Method for pre-oxidation sodium salt roasting of converter vanadium slag

Abstract

The invention discloses a pre-oxidation sodium salt roasting method for converter vanadium slag, and belongs to the technical field of hydrometallurgy. The method comprises the following steps: firstly, preserving the heat of the vanadium slag obtained by vanadium extraction in a converter at a specific oxygen concentration of 5-100% and a temperature of 500-1200 DEG C for 0.5-60 hours for pre-oxidation, so that low-valence substances in the vanadium slag are fully oxidized; carrying out crushing, iron removal and ore grinding on the pre-oxidized slag to obtain qualified refined vanadium slag; the refined vanadium slag and sodium salt are mixed according to the Na2O / V2O5 mass ratio of 0.4-2.0, and then are roasted for 30-360 minutes at the temperature of 700-850 DEG C; by means of the pre-oxidation step, the problems of material sintering and equipment bonding caused by centralized heat release in vanadium slag sodium salt roasting are fundamentally solved, non-return efficient roasting is achieved, the equipment processing capacity and the vanadium conversion rate (can reach 90% or above) are remarkably improved, energy consumption and production cost are reduced, the process is stable, and industrial application is easy.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hydrometallurgy, and particularly relates to a method for extracting vanadium from vanadium slag produced in a converter steelmaking process of vanadium-titanium magnetite. More particularly, it relates to a new method for realizing high-efficiency sodium roasting for extracting vanadium without returning material by pre-oxidizing the converter vanadium slag. BACKGROUND

[0002] Vanadium is an important strategic rare metal, which is widely used in the fields of steel, aerospace, chemical catalysts, energy storage, etc. Vanadium-titanium magnetite is one of the main sources of vanadium. The typical utilization process is to obtain vanadium-containing molten iron through blast furnace smelting, and then to obtain vanadium slag with high vanadium content through converter blowing for extracting vanadium. The vanadium slag thus becomes the main raw material for extracting vanadium pentoxide and other vanadium products.

[0003] Currently, there are many industrialized processes for extracting vanadium from vanadium slag, including but not limited to: vanadium slag sodium roasting-water leaching-ammonium salt vanadium precipitation process, vanadium slag calcium roasting-acid leaching-hydrolysis vanadium precipitation process (such as the Tula process in Russia), vanadium slag calcium roasting-acid leaching-ammonium salt vanadium precipitation process (such as the Pangang process), sub-molten salt vanadium extraction process, and blank roasting-alkali leaching vanadium extraction process, etc. Among them, sodium roasting and calcium roasting for extracting vanadium are relatively mature, and are the two most widely used methods in current production practice.

[0004] Regardless of the roasting process, the core purpose is to convert the stable vanadium oxide (mainly in the form of trivalent vanadium V(III) existing in spinel phases such as FeO·V2O3) in the vanadium slag into pentavalent vanadium salt (such as sodium metavanadate NaVO3 or calcium vanadate) which is soluble in water or acid. The conversion efficiency of the roasting process directly determines the vanadium recovery rate of the entire vanadium extraction process, and is a key link affecting technical and economic indicators.

[0005] However, the current vanadium slag roasting process (especially sodium roasting) faces a common and thorny technical problem: a large amount of low-valence substances (such as FeO, V2O3, etc.) contained in the vanadium slag will undergo intense oxidation (Fe 2+ →Fe 3+ ,V 3+ →V 5+ ) during the roasting process, accompanied by concentrated and large amounts of exothermic reactions. The huge amount of heat released in a short time is easy to cause the local temperature in the roasting system (especially in devices such as rotary kiln, multi-chamber furnace, etc.) to be too high, far exceeding the normal roasting temperature range of the material. The direct consequence is to cause the material to locally soften and melt, and then to cause serious sintering, kiln or furnace coking. This not only destroys the normal roasting conditions, leading to operation out of control and reduced conversion rate, but also seriously affects the continuous and stable operation of the equipment, increasing the frequency and cost of kiln cleaning.

[0006] To alleviate this contradiction, existing technologies typically involve adding a certain proportion of "inert" materials, such as vanadium extraction tailings (residue after leaching) or other inert additives, to the vanadium slag before roasting. The basic principle is to reduce the concentration of oxidizable substances in the unit charge through physical dilution, thereby slowing down the rate of oxidation and exothermic reaction, dispersing and reducing the peak heat of reaction, and enabling the roasting process to proceed within a controllable temperature range.

