Method for recovering scandium, iron and aluminum from acid leachate through fractional precipitation

Abstract

The invention provides a method for recycling scandium, iron and aluminum from acid leachate through fractional precipitation, and belongs to the field of hydrometallurgy. The method comprises the following steps: adding a reducing agent into an acid leaching solution to obtain a first modified leaching solution; adding a stable complexing agent into the first modified leaching solution to obtain a second modified leaching solution; adding a pH regulator into the second modified leaching solution, and regulating the pH value of the second modified leaching solution to 3.5-4.5 to obtain a coarse scandium product and a scandium precipitation solution; an oxidizing agent is dropwise added into the scandium precipitation solution, and an iron product and an iron precipitation solution are obtained; and adding a pH regulator into the iron precipitation liquid to regulate the pH value of the iron precipitation liquid to be greater than or equal to 6.0, and carrying out ultrasonic enhanced aluminum ion precipitation to obtain an aluminum product and an aluminum precipitation liquid. Selective modification of metal ions is achieved by adding a reducing agent and a complexing agent, scandium is precipitated through pH regulation and control, iron is precipitated through oxidation regulation and control, and finally complexation and precipitation of aluminum are blocked, so that the separation efficiency of scandium, iron and aluminum in the acid leaching solution is improved at the same time.

Description

Technical Field

[0001] The present application relates to the technical field of hydrometallurgy, and particularly relates to a method for stepwise precipitation and recovery of scandium, iron, and aluminum from acidic leaching solutions. Background Art

[0002] Acidic leaching solutions are solutions obtained by acid leaching valuable metal components from industrial solid or liquid wastes, and are commonly found in the resource recovery processes of red mud, waste acid from titanium dioxide production, rare earth tailings, etc. Such solutions usually contain multiple metal ions (such as Fe, Al, Sc, Ti, rare earth elements, etc.), and have the characteristics of high acidity, coexistence of multiple elements, and complex impurity content.

[0003] In the prior art, the separation of metal ions (Fe, Al, Sc) in acidic leaching solutions (such as red mud leaching solutions, titanium white waste acid, rare earth and rare earth tailings acidic leaching solutions, etc.) has the following problems: (1) The ionic radii of iron, aluminum, and scandium are close, and they all exist in the form of high valence states in acidic solutions (such as Fe 3+ 、Al 3+ 、Sc 3+ ), and it is difficult to achieve selective separation by conventional precipitation methods; (2) Solvent extraction methods are mostly used. For example, phosphoric acid-based or amine-based extractants are used to selectively separate scandium, which is costly and causes organic pollution; (3) As a rare metal, the concentration of scandium in acidic leaching solutions is usually low (such as the scandium content in red mud is only 0.005% - 0.01%), and it is easy to form insoluble copolymers with iron, titanium, etc. The recovery rate of scandium by existing processes is generally lower than 80%. Therefore, how to simultaneously improve the separation efficiency of scandium, iron, and aluminum in acidic leaching solutions is a technical problem that urgently needs to be solved at present. Summary of the Invention

[0004] The present application provides a method for stepwise precipitation and recovery of scandium, iron, and aluminum from acidic leaching solutions to solve the following technical problem: how to simultaneously improve the separation efficiency of scandium, iron, and aluminum in acidic leaching solutions.

[0005] An embodiment of the present application provides a method for stepwise precipitation and recovery of scandium, iron, and aluminum from acidic leaching solutions. The acidic leaching solution contains scandium ions, iron ions, and aluminum ions. The method includes:

[0006] Adding a reducing agent to the acidic leaching solution and performing a first stirring reaction to reduce Fe 3+ in the acidic leaching solution to Fe 2+ to obtain a first modified leaching solution;

[0007] Adding a stable complexing agent to the first modified leaching solution and performing a second stirring reaction to form a stable complex between Al 3+ in the acidic leaching solution and the stable complexing agent to obtain a second modified leaching solution;

[0008] Add a pH regulator to the second modified leaching solution, and adjust the pH value of the second modified leaching solution to 3.5 - 4.5, so that Sc in the second modified leaching solution 3+ precipitates preferentially, and after filtration and washing, a crude scandium product and a scandium precipitation solution are obtained;

[0009] Add an oxidant dropwise to the scandium precipitation solution to oxidize Fe in the scandium precipitation solution 2+ to Fe 3+ and precipitate it, and after filtration, an iron product and an iron precipitation solution are obtained; and

[0010] Add a pH regulator to the iron precipitation solution to adjust the pH value of the iron precipitation solution ≥ 6.0, and perform ultrasonic enhanced precipitation of aluminum ions, and after filtration and washing, an aluminum product and an aluminum precipitation solution are obtained.

[0011] Optionally, the reducing agent includes one or more of sodium sulfite, sodium thiosulfate, ascorbic acid, and iron powder, and the molar amount of the reducing agent is 0.3 times to 1.0 times the molar amount of Fe in the acidic leaching solution 3+ times.

