium leaching hot liquid in step 4 is hot water, and the corresponding vanadium leaching aid is sodium carbonate; After vanadium leaching, the pellets are dried and then directly supplied to the blast furnace.

2. The leaching method for vanadium in vanadium-containing iron ore powder according to claim 1, characterized in that: The vanadium-containing iron ore powder is vanadium-titanium magnetite concentrate and / or vanadium magnetite concentrate, wherein the iron content is greater than 62%, the vanadium content is not less than 0.10%, the proportion of ore powder particles with a diameter less than 0.074 mm is greater than 65%, and the specific surface area is greater than 1050 cm². 2 / g.

3. The leaching method for vanadium in vanadium-containing iron ore powder according to claim 1, characterized in that: The structural dimensions of the composite material pellets are further optimized as follows: diameter of 11-14 mm, core diameter of 7-10 mm, and surface thickness of 1.5-2.5 mm.

4. The leaching method for vanadium in vanadium-containing iron ore powder according to claim 1, characterized in that: Step 4 is optimized to involve soaking and / or washing the pellets in a hot leaching solution at a temperature of 90-100°C for 15-50 minutes after the pellets have cooled to a surface temperature of 90-100°C.

5. The leaching method for vanadium in vanadium-containing iron ore powder according to claim 1, characterized in that: After step 4 is completed, the pellets are rinsed with purified water to replenish the losses from evaporation and absorption during the leaching process. The purified water is heated by the hot leaching liquid from the pellets before rinsing.

6. The leaching method for vanadium in vanadium-containing iron ore powder according to claim 5, characterized in that: After rinsing, the pellets are pre-dried using the residual heat inside.

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