[0007] While this method alleviates the sintering kiln problem to some extent, its drawbacks are also quite obvious: First, the large amount of returned tailings or the addition of inert substances means a reduction in the effective processing material, significantly lowering the processing efficiency of the roasting equipment (i.e., the amount of vanadium-containing raw material processed per unit time and unit volume); second, heating and processing these materials that do not participate in the main reaction or have low reaction value results in energy waste and increases roasting energy consumption; finally, it also increases the complexity and cost of pre-treatment processes such as material mixing and conveying. Therefore, adding returned materials or inert substances is a "stopgap measure" at the cost of sacrificing efficiency and increasing costs.

[0008] There is an urgent need in this field for a new method that can fundamentally or significantly improve the exothermic behavior of vanadium slag roasting process, thereby achieving efficient roasting with no or low return material, in order to break through the bottleneck of existing technologies. Summary of the Invention

[0009] The primary objective of this invention is to overcome the problems of low processing efficiency and high energy consumption caused by the concentrated heat release in the existing vanadium slag sodium roasting process, which leads to material sintering and equipment sticking, thus necessitating the addition of tailings or inert substances.

[0010] Another objective of this invention is to provide a converter vanadium slag treatment method that can significantly improve vanadium conversion rate, stabilize the process, and is easy to apply industrially.

[0011] Another objective of this invention is to reduce production costs and improve the overall techno-economic efficiency of vanadium extraction from vanadium slag by optimizing process steps.

[0012] To achieve the above objectives, the inventors, through in-depth research and numerous experiments, discovered that the root cause of sintering and kiln formation during the vanadium slag roasting process lies in the presence of low-valence elements (such as Fe) in the material. 2+ V 3+The oxidation reaction of vanadium slag occurs rapidly within a short period, leading to a sharp accumulation of heat. The addition of tailings or inert substances essentially "dilutes" the heat of reaction. Based on this, this invention creatively proposes the core idea of ​​"pre-oxidation": before the vanadium slag enters the main sodium roasting process, under controlled conditions, most of the low-valence substances are pre-oxidized to high-valence states in a gradual and controlled manner. In this way, during the subsequent sodium roasting process, the intense exothermic reaction is essentially complete, leaving mainly the formation of vanadates, with significantly reduced and more gradual heat release, thus fundamentally avoiding heat accumulation and material sintering.

[0013] Based on the above concept, the present invention provides a method for pre-oxidation sodium roasting of converter vanadium slag, characterized by comprising the following steps: Vanadium extraction in converter and vanadium slag acquisition: vanadium is extracted by blowing oxygen into molten iron in the converter to obtain high-temperature liquid converter vanadium slag, which is usually delivered at a temperature higher than 1300℃.

[0014] Pre-oxidation treatment: The converter vanadium slag is subjected to heat preservation pre-oxidation treatment in an atmosphere with a specific oxygen concentration at a certain temperature.

[0015] The O2 concentration in the pre-oxidizing atmosphere is 5% to 100% (volume fraction), preferably 10% to 30%.

[0016] The temperature of the pre-oxidation treatment is 500°C to 1200°C, preferably 600°C to 1000°C.

[0017] The pre-oxidation treatment time is from 0.5 hours to 60 hours, preferably from 8 hours to 36 hours.

[0018] Pre-treatment powdering: The pre-oxidized converter vanadium slag is pre-treated, including crushing, iron removal (such as magnetic separation), ball milling, air classification and other processing methods, to obtain refined vanadium slag powder.

[0019] The particle size requirement of the refined vanadium slag is below 0.2 mm, and preferably the proportion of particles with a particle size below 0.096 mm (about 160 mesh) is greater than 80 wt.

[0020] The metallic iron content of the refined vanadium slag is required to be less than 5%, preferably less than 3%.

[0021] Ingredient preparation and sodium roasting: The refined vanadium slag and sodium salt additives are mixed evenly in proportion to obtain a mixture, and then subjected to high-temperature sodium roasting.

[0022] The mixing ratio of the refined vanadium slag and the sodium salt additive, based on the mass ratio of Na2O to V2O5 in the mixture, is 0.4 to 2.0, preferably 0.8 to 1.2.

[0023] The sodium calcination temperature is 700°C to 850°C, preferably 760°C to 800°C.

[0024] The sodium calcination time is 30 to 360 minutes, preferably 90 to 180 minutes.

[0025] The sodium roasting process can be carried out in an atmosphere with a certain oxygen concentration, and the O2 concentration in the exhaust gas can be controlled to be 8% to 20%, preferably 12% to 15%.