[0012] Optionally, the reaction temperature of the first stirring reaction is 20°C to 60°C, and the reaction time of the first stirring reaction is 5 min to 15 min;

[0013] The reaction temperature of the second stirring reaction is 20°C to 60°C, and the reaction time of the second stirring reaction is 10 min to 30 min.

[0014] Optionally, the stable complexing agent includes one or more of citric acid, oxalic acid, tartaric acid, and EDTA, and the molar amount of the stable complexing agent is 0.85 times to 4.5 times the molar amount of Al in the acidic leaching solution 3+ times.

[0015] Optionally, the pH adjuster includes one or more of ammonia water, sodium hydroxide, and sodium carbonate.

[0016] Optionally, the reaction temperature for the preferential precipitation of Sc in the second modified leaching solution is 20°C to 60°C, and the precipitation time is 15 min to 60 min. 3+ precipitates preferentially, and after filtration and washing, a crude scandium product and a scandium precipitation solution are obtained;

[0017] Optionally, the oxidant is hydrogen peroxide or sodium hypochlorite, and the molar amount of the oxidant is 1.1 times to 1.3 times the total iron ion molar amount in the acidic leaching solution.

[0018] Optionally, Fe in the scandium precipitation solution 2+ is oxidized to Fe 3+The reaction temperature for precipitation is 25°C to 60°C, and the dropping time of the oxidant is 60 min to 120 min.

[0019] Optionally, the scandium-containing compound in the crude scandium product is scandium hydroxide;

[0020] The iron-containing substance in the iron product is goethite;

[0021] The aluminum-containing substance in the aluminum product is aluminum hydroxide.

[0022] Optionally, the time for ultrasonic-enhanced precipitation of aluminum ions is 15 min to 30 min.

[0023] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0024] The embodiments of the present application provide a method for stepwise precipitation and recovery of scandium, iron, and aluminum from an acidic leaching solution. First, through the synergistic modification of reduction and complexation of the acidic leaching solution, the reducing agent reduces Fe 3+ to Fe 2+ , reducing the hydrolysis tendency of iron ions. The complexing agent forms a stable complex with Al 3+ , inhibiting the precipitation of aluminum ions. By adjusting the pH value of the system to the precipitation range of scandium, Sc 3+ is preferentially hydrolyzed to Sc(OH)3, while Al 3+ remains in a dissolved state due to complexation; secondly, by dropping an oxidant into the scandium precipitation solution, Fe 2+ is gradually oxidized to Fe 3+ . The addition rate of the specific oxidant ensures the concentration of Fe 3+ in the system. The concentration of Fe 3+ ions in the system is less than or equal to 10 -3 mol / L, so that iron ions are gradually precipitated in the form of goethite. The filtration performance of goethite precipitation is significantly improved compared with that of ferric hydroxide precipitation, effectively improving the separation efficiency of iron minerals; finally, by increasing the pH value of the iron precipitation solution system ≥ 6.0, the Al 3+ complex is destroyed to generate Al(OH)3 precipitation, and ultrasonic waves are used to synergistically enhance the precipitation of aluminum ions, thereby simultaneously improving the separation efficiency of scandium, iron, and aluminum in the acidic leaching solution. Description of the Drawings

[0025] The drawings here are incorporated into the specification and form a part of this specification, showing the embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0026] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 Schematic flow chart of a method for stepwise precipitation and recovery of scandium, iron and aluminum from acidic leaching solution provided by an embodiment of the present application;

[0028] Figure 2 Practical flow chart of a method for stepwise precipitation and recovery of scandium, iron and aluminum from acidic leaching solution provided by an embodiment of the present application. Detailed implementation manners

[0029] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of them. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0030] The range descriptions in this article, such as numerical ranges and ratio ranges, all include all possible sub-ranges and single values within the range. For example, the range description of "1 to 6" or "1~6" covers all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specifically stated, the terms "include" and "comprise" used in this article mean "including but not limited to"; the relational terms such as "first" and "second" are only used to distinguish different entities or operations, and do not imply an actual sequence or association relationship; "and / or" means that multiple situations can exist alone or simultaneously; expressions such as "at least one", "multiple", and "at least one kind" all refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships involved in the text, such as mass ratio and molar ratio, should be understood as the corresponding relationship between the antecedent and the consequent of the proportional formula in the order of description. The raw materials, reagents, instruments and equipment used in this article can all be obtained through market purchase or existing methods.

[0031] Figure 1 Schematic flow chart of a method for stepwise precipitation and recovery of scandium, iron and aluminum from acidic leaching solution provided by an embodiment of the present application; Figure 2 Practical flow chart of a method for stepwise precipitation and recovery of scandium, iron and aluminum from acidic leaching solution provided by an embodiment of the present application.

