Preparation method and decomposition method of digestion solution for tantalum-niobium-containing alloy waste

Abstract

A preparation method of a digestion solution for corrosion of tantalum-niobium-containing alloy waste comprises the following synthesis steps: taking a certain amount of halogenated iron salt, adding the halogenated iron salt into dilute halogen acid under high-speed stirring until the halogenated iron salt is completely dissolved, then adding hexafluorotitanic acid and titanyl sulfate solids according to a certain proportion to be completely dissolved, then adding excessive newly-prepared titanium hydroxide to react for a period of time, and finally adding a catalyst to react for a period of time; and filtering and adding graphite powder for later use. The decomposition method comprises the following steps: shearing and crushing the tantalum-niobium alloy-containing waste material to obtain the result; and adding the digestion solution into a small section with the diameter of 50 mm, heating to 40-70 DEG C, dropwise adding hydrogen peroxide, cooling the discharged gas, and enabling the condensed water to flow back to the system. Filtering after sampling and detecting that no metal exists, adjusting the filtrate to an initial state after analyzing components, adding a proper amount of sulfuric acid and hydrofluoric acid into a filter cake to adjust and dissolve until the filter cake meets the extraction requirement, and entering an extraction process line.

Description

Technical Field

[0001] This invention relates to the field of tantalum-niobium alloy waste treatment, specifically to a method for preparing a digestion solution and a decomposition method for tantalum-niobium alloy waste. Background Technology

[0002] Currently, the main methods for treating and recycling tantalum-niobium alloy waste both domestically and internationally include direct digestion with hydrofluoric acid decomposition solution and digestion after calcination. Direct digestion with hydrofluoric acid decomposition solution is the traditional process, directly converting the tantalum-niobium alloy waste into metal ion complexes such as fluorotantalic acid, fluoroniobic acid, fluorotitanic acid, and fluoroferric acid. However, its drawbacks include the generation of large amounts of hydrogen gas and heat during the decomposition process, posing a significant explosion risk. It requires very slow addition of metal waste and the use of large amounts of forced draft to prevent explosions, resulting in low production efficiency, dangerous operation, and a large volume of exhaust ventilation. Digestion after calcination suffers from high operating temperatures, incomplete waste decomposition, dense combustion oxides, and low acid decomposition rates.

[0003] Patent CN202411152449.X discloses a method for separating and recovering metallic niobium and metallic titanium from niobium-containing titanium alloy solid waste. The specific method mainly involves mixing iodine with alloy ore, heating and reacting, and then collecting the sublimation gas. This method can quickly separate niobium and titanium, but the market for the product is unknown, and there is no way to recover and reuse the expensive iodine. The low capacity of the sublimation device and the very high fixed investment are also potential problems.

[0004] Patent publication number CN202311169774.2 discloses a method for producing niobium oxide from niobium-tantalum-iron alloy. The specific method mainly involves crushing and roasting the alloy ore, followed by leaching of various metallic elements, including tantalum and niobium, through alkaline leaching and multi-stage acid leaching. This method avoids the generation of hydrogen gas; however, the ball milling process generates a large amount of metal dust, still posing a risk of dust explosion. The calcination furnace operates at high temperatures and consumes a lot of energy. Furthermore, the calcined products are difficult to dissolve, requiring multi-stage leaching to ensure a high decomposition rate.

[0005] Patent publication number CN201810966562.X discloses a method for preparing high-purity niobium oxide from niobium-tantalum-iron alloy. Its pretreatment method is the same as that in CN202311169774.2, and the problems are also the same. Summary of the Invention

[0006] This invention primarily addresses the problem of generating large amounts of hydrogen during the decomposition of tantalum-niobium alloy ores, while also avoiding the difficulty in decomposing calcination products caused by conventional methods for preventing hydrogen generation.

[0007] A method for preparing a digestion solution for corrosion of tantalum-niobium alloy waste includes the following synthesis steps: a certain amount of iron halide salt is added to dilute hydrogen halide acid under high-speed stirring until it is completely dissolved. Then, fluorotitanic acid and titanium oxysulfate solids are added in a certain proportion and completely dissolved. Then, excess freshly prepared titanium hydroxide is added and reacted for a period of time. After filtration, graphite powder is added for later use.