[0026] In this invention, the sodium salt additive may be selected from one or more of sodium carbonate, sodium sulfate, sodium chloride, sodium nitrate, etc., preferably sodium carbonate.

[0027] Compared with the prior art, the technical solution provided by the present invention has the following significant advantages and positive effects: Fundamentally eliminating the risk of sintering and kiln clogging: Through a pre-oxidation step, most of the easily oxidized FeO and other components in the vanadium slag are converted into the more chemically stable Fe2O3 before entering the roasting furnace, while some V(III) is also pre-oxidized. This makes the exothermic reaction in the subsequent sodium roasting process very gradual, completely avoiding localized overheating, material sintering, and equipment adhesion caused by concentrated heat release.

[0028] Achieving efficient roasting without backfill: Since the risk of sintering is eliminated, the method of this invention eliminates the need to add vanadium extraction tailings or any inert substances to dilute the furnace charge. This allows the roasting furnace to process effective vanadium-containing raw materials at full capacity, significantly improving equipment production efficiency (processing capacity can be increased by more than 20%), while saving costs associated with tailings transportation and mixing.

[0029] Reduced energy consumption: The pre-oxidation process can utilize the sensible heat of the vanadium slag itself (if carried out at high temperatures) or proceed slowly at medium to low temperatures, making the overall energy consumption controllable. Furthermore, by eliminating the need for recycle material, the roasting furnace processes a smaller total amount of material and eliminates the heating of ineffective components, thereby reducing the roasting energy consumption per unit product.

[0030] Improving vanadium conversion rate: Pre-oxidation promotes the decomposition of the spinel structure, making vanadium more readily react with sodium salts in subsequent sodium roasting to form soluble sodium vanadate. Examples show that this method can stabilize the vanadium roasting conversion rate at around 90% or higher.

[0031] The process is stable and easy to operate: the entire process (pre-oxidation-pretreatment-calcination) is under mild and controllable conditions, making it easy to achieve stable industrial production and reducing unplanned downtime and maintenance caused by kiln clogging.

[0032] Environmentally friendly: Reduces the circulating load of tailings and optimizes the material flow of the entire system. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the process flow of the converter vanadium slag pre-oxidation sodium roasting method described in this invention. Detailed Implementation

[0035] The embodiments of this disclosure will be further described in detail below with reference to the accompanying drawings and examples. The detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of this disclosure by way of example, but should not be used to limit the scope of this disclosure. This disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0036] These embodiments are provided to make the disclosure thorough and complete, and to fully express the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​set forth in these embodiments should be interpreted as exemplary only and not as limiting.

[0037] As used in this disclosure, the words “including” or “contains” or similar terms mean that the element preceding the word covers the element listed after the word, and do not exclude the possibility that it may also cover other elements.

[0038] All terms used in this disclosure have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein.

[0039] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0040] Combination Figure 1 In an embodiment of the present invention, a method 100 for pre-oxidation sodium roasting of converter vanadium slag includes the following steps: Step 101, Pre-oxidation treatment: The vanadium slag obtained from the converter vanadium extraction is pre-oxidized by holding it at a temperature of 500℃ to 1200℃ for 0.5 to 60 hours in an atmosphere with an oxygen concentration of 5% to 100%.

[0041] Step 102, Pretreatment: The pre-oxidized vanadium slag obtained in step (a) is crushed, iron removed and ground to obtain refined vanadium slag with a metallic iron content of less than 5% and a particle size of less than 0.2 mm.

[0042] Step 103, Batching and Calcination: Mix the refined vanadium slag obtained in step (b) with sodium salt additives, control the mass ratio of Na2O to V2O5 in the mixture to be 0.4 to 2.0, and then calcine at 700°C to 850°C for 30 to 360 minutes to obtain sodium-roasted clinker.

[0043] The following is combined Figure 1 The present invention will be further described in detail with reference to specific embodiments, but the implementation of the present invention is not limited thereto. Process parameters not specifically specified in the following embodiments are generally implemented under conventional conditions.

[0044] Example 1 Vanadium-containing molten iron is subjected to oxygen blowing in a converter to extract vanadium, resulting in liquid converter vanadium slag at approximately 1350℃. This high-temperature vanadium slag is then poured into a controlled atmosphere insulated container. A gas with an oxygen concentration of 10% (volume fraction, the remainder being N2 or air) is introduced into the container. The vanadium slag is then pre-oxidized at 1000℃ for 24 hours under this atmosphere.