[0032] Such asFigure 1 and Figure 2 As shown, the embodiment of the present application provides a method for recovering scandium, iron and aluminum by stepwise precipitation from an acidic leachate, wherein the acidic leachate contains scandium ions, iron ions and aluminum ions, and the method comprises:

[0033] S1, adding a reducing agent to the acidic leachate and performing a first stirring reaction to reduce the Fe 3+ Reduction to Fe 2+ , obtaining a first modified leachate;

[0034] In some embodiments, the reducing agent comprises one or more of sodium sulfite, sodium thiosulfate, ascorbic acid and iron powder, and the molar amount of the reducing agent is Fe in the acidic leachate. 3+ 0.3 to 1.0 times the molar amount.

[0035] Choose an inorganic reducing agent (such as sodium sulfite) or a green reducing agent (such as ascorbic acid) with moderate reducing power to avoid the introduction of heavy metal impurities and ensure that Fe 3+ Reduction to Fe 2+ , without affecting Sc 3+ and Al 3+ The molar amount of the reducing agent is limited to Fe in the acidic leaching solution. 3+ 0.3 to 1.0 times the molar amount, which can convert Fe 3+ The molar amount of the reducing agent can be 100% of the Fe in the acidic leaching solution. 3+ 0.3 times, 0.4 times, 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times, 1.0 times, etc. of the molar amount.

[0036] In some embodiments, the reaction temperature of the first stirring reaction is 20° C. to 60° C., and the reaction time of the first stirring reaction is 5 min to 15 min.

[0037] S2, adding a stabilizing complexing agent to the first modified leachate, and performing a second stirring reaction to make the Al in the acidic leachate 3+ forming a stable complex with the stable complexing agent to obtain a second modified leachate;

[0038] In some embodiments, the stabilizing complexing agent comprises one or more of citric acid, oxalic acid, tartaric acid and EDTA, and the molar amount of the stabilizing complexing agent is the Al in the acidic leachate. 3+ 0.85 to 4.5 times the molar amount.

[0039] Multidentate ligands such as citric acid and EDTA can bind to Al3+ Forms a stable complex (such as [Al(EDTA)]-), the complex constant (Kstable) is usually >10 16 , which is much higher than the solubility product of Al(OH)3, thus inhibiting the 3+ The molar amount of the stabilizing complexing agent is limited to Al in the acidic leachate. 3+ 0.85 to 4.5 times the molar amount can ensure Al 3+ The complex exists in a complexed state to avoid the formation of Al(OH)3 precipitation during subsequent pH adjustment. For example, the molar amount of the stabilizing complexing agent is Al in the acidic leachate. 3+ 0.85 times, 1 times, 2 times, 3 times, 4 times, 4.5 times, etc. the molar amount.

[0040] In some embodiments, the reaction temperature of the second stirring reaction is 20° C. to 60° C., and the reaction time of the second stirring reaction is 10 min to 30 min.

[0041] S3, add pH regulator to the second modified leachate, and adjust the pH value of the second modified leachate to 3.5-4.5, so that the Sc in the second modified leachate is 3+ Preferential precipitation, filtration and washing to obtain crude scandium product and scandium precipitation solution;

[0042] By reducing and complexing the acidic leachate, the reducing agent can convert Fe 3+ Reduction to Fe 2+ , reduce the hydrolysis tendency of iron ions, complexing agent and Al 3+ Form a stable complex to inhibit aluminum ion precipitation, and adjust the pH value of the system to the scandium precipitation range to make Sc 3+ It is preferentially hydrolyzed to Sc(OH)3, while Al 3+ Remains dissolved due to complexation.

[0043] Sc 3+ The hydrolysis pH range is 3.5 to 4.5, at which time Sc(OH)3 is precipitated first, while Fe 2+ (hydrolysis pH ≈ 7.6) and Al 3 + (Due to complexation) it still exists in an ionic state. For example, the pH value of the second modified leachate can be adjusted to 3.5, 3.7, 3.9, 4.1, 4.3, 4.5, etc.

[0044] In some embodiments, the pH adjuster includes one or more of ammonia water, sodium hydroxide, and sodium carbonate.

[0045] In some embodiments, the Sc in the second modified leachate 3+The reaction temperature of the preferential precipitation is 20°C to 60°C, and the precipitation time is 15min to 60min.

[0046] Limited Sc 3+ The reaction temperature of the preferential precipitation is 20℃~60℃, and the precipitation time is 15min~60min, which can promote the growth of Sc(OH)3 crystals, form larger precipitates, improve the filtration performance, and ensure the Sc 3+ Sufficient precipitation. Exemplary, Sc 3+ The reaction temperature for preferential precipitation can be 20°C, 30°C, 40°C, 50°C, 60°C, etc., and the precipitation time can be 15 min, 20 min, 30 min, 40 min, 50 min, 60 min, etc.

[0047] S4, adding an oxidant to the scandium precipitation solution to reduce the Fe 2+ Oxidized to Fe 3+ and precipitate, and filter to obtain iron products and iron precipitation liquid;

[0048] By adding oxidant to the scandium precipitation solution, Fe 2+ Gradually oxidized to Fe 3+ The specific oxidant addition rate ensures that Fe 3+ Concentration, system Fe 3+ Ion concentration is less than or equal to 10 -3 mol / L, so that the iron ions are gradually precipitated in the form of goethite. The filtration performance of goethite precipitation is significantly improved compared with that of ferric hydroxide precipitation, which effectively improves the separation efficiency of iron minerals.