[0008] Preferably, the ferrous halide is one or a mixture of ferrous fluoride, ferrous chloride, ferrous bromide, ferric fluoride (III), ferric chloride (III), and ferric bromide (III).

[0009] Preferably, the hydrohalic acid is one or a mixture of hydrofluoric acid, hydrochloric acid, and hydrobromic acid. Preferably, the molar ratio of ferric halide salt to dilute hydrohalic acid is 0.2-1.

[0010] Preferably, the molar ratio of ferric halide salt to fluorotitanic acid is 0.2-2 times.

[0011] Preferably, the molar ratio of ferric halide salt to titanium sulfate is 0.2-2.

[0012] Preferably, the total liquid volume to graphite powder weight ratio is 1000-5000, and the graphite powder particle size is 200-1000 mesh.

[0013] Preferably, the pH of the digestion solution is controlled between 2 and 5.

[0014] A method for decomposing tantalum-niobium alloy-containing waste includes the following steps: The tantalum-niobium alloy-containing waste is sheared and crushed into small segments <50mm. The digestion solution is added, and the mixture is heated to 40-70℃. Hydrogen peroxide is then added dropwise. After cooling and venting the gas, the condensate is returned to the system. This process continues until complete decomposition. After sampling and testing to ensure no metal is found, the mixture is filtered. The filtrate is analyzed, and the solution is adjusted back to its initial state. The filter cake is then acidified with appropriate amounts of sulfuric acid and hydrofluoric acid to meet extraction requirements before being introduced into the extraction process line.

[0015] In a controlled acidic environment, this invention utilizes a fluoride ion slow-release system with [TiF6]²⁻ as the core. With the oxidative assistance of iron ions and the electrochemical promotion of graphite powder, the passivation film on the surface of tantalum and niobium is continuously destroyed. By forming stable water-soluble fluoride complexes ([TaF7]²⁻, [NbF7]²⁻), efficient and selective dissolution of tantalum and niobium is achieved.

[0016] Beneficial effects: 1. This invention uses a ferric ion (Fe³⁺) oxidation mechanism to replace the traditional acid-derived hydrogen desorption pathway. Specifically, Fe³⁺ acts as the main electron acceptor, preferentially reacting with exposed metals in oxidation reactions (e.g., Ta + 2Fe³⁺ → Ta). 5The driving force of the reaction ⁺ + 2Fe²⁺ is much greater than that of the reduction reaction of hydrogen ions. Simultaneously, the added hydrogen peroxide (H₂O₂) continuously regenerates iron ions through the reaction 2Fe²⁺ + H₂O₂ + 2H⁺ → 2Fe³⁺ + 2H₂O, constructing a closed oxidation cycle. This design ensures that electron transfer is primarily accomplished via the Fe³⁺ / Fe²⁺ redox couple, rather than the H⁺ / H₂ pathway, thus significantly suppressing hydrogen production.

[0017] 2. This invention employs a hexafluorotitanate ([TiF6]²⁻) slow-release fluorine source technology. [TiF6]²⁻ establishes a hydrolysis equilibrium under acidic conditions, continuously releasing fluoride ions with strong complexing ability. These fluoride ions effectively attack the dense Ta₂O₅ / Nb₂O₅ crystal structure formed by calcination, converting it into a soluble heptafluoro complex through a coordination dissolution reaction (e.g., Ta₂O₅ + 12H⁺ + 14F⁻ → 2[TaF₇]²⁻ + 6H₂O). Particularly noteworthy is that the strong affinity of titanium ions for fluorine acts as a "fluorine buffer," ensuring a sufficient fluorine source supply while preventing premature consumption of free fluoride ions, thus ensuring their preferential use for the decomposition of the target oxide.