[0045] After pre-oxidation, the vanadium slag was allowed to cool naturally to room temperature. It was then pretreated: first coarsely crushed by a jaw crusher, then having metallic iron particles removed by a magnetic separator, followed by fine grinding in a ball mill. The milled product was then air-classified to obtain refined vanadium slag powder with a particle size distribution meeting the requirements. Analysis showed that the refined vanadium slag contained 13.88 wt.% V₂O₅, with 96 wt.% of particles smaller than 0.096 mm, and 2.6% metallic iron.

[0046] Weigh 100g of this refined vanadium slag and mix it thoroughly with 24g of sodium carbonate (analytical grade) in a mixer. The calculated mass ratio of Na2O to V2O5 in this mixture is approximately 1.0.

[0047] The uniformly mixed material was placed in a refractory crucible and then placed in a box-type muffle furnace for sodium calcination. The calcination temperature was set at 780℃, and the calcination time was maintained at 90 minutes. During the calcination process, the furnace chamber was filled with an air atmosphere (approximately 21% O2).

[0048] After roasting, the crucible was removed for observation. The clinker was in the form of loose granules or powder, without any sintering or clumping, and it did not adhere to the crucible wall.

[0049] Chemical analysis of the roasted clinker revealed a total vanadium (TV) content of 6.43% and a water-soluble vanadium content of 5.90%. The calculated vanadium conversion rate (water-soluble vanadium / total vanadium × 100%) was 91.81%.

[0050] Example 2 Similarly, vanadium slag from the converter was obtained. It was pre-oxidized in a controlled atmosphere furnace at 600°C with an oxygen concentration of 30% for 36 hours.

[0051] After cooling, the vanadium slag is obtained by crushing, magnetic separation (reducing the metallic iron content to 1.8%), ball milling, and air classification. The vanadium slag has a V2O5 content of 14.59 wt.% and a particle size of -0.096 mm of 96 wt.%.

[0052] Take 100g of this refined vanadium slag and mix it with 30g of sodium carbonate. The mass ratio of Na2O / V2O5 is approximately 1.2.

[0053] Calcination was carried out in a muffle furnace at 760°C for 180 minutes.

[0054] The resulting roasted clinker was loose and free of sintering and agglomeration. Analysis showed that the clinker had a TV of 6.56%, soluble vanadium of 6.03%, and a conversion rate of 91.85%.

[0055] Example 3 Obtain converter vanadium slag. Pre-oxidize it by introducing an atmosphere with a 20% oxygen concentration at 800℃ and holding it at that temperature for 12 hours.

[0056] The pretreated vanadium slag has a V2O5 content of 16.87 wt.%, a -0.096mm particle size of 96 wt.%, and a metallic iron content of 2.7%.

[0057] Take 100g of refined vanadium slag and mix it with 25g of sodium carbonate. The mass ratio of Na2O / V2O5 is approximately 0.86.

[0058] Calcination was carried out in a muffle furnace at 800°C for 90 minutes.

[0059] The obtained roasted clinker was in good condition. Analysis showed that the clinker had a TV of 7.76%, soluble vanadium of 6.98%, and a conversion rate of 89.80%.

[0060] Comparative Example 1 Vanadium slag from the same source as in Example 1, but without pre-oxidation treatment, was subjected to the same pretreatment to obtain refined vanadium slag (V2O5≈14%). To prevent sintering, it was mixed with sodium carbonate at a clinker:return tailings mass ratio of 7:3 (total Na2O / V2O5 ratio remained 1.0) and calcined at 780°C for 90 minutes. Although severe sintering did not occur, the clinker showed slight agglomeration. The conversion rate was approximately 85%. Furthermore, the effective material volume was only 70% of that without the return tailings, resulting in a corresponding increase in energy consumption.

[0061] Comparative Analysis of Effects Comparing Examples 1-3 with the comparative examples, the advantages of the present invention are obvious: Material state: The roasted clinker obtained by the method of the present invention is "loose", while the comparative example is "clumped".

[0062] Conversion rate: The conversion rate of the method of the present invention (89.80%-91.85%) is higher than that of the comparative example (approximately 85%).

[0063] Processing efficiency: This invention does not require the addition of recycled material, and the efficiency of the roasting furnace in processing effective vanadium slag is increased by about 43% compared with the traditional process that adds 30% recycled material.

[0064] Energy consumption and cost: Efficiency improvements and the omission of return material processing directly reduce the energy consumption and operating costs per unit of product.

[0065] Parameter range description Pre-oxidation temperature (500-1200℃): If the temperature is too low, the oxidation kinetics are slow and the required time is too long; if the temperature is too high, it may approach the melting point of some components, causing local sintering. 600-1000℃ is the preferred range for achieving efficient oxidation and avoiding pre-sintering.