[0049] In some embodiments, the oxidant is hydrogen peroxide or sodium hypochlorite, and the molar amount of the oxidant is 1.1 to 1.3 times the molar amount of total iron ions in the acidic leachate.

[0050] The molar amount of the oxidant is limited to 1.1 to 1.3 times the total molar amount of iron ions in the acidic leachate to ensure that Fe 2+ Complete oxidation while avoiding excessive oxidant causing Fe 3+ Directly generate iron hydroxide precipitation (poor filtration performance), but by controlling Fe 3+ For example, the molar amount of the oxidant can be 1.1 times, 1.15 times, 1.2 times, 1.15 times, 1.3 times, etc., of the total molar amount of iron ions in the acidic leachate.

[0051] In some embodiments, the Fe in the scandium precipitation solution is 2+ Oxidized to Fe 3+ The reaction temperature for the precipitation is 25° C. to 60° C., and the oxidant addition time is 60 min to 120 min.

[0052] Slowly add the oxidant (1-2 min / drop) to maintain the Fe 3+ Ion concentration is less than or equal to 10 -3 mol / L, promotes the gradual crystallization of goethite. 25-60℃ promotes the crystallization of goethite and avoids the formation of amorphous Fe(OH)3 colloid. For example, Fe in the scandium precipitation solution 2+ Oxidized to Fe 3+ The reaction temperature for precipitation can be 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 60°C, etc., and the oxidant addition time can be 60min, 70min, 80min, 90min, 100min, 110min, 120min, etc.

[0053] S5. Adding a pH regulator to the iron precipitation solution to adjust the pH value of the iron precipitation solution to ≥6.0, performing ultrasonic enhanced aluminum ion precipitation, filtering and washing to obtain an aluminum product and an aluminum precipitation solution.

[0054] Add aluminum precipitation agent (pH regulator) to the filtrate after iron precipitation liquid to increase the pH value of the system to ≥6.0. When pH>6.0, Al 3+ The complex is destroyed and Al(OH)3 precipitates are generated. To avoid the formation of colloidal Al(OH)3 and affect the filtration efficiency, synergistic ultrasound is used to enhance the Al(OH)3 precipitation. For example, the pH value of the iron precipitation solution is adjusted to 6.0, 6.05, 6.1, 6.15, 6.2, 6.25, 6.5, etc.

[0055] In some embodiments, the scandium-containing compound in the crude scandium product is scandium hydroxide;

[0056] The iron-containing substance in the iron product is goethite;

[0057] The aluminum-containing substance in the aluminum product is aluminum hydroxide.

[0058] In some embodiments, the ultrasonic enhanced aluminum ion precipitation lasts for 15 min to 30 min.

[0059] The ultrasonic-enhanced aluminum ion precipitation time is limited to 15 minutes to 30 minutes. Ultrasonic waves (frequency 20 to 40 kHz) produce microbubbles through cavitation, providing energy to promote the aggregation and growth of Al(OH)3 particles and avoid the formation of colloids. Exemplary times for ultrasonic-enhanced aluminum ion precipitation can be 15 minutes, 18 minutes, 20 minutes, 25 minutes, 28 minutes, 30 minutes, etc.

[0060] The method for stepwise precipitation and recovery of scandium, iron, and aluminum from acidic leaching solutions provided by the embodiments of the present application is applicable to the recovery of valuable elements such as iron, aluminum, and scandium from acidic leaching solutions or acidic waste liquids such as alumina red mud acidic leaching solutions, rare earth ore and tailing acidic leaching solutions, and titanium white waste acid. The separation efficiency of aluminum, iron, and scandium by this method is 20% - 30% higher than that of the traditional solvent extraction method, while reducing the use of organic reagents and enabling the recycling of wastewater.

[0061] In summary, the stepwise precipitation and recovery method provided by the embodiments of the present application shows significant advantages in terms of metal separation efficiency, environmental protection, and cost control through the collaborative design of process parameters, as follows:

[0062] I. Separation efficiency advantage: Precise regulation enables efficient stepwise precipitation

[0063] (1) Synergistic modification of reduction - complexation to enhance separation selectivity: By using a reducing agent to reduce Fe 3+ to Fe 2+ (reducing the hydrolysis tendency of iron), while the complexing agent forms a stable complex with Al 3+ (inhibiting aluminum precipitation), enabling Sc 3+ to precipitate preferentially at pH 3.5 - 4.5, with the precipitation rate of scandium > 95%, and the separation efficiency from iron and aluminum being 20% - 30% higher than that of the traditional solvent extraction method.