[0018] 3. The tantalum-niobium alloy waste decomposition liquid involved in this scheme is essentially a weakly acidic oxidation accelerator prepared according to a specific ratio. Its core mechanism of action lies in its ability to preferentially corrode and penetrate the dense passivated oxide layer on the surface of the alloy waste, creating a prerequisite for subsequent deep decomposition. When used in conjunction with oxidants such as hydrogen peroxide, it significantly accelerates the oxidative corrosion process on the alloy matrix. Crucially, this corrosion process is primarily completed through the redox reaction of metal ions (such as Fe³⁺), rather than the traditional acid-metal displacement reaction, thus fundamentally avoiding the generation of hydrogen gas. Furthermore, the key active components in this decomposition system act as catalysts or carriers in the reaction and are not consumed in large quantities, thus possessing excellent recyclability. After the waste is decomposed, the post-reaction liquid only needs simple filtration to remove solid residues, followed by analysis and correction of the concentrations of each component in the solution to restore its initial ratio. This allows for multiple recycling of the decomposition liquid, greatly improving economic and environmental benefits. Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments. Example

[0020] A certain alloy scrap 1 contains 48.5% niobium, 50.5% titanium, and 1% other components.

[0021] A certain alloy scrap 2 contains 30% niobium, 10% tantalum, 58% iron, and 2% other components.

[0022] Steps: Take 27.7g of iron fluoride trihydrate powder and add it to 1 liter of 7.5% diluted hydrofluoric acid. Stir at high speed until completely dissolved, then add 35mL of 50% fluorotitanic acid solution. Add 40.5g of titanium oxysulfate dihydrate and stir until dissolved. Then add 50g of freshly prepared titanium hydroxide and stir at high speed until the reaction is complete. Filter to remove the remaining titanium hydroxide. The pH should be 3.5. Then add 0.55g of 1000-mesh graphite powder to the clear solution.

[0023] (1) Take 500g of the above alloy waste 1, cut and crush it into small pieces <50mm, add the above digestion solution, heat to 70℃ and add hydrogen peroxide dropwise. After the exhaust gas is cooled, the condensate flows back into the system and the hydrogen content of the exhaust gas is detected by hydrogen electrode.

[0024] (2) Take 500g of the above alloy scrap 2, cut and crush it into small pieces <50mm, add the above digestion solution, heat to 70℃, then add hydrogen peroxide dropwise. After cooling and removing the vented gas, the condensate flows back into the system until complete decomposition. After sampling and testing to find no metal, filter. The relevant results are shown in Tables 1 and 2: Table 1 Experimental Results of the Invention scrap Dissolution completion time Hydrogen detection results Oxidation products Alloy Scrap 1 8h none gray paste-like precipitate Alloy Scrap 2 4h none Black paste-like precipitate Table 2 Experimental Detection Results of the Invention Original solution Alloy Scrap 1 Leachate Alloy Scrap 2 Leachate iron 9.5g / L 6g / L 18g / L titanium 18g / L 22g / L 13g / L sulfate 17.9g / L 18.5g / L 19g / L fluorine 33g / L 30g / L 31g / L Table 3 shows the reaction results using 500g of metal in the original process. scrap Sulfuric acid dosage 55% hydrofluoric acid dosage Water usage Acid dropping time Hydrogen production reaction system Alloy Scrap 1 1L 1.2L 2.4L 21h 380L grayish-white turbid liquid Alloy Scrap 2 1.3L 0.7L 2.5L 12h 220L Green turbid solution (3) The above filtrate can be reused by adding water, iron, titanium, sulfate, fluoride ions and graphite powder. The experimental results of the reuse are close to those of the first time.

[0025] In this embodiment, the filter cake in Table 1, i.e. the gray / black slurry precipitate, is a niobium-tantalum enrichment material that exists in an ionic state after oxidation. The subsequent tantalum-niobium extraction can directly adopt the existing conventional process, such as adding an appropriate amount of sulfuric acid or hydrofluoric acid to adjust the acidity and dissolve it to meet the extraction requirements, and then enter the extraction process line. There will be no corresponding hydrogen gas problem.

[0026] In Table 2, the original solution is the digestion solution itself before alloy treatment, and the leachate is the clear liquid obtained after filtration and precipitation of the mixed system after treatment. As can be seen from Table 2, the original solution has relatively similar contents of iron, titanium, sulfate and fluorine, which provides strong support for replenishment and recycling.