[0066] Pre-oxidation oxygen concentration (5%-100%): Oxygen concentrations below 5% result in too slow an oxidation rate; using pure oxygen is also costly. An oxygen concentration of 10%-30% strikes a good balance between cost and efficiency.

[0067] Pre-oxidation time (0.5-60h): Too short a time will result in insufficient oxidation; too long a time is uneconomical. 8-36h is sufficient to complete the oxidation under optimal conditions.

[0068] Vanadium slag particle size (<0.2mm, preferably -0.096mm>80%): ensures sufficient specific surface area to promote the roasting reaction.

[0069] Iron content (<5%, preferably <3%): Iron will also oxidize and release heat during roasting, and may interfere with the sodiumization reaction, so it needs to be controlled.

[0070] The Na₂O / V₂O₅ ratio (0.4-2.0, preferably 0.8-1.2) is optimal: too low a ratio will result in incomplete reaction; too high a ratio will waste sodium salt and may form low-melting-point eutectics. 0.8-1.2 is an economical ratio to ensure high conversion rates.

[0071] Calcination temperature (700-850℃, preferably 760-800℃): If the temperature is too low, the reaction rate is slow; if the temperature is too high, even after pre-oxidation, it may lead to the decomposition of sodium salt or the melting of a small amount of components. 760-800℃ is the suitable temperature for the formation of sodium vanadate.

[0072] Calcination time (30-360 min, preferably 90-180 min): to ensure the reaction proceeds fully.

[0073] In summary, by introducing a pre-oxidation step, this invention ingeniously solves the core problem in the sodium roasting process of vanadium slag, providing a reliable technical path for achieving green vanadium extraction with no return material, high efficiency, low energy consumption, and high recovery rate.

[0074] The embodiments of this disclosure have now been described in detail. To avoid obscuring the concept of this disclosure, some details known in the art have not been described. Those skilled in the art will fully understand how to implement the technical solutions disclosed herein based on the above description.

[0075] While specific embodiments of this disclosure have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and are not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments or equivalent substitutions can be made to some technical features without departing from the scope and spirit of this disclosure.

Claims

1. A method for pre-oxidation sodium roasting of converter vanadium slag, characterized in that, Includes the following steps: (a) Pre-oxidation treatment: The vanadium slag obtained from the converter vanadium extraction is pre-oxidized by holding it at a temperature of 500°C to 1200°C for 0.5 to 60 hours in an atmosphere with an oxygen concentration of 5% to 100%. (b) Pretreatment: The pre-oxidized vanadium slag obtained in step (a) is crushed, iron removed and ground to obtain refined vanadium slag with a metallic iron content of less than 5% and a particle size of less than 0.2 mm; (c) Batching and roasting: The refined vanadium slag obtained in step (b) is mixed with sodium salt additives, and the mass ratio of Na2O to V2O5 in the mixture is controlled to be 0.4 to 2.

0. Then, it is roasted at 700°C to 850°C for 30 to 360 minutes to obtain sodium-roasted clinker.

2. The method according to claim 1, characterized in that, In step (a), the oxygen concentration in the atmosphere of the pre-oxidation treatment is 10% to 30%.

3. The method according to claim 1 or 2, characterized in that, In step (a), the temperature of the pre-oxidation treatment is 600°C to 1000°C.

4. The method according to claim 1 or 2, characterized in that, In step (a), the pre-oxidation treatment takes 8 to 36 hours.

5. The method according to claim 1, characterized in that, In step (b), the portion of the refined vanadium slag with a particle size of less than 0.096 mm accounts for more than 80% of the total mass of the refined vanadium slag.

6. The method according to claim 1 or 5, characterized in that, In step (b), the metallic iron content of the refined vanadium slag is less than 3%.

7. The method according to claim 1, characterized in that, In step (c), the mass ratio of Na2O to V2O5 in the mixture is 0.8 to 1.

2.

8. The method according to claim 1, characterized in that, In step (c), the sodium salt additive is one or more of sodium carbonate, sodium sulfate, sodium chloride, or sodium nitrate.

9. The method according to claim 1, characterized in that, In step (c), the roasting temperature is 760°C to 800°C, and the roasting time is 90 to 180 minutes.

10. A roasted clinker for vanadium extraction from vanadium slag, characterized in that, The roasted clinker is prepared by the method of any one of claims 1 to 9, and the roasted clinker is in a loose state, with a vanadium roasting conversion rate of not less than 89%.

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