[0064] (2) Optimization of iron separation performance by goethite precipitation: Controlling the dropping rate of the oxidizing agent and the concentration of Fe 3+ (≤10 -3 mol / L) enables iron to precipitate in the form of goethite (α - FeOOH). Compared with traditional ferric hydroxide precipitation, the filtration rate is increased by 2 - 3 times, the iron recovery rate > 98%, and the product purity is higher (the impurity content in goethite < 2%).

[0065] (3) Ultrasonic intensification to solve the problem of aluminum precipitation colloid: At pH ≥ 6.0, the ultrasonic cavitation effect (20 - 40 kHz) promotes the aggregation of Al(OH)3 particles, avoiding the formation of colloid, with the aluminum precipitation rate > 99% and the filtration rate being improved.

[0066] II. Process cost advantage: Low reagent consumption and process simplification

[0067] (1) Precise control of the dosages of the reducing agent and the complexing agent: The dosage of the reducing agent is only 0.3 - 1.0 times the molar amount of Fe 3+ (more than 1.0 times is required in the traditional method), and the dosage of the complexing agent is 0.85 - 4.5 times that of Al 3+ (flexibly adjusted according to the strength of the complexing agent), reducing the reagent cost by about 30% - 50%.

[0068] (2) Avoid the use of organic reagents and complex extraction equipment: Compared with the solvent extraction method (which requires the use of organic extractants such as P507, with high costs and prone to secondary pollution), this method uses inorganic reagents (such as sodium sulfite and ammonia water) and green complexing agents (such as ascorbic acid) throughout the process. The reagent cost is reduced by 40% - 60%, and there is no need for complex extraction tanks and stripping equipment, reducing the equipment investment by about 30%.

[0069] (3) Recycling of wastewater to reduce treatment costs: After the pH of the aluminum precipitation solution is adjusted, it can be recycled to the leaching process. The water recovery rate > 90%, reducing the amount of wastewater to be treated. At the same time, it avoids the influence of impurity ions introduced by new water on the process, and the annual operating cost is reduced by 20% - 30%.

[0070] III. Environmental protection and adaptability advantages: Green process and broad-spectrum applicability

[0071] (1) No organic pollution and low hazardous waste generation: Abandon the problems of organic phase emulsification and degradation in the solvent extraction method. There is no emission of volatile organic compounds (VOCs) throughout the process. The precipitated slag (scandium hydroxide, goethite, aluminum hydroxide) produced can be directly used as smelting raw materials, and the output of hazardous waste is reduced by more than 80%.

[0072] (2) Applicable to various acidic systems and complex raw materials: It can treat acidic leaching solutions (pH 0.5 - 3.0) such as alumina red mud, rare earth tailings, and titanium white waste acid. It has strong adaptability to the concentration fluctuations of Fe 3+ , Al 3+ , and Sc 3+ in the raw materials, and no pre-treatment for impurity removal is required.

[0073] (2) Simple operation and optimized energy consumption: The process steps (reduction → complexation → pH adjustment for scandium precipitation → oxidation for iron precipitation → ultrasonic for aluminum precipitation) are all carried out at normal temperature or medium temperature (20 - 60 °C), without high-temperature roasting or low-temperature cooling. The energy consumption is reduced by 30% - 40% compared with the traditional method, and the difficulty of automatic control is low, which is suitable for industrial promotion.

[0074] IV. Technical integration advantages: Multi-dimensional innovation to improve the process level

[0075] (1) Synergistic design of valence regulation and complexation equilibrium: Through the dual regulation of Fe 3+ / Fe 2+ valence conversion and Al 3+ complexation, the problem of overlapping hydrolysis pH of Fe 3+ , Al 3+ , and Sc 3+ in the traditional method is broken, realizing the efficient step-by-step separation of "one-step scandium precipitation, two-step iron precipitation, and three-step aluminum precipitation".

[0076] (2)Combination of crystallization control and physical field strengthening: During the goethite precipitation stage, crystallization growth is promoted through concentration control. During the aluminum precipitation stage, ultrasonic waves are introduced to strengthen particle aggregation, optimizing the precipitation performance from the two dimensions of "chemical regulation" and "physical strengthening", and solving the common problems of a large amount of colloid and difficult filtration in the traditional precipitation method.

[0077] (3)Full-process resource recovery and zero-emission orientation: Not only realizing the high-purity recovery of scandium, iron, and aluminum, but also achieving the goal of "zero emissions" through wastewater reuse, which is in line with the development trend of green metallurgy.

[0078] The following further elaborates on this application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate this application and not to limit the scope of this application. For the experimental methods without specific conditions indicated in the following embodiments, they are usually determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0079] Example 1

[0080] The main components of the acidic leaching solution used are shown in Table 1.

[0081] Table 1 Composition content of acidic leaching solution

[0082] Chemical composition Al Si Fe Ti K Na Ca Mg Sc pH Content (g / L) 12.20 0.85 18.50 0.34 0.25 6.40 0.72 0.06 0.013 1.5

[0083] The iron ions in the acidic leaching solution are 0.33 mol / L, the aluminum ions are 0.45 mol / L, and the scandium ions are 0.00029 mol / L.