[0027] As can be seen from Tables 1-3 above, the present invention has the following advantages over existing processes: 1. Improved Safety: The original process generates a large amount of hydrogen, posing an explosion risk; this invention produces no detectable hydrogen, making it safer. 2. Increased Efficiency: Waste 1 processing time is reduced from 21 hours to 8 hours, and waste 2 from 12 hours to 4 hours, significantly shortening the processing time and making it faster. 3. Environmentally Friendly: Exhaust gases are condensed and recirculated, reducing volatilization and pollution; the original process emits harmful gases. 4. High Resource Utilization: The digestion solution can be recycled, and waste and costs are reduced by adding ions and graphite powder. 5. More Stable Reaction System: This invention produces a slurry-like precipitate, which is easy to filter; the original process produces a turbid liquid, which may be more difficult to process. 6. Reduced Acid Consumption: The original process uses large amounts of sulfuric acid and hydrofluoric acid; this invention uses diluted hydrofluoric acid and a small amount of additives, making it more economical. 7. Applicable to Multiple Wastes: This invention successfully processes two alloy wastes with different compositions, demonstrating its versatility.

[0028] The design of this decomposition solution is ingenious. It does not rely on strong oxidizing or strong acidity alone, but rather on the synergistic effect of multiple components, particularly the complexation of fluoride ions, to efficiently decompose extremely stable tantalum-niobium alloys. The core principle of this invention can be divided into the following key steps: 1. Damage to the surface passivation film Tantalum and niobium are well-known "valve metals" because their surfaces instantly form a dense, stable, and strongly adhering oxide film (mainly Ta₂O₅ and Nb₂O₅, and in water, a complex mixture of oxides and hydroxides, which will completely transform into oxides if not dissolved) in air or aqueous solutions. This passivation film gives them extremely high corrosion resistance to most inorganic acids (including aqua regia).

[0029] The role of H⁺: Hydrogen ions in the decomposition solution (from hydrohalic acid and sulfuric acid) first weaken and erode the oxide film.

[0030] The key role of fluoride ions: Fluoride ions are the core agents that break down this oxide film. Fluoride ions can react with Ta in the oxide film. 5 ⁺ and Nb 5 ⁺ A complexation reaction occurs (especially in newly formed loose hydroxyl-containing structures), generating soluble fluorine complexes, which "dissolve" the dense oxide film and expose the underlying metal atoms.

[0031] Example reaction: Ta₂O₅ + 12HF → 2H₂[TaF₇] + 5H₂O Nb₂O₅ + 12HF → 2H₂[NbF₇] + 5H₂O 2. Complexation and dissolution of exposed metals Once the surface oxide film is destroyed, the internal tantalum and niobium metals are exposed to the solution. At this point, an efficient and continuous complexation-dissolution process begins. A continuous source of F⁻: the hexafluorotitanate ions [TiF6]²⁻ in the decomposition solution act as a "fluorine reservoir" and "catalyst." It can slowly hydrolyze in solution, continuously releasing free F⁻, which reacts with the exposed fresh metal.

[0032] [TiF6]²⁻ + 4H₂O ⇌ [Ti(OH)₄F₂]²⁻ + 4HF (The generated HF immediately provides F⁻ and H⁺) Dissolution of the metal: The exposed tantalum / niobium metal is oxidized in the presence of H⁺ and an oxidizing agent (if Fe³⁺ is present) and immediately complexed with F⁻ to form extremely stable water-soluble complex anions, such as [TaF7]²⁻ and [NbF7]²⁻, thus entering the solution.

[0033] Taking tantalum as an example, in the absence of a strong oxidizing agent: 2Ta + 10H⁺ + 14F⁻ → 2[TaF₇]²⁻ + 5H₂ When Fe³⁺ is used as an oxidant (more efficient): Ta + 2Fe³⁺ → Ta 5 ⁺+2Fe²⁺ Ta 5 ⁺+7F⁻→[TaF7]²⁻ 3. Detailed Explanation of the Synergistic Effects of Each Component (1) The role of iron ions (Fe²⁺ / Fe³⁺): a. Oxidizing agents: especially ferric iron (Fe3+) ³⁺ H⁺ can be used as a medium-strong oxidant to directly oxidize tantalum and niobium, accelerating their dissolution. This is much faster than the reaction that relies solely on H⁺ to produce hydrogen gas.

[0034] b. Catalytic cycle: Fe²⁺ can be re-oxidized to Fe³⁺ by air or other oxidizing substances in the solution (such as trace oxygen), forming a redox cycle that continuously provides oxidizing power.