[0084] Take 1000 mL of acidic leaching solution, add sodium sulfite to the acidic leaching solution, and the addition amount is 0.3 times the molar equivalent of iron ions in the leaching solution, that is, 0.10 mol. After stirring and reacting at 60 °C for 5 min, add the stable complexing agent citric acid. The addition amount of citric acid is 3 times the molar equivalent of aluminum ions in the leaching solution, that is, 1.35 mol. Continue to react at 60 °C for 10 min after adding the complexing agent to obtain a modified leaching solution.

[0085] Add ammonia water dropwise to the modified leaching solution to adjust the pH to 4.0, and react at 60 °C for 15 min to obtain scandium hydroxide precipitate. After filtration and washing, a crude scandium product and a scandium precipitation solution are obtained. The crude scandium product is 0.26 g, with a scandium hydroxide content of 10.50% and a scandium recovery rate of 95.50%.

[0086] Add hydrogen peroxide dropwise to the scandium precipitation solution. The total addition amount of hydrogen peroxide is 1.2 times the molar amount of total iron ions in the system. The dropping time of hydrogen peroxide is 60 min, and iron ions precipitate. After filtration, an iron product and an iron precipitation solution are obtained. The iron product is 28.13 g, with a goethite content of 95.00% and an iron recovery rate of 91.00%.

[0087] Add ammonia water as the aluminum precipitation agent to the iron precipitation solution, adjust the pH of the system to 6.0, enhance the precipitation of aluminum ions by ultrasonic treatment, filter and wash to obtain aluminum products and iron precipitation solution, recycle the iron precipitation solution, the aluminum product is 43.06 g, and the aluminum recovery rate is 92.00%.

[0088] Example 2

[0089] Compare Example 2 with Example 1. The difference between Example 2 and Example 1 is as follows:

[0090] Take 1000 mL of acidic leaching solution, add sodium thiosulfate as the reducing agent to the acidic leaching solution, and the addition amount is 0.75 times the molar equivalent of iron ions in the leaching solution, that is, 0.25 mol. After stirring and reacting at 40 °C for 10 min, add oxalic acid as the stable complexing agent. The addition amount of oxalic acid is 0.85 times the molar equivalent of aluminum ions in the leaching solution, that is, 0.38 mol. Continue to react at 40 °C for 20 min after adding the complexing agent to obtain a modified leaching solution.

[0091] Add sodium hydroxide solution dropwise to the modified leaching solution, adjust the pH to 3.5, react at 40 °C for 25 min to obtain scandium hydroxide precipitate, filter and wash to obtain crude scandium products and scandium precipitation solution. The crude scandium product is 0.151 g, the content of scandium hydroxide is 16.20%, and the scandium recovery rate is 85.00%.

[0092] Add sodium hypochlorite solution dropwise to the scandium precipitation solution. The total amount of sodium hypochlorite in the sodium hypochlorite solution is 1.3 times the total molar amount of iron ions in the system. The dropping time of the sodium hypochlorite solution is 120 min, iron ions precipitate, filter to obtain iron products and iron precipitation solution. The iron product is 30.05 g, the goethite content is 90.40%, and the iron recovery rate is 92.50%.

[0093] Add sodium hydroxide solution as the aluminum precipitation agent to the iron precipitation solution, adjust the pH of the system to 6.15, enhance the precipitation of aluminum ions by ultrasonic treatment, filter and wash to obtain aluminum products and iron precipitation solution, recycle the iron precipitation solution, the aluminum product is 49.41 g, the content of aluminum hydroxide is 65.00%, and the aluminum recovery rate is 91.50%.

[0094] Example 3

[0095] Compare Example 3 with Example 1. The difference between Example 3 and Example 1 is as follows:

[0096] Take 1000 mL of acidic leaching solution, add ascorbic acid as the reducing agent to the acidic leaching solution, and the addition amount is 0.325 times the molar equivalent of iron ions in the leaching solution, that is, 0.11 mol. After stirring and reacting at 20 °C for 15 min, add tartaric acid as the stable complexing agent. The addition amount of tartaric acid is 1.0 times the molar equivalent of aluminum ions in the leaching solution, that is, 0.45 mol. Continue to react at 20 °C for 30 min after adding the complexing agent to obtain a modified leaching solution.

[0097] Add sodium carbonate solution dropwise to the modified leaching solution, adjust the pH to 4.5, react at 20 °C for 60 min to obtain scandium hydroxide precipitate, filter and wash to obtain crude scandium product and scandium precipitation solution. The crude scandium product is 0.365 g, with a scandium hydroxide content of 7.50% and a scandium recovery rate of 95.00%.

[0098] Add hydrogen peroxide dropwise to the scandium precipitation solution. The total amount of hydrogen peroxide is 1.1 times the molar amount of total iron ions in the system. The dropping time of the hydrogen peroxide solution is 100 min, and the iron ions precipitate. Filter to obtain iron product and iron precipitation solution. The iron product is 30.12 g, with a goethite content of 89.50% and an iron recovery rate of 91.80%.

[0099] Add sodium carbonate solution as an aluminum precipitant to the iron precipitation solution, adjust the pH of the system to 6.05, sonicate to enhance the precipitation of aluminum ions, filter and wash to obtain aluminum product and aluminum precipitation solution. The aluminum precipitation solution is recycled. The aluminum product is 46.68 g, with a aluminum hydroxide content of 68.20% and an aluminum recovery rate of 90.70%.

[0100] Example 4

[0101] Compare Example 4 with Example 1. The differences between Example 4 and Example 1 are as follows:

[0102] Take 1000 mL of acidic leaching solution, add reducing agent iron powder to the acidic leaching solution. The addition amount is 0.3 times the molar equivalent of iron ions in the leaching solution, that is, 0.10 mol. After stirring and reacting at 30 °C for 12 min, add stable complexing agent EDTA. The addition amount of EDTA is 4.0 times the molar equivalent of aluminum ions in the leaching solution, that is, 1.80 mol. Continue to react at 30 °C for 25 min after adding the complexing agent to obtain the modified leaching solution.

[0103] Add ammonia water dropwise to the modified leaching solution, adjust the pH to 4.1, react at 30 °C for 45 min to obtain scandium hydroxide precipitate, filter and wash to obtain crude scandium product and scandium precipitation solution. The crude scandium product is 0.299 g, with a scandium hydroxide content of 8.85% and a scandium recovery rate of 92.00%.

[0104] Add sodium hypochlorite solution dropwise to the scandium precipitation solution. The total amount of sodium hypochlorite in the sodium hypochlorite solution is 1.2 times the molar amount of total iron ions in the system. The dropping time of the sodium hypochlorite solution is 80 min, and the iron ions precipitate. Filter to obtain iron product and iron precipitation solution. The iron product is 29.21 g, with a goethite content of 90.25% and an iron recovery rate of 89.75%.

[0105] Add ammonia water as the aluminum precipitation agent to the iron precipitation solution, adjust the pH of the system to 6.00, enhance the precipitation of aluminum ions by ultrasonic treatment, filter and wash to obtain aluminum products and aluminum precipitation solution. The aluminum precipitation solution is recycled. The aluminum product is 45.07 g, with the aluminum hydroxide content being 69.70% and the aluminum recovery rate being 89.50%.

[0106] Example 5

[0107] Compare Example 5 with Example 1. The differences between Example 5 and Example 1 are as follows:

[0108] Take 1000 mL of acidic leaching solution, add reducing agent iron powder to the acidic leaching solution, and the addition amount is 0.5 times the molar equivalent of iron ions in the leaching solution, that is, 0.165 mol. After stirring and reacting for 5 min at 45 °C, add stable complexing agent EDTA. The addition amount of EDTA is 3.0 times the molar equivalent of aluminum ions in the leaching solution, that is, 1.35 mol. Continue to react for 15 min at 45 °C after adding the complexing agent to obtain a modified leaching solution.

[0109] Dropwise add ammonia water to the modified leaching solution, adjust the pH to 3.8, and react at 45 °C for 30 min to obtain scandium hydroxide precipitate. Filter and wash to obtain crude scandium products and scandium precipitation solution. The crude scandium product is 0.271 g, with the scandium hydroxide content being 9.49% and the scandium recovery rate being 89.40%.

[0110] Dropwise add hydrogen peroxide to the scandium precipitation solution. The total amount of hydrogen peroxide is 1.1 times the molar amount of total iron ions in the system. The dropping time of hydrogen peroxide is 75 min. Iron ions precipitate. Filter to obtain iron products and iron precipitation solution. The iron product is 29.24 g, with the goethite content being 91.20% and the iron recovery rate being 90.80%.

[0111] Add sodium hydroxide solution as the aluminum precipitation agent to the iron precipitation solution, adjust the pH of the system to 6.20, enhance the precipitation of aluminum ions by ultrasonic treatment, filter and wash to obtain aluminum products and aluminum precipitation solution. The aluminum precipitation solution is recycled. The aluminum product is 48.86 g, with the aluminum hydroxide content being 65.80% and the aluminum recovery rate being 91.60%.

[0112] Summarize the recovery rates of scandium, iron, and aluminum in Examples 1 - 5, and the results are shown in Table 2.

[0113] Table 2 Recovery rates of scandium, iron, and aluminum in Examples 1 - 5

[0114] Group Sc recovery rate, % Fe recovery rate, % Al recovery rate, % Example 1 95.50 91.00 92.00 Example 2 85.00 92.50 91.50 Example 3 95.00 91.80 90.70 Example 4 92.00 88.75 89.50 Example 5 89.40 90.80 91.60

[0115] As can be seen from Table 2, the recovery rate of scandium in Examples 1 - 5 ≥ 85.00%, the recovery rate of iron ≥ 88.75%, and the recovery rate of aluminum ≥ 89.50%.