[0035] c. Potential adjustment: The presence of the Fe³⁺ / Fe²⁺ redox couple can maintain a certain oxidation potential in the solution, which is beneficial for breaking the passivation film and dissolving the metal.

[0036] (2) The core role of titanium-based components ([TiF6]²⁻ and TiOSO4): a. Buffering and slow release of fluorine: Direct use of high-concentration hydrofluoric acid is very dangerous, and the reaction is violent and difficult to control. [TiF6]²⁻, as a stable fluorine source, can release F⁻ smoothly, making the corrosion process gentler and more controllable, and reducing the volatilization and loss of HF.

[0037] b. Preventing fluoride consumption: Ti present in the solution 4 ⁺ competes with F⁻ for binding, preferentially forming the very stable [TiF6]²⁻. This prevents F⁻ from being prematurely consumed by other impurity ions in the solution (such as Fe³⁺, Al³⁺, etc., which may dissolve from the alloy), ensuring that there is a sufficient amount of F⁻ to attack the primary targets—tantalum and niobium.

[0038] c. Self-regeneration cycle: The addition of freshly prepared Ti(OH)4, besides adjusting the pH, provides Ti after dissolution. 4 ⁺ This also supplements the "fluorine buffer system".

[0039] d. Role of graphite powder: Electrochemical role: Graphite has good electrical conductivity and can act as a micro cathode in the corrosive solution, forming a micro-galvanic cell with the alloy waste acting as the anode, thus accelerating the electrochemical corrosion process. Physical role: The suspension of graphite powder may help to peel off corrosion products from the alloy surface, exposing new reaction surfaces and preventing passivation. Simultaneously, it may disperse the hydrogen gas generated during the reaction, reducing the risk of hydrogen embrittlement and improving safety.

[0040] Obviously, the above embodiments of the present invention are merely illustrative examples and not intended to limit the implementation of the invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the present invention still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a digestion solution for the corrosion of tantalum- containing niobium alloy scrap, characterized by, The synthesis steps are as follows: a certain amount of halogenated iron salt is added into dilute hydrogen halide acid under high-speed stirring until completely dissolved, then a certain proportion of fluorotitanic acid and titanium sulfate solid are added for complete dissolution, then an excess of freshly prepared titanium hydroxide is added for a period of reaction, after filtration, graphite powder is added for standby.

2. The method according to claim 1, wherein the method is characterized by: The ferrous halide is one or more of ferrous fluoride, ferrous chloride, ferrous bromide, iron (III) fluoride, iron (III) chloride, and iron (III) bromide.

3. The method according to claim 1, wherein the method is characterized by: The hydrogen halide acid is one or more of hydrofluoric acid, hydrochloric acid, and hydrobromic acid.

4. The method according to claim 1, wherein the method is characterized by: The molar ratio of halogenated iron salt to dilute hydrogen halide acid is 0.2-1 times.

5. The method according to claim 1, wherein the method is characterized by: The molar ratio of halogenated iron salt to fluorotitanic acid is 0.2-2 times.

6. The method according to claim 1, wherein the method is characterized by: The molar ratio of halogenated iron salt to titanium sulfate is 0.2-2 times.

7. The method according to claim 1, wherein the method is characterized by: The total liquid volume to graphite powder weight ratio is 1000-5000, and the graphite powder particle size is 200-1000 mesh.

8. The method according to claim 1, wherein the method is characterized by: The liquid pH of the digestion liquid product is controlled to be between 2-5.

9. A method for decomposing tantalum-niobium alloy-containing waste, comprising the following steps: shearing and crushing the tantalum-niobium alloy-containing waste into small pieces of less than 50 mm, adding the digestion liquid according to any one of claims 1-8, heating to 40-70°C, then adding hydrogen peroxide dropwise, cooling the exhaust gas, and then condensing the water stream back into the system until complete decomposition, sampling and detecting no metal, then filtering, analyzing the composition of the filtrate, and adjusting it back to the initial state, adding an appropriate amount of sulfuric acid and hydrofluoric acid to the filter cake to adjust the acidity and dissolve it to meet the extraction requirements, and then entering the extraction process line.