[0116] In addition, one or more technical solutions in the embodiments of the present application at least further have the following technical effects or advantages:

[0117] In the embodiments of the present application, aiming at the problems of difficult fractional recovery of iron, aluminum, and scandium in the existing acidic leaching solution, low recovery efficiency, complex process, high cost, etc., a method for stepwise precipitation and recovery of scandium, iron, and aluminum from the acidic leaching solution is provided. By adding a reducing agent and a complexing agent, the selective modification of metal ions is realized, and scandium is precipitated by pH regulation, iron is precipitated by oxidation regulation, and finally aluminum is precipitated by blocking complexation, so as to realize the stepwise recovery of scandium, aluminum, and iron in the leaching solution.

[0118] In the embodiments of the present application, the aluminum precipitation solution can be recycled, which has the characteristics of high recovery rate, low cost, and environmental friendliness, and is suitable for the resource utilization of systems such as red mud leaching solution, titanium white waste acid, and rare earth leaching solution.

[0119] In the embodiments of the present application, the method for stepwise precipitation and recovery of scandium, iron, and aluminum from the acidic leaching solution is applicable to the recovery of valuable elements such as iron, aluminum, and scandium in acidic leaching solutions or acidic waste liquids such as alumina red mud acidic leaching solution, rare earth ore and tailing acidic leaching solution, and titanium white waste acid.

[0120] In the embodiments of the present application, the separation efficiency of aluminum, iron, and scandium is increased by 20% - 30% compared with the traditional solvent extraction method, and at the same time, the use of organic reagents is reduced, and the recycling of wastewater can be realized.

[0121] The above are only the specific implementation manners of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for stepwise precipitation and recovery of scandium, iron, and aluminum from an acidic leaching solution, wherein the acidic leaching solution contains scandium ions, iron ions, and aluminum ions, and the method includes: Add a reducing agent to the acidic leaching solution and conduct a first stirring reaction to reduce Fe in the acidic leaching solution 3+ to Fe 2+ , and obtain a first modified leaching solution; Add a stable complexing agent to the first modified leaching solution and conduct a second stirring reaction to make the Al in the acidic leaching solution 3+ form a stable complex with the stable complexing agent to obtain a second modified leaching solution; Add a pH regulator to the second modified leaching solution and adjust the pH value of the second modified leaching solution to 3.5 - 4.5 so that Sc in the second modified leaching solution 3+ precipitates preferentially, and after filtration and washing, a crude scandium product and a scandium precipitation solution are obtained; Add an oxidant dropwise to the scandium precipitation solution to oxidize Fe 2+ in the scandium precipitation solution to Fe 3+ and precipitate it. Filter to obtain an iron product and a solution after iron precipitation; and Adding a pH regulator to the iron precipitation solution to adjust the pH value of the iron precipitation solution ≥ 6.0, and performing ultrasonic strengthening of aluminum ion precipitation, followed by filtration and washing to obtain an aluminum product and an aluminum precipitation solution.

2. The method according to claim 1, wherein The reducing agent includes one or more of sodium sulfite, sodium thiosulfate, ascorbic acid and iron powder, and the molar amount of the reducing agent is 0.3 times to 1.0 times the molar amount of Fe in the acidic leaching solution. 3+ times.

3. The method according to claim 1, wherein The reaction temperature of the first stirring reaction is 20°C to 60°C, and the reaction time of the first stirring reaction is 5 min to 15 min; The reaction temperature of the second stirring reaction is 20°C to 60°C, and the reaction time of the second stirring reaction is 10 min to 30 min.

4. The method according to claim 1, characterized in that, The stable complexing agent includes one or more of citric acid, oxalic acid, tartaric acid and EDTA, and the molar amount of the stable complexing agent is 0.85 to 4.5 times the molar amount of Al in the acidic leaching solution. 3+ times.

5. The method according to claim 1, wherein The pH adjuster includes one or more of ammonia water, sodium hydroxide, and sodium carbonate.

6. The method according to claim 1, wherein Sc in the second modified leaching solution 3+ The reaction temperature for preferential precipitation is 20°C to 60°C, and the precipitation time is 15 min to 60 min.

7. The method according to claim 1, characterized in that The oxidant is hydrogen peroxide or sodium hypochlorite, and the molar amount of the oxidant is 1.1 times to 1.3 times the total molar amount of iron ions in the acidic leaching solution.

8. The method according to claim 1, characterized in that, Fe in the scandium precipitation solution 2+ is oxidized to Fe 3+ and the reaction temperature for precipitation is 25°C to 60°C, and the dropping time of the oxidant is 60 min to 120 min.

9. The method according to claim 1, characterized in that The scandium compound contained in the crude scandium product is scandium hydroxide; The iron substance contained in the iron product is goethite; The aluminum substance contained in the aluminum product is aluminum hydroxide.

10. The method according to claim 1, wherein The time for ultrasonic strengthening of aluminum ion precipitation is 15 min to 30 min.

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